P. Fettweis

Identification of new germanium isotopes in fission: Decay properties and nuclear charge distribution in the A = 78 to 84 mass region

Abstract By means of a fast radiochemical separation, germanium was isolated at short time intervals from 235 U irradiated with thermal neutrons. By extrapolating γ- or β-activities of known descendants, the half-lives of the following isotopes were determined, several of these being unreported previously: 78 Ga : 4.8±1.3 s , 79 Ge : 41.1±4.3 s , 80 Ge : 24.5±1.0 s , 81 Ge : 10.1±0.8 s , 82 Ge : 4.60±0.35 s , 83 Ge : 1.9±0.4 s , 84 Ge : 1.2±0.3 s . It is shown that 82 Ge decays only to the low-spin isomer of 82 As whose half-life was redetermined as 22.6±1.4 s. The main γ-ray energies and intensities were measured for the longer-lived isotopes and partial schemes are given for the decay of 81 Ge, 81 As and 82 As. From the relative fission-yield measurements, nuclear-charge distribution is discussed for this mass region.

Study of short-lived Ru-isotopes produced in thermal neutron fission of235U

Short lived Ru isotopes produced in thermal fission of235U have been chemically separated from the other fission products. Successiveγ-ray spectra were taken by means of Ge(Li) detectors. The observedγ-lines have been assigned to the various Ru isotopes (A=107 to 110) or to their daughter elements on the basis of their half-lives, intensity ratios and known level properties. Partial decay schemes are discussed and relative fission yields are given.111Ru has been identified (T12: 1.5±0.3 s).

On the Delayed Neutron Yields of the Longer-lived Halogen Precursors in Thermal Neutron Fission of 235U

The 1S7I/87Br and 88Br/87Br delayed neutron ratios were measured respectively as 4.85 + 0.20 and 1.7 + 0.2 after chemical separation from thermal neutron fission of 236U. Delayed neutron yields are proposed for 87Br, 88Br and 187I and the halflives of 87Br and 137I are remeasured with higher precision. By comparing the neutron activities of 87Br and 1 3 ,I to the y-activities of their daughters 87Kr and 137Xe, their Pn values are evaluated.

First identification of γ-rays in the β+/EC decay of 104,105Sn

The beta +/EC decay of mass-separated 104Sn and 105Sn isotopes was studied by X-ray and gamma -ray singles, as well as by X- gamma and gamma - gamma coincidences. Sources were produced in the reactions 92Mo (20Ne,ypxn). The nucleus 50104Sn with T12/=23+or-2 s was identified. A partial decay scheme of 105Sn is proposed.

Collective and shell-model excitations in 9745Rh52

Abstract 97Rh has been studied by deexcitation of the compound nucleus formed through the reactions 96Ru(3He,pn) at 20 MeV and 96Ru(2H,n) at 9 MeV. Direct γ-spectra, multidimensional γγ coincidences and angular distribution measurements lead to a proposed level scheme. These levels are compared to calculations based on the interacting boson-fermion approximation IBFA model in which the odd particle moves in the 1 g 9 2 orbital. Evidence for the observation of shell-model states outside the sd boson configuration space in 97Rh is obtained.

Excited states of97Pd

The97Pd nucleus has been studied from the reaction96Ru(3He, 2n)97Pd. From in and out beam directγ-spectra andγ-γ coincidences a partial level scheme is proposed. The observed high spin states can be explained by the coupling of the even proton core with the d5/2 51st neutron.

The decay of 97Pd

Abstract 97 Pd has been obtained by the reaction 96 Ru( 3 He, 2n) 97 Pd. Chemically separated samples from natural Ru targets showed that it decayed mostly to 97g Rh and gave absolute γ-yields. Direct γ-spectra, γ-γ and β-γ coincidences were measured on irradiated 96 Ru enriched targets. A Q EC of 4.8 ± 0.3 MeV has been obtained. Of the 55 γ-transitions assigned to the decay of 97 Pd, 46 have been included in a level scheme. Anomalous low-lying 7 2 + and 5 2 + states are found and compared to those of neighbouring isotopes. An attempt is made to explain these levels in the frame of the dressed 3QP model of Kuriyama et al .