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Using the high-resolution O-18(He-3, t)F-18 reaction at 0 degrees and at 140 MeV/nucleon, Gamow-Teller (GT) transitions were studied. A high energy resolution of 31 keV was achieved by applying dispersion matching techniques. The main part of the observed GT transition strength is concentrated in the transition to the F-18 ground state (g.s.). The absolute values of the reduced GT transition strengths, B(GT), were derived up to E-x = 12 MeV assuming proportionality between the B(GT) values and the reaction cross sections at 0 degrees. The B(GT) value obtained from the beta decay of F-18 (g.s.) -> O-18 (g.s.) was used to determine the proportionality constant. A total B(GT) of 4.06(5) was found and 76(1)% of the strength is concentrated to the ground state of F-18. The obtained B(GT) values were compared with those from the O-18(p, n) F-18 reaction and the mirror symmetric beta(+) decay of Ne-18 -> F-18. The candidates for 1(+) states with isospin T = 1 were identified by comparison with the O-18(p, p') data. The results of shell-model and quasiparticle-random-phase approximation calculations suggest constructive contributions of various configurations to the F-18 ground state, suggesting that this state is the low-energy super GT state.

Using the high-resolution O18(He3,t)F18 reaction at 0 and at 140 MeV/nucleon, Gamow-Teller (GT) transitions were studied. A high energy resolution of 31 keV was achieved by applying dispersion matching techniques. The main part of the observed GT transition strength is concentrated in the transition to the F18 ground state (g.s.). The absolute values of the reduced GT transition strengths, B(GT), were derived up to Ex=12 MeV assuming proportionality between the B(GT) values and the reaction cross sections at 0. The B(GT) value obtained from the β decay of F18 (g.s.) →O18 (g.s.) was used to determine the proportionality constant. A total B(GT) of 4.06(5) was found and 76(1)% of the strength is concentrated to the ground state of F18. The obtained B(GT) values were compared with those from the O18(p,n)F18 reaction and the mirror symmetric β+ decay of Ne18→F18. The candidates for 1+ states with isospin T=1 were identified by comparison with the O18(p,p′) data. The results of shell-model and quasiparticle-random-phase approximation calculations suggest constructive contributions of various configurations to the F18 ground state, suggesting that this state is the low-energy super GT state.

大阪大学のリングサイクロトロンにて$^{18}$O($^3$He,$t$)$^{18}$F反応実験を行い、その荷電交換反応の断面積から、$^{18}\textrm{O}\to^{18}\textrm{F}$のガモフテラー遷移分布$B(\textrm{GT})$の励起エネルギー分布を測定した。その結果、$^{18}$Fの基底状態への$B(\textrm{GT})$が3.1と非常に大きく、その他の励起状態への遷移強度は小さいことがわかった。この実験結果を大規模殻模型計算や乱雑位相近似計算と比較し、基底状態への強い遷移が理論計算によってよく説明されることがわかった。

To study the Gamow-Teller (GT) transitions from the T-z = +1 nucleus Ca-42 to the T-z = 0 nucleus Sc-42, where T-z is the z component of isospin T, we performed a (p, n)-type (He-3, t) charge-exchange reaction at 140 MeV/nucleon and scattering angles around 0 degrees. With an energy resolution of 29 keV, states excited by GT transitions (GT states) could be studied accurately. The reduced GT transition strengths B(GT) were derived up to the excitation energy of 13 MeV, assuming the proportionality between the cross sections at 0 degrees and B(GT) values. The main part of the observed GT transition strength is concentrated in the lowest 0.611-MeV, J(pi) = 1(+) GT state. All the other states at higher energies are weakly excited. Shell-model calculations could reproduce the gross feature of the experimental B(GT) distribution, and random-phase-approximation calculations including an attractive isoscalar interaction showed that the 0.611-MeV state has a collective nature. It was found that this state has all of the properties of a "low-energy super-Gamow-Teller state." It is expected that low-lying J(pi) = 1(+) GT states have T = 0 in the T-z = 0 nucleus Sc-42. However, T = 1 states are situated in a higher energy region. Assuming an isospin-analogous structure in A = 42 isobars, analogous T = 1, 1(+) states are also expected in Ca-42. Comparing the Ca-42(He-3, t)Sc-42 and Ca-42(p, p') spectra measured at 0 degrees, candidates for T = 1 GT states could be found in the 10-12-MeV region of Sc-42. They were all weakly excited. The mass dependence of the GT strength distributions in Sc isotopes is also discussed.

In order to study the Gamow-Teller (GT) transitions from the T z=+2 nucleus 44Ca to the Tz=+1 nucleus 44Sc, where T z is the z component of isospin T, we performed the (p,n)-type (3He,t) charge-exchange (CE) reaction at 140 MeV/nucleon and the scattering angles 0â̂̃ and 2.5â̂̃. 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 (Ex) 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 Tz=+2→+1 and Tz=-2→-1 mirror GT transitions should have the same properties, where the latter can be studied in the β decay of 44Cr to 44V. First, we confirmed that the β-decay half-life T1/2 of 44Cr can be reproduced using the B(GT) distribution from the 44Ca(3He,t) measurement. Then, the 0â̂̃, (3He,t) spectrum was modified to deduce the "β-decay spectrum" and it was compared with the delayed-proton spectrum from the 44Cr 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 44Ca, the (3He,t) can excite GT states (state populated by GT transitions) with T=1, 2, and 3. On the other hand, the 44Ca(p,p ′) reaction can excite spin-M1 states (states populated by spin-M1 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 Ex=11.5-13.7 MeV region. (iii) It has been suggested that the T=2, Jπ=0+ double isobaric analog state (DIAS) at 9.338 MeV in the Tz=0 nucleus 44Ti forms an isospin-mixed doublet with a subsidiary 0+ state at 9.298 MeV. Since no corresponding state was found in the Tz=+1 nucleus 44Sc, we suggest T=0 for the subsidiary state. © 2013 American Physical Society. ispartof: Physical Review C, Nuclear Physics vol:88 issue:1 status: published

Given the importance of Gamow-Teller (GT) transitions in nuclear structure and astrophysical nuclear processes, we have studied T z =+ 3 / 2 →+ 1 / 2, GT transitions starting from the 47 Ti nucleus in the ( 3 He ,t ) charge-exchange reaction at 0 ◦ and at an intermediate incident energy of 140 MeV / nucleon. The experiments were carried out at the Research Center for Nuclear Physics (RCNP), Osaka, using the high-resolution facility with a high-dispersion beam line and the Grand-Raiden spectrometer. With an energy resolution of 20 keV, individual GT transitions were observed and GT strength was derived for each state populated up to an excitation energy ( E x ) of 12.5 MeV. The GT strength was widely distributed from low excitation energy up to 12.5 MeV, where we had to stop the analysis because of the high level density. The distribution of the GT strengths was compared with the results of shell model calculations using the GXPF1 interaction. The calculations could reproduce the experimental GT distributions well. The GT transitions from the ground state of 47 Ti and the M 1 transitions from the isobaric analog state in 47 V to the same low-lying states in 47 V are analogous. It was found that the ratios of GT transition strengths to the ground state, the 0.088-MeV state, and the 0.146-MeV state are similar to the ratios of the strengths of the analogous M 1 transitions from the isobaric analog state (IAS) to these states. The measured distribution of the GT strengths was also compared with those starting from the T z =+ 3 / 2 nucleus 41 Ktothe T z =+ 1 / 2 nucleus 41 Ca. ispartof: Physical Review C, Nuclear Physics vol:87 issue:1 pages:1-12 status: published

In order to study the Gamow-Teller (GT) transitions from the Tz=+2 nucleus 44Ca to the Tz=+1 nucleus 44Sc, where Tz is the z component of isospin T, we performed the (p,n)-type (3He,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 (Ex) 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 Tz=+2→+1 and Tz=-2→-1 mirror GT transitions should have the same properties, where the latter can be studied in the β decay of 44Cr to 44V. First, we confirmed that the β-decay half-life T1/2 of 44Cr can be reproduced using the B(GT) distribution from the 44Ca(3He,t) measurement. Then, the 0∘, (3He,t) spectrum was modified to deduce the "β-decay spectrum" and it was compared with the delayed-proton spectrum from the 44Cr 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 44Ca, the (3He,t) can excite GT states (state populated by GT transitions) with T=1, 2, and 3. On the other hand, the 44Ca(p,p') reaction can excite spin-M1 states (states populated by spin-M1 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 Ex=11.5-13.7 MeV region. (iii) It has been suggested that the T=2, Jπ=0+ double isobaric analog state (DIAS) at 9.338 MeV in the Tz=0 nucleus 44Ti forms an isospin-mixed doublet with a subsidiary 0+ state at 9.298 MeV. Since no corresponding state was found in the Tz=+1 nucleus 44Sc, we suggest T=0 for the subsidiary state.