Half-life measurements of intrinsic states in deformed odd-mass nuclei

The half-lives of the following intrinsic states in deformed odd-mass nuclei has been measured by delayed coincidences with a time-to-amplitude converter:

1. 5/2 5/2⁺[642] at 86.5 keV in¹⁵⁵Gd:T _1/2=6.7±0.3 ns, which results in the determination of theE1,ΔK=1 transition probability to the ground state 3/2 3/2^?[521] and first rotational state 5/2 3/2^?[521], yielding hindrance factors ofF _N ≈5.5 and ≈1.8 (F _W =3.1×10⁴ and 2.3×10⁴) respectively.
2. (3) 5/2 5/2^?[512] at 191.4 keV in¹⁶⁹Yb:T _1/2=3.35±0.15 ns and at 122.39 keV in¹⁷¹Yb:T _1/2=265±20 ns which results in the determination of the transition probabilities of theE1,ΔK=1 transitions to the ground states 7/2 7/2⁺[633], of theK-forbiddenM1 transitions to the 5/2 and 3/2 1/2^?[521] and of theE2 transitions to the 5/2, 3/2 and 1/2 1/2^?[521] states in both nuclei.

TheE1 transition probabilities are compared to the transitions between the same Nilsson states in¹⁷³Yb and¹⁷⁵Hf discussing the influence of the position of the Fermi surface — obtained from recent stripping and pick-up reactions — on these transition probabilities. Additional information on the decay scheme of¹⁷¹Lu→¹⁷¹Yb is obtained by delayed coincidence measurements. For testing the used time-to-amplitude converter the well known half-lives of the 482 keV level in¹⁸¹Ta (T _1/2=10.4±0.3 ns) and of the 279 keV level in²⁰³Tl (T _1/2=0.285 ±0.015 ns) were measured, in good agreement with other measurements.     

Transition rates between negative-parity states in odd-mass gold nuclei

The half-lives of low-lying negative-parity states in ¹⁸⁵Au and ¹⁸⁷Au have been measured using mass-separated sources from the ISOCELE separator. The results,

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, are discussed within the generalized particle-plus-asymmetric-rotor model, giving information on the structure of the states and on the nuclear-shape parameters.     

Collective states in even Sn nuclei

0⁺, 2⁺, 4⁴ and 3^? states in ^112–124Sn have been studied with the (p, p′γ) reaction and in Coulomb excitation. Absolute E2 transition rates between these levels have been extracted with the aid of the Winther-de Boer code. For ^116,118Sn, B(E2; 4₁⁺ → 2₁⁺) ≈ 20 W.u., suggesting a two-phonon character of the 4₁⁺ states. For the lighter and heavier isotopes, this value is significantly smaller. All observed values of B(E2; 2₂⁺ → 2₁⁺) and B(E2; 2₃⁺→ 2₁⁺) are about 5 W.u. Also. values of B(E3; 0₁⁺ → 3^?₁) have been measured for all stable even Sn nuclei. In ¹¹⁶Sn the branching ratio (3₁^? → 0₁⁺)/(3₁^? → 2₁⁺) has been measured. From this we obtain a half-life of 0.34±0.07 ps for the first 3^? level in ¹¹⁶Sn and B(E1; 3₁^? → 2₁⁺) = (1.4±0.3) × 10^?5'e² · b, corresponding to a hindrance factor of 10³.     

Multilevel calculations in odd-mass nuclei (I). Negative-parity states

We present the results of an analysis of the negative-parity states in the odd-mass transitional isotopes of xenon and barium, within the framework of the interacting boson-fermion model. We compare the predictions of a simple, single j-orbit calculation including the $\text{1}\text{h}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext>}}$ orbital with those of a multilevel approach. Our findings indicate that the low-lying collective structures in these nuclei are strongly influenced by admixtures of higher-lying single-particle degrees of freedom, notably the $\text{2}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{and}\text{1}\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ levels.     

High spin states in doubly even pf-shell nuclei

High spin states of the yrast band in ⁵⁰Ti, ⁵²Cr, ⁵⁴ and ⁴⁶Ti are investigated in a microscopic approach allowing a coupling of rotations, vibrations and quasiparticle excitations. The lowering of the 6⁺ state in N = 28 nuclei is shown to originate mainly from proton K = 0 two-quasiparticle excitations. Using as a basis the entire pf-shell 8⁺ and 10⁺ states can be predicted for ⁵⁰Ti and ⁵⁴Fe.     

The importance of nucleon substructure in nuclear ground states

Using a potential model, constrained by the hadron spectrum, for the confinement of relativistic quarks we explore the consequences of the substructure of nucleons for the binding energy and ground state wavefunction of ⁴He. In its simplest form, this model gives a binding energy of 19 MeV. Quark wavefunctions differ from those associated with free nucleons by less than 10%, the rms quark radius is 1.34 fm and the resulting structure differs considerably from that of an expansion beginning from the (0s)⁴ shell model. Considerable contributions to the binding energy, attractive from quark delocalization and repulsive from the quark hyperfine interaction, appear unavoidable. We conclude that these effects cannot be excluded from a detailed understanding of the properties of nuclear ground states.     

Cluster radioactivities of odd-mass nuclei

The partial half-lives of the hypothetical even-even equivalent of an odd-mass nucleus for cluster transitions toward various excited states of the daughter, used as a reference to find the hindrance factor, can be calculated within analytical superasymmetric fission model, by taking into account the angular momentum of the emitted cluster. Detailed tables are presented for ¹⁴C radioactivity of ²²¹Fr, ^221,223Ra, ²²⁵Ac; ²⁴Ne radioactivity of ²³³U, ²³¹Pa, and ²³F decay of ²³¹Pa, showing that, except for ²²⁵Ac, the existing experimental evidences, do not exclude (moderate) hindered transitions to the ground states of the daugther nuclei.     

Muonic atoms of odd-mass nuclei

The effect of the single particle excitations on the spectra of muonic atoms with odd-mass nuclei is studied in the frame work of the unified model. The theoretical spectra are compared with the experimental ones and the excitation strengths of the nuclear states as well as the nuclear polarization due to the muon are calculated.     

Rotational bands in the light odd-mass Tl nuclei

The odd-mass nuclei ^191–197Tl have been formed in a variety of (HI, xn) reactions and studied by in-beam spectroscopic techniques. The decay of the high-spin Pb isomers, also formed in (HI, xn) reactions, leading to ^193–197Tl has also been investigated. Evidence is presented for the existence of levels of the previously proposed $\text{9}\text{2}{}^{\mathrm{?}}\text{[505]}$rotational bands in the nuclei. Tentative evidence is given for the existence of oblate rotational bands, based on the $\text{13}\text{2}{}^{\mathrm{+}}\text{[606]}$ state, in ^191–195Tl.     

Low-spin states of odd-mass xenon isotopes

In this work, we analyse the positive parity of states of odd-mass nucleus within the framework of interacting boson-fermion model. The result of an IBFM-1 multilevel calculation with the 2d_5/2, 1g_7/2, 3s_1/2, 2d_3/2 and 1h_11/2, single particle orbits is reported for the positive parity states of the odd-mass nucleus ^125–129Xe. Also, an IBM-1 calculation is presented for the low-lying states in the even-even ^124–128Xe core nucleus. The energy levels and B(E2) transition probabilities were calculated and compared with the experimental data. It was found that the calculated positive parity low-spin state energy spectra of the odd-mass ^125–129Xe isotopes agree quite well with the experimental data.      

Application of Dyson mapping to odd-mass nuclei

The Dyson mapping is applied to the analysis of low-lying collective states in odd-mass nuclei. The original fermion (quasiparticle) space is truncated to a collective subspace which consists of products of collective phonons and a single fermion (quasiparticle). This subspace is mapped on an ideal boson-fermion space by the Dyson mapping and a simple but non-hermitian hamiltonian is obtained. The eigenvalue equations for the hamiltonian are numerically solved for the cases of the unique-parity states in the odd-mass Rh isotopes. The results show that the Dyson mapping is quite useful for analyses of phonon-particle coupling in odd-mass nuclei.     

Quasiparticle-phonon nuclear model for odd-mass nuclei — Recent developments

An enhanced theory, based on the Extended Boson Approximation, for the lowest-lying states in odd-mass nuclei is presented. Our approach has built on the Quasi-particle Phonon Model extending it to take into account the ground state correlations due to the action of the Pauli principle more accurately than in the conventional theory.     

Exchange magnetic moments of some odd-mass nuclei

The exchange magnetic moment has been calculated for the nuclei ⁹¹Zr, ⁸⁹Sr and ⁸⁷Kr in the ground state. By adding the core polarization contribution to the magnetic moments computed earlier, an improved value is obtained for the magnetic moments of these nuclei.     

On the foundation of the VMI models for the ground state collective modes of doubly even nuclei

The aim of the present paper is to propose a justification for the well-known VMI models of Diamond et al. and Mariscotti et al. based upon the method of generator coordinates. On discussing their relative domains of application one concludes that, contrary to the general trend, the stretching model is to be preferred over the region of good vibrators, a result which seems to be confirmed by the scarce experimental data.