Nuclear levels in43Sc at low excitation energies

Properties of levels up to 3.5 MeV in⁴³Sc were studied using⁴⁰Ca (α, p)⁴³Sc and⁴⁰Ca(α, pγ)⁴³Sc reactions atE _α =12 MeV. Level energies, branching ratios, mean lifetimes, spins and mixing ratios were obtained for a number of levels. Relevant results are compared with many-particle shell-model predictions.     

Electric spin resonances in light nuclei

Very recent pion inelastic scattering experiments at LAMPF have revealed the existence of strong spin-flip E1 resonances in the vicinity of the GDR in several light nuclei. We present here the results of shell-model calculations of S = 0 and S = 1 E1 strength distributions which offer a broad theoretical context for the discussion of electric spin excitations. Our results for ¹⁶O and ⁴⁰Ca corroborate the LAMPF data and indicate that a major fraction of the spin-flip strength still lies above the GDR.     

Preliminary spectral distribution study in the lower f—p shell

The spectral distribution method is used to calculate binding energies for elements in the shell-model f—p shell using renormalized Sussex interaction matrix elements appropriate to a ⁴⁰Ca core. Comparison is made between Coulomb corrected empirical values and the results of the above calculation.     

The description of hypernuclei in the continuum shell-model

The advantage of the continuum shell-model in describing nuclear reactions producing hypernuclei is discussed. Numerical results obtained within this model for the (K ^?,π ^?) reaction on⁹Be,¹²C,¹⁶O and⁴⁰Ca are presented.     

Coexistence of α-clustering and shell structure in40Ca

The energy spectrum and α-spectroscopic factors of⁴⁰Ca are calculated by using an α+³⁶Ar orthogonality condition model. Overall agreement is obtained with the experimental data. The model successfully produces the parity-doubletK ^π=O ⁺ and O^? α+³⁶Ar cluster bands. It is shown that the coexistence and interference of α-cluster states and shell-model states are indispensable to understand the structure of⁴⁰Ca.     

Shell-model results in <Emphasis Type="Italic">fp</Emphasis> and <Emphasis Type="Italic">fpg</Emphasis><Subscript>9/2</Subscript> spaces for <Superscript>61,63,65</Superscript>Co isotopes

Low-lying spectra and several high-spin states of odd-even ^61,63,65Co isotopes are calculated in two different shell-model spaces. First set of calculations have been carried out in fp-shell valence space (full fp space for ^63,65Co and a truncated one for ⁶¹Co) using two recently derived fp-shell interactions, namely GXPF1A and KB3G, with ⁴⁰Ca as core. Similarly, the second set of calculations have been performed in fpg _9/2 valence space using an fpg effective interaction due to Sorlin et al., with ⁴⁸Ca as core and imposing a truncation. It is seen that the results of GXPF1A and KB3G are reasonable for ^61,63Co. For ⁶⁵Co, shell-model results show that the fpg interaction adopted in the study is inadequate and also points out that it is necessary to include orbitals higher than 1g _9/2 for neutron-rich Co isotopes.     

Microscopic description of low-energy neutron scattering by nuclei

The Bloch and Gillet shell-model formalism extended to continuum states is applied to lowenergy neutron scattering by nuclei. It is shown that complete antisymmetrization leads in the r-representation to corrective terms which yield important corrections to the scattering lengths. Calculations are performed within a model restricted configuration space for the target nuclei ¹²C, ¹³C, ¹⁶O, ¹⁷O and ⁴⁰Ca. We predict values for the spin-dependent scattering amplitude for ¹³C and ¹⁷O. The antisymmetrization problem in the case of a large configuration mixing is studied for the ¹⁹F target nucleus. The resonant effects of the compound nucleus are then very important and the results become very sensitive to the configuration space and the interaction parameters.     

Effects of proton pair vibrations in the low-lying spectrum of closed-shell nuclei: Structure of 48Ca

The importance of proton pair vibrations in the low-lying spectra of closed-shell nuclei with Z ≠ N is emphasized. Indications for the occurrence of these states in ⁴⁸Ca are obtained from a restricted shell-model calculation with both active neutrons and protons.     

New data on nuclear subshells obtained from the analysis of the information from the international database on nuclear structure ENSDF

In the last decade, a large amount of experimental nuclear spectroscopy data was obtained. This is good progress really, but a new very serious problem appears. Due to significant systematic errors of the data, one is often forced to deal with very discrepant data and often it is difficult to obtain reliable information from them. To solve this problem and to remove the systematic errors, new technologies in working with the data were developed. Using these new technologies, one can obtain information with a high accuracy and reliability, and in many cases, new information has not been or could not be obtained experimentally. Below, an approach of this kind is presented concerning spectroscopic data on Ca and Zr isotopes. It is shown that the behavior of the energy of the first 2⁺ level in Zr isotopes can be explained in the framework of a shell-model approach. A separation of the 2d_5/2 subshell in ⁹⁶Zr (as is for the 1f_7/2 subshell in ⁴⁸Ca) is found, so that the neutron number N=56 becomes like a magic number for Z=40. To explain a similarity in decaying properties of ⁴⁸Ca and ⁹⁶Zr, an additional interaction between closed structures consisting of 20 and 28 nucleons is proposed. Irregularities of the ground-state spin values in the K isotopic chain are explained in the framework of the shell-model approach by the inversion of the proton 1d_3/2 and 2s_1/2 orbitals.     

High-resolution measurements of beta-delayed protons from 37Ca and 41Ti

Protons with energies from 870 keV to 5.4 MeV have been observed following bombardment of a ⁴⁰Ca target with ³He at beam energies of 29.5, 36.5 and 60 MeV, as well as from 40 MeV ³He bombardment of an ³⁶Ar gas target. These data, and those resulting from 20 MeV proton bombardment of ⁴⁰Ca, permit accurate identification of proton unbound levels in ⁴¹Sc, ³⁷K, and ⁴⁰Ca fed by allowed beta decay from ⁴¹Ti, ³⁷Ca or ⁴⁰Sc, respectively. Absolute ft values have been determined for beta decay to these levels. The half-life of ⁴¹Ti has been remeasured to be 80±2 ms and the log ft for its superallowed decay branch has been found to be 3.35±0.02, indicating an isospin purity for the lowest $\text{T =}\text{3}\text{2}\text{state in}{}^{41}\text{Sc of}\text{≈ 91 \%}$. The $\text{ft}\text{values for}{}^{37}\text{Ca}\text{β}{}^{\mathrm{+}}$ decay are compared to shell-model calculations for beta-decay in A = 37 nuclei.     

Spectroscopy of 42Ca from 41Ca(d,p)

Energy levels in ⁴²Ca up to 7.8 MeV have been studied in the neutron capture reaction ⁴¹Ca(d, p)⁴²Ca with 12 MeV bombarding energy. Ninety-four excited states have been identified and angular distributions have been measured in the interval from 5° to 110° by means of a broad-range magnetic spectrograph. The angular distributions together with DW calculations have been used to determine I_n values and spectroscopic factors. The $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ strength sum agrees with shell-model expectations if the f_{$\text{7}\text{2}$} spectroscopic factors are renormalized by $\text{1}\text{0.75}$, in line with other $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$. transfer experiments on ⁴⁰Ca and ⁴¹Ca. A similar renormalization of the l_n = 1 spectroscopic factors brings this strength sum in accordance with the shell-model calculations. The effective ($\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}{}^2$) matrix elements for ⁴²Ca are compared with the corresponding matrix elements of ⁴²Sc and ⁴⁸Sc. The differences between the three sets of matrix elements are of the order of a few hundred keV or less. The monopole centroid energy of the ($\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^2$ multiplet is shifted downwards in the mass-42 nuclei compared to ⁴⁸Sc, possibly indicating the importance of the monopole pairing force near ⁴⁰Ca.     

Semi-microscopic analysis of multi-nucleon transfer and the 40Ca(α, p)43Sc reaction

A semi-microscopic model for analyzing multi-nucleon transfer reactions in the distorted-wave Born approximation is presented. This model, which is shown to be compatible with other semi-microscopic models, employs cluster form factors. The cluster spectroscopic factors are calculated using shell-model wave functions. Data from the ⁴⁰Ca(α, p)⁴³Sc reaction are presented and used to test the model. The relative cluster spectroscopic factors for a number of levels are found to be in agreement with those calculated using wave functions in an $\text{(}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^3$ basis.     

Structure of odd Ge isotopes with 40 < N < 50

We have interpreted recentlymeasured experimental data of ⁷⁷Ge, and also for ^73,75,79,81Ge isotopes in terms of state-of-the-art shell-model calculations. Excitation energies, B(2) values, quadrupole moments and magnetic moments are compared with experimental data when available. The calculations have been performed with the recently derived interactions, namely with JUN45 and jj44b for f _5/2pg9/2 space. We have also performed calculation for fpg _9/2 valence space using an fpg effective interaction with ⁴⁸Ca core and imposing a truncation to study the importance of the proton excitations across the Z = 28 shell in this region. The predicted results of jj44b interaction are in good agreement with experimental data.     

Nuclear moments for the neutrinoless double beta decay

A derivation of the neutrinoless double beta decay rate, specially adapted for nuclear structure calculations, is presented. It is shown that the Fourier-Bessel expansion of the hadronic currents, jointly with angular momentum recoupling, leads to very simple final expressions for the nuclear form factors. This greatly facilitates the theoretical estimate of the half-life. Our approach does not require the closure approximation, which, however, can be implemented if desired. The method is exemplified for ββ decay ⁴⁸Ca → ⁴⁸Ti, both within the QRPA and a shell-model like model.     

Possible mesonic effects on inelastic proton scattering to the 10.24 MeV 1+ state in 48Ca

Differential cross sections and analyzing powers were measured for inelastic scattering of 160 MeV protons to the ⁴⁸Ca 10.24 MeV, 1⁺ state. DWIA calculations with shell-model wave functions which fit inelastic electron scattering form factors predict too much cross section at small q and too little at large q for inelastic proton scattering. These results are consistent with the q-dependent modification of magnetic transitions anticipated from mesonic effects such as virtual Δ(1232)-hole excitations.     

Lifetimes of levels in 25Na and 26, 27Mg excited via the 26Mg bombardment of 3H

Lifetimes have been measured for nine levels in ²⁵Na, the first two excited states of ²⁷Mg, and the First excited state of ²⁶Mg by bombarding a Ti³H target with 40 MeV ²⁶Mg ions. Mean lifetimes were determined by fitting the Doppler-broadened γ-ray lineshapes with lineshapes calculated using experimentally-measured stopping powers. The ²⁵Na results are compared to predictions of recent shell-model calculations.     

α-Cluster Optical Potential Model of <Superscript>40</Superscript>Ca

Elastic scattering of α + ⁴⁰Ca is analyzed in the framework of the optical model. We adopted an independent α-cluster model to generate the α-cluster and matter density of ⁴⁰Ca. We proposed a parametrized form for the α-cluster density and fixed its parameters according to the available experimental data about the α-particle and ⁴⁰Ca nuclei. The obtained α-cluster density of ⁴⁰Ca is used to generate the real part of the optical potential. The single folding procedure is used to generate this real optical potential with two different effective α–α interactions. The real calculated potential supplied with an imaginary Woods–Saxon squared potential is used to analyze 20 sets of experimental data in the energy range between 18 and 166 MeV. We found that our model is successful in reproducing the data for energies above 40 MeV and still doubtful for lower energies.