0000000000034419
AUTHOR
H. Gabelmann
The beta-decay of95Rb and97Rb
Theβ-decay of 377 ms95Rb and 168ms97Rb has been thoroughly investigated by means ofγ-ray, conversion electron andβ-delayed neutron spectroscopy. More than 97% of theβ-decay to particle-bound states has been placed in level schemes of95Sr and97Sr. High-resolution neutron spectroscopic studies have allowed to extend the knowledge of the excitation spectra up to 9 MeV, respectively 10 MeV. The density of neutron-unbound levels in95Sr and97Sr has been derived from peak stripping analyses of the neutron spectra. Beta-strength functions (S β(E)) have been investigated in detail. They indicate that Gamow-Tellerβ-decay of both precursors is dominated by nuclear structure. The discovered pronounced …
The beta-decay half-life of 48 130 Cd82 and its importance for astrophysicalr-process scenarios
The s-decay half-life of130Cd has been measured and its importance as N=82 ‘waiting-point’ nucleus for astrophysical rapid neutron capture (r−) process scenarios is discussed.
Level scheme ofZr101and structure of theN=61 Sr, Zr, and Mo isotones
The neutron-rich nucleus $_{40}^{101}\mathrm{Zr}_{61}$ has been studied at the isotope separator ISOLDE via the \ensuremath{\beta} decay of $^{101}\mathrm{Y}$. A detailed level scheme has been obtained from \ensuremath{\gamma}-ray singles, \ensuremath{\gamma}-\ensuremath{\gamma}-t and \ensuremath{\beta}-\ensuremath{\gamma}-t coincidence measurements. The level structure of $^{101}\mathrm{Zr}$ is similar to that of its isotone $^{103}\mathrm{Mo}$ showing that, in contrast to their Sr neighbors, the Zr isotopes do not reach maximum of deformation immediately at its onset. This result is rather well reproduced by particle-rotor coupling calculations. A level systematics for the deformed N=61 i…
The decay of $^{31}$Ar
10 pages, 1 table, 4 figures.
The new neutron-rich isotope228Rn
2 pages, 1 table, 2 figures.-- PACS nrs.: 23.90.+w; 27.90.+b.-- Section: Short Notes.
Lifetime measurements in99Sr and100Zr
The lifetime of the first excited state in99Sr has been determined by the delayed γ-γ coincidence method. The value of t/2=0.58(9) ns corresponds to a deformation parameter s=0.38(4). The deduced value confirms the previously proposed ν[411]3/2 Nilsson assignment for the99Sr ground state. In addition, lifetime values for the 2+ (t1/2=0.40(8) ns) and 0+ (t1/2=5.36(23) ns) states in100Zr are obtained, which deviate from older measurements and indicate a larger deformation of s=0.39(4).
Identical transitions in the strongly deformed99Srand100Sr
The decay of the very neutron-rich nucleus ${}^{100}\mathrm{Rb}$ has been studied by \ensuremath{\gamma} spectroscopy of online mass-separated samples. Schemes for \ensuremath{\beta} decay to ${}^{100}\mathrm{Sr}$ and $\ensuremath{\beta}n$ decay to ${}^{99}\mathrm{Sr}$ are presented. New sets of transitions in ${}^{99}\mathrm{Sr}$ and ${}^{100}\mathrm{Sr}$ with identical energies are observed. All identical bands so far observed in neutron-rich Sr isotopes obey a simple energy rule valid for even-even, odd-even, and odd-odd bands.
Nuclei Far from Stability and the R-Process Waiting-Point Concept
The nucleosynthesis process by rapid neutron captures (the r-process) is responsible for the formation of about half of the nuclear species in nature beyond Fe. While the astrophysical site for the r-process is not yet unambiguously identified, its association with the cores of low-mass stars undergoing type II supernova (SN) events is strongly suggested (see, e.g., Refs.1,2).
Beta-delayed neutron emission from93?100Rb to excited states in the residual Sr isotopes
Beta-delayed neutron emission from the precursors93–100Rb to excited states in the residual nuclei92–99Sr has been measured by means ofγ-ray and neutron spectroscopy. In general, considerable neutron feeding of excited final states is observed. The experimental branching ratios (P ) are compared to predictions from statistical model calculations. It is demonstrated that the main parameter affecting theP -values is the shape of theβ-strength function (S β). For several Rb isotopes hindrance, respectively enhancement of neutron branches to specific final states is observed giving evidence for the persistence of intermediate structure of the neutron-emitting states. By the example of98Rb it is…
The nuclear structure of $^{223}$Fr
Abstract The γ-rays following the β− decay of 223Rn have been investigated by means of γ-ray singles including multispectrum analysis, and γγ-coincidence measurements using Ge detectors. Multipolarities of 38 transitions in 223Fr have been established by measuring conversion electrons with a mini-orange electron spectrometer. Most of the observed transitions could be placed in a level scheme comprising 53 excited states of 223Fr. The level structure is interpreted in terms of K π = 3 2 ± and 1 2 ± parity doublet bands, and a second K π = 3 2 ± higher-lying parity doublet. The experimental data are compared with the theoretical predictions of the reflection-asymmetric rotor model.
K-isomeric state in even-even100Sr
A t1/2=85 ns isomer has been identified at 1619 keV in100Sr. The halflife is attributed to a ΔK=4 hindered decay. The configuration is proposed to be built on the [411]3/2 and the [532]5/2 neutron quasiparticle orbitals.
Evidence for excited 0+ states in94Sr
Beta-delayed neutron measurements on95Rb have indicated evidence for two heretofore unknown excited O+ states in94Sr which are not fed by s -decay from the Jπ = 3− ground state of94Rb.
Search for stable octupole deformation in $^{225}$Fr
Levels in $^{225}$Fr have been studied by $\gamma$-ray and conversion-electron spectroscopy following the $\beta$-decay of $^{225}$Rn, and by the $^{226}$Ra(t,$\alpha$)$^{225}$Fr single-proton-pickup reaction. Multipolarities were obtained for $\sim$ 50 $\gamma$-transitions, and a level scheme was established in which definite spin-parity values were determined for over 20 of the 48 levels. Although low-lying rotational bands of both parities exist for $K=1/2$ and $K=3/2$, there is no experimental evidence to claim these are parity doublets. E1 strengths connecting the $K^\pi=3/2^\pm$ bands are intermediate between those for nuclides which are reflection symmetric and those claimed to be oc…
AK=3two-quasiparticle isomer in98Sr
The decay of on-line mass-separated ${}^{98}\mathrm{Rb}$ to ${}^{98}\mathrm{Sr}$ is studied by $\ensuremath{\gamma}$ spectroscopy. The revised decay scheme adds further evidence of the coexistence of very different shapes in ${}^{98}\mathrm{Sr}.$ A set of levels is proposed to originate from particle-hole pair excitations across the $Z=40$ spherical gap in analogy with ${}^{96}\mathrm{Sr}.$ A deformed $K=3$ band with probable even parity is built on a 7.1-ns isomer at 1838 keV. It is interpreted as a two-quasineutron excitation in accordance with a quantum Monte Carlo pairing calculation based on a deformed shell model. Configurations of the calculated lowest-lying two-quasiparticle levels …
Decay properties of exoticN≃28 S and Cl nuclei and theCa48/46Ca abundance ratio
Beta-decay half-lives and \ensuremath{\beta}-delayed neutron-emission probabilities of the very neutron-rich nuclei $^{44}\mathrm{S}$ and $^{45--47}\mathrm{Cl}$ have been measured. These isotopes, which lie at or close to the N=28 magic shell, were produced in interactions of a 60 MeV/u $^{48}\mathrm{Ca}$ beam from GANIL (Grand Acc\'el\'erateur National d'Ions Lourds) with a $^{64}\mathrm{Ni}$ target, and were separated by the doubly achromatic spectrometer LISE (Ligne d'Ions Super Epluch\'es). Their decay was studied by a \ensuremath{\beta}-n time correlation measurement. The results are compared to recent model predictions and indicate a rapid weakening of the N=28 shell effect below $_{2…
Structure of the highly deformed nucleus101Sr63 and evidence for identical K=3/2 bands
The low-energy level scheme of theN=63 nucleus101Sr has been obtained from a β-decay study of101Rb. The ν[532]5/2 and ν[411]3/2 orbitals are well established as the ground state and a band head at 271.2keV, respectively. The general properties of the level scheme indicate a quadrupole deformation ofβ ≃ 0.4, confirming the unique feature of saturation of deformation inN ≥ 60 Sr isotopes. The energies of theK=3/2 intraband transitions in the odd-neutron neighbours99Sr61 and101Sr63 are very similar. More generally, the identical bands at low spin in98–101Sr nuclei are correlated with the mass-independent moments of inertia in this region.
Identical transitions in the strongly deformed 99Sr and 100Sr
The decay of the very neutron-rich nucleus 100 Rb has been studied by γ spectroscopy of online mass-separated samples. Schemes for β decay to 100 Sr and β n decay to 99 Sr are presented. New sets of transitions in 99 Sr and 100 Sr with identical energies are observed. All identical bands so far observed in neutron-rich Sr isotopes obey a simple energy rule valid for even-even, odd-even, and odd-odd bands. peerReviewed
Neutron-rich isotopes around the r-process ?waiting-point? nuclei 29 79 Cu50 and 30 80 Zn50
Beta-decay half-lives (T1/2) and delayed-neutron emission probabilities (Pn) of very neutron-rich Cu to As nuclei have been measured, among them the new isotopes77Cu48,79Cu50,81Zn51 and84Ga53. With the T1/2 and Pn-values of now four N ∼-50 ”waiting-point” nuclei known, our hypothesis that the r-process has attained a local β-flow equilibrium araound A∼-80 is further strengthened.
Onset of deformation in neutron-rich krypton isotopes
Beta-decay properties of neutron-rich35Br isotopes confirm the predicted smooth onset of quadrupole deformation for Z<37 already below N=60. The observed increase of the energy of the first 2+ state in the N=56 nucleus92Kr may indicate octupole softness.
First observation of beta-delayed deuteron emission
5 pages, 2 figures.
Saturation of deformation atN=60 in the Sr isotopes
From the halflife oft 1/2=3.91 (16) ns for the 21 + state in100Sr a deformation parameter ofβ=0.40(1) has been derived. Within the given uncertainties, this value is equal to the recently determinedβ-parameters for98Sr and99Sr, indicating that in the Sr isotopes saturation of deformation is reached immediately at its onset well before neutron midshell. This behaviour is reflected by the “twin” character of98Sr and100Sr with identical features of their unperturbed ground-state rotational bands. These observations are discussed in terms of strong two-nucleon interactions.
New neutron-rich isotopes of astatine and bismuth
Neutron-rich isotopes of astatine have been produced through spallation reactions with 600 MeV protons on a232Th target and identified by spectroscopic techniques combined with one-line mass separation at the ISOLDE facility. The half-lives of218At and219At have been remeasured to be 1.5(3) s and 57(4) s, respectively. Four new isotopes of astatine,220−223At, have been observed for the first time, and their half-lives were found to be 3.73(13) min, 2.3(2) min, 54(10) s, and 50(7) s, respectively. Another nuclide,216Bi, has been observed for the first time as the daughter product of the220At alpha decay, and its half-life has been measured to be 6.6(21) min.
Identical transitions in the strongly deformed Sr-99 and Sr-100
The decay of the very neutron-rich nucleus Rb-100 has been studied by gamma-spectroscopy of on-line mass-separated samples. Schemes for beta-decay to Sr-100 and beta-n-decay to Sr-99 are presented. New sets of transitions in Sr-99 and Sr-100 with identical energies are observed. All identical bands so far observed in neutron-rich Sr isotopes obey a simple energy rule valid for even-even, odd-even and odd-odd bands.
R-Process Abundances and Nuclear Properties Far from Stability
Recent measurements of β-decay properties of the ‘waiting-point’ nuclei 79Cu, 80Zn and 130Cd, together with new QRPA shell-model predictions of so far unknown N ≃ 50 and N ≃ 82 isotopes in the r-process path, have allowed to explain the detailed isotopic composition in the A ≃ 80 and A ≃ 130 r-abundance peaks. The correlation between nuclear data far from stability and r-abundances suggests that the r-process involves a high-neutron-density β-flow equilibrium environment. Based on these results, the r-process components of nuclei in the 90 ≤ A ≤ 100 mass range were predicted for freeze-out conditions (nn ≃ 1020, T9 ≃ 1) and compared to the solar-system r-process abundances.
P n-values of short-lived Sr, Y, Ba and La precursors
Beta-delayed neutron emission probabilities (Pn) of short-lived Sr, Y, Ba and La precursors were measured. As expected from systematics, but in disagreement with recent data from the SOLIS-group, only small Pn -values were obtained.