Author:

Keywords:

Science & Technology, Physical Sciences, Physics, Nuclear, Physics, WEAK-INTERACTION RATES, INTERMEDIATE-MASS NUCLEI, CHARGE-EXCHANGE REACTIONS, SPIN-FLIP TRANSITIONS, N=28 ISOTONES, ENERGY-LEVELS, M1 STRENGTH, BETA-DECAY, BEAM LINE, 1+ STATES, 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics, 5106 Nuclear and plasma physics

Abstract:

In order to study the Gamow-Teller (GT) transitions from the T z =+ 2 nucleus 44 Ca to the T z =+ 1 nucleus 44 Sc, where T z is the z component of isospin T , we performed the ( p, n )-type ( 3 He ,t ) charge-exchange (CE) reaction at 140 MeV / nucleon and the scattering angles 0 ◦ and 2 . 5 ◦ . An energy resolution of 28 keV, that was realized by applying matching techniques to the magnetic spectrometer system, allowed the study of fragmented states. The GT transition strengths, B (GT), were derived up to the excitation energy ( E x ) of 13.7 MeV assuming the proportionality between cross sections and B (GT) values. The total sum of B (GT) values in discrete states was 3.7, which was 31% of the sum-rule-limit value of 12. Shell model calculations using the GXPF1J interaction could reproduce the gross features of the experimental B (GT) distribution, but not the fragmentation of the strength. By introducing the concepts of isospin, properties of isospin analogous transitions and states were investigated. (i) Assuming isospin symmetry, the T z =+ 2 →+ 1and T z =− 2 →− 1 mirror GT transitions should have the same properties, where the latter can be studied in the β decay of 44 Cr to 44 V. First, we confirmed that the β -decay half-life T 1 / 2 of 44 Cr can be reproduced using the B (GT) distribution from the 44 Ca( 3 He ,t ) measurement. Then, the 0 ◦ ,( 3 He ,t ) spectrum was modified to deduce the “ β -decay spectrum” and it was compared with the delayed-proton spectrum from the 44 Cr β decay. The two spectra were mostly in agreement for the GT excitations, but suppression of the proton decay was found for the T = 2 isobaric analog state (IAS). (ii) Starting from the T = 2 ground state of 44 Ca, the ( 3 He ,t ) can excite GT states (state populated by GT transitions) with T = 1, 2, and 3. On the other hand, the 44 Ca( p, p ) reaction can excite spin- M 1 states (states populated by spin- M 1 transitions) with T = 2 and 3 that are analogous to the T = 2 and 3 GT states, respectively. By comparing the spectra from these two reactions, a T value of 2 is suggested for several GT states in the E x = 11 . 5–13.7 MeV region. (iii) It has been suggested that the T = 2, J π = 0 + double isobaric analog state (DIAS) at 9.338 MeV in the T z = 0 nucleus 44 Ti forms an isospin-mixed doublet with a subsidiary 0 + state at 9.298 MeV. Since no corresponding state was found in the T z =+ 1 nucleus 44 Sc, we suggest T = 0 for the subsidiary state.