Population of isomers in the decay of the giant dipole resonance

Abstract

The value of an isomeric ratio (IR) in N=81 isotones ( 137 Ba, 139 Ce, 141 Nd and 143 Sm) is studied by means of the (γ, n) reaction. This quantity measures a probability to populate the isomeric state in respect to the ground state population. In (γ, n) reactions, the giant dipole resonance (GDR) is excited and after its decay by a neutron emission, the nucleus has an excitation energy of a few MeV. The forthcoming γ decay by direct or cascade transitions deexcites the nucleus into an isomeric or ground state. It has been observed experimentally that the IR for 137 Ba and 139 Ce equals about 0.13 while in two heavier isotones it is even less than half the size. To explain this effect, the structure of the excited states in the energy region up to 6.5 MeV has been calculated within the Quasiparticle Phonon Model. Many states are found connected to the ground and isomeric states by E1, E2 and M 1 transitions. The single-particle component of the wave function is responsible for the large values of the transitions. The calculated value of the isomeric ratio is in very good agreement with the experimental data for all isotones. A slightly different value of maximum energy with which the nuclei rest after neutron decay of the GDR is responsible for the reported effect of the A-dependence of the IR.

Electromagnetic character of the competitive γγ/γ-decay from 137mBa

“…The influence of the g eff s parameter on the experimental observables related to electromagnetic transitions of lowest-lying states and doubleγ decay probability coefficients was investigated by carrying out EDF + QPM calculations for several choices of this parameter between 0.6 and 1 of the value of the 'bare' spin-magnetic moment, g bare s . The theoretical observations indicate that the values g eff s ¼ 0:6 À 0:7g bare s which are in agreement with our previous findings 27,28,32 reproduce quite well the experimental data on M1 and M2 transition strengths and the angular distribution of the two photons of the doubleγ decay.…”

High-lying single-particle modes, chaos, correlational entropy, and doubling phase transition

“…By this reason, even a rather simple wave function, truncated, for example, by the quasiparticle and quasiparticle-plus-phonon components, can be used to describe the transition probabilities connecting high-lying and low-lying excited states. For this purpose, a simple practical procedure of averaging high-lying single-particle strength can be used [25].…”

The Study of Isomeric Ratios in Photonuclear Reactions Forming High Spin Isomers in the Giant Dipole Resonance Region

“…The isomeric ratios furnish valuable information about the energy level structure of nuclei and the nuclear reaction mechanism involved [1][2][3][4][5]. This quantity depends on the spin of target nucleus and the intake angular momentum determined by the mass and the energy of projectile particles.…”