U. Keyser

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,Qβ-values and mass excesses are calculated and compared with the results obtained in direct mass determinations.

Experimental beta-decay energies of several neutron-rich nuclides with mass number 131≦A≦146

With sources obtained from the on-line mass separator LOHENGRIN the beta-decay energies of131Sn,134Sb,135,136Te,143,146Ba and146La have been determined from measuredβ-endpoint energies. The experimental values are compared with the predictions of several mass formulae.

ExperimentalQβ-values of several short-lived nuclides with mass number 85≦A≦103

TheQβ-values of85, 86Se,90Br,93Kr,103Nb and103Tc were measured using massseparated sources produced at the on-line mass separator LOHENGRIN. The experimental values are compared with mass formula predictions. Taking also into account earlier results, a subshell-closure effect for the neutron numberN=56 and proton numberZ=38 is shown to exist.

Experimental beta-decay energies of very neutron-rich Cs isotopes

TheQβ-values of the very neutron-rich cesium isotopes with mass number 142≤A≤146 have been measured with a plastic scintillation detector telescope at the fission product separator OSTIS. The mass excesses calculated from these decay energies agree well with the values obtained by direct mass determinations.

Experimental beta-decay energies of very neutron-rich isobars with mass numbers A=101 and A=102

TheQβ-values of101Rb,101,102Sr and101,102Y have been measured for the first time at the mass separator ISOLDE by means ofβγ-coincidence techniques with a plastic scintillation detector telescope and a large Ge(HP)-detector. For some of these nuclei, also new details of their decay schemes could be derived from the measuredβ-decay properties. The experimental results are discussed, as far as the systematics of two-neutron separation energies derived from them is concerned. In addition, the nuclear masses deduced from theseQβ-values are compared with the predictions of recent mass calculations.

Beta decay energies and nuclear masses of148Ba,148La and151Pr

Theβ-decay energy of the neutron-rich isotopes148Ba,148La and151Pr has been measured at the Institute Laue-Langevin (ILL). The148Ba- and148La-nuclei were produced using a high-temperature ion source at the OSTIS separator of this institute, whereas samples of151Pr were obtained from the thermal fission of239Pu, used as a target in the mass separator LOHENGRIN. At both instruments,βγ-coincidences were measured with a plastic scintillator telescope and a Ge(I)-detector, together withβ-singles andγ-singles spectra. Theβ-spectra emitted in coincidence with 44γ-lines in the decay of these nuclei have been evaluated. From their endpoint energies, the followingQβ-values have been obtained:Qβ(148Ba)=5115±60keV;Qβ(148La)=7255±55 keV;Qβ(151Pr)=4170±75 keV. Using these results, the nuclear massesA of these nuclei can be calculated with a relative error ΔA/A≃5·10−7. In addition, the two-neutron separation energies and the mass excesses have been derived; the results are compared with recent predictions of theoretical mass calculations.

Beta-decay energies of neutron-rich nuclei in the mass region 142≦A≦150

The β-endpoint energies of 6 neutron-rich nuclei with mass numbersA=146 andA=147 have been measured with a plastic scintillator telescope at the on-line mass separator OSTIS. With theQβ-values derived from these experiments and with those obtained in earlier studies, nuclear structure effects in this part of the nuclear chart are investigated. In addition, nuclear masses derived from the experimentalQβ-values are compared with the predictions of theoretical mass calculations.

Q β -Values and masses of neutron-rich nuclei withA=99 and 100

The Qβ-values of99Rb,99,100Sr and100Y have been measured for the first time at the mass separator OSTIS of the ILL; for99Y,99,100Zr and100Nb, the results of earlier experiments were confirmed with reduced experimental errors. The two-neutron binding energies derived from the experimental Qβ-values clearly indicate that the nuclei100Sr and100Y are strongly deformed.

Beta-Decay Energies of Neutron-Rich Fission Products in the Vicinity of Mass Number 100

Beta-decay energies of neutron-rich fission products have been measured by different groups using different experimental techniques and data evaluation methods at the mass separator LOHENGRIN and OSTIS installed at the high flux reactor of the Institute Laue-Langevin in Grenoble. In this communication, recent results of such experiments will be presented for light fission products; some results obtained for heavy fission products will be discussed in another contribution to this conference1. The decay energies have been derived from measurements with a plastic scintillation counter telescope to detect the electrons emitted in beta-decay. In most cases, the β-spectra have been measured in coincidence with γ-rays recorded with a big Ge(Li)-detector. The β-detector telescope has been calibrated by measuring β-spectra with well-known endpoint energies under the same conditions as during the main experiment. Therefore, it is not necessary for the evaluation of the experimental data to know the efficiency and response function of the detector. In some cases, β-ray singles spectra have also been recorded with a high-purity Ge-detector. More details concerning the preparation and counting of the sources and the handling of the data are given elsewhere2.

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 experimentalQβ-values and compared with different mass predictions.