9,361 research outputs found
New magic number for neutron rich Sn isotopes
The variation of E(2+_1) of (134-140)Sn calculated with empirical SMPN
interaction has striking similarity with that of experimental E(2+_1) of
even-even (18-22)O and (42-48)Ca, showing clearly that N=84-88 spectra exhibit
the effect of gradual filling up of \nu(2f_{7/2}) orbital which finally
culminates in a new shell closure at N=90. Realistic two-body interaction CWG
does not show this feature. Spin-tensor decomposition of SMPN and CWG
interactions and variation of their components with valence neutron number
reveals that the origin of the shell closure at 140Sn lies in the three body
effects. Calculations with CWG3, which is obtained by including a simple
three-body monopole term in the CWG interaction, predict decreasing E(2+_1) for
(134-138)Sn and a shell closure at 140Sn.Comment: 4 pages, 5 figure
Understanding Nuclei in the upper sd - shell
Nuclei in the upper- shell usually exhibit characteristics of spherical
single particle excitations. In the recent years, employment of sophisticated
techniques of gamma spectroscopy has led to observation of high spin states of
several nuclei near A 40. In a few of them multiparticle, multihole
rotational states coexist with states of single particle nature. We have
studied a few nuclei in this mass region experimentally, using various
campaigns of the Indian National Gamma Array setup. We have compared and
combined our empirical observations with the large-scale shell model results to
interpret the structure of these nuclei. Indication of population of states of
large deformation has been found in our data. This gives us an opportunity to
investigate the interplay of single particle and collective degrees of freedom
in this mass region.Comment: 8 pages, 13 figures, submitted for publication in the Proceedings of
"Frontiers in Gamma-Ray Spectroscopy 2012 (FIG12), held at New Delhi, March
5th - 7th, 2012, Organized by Inter University Accelerator Center, New Delhi,
Indi
Structure of A=138 isobars above the 132Sn core and the N-N interaction in the neutron-rich environment
Large basis untruncated shell model calculations have been done for the A=138
neutron -rich nuclei in the pi(gdsh) X nu(hfpi) valence space above the 132Sn
core. Two (1+2) -body nuclear Hamiltonians, viz., realistic CWG and empirical
SMPN in this model space have been used. Calculated ground state binding
energies, level spectra and other spectroscopic properties have been compared
with the available experimental data. Importance of untruncated shell model
calculations in this model space has been pointed out. Shell model results for
the very neutron rich Sn isotope (138Sn, N/Z=1.76) of astrophysical interest
for which no spectroscopic information except beta -decay half life is
available, have been presented. Shell structure and evolution of collectivity
in the even-even A=138 isobars have been studied as a function of valence
neutron and /or proton numbers. Calculations done for the first time, reproduce
remarkably well the collective vibrational states in 138Te and 138Xe.
Comparison of some of the important two-body matrix elements of the empirical
SMPN, CW5082 and the realistic CWG interactions has been done. These matrix
elements are important for ground state binding energies and low-lying spectra
of nuclei in this region. Consideration of the predictability of the two
interactions seems to suggest that, in order to incorporate the special
features of the N-N interaction in such exotic n-rich environment above the
132Sn core, the use of local spectroscopic information from the region might be
essential.Comment: 22 pages, 14 figure
Astrophysical Implication of Low E(2^+_1) in Neutron-rich Sn Isotopes
The observation and prediction of unusually depressed first excited 2^+_1
states in even-A neutron - rich isotopes of semi-magic Sn above 132Sn provide
motivations for reviewing the problems related to the nuclear astrophysics in
general. In the present work, the beta-decay rates of the exotic even Sn
isotopes (134,136Sn) above the 132Sn core have been calculated as a function of
temperature (T). In order to get the necessary ft values, B(GT) values
corresponding to allowed Gamow Teller (GT-) beta-decay have been theoretically
calculated using shell model. The total decay rate shows decrease with
increasing temperature as the ground state population is depleted and
population of excited states with slower decay rates increases. The abundance
at each Z value is inversely proportional to the decay constant of the waiting
point nucleus for that particular Z. So the increase in half-life of isotopes
of Sn, like 136Sn, might have substantial impact on the r-process
nucleosynthesis.Comment: 4th International Workshop on Nuclear Fission and Fission Product
Spectroscopy, CEA Cadarache, May 13 - 16, 2009, 4 pages, 2 figure
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