TRITON CLUSTERING IN (n,t) REACTIONS

Аннотация

According to the traditional definition of a nucleus, protons and neutrons in the nucleus have a
roughly homogeneous distribution. At the beginning of nuclear physics it was known that nuclear clustering was
extremely important in determining the structure of nuclei. The discovery of alpha-decay of heavy-nuclei initiated
the idea that clusters of nucleons might be preformed prior to emission. Afterwards Gamow, Gurney and Condon
described the alpha particle as undergoing quantum mechanical tunneling from inside the decaying nucleus.
Furthermore, an alpha particle model with bonds connecting clusters for N=Z even-even nuclei was suggested. In
1941, Margenau used a Slater determinant wave function for alpha clusters to compute an effective alpha-alpha
interaction. Moreover, Morigana supposed to apply linear chains of alpha clusters for describing some states of
alpha-like nuclei. Cluster structures are typically observed as excited states close to the corresponding decay
threshold. The origin of this phenomenon lies in the effective nuclear interaction, but the detailed mechanism of
clustering in nuclei has not yet been fully understood.
Clustering properties of nuclei would be helpful to understand both the nuclear structure and nuclear reaction
mechanisms. Different kind of clusters can be in principle exist in nuclei, for example, light (two, three and four
nucleons) and heavy ones. The clustering effect of nuclei has been investigated for a long time using different
methods based on various theoretical approaches. However, most of these studies were devoted to the α-clustering in
the α-decay, α-particle scattering, α-particle transfer and emission reactions, and molecule like α-cluster structure of
light nuclei. A famous example is Be isotopes for alpha-clustering. 8Be has a tight two-alpha cluster structure and the
nucleus is unstable. If we consider another isotope of 9Be (adding one neutron into 8Be), the cluster structure is
stabilized and the system is bound.
In the last years we have been studying the α-clustering in fast and slow neutrons induced (n,α) reactions using
the statistical model and knock-on mechanism. In this work in the framework of the compound and direct reaction
mechanisms, triton clustering factors (or probabilities) were first obtained for (n,t) reactions. In the case of
compound mechanism, the statistical model based on the evaporation model and constant nuclear temperature
approximation was used. For the direct reaction mechanism, the knock-on model was utilized. It was shown that the
triton clustering factors obtained by the knock-on model are much larger than ones found by the statistical model. At
the same time, the triton clustering factors for even-even target nuclei are on an average one order of magnitude
lower than ones for odd-even nuclei.
In addition, the triton clustering factors are much lower than the α-clustering in (n,α) reactions at the same
neutron energy range for medium-mass nuclei.