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Register a new userFermionic-bosonic couplings in a weakly-deformed odd-mass nucleus, $^{93}_{41}$Nb
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A comprehensive decay scheme of $^{93}$Nb below 2 MeV has been constructed from information obtained with the $^{93}$Nb(n,n$^prime$$gamma$) and $^{94}$Zr(p,2n$gamma$$gamma$)$^{93}$Nb reactions. Branching ratios, lifetimes, transition multipolarities and spin assignments have been determined. From $M1$ and $E2$ strengths, fermionic-bosonic excitations of isoscalar and isovector character have been identified from the weak coupling $pi1g_{9/2}$$otimes$$^{92}_{40}$Zr and $pi2p_{1/2}^{-1}$$otimes$$^{94}_{42}$Mo configurations. A microscopic interpretation of such excitations is attained from shell-model calculations using low-momentum effective interactions.
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The low-spin structure of 93Nb has been studied using the (n,n gamma) reaction at neutron energies ranging from 1.5 to 3.0 MeV and the 94Zr(p,2n gamma)93Nb reaction at bombarding energies from 11.5 to 19 MeV. States at 1779.7 and 1840.6 keV, respectively, are proposed as mixed-symmetry states associated with the coupling of a proton hole in the p_1/2 orbit to the 2+_1,ms state in 94Mo. These assignments are derived from the observed M1 and E2 transition strengths to the symmetric one-phonon states, energy systematics, spins and parities, and comparison with shell model calculations.
We discuss the role of deformation of the target nucleus in the fusion reaction of the $^{15}$C + $^{232}$Th system at energies around the Coulomb barrier, for which $^{15}$C is a well-known one-neutron halo nucleus. To this end, we construct the potential between $^{15}$C and $^{232}$Th with the double folding procedure, assuming that the projectile nucleus is composed of the core nucleus, $^{14}$C, and a valance neutron. By taking into account the halo nature of the projectile nucleus as well as the deformation of the target nucleus, we simultaneously reproduce the fusion cross sections for the $^{14}$C + $^{232}$Th and the $^{15}$C + $^{232}$Th systems. Our calculation indicates that the net effect of the breakup and the transfer channels is small for this system.
Two opposite parity dipole bandlike structures DB I and DB II of $^{142}$Eu are investigated by the Indian National Gamma Array (INGA), using the fusion evaporation reaction $^{31}$P + $^{116}$Cd @ 148 MeV. The decreasing trend as well as magnitude of the measured $B(M1)$ and $B(E2)$ transition rates of the band DB II has been reproduced well within the shears mechanism with the principal axis cranking model calculations. This calculation reflects the fact that the maximum contribution of the angular momentum of the states in DB II has been generated from the magnetic rotation (MR) phenomenon. The enhanced $B(E1)$ rates of the connecting $E1$ transitions from the states of DB II to DB I are demanding the octupole correlation due to the involvement of the octupole driving pair of orbitals $pi{h_{11/2}}$ and $pi{d_{5/2}}$ as evident from the quasiparticle alignment ($i_{x}$), the experimental routhians (e$^{}$) and the calculated neutron and proton quasiparticle energies against the rotational frequency ($omega$).
The bremsstrahlung flux-averaged cross sections for the photoneutron reactions $^{text{93}}$Nb($gamma $,xn;x=1-5)$^{text{(93-x)m,g}}$Nb were measured in the range of boundary energies of bremsstrahlung $gamma $-quanta $E_{gamma text{max}}$=33-93 MeV with a step $Delta E_{gamma text{max}}approx $ 2 MeV. The isomeric ratios of the average cross-sections of the products of the reactions $^{text{93}}$Nb ($gamma $ ,4n)$^{text{89m,g}}$Nb and $^{text{93}}$Nb($gamma $,5n)$^{text{88m,g}}$ Nb were determined in the energy ranges $E_{gamma text{max}}$ = 50-93 and 70-93 MeV, respectively. The experiments were carried out on the beam of the linear electron accelerator LU-40 of the Science and Research Establishment (SRE) Accelerator at National Science Center Kharkov Institute of Physics and Technology (NSC KIPT) using the method of induced activity. Calculations of the cross sections, average cross sections, and isomeric ratios of the reaction products were performed using the TALYS 1.9 code with default parameters and the GEANT4 code. The tendency of a more successful description of the average cross sections of photoneutron reactions with the formation of final odd-even Nb nuclei than odd-odd Nb nuclei is revealed. The experimental average cross sections for the reactions ($gamma $,2n) and ($gamma $,4n) are in good agreement with theory, while in the case of reactions ($gamma $,n), ($gamma $,3n), and ($ gamma $,5n), some discrepancies are observed. The results obtained for the reactions ($gamma $,n), ($gamma $,3n) and ($gamma $,4n) are in satisfactory agreement with the known literature data. The average cross sections for the reactions ($gamma $,2n) and ($gamma $,5n) and the isomeric ratios of the reaction products $^{text{93}}$Nb($gamma $,5n)$^{text{88m,g}}$Nb were measured for the first time.
We present the mass excesses of 52-57Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)(+0 -54) MeV and -21.0(1.3) MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass-chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We found that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in A=56 nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-A nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.
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