Isospin symmetry is expected for the T(z)=+/-1-->0 isobaric analogous transitions in isobars with mass number A, where T(z) is the z component of isospin T. Assuming this symmetry, strengths of ...analogous Gamow-Teller (GT) transitions within A = 50 isobars were determined from a high energy-resolution study at 0 degrees in combination with the decay Q value and lifetime from the beta decay. This method can be applied to other pf-shell nuclei and can be used to study GT strengths of astrophysical interest.
We examine a quantum phase transition in gamma-soft nuclei, where the O(6) limit is simultaneously a dynamical symmetry of the U(6) group of the interacting boson model and a critical point of a ...prolate-oblate phase transition. This is the only example of phase transitional behavior that can be described analytically for a finite s,d boson system.
The schematic shell model without residual interaction (SSM) assumes the same excitation energy for all spins in each particle-hole configuration multiplet. In {sup 208}Pb, more than forty states are ...known to contain almost the full strength of a single particle-hole configuration. The experimental excitation energy for a state with a certain spin differs from the energy predicted by the SSM by -0.2 to +0.6 MeV. The multiplet splitting is calculated with the surface delta interaction; it corresponds to the diagonal matrix element of the residual interaction in the SSM. For states containing more than 90% strength of a certain configuration and for the centroid of several completely observed configurations, the calculated multiplet splitting often approximates the experimental excitation energy within 30 keV. The strong mixing within some pairs of states containing the full strengths of two configurations is explained.
Excited states in 157Dy have been studied by γ-γ coincidence measurements via the reaction 124Sn(36S,3n) at a beam energy of 155MeV. Lifetimes of the relatively lower-spin states in 157Dy were ...measured by means of the Recoil Distance Dopplershift technique in the coincidence mode. The experiment was performed at the Laboratori Nazionali di Legnaro with the GASP array and the Cologne plunger device. With the same setup a Doppler- shift attenuation (DSA) lifetime measurement was performed for the higher spin states. The Differential decay-curve method was applied for the lifetime determination.
Analytical expressions are derived for the components of the intrinsic frame inverse mass tensor of the Bohr Hamiltonian. These expressions contain parameters which are determined by the experimental ...data on the
B
(
E
2)’s and the excitation energies of the low-lying collective states. It is shown that the nondiagonal component of the intrinsic frame mass tensor has a small effect on the collective motion. It is shown also that the values of the
B
ββ
,
B
γγ
and the rotational mass coefficient
B
1
differ in the well-deformed nuclei by factor 3 or more.
The concept of critical points in nuclear phase transitional regions is discussed from the standpoints of Q-invariants, simple observables and wave function entropy. It is shown that these critical ...points very closely coincide with the turning points of the discussed quantities, establishing the singular character of these points in nuclear phase transition regions between vibrational and rotational nuclei, with a finite number of particles.
A new experimental approach to the famous problem of the anomalously slow Gamow-Teller (GT) transitions in the beta decay of the A=14 multiplet is presented. The GT strength distributions to excited ...states in 14C and 14O were studied in high-resolution (d,2He) and (3He,t) charge-exchange reactions on 14N. No-core shell-model calculations capable of reproducing the suppression of the beta decays predict a selective excitation of Jpi=2+ states. The experimental confirmation represents a validation of the assumptions about the underlying structure of the 14N ground state wave function. However, the fragmentation of the GT strength over three 2+ final states remains a fundamental issue not explained by the present no-core shell model using a 6homega model space, suggesting possibly the need to include cluster structure in these light nuclei in a consistent way.
A new procedure for lifetime determination in singles measurements performed by means of the Doppler-shift attenuation method is proposed. An explicit separation of the shifted and unshifted ...fractions of the line-shape is achieved employing a summation over recoil histories calculated using a Monte-Carlo simulation. The lifetime is derived according to the Differential decay-curve approach. Tests with simulated data and experimental data analyzed earlier by a different method confirm the applicability of the procedure. Practical aspects of the new approach are investigated and discussed.
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