P. Banerjee

Coulomb dissociation of 11Li and 11Be in a direct fragmentation model

Abstract The Coulomb dissociation contribution to the two-neutron and one-neutron removal cross section of, respectively, 11 Li and 11 Be projectiles has been calculated in a direct fragmentation model. The model is formulated within the framework of the post form distorted-wave Born approximation. In this theory, the “post acceleration effect” of the 9 Li and 10 Be fragments in the final channel is accounted for properly. The Coulomb break-up can explain aprroximately upto 80% of the experimental 2n removal cross section of 11 Li for the 197 Au target at the incident energy of 29 MeV/ A . The beam energy dependence of the calculated cross sections is in good agreement with the few experimental points presently available. The angular distributions of the 9 Li as well as of 2n system are found to be concentrated in the very forward angles.

Structure of C-19 from Coulomb dissociation studies

We investigate the structure of the neutron rich nucleus ^{19}C through studies of its breakup in the Coulomb field of target nuclei. The breakup amplitude is calculated within an adiabatic treatment of the projectile excitation, which allows the use of the realistic wave functions for the relative motion between the fragments in the ground state of the projectile. The angular distribution of the center of mass of ^{19}C, longitudinal momentum distribution of ^{18}C and relative energy spectrum of the fragments (neutron - ^{18}C) following the breakup of ^{19}C on heavy targets at beam energies below 100 MeV/nucleon have been computed using different configurations for the ground state wave function of ^{19}C. In all the cases, the data seem to favor a ^{18}C(0

Coulomb and nuclear effects in the fragmentation of exotic nuclei

^+)otimes1s_{1/2}

Characteristics of a Compton suppressed Clover detector up to 5 MeV

configuration for the ground state of ^{19}C, with the one-neutron separation energy of 0.53 MeV.

Level density distribution for one-dimensional vertex models related to Haldane-Shastry like spin chains

Abstract The role of the nuclear and the Coulomb interactions in the dissociation of the neutron-rich exotic nuclei 11 Li, 11 Be and 14 Be incident on a number of targets has been studied. The two-neutron removal cross sections of 11 Li and 14 Be and one-neutron removal cross section of 11 Be have been calculated. The theory of diffraction dissociation and diffraction stripping has been used to account for the nuclear effects. The Coulomb-dissociation cross sections have been calculated within the framework of a direct fragmentation model formulated earlier. The Coulomb dissociation along with the nuclear cross sections explain satisfactorily the target-mass dependence of the experimental total two-neutron removal cross sections of 11 Li and 14 Be around 30 MeV/ A incident energy. The beam-energy dependence of this cross section is also well reproduced. The stripping contributions dominate the nuclear cross sections. The dependence of the reaction mechanism underlying the two-neutron removal process on the separation energy of the two-neutron system in the projectile is discussed. The role of the “post-acceleration effect” on the energy spectra of the produced fragments is investigated.

Band structure of 79Br

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

Doppler shift attenuation measurements on57Fe and57Co

The energy level density distributions of some Haldane-Shastry like spin chains associated with the AN − 1 root system have been computed recently by Enciso et al., exploiting the connection of these spin systems with inhomogeneous one-dimensional vertex models whose energy functions depend on the vertices through specific polynomials of first or second degree. Here we consider a much broader class of one-dimensional vertex models whose energy functions depend on the vertices through arbitrary polynomials of any possible degree. We estimate the order of mean and variance for such energy functions and show that the level density distribution of all vertex models belonging to this class asymptotically follow the Gaussian pattern for large number of vertices. We also present some numerical evidence in support of this analytical result.

Coulomb dissociation of 9 Li and the rate of the 8 Li(n ,γ ) 9 Li reaction

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.

Structure of positive-parity yrast band in 80 Br

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

We calculate the Coulomb dissociation of Li9 on Pb and U targets at 28.5 MeV/A beam energy within a finite range distorted wave Born approximation formalism of the breakup reactions. Invoking the principle of detailed balance, these cross sections are used to determine the excitation function and subsequently the rate of the radiative capture reaction 8Li(n,γ)9Li at astrophysical energies. Our method is free from the uncertainties associated with the multipole strength distributions of the Li9 nucleus. The rate of this reaction at a temperature of 10 K is found to be about 2900 cm3 mole-1 s-1.