Cross sections of fast neutron induced reactions on selenium isotopes

Abstract

Cross sections for 74, 76, 77,788e(n ' p) 74, 76, 77, 78As ' 76Se(n ' 2n)TSSe and 8~ ~)77Ge reactions have been measured in the energy range from 13.0 to 16.6 MeV by the activation technique using Ge(Li) detector 7-ray spectroscopy. Samples of selenium of natural isotopic composition were used as targets. The measurements provide information on the evolution of the (n, p) excitation functions with the increasing target neutron number (isotopic effect). The reaction model combining the compound nucleus and the preequilibrium emission processes is used to interpret these three types of reactions. The isotopic trend for the (n, p) reactions due to the neutron-proton competition in the compound nucleus is satisfactorily reproduced. However, a further experimental and theoretical work is needed for a better understanding of the origins of discrepancies which are suggested to be related to the precompound aspects of the assumed reaction model.

Activation cross sections and isomeric ratios in reactions induced by 14.5 MeV neutrons on152Sm,154Sm and178Hf

“…The straight lines drawn in this way are close to the data and allow the author of [ 11 ] to infer, that "no systematic variations" other than even-odd effects due to changes in Q-values in crn, p data "can be observed in the region of closed proton shells either in the target nuclei or in the residual nuclei." In fact odd-even effects might be the reason for the undiscussed deviation of the 778e cross section from the straight line isotopic dependence in [2].…”

“…GMAxFxS~emfm a x = a m GsAmFMSmexfx" (2) Here x and M denote the isotope under investigation and the monitor, G is the weight of the isotopes, A is the atomic weight, S, f and e are the peak area, the absolute intensity of the gamma line and the corresponding detector efficiency. We have devided the irradiation time tl into n intervals, each of duration At, during which we assume that the flux was constant and have replaced the usual form of the time factor F [14] by the expression:…”

“…This dependence is shown [9,10] to be determined by the systematic change of the Q-value for the (n,p) reaction with the mass number. The slope decrease of the isotopic dependence of the (n,p) cross sections for 74'76'77'785e with increasing neutron energy (13, 14.5 and 16.6 MeV) [2] is due to decrease of the CN part of the cross section with increasing projectile energy. The change in the slope reflects the difference in the ways the Q-value affects the (n,p) cross section for the CN and PE mechanisms [9].…”

“…The continuous interest [1,2] in activation cross section measurements with 14 MeV neutrons is due to the fact that they provide in a simple way, nuclear data necessary for a detailed understanding of the nuclear reaction mechanisms at low energies. The simple exit channels (n,p), (n, 2 n), (n, c~), (n, d), (n, ?J), which dominate the cross section, provide valuable data for testing the predictive power of contemporary theoretical and empirical models [3][4][5].…”

Calculations of (n,2n) reaction cross sections for74,76,78,80,82Se up to 20 MeV

“…In past years the cross section of selenium isotopes ( 74,76,78,80,82,84 Se) around 14-15 MeV have been measured by many researches such as Hille and Münzer [3]; Minetti and Pasquarelli [4]; Casanova and Sanchez [5]; Hoang et al [6] and Guozhu He [7].…”