Development of a measurement system for the determination of (n,γ) cross-sections using multi-nucleon transfer reactions

摘要

We have installed a new experimental apparatus to measure y-rays from highly excited states populated by the multi-nucleon transfer reactions with heavy-ion projectiles to determine the (n, γ) cross-sections by means of the surrogate reaction method. An apparatus consists of two anti-Compton LaBr_3(Ce) spectrometers to measure the γ-rays and a Si ΔE-E detector system to detect outgoing projectile-like particles. Reactions of 153-MeV ~(18)O beams with ~(155)Gd and ~(157)Gd targets were used to study the performance of apparatus. By using the LaBr_3(Ce) scintillators with relatively large volume (101.6 mm in diameter and 127 mm in length), we have successfully measured γ-rays frorn the compound nuclei, which have excitation energy above neutron separation energy, populated by ~(155)Gd(~(18)O,~(16)O)~(157)Gd and ~(157)Gd(~(18)O, ~(16)O)~(159)Gd two-neutron transfer reactions. To measure in-beam γ-rays through heavy-ion-induced transfer reaction, it is important to assign the reaction channel clearly, since the cross-sections of the transfer reactions are much smaller than those of competing reactions such as Coulomb excitation and fusion reactions. The Si ΔE-E detector system was used to separate outgoing particles. The present study has demonstrated high capability of apparatus to measure the de-excitation γ-rays in the compound nuclei produced by the multi-nucleon transfer reactions for determination of the (n, γ) cross-sections by using the surrogate reaction method.