Nuclear structure of calcium isotopes from inelasticαscattering

Abstract

Angular distributions were measured for elastic and inelastic & scattering from Ca at 24. 0, 28.5, and 31.0 MeV, from 4lCa at 24.0 MeV and from 43'44Ca at 25.5 MeV. Analyses in terms of distorted-wave Born-approximation and coupled-channel theory, employing a vibrational collective model form factor, yield inelastic transition strengths, and many new spin and parity assignments or restrictions for levels in ' '4 ' Ca. The inelastic multipole transition strengths are in excellent agreement with known electromagnetic strengths. Quadrupole strengths are interpreted in terms of the coexistence model. The data imply that the ground-state excited-core admjxtures to ( f p)" spherical configurations are 4% in Ca, 10% in ' Ca, 14% in 3Ca, and 30% in '4 Ca. The octupole inelastic strength is strong and mainly localized in the lowest 3 s~te in Ca, but becomes more fractionated and weaker with addition of neutrons and exhibits in 4~Ca characteristic weak-coupling fragmentation of the lowest 3 state in 40Ca. The...~, results are consistent with previous observations that the structure of the 4 Ca ground siate is with high purity a 1 f&y2 neutron coupled to the 4'Ca ground state. I NUCLEAR REACTIONS 4oCa(n, e), E=24. 0, 28.5, 31.0 MeV, 4lCa(n,~) , E =24.0 MeV, 4 '44Ca(0, 0. ), E=25.5 MeV, measured 0(&), E~DWBA, coupledchannel analyses, 4~'4~'43'44Ca deduced levels, J, m, B(IS,l) t for l =2, 3, 4, 5. Enriched targets. Coexistence model, deduced excited-core admixtures in 40, 41, 42, 43, 44, 48( a I. INTRODUCTlONiThe observed' ' coexistence of strongly deformed core-excited configurations with (fP)" spherical configurations for low-lying states in light 1f», nuclei has provoked considerable experimental and theoretical' ' interest in the structure of these nuclei. The coexistence model' ' has been remarkably successful in reproducing the low-lying spectra and known electric quadrupole moments and transition strengths. These measured quantities in '"'"Ca directly determine the quadrupole properties of the lowest deformed coreexcited band. It has been sho~n' that this band has a prolate asymmetric shape, soft to y vibrations with P™=0. 37 and r =18". The coexistence model also reproduces nicely all the available single nucleon pickup and stripping data on a "Ca target. ' 'The present paper describes an investigation of the spin, parity, and ground-state transition strengths in Ca, "Ca, "Ca, and Ca by means of inelastic n scattering experiments. The primary purpose of this work was to investigate the structure of the odd mass nuclei "Ca and "Ca.This work is part of a program, which encompasses studies of excited-state static-electric quadrupole moments, ' "" lifetimes and y-ray correlation studies, " " singleand multinucleon transfer reaction studies, "'" inelastic proton scattering" on "Ca, and incorporates several shell-model calculations on fP-shell nuclei. Previous work" " already has shown that (fP)" spherical shell-model calculations reproduce the properties of low-lying levels in X=26 to 28 nuclei but admixtures of deformed ...

Coulomb excitation ofCa44andAr46

“…Given the presently uncertain situation, we remeasured the B(E2; 0 + g.s. → 2 + 1 ) value of 46 Ar in an absolute manner and relatively to the well-known value in 44 Ca. The latter study is interesting as it suppresses most of the systematic …”

“…Mean field approaches [6][7][8][9] as well as shell model calculations [10][11][12][13][14] predict a close-to-spherical 46 Ar, a shape mixing or shape coexistence in 44 S, and a large oblate deformation in 42 Si. The properties of the recently discovered low-lying isomeric 0 + 2 state in 44 S [15] supports a shape mixing between the 0 + 1 and 0 + 2 states. Being located two protons away from the doubly magic 48 Ca, 46 Ar should in principle be considered as a semimagic nucleus, as confirmed by the following experimental results.…”

“…In particular, the gradual decrease of the 2 + 1 energies in the N = 28 isotones from 3831 keV in 48 Ca, 1577 keV in 46 Ar [2], 1329 keV in 44 S [3], and 770 keV in 42 Si [4,5] indicates that a large deformation is steadily establishing toward 42 Si. Mean field approaches [6][7][8][9] as well as shell model calculations [10][11][12][13][14] predict a close-to-spherical 46 Ar, a shape mixing or shape coexistence in 44 S, and a large oblate deformation in 42 Si. The properties of the recently discovered low-lying isomeric 0 + 2 state in 44 S [15] supports a shape mixing between the 0 + 1 and 0 + 2 states.…”

“…→ 2 + 1 ) of the 46 Ar and 44 Ca nuclei were studied using the Coulomb excitation technique at intermediate energy at the LISE/GANIL facility. The in-flight γ rays, emitted after the Coulomb excitation of their first 2 + states, were detected in an array of 64 BaF 2 crystals.…”

“…The in-flight γ rays, emitted after the Coulomb excitation of their first 2 + states, were detected in an array of 64 BaF 2 crystals. The present B(E2 ↑) value for 44 Ca, 475 (36) 46 Ar from an absolute and a relative measurement, normalized to the 44 Ca value. Both results agree with the ones obtained with the same experimental technique at the NSCL facility but are a factor of 2 smaller than the shell model predictions.…”