Electron capture ratios in206Bi

The level scheme of⁹⁷Tc has been investigated by observing theγ-rays following the decay of 2.9-d⁹⁷Ru.γ-singles andγγ-coincidence measurements were carried out with Ge(Li)-detectors. The time difference of coincident γ-rays was measured as a third parameter. From the coincidence events, the intensities ofγγ-cascades were extracted. The⁹⁷Ru decay gives rise to 18γ-lines which could be fitted into a level scheme of⁹⁷Tc consisting of 9 levels. Spin and parity assignments of the levels were made from log(ft) values andγ-ray branching ratios. Discrepancies concerning the energy of the first 3/2^? state and the existence of a 946 keV level are discussed.     

Ground state properties and β-decay half-lives near 132Sn in a self-consistent theory

The level scheme of⁹⁵Tc has been investigated with Ge(Li)-detectors by observing the γ-rays after the decay of 1.65 h⁹⁵Ru. The energies and intensities of theγtransitions were extracted fromγ-singles andγγ-coincidence spectra. In the decay of⁹⁵Ru 88γ-transitions were observed; a scheme of⁹⁵Tc with 25 levels is proposed into which 86 transitions could be accomodated. Spin and parity assignments were made from log (ft) values andγ-ray branching ratios. The level structure of⁹⁵Tc is compared with that of the other odd Tc isotopes.     

The decay of105Tc to levels in105Ru

Theβ ^?-decay of 7.6-min¹⁰⁵Tc has been investigated byβ- andγ-ray singles and coincidence measurements. The activities have been produced by thermal-neutron-induced fission of²³⁵U or²³⁹Pu and subsequent chemical separation of the technetium fraction from the fission product mixture. AQ _β-value of 3.2±0.2 MeV has been determined. In a delayed coincidence experiment the lifetime of the first excited state in¹⁰⁵Ru at 20.55 keV has been measured to be 340±15 nsec. A level scheme of¹⁰⁵Ru is proposed and compared with the results of recent nuclear reaction studies like¹⁰⁴Ru(d, p) and¹⁰⁴Ru(n, γ). From beta branching ratios to levels in¹⁰⁵Ru, ground state spin and parity of 5/2⁺ can be suggested for¹⁰⁵Tc in accordance with the trend observed in neutron rich technetium isotopes.     

Nuclear spectroscopy of neutron-richA=145 nuclei

A study of theβ-decay of neutron-richA=145 fission products was undertaken by the use of the two recoil separators LOHENGRIN and JOSEF and the ISOL-type separator OSTIS. Theβ-decaying isotopes¹⁴⁵Ba,¹⁴⁵La and¹⁴⁵Ce were extensively studied. Level schemes for¹⁴⁵La,¹⁴⁵Ce and¹⁴⁵Pr were deduced fromγ and conversion electron spectra,γγ, X γ delayed andβγ coincidences. TheQ _β -values have been measured for the¹⁴⁵Ba,¹⁴⁵La and¹⁴⁵Ce decays.     

Spin-flipβ − decay of even-even deformed nuclei110Ru and112Ru

Neutron-rich nuclides¹¹⁰Ru and¹¹²Ru produced in symmetric fission of²³⁸U by 20 MeV protons have been studied at the IGISOL facility by means ofβ-ray,γ-ray and conversion electron spectroscopy. A total of 12 and 6γ-transitions were observed in the decays of¹¹⁰Ru and¹¹²Ru, respectively. Multipolarities were determined for a few transitions. The beta decay half-life was determined to be 11.6±0.6 s for¹¹⁰Ru and 1.75±0.07 s for¹¹²Ru. As a side product, a new value of 2.1±0.3 s for theβ half-life of the¹¹²Rh 1⁺ state was obtained. The decay energy measured with the plastic scintillator was 2.81 ±0.05 MeV for¹¹⁰Ru and 4.52 ±0.08 MeV for¹¹²Ru. The beta decay schemes of¹¹⁰Ru and¹¹²Ru isotopes indicate that the main fraction of their beta strength resides in two 0⁺→1⁺ spin-flip transitions with their logf t values between 4.4 and 4.7. The decay energies and the energies of the 1⁺ GT states are compared with the macroscopic-microscopic model calculations. The observed GT-strengths are discussed in the framework of the deformed single-particle model.     

Gamma radiation from the ground state decay of95Tc

The 20 h^95gTc decay to levels of⁹⁵Mo has been investigated studyingγ-singles andγγ-coincidences. The first excited state of⁹⁵Mo at 204 keV, previously assumed to be populated in the^95m Tc decay only, is found to be fed by aγ-transition of 870 keV deexciting the level at 1074 keV which is populated in the^95g Tc decay. More over three newγ-transitions of 477, 786 and 1552 keV deexciting the level at 1552 keV have been found. For the levels at 1074 and 1552 keV the range of possibleJ ^π assignments could be reduced.     

The decay of93g Ru,93m Ru,91g Mo,91m Mo,91g Tc and91m Tc

Decay studies on a number of short-lived odd nuclei in theN=50 region are described. The 59.6-s ⁹³Ru ground state decay was studied in detail for the first time; in these experiments the 10.8-s activity^93m Ru was discovered. The⁹¹Tc activities were also observed for the first time. The ground state and an isomeric state of this nucleus decay with nearby equal half-lives (3.14 and 3.3-min). The activities^91g Mo (16.6-min) and^95m Mo (65.1-s) have been reinvestigated. A number ofγ-rays, previously erroneously assigned to the⁹¹Mo activities, could be eliminated. A strong similarity is noted for the decay schemes of theN=49 isotones^91m Mo and^93m Ru. The energy of the 1/2^? isomeric state in⁹³Ru and theB(M4)-value of the isomeric transition fit well into the systematics of the previously knownN=49 isotones.     

On the stability of the nuclei of element 108 withA=263–265

In bombarding²⁰⁹Bi and^{207, 208}Pb targets by⁵⁵Mn and⁵⁸Fe ions the yields of “cold fusion” reactions have been determined using a sensitive technique for detectingT _1/2≧1 ms spontaneous fission and theα-decay of heavy actinide elements. It has been shown that theA = 263–265 isotopes of element 108, including the even-even isotope²⁶⁴108, undergo mainlyα-decay. The obtained results, together with the known data on the properties of the isotopes of elements 104 and 106, provide evidence for the enhanced stability of theZ=108 nuclei against spontaneous fission.     

Specific heat of the superfluid neutron matter in neutron star crusts

By means of X-γ andγ-γ coincidence measurements of the³⁵Cl+⁵⁸Ni reaction products, 38γ lines have been identified to be in coincidence with KX(Tc)-rays and assigned to the decay of⁹⁰Ru. Its half-life of 11±3 s has been deduced from the 154.6 keVγ-decay. The result supports our previous identification of⁹⁰Ru produced in the same reactions.     

Directional correlations in the decay of 1200y 166Ho

γγ-directional correlations have been measured between the ground state band transitions 6→4, 4→2 and 2→0 and the γ-rays depopulating the levels of the gamma vibrational band and the negative parity states of¹⁶⁶Er. Thereby angular momenta could be assigned to the latter states andM2/E1 multipole mixtures determined for the depopulating γ-transitions. TheE2/M1 mixing ratios were obtained for a series ofI _γ→I _g transitions up toI _γ=8⁺. These are used to investigate the angular momentum dependence of theE2/M1 admixtures.     

Levels in104Ru populated by the β−-decay of104Tc

Theβ ^? — andγ-activities of 18.4 min¹⁰⁴Tc have been studied with singles and coincidence measurements. Sources were prepared by chemical separation of technetium from the fission products of thermal-neutron-induced fission of²³⁵U. A revised level scheme of¹⁰⁴Ru up to an excitation energy of 4.26 MeV is proposed. Fromβ-γ coincidence measurements, aQ _β-value of 5.62±0.07 MeV has been obtained.     

An investigation of short-lived isomers in the nuclei90,92Nb,99Mo,98,100,101Tc and101Ru

Short-lived isomers in the nuclei^90,92Nb,⁹⁹Mo,^98,100,101Tc and¹⁰¹Ru populated in photonuclear reactions were studied by pulsed beam techniques. Energy and half-life of theγ-rays deexciting the isomeric levels were measured by recording energy-time spectra. The delayedγ-rays andK X-rays were detected by means of an intrinsic Ge-detector of high resolution. From the measured intensity ratios internal conversion coefficients were determined. The multipolarities of the isomeric transitions could be deduced in most cases. A classification of the observed isomers has been tried on the basis of the obtained experimental results and most recent literature data.     

Excited states of100Tc from100Mo(p,nγ)100Tc reaction and the parabolic rule

γ-spectra and excitation functions of the¹⁰⁰Mo(p, nγ)¹⁰⁰Tc reaction were measured in the 1.2–3.6 MeV proton energy range by using thick, enriched targets, Ge(Li) and low energy photon (hyperpure Ge) spectrometers. These detectors were used inγγ-coincidence experiments, too. Conversion electron spectrum measurements were performed by means of a superconducting magnet transporter Si(Li) spectrometer (SMS) atE _p =4 MeV and multipolarities of some transitions have been determined. Based on the experimental results a level scheme of¹⁰⁰Tc has been constructed. Level energies of¹⁰⁰Tc were calculated on the basis of the parabolic rule, derived from the cluster-vibration model.     

High-spin states in108Sn

High spin states in¹⁰⁸Sn have been investigated using the⁹²Mo(¹⁹F,p2nγ)¹⁰⁸Sn reaction. In-beam measurements ofγ-γ-coincidences,γ-ray excitation functions andγ-ray angular distributions were performed with Ge(Li)-detectors, one of which had a Nal Compton suppression shield. A level scheme for¹⁰⁸Sn has been constructed up to anI ^π=(14^?) state.     

Levels in 106Ru and 108Ru

The decay schemes of 36 s ¹⁰⁶Tc and 5 s ¹⁰⁸Tc have been studied with γ-ray singles and γ-γ coincidence measurements. To separate the technetium nuclides from the fission products of ²³⁹Pu, an on-line chemical separation procedure has been developed which is based on multistep chemical separations of liquid phases by fast-rotating centrifuges (“SISAK”). The resulting level schemes of ¹⁰⁶Ru and ¹⁰⁸Ru, together with those of ¹⁰²Ru and ¹⁰⁴Ru, are interpreted in terms of the generalized collective model of Gneuss and Greiner. The potential-energy surfaces calculated from the spectroscopic data show a trend towards triaxial shapes for the very neutron-rich Ru nuclei.     

Gamma-gamma angular correlation measurements of transitions in98Sr and98Zr and confirmation of shape coexistence in98Sr

γγ-coincidence and angular correlation measurements were performed for transitions in⁹⁸Sr and⁹⁸Zr at the on-line-separator facility OSTIS at the Institute Laue-Langevin (ILL) in Grenoble, France. These nuclei were populated byβ-decay from isotopically pure⁹⁸Rb produced by thermal fission of²³⁵U.γγ-angular correlations were measured allowing spin assignments for most levels up to 2 MeV in both nuclei. Listings of angular correlation coefficients and multipole mixing ratios are given. The appearance of shape coexistence is discussed for⁹⁸Sr and⁹⁸Zr in the framework of level systematics as well as neutron-separation energies.     

Experimental Beta-decay energies of very neutron-rich fission products with 107≦A≦109

Theβ-decay of neutron-rich fission products with mass numbersA=107, 108 and 109 has been investigated at the mass separator LOHENGRIN of the Institute Laue-Lange-vin (ILL) in Grenoble by measuringβγ-coincidences with a large plastic scintillator telescope and a Ge(I)-detector. Theβ-decay energies of 8 nuclei were obtained from the evaluation of more than 40β-endpoint energies. For the nuclei¹⁰⁷ Mo,¹⁰⁷Tc,¹⁰⁸Tc,¹⁰⁹Tc and¹⁰⁹Ru, theβ-decay energies were determined for the first time; the experimental error in the decay energy of three daughter nuclei was considerably reduced. In addition, the two-neutron separation energies and the nuclear mass excesses were calculated from these experimentalQ _β-values and compared with different mass predictions.     

Angular distributions of elastic and quasi elastic heavy-ion collisions. pattern analysis

From classical in-beam spectroscopy on the¹⁰⁶Cd+¹²C reaction, unambiguousγ-ray assignments have been done for¹¹⁶Xe,¹¹⁶I and¹¹⁶Te nuclei. The ground band levels observed in¹¹⁶Xe have been compared to those of heavier even-even xenon isotopes and to the IBA theoretical predictions. In addition, using the newγ-ray assignments, evaporation cross-sections of the¹¹⁸Xe compound nucleus have been estimated and compared to the evaporation model calculations.     

Beta-decay of148,150,152Pr into levels of148,150,152Nd

Theβ ^?-decay of^148,150,152Pr into levels of^148,150,152Nd has been studied byγ-singles,γγ-coincidence and for¹⁴⁸Pr also byγγ-angular correlation measurements. The praseodymium activities have been obtained by thermal neutron-induced fission of²³⁵U followed by on-line mass separation with the helium-jet coupled mass separator HELIOS. Decay schemes for these heaviest praseodymium nuclides are proposed. From the angular correlation measurements spin values for the seven lowest levels of¹⁴⁸Nd are deduced. Spin and parity assignments for the lower levels in^150,152Nd have been extrapolated from level systematics.