Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userIs Seniority a Partial Dynamic Symmetry in the First $ u g_{9/2}$ Shell?
61
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The low-lying structures of the midshell $ u g_{9/2}$ Ni isotopes $^{72}$Ni and $^{74}$Ni have been investigated at the RIBF facility in RIKEN within the EURICA collaboration. Previously unobserved low-lying states were accessed for the first time following $beta$ decay of the mother nuclei $^{72}$Co and $^{74}$Co. As a result, we provide a complete picture in terms of the seniority scheme up to the first $(8^+)$ levels for both nuclei. The experimental results are compared to shell-model calculations in order to define to what extent the seniority quantum number is preserved in the first neutron $g_{9/2}$ shell. We find that the disappearance of the seniority isomerism in the $(8^+_1)$ states can be explained by a lowering of the seniority-four $(6^+)$ levels as predicted years ago. For $^{74}$Ni, the internal de-excitation pattern of the newly observed $(6^+_2)$ state supports a restoration of the normal seniority ordering up to spin $J=4$. This property, unexplained by the shell-model calculations, is in agreement with a dominance of the single-particle spherical regime near $^{78}$Ni.
rate research
Read More
Linear polarization measurements have been performed for $gamma$-rays in $^{91}$Ru produced with the $^{58}$Ni($^{36}$Ar, $2p1n$$gamma$)$^{91}$Ru reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the $gamma$-$gamma$ coincidences, $gamma$-ray linear polarization and $gamma$-ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3$-$1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in $^{91}$Ru. More specifically, calculations using a semi-empirical shell model were performed to understand the structures of the first and second (21/2$^{+}$) and (17/2$^{+}$) levels. The results are in good agreement with the experimental data, supporting the interpretation of the non yrast (21/2$^{+}$) and (17/2$^{+}$) states in terms of the $J_{rm max}$ and $J_{rm max}-2$ members of the seniority-three $ u(g_{9/2})^{-3}$ multiplet.
The 119-126Sn nuclei have been produced as fission fragments in two reactions induced by heavy ions: 12C+238U at 90 MeV bombarding energy, 18O+208Pb at 85 MeV. Their level schemes have been built from gamma rays detected using the Euroball array. High-spin states located above the long-lived isomeric states of the even- and odd-A 120-126Sn nuclei have been identified. Moreover isomeric states lying around 4.5 MeV have been established in 120,122,124,126Sn from the delayed coincidences between the fission fragment detector SAPhIR and the Euroball array. The states located above 3-MeV excitation energy are ascribed to several broken pairs of neutrons occupying the nu h11/2 orbit. The maximum value of angular momentum available in such a high-j shell, i.e. for mid-occupation and the breaking of the three neutron pairs, has been identified. This process is observed for the first time in spherical nuclei.
The population of the 9.50 MeV 9/2+ resonance in 13C by single neutron transfer reactions is expected to be dominated by the two-step route through the 12C 2+ (4.44 MeV) state, with another possible contribution via the strongly excited 3- (9.64 MeV) resonance in 12C. However, we find that a good description of the angular distribution for population of this state via the 12C(d,p)13C reaction is only possible when both direct 0+ x g_9/2 and two-step (via the 4.44 MeV 12C 2+ state) 2+ x d_5/2 paths are included in a coupled reaction channel calculation. While the calculated angular distribution is almost insensitive to the presence of the two-step path via the 9.64 MeV 12C 3- resonance, despite a much greater contribution to the wave function from the 3- x f_7/2 configuration, its inclusion is required to fit the details of the experimental angular distribution. The very large interference between the various components of the calculations, even when these are small, arises through the ``kinematic effect associated with the different transfer routes.
The FSU $spsdfp$ cross-shell interaction for the shell model was successfully fitted to a wide range of mostly intruder negative parity states of the $sd$ shell nuclei. This paper reports the application of the FSU interaction to systematically trace out the relative positions of the effective single-particle energies of the $0f_{7/2}$ and $1p_{3/2}$ orbitals, the evolution from normally ordered low-lying states to the Island of Inversion (IoI), and the behavior of a wide range of excited states with a $0f_{7/2}$ proton and neutron coupled to maximum spin of $7 hbar$. Above a proton number of about 13 the $0f_{7/2}$ orbital lies below that of $1p_{3/2}$, which is considered normal ordering, but systematically at $Z = 10$ to $12$ the orbitals cross. The calculations reproduce well the 2p2h - 0p0h inversion in the configurations of nuclei inside the IoI, they reproduce the absolute binding energies and the transition to normal ordering as the proton number approaches that of the neutrons. The important role of $1p_{3/2}$ neutron pairs in the IoI is also demonstrated. The calculations account well for the energies of the fully aligned states with 0, 1, or 2 individual $sd$ nucleon aligned in spin with the aligned $pi 0f_{7/2}$ - $ u 0f_{7/2}$ pair and reproduce well their systematic variation with $A$ and number of aligned $sd$ nucleons. The results presented in this paper give hope for the predictive power of the FSU interaction for more exotic nuclei to be explored in near future.
Recent high-precision mass measurements of $^{9}$Li and $^{9}$Be, performed with the TITAN Penning trap at the TRIUMF ISAC facility, are analyzed in light of state-of-the-art shell model calculations. We find an explanation for the anomalous Isobaric Mass Multiplet Equation (IMME) behaviour for the two $A$ = 9 quartets. The presence of a cubic $d$ = 6.3(17) keV term for the $J^{pi}$ = 3/2$^{-}$ quartet and the vanishing cubic term for the excited $J^{pi}$ = 1/2$^{-}$ multiplet depend upon the presence of a nearby $T$ = 1/2 state in $^{9}$B and $^{9}$Be that induces isospin mixing. This is contrary to previous hypotheses involving purely Coulomb and charge-dependent effects. $T$ = 1/2 states have been observed near the calculated energy, above the $T$ = 3/2 state. However an experimental confirmation of their $J^{pi}$ is needed.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
