arXiv subjects

A. Bisoi

Publications and source records attributed to A. Bisoi.

7 recordsLinked to original sources

arXiv2026

Low lying excitations in $^{150}$Pm

The low lying excitations in odd-odd $^{150}$Pm have been studied through proton induced reaction with an array of five Compton suppressed Clover HPGe and one segmented planar Ge detectors. The relative excitation functions for the observed $\gamma$ rays have been studied using singles data at two beam energies of 8~MeV and 9~MeV. 16 new $\gamma$ rays and 15 new levels have been placed in the level scheme of $^{150}$Pm based on $\gamma-\gamma$ coincidence data. The relative intensities for the observed $\gamma$ rays have been determined using total and gated projections. Tentative spin-parity assignments were made to few low lying excitations of $^{150}$Pm, using limited angular distribution data and other information. Lifetimes were estimated for two excited levels in this nucleus using using generalized centroid difference analysis, applied in the nanosecond range, with Ge detectors. Large basis shell model and projected shell model calculation were performed to interpret the experimentally observed levels. The present work indicates 1$^-$ ground state, a 2$^-$ state close to the ground state ($\sim$50~keV) and a low lying 6$^-$ isomeric state in this odd-odd nucleus along with emerging band structures developed with two quasiparticle configurations.

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arXiv2026

Evidence of the Excited X(5)-like Critical-Point Symmetry Structures in 152Sm

The positive-parity structure of 152Sm has been investigated through high-statistics {\gamma}-ray spectroscopy following the (150Nd({\alpha},2n)152Sm reaction at Elab = 26 MeV. Several collective structures built on excited 0+ states have been extended through the observation of new levels and {\gamma}-ray transitions, and spin-parity assignments have been established using directional-correlation and linear-polarization measurements. Electromagnetic transition strengths (B(E2)), deduced from measured branching ratios and known level lifetimes, reveal pronounced collectivity among the excited configurations. The resulting level scheme provides evidence for a sequence of excited collective bands extending beyond the well-known ground-state and first excited 0+ structures. The excitation energies and transition strengths are examined within the framework of the X(5) critical-point description of the first-order U(5)-SU(3) shape-phase transition. In addition to the established X(5)-like features of the low-lying spectrum, the observed systematics of the higher-lying bands are found to be consistent with excited collective structures exhibiting X(5)-like characteristics. The results provide new constraints on the realization of critical-point behavior in finite nuclei and on the evolution of collectivity in the N=90 region.

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arXiv2025

A New Evidence of Interplay Between Tetrahedral and Octahedral Symmetries and Symmetry Breaking: Exotic Rotational Bands in $^{152}$Sm

We report on an experimental evidence for a new, second tetrahedral band in $^{152}_{\;\;62}$Sm$^{}_{90}$. It was populated via fusion evaporation reaction, $^{150}{\rm Nd}(\alpha, 2n)^{152}$Sm, employing 26 MeV beam of $\alpha$ particles from K-130 cyclotron at Variable Energy Cyclotron Centre, Kolkata, India. The newly observed possible mixed parity sequence with absence of E2 and strong indication of E3 transitions is consistent with the spectroscopic criteria for a tetrahedral-symmetry rotational band that could be constructed from the allowed spin-parity assignments. This structure differs from the structure of the band previously found in the same nucleus, the new one manifesting tetrahedral symmetry not accompanied by the octahedral one. Our new experimental results are interpreted in terms of group representation theory and collective nuclear-motion theory of Bohr. We propose to generalize the notion of the tetrahedral vibrational bands and believe that our new experimental results support a number of theory predictions related to nuclear tetrahedral symmetry published earlier and bring a new light into the issue of spontaneous symmetry breaking in heavy nuclei.

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arXiv2022

High spin states of $^{204}$At: isomeric states and shears band structure

High-spin states of neutron deficient Trans-Lead nucleus $^{204}$At were populated up to $\sim 8\,{\rm MeV}$ excitation through the $^{12}$C + $^{197}$Au fusion evaporation reaction. Decay of the associated levels through prompt and delayed $γ$-ray emissions were studied to evaluate the underlying nuclear structure. The level scheme, which was partly known, was extended further. An isomeric $16^+$ level with observed lifetime $τ=52 \pm 5\, {\rm ns}$, was established from our measurements. Attempts were made to interpret the excited states based on multi quasiparticle and hole structures involving $2f_{5/2}$, $1h_{9/2}$, and $1i_{13/2}$ shell model states, along with moderate core excitation. Magnetic dipole band structure over the spin parity range:~$16^+ - 23^+$ was confirmed and evaluated in more detail, including the missing cross-over $E2$ transitions. Band-crossing along the shears band was observed and compared with the evidence of similar phenomena in the neighbouring neutron deficient $^{202}$Bi, $^{205}$Rn isotones and the $^{203}$At isotope. Based on comparison of the measured $B(M1)/B(E2)$ values for transitions along the band with the semiclassical model based estimates, the shears band of $^{204}$At was established along with the level scheme.

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arXiv2020

Study of proton capture resonant state of ^{15}O at 7556 keV

The slowest reaction in the CNO cycle 14N(p, gamma)15O has been studied by populating the E^lab_p =278 keV (E^r_c.m.=259 keV) proton capture resonant state of ^{15}O at 7556 keV. The strength of the resonance has been determined from the experimental data. The level lifetime of the sub-threshold resonant state at Ex=6792 keV, as well as the lifetimes of the 5181 keV and 6172 keV states, have been measured using the Doppler shift attenuation method (DSAM). The structural properties of the nucleus ^{15}O, such as, the level energies, transition strengths, level lifetimes, and spectroscopic factors, have been calculated theoretically by using the large basis shell model, which agrees reasonably well with the present as well as the previous experimental data.

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arXiv2020

The determination of α-spectroscopic factors and ANC of 16O states using 12C(20Ne,16O)16O reaction at Elab=150 MeV incident energy

The 12C(20Ne,16O)16O α-transfer reaction at Elab=150 MeV is first time used to determine the ANC of the 6.92 MeV and 7.12 MeV states of 16O. The 20Ne+ 12C potential parameters are also obtained from elastic scattering. The direct reaction code FRESCO is used to determine the α-spectroscopy factor (Sα ) of the three states of 16O (6.92 MeV, 7.12 MeV and 11.52 MeV) and ANC of the two states (6.92 MeV and 7.12 MeV) of 16O. The extracted ANC and Sα are compareable to previous measurements.

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arXiv2019

Characterization of an electrically cooled BEGe detector till E$_γ\sim7$ MeV

An electrically cooled Broad Energy Germanium (BEGe) detector has been characterized in the energy range E$_γ$ $\sim$ 0.122 - 7 MeV by utilizing the $γ$- rays emitted by a short-lived resonance state in $^{15}$O populated through $^{14}$N(p,$γ$) reaction and standard radioactive source ($^{152}$Eu). The experimental results have been reproduced through simulations with GEANT4 code, including vendor specified detector geometry along with the detailed construction of the target holder flange, to delineate the effects of the holder at various energies and detector position. Later the efficiency with a bare point source has been simulated. It has been found that the electrically cooled BEGe detector is suitable for usage in the $γ$-ray spectroscopy as well as for the study of resonance phenomena in nuclear astrophysics.

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