J.M. Chatterjee

Characteristics of a Compton suppressed Clover detector up to 5 MeV

The Clover detectors in their addback mode are excellent tools for detecting high-energy gamma rays ðX2 MeVÞ: The characteristics ofthese detectors, at energies above 2 MeV ; are usually determined from simulation data or from extrapolation ofthe empirical data. This is the first time that the characteristics ofa Compton suppressed Clover germanium detector have been studied up to 5 MeV using a radioactive 66 Ga ðT1=2 ¼ 9:41 hÞ source. r 2002 Elsevier

Band structure of 79Br

Abstract High-spin states of 79Br have been studied in the reaction 76 Ge( 7 Li , 4nγ) at 32 MeV. A gamma-detector array with twelve Compton-suppressed HPGe detectors was used. The positive-parity yrast states, interpreted as a rotationally aligned g 9 2 proton band, and the negative-parity ground state band have been extended to spins of ( 33 2 + ) and ( 25 2 − ), respectively. Lifetime measurements indicate that both bands have a similar quadrupole deformation of β2 ∼ 0.2. The positive-parity α = −1 2 band has been identified. Several new inter-band transitions are observed. A cranked-shell model analysis shows that the νg 9 2 alignments occur in the positive-parity and the negative-parity bands at rotational frequencies of ℏω ∼ 0.6 and 0.4 MeV, respectively. The level energies and the electromagnetic properties of the g 9 2 band can be well reproduced by a particle-rotor model calculation with an axially symmetric core.

Doppler shift attenuation measurements on57Fe and57Co

SummaryLifetime measurements by the Doppler shift attenuation method for levels in the nuclei57Fe and57Co, populated via the reactions55Mn(α, pnγ)57Fe and55Mn(α, 2nγ)57Co, respectively, are reported. The relative γ-ray intensities and the branching ratios for levels in the two nuclei are also presented. In57Fe, mean lifetime values of τ=(0.20±0.09) ps and (0.26±0.10) ps are obtained for the levels at 1007.0 keV and 1356.8 keV, respectively, for which no lifetime information existed previously and values of τ=0.08±0.03, 0.54−0.15+0.30 and (0.16±0.06) ps are determined for the levels at 2355.7, 3269.1 and 6185.6 keV, respectively, for which only the limits of lifetimes were reported earlier. For the 2455.2 keV level in57Fe a lower limit of 2 ps is obtained for its mean life. In57Co lifetimes of eight levels withJπ≤19−/2 have been measured and compared with the earlier reported values. The results of lifetime measurements and reduced transition probabilities for both the nuclei are discussed and compared with the available shell model calculations.RiassuntoSi riportano le misure di vita media mediante il metodo di attenuazione dello spostamento Doppler per livelli nei nuclei57Fe e57Co popolati mediante le reazioni55Mn(α, pnγ)57Fe e55Mn(α, 2nγ)57Co, rispettivamente. Si presentano anche le intensità relative dei raggi γ e i rapporti di diramazione nei due nuclei. Per57Fe si ottengono i valori di vita media di τ=(0.20±0.09) ps e (0.26±0.10) ps per i livelli a 1007.0 keV e 1356.8 keV, rispettivamente, per i quali non esistevano precedentemente informazioni sulla vita media, e si determinano i valori di τ=0.08±0.03, 0.54−0.15+0.30 e (0.16±0.06) ps per i livelli a 2355.7, 3269.1 e 6185.6 keV, rispettivamente, per i quali si erano stati riportati precedentemente solo i limiti di vita media. Per il livello a 2455.2 keV nel57Fe si ottiene per la sua vita media un limite inferiore di 2 ps. Nel57Co le vite medie degli otto livelli conJπ≤19−/2 sono state misurate e confrontate con valori riportati precedentemente. Si discutono i risultati delle misure di vita media e le probabilità di transizione ridotte per entrambi i nuclei e si confrontano con i calcoli disponibili del modello a strati.

Structure of 96 Mo at high spins

Abstract High-spin states of 96 Mo ( Z=42 , N=54 ) nucleus have been investigated through the 82 Se( 18 O , 4n ) reaction at E b =60 MeV. The excited states have been extended upto 10 MeV and the levels with J π =20 + spins have been observed in the present experiment while the earlier information for the same was available only upto 4.8 MeV. A significant modification of the existing level scheme is also being proposed. The properties of the observed levels have been compared with shell-model calculations using OXBASH code. The analysis of the result shows that level structure exhibits mainly single particle character.

A semiempirical method based on the LSS formalism for estimating electronic energy loss

Abstract A modified semiempirical expression for the LSS parameter ξe valid for ions with nuclear charge ⩽ 92 is presented and its applicability for predicting electronic stopping powers is discussed.

High Spin States in the Odd–Odd 150Eu Nucleus

High spin rotational bands in the odd–odd 150Eu nucleus, produced in the 148Nd(7Li,5n) reaction, were investigated by in-beam γ spectroscopy. Seven bands above the 588.8 keV (45 ns) isomeric level were observed. Probable single- and double-octupole-phonon coupling states were identified. Two positive parity bands are interpreted in terms of two quasiparticles (a proton and a neutron) coupled to an axially symmetric rotor core. Otherwise, the rest of the high spin levels are described by multiparticle–hole excitations.