MANUFACTURING 48V TARGET FOR NEUTRON REACTION CROSS-SECTION MEASUREMENTS

Many areas in nuclear science utilize simulation models of neutron reaction networks to predict the outcomes of chaotic events, such as stellar nucleosynthesis and nuclear detonations. The fidelity of these predictions can be improved by obtaining accurate nuclear reaction cross-section data. Much of the cross-section data on radioactive nuclei has not been measured before and performing these measurements would be beneficial for end users of evaluated nuclear data. Obtaining accurate nuclear reaction measurements of 48V, a radioisotope of V (t1/2 = 15.974(3) days), would be advantageous for the United States Stockpile Stewardship program as that data can enhance the fidelity of simulation models on neutron reaction networks and ultimately lead to better validation of the United States nuclear stockpile.Although there are many different types of nuclear reactions that can occur, the two reactions that dominate the destruction pathway for 48V with low energy neutrons are the 48V(n, γ)49V and 48V(n, p)49V reactions. Measuring total cross-section for the 48V(n, γ)49V reaction can be accomplished using the activation method, while a direct measurement technique that allows for the detection of outgoing protons and neutron energy (via neutron time-of-flight measurements) would be the best method for determining the 48V(n, p)49V cross-section. Both techniques require the fabrication of a stationary 48V target (containing mCi quantities of 48V) that meets specific purity, geometric, and stability requirements. In general, these targets need to be physically stable during the irradiation, free of impurities that would be detrimental for the measurement, uniform, and of the appropriate thickness to allow for accurate measurements to be made. The most important requirement for the target being measured via the activation method is the isotopic purity of the 48V, specifically with respect to 49V (>104 atoms of 48V/atom of 49V), while the 48V target for direct neutron-induced charged particle reaction measurements must be thin and uniform to minimize the attenuation of outgoing protons and the measurement time and error. To produce 48V in high isotopic purity and manufacture a thin and uniform 48V target, an isotope production method and a target fabrication method must be identified. Two different isotope production methods were investigated to discern the best method for producing 48V in high isotopic purity relative to 49V: a conventional α irradiation of natural Sc foil method and a novel method called isotope harvesting that focused on harvesting 48Cr from the aqueous beam dump at the Facility for Rare Isotope Beams and setting up a 48Cr/48V generator for pure 48V production. Isotope harvesting was found to be the best method for producing mCi quantities of 48V that meet or exceed the purity requirements for a 48V target to be used in neutron activation studies. Meanwhile, two 48V target manufacturing techniques were also examined: a conventional electrodeposition technique and a novel method called microjet printing. The electrodeposition method was found to be extremely pH dependent and would be challenging to use to produce a radioactive target, while microjet printing has the highest potential at being the most effective method for fabricating thin and relatively uniform 48V targets. Overall, a recommended thin 48V target manufacturing protocol was identified and covers all the steps from the in the process to produce mCi levels of 48V in high isotopic purity relative to 49V along with those necessary for the fabrication of a thin and uniform 48V target for neutron-induced reaction studies.