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Praveen C. Srivastava

Publications and source records attributed to Praveen C. Srivastava.

At least 55 records · Page 3Linked to original sources

Forbidden beta decay properties of $^{135,137}$Te using shell-model

In this work, the large-scale shell-model calculations for $β$-decay properties have been done. The $β$-delayed $γ$-ray spectroscopy has been performed recently at ILL, Grenoble [M. Si \textit{et al.}, Phys. Rev. C {\bf 106}, 014302 (2022)] to study $β$-decay properties corresponding to $^{137}$Te (($7/2^-))$ $\rightarrow$ $^{137}$I ($J_f$) transitions. We have done a systematic shell-model study for nuclear structure properties and compared the obtained results with the experimental data. Finally, the $β$-decay properties such as the $\log ft$ values and average shape factors have been reported. This is the first theoretical calculation for the $\log ft$ values corresponding to these new experimental data. In addition, we have also reported calculated $\log ft$ results for $^{135}$Te (($7/2^-))$ $\rightarrow$ $^{135}$I ($J_f$) transitions.

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Ab initio no-core shell model description of $^{10-14}$C isotopes

We present a systematic study of the $^{10-14}\text{C}$ isotopes within the \textit{ab initio} no-core shell model theory. We apply four different realistic nucleon-nucleon (NN) interactions: (i) the charge-dependent Bonn 2000 (CDB2K) potential (ii) the inside non-local outside Yukawa (INOY) potential (iii) the next-to-next-to-next-to-leading order (N$^3$LO) potential, and (iv) the optimized next-to-next-to-leading order (N$^2$LO$_{opt}$) potential. We report the low-lying energy spectra of both positive and negative parity states for the $^{10-14}\text{C}$ isotopes and investigate the level structures. We also calculate electromagnetic properties such as transition strengths, quadrupole and magnetic moments. The dependence of point-proton radii on the harmonic oscillator frequency and basis space is shown. We present calculations of the translation invariant one-body density matrix in the no-core shell model and discuss isotopic trends in the density distribution. The maximum basis space reached is $10 \hbar Ω$ for $^{10}\text{C}$ and $8 \hbar Ω$ for $^{11-14}\text{C}$, with a maximum M-scheme dimension of $1.3 \times 10^{9}$ for $^{10}\text{C}$. We found that while the INOY interaction gives the best description of the ground state energies, the N$^3$LO interaction best reproduces the point-proton radii.

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Ab initio no-core shell model study of neutron-rich $^{18,19,20}$C isotopes

We implement the ab initio no-core shell model approach to study neutron-rich $^{18}$C, $^{19}$C and $^{20}$C isotopes. For this purpose, we employ charge-dependent Bonn 2000 (CDB2K), inside non-local outside Yukawa (INOY) and chiral next-to-next-to-next-to-leading order (N$^{3}$LO) nucleon-nucleon interactions. Low-lying energy spectra, electromagnetic properties and point-proton radii for these nuclei up to basis space $N_{\rm max}$ = 4 are calculated. Binding energies obtained with INOY interaction are in better agreement with the experimental values as compared to other \textit{ab initio} interactions. We also show the behavior of ground state energy and point-proton radii with the NCSM parameters, $\hbar$$Ω$ and $N_{\rm max}$. We report a strong sensitivity of the B(E2) values from the first excited $2^+$ to the ground state of $^{18}$C and $^{20}$C to the nuclear interaction. Shell model calculations with YSOX interaction are also performed, and corresponding results are compared with ab initio one.

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Shell-model description for the properties of the forbidden $β^-$ decay in the region "north-east" of $^{208}$Pb

In the present work, we report a comprehensive shell-model study of the $\log ft$ values for the forbidden $β^-$ decay transitions in the north-east region of $^{208}$Pb. For this we have considered $^{210-215}$Pb $\rightarrow$ $^{210-215}$Bi and $^{210-215}$Bi $\rightarrow$ $^{210-215}$Po transitions. We have performed shell-model calculation using KHPE interaction in valence shell 82-126 for protons and 126-184 for neutrons without any truncation. We have also calculated half-lives and Q-values for the concerned nuclei. Recently several $\log ft$ values are observed corresponding to $β^-$ decay from (8$^-$) isomeric state of $^{214}$Bi$^m$ at CERN-ISOLDE facility [Phys. Rev. C {\bf 104}, 054301 (2021)], and for the first time we have reported shell-model results for these transitions.

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Systematic shell model study for $N=82$ and $N=126$ isotones and nuclear isomers

In the present work, we have done a systematic shell model study of $N=82$ and $N=126$ isotones. For the $N=82$ isotones, we have performed calculations using SN100PN interaction, while for $N=126$ isotones, we have used KHPE interaction. Similarities between these two isotonic chains have been reported, using the strong resemblance between the high-$j$ orbitals. Apart from the nuclear spectroscopic properties, we have also explained different isomeric states in these two regions. In the $N$ =82 region, we have mainly discussed the properties of the $6^+$ and $17/2^+$ isomers, while in the $N=126$ region for $8^+$, $11^-$, $21/2^-$ and $29/2^+$ isomers. We have reported $B(E2)$, $B(E3)$, $g$-factor, and quadrupole moments of the isomeric states for comparison in these two isotonic chains.

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Shell-model study for GT-strengths corresponding to $β$ decay of $^{60}$Ge and $^{62}$Ge

In the present work, we have reported a comprehensive shell-model study of GT-strengths for recently available experimental data for $^{60}$Ga and $^{62}$Ga from RIKEN Nishina Center [Phys. Rev. C 103, 014324 (2021)] populated by $β$ decay of the $^{60}$Ge and $^{62}$Ge, respectively. We have performed shell-model calculations in two different model spaces, the first set of calculations in the $fp$ model space using KB3G and GXPF1A interactions, while the second set in $f_{5/2}pg_{9/2}$ model space using JUN45 and jj44b effective interactions. Our shell-model results in $fp$ model space are in a reasonable agreement with the available experimental data.

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Systematic shell-model study of Rn isotopes with $A=$ 207 to 216 and isomeric states

We present systematic large-scale shell-model calculations for Rn isotopes with $A=$ 207 to 216. For the $^{207-212}$Rn isotopes, we perform calculations with KHH7B interaction, while for $^{213-216}$Rn isotopes with KHPE and KHH7B interactions. The calculated energies and electromagnetic properties are compared with the available experimental data and predicted where experimental data are not available. We also suggest spins and parities of several unconfirmed states available from the recent experimental data. Comprehensive study of several isomeric states from the calculated shell-model configurations and half-lives is also reported.

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Second-forbidden nonunique $β^-$ decays of $^{59,60}$Fe: Possible candidates for $g_A$ sensitive electron spectral-shape measurements

In this work, we present a theoretical study of the electron spectral shapes for the second-forbidden nonunique $β^-$-decay transitions $^{59}\textrm{Fe}(3/2^-)\to\,^{59}\textrm{Co}(7/2^-)$ and $^{60}\textrm{Fe}(0^+)\to\,^{60}\textrm{Co}(2^+)$ in the framework of the nuclear shell model. We have computed the involved wave functions by carrying out a complete $0\hbarω$ calculation in the full $fp$ model space using the KB3G and GXPF1A effective interactions. When compared with the available data, these interactions predict the low-energy spectra and electromagnetic properties of the involved nuclei quite successfully. This success paves the way for the computations of the $β$-decay properties, and comparison with the available data. We have computed the electron spectral shapes of the mentioned decay transitions as functions of the value of the weak axial coupling $g_{\rm A}$. By comparing these computed shapes with the measured spectral shapes allows then to extract the effective value of $g_{\rm A}$ for these decay transitions. This procedure, coined the spectrum-shape method (SSM) in several earlier studies, complements the method of determining the value of $g_{\rm A}$ by reproducing the (partial) half-lives of decay transitions. Here we have enhanced the original SSM by constraining the value of the relativistic vector matrix element, $^V\mathcal{M}^{(0)}_{KK-11}$, using the conserved vector-current hypothesis (CVC) as a starting point. We hope that this finding would be a strong incentive to measure the spectral shapes in the future.

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Shell-model description for the first-forbidden $β^-$ decay of $^{207}$Hg into the one-proton-hole nucleus $^{207}$Tl

In this work, we have performed large-scale shell-model calculations for the first-forbidden $β^{-}$ decay of $^{207}$Hg into the one-proton-hole nucleus $^{207}$Tl corresponding to the recently available experimental data from ISOLDE-CERN [T. A. Berry et al., Phys. Rev. C 101, 054311 (2020)]. We have used the one-particle one-hole ($1p$-$1h$) truncation for both protons and neutrons simultaneously across the doubly-shell closure at $^{208}$Pb in the final states of $^{207}$Tl. In our calculations, we have also considered the effect of mesonic enhancement $ε_{\mathrm{mec}}=2.01\pm 0.05$ in the rank-0 for the axial-charge matrix element $γ_{5}$. Here, we have calculated the $\log ft$ values from the ground-state of $^{207}$Hg to the several excited states of $^{207}$Tl and obtained a good agreement between the calculated and the experimental data. In the experimental data spin and parity for some states are not yet confirmed, thus based on the shell-model results for the $\log ft$ values we have given the prediction for these states. This is the first theoretical calculation for the $\log ft$ values for these transitions.

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Structure of $^{46,47}$Ca from the $β^-$ decay of $^{46,47}$K in the framework of nuclear shell model

In the present work, we report a comprehensive theoretical study of the $\log ft$ values for the allowed and forbidden $β^-$ decay transitions of $^{46}$K and $^{47}$K corresponding to recently available experimental data from the GRIFFIN spectrometer at TRIUMF-ISAC [Phys. Rev. C {\bf 100}, 054327 (2019); Phys. Rev. C {\bf 102}, 054314 (2020)]. We perform the nuclear shell-model calculation in $sdpf$-valence space, with the SDPF-MU interaction, to calculate low-lying energy spectra of $^{46,47}$K and $^{46,47}$Ca. For further investigation, we also calculate spectroscopic properties of $^{46,47}$K, $^{46,47}$Ca and compare the results with the experimental data. We suggest spin-parity of several levels, which were previously tentative, in both the calcium isotopes. Based on the energy and $\log ft$ values, we conclude that the state at 3.984 MeV in $^{46}$Ca could be either $3^{-}$ or $2^{+}$ and a state at 4.432 MeV might be $3^{-}$. The spin-parity of the states at 2.875, 3.951 and 4.453 MeV are predicted to be $1/2^-$, $3/2^-$ and $1/2^-$ or $1/2^+$, respectively, in $^{47}$Ca. We also give the confirmation to spin-parity of 2.850, 3.889 and 4.606 MeV states for $^{47}$Ca. Our results of level schemes of $^{46,47}$K are in a reasonable agreement with the experimental data, while the agreement of calculated $\log ft$ values for the $β^-$ decay with the experimental data is limited.

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Ab-initio no-core shell model study of $^{10-14}$B isotopes with realistic NN interactions

We report a comprehensive study of $^{10-14}$B isotopes within the \textit{ab-initio} no-core shell model (NCSM) using realistic nucleon-nucleon (\textit{NN}) interactions. In particular, we have applied the inside non-local outside Yukawa (INOY) interaction to study energy spectra, electromagnetic properties and point-proton radii of the boron isotopes. The NCSM results with the charge-dependent Bonn 2000 (CDB2K), the chiral next-to-next-to-next-to-leading order (N$^3$LO) and optimized next-to-next-to-leading order (N$^2$LO$_{opt}$) interactions are also reported. We have reached basis sizes up to $N_{\mbox{max}}$ = 10 for $^{10}$B, $N_{\mbox{max}}$ = 8 for $^{11,12,13}$B and $N_{\mbox{max}}$ = 6 for $^{14}$B with m-scheme dimensions up to 1.7 billion. We also compare the NCSM calculations with the phenomenological YSOX interaction using the shell model to test the predictive power of the \textit{ab-initio} nuclear theory. Overall, our NCSM results are consistent with the available experimental data. The experimental ground state spin $3^{+}$ of $^{10}$B has been reproduced using the INOY \textit{NN} interaction. Typically, the 3\textit{N} interaction is required to correctly reproduce the aforementioned state.

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Shell model study of high-spin states and band terminations in $^{67}$As

In the present work, recently available experimental data for different bands of $^{67}$As [Phys. Rev. C {\bf 98}, 024313 (2018)] have been interpreted within the framework of the shell model in full $f_{5/2}pg_{9/2}$ model space using JUN45 and jj44b effective interactions. The variation of $E$ - $E_{rot}$ energy versus spin for different bands is shown to obtain useful information about band termination. We have also reported the electromagnetic transition probabilities, quadrupole and magnetic moments of $^{67}$As. Except for some tentative high-spin states, the results are in good agreement with the available experimental data.The states $29/2^+$-$45/2^+$ are described by three particles in $g_{9/2}$, while $47/2^+$ and $51/2^+$ states are described by five particles in $g_{9/2}$. The shell model results corresponding to nine tentative states such as $41/2_1^+$ and $45/2_1^+$ in band-1b; $41/2_2^+$ and $45/2_2^+$ in band-1a; $43/2_2^+$, $47/2_2^+$ and $51/2_1^+$ in band-2a; $43/2_1^+$ and $47/2_1^+$ in band-2b are reported and discussed.

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Second-forbidden nonunique $β^-$ decays of $^{24}$Na and $^{36}$Cl assessed by the nuclear shell model

We have performed a systematic study of the log$ft$ values, shape factors and electron spectra for the second-forbidden nonunique $β^-$ decays of $^{24}$Na$(4^+) \rightarrow ^{24}$Mg$(2^+)$ and $^{36}$Cl$(2^+) \rightarrow ^{36}$Ar$(0^+)$ transitions under the framework of the nuclear shell model. We have performed the shell model calculations in the $sd$ model space, using more recent microscopic effective interactions such as Daejeon16, chiral N3LO, and JISP16. These interactions are derived from the no-core shell model wave functions using Okubo-Lee-Suzuki transformation.For comparison, we have also shown the results obtain from the phenomenological USDB interaction. To test the predictive power of these interactions first we have computed low-lying energy spectra of parent and daughter nuclei involved in these transitions. The computed results for energy spectra, nuclear matrix elements, log$ft$ values, shape factors, electron spectra and decomposition of the integrated shape factor are reported and compare with the available experimental data.

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Shell model results for $^{47-58}$Ca isotopes in the $fp$, $fpg_{9/2}$ and $fpg_{9/2}d_{5/2}$ model spaces

We have reported shell-model results for $^{47-58}$Ca isotopes in the $fp$, $fpg_{9/2}$ and $fpg_{9/2}d_{5/2}$ model spaces using realistic $NN$ interaction. We have also performed a systematic shell-model study using interactions derived from in-medium similarity-renormalization group (IM-SRG) targeted for a particular nucleus with chiral $NN$ and $3N$ forces. The results obtained are in a reasonable agreement with the available experimental data in $fp$ model space with $NN$ interaction. It is shown that the $g_{9/2}$ and $d_{5/2}$ orbitals play an important role for heavier neutron-rich $^{54-58}$Ca isotopes, while it is marginal for $^{47-52}$Ca. We have also examined spectroscopic factor strengths using $NN$ and $NN+3N$ interactions for recently available experimental data.

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Gamow-Teller transition strengths for selected ${fp}$ shell nuclei

We have reported a systematic shell model description of the experimental Gamow-Teller transition strength for $^{44}$Sc $\rightarrow$ $^{44}$Ca, $^{45}$Ti $\rightarrow$ $^{45}$Sc, $^{48}$Ti $\rightarrow$ $^{48}$V, $^{66}$Co $\rightarrow$ $^{66}$Ni, and $^{66}$Fe $\rightarrow$ $^{66}$Co transitions using KB3G and GXPF1A interactions for $fp$ model space. In order to see the importance of higher orbital for $^{66}$Co $\rightarrow$ $^{66}$Ni and $^{66}$Fe $\rightarrow$ $^{66}$Co transitions, we have reported the shell model results with $fpg_{9/2}$ space using GXPF1Br+$V_{MU}$ interaction. We have obtained the qualitative agreement for the individual transitions, while the calculated summed transition strengths closely reproduce the observed ones.

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Shell model results for nuclear $β^-$-decay properties of $sd$ shell nuclei

We evaluate the allowed $β^-$-decay properties of nuclei with $Z = 8 - 15$ systematically under the framework of the nuclear shell model with the use of the valence space Hamiltonians derived from modern $ab~intio$ methods, such as in-medium similarity renormalization group and coupled-cluster theory. For comparison we also show results obtained with fitted interaction derived from the chiral effective field theory and phenomenological USDB interaction. We have performed calculations for O $\rightarrow$ F, F $\rightarrow$ Ne, Ne $\rightarrow$ Na, Na $\rightarrow$ Mg, Mg $\rightarrow$ Al, Al $\rightarrow$ Si, Si $\rightarrow$ P and P $\rightarrow$ S transitions. Theoretical results of $B(GT)$, log$ft$ values and half-lives, are discussed and compared with the available experimental data.

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Ab initio no-core shell model study of $^{18-23}$O and $^{18-24}$F isotopes

In the present work, we have done a comprehensive study of low-lying energy spectrum for oxygen and fluorine chains using $ab~initio$ no core shell model. We have used inside nonlocal outside Yukawa (INOY) potential, which is a two body interaction but also has the effect of three body forces by short range and nonlocal character. Also, we have performed calculations with N3LO and N2LOopt interactions and compared corresponding results with the experimental data and phenomenological USDB interaction. We have reached up to $N_{max}$=6 for $^{18-21}$O and $^{18-19}$F, $N_{max}$=4 for other oxygen and fluorine isotopes, respectively. We have also discussed the binding energy of oxygen and fluorine chains. Over binding in the ground state (g.s.) energy in neutron rich oxygen isotopes is observed in our largest model space calculations.

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