Gamow-Teller strengths in proton-rich exotic nuclei deduced in the combined analysis of mirror transitions

Isospin symmetry is expected for the T-z=+/- 1 -> 0 isobaric analogous transitions in isobars with mass number A, where T-z is the z component of isospin T. Assuming this symmetry, strengths of analogous Gamow-Teller (GT) transitions within A=50 isobars were determined from a high energy-resolution T-z=+1 -> 0, Cr-50(He-3,t)Mn-50 study at 0 degrees in combination with the decay Q value and lifetime from the T-z=-1 -> 0, Fe-50 ->Mn-50 beta decay. This method can be applied to other pf-shell nuclei and can be used to study GT strengths of astrophysical interest.

Complete Electric Dipole Response and the Neutron Skin inPb208

A benchmark experiment on Pb-208 shows that polarized proton inelastic scattering at very forward angles including 0 degrees is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r(skin) = 0.156(-0.021)(+0.025) fm in Pb-208 derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence relevant to the description of neutron stars.

Observation of Low- and High-Energy Gamow-Teller Phonon Excitations in Nuclei

Y. Fujita et al. ; 5 pags. ; 3 figs. PACS numbers: 24.30.Cz, 25.55.Kr, 27.40.+z

Pygmy dipole resonance in208Pb

Scattering of protons of several hundred MeV is a promising new spectroscopic tool for the study of electric dipole strength in nuclei. A case study of 208Pb shows that at very forward angles J^pi = 1- states are strongly populated via Coulomb excitation. A separation from nuclear excitation of other modes is achieved by a multipole decomposition analysis of the experimental cross sections based on theoretical angular distributions calculated within the quasiparticle-phonon model. The B(E1) transition strength distribution is extracted for excitation energies up to 9 MeV, i.e., in the region of the so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows sensitivity to…

Gamow-Teller Transitions Starting from T[sub z] = +3∕2 Nucleus [sup 47]Ti

Gamow‐Teller (GT) transitions are mediated by the στ operator. Owing to its simplicity and also its spin‐isospin nature, GT transitions play key roles in the studies of nuclear structure as well as astro‐nuclear processes. In violent neutrino‐induced reactions at the core‐collapse stage of type II supernovae, Gamow‐Teller (GT) transitions starting from stable as well as unstable pf‐shell nuclei play important roles. We study GT transitions starting from 47Ti in a high‐resolution (3He,t) charge‐exchange reactions at 0° and at an intermediate incident energy of 140 MeV/nucleon at Research Center for Nuclear Physics (RCNP), Osaka. Individual GT transitions up to high excitations were observed.…

Complete dipole response in [sup 208]Pb from high-resolution polarized proton scattering at 0°

At the Research Center for Nuclear Physics, Osaka, Japan, the 208Pb(p,p´) reaction was measured at Ep=295 MeV and scattering angles Θlab= 0° - 10°. A high energy resolution of the order of ΔE/E ≈ 8x10^-5 was achieved, corresponding to ΔE=25-30 keV (FWHM). Cross sections were extracted by a multipole decomposition analysis of the angular distributions. Dominant contributions at very forward angles originate from E1 excitation due to Coulomb projectile-target interaction and spin M1 transitions caused by the spin-isospin part of the proton-nucleus interaction. A separation of these contributions was performed with two independent methods, viz. a multipole decomposition of the angular distribu…

Nuclear weak response from the combined study of beta-decay and charge-exchange reaction

Studying the weak nuclear response, especially the Gamow-Teller (GT) transitions, of stable as well as unstable pf-shell nuclei, is one of the key issues in nuclear and astro-nuclear physics. We study the decay half-lives and the GT transitions starting from Tz = ±1 and ±2 mirror nuclei, respectively, by means of β decays and complementary hadronic (3 He , t) charge-exchange reactions. Under the assumption that isospin is a good quantum number, symmetry is expected for mirror nuclei and the GT transitions starting from the mirror nuclei. The half-lives and branching ratios and the measured strength distributions of GT transitions are compared and also combined for the understanding of the …

High-resolution study ofTz=+2→+1Gamow-Teller transitions in the44Ca(3He,t)44Sc reaction

High-resolution (3He,t) reaction on the double-βdecaying nucleus136Xe

A (${}^{3}\text{He},t$) charge-exchange reaction experiment on the double-beta decaying nucleus ${}^{136}$Xe has been performed at an incident energy of 420 MeV with the objective to measure the Gamow-Teller (GT) strength distribution in ${}^{136}$Cs. The measurements have been carried out at the dispersion-matched WS beam line and the Grand Raiden spectrometer of the Research Center for Nuclear Physics in Osaka, where an energy resolution of 42 keV was achieved. A new gas cell with thin windows made of polyethylene naphthalate has been employed as a target. The extracted GT strength distribution is confronted with the rather long $2\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ deca…

The (150)Nd((3)He,t) and (150)Sm(t,(3)He) reactions with applications to beta beta decay of (150)Nd

The Nd-150(3He,t) reaction at 140 MeV/u and Sm-150(t,He-3) reaction at 115 MeV/u were measured, populating excited states in Pm-150. The transitions studied populate intermediate states of importance for the (neutrinoless) beta beta decay of Nd-150 to Sm-150. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of the quasiparticle random-phase approximation, which is one of the main methods employed for estimating the half-life of the neutrinoless beta beta decay (0 nu beta beta) of Nd-150. The present results th…

Experimental study of Gamow-Teller transitions via the high-energy-resolution O18(He3,t)F18 reaction: Identification of the low-energy “super” -Gamow-Teller state

The $T_{z} = \pm 1 \to 0$ and $\pm 2 \to \pm 1$ Mirror Gamow--Teller Transitions in $pf$-shell Nuclei

Gamow–Teller (GT) transitions are the most common weak-interaction processes in the Universe. They play important roles in various processes of nucleosynthesis, for example, in the rapid proton-capture process (rp-process). In the pf-shell region, the rp-process runs through neutron-deficient nuclei with Tz = −2, −1, and 0 mainly by means of GT and Fermi transitions, where Tz is the z component of isospin T defined by Tz = (N − Z)∕2. Under the assumption of isospin symmetry, mirror nuclei with reversed Z and N numbers, and thus with opposite signs of Tz, have the same structure. Therefore, symmetry is also expected for the GT transitions starting from and ending up in mirror nuclei. We have…

TheNd150(He3,t) andSm150(t,He3) reactions with applications toββdecay ofNd150

The {sup 150}Nd({sup 3}He,t) reaction at 140 MeV/u and {sup 150}Sm(t,{sup 3}He) reaction at 115 MeV/u were measured, populating excited states in {sup 150}Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) {beta}{beta} decay of {sup 150}Nd to {sup 150}Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of the quasiparticle random-phase approximation, which is one of the main methods employed for estimating the half-life of the neutrinoless {beta}{beta} decay (0{nu}{b…

Rapid onset of mafic magmatism facilitated by volcanic edifice collapse: MAFIC MAGMATISM FACILITATED BY VOLCANIC EDIFICE COLLAPSE

Volcanic edifice collapses generate some of Earth's largest landslides. How such unloading affects the magma storage systems is important for both hazard assessment and for determining long-term controls on volcano growth and decay. Here we present a detailed stratigraphic and petrological analyses of volcanic landslide and eruption deposits offshore Montserrat, in a subduction zone setting, sampled during Integrated Ocean Drilling Program Expedition 340. A large (6–10 km3) collapse of the Soufriere Hills Volcano at ~130 ka was followed by explosive basaltic volcanism and the formation of a new basaltic volcanic center, the South Soufriere Hills, estimated to have initiated <100 years after…

Nonquenched Isoscalar Spin-M1Excitations insd-Shell Nuclei

Differential cross sections of isoscalar and isovector spin-M1 (0(+)→1(+)) transitions are measured using high-energy-resolution proton inelastic scattering at E(p)=295  MeV on (24)Mg, (28)Si, (32)S, and (36)Ar at 0°-14°. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to E(x)=16  MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transi…

High-resolution study of Gamow-Teller transitions in the47Ti(3He,t)47V reaction

In this work we have studied ${T}_{z}=+2\ensuremath{\rightarrow}+1$, Gamow-Teller (GT) transitions in the $^{48}\mathrm{Ti}(^{3}\mathrm{He},t)^{48}\mathrm{V}$ charge-exchange reaction at 140 MeV/nucleon and ${0}^{\ensuremath{\circ}}$ at the Research Center for Nuclear Physics, Osaka. From the high-resolution facility, consisting of a high-dispersion beamline and the Grand Raiden spectrometer, the spectrum had an energy resolution of 21 keV, among the best achieved. Individual GT transitions were observed and GT strength was derived for each state populated up to an excitation energy of 12 MeV. The total sum of the $B$(GT) strength observed in discrete states was 4.0, which is 33% of the sum…

High-resolution study of Gamow-Teller excitations in theCa42(He3,t)Sc42reaction and the observation of a “low-energy super-Gamow-Teller state”

Y. Fujita et al.; 15 pags.; 6 figs.; 7 tabs.; PACS number(s): 21.10.Hw, 25.55.Kr, 27.40.+z, 25.40.Ep

Measurement of high energy resolution inelastic proton scattering at and close to zero degrees

13 pages, 15 figures.-- Printed version published Jul 1, 2009.

Gamow-Teller Transitions and β-decay Half-life in Proton Rich pf-shell Nuclei

In violent neutrino‐induced reactions at the core‐collapse stage of type II supernovae, Gamow‐Teller (GT) transitions starting from stable as well as unstable pf‐shell nuclei play important roles. In the β‐decay study of these unstable pf‐shell nuclei, half‐lives can be measured rather accurately. On the other hand, in high‐resolution (3He,t) charge‐exchange reactions at 0°, individual GT transitions up to high excitations can be studied. Assuming the isospin symmetry for the strengths of Tz = ±2→±1 analogous GT transitions, we present a “merged analysis” for the determination of GT transition strengths starting from proton‐rich Tz = −2 nuclei. We applied this analysis to the A = 52, T = 2 …

Gamow-Teller transitions in theA=40isoquintet of relevance for neutrino captures inAr40

Background: The Gamow-Teller response of $^{40}\mathrm{Ar}$ is important for the use of liquid argon as a medium for neutrino detection. An ambiguity about the Gamow-Teller strength for the excitation of ${1}^{+}$ states at 2290 and 2730 keV in $^{40}\mathrm{K}$ results in a significant uncertainty for neutrino capture rates. This ambiguity is caused by the large discrepancy observed between strengths extracted from $^{40}\mathrm{Ar}$($p$, $n$) charge-exchange data and the transition strengths for the analog transitions studied in the $\ensuremath{\beta}$ decay of $^{40}\mathrm{Ti}$.Purpose: This study was aimed at resolving the ambiguity between the results from the $^{40}\mathrm{Ar}$($p$,…

Gamow–Teller transitions in exotic pf-shell nuclei relevant to supernova explosion

Gamow–Teller (GT) transitions starting from unstable pf-shell nuclei are of interest not only in nuclear physics, but also in astrophysics, e.g. in violent neutrino induced reactions at the core-collapse stage of type II supernovae. In the β-decay study of these pf-shell nuclei, half-lives can be measured rather accurately. On the other hand, in high-resolution (3He, t) charge-exchange reactions at 0°, individual GT transitions up to high excitations can be studied. Assuming the isospin symmetry for the strengths of Tz = ±1 → 0 analogous GT transitions, we present a unique 'merged analysis' for the determination of absolute B(GT) values.

Gamow--Teller Excitations Studied by Weak and Strong Interactions

The $^{150}$Nd($^3$He,$t$) and $^{150}$Sm($t$,$^3$He) reactions with applications to $\beta\beta$ decay of $^{150}$Nd

The $^{150}$Nd($^3$He,$t$) reaction at 140 MeV/u and $^{150}$Sm($t$,$^3$He) reaction at 115 MeV/u were measured, populating excited states in $^{150}$Pm. The transitions studied populate intermediate states of importance for the (neutrinoless) $\beta\beta$ decay of $^{150}$Nd to $^{150}$Sm. Monopole and dipole contributions to the measured excitation-energy spectra were extracted by using multipole decomposition analyses. The experimental results were compared with theoretical calculations obtained within the framework of Quasiparticle Random-Phase Approximation (QRPA), which is one of the main methods employed for estimating the half-life of the neutrinoless $\beta\beta$ decay ($0\nu\beta\…

Tz = ±1 → 0 ISOSPIN SYMMETRY GAMOW-TELLER TRANSITIONS IN pf-SHELL NUCLEI

Studying the Gamow-Teller (GT) transitions of stable as well as unstable pf-shell nuclei is one of the key issues in nuclear and astro-nuclear physics. Under the assumption that isospin T is a good quantum number, symmetry is expected for mirror nuclei and the GT transitions starting from the mirror nuclei. We study the GT transitions starting from Tz = ±1 mirror nuclei, respectively, by means of hadronic (3 He , t) charge-exchange reactions and complementary β decays.

Beta Decay Study of the Tz=−2 56Zn Nucleus and the Determination of the Half-Lives of a Few fp-shell Nuclei

Abstract This paper concerns the experimental study of the β decay properties of few proton-rich fp -shell nuclei. The nuclei were produced at GANIL in fragmentation reactions, separated with the LISE spectrometer and stopped in an implantation detector surrounded by Ge detectors. The β -delayed gammas, β -delayed protons and the exotic β -delayed gamma-proton emission have been studied. Preliminary results are presented. The decay of the T z = − 2 nucleus 56 Zn has been studied in detail. Information from the β -delayed protons and β -delayed gammas has been used to deduce the decay scheme. The exotic beta-delayed gamma-proton decay has been observed for the first time in the fp -shell. Th…

Gamow-Teller Transitions in Proton Rich Exotic pf-shell Nuclei Deduced from Mirror Transitions

The rp‐process nucleosynthesis proceeds through nuclei near the proton drip‐line, in which Gamow‐Teller (GT) transitions starting from unstable pf‐shell nuclei play important roles. In the β‐decay study of these nuclei, half‐lives can be measured rather accurately. On the other hand, in the high‐resolution (3He, t) charge‐exchange reactions on mirror nuclei, individual GT transitions can be studied up to high excitations. For the accurate study of the GT transition strengths in the A = 52, T = 2, system, we compare and combine the β‐decay study of the proton‐rich nucleus 52Ni and the 52Cr(3He, t) measurement assuming the isospin symmetry of the Tz = ±2→±1 transitions.