Angular distribution effect on the integrated cross section for radiative capture of 14 MeV neutrons

In the past, many reported integrated cross sections for the 14 MeV neutron radiative capture were measured at 90 degrees relative to the neutron beam direction and multiplied by 4 pi, so as to obtain a measure of the angle-i ntegrated cross sections. In such a procedure, an isotropic angular distribution of gamma-rays is ass umed. We calculated this distribution using the consistent direct-semi-dire ct model, in which the need for the model-free parameters has been eliminat ed. The result is that the a(1) Legendre polynomial, averaged over the boun d state transitions, is practically zero (distribution is forward-backward symmetric) and that the a(2) coefficient is a smooth function of the mass n umber with the values between -0.4 and -0.6, indicating anisotropy of the d istribution. Reported integrated cross sections are therefore for about 20% to 30% too high relative to the properly angle integrated cross sections. (C) 1999 Elsevier Science B.V.