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摘要
Spallation neutrons produced in the collision of a 2.33 GeV deuteron beam with a large lead target are moderated by a thick graphite block surrounding the target and used to activate the radioactive samples of U-nat and Th put at three different positions, identified as holes "a", "b" and "c" in the graphite block. Rates of the (n, f), (n, gamma) and (n, 2n) reactions in the two samples are determined using the gamma spectrometry. The ratios of the experimental reaction rates, R(n, 2n)/R(n, f), for 232 Th and U-nat are estimated in order to understand the role of the (n, xn) kind of reactions in Accelerator-Driven Subcritical Systems. For the Th-sample, the ratio is similar to 54(10)% in the case of hole "a" and similar to 95(57)% in the case of hole "b" compared to 1.73(20)% for hole "a" and 0.710(9)% for hole "b" in the case of the U-nat sample. Also the ratio of fission rates in uranium to thorium, nat U (n, f)/(232) Th(n, f), is similar to 1.2(17) in the case of hole "a" and 26.8(85) in hole "b". Similarly, the ratio U-238 (n, 2n)/(232) Th (n, 2n) is 0.36(4) for hole "a" and 0.20(10) for hole "b" showing that Th-232 is more prone to the (n, xn) reaction than U-238. All the experimental reaction rates are compared with the simulated ones by generating neutron fluxes at the three holes from MCNPX 2.6c and making use of the LA150 library of cross-sections. The experimental and calculated reaction rates of all the three reactions are in reasonably good agreement. The transmutation power, P-norm as well as P-norm/P-beam of the set-up is estimated using the reaction rates of the (n, gamma) and (n, 2n) reactions for both the samples in the three holes and compared with some of the results of the "Energy plus Transmutation" set-up and TARC experiment.
- 出版日期2011-7
