23 research outputs found
Shapes of the Pb ground states from beta decay studies using the total absorption technique
The beta decay of Pb has been studied using the total absorption
technique at the ISOLDE(CERN) facility. The beta-decay strength deduced from
the measurements, combined with QRPA theoretical calculations, allow us to
infer that the ground states of the Pb isotopes are spherical.
These results represent the first application of the shape determination method
using the total absorption technique for heavy nuclei and in a region where
there is considerable interest in nuclear shapes and shape effects
Half-Life Systematics across the N=126 Shell Closure:Role of First-Forbidden Transitions in the beta Decay of Heavy Neutron-Rich Nuclei
This Letter reports on a systematic study of β-decay half-lives of neutron-rich nuclei around doubly magic ^{208}Pb. The lifetimes of the 126-neutron shell isotone ^{204}Pt and the neighboring ^{200-202}Ir, ^{203}Pt, ^{204}Au are presented together with other 19 half-lives measured during the "stopped beam" campaign of the rare isotope investigations at GSI collaboration. The results constrain the main nuclear theories used in calculations of r-process nucleosynthesis. Predictions based on a statistical macroscopic description of the first-forbidden β strength reveal significant deviations for most of the nuclei with N<126. In contrast, theories including a fully microscopic treatment of allowed and first-forbidden transitions reproduce more satisfactorily the trend in the measured half-lives for the nuclei in this region, where the r-process pathway passes through during β decay back to stability
Decay of the Fr nucleus
γ rays following the EC/β+ and α decay of the Fr nucleus have been observed at the CERN isotope separator on-line (ISOLDE) facility with the help of γ-ray and conversion-electron spectroscopy. These γ rays establish several hitherto unknown excited states in Rn. Also, five new α-decay branches from the Fr ground state have been discovered. Shell model calculations have been performed to understand the newly observed states in Fr
β-decay study of , and : Candidates for a monoenergetic neutrino beam facility
The beta decays of Er-150, Yb-152, and Yb-156 nuclei are investigated using the total absorption spectroscopy technique. These nuclei can be considered possible candidates for forming the beam of a monoenergetic neutrino beam facility based on the electron capture (EC) decay of radioactive nuclei. Our measurements confirm that for the cases studied the EC decay proceeds mainly to a single state in the daughter nucleus
High-resolution study of Gamow-Teller transitions in the Ti-47(He-3, t)V-47 reaction
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.status: publishe
High-resolution study of Tz=+2→+1 Gamow-Teller transitions in the 44Ca(3He,t)44Sc reaction
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