odd-A Isotopes Research Articles

Description of Properties of Triaxial Superdeformed Bands in Odd-A Lu Isotopes

Properties of the triaxial superdeformed (TSD) bands of odd-A Lu isotopes are investigated systematically within the supersymmetry scheme including many-body interactions and a perturbation possessing the SO(5) (or SU(5)) symmetry on the rotational symmetry. Quantitatively good results of the γ-ray energies, the dynamical moments of inertia and the spin of the TSD bands in odd-A Lu isotopes are obtained. The calculation shows that the competition between the pairing and anti-pairing effects exists in these TSD bands. Meanwhile, the SU(3) symmetry in TSD bands are broken more seriously than in superdeformed (SD) bands.

Spectroscopy and high-spin structure ofFr209

Excited states in $^{209}\mathrm{Fr}$ have been studied using the $^{197}\mathrm{Au}(^{16}\mathrm{O},4n)^{209}\mathrm{Fr}$ reaction with pulsed beams and $\ensuremath{\gamma}$-ray and electron spectroscopy. A comprehensive scheme has been established up to an excitation energy of about 6 MeV and spins of about $49/2\ensuremath{\hbar}$. Several isomers have been identified including a ${J}^{\ensuremath{\pi}}=25/{2}^{+}$, $\ensuremath{\tau}=48(3)$ ns state at 2130 keV and a $606(26)$ ns, $45/{2}^{\ensuremath{-}}$ state at 4660 keV. The latter state decays via an enhanced $E3$ transition with a strength of 28.8(12) W.u. It can be identified with a similar isomer in the heavier odd isotopes $^{211}\mathrm{Fr}$ and $^{213}\mathrm{Fr}$, arising from the maximal coupling of the five valence protons in the $\ensuremath{\pi}{h}_{9/2}^{3}{i}_{13/2}^{2}$ configuration. The systematics of the yrast states in the odd-$A$ isotopes are discussed, including the presence of states arising from the main proton configurations coupled to the ${p}_{1/2}$, ${f}_{5/2}$, and ${i}_{13/2}$ neutron holes. Shell-model configurations are assigned to many of the observed states. The isotopic assignment differs from earlier work, which is shown to be erroneous.

Spectroscopy ofSc52,53

Excited states of neutron-rich odd-A and odd-odd Sc isotopes, populated in deep inelastic multinucleon transfer reactions, induced by a {sup 238}U beam on a thin {sup 48}Ca target, have been identified. A strong feeding of both yrast and nonyrast states in such a reaction is illustrated using a combination of a large efficiency spectrometer and a {gamma} detector array. The structure of the populated states is interpreted in terms of the role of the valence proton and neutrons and compared to shell model calculations in the full pf shell.

Study of the neutron deficient 182–190Pb isotopes by simultaneous atomic- and nuclear-spectroscopy

Mean-square charge radii and magnetic moments have been measured for the neutron deficient lead isotopes, 182–190Pb. The measurement was performed at the ISOLDE online mass separator, using the in-source resonance ionization spectroscopy technique. The wavelength of the first excitation step for the resonance ionization laser ion source (RILIS) was scanned over the resonance(s) whilst the α- and γ-ray spectra from the decay of the Pb isotopes were recorded as a function of the wavelength. The isotope shift and, in the case of odd-A isotopes, the hyperfine splitting were deduced. The rms-charge radii of the very neutron deficient Pb isotopes follow the smooth trend of the heavier isotopes. This finding indicates a spherical shape for the lead ground states at the neutron mid-shell (N=104), where the excitation energy of the oblate 0+ state in the even isotopes reaches its minimum.

Exotic nuclei near 78Ni in a shell model approach

The shell model predictions for even 68–76Ni isotopes and odd-A Cu isotopes with newly derived effective interaction for the f 5/2 p 3/2 p 1/2 g 9/2 model space are presented.

Identification of a pairing isomeric band inSm152

A coexisting band structure is identified in {sup 152}Sm through {gamma}-ray coincidence spectroscopy following {beta} decay of {sup 152m,g}Eu and following multi-step Coulomb excitation. This structure is interpreted as a pairing isomer analogous to a similar band identified in {sup 154}Gd, based upon relative B(E2) values for transitions out of the band and two-neutron transfer reaction population of the 0{sup +} and 2{sup +} band members. Systematics for odd-A isotopes near N = 90 suggest that there should be a low-lying pairing isomer in {sup 156}Dy, and similar structures at higher energy in {sup 150}Nd and {sup 158}Er.

βdecay in odd-Aand even-even proton-rich Kr isotopes

Beta-decay properties of proton-rich odd-A and even-even Krypton isotopes are studied in the framework of a deformed selfconsistent Hartree-Fock calculation with density-dependent Skyrme forces, including pairing correlations between like nucleons in BCS approximation. Residual spin-isospin interactions are consistently included in the particle-hole and particle-particle channels and treated in Quasiparticle Random Phase Approximation. The similarities and differences in the treatment of even-even and odd-A nuclei are stressed. Comparison to available experimental information is done for Gamow-Teller strength distributions, summed strengths, and half-lives. The dependence of these observables on deformation is particularly emphasized in a search for signatures of the shape of the parent nucleus.

Comparative quadrupole moments of superdeformed bands in 193−196Pb

Lifetimes have been measured for states in five superdeformed yrast bands in 193−196Pb using the Gammasphere spectrometer array. Centroid shifts and lineshapes of transitions showing attenuated Doppler shifts have been analyzed. Transition quadrupole moments are deduced for the five bands including, for the first time, bands of two odd-A Pb isotopes. The quadrupole moments are found to be remarkably similar for the yrast bands in 194Pb (band 1), 195Pb (bands 1 and 2) and 196Pb (band 1) (Q t ≈20 b). However, for 193Pb a smaller value, Q t =17.3(7) b, is obtained. This can be explained in terms of the occupation of the neutron N = 7 intruder orbitals.

Pairing effects in Sn isotopes

An extensive study of pairing effects in the Sn isotopes is carried out. The pairing Hamiltonian is treated by the chain-calculation method which provides practically exact solutions while involving less computational work than a complete-basis diagonalization. The coupling strength is fixed by reproducing the energy of the 9− state in116Sn, while the single-particle energies have been determined by an analysis of the experimental low-energy spectra of the odd-A isotopes. A detailed comparison of the calculated results with experimental data evidences the importance of neutron pairing correlations in the 50–82 shell. The results of this paper complement those of our previous study of theN=82 isotones. It turns out that the role of pairing correlations is similar to a large extent in both cases.

Moments and mean square charge radii of short-lived argon isotopes

Abstract We report on the measurement of optical isotope shifts for 32–40Ar and for 46Ar from which the changes in mean square nuclear charge radii across the N = 20 neutron shell closure are deduced. The investigations were carried out by collinear laser spectroscopy in fast beams of neutral argon atoms. The ultra-sensitive detection combines optical pumping, state-selective collisional ionization and counting of β-radioactivity. By reaching far into the sd shell, the results add new information to the systematics of radii in the calcium region (Z ≈ 20). Contrary to all major neutron shell closures with N ⩾ 28, the N = 20 shell closure causes no significant slope change in the development of the radii. Information from the hyperfine structure of the odd-A isotopes includes the magnetic moments of 33Ar ( I = 1 2 ) and 39Ar ( I = 7 2 ), and the quadrupole moments of 35Ar, 37Ar ( I = 3 2 ) and 39Ar. The electromagnetic moments are compared to shell-model predictions for the sd and fp shells. Even far from stability a very good agreement between experiment and theory is found for these quantities. The mean square charge radii are discussed in the framework of spherical SGII Skyrme-type Hartree-Fock calculations.

Response of mica to weakly interacting massive particles.

We calculate spin-dependent cross sections for the scattering from mica of hypothetical weakly interacting dark-matter particles such as neutralinos. The most abundant odd-A isotopes in mica, $^{27}\mathrm{Al}$ and $^{39}\mathrm{K}$, require different shell-model treatments. The calculated cross sections will allow the interpretation of ongoing experiments that look for tracks due to the interaction of dark-matter particles with nuclei in ancient mica.

Electromagnetic properties and shapes of ground states in Pt−Au−Hg region

We present a comprehensive calculation of odd-A isotopes of Pt, Au and Hg in the mass region 177≤A≤195. Two nuclear models have been used. The particle-triaxial rotor model with modified oscillator s.p. potential (PTR-MO) yielded deformation parameters e2 and γ as a result of fitting to a wide range of experimental data. Also, mean field calculations based on the Woods-Saxon potential with Strutinsky shell corrections were performed to predict deformation parameters β2, β4 and γ form Total Routhian Surfaces (TRS). Subsequent PTR calculation using these deformation parameters and Woods-Saxon s.p. potential (PTR-WS) yielded ground state properties of all nuclei in question in very good agreement with experiment. The deformation parameters e2 and β2 showed the same general trend as a function of neutron number. The fitted parameter γ from (PTR-MO) calculation indicated a smooth change from prolate (N≈100) to oblate shape (N≈115) via triaxial in Pt, Au and Hg. The value of γ extracted from TRS calculations predicts a smooth change in Pt isotopes but much sharper change in Au and Hg nuclei.

The role of the Coriolis potential in the pseudo SU(3) description of well deformed odd-A isotopes

The energy spectrum of 179Ta has been predicted using the quadrupole plus the Coriolis interaction in the pseudo SU(3) scheme. The doublet structure of the 1/2+ band members has been generated to fit exactly the experimental situation, a vast improvement over the mispairing obtained with the quadrupole interaction alone as the two-body interaction, obtained in a previous study. The effect of the Coriolis term on the spacings of low-lying rotational levels, especially of the 1/2+ band, was studied at two different strengths. It is shown that the particle-rotation coupling is important at the strongly deformed regions.

Mean square charge radii of radium isotopes and octupole deformation in the 220–228Ra region

The first investigation of isotope shifts in both the atomic and ionic resonance lines of radium has been carried out using the technique of on-line collinear fast-beam laser spectroscopy at the ISOLDE facility at CERN. The measurements cover 19 isotopes in the mass range 208⩽A⩽232 with half-lives between 23 ms and 1600 y. The differences in the nuclear mean square charge radii δ〈r2〉 have been evaluated and - together with earlier published spins and moments from the hyperfine structure - related to nuclear deformation. In particular the inversion of the odd-even staggering effect for the isotopes 221Ra, 223Ra and 225Ra can be interpreted by the presence of octupole instability and adds weight to the concept of near-stable octupole deformation in the odd-A isotopes which already explained their spins and magnetic moments.

On the hyperfine structure and isotope shift of radium

The hyperfine structure and isotope shift of the heaviest known alkaline earth element radium (Z=88) have been studied in both the atomic Ra I and ionic Ra II spectra. The measurements, carried out by on-line collinear fast-beam laser spectroscopy, yield the hyperfine constantsA andB of the 7s and 7p1/2 states in Ra II, of all states of the excited 7s 7p configuration and the 7s 7d3D3 state in Ra I. The data allow a consistent evaluation of the nuclear moments for eight odd-A radium isotopes. In particular, a complete analysis of the hyperfine structure of thesp configuration in the two-electron system provides a stringent test of the validity of the semi-empirical modified Breit-Wills theory. It is shown that the effective operator formalism is equivalent, if relativistic correction functions are used to reduce the number of parameters. The semi-empirical hyperfine fields are evaluated and found to agree generally with those from ab-initio calculations. The isotope shifts in thes−p,s2−sp,sp−sd transitions are analysed semi-empirically and compared with ab-initio calculations. The consistency of the different analyses proves their validity and classifies the spectrum of Ra I as a model case for a simple and clean two-electron spectrum.

Hyperfine structure and isotope shift investigations in202–222Rn for the study of nuclear structure beyond Z=82

The hyperfine structure (hfs) and isotope shift (IS) in the isotopic chain of the radioactive element radon have been studied for the first time. The measurements were carried out by collinear fast-beam laser spectroscopy at the mass separator facility ISOLDE at CERN. The IS between 16 isotopes in the mass range 202≦A≦222 and the hfs of 7 odd-A isotopes were determined in the transitions 7s [3/2]2-7p [5/2]3 (745 nm) of Rn I. The nuclear spins and moments, as well as the observed inversion of the odd-even staggering for218–222Rn, can be associated with the effects of octupole instability around N=134.

Iodine magnetic moments measured by on-line nuclear orientation

On-Line measurements of magnetic dipole moments of117–122I are interpreted using coupling of the odd particles to a deformed core. The results show interesting effects of g7/2, d5/2 orbital admixtures in the odd-A isotopes, which are close to spherical. The odd-odd isotopes118, 120I show clear examples of shape co-existence.

Larmor precession measurement of the nuclear g1factor of135,137Ba isotopes in a fat atomic beam

An original method of determining the nuclear Lande factor for atoms with a diamagnetic ground state is illustrated with the two odd-A isotopes 135Ba and 137Ba. The method, based on the fast atomic beam laser spectroscopy technique, consists of detecting the in-flight Larmor precession of the nuclear magnetic dipolar moment in a static magnetic field, via the fluorescence induced by resonant laser light. When the magnetic-field amplitude is varied the fluorescence signal exhibits a fringed structure from which the g1 factor can be deduced.

Core polarization for M2 transitions in odd-A tin isotopes

The reduced M2 transition probabilities 112−1 → 72+1 in the odd-A isotopes 109–121Sn are found to reveal a specific behaviour. B(M2) values are calculated in the framework of the quasiparticlephonon model. The coupling of a quasineutron with the 2+, 3− and 2− one-phonon core excitation is taken into account. Inclusion of all one-phonon 2− states up to 24 MeV in the wave functions of the excited states 112−1and72+1 reduces the theoretical B(M2) values by 3–4 times as compared to the single-particle values. The specific B(M2) dependence on the mass number appears to be due to the pairing effect.

Correlation between band excitation energies and strength parameters in the pseudo-SU(3) model

Low-lying energy spectra of some odd-A isotopes of Lu and Ta are predicted using the quadrupole-quadrupole interactions as the effective residual interaction together with the usual spin-orbit and extrapolation terms in the Hamiltonian. It is suggested that the Coriolis antipairing (CAP) force might generate the correct doublet structure of the 1/2+ bands, especially in highly deformed regions. It is shown that the pseudo-SU(3) model satisfies the general requirement that it is capable of describing the spectral behaviour of different nuclei with only minor variations in the strength parameters. Correlations between the band excitation energies and the strength parameters are also given in a first approximation. The ratios of interband M1 transition probabilities are also presented.