Multinucleon-transfer-induced fission

多核子移行反応による核分裂

西尾 勝久   

Nishio, Katsuhisa

Transfer and multinucleon transfer (MNT) reaction are among the reactions possible in a collision between nuclei. The reactions produce different compound nuclei, depending on the number of neutrons and protons exchanged between colliding nuclei. Also, the excitation energy of compound nuclei will have a distribution of values. These properties offer a unique opportunity for fission studies. First of all, fission barrier height can be derived from the measurement of fission probability as a function of excitation energy and finding the threshold at which the fission probability rises. Also, fission properties such as fission-fragment mass distributions can be obtained for many nuclei by combining detectors to identify ejectile nucleus, and thus determine compound nucleus, with fission-fragment detectors. As the excitation energy can also be identified event by event, excitation-energy dependence of fission properties can be obtained. Recently, the inverse-kinematics method using a U beam has been introduced in MNT induced fission research. This opens a new opportunity to obtain new fission data, such as fragment-charge distributions, not realized in normal kinematics. Still an advantage in the normal kinematics is that many radioactive target nuclides can be used, thus allowing the study of fission for neutron-rich heavy-elements. After a brief introduction of the fission process and some results from transfer-induced fissions, recent experimental technique and related new data are discussed, including effects of multichance fission on fission-fragment mass distribution and on the neutron excess of fission fragments. Also angular-momentum transfer in the MNT process, as determined from the measurement of fission-fragment angular distribution, is discussed.