Neutron capture probabilities for thick samples at resonance energies

Capture and scattering probabilities for neutrons impinging on thick samples were measured by the Japan Atomic Energy Research Institute Linac time-of-flight spectrometer and were compared with those by Monte Carlo calculation. Sweeping the indicent neutron energy, the capture probability shows peaks at resonance energies in the case of a thin sample, whereas it shows dips for a thick sample, i.e., saturation occurs just at resonance energies. This saturation phenomenon is analyzed by Monte Carlo calculation for a distribution of path lengths of incident neutrons in the sample until capture in the sample. The saturation values of capture probability at resonance energies P/sub co/ are defined, and their dependence on the resonance parameters GAMMA/sub n//GAMMA is examined. The relations between P/sub co/ and GAMMA/sub n//GAMMA, with parameters including recoil energy, are obtained by Monte Carlo calculation. The relations are verified by measurement of P/sub co/ for many resonances of various GAMMA/sub n//GAMMA values. With the relation, GAMMA/sub n//GAMMA can be determined from P/sub co/, which is not sensitive to sample thickness