The Monte Carlo simulation code MCNPX has been used to simulate the
production of 124I by 124,125Te(p, xn) and 123,124Te(d,xn) reactions to form
high activity 124I. For this reason, the TALYS-1.8 and ALICE/ASH codes were
used to calculate the reaction cross-section. The optimal energy range of
projectile is selected for this production by identifying the maximum
cross-section and the minimum impurity due to other emission channels. Target
geometry is designed by SRIM code based on stopping power calculations with
identical dimensions as the experimental data. The thick target yield of
reactions is predicted because of the excitation functions and stopping
power. All of the prerequisites obtained from the above interfaces are
adjusted in MCNPX code and the production process is simulated according to
benchmark experiments. Thereafter, the energy distribution of proton in
targets, the amount of residual nuclei during irradiation, were calculated.
The results are in good agreement with the reported data, thus confirming the
usefulness and accuracy of MCNPX as a tool for the optimization of other
radionuclides production. Based on the results, the 124Te(p,n)124I process
seems to be the most likely candidate to produce the 124I in low-energy
cyclotrons.
Regarding the low thermal conductivity of natTe element, the provision of an effective cooling system is one of the critical issues in cyclotron targetry to prevent melting of target matter during the irradiation to 124I production via natTe(p,xn)124I reaction. Heat transfer on Te target and efficiency of cooling fluid in the solid target system have been simulated based on a Finite Element Analysis (FEA) code for the thermal behavior of the target during the irradiation and under different beam currents, coolant flow rates, substrate matters and target geometry. The results on the routinely used solid target in Radiation Application Research School (RARS) cyclotron showed that in a 3 m/s coolant flow rate, by using a fined-cooling system and a nickel substrate coated on copper backing plate, the irradiation beam current can be raised up to 180 μA without any risk of melting. The cooling flow rates greater than 3 m/s do not noticeably improve the heat dispersion of target layer. As expected, a linear increase was observed for the temperature and temperature gradient of plates in the beam currents of 100–300 μA.
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