B. Weiss

Level structures of 131,129Ce observed in beta decay

Abstract The low-lying levels of the odd-mass nuclei 131 Ce and 129 Ce have been investigated by means of the β + EC decays of 131g+m Pr and 129 Pr, respectively, The Pr nuclei were obtained by bombarding 94,96 Mo targets with a 255 MeV 40 Ca beam. The radioactivities produced in the reactions were transported with a He-jet device and γγt , X γt , e − γt coincidence measurements were performed. Conversion electrons were measured with a magnetic spectrometer and transition multipolarities were deduced. On-line mass separation was used to select the 129 Pr β-decay. The resulting level schemes of 131,129,127 Ce are discussed in connection with level systematics and calculations performed by using the Interacting Boson-Fermion Model (IBFM).

Low-lying states in the doubly odd nucleus 132Pr from beta decay of 132Nd

Abstract The low-lying level scheme of the odd-odd nucleus 132Pr has been investigated for the first time. The radioactive nuclei were produced by bombarding 96Mo targets with a 225 MeV 40Ca beam. Levels in 132Pr have been populated from the 132Nd β-decay. A new value of its half-life has been measured: T 1 2 = 88 ± 7 s . The activities produced in the reaction have been transported with a He-jet device and γγt, Xγt, e−γt coincidence measurements performed. Internal conversion coefficients have been measured with a magnetic lens spectrometer. The experimental level scheme of 132Pr is compared to theoretical calculations performed with the interacting boson-fermion-fermion model (IBFFM).

Non-yrast level structures in the isotopes 131pr and 131La

Abstract Low-lying levels of 131 Pr and 131 La isotopes have been investigated by means of β/EC decays of 131 Nd and 131 Ce, respectively. The radioactive nuclei were produced in the 94 Mo+ 40 Ca reaction at a bombarding energy of 255 MeV and transported with a He-jet system. The identification and the characteristics of the 131m Pr isomer (5.7 s) were obtained by applying both He-jet techniques and on-line gamma-ray spectroscopy with mechanically pulsed beams. γγt , X γt , e − γt coincidence measurements as well as time multi-analysis were performed. Internal conversion electrons were recorded with a magnetic selector and multipolarities deduced. Level schemes of 131 Pr and 131 La are discussed and compared to those of neighboring odd-Z Pr and La isotopes using calculations made in the frame of the Interacting Boson-Fermion Model.

First observation of low lying states in the doubly odd nucleus132Pr from beta decay of132Nd

The lowlying level scheme of the oddodd nucleus132Pr has been investigated for the first time. The radioactive nuclei were produced by bombarding96Mo targets with 225 MeV40Ca beam. Levels have been populated from the132Nd β- decay. A new value of its halflife has been measured: T1/2=88±7 s. The mass identification has been made with an ionguide coupled with an online isotope separator. γ- γ- t, X-γ-t and e−-γ-t coincidence measurements have been performed. The observed distribution of the level feedings is similar to that of the neighbouring odd-odd nuclei.

Non-yrast level structure of121Xe via beta decay of121m+gCs

The results of measurements of the gamma-ray and conversion-electron singles and coincidence spectra from the decay of the 122 s121mCs and the 155 s121gCs to levels of121Xe are reported. TheM 3 multipolarity of the 68.5 keV isomeric transition in121Cs has been deduced. Numerous low-lying levels below 1.6 MeV excitation energy are found. A negative-parity level at 355.9 keV is observed for the first time. The results supplement the low lying energy level systematics in odd-A xenons. A comparison is made with theN=67 barium isotone.

Rotational bands in doubly-odd124Cs and residual proton-neutron interaction

For the first time, collective bands have been observed in the doubly-odd nucleus124Cs. They are proposed to result in the coupling of an h11/2 proton to h11/2 and positive parity neutrons. The relative residual protonneutron interaction in124Cs is calculated and compared to that of neighbouring odd-odd nuclei.

124Ba Decay to the 55 124 Cs69 low-spin levels

The decay of124Ba to the levels of odd-odd124Cs has been studied with on-line mass-separated sources delivered at the Isocele facility. The energy level scheme has been established fromγ-ray singles,γ−γ−t coincidence ande−γ−t coincidence spectra. Spin and parity of several low-lying levels have been assigned on the basis of internal conversion coefficient measurements andβ-branchings. A completely new level pattern including approximately 50 levels and 180γ-rays is proposed for124Cs. Several features of this level scheme are discussed and compared to those of neighbouring isotopes.