Bremsstrahlung-induced fission and spallation of the pre-actinide nucleus ${}^{181}\mathrm{Ta}$

A study of photofission on ${}^{181}\mathrm{Ta}$ induced by bremsstrahlung with endpoint energies of 50 and 3500 MeV has been performed. The fission yields have been measured by using the induced-activity method in an off-line analysis. The total photofission yields for the tantalum target at 50 and 3500 MeV are found to be $5.4\pm 1.1 \mu \mathrm{b}$/ equivalent quanta per second (eq.q) and $0.77\pm 0.11$ mb/eq.q, respectively, and the corresponding deduced fissilities are $\left(0.23\pm 0.05\right)\times {10}^{-3}$ and $\left(2.9\pm 0.5\right)\times {10}^{-3}$. Mass- and charge-yield distributions were derived from the data. The results were compared with the simulated results from the crisp code for multimodal fission by the assuming symmetrical fission mode.

Figure 1

Mass-yield distribution for photofission of ${}^{181}\mathrm{Ta}$ at endpoint energy of 50 MeV. The present experimental data are shown by solid square symbols and the results of CRISP code calculation for fission and spallation are given by the dotted line curve and the dashed line curve, respectively.

Figure 2

Mass-yield distribution of photofission of ${}^{181}\mathrm{Ta}$ at endpoint energy of 3500 MeV. The present experimental data are shown by the solid square symbols. The open circle symbols correspond to data taken from Ref. [17], which also include spallation contributions. The results of the crisp code calculation for fission and spallation are given by the dotted line and the dashed line curve, respectively. The black solid line indicates the sum of the calculated fission and spallation yields.