Half-lives of the neutron-rich isotopes100Sr,100Y,148Ba and148La

We have deduced the linear momentum transferred from the projectile to the fissioning nucleus in the reaction²⁰Ne+¹⁹⁷Au at 30 MeV/A by measuring the folding angle between the two fission fragments. We found that the most probable linear momentum transfer represents 76% of the initial value.     

Beta decay and nuclear structure: Rb86

It was aimed to gain information on the nuclear structure of Rb⁸⁶ by investigation of the 2^?→2⁺ β transition. For this purpose the energy dependence of theβγ angular correlation and the angle dependence of theβγ circular polarization correlation have been measured. A novel experimental set-up has been used for the angular correlation measurement allowing a simultaneous determination of the anisotropy coefficientsA ₂ andA ₄ under considerable reduction of systematical and statistical errors. For the polarization correlation measurement an unusual experimental arrangement has been applied providing the possibility of simultaneous observation under four different angles. Employing additional data on shape factor measurements and energy dependent circular polarization correlations from other authors the nuclear structure of the 2^? state in Rb⁸⁶ and the 2⁺ first excited state in Sr⁸⁶ have been evaluated. For the latter purpose the unified model with weak coupling has been chosen.     

Precise atomic masses of147Eu,147Gd,and151Tb derived from their decay properties

Theβ-decay energies of¹⁴⁷Eu,¹⁴⁷Gd, and¹⁵¹Tb were determined by usingγ-spectroscopical methods. The comparison of experimental with calculatedK-capture probabilities yielded theQ _EC values 1.690( _?16 ⁺²¹ )MeV and 2.203( _?13 ⁺¹⁹ )MeV for¹⁴⁷Eu and¹⁴⁷Gd, respectively. By measuring the ratio of positron decay to electron capture for two branches in¹⁴⁷Eu decay, the decay energiesQ _EC=1.702(13) MeV andQ _EC=1.709(18)MeV were derived. Also fromEC/β ⁺ ratios the valuesQ _EC=2.225(75) MeV for¹⁴⁷Gd, andQ _EC=2.566(12)MeV for¹⁵¹Tb were obtained. Earlier discrepancies in the mass adjustment of these isotopes were removed. In course of the present studiesγ-decay properties of¹⁴⁷Eu and¹⁴⁷Gd were reinvestigated.     

Atomic masses of rare earth isotopes145Pm,145Sm and151Gd,derived from decay measurements of145Sm and151Gd

The comparison of experimental with calculated K-capture probabilities yielded the decay energies of¹⁴⁵Sm and¹⁵¹Gd,Q _EC=622(5) and 463(3) keV, respectively. Earlier discrepancies in the mass adjustment of these isotopes were removed and adjusted masses for¹⁴⁵Sm,¹⁴⁵Pm and¹⁵¹Gd derived. In the decay of¹⁵¹Gd five newγ-rays were found and the half-life remeasured to be 129(4) d.     

Structure of129Ba from the decay of129La

The structure of¹²⁹Ba is investigated through the beta decay of¹²⁹La, whose half-life is measured to be 11.6±0.2 m. The decay properties are studied by means of beta, gamma and conversion electron spectroscopy techniques. Many transitions are observed and a level scheme of¹²⁹Ba with deduced¹²⁹Ba values is proposed. The total decay energy of¹²⁹Ba is measured to be 3.72±0.05 MeV, which is compared with predictions of mass formulae. Low-lying structure of¹²⁹Ba is discussed in terms of collective models.     

Atomic masses of147m, 148m, 149m Tb,148Dy,150m, 152m Ho derived from decay properties

Using nuclear fusion reactions of⁴⁰Ar ions with¹¹²Cd,¹¹⁴Sn and¹¹⁶Sn and subsequentγ-ray spectroscopy, the probability ratios of positron emission and electron capture,β ⁺/EC _k andβ ⁺/(EC+β ⁺), are determined for individualβ-transitions in the decay of^147m ,^148m ,^149m Tb,¹⁴⁸Dy and^150m ,^152m Ho. From comparison with theoretical ratios the followingQ _EC values, given in keV, are derived:^147m Tb, 4.620(60);^148m Tb, 5.730(30);^149m Tb, 3.610(50);¹⁴⁸Dy, 2.680(30);^150m Ho, 6.625(120) and^152m Ho, 6.470(80). The present decay-energy data are compared with earlier measurements and the new information obtained for the mass surface around¹⁴⁶Gd is discussed.     

Beta-decay energies and nuclear masses of very neutron-rich Rb and Cs isotopes

Theβ-endpoint energies of very neutron-rich Rb and Cs isotopes with mass numbers 94≦A≦98 and 142≦A≦146, respectively, have been measured with a plastic scintillatorβ-telescope at the on-line mass separator OSTIS. From these,Q _β-values and mass excesses are calculated and compared with the results obtained in direct mass determinations.     

The congruence energy: a contribution to nuclear masses,deformation energies and fission barriers

The difference between measured binding energies and those calculated using a shell- and pairing-corrected Thomas-Fermi model can be described approximately by C(I) = −10 exp(−4.2{I}) MeV, where I = (N - Z)/A. Our interpretation of this extra binding is in terms of the granularity of quantal nucleonic density distributions, which leads to a stronger interaction for a neutron and proton with congruent nodal structures of their wave functions. The predicted doubling of this congruence energy in fission is supported by an analysis of measured fission barriers and by a study of wave functions in a dividing Hill-Wheeler box potential. A semi-empirical formula for the shape-dependent congruence energy is described.     

Beta decay and hyperfine interactions

Experimental searches for the second-class currents and the soft pion effects in the nuclear weak axial currents are discussed. Also discussed are the hyperfine interactions of light interstitial impurities in ferromagnetic Fe and Ni, as well as in fcc and bcc non-magnetic metals. For these spin-ray correlation experiments, it is emphasized that the technical developments and improvements of the nuclear spin control by NMR and the production of polarization in the short-lived nuclear states are vital necessities.     

The 1S0 emission from the minor site of Pr3+ in (Ba,La)F2:Pr

In this paper we present and discuss results of detailed spectroscopy studies of Pr³⁺ luminescence from the (Ba,La)F₂:0.2 m%Pr crystals under UV and VUV synchrotron excitation.We have measured time resolved emissions from the minor site Pr³⁺ in (Ba,La)F₂:Pr at 10 and 300 K. The spectra clearly show the ¹S₀ emission from the Pr³⁺ ions in some low symmetry Pr-sites (we designate them La-sites) previously identified in higher concentration (0.3 m%Pr and more) crystals. However most of emission from the Pr activated (Ba,La)F₂ crystals originates in Pr³⁺ ions in other sites which produce an efficient d-f emission. As demonstrated by excitation spectra, the emission from some of these sites (denoted as Ba-sites) closely resembles the d-f emission from BaF₂.The La-site, time resolved and long delay emission spectra are dominated by hypersensitive transitions from the ¹S₀ and ³P₀ levels to lower energy levels of the 4f² configurations. Only these transitions contribute to the photon cascade emission desired for some mercury free phosphor applications.     

On the decay of148Pm

In the frame of a soluble coupled channels model we compare the exact lifetimeτ of a resonant state with two approximate estimates for thisτ. The exactτ value is related to the exact total widthΓ byτ=?Γ ^?1. The first approximate method has been derived by Fermi. It consists in a first order perturbation calculation ofΓ. The second one is Smith's time-delay method which leads to a direct relation betweenτ and the behaviour of theS-matrix along the real energy axis. We show that the Smith's method is the most useful one.     

Beta decay of57Ni

The decay of⁵⁷Ni was studied using both single and coincidence gamma-ray spectroscopy. Four new low-intensity transitions were observed in the single spectra. The energies and intensities of these transitions related to the 1378 keV transition were determined as 304.1 keV, 0.002%; 696.0 keV, 0.001%, 1350.5 keV, 0.002% and 1603.3 keV, 0.005%. Weak transitions at 541.9, 755.3 and 1279.9 keV were confirmed in agreement to earlier works, and their intensities related to 1378 keV were determined as 0.005%, 0.007% and 0.0012%, respectively.     

Beta decay of 103Sn

The β decay of ¹⁰³Sn, a three-neutron-particle nucleus with respect to the ¹⁰⁰Sn core, was investigated at the GSI on-line mass separator using an array of 17 germanium crystals and a total absorption spectrometer. A total of 31 β-delayed γ-rays (29 new) of the ¹⁰³Sn →¹⁰³ In decay were observed and, on the basis of β-γ-γ coincidences, the ¹⁰³Sn decay scheme was established for the first time. By means of total absorption spectroscopy, β intensities, the Gamow-Teller strength distribution and the summed Gamow-Teller strength value of 3.5±0.5 were determined for this decay. Its half-life and Q_EC value were found to be 7.0±0.2 s and 7.64±0.7 MeV, respectively. The β-delayed proton branching ratio was measured to be 1.2±0.1%. The results are discussed in comparison with shell-model predictions based on realistic and empirical interactions.     

Beta decay of 101Sn

The β decay of the very neutron-deficient isotope ¹⁰¹Sn was studied at the GSI on-line mass separator using silicon detectors for recording charged particles and germanium detectors for γ-ray spectroscopy. Based on the β-delayed proton data the production cross-section of ¹⁰¹Sn in the ⁵⁰Cr + ⁵⁸Ni fusion-evaporation reaction was determined to be about 60nb. The half-life of ¹⁰¹Sn was measured to be 1.9(3)s. For the first time β-delayed γ-rays of ¹⁰¹Sn were tentatively identified, yielding weak evidence for a cascade of 352 and 1065keV transitions in ¹⁰¹In. The results for the ¹⁰¹Sn decay as well as those from previous work on the ¹⁰³Sn decay are discussed by comparing them to predictions obtained from shell model calculations employing a new interaction in the ⁸⁸Sr to ¹³²Sn model space.     

Beta decay of22O

The beta-gamma spectroscopic study of²²O is presented. This nucleus, produced as a projectile-like fragment from the interaction of a 60 MeV/n⁴⁰Ar beam with a Be target, has been separated by the LISE spectrometer. Several gamma rays from²²O decay have been observed, from which a half-life of (2.25±0.15)s has been determined. Accurate excitation energies have been deduced for several states in²²F. A partial beta decay scheme of²²O has been established. Experimental results have been compared with shell model calculations.     

Beta decay of 61Ga

The β decay of ⁶¹Ga to its mirror nucleus ⁶¹Zn has been measured for the first time by using on-line mass separation and β-delayed gamma-ray spectroscopy. The observed decay strength to the ground state implies superallowed character in accordance with the systematics of the mirror decays in the sd and fp shell. The β feedings observed to four excited states in ⁶¹Zn are consistent with earlier spin-parity assignments based on in-beam experiments. The ground-state spin and parity for ⁶¹Ga were determined to be 3/2⁻. Received: 28 April 1998 / Revised version: 6 October 1998     

Beta decay of 93Pd

The very neutron-deficient isotope ⁹³Pd was produced in fusion-evaporation reactions of a ⁴⁰Ca beam on a ⁵⁸Ni target. The reaction products were separated at the GSI Online Mass Separator, using ion sources of the FEBIAD type. The -decay properties of ⁹³Pd were studied by detecting -delayed protons and -delayed -rays. The feeding of excited levels in the daughter nucleus ⁹³Rh and the -decay half-life of ⁹³Pd were determined. The experimental results are discussed in comparison to shell model predictions. Received: 19 April 2000 / Accepted: 17 June 2000     

Beta decay of 157Dy

The decay of ¹⁵⁷Dy(T_1/2 = 8.14(4)h) is investigated. Spectra of γ-rays, internal conversion electrons and γ ? γ coincidences are measured. The 983.50 and 991.70 keV transitions show E0 admixtures. Our experimental results made it possible to extend substantially the decay scheme. From the coincidence relationships we established four new excited states of ¹⁵⁷Tb at 883.32, 895.06, 925.29, 970.38 keV and confirmed the 357.66 keV state. The levels at 1160.71 and 1318.62 keV are introduced from the energy balance. Tentative evidence is given for the existence of five new levels at 252.58, 327.65, 658.36, 793.52 and 922.69 keV. We assign Nilsson’s quantum characteristics to all introduced levels. The structure of the excited states of ¹⁵⁷Tb is discussed in terms of current nuclear models.     

Beta decay of 50Ni

The very neutron-deficient isotope ⁵⁰Ni was produced in fragmentation reactions between a A MeV ⁵⁸Ni beam and a ⁹Be target. For the first time the decay of this nucleus was investigated, leading to the determination of the half-life as 12⁺³_-2 ms and the branching ratio for -delayed proton emission of ( )%.Received: 16 April 2003, Published online: 22 July 2003PACS: 21.10.Tg Properties of nuclei; nuclear energy levels: Lifetimes - 23.40.-s decay; double decay; electron and muon capture - 29.30.Ep Charged-particle spectroscopyR. Grzywacz: Present address : Physics Division, ORNL, Oak Ridge, TN 37831-6371, USA.I. Mukha: Present address : Instituut voor Kern- en Stralingsfysika, University of Leuven, B-3001 Leuven, Belgium.     

Beta decay of 31Ar

A complete study of ³¹Ar beta decay has been made by high-resolution charged-particle and gamma-ray spectroscopy. Beta-delayed radiation was detected by an array of three charged-particle detectors and a large-volume germanium detector. Fifteen new energy levels were discovered in ³¹Cl. The beta-strength distribution, measured to 14.5 MeV, is compared with a shell-model calculation in the full sd space. The quenching of the Gamow-Teller strength and the isospin impurity of the IAS in ³¹Cl are discussed.