PREPARATION FOR NOVEL ISOTOPE HARVESTING METHODS AND CHEMISTRY 
FOR USER BEAM DEVELOPMENT 

By 

Andrew C. Candia 

A THESIS 

Submitted to 
Michigan State University 
in partial fulfillment of the requirements   
for the degree of 

Chemistry – Master of Science 

2024 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
ABSTRACT 

At the Facility for Rare Isotope Beams (FRIB), development has been underway to collect 

radionuclides that are produced as by-products of dumping the unused portion of the primary 

beam into a flowing-water beam stop. This technique, known as ‘isotope harvesting,’ has been 

tested in several exploratory studies and demonstrated its capability to collect isotopes from the 

water system. Isotope harvesting is predicted to be a promising source of isotopes, essential for 

advancing both basic and applied sciences. However, this method is inherently non-selective, and 

most isotopes can only be recovered from the water at limited radioisotopic purity. A viable 

method to improve the purity of the harvested samples is by implementing a mass-separation step.  

Metal oxides were proposed as potential novel sorbent materials, as their refractory nature 

makes them compatible with the high-temperature environment of the plasma ion source of the 

mass separator, a feature that makes the envisioned combined approach possible. In the here-

performed research, the feasibility of using metal oxides for isotope collection has been 

investigated. Simulation studies have been performed with nickel, which represents our main 

isotopes of interest, and nine other stable elements that are the main co-produced isotopes, under 

conditions similar to the predicted harvesting environment in the aqueous beam dump. Several of 

the tested metal oxides demonstrated adequate adsorption abilities for certain elements, while 

magnesium oxide emerged as the most promising for Ni capture. This was used to produce a 

sample of magnesium oxide with adsorbed, stable, enriched 61Ni for a proof-of-principle mass-

separation experiment. The results showed that mass separation performance with oxide-based 

samples is highly challenging due to the formation of various, partially refractory, species. In 

retrospect, it was also observed that the use of certain metal oxides, particularly magnesium oxide, 

results in the release of ions into the aqueous environment, which is undesirable. Based on these 

findings, while the insoluble metal oxides could see applications for the adsorption of particular 

elements, it was decided to consider different targetry options for the mass-separation step. 

In the second part of this work, research was also done to develop a 73As source material 

for the low-energy and stopped user beam program at FRIB. The source sample was prepared 

through precipitation of aqueous 73As, after addition of stable As carrier, as silver arsenate. The 

73As source was submitted and used to successfully create a 73As beam. Characterization via 

Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDS) and X-Ray Photoelectron 

Spectroscopy (XPS) was done with an analogously prepared stable As source sample. 

 
 
ACKNOWLEDGMENTS 

I want to spend some time acknowledging the many people who all deserve my thanks and 

praise. I first want to give special thanks to my advisor, Dr. Katharina Domnanich, who 

welcomed me to her group during a time when my future was uncertain at Michigan State 

University. I know that things were never easy, especially with me, but I am forever grateful that I 

got the chance to work with such a capable and successful scientist as yourself. From transitioning 

lab groups to helping me decide my academic future, you helped me every step of the way. I want 

to also thank your patience, as I know there were times I struggled to meet expectations, I am so 

happy to have been through this journey with you. Truly, thank you Kathi. I want to also thank 

each member of my committee: Dr. Alyssa Gaiser, Dr. Sean Liddick, Dr. Gregory Severin, and 

Dr. Kyle Brown, for your patience and support in guiding my academic future beyond MSU. I 

want to thank the other scientists and people I got to meet while here at MSU. Specifically, for the 

folks with BMIS, Dr. Chandana Sumithrarachchi, Christopher Izzo, and Nadeesha Gamage, and 

the scientists with ISOLDE, thank you for giving me the research opportunities at FRIB, and wish 

the best in your future work toward isotopes and isotope harvesting. Thanks as well to Abigail 

Vanderberg and Per Askeland for your help with all my source sample work. Thank you, Dr. 

Weiwei and Jose Jimenez Gonzalez, for providing me with the materials and needed assistance to 

also refine my research.  

I also want to thank some peer researchers from these groups. As a whole, I want to just 

thank you all for sitting through my practice talks and giving me feedback and advice for my 

papers, including this thesis. Without any of you, the quality of my work would not be where it is 

now. First, to Deepika; although you have only joined our group I leave feeling confident 

knowing Kathi is with such a strong scientist and person. For all the times you helped with 

research, or even simple car rides and conversations, they meant a lot to me. I am so proud to call 

you my friend. Our summer student Suvan, your time was short, but the work you had done in 

just one summer has helped our research. It cannot be understated that this work would not have 

been possible without your contributions, and only wish the best in your future career aspirations. 

Finally, Kiersten; you joined recently as an undergrad, but your contribution has not gone 

unnoticed. I am happy to have helped you during your research and thankful for your assistance 

with mine. Since joining the nuclear team, I am so happy to have worked with Chloe, Vlad, and 

Jose; our time was always sporadic, but I am glad to have met each and every one of you. I also 

iii 

 
 
 
want to include Chirag, Wes, and Samridhi; thank you for your time and feedback during our 

Friday meetings. To everyone in the Gaiser group, thank you for providing a space to always 

present and get help with our work, and special thanks to Nicholas, Trenton, Mike, and Michaela. 

I am not a good talker, so I know that we never were close, but I am still happy that the times I 

needed help with a presentation or paper, you all were willing to listen. It truly means a lot to me. 

Thank you all for getting me to where I am today.  

I want to thank the friends and people I met while at MSU, for their support outside of the 

college, and even sometimes during it. A huge thanks to my best friend Jess, the best person 

anyone could ask for. We had a lot of laughs, game nights, and random Biggby runs. The 

memories spent while at MSU will always be with me. Thank you for being you, and staying with 

me throughout all of this. To all the folks, past and present, with Board Game Night, there were so 

many nights, days, and celebrations that I got to be a part of, so thank you all for the time spent. 

Thank you to Shommo and Kahini, my oldest friends, I am still so happy that you are but a text 

away and still a part of my life. The same for Susana, I never call as much, but we have seen each 

other through hard times. Thank you for still wanting to be a part of my life. 

I finally wish to thank all my family and loved ones. To my mom, Kimberly, and dad, 

Gabriel, you always were a phone call away, and were always there during the best and worst of 

me. Words alone cannot express what you mean to me, and how I am only where I am today 

through you both. For Abuela and Abuelo, there is always love and comfort, the chances I get to 

see you both were always the best knowing I got to be with you. For Uncle Michael and Nataly, 

the same is true with you, where when we were all together, there was never a shortage of love. 

To my sisters, Kaylee and Danielle, and my brother Darren, the fun days and game sessions we all 

had are not lost to me and I love you all. To Reggie, my brothers Julian and JP, Titi Desi, 

Grandma Gladys, and all the other folks from my other family, while our time is always so short 

and I wish we were still together like before, I am still happy that you are all a part of my life and 

hope that despite the challenges, you get the best because you deserve it. To everyone, mi familia, 

I am happy that I got to share my life with everyone.  

In loving memory of my mom, Julie, I want to dedicate the rest of the thesis to you. I wish 

you were here to witness all that I have done, but can only hope that I continue to do you proud. 

You always put the family over yourself, and I hope to one day get to become the same person as 

you were. Miss you everyday. I love you Mom. 

iv 

 
 
TABLE OF CONTENTS 

CHAPTER 1: Introduction  ..............................................................................................................1 
1.1: Isotopes and Applications  ............................................................................................1 
1.2: Nickel Radioisotopes ....................................................................................................1 
1.3: FRIB and Isotope Harvesting  .......................................................................................2 
1.4: Mass Separation and BMIS  ..........................................................................................3 

CHAPTER 2: Metal Oxides  ............................................................................................................6 
2.1: Background  ..................................................................................................................6 
2.2: Metal Oxide Characterization  ......................................................................................6 
2.3: Stock Solution Preparation  ...........................................................................................7 
2.4: Testing the Metal Oxide Adsorption  ............................................................................9 
2.5: ICP-OES Analysis  ........................................................................................................9 
2.6: Point of Zero Charge (PZC) Determination  ............................................................... 10 
2.7: X-Ray Diffraction (XRD) ........................................................................................... 10 
2.8: Point of Zero Charge Data .......................................................................................... 12 
2.9: Pourbaix Diagrams  ..................................................................................................... 14 
2.10: Adsorption Data  ....................................................................................................... 16 
2.11: Equilibration of Silicon Dioxide  .............................................................................. 18 
2.12: Stable 61Ni Experimentation  ..................................................................................... 20 
2.13: Conclusions and Future Directions  .......................................................................... 21 

CHAPTER 3: Preparation of Source Samples for the BMIS  ........................................................ 22 
3.1: 73As Source Sample Preparation  ................................................................................ 22 
3.2: Background  ................................................................................................................ 22 
3.3: Stable and Radioactive Arsenic Isotopes for Sample Preparation  .............................. 23 
3.4: Chemicals  ................................................................................................................... 23 
3.5: Instruments  ................................................................................................................. 23 
3.6: Stable Silver Arsenate Precipitation  ........................................................................... 24 
3.7: Stable Source Sample Preparation  ............................................................................. 24 
3.8: 73As Precipitation and Source Sample Preparation  .................................................... 25 
3.9: 73As Beam Delivery  ................................................................................................... 25 
3.10: Stable Silver Arsenate Source Sample Preparation  .................................................. 26 
3.11: 73As Source Sample Preparation  .............................................................................. 27 
3.12: Sample Characterization via SEM-EDS  ................................................................... 28 
3.13: XPS Analysis  ........................................................................................................... 30 
3.14: 73As Beam Delivery  ................................................................................................. 31 
3.15: Conclusions  .............................................................................................................. 33 
3.16: 232Th Source Preparation and Analysis of ThCl4  ...................................................... 33 
3.17: Conclusions  .............................................................................................................. 34 

CHAPTER 4: Conclusion  ............................................................................................................. 36 

BIBLIOGRAPHY  ......................................................................................................................... 37 

v 

 
 
1.1: Isotopes and Applications 

CHAPTER 1: Introduction 

The nuclear science community has consistently emphasized a growing need for non-

standard radioisotopes in the U.S., as demands are surpassing the existing supply capabilities. 

This was underlined by the 2015 published report from the Nuclear Science Advisory Committee 

– Isotopes Subcommittee. The significance of radioisotopes cannot be understated: clinical 

treatment and pharmaceuticals utilize the energy emitted from radioisotopes as a ‘tracer’ to better 

diagnose diseases in the body and use this radiation to treat and monitor various diseases. 

Radioisotopes as radiotracers are also used in environmental studies, as the radiation can 

accurately follow the chemical and biological pathways of different ecosystems. In the leading 

nuclear facilities across the U.S., enriched isotopes provide beams to study nuclear structure, 

quantum mechanics, and other physics research. The National Nuclear Security Administration 

(NNSA) uses radioisotopes to detect nuclear material, and the Transportation Security 

Administration (TSA) uses them in detectors for regularly screening incoming cargo and airport 

security.1,2 While there is a wide range of highly interesting radioisotopes, our main focus is 

directed towards the production of highly pure radioactive nickel isotopes. 

1.2: Nickel Radioisotopes 

Our research group is particularly interested in nickel isotopes. Nickel has five naturally 

occurring isotopes: 58Ni, 60Ni, 61Ni, 62Ni, and 64Ni that see applications in nuclear physics and 

synthesizing various copper isotopes (60, 61, 64Cu) that are important for applications in nuclear 

medicine.3,4 The nickel radioisotopes: 56Ni, 57Ni, 59Ni, and 63Ni are relevant for a variety of 

disciplines, such as astrophysics research, material science, nuclear medicine, biological tracers, 

and national security. In nuclear astrophysics, 56Ni and 63Ni are highly desired target materials for 

reaction rate studies, which will contribute to shed light on the formation of the elements in the 

universe.5 The positron-emission of 57Ni shows promise as a useful radioisotope for Positron-

Emission Tomography (PET) imaging, as well as a radiotracer in studying the toxicokinetics of 

nickel.6,7 Both 59Ni and 63Ni are used as biomedical tracers, detector materials, and in cosmic 

radiation studies, alongside applications for astrophysics research.8 In particular, 59Ni is used to 

study the radiation of extraterrestrial matter, while 63Ni is used in national security applications as 

an ionization source for explosive residue detectors and in Electron Capture Detectors (ECD) for 

analytical instruments, such as gas chromatographs.9–11 During irradiation of stable 58Ni inside 

1 

 
fusion reactors, which is a part of many structural components, the (n, γ) reaction produces 59Ni 

that ultimately undergoes an (n, α) reaction to 56Fe, releasing helium that can cause damage to the 

structural material of these reactors.12,13 Researchers are therefore interested in investigating the 

cross-section of the 59Ni (n, α) reaction, and would require 59Ni source materials to perform such 

measurements. Considering the wide range of applications for Ni radioisotopes, there is a strong 

rationale for investigating methods to produce them at high radioisotopic purities.  

With the promise of utilizing nickel isotopes in these disciplines, the difficulty is the 

generation of sufficient quantities at high radioisotopic purities. For example, radioisotopes as 

reaction targets in nuclear astrophysics have to be available in sizeable quantities and with 

sufficient radioisotopic purity to be a viable sample material, with similar requirements for 

nuclear medicine, biological tracers, and detectors.14,15 Despite the wide interest in Ni isotopes, a 

production method that can yield the desired quantities of high-purity samples is still lacking. In 

the following work, one aspect of this challenge will be addressed. 

1.3: FRIB and Isotope Harvesting 

At the Facility for Rare Isotope Beams (FRIB), rare isotope beams are generated for 

nuclear physics research. FRIB consists of a super-conducting radiofrequency heavy-ion linear 

accelerator that is predicted to deliver beam powers of 400kW and accelerate all stable isotopes, 

ranging from hydrogen to 238U. This accelerator will create heavy-ion primary beams that impinge 

on a target. Only a small percentage of the primary beam will react with the target to produce a 

variety of isotopes. The generated isotopes enter a dipole magnet separator that separates the 

isotopes and delivers the desired exotic secondary beams to scientific user experiments. The 

unused primary beam is usually directed into a solid beam blocker.16–18  

Figure 1: Schematic for Isotope Harvesting at FRIB provided by G. Severin. 

By replacing the solid beam blocker with a water-filled target, a large portion of the 

2 

 
 
unused primary beam can be collected. In this process, nuclear reactions between the primary 

beam and the water molecules (fragmentation, spallation, fusion-evaporation) will produce a 

variety of radioisotopes. These species can be extracted from the water, which became known as 

‘isotope harvesting’. This process is visualized in Figure 1. Through isotope harvesting, exotic 

isotopes can be accessed, which are produced as by-products of standard accelerator operation 

without requiring costly irradiation time. The collection process occurs in the background and 

does not interfere with the usual operation of FRIB. The feasibility of isotope harvesting was 

demonstrated at FRIB’s predecessor facility, the National Superconducting Cyclotron Laboratory 

(NSCL). Beams of 24Na, 40Ca, 48Ca, 76Ge, and 78Kr were captured in a liquid water matrix. The 

generated aqueous radioisotopes were harvested from the water using ion exchange beds, while 

cooled stainless-steel traps were used to collect the gaseous radioisotopes. The harvested 

radioisotopes from these experiments encompass 24Na, 47Ca, 48V, 62Zn, 67Cu, and 76,77Kr.18–26 It is 

notable, that the aqueous phase in the isotope harvesting setup has a neutral pH and consists of 

pure water that is devoid of any ions.  

So far, the main focus of isotope harvesting was laid on generator isotopes – harvesting 

the longer-lived parent radionuclides, followed by purification, and then decay to the desired 

daughter isotope.23 This approach, however, does not work efficiently with parent radionuclides 

that have too short half-lives. When directly harvesting the daughter radioisotope and even after 

performing chemical separation, the purified sample will still contain a range of isotopes of the 

same element. An alternative technique is required in order to broaden the spectrum of 

harvestable isotopes at FRIB that can be obtained at high radioisotopic purity. 

1.4: Mass Separation and BMIS 

Mass separation is a way to separate individual isotopes based on their mass, resulting in 

samples with enhanced radioisotopic purity. In an attempt to combine isotope harvesting with 

mass separation, the radioisotopes from the water dump system will be collected on a sorbent 

material, like metal oxides. Metal oxides exhibit refractory properties, which makes it possible to 

directly introduce the entire assembly into the high-temperature environment of the mass 

separator’s plasma ion source. With this, the direct combination of isotope harvesting and mass 

separation comes into reach. For the mass separation system, the already existing infrastructure at 

FRIB will be used. The key elements are the Batch Mode Ion Source (BMIS), a plasma ion source 

(shown in Figure 2), and a magnet, which are situated on the same beamline (a more detailed 

3 

 
discussion of BMIS operation can be found in section 3.1.1). The introduced sample is heated, 

atomized, and finally ionized. The ion beam enters the mass separator that separates each isotope 

by mass. So far, this setup has been used to deliver offline beams to other user facilities at FRIB.27 

To run offline samples within BMIS, a source sample is prepared onto a sheet of tantalum, and 

deposited into the oven, shown in Figure 2.28 Similar mass separation systems are currently in 

place with the Isotope Separation On-Line facilities at the European Organization for Nuclear 

Research (ISOLDE-CERN), as well as its Medical Isotopes facilities (CERN-MEDICIS).29,30 For 

our research, we envision the collection of the separated isotopes on individual metallic foils in 

the future. Any co-implanted isobaric impurities and the bulk amount of matrix material can be 

removed via chemical separation. What remains would be the desired radioisotope with enhanced 

radioisotopic purity. Figure 3 outlines this projected scheme.  

Figure 2: Image of the Batch Mode Ion Source. Image provided by K. Domnanich. 

Figure 3: Flow diagram of the proposed isotope harvesting process. Radioisotopes are first 
produced in the aqueous phase. Metal oxides will adsorb the isotopes and the entire 
assembly will be directly introduced into BMIS. This will be followed by mass separation of 
the isotopes. The purified isotopes will then be collected onto foils and chemically separated 
to obtain a radioisotopically pure sample. 

The BMIS is able to work at minimum temperatures of 300ºC and can go as high as 

around 1800ºC.28 These temperatures can allow for efficient atomization of the inserted samples; 

however, these operating conditions require a matrix that can survive those temperatures. In the 

4 

 
 
 
past, isotope separation used ion exchange resins as a sorbent due to their affordability and 

reliable application.31 However, most ion exchange resins would degrade under the BMIS 

temperature conditions. Our research group proposed the use of metal oxides as a sorbent 

material: their refractory nature would ensure thermal stability.32 In addition, the metal oxides 

would provide a seamless combination of isotope harvesting and mass separation.  

One goal of this work was to assess the adsorption capabilities of metal oxides as a 

potential sorbent for isotope harvesting. This was accomplished through simulation experiments 

with stable element samples and applying the expected isotope harvesting conditions. During the 

simulation with metal oxides, a collaboration was held with the BMIS researchers in the 

development of a source sample to allow the generation of offline beams for user experiments. 

This work would allow for the acquisition of the necessary expertise within our research team in 

assessing the necessary qualities a sample must have to perform a successful run. Herein we 

describe the research progress in both: the development of the mass-separation option by testing 

the adsorption capability of various metal oxides, as well as the efforts in the preparation of a 73As 

source sample for BMIS operation. 

5 

 
 
 
2.1: Background 

CHAPTER 2: Metal Oxides 

Metal oxides are considered as an alternative sorbent material for isotope harvesting. Their 

refractory nature would make them compatible with the high temperatures inside the BMIS, and 

provide a direct combination of isotope harvesting and mass separation. Metal oxides have 

already seen use as a sorbent for wastewater treatment and water purification.33 Researchers at 

ISOLDE, CERN have also demonstrated success in using metal oxides as target materials.29 The 

work done then hopes to use such metal oxides for our isotope harvesting setup at FRIB. In order 

to assess the sorption abilities of the metal oxides, adsorption studies were done with 10 stable 

elements that would represent the radioisotopes of interest. Our group was especially interested in 

the adsorption of nickel, though the adsorption of the other elements was also investigated as 

those radioisotopes are also of significant scientific interest. When metal oxides come into contact 

with an aqueous solution, their surface becomes hydroxylated (MOH). This hydroxyl layer can be 

protonated or deprotonated, resulting in an electrical surface charge. This charge can dictate the 

species that readily adsorb to the metal oxides.34 The overall charge on each metal oxide depends 

on the larger concentration of ions present, according to the equations below: 

MOH(surf) + H2O ⇌ MOH2

+(surf) + OH-(aq) 

MOH(surf) + H2O ⇌ MO-(surf) + H3O+(aq)   

        (2) 

        (3) 

The point at which the net charge of the metal oxide surface is zero is the Point of Zero 

Charge (PZC). The PZC of the metal oxide determines the expected surface charge at a certain 

pH. If the solution pH is below the PZC, the metal oxide will have a positively charged surface 

(MOH2

+), and if the solution pH is above the PZC, the metal oxide has a negatively charged 

surface (MO-).34,35 By plotting the initial pH against the change in pH (ΔpH), the PZC of the 

metal oxide can be determined. Work had also been done to determine the PZC of each metal 

oxide to predict the adsorption of each element to the oxide. A large part of the resulting 

adsorption data and PZC data was obtained by Suvan Campbell as a part of his summer research 

program. It is important to note that the harvesting conditions of the water system are kept at a 

neutral pH, and devoid of any ions. 

2.2.: Metal Oxide Characterization 

The metal oxide structure was characterized via Powder X-Ray Diffraction (XRD) using a 

Rigaku Miniflex Powder Diffractometer. The metal oxides used in this work are listed in Table 1. 

6 

 
 
 
     
 
        
 
 
 
The available metal oxides were grounded, placed on a 0.2mm thick silicon rectangular sample 

holder, and the XRD spectra were acquired using the DIFFRAC.EVA software. The resulting 

spectra are compared with the references available in the Crystallographic Open Database (COD). 

The output consists of a list of the possible phases and the percentage match. 

Table 1: Compiled list of the tested sorbent materials, including the chemical formula, 
reported particle size, purity, and retailer details.  

Sorbent 

Formula  Particle Size  Purity 

Company 

Zirconium (IV) Oxide  ZrO2 

5µm 

99% trace 

Sigma-Aldrich 

metals basis 

Yttrium (III) Oxide 

Y2O3 

- 

99.99% trace 

Sigma-Aldrich 

metals basis 

Magnesium Oxide 

MgO 

-325 mesh 

≥99% trace 

Sigma-Aldrich 

metals basis 

Titanium (IV) Oxide 

TiO2 

- 

99-100.5% 

Sigma-Aldrich 

Cerium (IV) Oxide 

CeO2 

<5µm 

99.9% trace 

Sigma-Aldrich 

metal basis 

Silica Gel 

SiO2 

63-200µm 

High-Purity 

Sigma-Aldrich 

Titanium Dioxide 

TiO2 

100nm 

Nano-powder 

Grade 

99.9% 

US Research 

Nanomaterials Inc. 

Graphite 

C 

50 mesh 

99.50% 

ACS Material 

2.3: Stock Solution Preparation 

To evaluate the efficiency of metal oxide adsorption, testing was done with 10 stable 

elements. The 10 elements represent the isotopes that are expected to be mainly produced in the 

beam dump by 58Ni and 78Kr primary beams. Table 2 lists each element and the available ICP 

stock solutions. Before using these solutions for the planned experiments, the nitric acid (HNO3) 

matrix was removed. Several 10mL beakers were rinsed with De-Ionized (DI) water and left 

briefly to incubate in 1M HNO3. After discarding the acid, the beakers were rinsed with MilliQ 

water (conductivity of 18.20MΩ*cm). A volume of 3mL of each stock solution was pipetted into 

each beaker, placed on a few hot plates set to 120ºC, and brought down to a residue. These formed 

7 

 
 
residues were reconstituted with 500µL MilliQ water. In case the residue did not dissolve in 

water, the mixture was heated, and if any solid remained, the solution would be treated with 

350µL 70% HNO3. This was followed by subsequent evaporation and reconstitution with MilliQ 

water. These reconstituted solutions were transferred into 10 pre-weighed 5mL Eppendorf tubes. 

The beakers were rinsed three times with a small volume of MilliQ water, and those rinses were 

transferred to the respective tubes and weighed.  

Table 2: Reagent data for all used ICP element solutions. The data includes the 
concentration and error, the given matrix, and the manufacturer. 

Element 

Concentration (ppm)  Error (ppm)  Matrix 

Company 

Arsenic 

Chromium 

Cobalt 

Copper 

Manganese 

Nickel 

Scandium 

Selenium 

Vanadium 

Zinc 

997 

1000 

1000 

1000 

1003 

1000 

1000 

1000 

1000 

1000 

±4 

- 

±2 

- 

±5 

±2 

±10 

±10 

±10 

±10 

3-5% HNO3 

Sigma-Aldrich 

3-5% HNO3  GFS Chemicals 

3-5% HNO3 

Sigma-Aldrich 

2% HNO3 

SPEX CertiPrep 

2% HNO3 

Sigma-Aldrich 

2% HNO3 

Sigma-Aldrich 

5% HNO3 

GFS Chemicals 

5% HNO3 

GFS Chemicals 

5% HNO3 

GFS Chemicals 

5% HNO3 

GFS Chemicals 

To confirm the concentrations of each element in each tube, the concentrations were 

quantitatively measured using an Agilent 5900 Inductively Coupled Plasma-Optical Emission 

Spectroscopy (ICP-OES). The reconstituted solutions were diluted by a ratio of 1:100 using 3% 

HNO3 as the matrix to reach concentrations of about 10ppm. This dilution was used to make two 

dilutions of 1:5 and 1:10 respectively. Another set of samples was also prepared as calibration 

standards using each element stock solution; each ICP standard from Table 2 was diluted by a 1:5 

ratio with 3% HNO3 to reach a concentration of 200ppm. A portion of each 200ppm solution was 

used to make a 10ppm mixed metal standard. Portions of this mixed metal standard were used to 

prepare calibration standards of 1, 5, and 10ppm respectively. A 3-point calibration curve using 

these standards was generated and allowed to accurately determine the concentration of each 

present element in the reconstituted solutions. 

8 

 
2.4: Testing the Metal Oxide Adsorption 

While the pH of the water in the isotope harvesting system will have a neutral pH, the 

following experiments were conducted at a pH of 5.6. This was done to reflect the pH of MilliQ 

water, which is usually around 5.6 at ambient conditions.36,37 It is believed that these slightly 

different conditions still reasonably reflect the conditions of the neutral isotope harvesting water. 

For our experiments, this was aimed to be around pH 5.6, which was achieved without the use of 

any buffers to keep the level of background ions at a very low level. After each stock solution was 

prepared according to the description in section 2.2.2, four solutions were made that comprised 

the individual elements, diluted to about 1ppm with MilliQ water. Individually, solution 1 

encompassed cobalt, copper, and manganese, solution 2 consisted of arsenic, selenium, and zinc, 

solution 3 of nickel and scandium, and solution 4 of chromium and vanadium. The pH of each 

solution was adjusted to 5.6±0.1 using dilute solutions of sodium hydroxide (NaOH) and HNO3, 

together with a multi-point calibration pH meter (Seven CompactTM Duo S213 pH/Conductivity 

Meter). After this initial adjustment, each solution was left to equilibrate overnight, after which 

the pH was checked and re-adjusted, if necessary. 

After the equilibration and final pH adjustment, the prepared metal solutions were used for 

the adsorption experiments with the metal oxides. A mass of about 100mg of each metal oxide 

was weighed out in triplicate for each tested solution into 25mL Eppendorf tubes. To each tube, 

10mL of each test solution was added. A blank solution with no added metal oxide powder was 

also included with each test series. The samples were placed inside a shaking incubator (New 

Brunswick Innova 42 Incubator) set to 300rpm at 20ºC for 24 hours. After the incubation period, 

the samples were centrifuged three times in a Sorvall ST8 benchtop centrifuge (ThermoFisher 

Scientific) at 4000rpm for 10 minutes. After centrifugation, two layers formed: the metal oxide 

which contained any of the potentially adsorbed elements, and the supernatant which contained 

the un-adsorbed elements. The supernatant solutions were carefully transferred into separate 

25mL tubes.  

2.5: ICP-OES Analysis 

For ICP-OES analysis, all samples, which included all supernatants, sample blanks, and 

aliquots of the initial test solutions, were diluted in a 1:2 and 1:3 ratio with 3% HNO3 as the 

matrix. A series of five standards at concentrations of 0.01, 0.05, 0.1, 0.5, and 1ppm respectively, 

which included all elements that were present in the samples, were prepared with 3% HNO3 as the 

9 

 
 
 
matrix. The 3% HNO3 solution also served as the measurement blank.  

2.6: Point of Zero Charge (PZC) Determination 

To determine the PZC for each metal oxide, 12 solutions were prepared: six solutions of 

MilliQ water and six solutions of 0.1M sodium nitrate (NaNO3). Using the pH meter, the pH of 

each solution was adjusted using dilute solutions of either HNO3 or NaOH to create a series with 

pH 2, 4, 5, 6, 8, and 10. After adjustment, 20mL of each solution was added to pre-weighed 25mL 

tubes that contained about 100mg of metal oxide. The samples then were placed inside the 

incubator shaker, set to 300rpm at 20ºC for 24 hours. Post-incubation, the samples were 

centrifuged at 4000rpm for 10 minutes, and the supernatant of each solution was transferred into a 

new 25mL tube. The pH of each supernatant was determined and used to calculate the ΔpH. 

Using the initial pH of each solution and the ΔpH, the PZC plot of each metal oxide was 

generated. 

2.7: X-Ray Diffraction (XRD) 

Powder XRD is a frequently used technique for the characterization of materials, 

providing information on the sample composition and phase identification.38 The characterization 

of each metal oxide allows for a comparison of the vendor-provided speciation with experimental 

data. Figure 4 includes all resulting spectra for each metal oxide, excluding silicon dioxide, 

against a reference spectra from the COD. A summary of the tested metal oxides and the best 

phase matches are given in Table 3. The results match with what is expected from the vendor 

information, with no significant impurities or other elements that could compromise any 

subsequent experiments. Of all the tested compounds, silicon dioxide was unable to generate an 

XRD spectrum. The utilized silicon dioxide is amorphous, which results in output signals of low 

intensities.39  

10 

 
 
 
 
 
(a)  

(b) 

(c) 

 (d) 

(e)  

(f) 

Figure 4: Powder XRD spectrum, with reference spectrum (red lines), of (a) Magnesium 
oxide.  (b) Cerium (IV) oxide. (c) Titanium dioxide. (d) Titania nanoparticles. (e) Yttrium 
(III) oxide. (f) Zirconium (IV) oxide. 

11 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table 3: List of all tested metal oxides, the reported phases are the ones with the best match 
from the database. 

Phase 

1st Match % 

ID 

ZrO2 

Y2O3 

CeO2 

MgO 

TiO2 

monoclinic 

cubic 

cubic 

cubic 

tetragonal 

TiO2 (NP) 

tetragonal 

70 

98 

76 

96 

99 

99 

SiO2 

amorphous 

---------------- 

2.8: Point of Zero Charge Data 

When making PZC plots of each metal oxide, sodium nitrate was included as a matrix 

alongside MilliQ water. It is predicted that electrostatic interactions govern the adsorption of the 

elements onto the oxides; however, electrolyte-specific effects could influence element 

adsorption. As a result, most literature that determine the PZC of metal oxides do so with a 

background electrolyte.40,41 The tests were done with sodium nitrate solution to be comparable to 

the literature PZC, as well as in MilliQ water to simulate the conditions during the isotope 

harvesting process. 

By determining the PZC of each metal oxide, the pH at which the surface charge is zero 

will be elucidated. The surface charge is an important parameter in the adsorption of metals onto 

metal oxide surfaces. Figure 5 lists all the generated PZC plots for each metal oxide. Looking at 

the PZC plot for zirconium (IV) oxide, the PZC is at around pH 4; given the pH of the water 

solution is 5.6, zirconium (IV) oxide is expected to have a negatively charged surface. Yttrium 

(III) oxide has its PZC at roughly pH 7, therefore yttrium (III) oxide should have a positively 

charged surface. From the PZC plots, it also is evident that the PZC exhibited no major 

differences between the MilliQ water and sodium nitrate matrices. Table 4 is a summary of all the 

metal oxide PZC pH, and the expected surface charge at the pH of the isotope harvesting water, 

alongside some literature PZC. It is worth noting that the literature data on the PZC with metal 

oxides varies strongly, depending on the tested matrix (background electrolytes), methods done 

(instrument, pre-conditioning, etc.), and manufacturer information (morphology, particle size, 

12 

 
 
etc.). While most of the here acquired data agree with the provided literature PZC, those that 

deviate, such as zirconium (IV) oxide and titanium dioxide, can be attributed to the inclusion of 

the background electrolytes and differences in the metal oxide material.41 

Figure 5: PZC plot of (a) Zirconium (IV) oxide*. (b) Yttrium (III) oxide*. (c) Magnesium 
oxide*. (d) Titanium (IV) oxide*. (e) Cerium (IV) oxide*. (f) Titania nanoparticles*. (g) 
Silicon dioxide. (*data was collected by Suvan Campbell) 

13 

 
 
 
 
 
Table 4: List of all the tested metal oxides, the pH PZC, the expected surface charge at pH 
5.6, and a set of literature PZC data for comparison.41 (*data was collected by Suvan 
Campbell) 

Metal Oxide 

PZC 

Literature PZC 

Expected Charge (at pH 5.6) 

Zirconium (IV) Oxide 

Yttrium (III) Oxide 

Magnesium Oxide 

Titanium (IV) Oxide* 

Cerium (IV) Oxide* 

Titania Nanoparticles* 

Silicon Dioxide 

~4 

~7 

~11 

~4 

~6.5 

~7 

~7 

2.9: Pourbaix Diagrams 

6.1 

7.5 

9.8 

6 

6 

6 

<5 

(-) 

(+) 

(+) 

(-) 

(+) 

(+) 

(+) 

In tandem with the PZC of the metal oxide, another parameter to consider is the charge of 

each species in solution. The pH of the surrounding solution impacts the charge of the metal oxide 

surface; additionally, the pH can also influence the expected charge of each element in the water. 

Pourbaix Diagrams visualize the expected speciation of an element by plotting its electrochemical 

potential (Eh) against the pH in an aqueous solution.42 The diagrams referenced in this experiment 

can be found in a compilation of Pourbaix Diagrams.43 Figure 6(a) shows the Pourbaix Diagram 

of zinc. Due to the aerated environment of the adsorption experiment, it is expected that the 

solutions rather have a positive potential. This is also expected for the water during isotope 

harvesting, where the generated hydrogen peroxide due to radiolysis creates a strongly oxidative 

environment.18 For a pH of 5.6, zinc is predicted to exist as a Zn2+ cation over a broad range of 

electrochemical potentials.44 Table 5 lists the expected charge of each species in the performed 

experiment.  

14 

 
 
                                                  (a)                                                                                          (b) 

Figure 6: (a) Pourbaix Diagram of Zinc. (b) Pourbaix Diagram of Vanadium.43 

Table 5: List of the expected species and charge of each element at pH 5.6 from their 
respective Pourbaix Diagrams.43 

Element  Expected Charge (at pH 5.6) 

Arsenic 

Chromium 

Cobalt 

Copper 

Manganese 

Nickel 

Scandium 

Selenium 

Vanadium 

Zinc 

(-) 

(-) 

(+) 

(+) 

(+) 

(+) 

(+) 

(-) 

(-) 

(+) 

However, these predictive estimations are subject to certain limitations, since the precise 

electrochemical potential of the water is not well known and is also subject to changes. Looking 

for example at Figure 6(b) and the Pourbaix Diagram of vanadium, a higher potential could see 

the dominant species from solid vanadium to VO3[-] and would then have a negative charge. In 

15 

 
              
              
 
addition, multiple species of each element may also still be present in solution.  

2.10: Adsorption Data 

Using ICP-OES, the adsorption of each element onto the metal oxides was quantified. 

Figure 7 and 8 are the adsorption data for each metal oxide. The PZC and Pourbaix Diagrams do 

explain some of the adsorption mechanisms for the metal oxides. For example, chromium showed 

strong adsorption onto yttrium (III) oxide (99.8%). The PZC data supports that yttrium (III) oxide 

has a positively charged surface, and the Pourbaix Diagram of chromium suggests that it is 

present as an anion in solution, so electrostatic attractions allow for efficient adsorption. There are 

exceptions to these interactions since many of the metal oxides still demonstrated strong 

adsorption to a wide variety of elements. Silicon dioxide showed strong adsorption for zinc 

(98.9%), but the PZC suggests a positively charged surface, while the Pourbaix Diagram also 

predicts a cationic species, leading to the expectation of electrostatic repulsions that translate to a 

low adsorption. Aside from Van Der Waals interactions, there can also be chemisorption of the 

elements onto the metal oxide surfaces; the presence of hydroxy species could allow for the 

precipitation of specific elements that otherwise would not adsorb due to charge. There also can 

be other chemical interactions occurring in solution, like the formation of metal aquo complexes, 

which can affect the adsorption of particular elements. Other effects on adsorption can include the 

radius of the adsorbed species, as well as the particle size of the metal oxides.45–48 Magnesium 

oxide demonstrated the best adsorption across all 10 elements and the PZC data (pH ~11) 

supports a basic nature. There would be a surplus of hydroxy ions present in solution, leading to 

the formation of hydroxy species with subsequent precipitation onto the magnesium oxide 

surface.  

16 

 
 
Figure 7: (a) Adsorption plot of the seven tested metal oxides for arsenic, cobalt, chromium, 
copper, and manganese. (b) Adsorption plot of the seven tested metal oxides for nickel, 
scandium, selenium, vanadium, and zinc. 

17 

ZrO2Y2O3MgOTiO2CeO2TiO2 (NP)SiO2020406080100% Adsorption As Co Cr Cu Mn(a)ZrO2Y2O3MgOTiO2CeO2TiO2 (NP)SiO2020406080100% Adsorption(b) Ni Sc Se V Zn 
 
 
 
 
 
Figure 8: Data of the percent adsorption of the 10 elements to each of the tested metal 
oxides, alongside the expected species charge and metal oxide charge at pH 5.6. (*data was 
collected by Suvan Campbell). 

The obtained data suggests that selected metal oxides are more efficient in adsorbing 

certain species than others, which could be applicable for selectively adsorbing particular species. 

Magnesium oxide, however, demonstrated the best adsorption across all 10 elements, showing 

promise as a broad-range sorbent material. A concern with the use of magnesium oxide is its 

partial water solubility, which could limit its application as a sorbent material for isotope 

harvesting. 

2.11: Equilibration of Silicon Dioxide 

It was evident that magnesium oxide demonstrated suitable sorbent capabilities, which 

were limited by the partial solubility in water. The concern was if any of the metal oxides were 

used as a sorbent for the water dump system, they would introduce ions to the water. A potential 

solution was to examine if equilibrating the metal oxide surface would mitigate the ability to alter 

the solution pH. It was determined whether the pre-equilibration of silicon dioxide in water, as it 

is water-insoluble, would demonstrate a comparable PZC and similar adsorption to the non-

18 

 
 
 
equilibrated SiO2. An aliquot of the stock silicon dioxide powder was vortexed with 20mL of 

MilliQ water and left to equilibrate. The silicon dioxide was vacuum-filtrated and dried at 

elevated temperatures to remove any excess water. The PZC of the equilibrated silicon dioxide 

was determined as outlined in section 2.2.5. Figure 9 highlights the PZC plots for both normal 

silicon dioxide and the equilibrated silicon dioxide. The data highlights minimal differences in 

PZC (~6.5) with the normal and equilibrated oxides, demonstrating that equilibrating the metal 

oxides would not mitigate its ability to alter the solution pH. 

Figure 9: (a) PZC plots of the equilibrated silicon dioxide versus the non-equilibrated silicon 
dioxide in MilliQ water. (b) PZC plots of the equilibrated silicon dioxide versus the non-
equilibrated silicon dioxide in sodium nitrate. 

Another potential solution would be to implement other sorbent materials. Graphite was 

considered as an inexpensive sorbent for isotope harvesting. The examination of the adsorption 

capability followed the same procedures outlined from section 2.2.2 to section 2.2.4. However, 

the poor adsorption capability of graphite across the 10 elements (shown in Table 6) precluded 

any further investigations.  

Table 6: Adsorption data of graphite for the 10 tested elements. 

Element  % Adsorption  

Mn 

0 

Co 

Cu 

Se 

As 

Zn 

Ni 

1.23 ± 0.22 

16.12 ± 0.67 

1.85 ± 0.43 

12.54 ± 2.59 

0 

0 

19 

 
 
Table 6 (cont’d) 

Sc 

Cr 

V 

11.83 ± 1.12 

15.70 ± 0.75 

17.93 ± 3.95 

2.12: Stable 61Ni Experimentation 

The promising adsorption capability of magnesium oxide towards most tested elements, 

particularly towards nickel, promoted the preparation of a sample to test the applicability for mass 

separation and the high-temperature environment of the BMIS. For this, a stock solution of stable 

61Ni (99.42% isotopic enrichment, Isoflex USA) was prepared, following the procedure outlined 

in section 2.2.2. The adsorption procedure onto magnesium oxide followed similar steps outlined 

in sections 2.2.3 to 2.2.4, with nickel-61 chloride as the only solution. After separating the 

supernatant, the magnesium oxide was left inside a fume hood to evaporate any residues of water. 

For the mass-separation experiment, a sample mass of about 1μg 61Ni (9.88*1015 atoms) was 

utilized, which translated to 21mg dried magnesium oxide that was transferred onto a 50x50mm 

sheet of 0.006mm thickness tantalum foil (99.9% purity, GoodFellow).  

The stable sample was folded up and inserted into the BMIS for 61Ni extraction. Nitrogen 

trifluoride (NF3) gas was used during evaporation to help volatilize the sample. Several mass 

scans were recorded at different temperature conditions. Figure 10 shows all mass scans taken 

from this experiment. It is evident from the mass scans that 61Ni formed many complex species 

with the magnesium oxide and the introduced fluorides from NF3. With the oxygen, many 

refractory oxygen-containing compounds formed, which rendered the extraction from BMIS 

highly challenging and resulted in low yields. Additionally, the amount of 61Ni was distributed 

over many different species, thereby reducing the current available for extraction of one single 

mass. Considering the challenges in preparing the adsorbed metal oxide samples and extracting a 

viable current from the BMIS, it was concluded that metal oxides are not particularly suitable as 

target materials for metallic radionuclides. Therefore, it was decided to disconnect the collection 

of isotopes and the preparation of samples for mass separation. This provides the option to include 

a chemical pre-separation step to produce cleaner samples and also offers more flexibility to tailor 

the targetry for the mass-separation step. 

20 

 
Figure 10: Mass scans of the stable 61Ni on magnesium oxide across several temperatures 
inside BMIS, with and without the addition of NF3. 

2.13: Conclusions and Future Directions  

The adsorption of 10 stable elements was simulated onto metal oxides to determine future 

applications towards isotope harvesting. The use of metal oxides could allow for a seamless 

combination of harvesting isotopes and mass separation. After analyzing several metal oxides, 

magnesium oxide was determined to be the most efficient in adsorbing all interesting species. 

However, it was evident that certain metal oxides, particularly magnesium oxide, would 

drastically shift the aqueous solution pH, introducing ions into solutions that should be avoided if 

applied to the water-dump system. Equilibrating the metal oxide surface was done using silicon 

dioxide as a potential solution, though it was not able to mitigate these pH changes. A first mass-

separation experiment involving a sample of stable 61Ni adsorbed onto magnesium oxide was 

performed. However, the extraction of 61Ni from the oxide matrix proved exceedingly difficult, 

compounded by less than satisfactory adsorption chemistry. Subsequently, it was concluded to 

disconnect the isotope harvesting and mass-separation steps, as this offers additional advantages 

of implementing a chemical pre-separation and to have more flexibility for tailoring the targetry. 

While the results indicated limited applicability of metal oxides as target materials for the BMIS, 

the adsorption of specific elements on certain metal oxides could be useful for specific 

applications. For example, while magnesium oxide is not suitable for aqueous harvesting due to 

its partial water solubility, silicon dioxide is an insoluble oxide that has a negligible effect on the 

water pH and could be useful for specific harvesting tasks. Species such as copper and zinc 

showed good adsorption onto SiO2, indicating a potential application for collection. 

21 

 
 
 
 
 
CHAPTER 3: Preparation of Source Samples for the BMIS 

3.1: 73As Source Sample Preparation 

The following work is intended for submission as a Short Communications paper to the 

Journal of Applied Radiation and Isotopes, entitled as “Preparation of a 73As Source Sample 

for Application in an Offline Ion Source.” For the purpose of this thesis, the text presented 

here has been rephrased. 

3.2: Background 

The Facility for Rare Isotope Beams (FRIB) is a state-of-the-art national research facility 

dedicated to advancing nuclear science. Typically, rare isotope beams crucial for cutting-edge 

research are generated through the fragmentation of stable primary beams.49 However, for specific 

user experiments, ion beams can be alternatively produced in what is termed 'offline mode' using 

either radioactive or stable source samples.28 One such radioisotope, 73As, notable for its 80.3-day 

half-life and primary gamma-ray emission at 53.437keV (Iγ=10.6%), finds application in nuclear 

data studies and cross-section measurements in nuclear astrophysics.50–52 A possible way to 

produce 73As beams for user experimentation at FRIB is through using source samples inside the 

Batch Mode Ion Source (BMIS). BMIS is an oven-ion source combination, where the introduced 

source samples undergo evaporation and atomization within the oven, followed by ionization in 

the plasma ion source. A mass analyzer selects the desired ion beams before transmission through 

the beamline for diverse research endeavors.28 These beams can be directed to the Re-Accelerator 

(ReA) or to other various user end stations, including the Low-Energy Beam and Ion Trap facility 

(LEBIT), the Beam Cooler and Laser Spectroscopy facility (BECOLA), and a beamline for 

experimenter instrumentation.53,54 Notably, the offline configuration of BMIS enables 

independent operation of these stopped and reaccelerated beam facilities, allowing concurrent 

execution of multiple user experiments at FRIB.27,28 Since coming online in 2021, the BMIS team 

has successfully delivered a chosen set of offline-generated isotope beams for user experiments. 

A suitable source sample for BMIS must meet several criteria. The material must be solid 

and readily vaporizable within BMIS operating temperatures (ranging from approximately 300ºC 

up to generally ~1000 ºC, but temperatures up to 2000ºC are possible). Additionally, volatile 

matrix components and isobaric impurities shall be minimized or eliminated. Responding to the 

strong interest from the FRIB user community for a low-energy 73As beam, this paper outlines the 

preparation of a 73As source sample to support the experimental user beam program at FRIB. 

22 

 
 
Utilizing an acidic 73As solution, silver arsenate was produced due to its favorable volatility 

within the BMIS operating temperature range. This conversion was achieved through an 

optimized precipitation reaction after the addition of a stable arsenic carrier. Ultimately, a source 

sample containing approximately 1.6mCi (5.76*1014 atoms) of 73As was prepared and effectively 

utilized in BMIS to provide a 73As beam for user experimentation. 

3.3: Stable and Radioactive Arsenic Isotopes for Sample Preparation 

The 73As solution was sourced from the National Isotope Distribution Center (NIDC), 

with an initial activity of 3mCi. It contained less than 0.01mCi of 74As and was in a 0.1N 

hydrochloric acid (HCl) matrix. Stable arsenic was obtained from a +3 arsenic ICP solution from 

High-Purity Standards (HPS), with a concentration of 1000 ± 20ppm As in a 2% HCl matrix. 

3.4: Chemicals 

To prepare the source samples, hydrogen peroxide (H2O2, 30%, ACS grade, Fisher 

Scientific), glacial acetic acid (CH3COOH, ≥99%, GR-ACS, Millipore Sigma), ammonium 

hydroxide solution (NH4OH, 30%, Sigma Aldrich), hexane (C6H14, Supelco, Sigma Aldrich), and 

silver nitrate (AgNO3, Reagent ACS, ChemPure Brand Chemicals) were utilized. Stable element 

analysis was conducted in a 3% volume matrix of nitric acid (HNO3, 70%, Sigma Aldrich). A 

50x50mm sheet of tantalum foil with a thickness of 0.006mm (99.9% purity, GoodFellow) served 

as the support material, while acetone (C3H6O, for liquid chromatography, Supelco, Sigma 

Aldrich) was used for rinsing. MilliQ water with a conductivity of 18.20MΩ*cm obtained from a 

Thermo Scientific Barnstead MicroPure Water System was used for all dilutions. Stock solutions 

of ICP arsenic standard (997mg/L ± 4mg/L, 5% HNO3 matrix, Sigma Aldrich) and ICP silver 

standard (Transition Metal Mix 1 for ICP, 100mg/L, 2% HNO3 matrix, Sigma Aldrich) were 

employed for the stable element analysis. 

3.5: Instruments 

Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES, Agilent 5900) 

was employed for the analytical determination of stable element concentrations. The activity of 

73As was quantified using a High-Purity Germanium Detector (HPGe, BEGe gamma-ray detector, 

BE2020, Canberra), using the characteristic gamma-line at 53.43keV, with Iγ=10.6%. Energy and 

efficiency calibration were conducted using europium-154 (Eu-154, Eckert & Ziegler, 1.054μCi, 

reference date 15-Sep-2020, Eγ=123.07keV (40.4%), 247.92keV (6.89%), 591.75keV (4.95%), 

723.30keV (20.06%), 873.18keV (12.08%), 1004.76keV (18.01%), 1274.42keV (34.8%)) and 

23 

 
 
 
 
americium-241 (Am-241, Eckert & Ziegler, 1.040μCi, reference date 15-Sep-2020, Eγ=59.54keV 

(35.9%)) point sources, positioned at distances of 15cm, 25cm, and 100cm. 

For characterization purposes, Scanning Electron Microscopy-Energy Dispersive X-Ray 

(SEM-EDS, JEOL 7500F, Oxford Instruments AZtec system) analysis and X-Ray Photoelectron 

Spectroscopy (XPS, CasaXPS, Physical Electronics 5400 System) were employed on the prepared 

stable arsenic source samples. Chemical processing utilized a benchtop vortex mixer (Digital 

Vortex Mixer, VWR), a hot plate (Cimarec, Barnstead Thermolyne), and a benchtop centrifuge 

(Sorvall ST8, ThermoFisher Scientific). 

3.6: Stable Silver Arsenate Precipitation 

The stable arsenic used was sourced from a +3 arsenic ICP solution that had to be 

converted to the +5 oxidation state by adding 1mL of the 1000ppm As3+ solution to 30% 

hydrogen peroxide at a 1:5 volumetric ratio.55 This solution was covered and left at room 

temperature overnight; subsequently, the solution was evaporated completely at 90ºC. The 

resulting residue in the sample container was dissolved in approximately 500µL MilliQ water and 

transferred to an Eppendorf tube. The beaker was rinsed three times with MilliQ water, and the 

rinse solutions were also added to the tube. 

The precipitation process followed a similar procedure outlined by L. J. Curtman and P. 

Daschavsky.56 A stock solution of silver nitrate was prepared at a concentration of 5000ppm Ag 

and stored in the dark to prevent photo-reduction. Around 0.5mL of the prepared As(V) solution, 

containing 80μg As, was used for precipitation. Silver nitrate stock solution was added to achieve 

molar ratios of Ag:As of 1.3:1, 5.7:1, and 12.7:1. The pH of the solution was adjusted to 7-8 using 

a few drops of 1M ammonium hydroxide and 10% acetic acid. After pH adjustment and 

vortexing, a visible brown precipitate formed. The sample was sealed with parafilm and left to 

react overnight. The mixture was then centrifuged, and the supernatant was separated off and 

transferred to another tube. The concentrations of arsenic and silver in the supernatant were 

quantified via ICP-OES to assess the precipitation yield. 

3.7: Stable Source Sample Preparation 

The stable silver arsenate precipitate, prepared with an optimized Ag:As ratio of 5.7:1, 

was utilized for the preparation of stable source samples. A 50x50mm sheet of tantalum foil was 

used as the support material; this sheet was cleaned with acetone and left to air-dry. The 

precipitate was suspended in solution and transferred onto the foil, which was kept inside a small, 

24 

 
 
in-house-made aluminum boat. The entire assembly of the foil and aluminum boat was placed on 

a hot plate set to 150ºC to evaporate off the solution. Any remaining silver arsenate was rinsed 

from the tube three times with approximately 0.6mL hexane, pipetted onto the foil, and 

evaporated. These stable samples were employed to develop the beam extraction from the BMIS 

and optimize the ion beam delivery process. Additionally, the prepared stable source samples 

were characterized by SEM-EDS and XPS to identify the present elements, their relative atomic 

percentages, and obtain further information about compound speciation. 

3.8: 73As Precipitation and Source Sample Preparation 

Activity monitoring was maintained throughout the precipitation process to track radiation 

levels and adjust for any activity losses. A volume of 0.259mL of the 73As solution, containing 

2.8mCi of 73As, was utilized for the reaction. To facilitate quantitative precipitation of the 

radioactive arsenic, the 73As sample was spiked with 80µg of stable arsenic (equivalent to 27.2μL 

of a 2949ppm stable As solution). The oxidation with 30% H2O2 and the subsequent steps for 

stable precipitate formation (section 3.2.4) were done by following the optimized procedure for 

stable precipitate formation. After oxidation and evaporation, the reconstituted solution (287.2μL) 

was employed for the precipitation reaction. This involved using the previously optimized 5.7:1 

ratio of Ag:As and adjusting the pH of the solution to 7-8. Once visible precipitation occurred and 

incubation was completed, the precipitate was separated via centrifugation and the supernatant 

was removed. The resulting precipitate was utilized for source sample preparation. The radio-

silver arsenate was transferred onto a clean sheet of tantalum foil on a hot plate set to 150ºC. 

During transfer and subsequent rinsing of the tube using hexane, the sample activity was 

monitored, ensuring approximately 6.67*1014 atoms (1.8mCi) of 73As were transferred onto the 

tantalum foil. The prepared source sample was transported to FRIB and utilized for generating the 

73As beam. 

3.9: 73As Beam Delivery 

The tantalum foil covered with 73As was tightly folded and inserted into the BMIS oven. 

The oven was heated to 500-1000ºC, causing the sample material to evaporate, followed by 

effusion into the ion source. Through ionization, monovalent 73As+ ions were formed, and the 

resulting ion beam was extracted, containing 73As+, stable 75As, and other contaminants. 

Following acceleration to 30keV, the beam underwent mass separation, with the desired 73As+ 

ions being selected and further accelerated to low energies in the ReAccelerator, allowing for 

25 

 
successful delivery to the scientific low-energy beam program. 

3.10: Stable Silver Arsenate Source Sample Preparation 

Arsenic +3 compounds are typically highly volatile, which may lead to considerable losses 

during subsequent sample preparation procedures.57 Initial explorations into evaporating a stable 

arsenic (III) solution showed recoveries below 0.5%. However, upon the addition of hydrogen 

peroxide at a five-fold molar excess, the arsenic in solution was oxidized to the less volatile +5 

oxidation state. This transformation was validated by achieving arsenic recovery rates of 

approximately 100% after evaporation. 

In order to ensure complete precipitation of a low-mass arsenic sample of 80µg, multiple 

experiments were conducted to determine the optimal Ag:As ratio. The selected low amount of 

stable As represents the upper limit of stable arsenic carrier, which is in alignment with the 

chemical toxicity limit set by the Occupational Safety and Health Administration (OSHA) for the 

specific space settings in the accelerator vault. This amount was consistently applied throughout 

the optimization process. With a 1.3-fold ratio of Ag, the quantitative formation of silver arsenate 

was induced, resulting in a precipitation yield of around 95% (±4.12%) (see Figure 11). However, 

complete precipitation of 100% (±4.24%) was achieved with 5.7- and 12.7-fold excesses of Ag. 

Based on these findings, the 5.7:1 ratio of Ag:As was chosen to ensure optimized precipitation 

yields of silver arsenate while minimizing the silver amount in the sample. Notably, the ICP-OES 

analysis of the silver in the supernatant suggested a silver depletion that would support the 

presence of an approximate 3:1 stoichiometric ratio of Ag:As in the precipitate.  

26 

 
Figure 11: Bar graph of the percent stable arsenic precipitated with different ratios of 
silver. Quantification was done via ICP-OES. The error bars include the propagated error 
from the ICP-OES analysis and the respective dilution factors. 

3.11: 73As Source Sample Preparation 
Once the optimized method was established through stable arsenic experiments, it was 

applied to create a silver arsenate precipitate with the radioactive 73As material. Despite the 

typically high volatility of arsenic compounds, utilizing them for source samples in BMIS would 

lead to rapid depletion and limited ion rates towards the end of extended beam experiments. 

Given that the melting point of silver arsenate is 830ºC, falling within the operational temperature 

range of BMIS, it was deemed suitable for sustaining adequate beam rates over prolonged 

durations.58 

Throughout the formation of the radio-silver arsenate precipitate and the preparation of the 

source sample, activity levels were consistently monitored via gamma-spectroscopic 

measurements. The formation of silver arsenate was highly quantitative, with only 0.013mCi of 

73As (±0.00040mCi) remaining in the supernatant. This indicates a precipitation yield of 99.4%, 

which is comparable to the stable arsenic sample preparation achieving a 100% yield. However, 

during the transfer of the precipitate onto the tantalum foil, 0.698mCi of 73As (±0.0179mCi) 

adhered to the pipette tip and the surface of the Eppendorf tube. Despite multiple rinse cycles with 

hexane, only µCi quantities of 73As could be removed. Following the transfer of 1.556mCi of 73As 

27 

1.3/1 Ag/As5.7/1 Ag/As12.7/1 Ag/As050100Precipitation Yield (%)Ag/As Ratios 
 
(±0.1011mCi) onto the tantalum foil, the resulting source sample was introduced into the BMIS 

oven. A significant loss of 0.512mCi (±0.0168mCi) of 73As occurred due to adsorption onto the 

surface of the Eppendorf tube, while the rest was lost to the pipette tips. However, in retrospect, 

rinsing with 2mL of 3% HNO3 was identified as an effective method for removing any residual 

73As, leaving only 0.0183mCi of 73As in the tube after this step. These findings could be of 

importance for future source sample preparation endeavors. 

3.12: Sample Characterization via SEM-EDS 

Due to certain analytical instruments not being approved for handling radioactive 

materials, characterization was conducted using stable source samples, as their chemical behavior 

was anticipated to mirror that of the radioactive samples. Following the outlined procedure, it was 

anticipated that the arsenic sample would generate silver arsenate with arsenic in the +5 oxidation 

state. Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy (SEM-

EDS) provided insights into the morphology of the stable arsenic precipitate and identified the 

constituent elements. Figure 12(a) depicts a section from a large part of the precipitate on the foil. 

The prepared source sample exhibited an irregular morphology, featuring regions entirely covered 

with precipitate interspersed with sections of exposed tantalum substrate (the darker regions in 

Figure 12(a)). Variations in drying rates could lead to an uneven distribution of the precipitate on 

the foil. Nevertheless, this uneven distribution did not hinder the application of the samples in the 

ion source. Figure 12(b) illustrates one EDS spectrum taken from point 1 on the map (indicated as 

Spectrum 1 in Table 7). The presence of predominant species, including silver, arsenic, and 

oxygen, was expected from each spectrum. To characterize the precipitate, spectra were taken 

from three different regions of the precipitate. The obtained data from recording these spectra 

(Spectra 1-3) are presented in Table 7. Spectra 1 and 2 were taken from spots in the central 

region, while Spectrum 3 was recorded on an edge region of the section in Figure 12(a). The EDS 

analysis indicated the presence of carbon, likely derived from the hexane rinses employed during 

the transfer of the precipitate onto the tantalum substrate. The atomic percentages of silver, 

arsenic, and oxygen were utilized to estimate the stoichiometric ratios of each element within the 

precipitate. The stoichiometric ratios between Ag, As, and O in Spectra 1 and 2 would allow to 

assume the presence of either silver arsenate (Ag3AsO4) or silver arsenite (Ag3AsO3). Both 

compounds exhibit an Ag-to-As ratio of 3 to 1, a finding corroborated by the ICP-OES analysis, 

which also indicated this 3:1 ratio. However, obtaining reliable quantitative estimates for oxygen 

28 

 
through EDS is challenging. Therefore, the oxygen amount was not used to determine the specific 

silver-arsenic compound. Spectrum 3 however, suggests a considerably higher Ag:As ratio. This 

spectrum was taken at an edge region in contrast to the first two spectra that were taken at the 

center region.59–61 During the preparation of the source sample, some excess silver nitrate from 

the supernatant could have become entrained in the precipitate. During the evaporation step, the 

silver nitrate could have also migrated towards the edges, causing a higher silver content around 

the precipitate edges. Therefore, Spectra 1 and 2 are a better representation of the majority of the 

precipitate.62  

(a) 

(b) 

Figure 12: (a) SEM image of the stable arsenic precipitate. (b) EDS spectrum of the stable 
arsenic precipitate taken from a point (Spectrum 1) in the shown SEM image. 

29 

 
 
 
 
 
 
Table 7: Atomic percentages of the detected elements from each spectrum, and the 
calculated ratio of each element for the precipitate.  

ID 

Spectrum 1 

Ag  
(atomic %) 
17.1 

As  
(atomic %) 
4.9 

O  
(atomic %) 
16.2 

C  
(atomic %) 
61.7 

Predicted Ratio 
(Ag:As:O) 
3.5:1:3.3 

Spectrum 2 

15.8 

Spectrum 3 

36.6 

4.9 

3.8 

12.6 

57.5 

66.7 

2.1 

3.2:1:2.6 

9.6:1:15.0 

3.13: XPS Analysis 

X-Ray Photoelectron Spectroscopy (XPS) was also performed on the stable arsenic 

sample, as depicted in Table 8, revealing the presence of the same elements observed in the SEM-

EDS measurements. The quantities of silver, arsenic, and oxygen are also comparable with the 

SEM-EDS results. Furthermore, the detection of carbon on the precipitate was similarly 

confirmed via XPS. The small amount of nitrogen identified could potentially be attributed to a 

stray peak from another element noted in the spectrum. 

The enlarged portion of the XPS spectrum, illustrated in Figure 13, can be attributed to the 

peak arising from the As-O bond. The spectrum was fitted to illustrate the contributions of As-O 

bonds in the As(III) and As(V) compounds to the As 3d5/2 peak. Literature indicates that the As 

3d5/2 position for oxygen-containing compounds of As(III) falls within the range of 44.7 – 

45.1eV, while for As(V) counterparts, it typically ranges slightly higher, between 45.8 – 46.2eV.63 

The fitted spectrum suggests that the arsenic-based precipitate comprises a combination of As(III) 

and As(V), with proportions of 78.3% and 21.7%, respectively. During the initial step of sample 

preparation, arsenic was fully converted from the +3 to +5 oxidation state and the majority of As 

in the precipitate was expected to be present as arsenic (V). Literature suggests the X-ray-induced 

photo-reduction of arsenic oxides could be a potential influence factor on this measurement, 

translating to the reduction of arsenic (V) species to arsenic (III). This reduction is magnified 

depending on the intensity of the X-rays and the presence of carbon. X-ray irradiation on 

hydrocarbons can induce the formation of highly energetic radicals that can strip oxygen from the 

arsenic oxide surface, further reducing it to arsenic (III).64 The addition of hexane rinses 

introduced an excess of carbon to the source sample, thereby promoting the probability for the 

reduction of arsenic. Therefore, using XPS to determine the oxidation state of As in this sample, 

which could point towards a specific silver-arsenic compound, showed to be of limited 

30 

 
significance. 

Figure 13: Arsenic spectrum obtained from XPS. 

Table 8: Data table of all detected elements from the stable arsenic sample, along with their 
percent compositions. 

ID 

Composition (Atomic %) 

C 

O 

Ta 

As 

Ag 

N 

33.75 

32.3 

5.45 

8.0 

18.0 

2.5 

However, considering the composition of the precipitate estimated via XPS, together with 

the results from the SEM-EDS analysis and the ICP-OES data from the supernatant, it can be 

deduced that a compound containing Ag, As, and O at a stoichiometric ratio that points towards 

silver arsenate or silver arsenite was produced. Furthermore, both SEM-EDS and XPS findings 

highlight the presence of carbon, indicating that in subsequent source sample preparations, the use 

of hexane rinses should be avoided. 

3.14: 73As Beam Delivery 

The fabricated 73As source sample was introduced into BMIS, where the 73As was 

extracted as a monovalent ion, 73As+, with a mass of 73. Scientific users utilized the resulting 73As 

31 

 
 
beam to investigate the reaction 73As(p,γ)74Se, crucial for the production of 74Se in stellar 

environments.65 Figure 14 illustrates the mass scans of the relevant region obtained from a stable 

silver arsenate sample, depicting stable silver and arsenic species at masses 107, 109, and 75, 

respectively. This source sample was employed for the development of the beam extraction and 

beam delivery. However, the mass scan for the radioactive 73As source sample was similar, only 

showing the stable species, while the low-level 73As signal at mass 73 would remain indiscernible. 

Such behavior is anticipated for a low-mass sample; nonetheless, mass 73 was selected by the 

mass analyzer, and the ion beam was accelerated and delivered at an average rate of 5*105 

particles per second to the ReAccelerator, achieving beam impurities close to 100%. However, to 

attain sufficient beam rates, the oven temperature needed to be elevated to approximately 870ºC. 

This observation aligns with the reported melting point of silver arsenate, noted at 830ºC. The two 

peaks observed at masses 107 and 109 originate from the two naturally occurring silver isotopes: 

107Ag (51.839%) and 109Ag (48.161%).50 The observed strong signal can be attributed to the nine-

fold excess of silver used to initiate the precipitation reaction. 

Figure 14: Mass scans of introduced stable source sample of 75As, alongside the co-present 
stable silver isotopes, 107Ag and 109Ag, at oven temperatures ranging from 500ºC to 941ºC. 

After the 73As beam was extracted from BMIS, it was sent to the ReAccelerator, where the 

beam was accelerated to the desired low energy requested by the scientific users. Figure 15 shows 

the measurement of 73As on a silicon detector, where the strong signal at 356MeV translates to a 

beam energy of 4.88MeV/u that matches with the expected beam energy for 73As, thereby serving 

as a means of identification. 

32 

 
 
Figure 15: Spectrum of the 73As beam after passing through the ReAccelerator. 

3.15: Conclusions 

This study demonstrates the preparation of a 73As source sample utilized in the offline ion 

source BMIS to generate a 73As beam, facilitating the low-energy scientific user program at FRIB. 

Silver arsenate, chosen for its favorable volatility within the operating temperature range of 

BMIS, was synthesized via chemical precipitation, yielding high precipitation yields (99.4%) with 

the 73As sample. The prepared 73As source sample (1.556mCi, 5.76*1014 atoms 73As) was utilized 

to successfully deliver a pure 73As+ ion beam at a suitable rate for an eight-day-long user 

experiment. Characterization via SEM-EDS and XPS revealed a silver arsenic compound, though 

determining exact stoichiometry proved challenging. Several improvements for refining the 

source sample manufacturing process were identified, such as avoiding the use of hexane and 

enhancing the quantitative transfer of 73As activity through the use of nitric acid. This developed 

preparation method expands the array of low-energy and stopped ion beams for FRIB's offline 

beam program, particularly enriching nuclear sciences with the inclusion of the 73As beam. 

3.16: 232Th Source Samples Preparation and Analysis of ThCl4 

After preparation of the 73As source sample, the BMIS team had interest in developing a 

232Th beam, which would serve as a surrogate for a 229Th beam requested by scientific users. This 

would be the first heavy element beam that would be generated from BMIS. For this initial 

experiment, about 5mL of ICP standard solution, containing 1000 ± 10ppm thorium in 5% HNO3 

(GFS Chemicals), was first precipitated as thorium hydroxide by the addition of ammonium 

hydroxide (reaction 4), followed by the dissolution in hydrochloric acid to form thorium chloride 

(reaction 5).66,67  

Th(NO3)4(aq) + 4NH4OH(aq) → Th(OH)4(s) + 4NH4NO3(aq) 

Th(OH)4(s) + 4HCl(aq) → ThCl4(aq) + 4H2O  

       (4) 

       (5) 

33 

 
 
 
 
      
Thorium chloride was chosen as its melting point is 770ºC, which falls within the 

operating temperature range of BMIS.68 The BMIS team intended to utilize a source sample of 

500µg thorium chloride for their initial test run. A small volume of the thorium ICP standard was 

brought to a residue and reconstituted in MilliQ water, following the stock preparation procedure 

outlined in section 2.2.2. After the stock preparation, 1M ammonium hydroxide was added until 

no more visible precipitation formed. The mixture was centrifuged and rinsed several times to 

remove any nitrate impurities. The thorium hydroxide was dissolved using 37% HCl and 

transferred onto a sheet of tantalum foil, similar to the source sample preparation described in 

section 3.2.5. 

After inserting the prepared source sample into BMIS, it was exceedingly challenging to 

extract a thorium beam. A possible reaction might be that the thorium chloride transformed into 

highly refractory thorium oxide in the high-temperature environment of BMIS. This is further 

corroborated by the observation that the prepared thorium source sample started to adsorb water 

immediately after it was removed from the hot plate. SEM-EDS was done and could support those 

presumptions; Table 9 from each spectra indicates that some oxygen is also present. It is possible 

that under atmospheric conditions, the thorium chloride adsorbs the moisture from the air due to 

its hygroscopic nature.69 In the BMIS environment, the entrained water in the source samples 

forms the highly refractory thorium oxide. The exceedingly high melting point of thorium oxide 

(3350ºC) would explain the small extracted beam current, as this temperature is well above the 

operating temperature range of BMIS.68 Further investigation is necessary to develop a suitable 

thorium source sample.  

Table 9: SEM-EDS data of all the spectra taken from the thorium sample, alongside the 
percentage of thorium, chlorine, and oxygen present in the sample. 

Spectrum #  Th (%)  Cl (%)  O (%) 

1 

2 

3 

4 

61.7 

62.9 

63.0 

61.1 

29.0 

28.5 

27.2 

29.4 

9.3 

8.6 

9.8 

9.4 

3.17: Conclusions 

A preliminary 232Th source sample was prepared, which was the first test extraction of a 

heavy element from the BMIS. Sample preparation was done by precipitation as thorium 

34 

 
 
hydroxide, and dissolution in hydrochloric acid to yield thorium chloride. Through SEM-EDS, the 

presence of thorium, chlorine, and some oxygen was corroborated. The initial run in the BMIS 

and the results of the SEM-EDS analysis support that due to the hygroscopic nature of the thorium 

chloride, a highly refractory compound formed. Further research into different targetry options 

and beam extraction are required to extract thorium beams at the required higher currents. 

35 

 
 
 
 
CHAPTER 4: Conclusion 

The work herein outlined in this dissertation aimed to further advance the endeavors in the 

proposed methodology for isotope harvesting endeavors at FRIB. The goals were to demonstrate 

the potential for metal oxides as a sorbent for aqueous isotope harvesting. These materials are 

interesting, as they would allow a direct combination with a subsequent mass-separation step that 

is necessary to produce samples of high radioisotopic purity. The sorption abilities of seven 

commercially available metal oxides were evaluated towards 10 stable elements that represent the 

interesting Ni isotopes, as well as the other primarily formed isotopes. Magnesium oxide 

demonstrated promising sorbent properties for all tested species, though it is partially water-

soluble and strongly altered the pH of the water solution, thereby introducing ions into the water. 

Nevertheless, a magnesium oxide sample with adsorbed stable 61Ni was prepared and the 

extraction of a 61Ni beam from this support material was tested in the BMIS. The extraction of 

61Ni from the oxide matrix proved exceedingly difficult, in part due to the formation of highly 

refractory species. Compounded by adsorption results that did not meet our requirements, it was 

decided to disconnect the mass-separation step and isotope harvesting. This offers additional 

advantages of implementing a chemical pre-separation to produce cleaner samples and also offers 

more flexibility for tailoring the targetry for mass separation. However, the adsorption of specific 

elements on certain, water-insoluble metal oxides, like silicon dioxide, could be considered for 

specific harvesting applications in the future. 

Furthermore, the collaboration with the BMIS team also extended towards the preparation 

of source samples to generate low-energy and stopped beams for the FRIB user program. Through 

this work, further insight into the operation and requirements of samples for mass separation 

could be gained. The first effort involved developing a 73As source sample. The 73As source was 

prepared through precipitation into silver arsenate. Sample characterization through SEM-EDS 

and XPS of the stable silver arsenate confirmed the elements present and that a silver-arsenic 

precipitate did form, though the exact species of arsenic that formed was not readily determined. 

After preparation of the 73As source sample, the BMIS team was able to deliver a 73As beam that 

was employed by scientific users to gain insights into the astro-physically significant 

73As(p,γ)74Se reaction. The outcome of the sample sample preparation work is intended for 

publication as a Short Communication paper in the Journal of Applied Radiation & Isotopes.  

36 

 
 
 
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