Search

The three-cluster generator coordinate method is applied to the 7Li(n, γ)8Li and 7Be(p, γ)8B capture reactions. The 8B (or 8Li) nucleus is defined by a mixing of (α+3He)+p and (α + p) + 3He (or mirror) configurations. We investigate the sensitivity of different observables with respect to the nucleon-nucleon interaction by considering four different Volkov forces. For all of them, the model fairly reproduces most of the experimentally known spectroscopic properties of the 8B and 8Li mirror nuclei. Recent measurements of the quadrupole moments are well explained without a halo structure. The 7Li(n, γ)8Li cross section supports the data of Imhof et al. rather than those of Wiescher et al. At zero energy, the 7Be(p, γ)8B astrophysical S-factors slightly depend on the nucleon-nucleon interaction. They are consistent with the currently accepted value, but contradict lower estimates.

The root-mean-square (rms) radii of the last nucleons in the 2s1/2 states of 21Ne, 21Na, 17O and 17F are found to be 4.4±0.5, 5.2±0.6, 4.3±0.5 and 5.0±0.6 fm, respectively, from transfer reaction data. The results show that the 2s1/2 states of 21Na and 17F are proton halo states, while the analogous states in their mirror nuclei 21Ne and 17O can be considered as neutron skin states. Comparisons among the rms radii of these states lead us to expect that a neutron halo nucleus has a proton halo mirror partner, and the Coulomb barrier is a determinant factor limiting the extension of the rms radius of the loosely bound proton.

Excited states in the N = Z - 2 nucleus (44)V have been observed for the first time. The states have been identified through particle-gamma-gamma coincidence relationships and comparison with analog states in themirror nucleus (44)Sc. Mirror energy differences have been extracted and compared to state-of-the-art shell-model calculations which include charge-symmetry-breaking forces. Observed decay pattern asymmetries between the mirror pair are discussed in terms of core excitations, electromagnetic spin-orbit effects and isospin mixing.

The questions of charge symmetry and charge independence (isospin conservation) and their possible breaking have always been important, also as a field where mass differences between up and down quarks in the nucleons might show up. Examples for such effects are the Nolen-Schiffer anomaly of the Coulomb energy differences of mirror nuclei [1] and the difference between the scattering lengths \(a_{\rm nn},\,a_{\rm pp},\) and \(a_{\rm np}\) of the singlet \(^1S_0\) nucleon-nucleon interaction (for a recent discussion see Ref. [2]). When initiating nuclear reactions with protons and comparing them to their neutron-induced mirror reaction, after correctly subtracting the “trivial” Coulomb part of the interaction, under isospin conservation the remaining observables should be equal. This is of course true for all, i.e. also polarization observables. Therefore, the use of polarized neutrons which normally have to be produced in special nuclear reactions (see Sect. 10.2) is very important. Examples are the intensive study of the three-particle breakup reaction \(^{2}\hbox{H(p,pp)n}\) and comparison with \(^{2}\hbox{H(n,nn)}^{1}\hbox{H},\) as well as of the elastic scatterings \(^{2}\hbox{H(p,p)}^{2}\hbox{H}\) and \(^{2}\hbox{H(n,n)}^{2}\hbox{H}.\) Although neutron-induced reactions are technically more difficult and in general less precise than their proton-induced counterparts they are important because the realistic inclusion of the long-range Coulomb interaction into “numerically exact” Faddeev calculations has been achieved only recently allowing now the realistic study of charged-particle three-body reactions. The comparison between both revealed not only discrepancies between them, but of both with most advanced theories such as meson exchange or EFT Faddeev-type calculations (for recent discussions of these low-energy discrepancies see e.g. Refs. [3, 4]).

The stellar reaction ${}^{26}$Si($p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma}$)${}^{27}$P was studied in the Coulomb dissociation of ${}^{27}$P. Two known resonance levels in ${}^{27}$P were excited and a candidate for the third excited state was found in the ${}^{26}$Si $p$ relative energy spectrum. The $E$2 resonance strengths $\ensuremath{\omega}\ensuremath{\gamma}$ were obtained to be $(6.5\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}$, $(6.0\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$, and $(1.10\ifmmode\pm\else\textpm\fi{}0.27)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ MeV. The total ($E2+M$1) $\ensuremath{\omega}\ensuremath{\gamma}$ value for the first excited state was evaluated to be $1.{9}_{\ensuremath{-}1.1}^{+1.9}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ MeV with the help of the shell model. The error was estimated from the deviation of theoretical predictions with the same shell model from experimental strengths obtained in the present study for ${}^{27}$P and earlier ones for the mirror nucleus ${}^{27}$Mg. The astrophysical reaction rate for the ${}^{26}$Si($p,\phantom{\rule{-0.16em}{0ex}}\ensuremath{\gamma}$)${}^{27}$P reaction was also calculated and compared with previous estimations.

The reactions 26Alg(p,γ)27Si and 26Alm(p,γ)27Si are important for influencing the galactic abundance of the cosmic γ-ray emitter 26Alg and for the excess abundance of 26Mg found in presolar grains, respectively. Precise excitation energies and spin assignments of states from the ground state to the region of astrophysical interest in 27Si, including the identification and pairing of key astrophysical resonances with analog states in the mirror nucleus 27Al, are reported using γ rays observed in the 12C + 16O fusion reaction. The detailed evolution of Coulomb energy differences between the states in 27Si and 27Al is explored, including the region above the astrophysical reaction thresholds. © 2011 American Physical Society.

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. Assuming the isospin symmetry for the strengths of Tz = ±3/2→±1/2 analogous GT transitions, we can deduce the detailed strength distribution starting from mirror unstable nucleus 47Mn.

We discuss a possible measurement of the ratio of nucleon structure functions, F2n/F2p, and the ratio of up to down quark distributions, u/d, at large Bjorken x, by performing deep inelastic electron scattering from the 3H and 3He mirror nuclei with the 11 GeV upgraded beam of Jefferson Lab. The measurement is expected to be almost free of nuclear effects, which introduce a significant uncertainty in the extraction of these two ratios from deep inelastic scattering off the proton and deuteron. The results are expected to test perturbative and non‐perturbative mechanisms of spin‐flavor symmetry breaking in the nucleon, and constrain the structure function parametrizations needed for the interpretation of high energy collider and neutrino oscillations data. The precision of the expected data can also test models of the nuclear EMC effect and provide valuable input for its full explanation.

Expérience GANIL e521, SPIRAL; International audience; The unbound nucleus 18Na, the intermediate nucleus in the two-proton radioactivity of 19Mg, is studied through the resonant elastic scattering 17Ne(p,17Ne)p. The spectroscopic information obtained in this experiment is discussed and put in perspective with previous measurements and the structure of the mirror nucleus 18N.

New results for the Coulomb energy differences in the A=47 mirror nuclei 47Cr and 47V for yrast states up to spin 312ℏ are presented and shown to agree with earlier predictions made within a deformed, crancked shell model approach. The observed total difference in Coulomb displacement energies at low and high angular momenta is also explained within the spherical shell model. The first example of alignment in an N=Z nucleus, 48Cr, is reported.

Recent improvements in isotope separators can be utilized along with the availability of a wide range of nuclear species from the heavy-ion fragmentation process to study hyperfine interactions. We have measured the magnetic moments of mirror nuclei using this method at the Lawrence Berkeley Laboratory's Bevalac heavy-ion accelerator. We present the merits, applicability and limitations of the technique.

Electric quadrupole (E2) moments in light mirror nuclei are studied by shell model calculations with the proton-neutron formalism. Our calculations describe successfully theQ-moments of both loosely-bound andwell-bound nuclei when the effect of the separation energies is taken into consideration in the Woods-Saxon wave functions. The large enhancement of theQ-moments in8B and17F shows a clear evidence of the proton halos.

The works of the Sendai group on investigations of the properties of the trinucleon bound states3H and3He are reviewed in detail. For these mirror nuclei, results are summarized that have been obtained from rigorous solutions of the (Coulomb-modified) Faddeev equations for various realistic nucleon-nucleon potentials with inclusion of three-nucleon forces as well as chargeindependence-and charge-symmetry-breaking forces. It becomes evident that for most trinucleon bound-state observables quite reasonable results have been achieved.

A theoretically consistent approach to the calculation of the Coulomb energy of nuclei is presented. New contributions to the single-particle energies are taken into account. We show that the interplay between the Coulomb interaction and the strong interaction leads to an upward shift of the proton single-particle levels, affecting the position of the calculated proton drip line. The same contributions are responsible for significant corrections to the mass difference of the mirror nuclei (Nolen-Schiffer anomaly) and to the effective proton mass.

We predict values of the magnetic moments of $T=3/2$ proton-rich $\mathit{fp}$-shell nuclei in the mass range $A=43$--$53$, by using known values for their neutron-rich mirrors together with shell-model estimates for small quantities. We extend the analysis to those $T=3/2$ $\mathit{sd}$-shell mirror pairs for which both the ${T}_{z}=\ensuremath{-}3/2$ and ${T}_{z}=+3/2$ magnetic moments have been measured. We find that these obey the same linear relation as previously deduced for $T=1/2$ mirror pairs.

Recent experimental data have revealed large mirror energy differences (MED) between high-spin states in the mirror nuclei {sup 67}Se and {sup 67}As, the heaviest pair where MED have been determined so far. The MED are generally attributed to the isospin symmetry breaking caused by the Coulomb force and by the isospin-nonconserving part of the nucleon-nucleon residual interaction. The different contributions of the various terms have been extensively studied in the fp shell. By employing large-scale shell-model calculations, we show that the inclusion of the g{sub 9/2} orbit causes interference between the electromagnetic spin-orbit and the Coulomb monopole radial terms at high spin. The large MED are attributed to the aligned proton pair excitations from the p{sub 3/2} and f{sub 5/2} orbits to the g{sub 9/2} orbit. The relation of the MED to deformation is discussed.

Equilibration and equilibration rates have been measured by colliding Sn nuclei with different isospin asymmetries at beam energies of E/A=35 MeV. Using the yields of mirror nuclei of {sup 7}Li and {sup 7}Be, we have studied the diffusion of isospin asymmetry by combining data from asymmetric {sup 112}Sn+{sup 124}Sn and {sup 124}Sn+{sup 112}Sn collisions with those from symmetric {sup 112}Sn+{sup 112}Sn and {sup 124}Sn+{sup 124}Sn collisions. We use these measurements to probe isospin equilibration in central collisions where nucleon-nucleon collisions are strongly blocked by the Pauli exclusion principle. The results are consistent with transport theoretical calculations that predict a degree of transparency in these collisions, but inconsistent with the emission of intermediate mass fragments by a single chemically equilibrated source. Comparisons with quantum molecular dynamics calculations are consistent with results obtained at higher incident energies that provide constraints on the density dependence of the symmetry energy.

The critical phenomenon of the liquid-gas phase transition has been investigated in the reactions $^{78,86}\mathrm{Kr}$$+$$^{58,64}\mathrm{Ni}$ at beam energy of 35 MeV/nucleon using the Landau free energy approach with isospin asymmetry as an order parameter. Fits to the free energy of fragments showed three minima, suggesting that the system is in the regime of a first-order phase transition. The relation m $=$ \ensuremath{-}\ensuremath{\partial}F/\ensuremath{\partial}H, which defines the order parameter and its conjugate field $H$, has been experimentally verified from the linear dependence of the mirror nuclei yield ratio data on the isospin asymmetry of the source. The slope parameter, which is a measure of the distance from a critical temperature, showed a systematic decrease with increasing excitation energy of the source. Within the framework of the Landau free energy approach, isoscaling provided similar results as obtained from the analysis of mirror nuclei yield ratio data. In the present work, it is shown that the external field is primarily related to the minimum of the free energy, which implies a modification of the source concentration \ensuremath{\Delta} used in isospin studies.

The macroscopic-microscopic mass formula is further improved by considering mirror nuclei constraint. The rms deviation with respect to 2149 measured nuclear masses is reduced to $0.441$ MeV. The shell corrections, the deformations of nuclei, the neutron and proton drip lines, and the shell gaps are also investigated to test the model. The rms deviation of $\ensuremath{\alpha}$-decay energies of 46 superheavy nuclei is reduced to $0.263$ MeV. The predicted central position of the superheavy island could lie around $N=176~178$ and $Z=116~120$ according to the shell corrections of nuclei.

The first direct measurement of the proton separation energy, Sp, for the proton-unbound nucleus 69Br is reported. Of interest is the exponential dependence of the 2p-capture rate on Sp which can bypass the 68Se waiting-point in the astrophysical rp process. An analysis of the observed proton decay spectrum is given in terms of the 69Se mirror nucleus and the influence of Sp is explored within the context of a single-zone X-ray burst model., 6 pages, 6 figures, INPC 2010 conference proceedings

Based on a microscopic cluster model that reproduces well the {sup 17}C spectrum below the neutron threshold, we study the spectrum of its mirror nucleus {sup 17}Na. We find that the {sup 17}Na ground state should be located at 2.4 MeV above the {sup 16}Ne(0{sub 1}{sup +})+p threshold, being a broad 1/2{sup +} resonance with a width of 1.4 MeV. However, there should exist at least four narrow excited states in {sup 17}Na; three of them, 3/2{sub 1}{sup +}, 7/2{sub 1}{sup +}, and 9/2{sub 1}{sup +}, decay into the {sup 16}Ne(2{sub 1}{sup +})+p channel, and the other, 5/2{sub 1}{sup +}, decays mainly into the {sup 16}Ne(0{sub 1}{sup +})+p channel. Because the daughter nucleus {sup 16}Ne is a two-proton emitter, the narrow {sup 17}Na states must undergo a sequential three-proton decay via intermediate states in {sup 16}Ne.

The production of $^{22}\mathrm{Na}$ in ONe novae can be influenced by the $^{22}\mathrm{Mg}$$(p,\ensuremath{\gamma})$$^{23}\mathrm{Al}$ reaction. To investigate this reaction rate at stellar energies, we have determined the asymptotic normalization coefficient (ANC) for $^{22}\mathrm{Mg}$$+p\ensuremath{\rightarrow}$$^{23}\mathrm{Al}$ through measurements of the ANCs in the mirror nuclear system $^{22}\mathrm{Ne}$$+n\ensuremath{\rightarrow}$$^{23}\mathrm{Ne}$. The peripheral neutron-transfer reactions $^{13}\mathrm{C}$($^{12}\mathrm{C}$,$^{13}\mathrm{C}$)$^{12}\mathrm{C}$ and $^{13}\mathrm{C}$($^{22}\mathrm{Ne}$,$^{23}\mathrm{Ne}$)$^{12}\mathrm{C}$ were studied. The identical entrance and exit channels of the first reaction make it possible to extract independently the ground-state ANC in $^{13}\mathrm{C}$. Our experiment gives ${C}_{{p}_{1/2}}^{2}$($^{13}\mathrm{C}$)$=2.24\ifmmode\pm\else\textpm\fi{}0.11$ fm${}^{\ensuremath{-}1}$, which agrees with the value obtained from several previous measurements. The weighted average for all the obtained ${C}_{{p}_{1/2}}^{2}$ is $2.31\ifmmode\pm\else\textpm\fi{}0.08$ fm${}^{\ensuremath{-}1}$. This value is adopted to be used in obtaining the ANCs in $^{23}\mathrm{Ne}$. The differential cross sections for the reaction $^{13}\mathrm{C}$($^{22}\mathrm{Ne}$,$^{23}\mathrm{Ne}$)$^{12}\mathrm{C}$ leading to the ${J}^{\ensuremath{\pi}}=5/{2}^{+}$ and $1/{2}^{+}$ states in $^{23}\mathrm{Ne}$ have been measured at 12 MeV/u. Optical model parameters for use in the DWBA calculations were obtained from measurements of the elastic scatterings $^{22}\mathrm{Ne}+^{13}\mathrm{C}$ and $^{22}\mathrm{Ne}+^{12}\mathrm{C}$. The extracted ANC for the ground state in $^{23}\mathrm{Ne}$, ${C}_{{d}_{5/2}}^{2}=0.86\ifmmode\pm\else\textpm\fi{}0.08\ifmmode\pm\else\textpm\fi{}0.12$ fm${}^{\ensuremath{-}1}$, is converted to its corresponding value in $^{23}\mathrm{Al}$ using mirror symmetry to give ${C}_{{d}_{5/2}}^{2}$($^{23}\mathrm{Al}$)$=(4.63\ifmmode\pm\else\textpm\fi{}0.77)\ifmmode\times\else\texttimes\fi{}{10}^{3}$ fm${}^{\ensuremath{-}1}$. The astrophysical $S$ factor $S(0)$ for the $^{22}\mathrm{Mg}$($p,\ensuremath{\gamma}$) reaction was determined to be $0.96\ifmmode\pm\else\textpm\fi{}0.11$ keV b. The consequences for nuclear astrophysics are discussed.

A Gamma-ray spectroscopic study of excited states of isobaric multiplets has been performed in recent years, with a view to gaining a quantitative understanding of energy differences between excited states in terms of a range of Coulomb and other isospin breaking phenomena. Recently, the experimental programme has been augmented by a study of isobaric analogue states of mirror nuclei populated in mirrored fragmentation reactions. In this presentation, recent results on the [Formula: see text] analogue states in the [Formula: see text] mirror pair 53 Ni /53 Mn will be summarised. In this work, further strong evidence is found for the need to include an anomalous isospin-breaking two-body matrix element for angular-momentum couplings of J = 2, in addition the expected Coulomb contribution, in order to account for the experimental data.

We predict values of the magnetic moments of T=3/2 proton-rich fp-shell nuclei in the mass range A=43-53, by using known values for their neutron-rich mirrors together with shell-model estimates for small quantities. We extend the analysis to those T=3/2 sd-shell mirror pairs for which both the T{sub z}-3/2 and T{sub z}=+3/2 magnetic moments have been measured. We find that these obey the same linear relation as previously deduced for T=1/2 mirror pairs.

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.

The isospin breaking effects due to the Coulomb interaction in weakly-bound nuclei are studied using the Gamow Shell Model, a complex-energy configuration interaction approach which simultaneously takes into account many-body correlations between valence nucleons and continuum effects. We investigate the near-threshold behavior of one-nucleon spectroscopic factors and the structure of wave functions along an isomultiplet. Illustrative calculations are carried out for the T=1 isobaric triplet. By using a shell-model Hamiltonian consisting of an isoscalar nuclear interaction and the Coulomb term, we demonstrate that for weakly bound or unbound systems the structure of isobaric analog states varies within the isotriplet and impacts the energy dependence of spectroscopic factors. We discuss the partial dynamical isospin symmetry present in isospin-stretched systems, in spite of the Coulomb interaction that gives rise to large mirror symmetry breaking effects., Comment: 10 pages, 5 figures ; published version

The Gamow‐Teller transition strength B(GT) of 24Si was measured to investigate characteristic structure of proton‐rich nuclei induced by a weakly‐bound proton. By combining the results of the delayed γ‐ray and proton measurements, the entire decay scheme of 24Si was reconstructed, then the B(GT) of 24Si was deduced. Focusing to the low‐lying states, the B(GT) of 24Si to the 11+ and 12+ states in 24Al were smaller than that of the mirror nucleus 24Ne by 22% and 10%, respectively. The mirror asymmetry of B(GT) indicates the configuration change in the wave function. Through the comparison with theoretical shell‐model calculations, it is implied that the configuration change is attributed to the lowering of the 1s1/2 orbital. The applicability of the theoretical calculations was checked using overall B(GT) distribution.

The approximate expression for matrix elements of Coulomb interaction in the supermultiplet basis, taking into account the orbitally non-symmetric terms, is obtained. The quantum numbers for the orbital part of the interaction are not specified. The expression can be used in nuclear models employing the supermultiplet scheme. The obtained expression has been used to calculate the Coulomb energy of light (4

The nuclear dependence of the neutron-proton mass difference is examined in a relativistic harmonic quark model with the assumption of a swelling of the individual nucleon originated by a decrease of the spring constant inside the nuclear medium. A decrease of the neutron-proton mass difference is obtained which is reasonably small and in the right direction to cope with the Nollen-Schiffer anomaly in mirror nuclei.

Coulomb energy differences (Nolen-Schiffer anomalies) of mirror nuclei 17O-17F and 41Ca-41Sc are studied by using realistic Hartree-Fock and Woods-Saxon single-particle wave functions which are determined precisely through the analysis of the magnetic form factors of electron scattering. These single-particle wave functions are used to evaluate the Coulomb energy differences due to charge symmetry breaking forces, with new coupling constants determined by the analysis of the scattering lengths of pp and nn system which have been successfully applied to the Coulomb energy difference of 3He-3H. We also evaluated the effects of the charge symmetry breaking forces using Hartree-Fock wave functions. Together with various other contributions, our calculated values of the Coulomb energy differences, which showed deviations of 3–9% from the experimental values in the previous analysis of Nolen and Schiffer, agree with the experimental values within 1% (2%) accuracy for A = 17 (41).

We report a measurement of the Gamow-Teller (GT) strength distribution for $^{40}\mathrm{Ar}\ensuremath{\rightarrow}^{40}\mathrm{K}$ using the ${0}^{\ifmmode^\circ\else\textdegree\fi{}}(p,n)$ reaction. The measurement extends observed GT strength distribution in the $A=40$ system up to an excitation energy of $~8$ MeV. In comparing our results with those from the $\ensuremath{\beta}$ decay of the isospin mirror nucleus $^{40}\mathrm{Ti}$, we find that, within the excitation energy region probed by the $\ensuremath{\beta}$-decay experiment, we observe a total GT strength that is in fair agreement with the $\ensuremath{\beta}$-decay measurement. However, we find that the relative strength of the two strongest transitions differs by a factor of $~1.8$ in comparing our results from ($p,n$) reactions with the $\ensuremath{\beta}$ decay of $^{40}\mathrm{Ti}$. Using our results we present the neutrino-capture cross section for $^{40}\mathrm{Ar}$.

$\ensuremath{\beta}$-decay spectroscopy of the proton-rich nucleus $^{24}\mathrm{Si}$ was performed. The decay scheme was reconstructed from results of delayed $\ensuremath{\gamma}$-ray and proton measurements. We observed two $\ensuremath{\beta}$ branches to bound states in $^{24}\mathrm{Al}$ for the first time. The branching ratios were determined to be $31(4)%$ and $23.9(15)%$ for the ${1}_{1}^{+}$ state at $0.426$ MeV and the state at $1.090$ MeV, respectively. The observation of an allowed transition to the $1.090$-MeV state enabled us to firmly determine its spin-parity as ${1}^{+}$. In the proton measurements performed with the $\ensuremath{\Delta}E\text{\ensuremath{-}}E$ method, we observed a new unbound level at $6.735$ MeV. The branching ratios to three unbound states, including the new level, were also determined for the first time. Based on the decay scheme, the $B(\mathrm{GT})$ values of $^{24}\mathrm{Si}$ were deduced. The $B(\mathrm{GT})$ values were smaller than those of the mirror nucleus $^{24}\mathrm{Ne}$ by $22%$ and $10%$ for the ${1}_{1}^{+}$ and ${1}_{2}^{+}$ states, respectively. The mirror asymmetries of $B(\mathrm{GT})$, observed in both the ${1}_{1}^{+}$ and the ${1}_{2}^{+}$ states, indicate changes in configuration in the wave function associated with the Thomas-Ehrman shift. To clarify the mechanism of this asymmetry, a comparison with shell-model calculations is also discussed. The calculations attribute the changes in configuration to the lowering of the $1{s}_{1/2}$ orbital.

A global nucleon-nucleus optical potential for elastic scattering has been produced which replicates experimental data to high accuracy and compares well with other recently formulated potentials. The calculation that has been developed describes proton and neutron scattering from target nuclei ranging from carbon to nickel and is applicable for projectile energies from 30 to 160 MeV. With these ranges it is suitable for calculations associated with experiments performed by exotic beam accelerators. The potential is also isospin dependent and has both real and imaginary isovector asymmetry terms to better describe the dynamics of chains of isotopes and mirror nuclei. An analysis of the validity and strength of the asymmetry term is included with connections established to other optical potentials and charge-exchange reaction data. An on-line observable calculator is available for this optical potential., 31 pages, 21 figures, 4 tables; Accepted to Phys. Rev. C. This version includes corrections to Eq. 1 and Table 1. Erratum sent to Phys. Rev. C

We study the ground and the first excited intrinsic states of {sup 53}Co and its mirror nucleus {sup 53}Fe, within the frameworks of the relativistic and nonrelativistic mean field formalisms. The analysis of the single-particle energy spectra of these nuclei show a competition of spins 1/2{sup -} and 3/2{sup -} in a low-lying excited state, which agrees well with the recent experimental observation [D. Rudolph et al., Eur. Phys. J. A 36, 131 (2008)] of spin and parity J{sup {pi}}=3/2{sup -} for the isomeric configuration in {sup 53}Co.

The Vud element of the Cabibbo‐Kobayashi‐Maskawa matrix can be determined from several different experimental approaches: based on either 0+→0+ superallowed nuclear β decays, neutron decay, nuclear mirror decays, or pion β decay. Currently all give consistent results but, because the nuclear superallowed value has an uncertainty at least a factor of six less than all other results, it dominates any average. We present the results from all four approaches and recommended the value |Vud| = 0.97425(22).

This work focus on the electromagnetic decay properties of the heaviest known mirror pair 67As and 67Se, produced in the fusion evaporation reaction 32S+40Ca, with a E = 90 MeV beam provided by the ATLAS accelerator at Argonne National Laboratory. The high selectivity required to investigate these proton‐rich nuclei was achieved with the concurrent employment of Gammasphere, Neutron‐Shell, and Microball. The full array allowed to obtain the level scheme of the 67Se nucleus up to 5.56 MeV, and 5 new transitions were assigned to the known 67As level‐scheme. The level spin and parities were assigned using the ADO analysis and symmetry arguments.

The β‐decay spectroscopy on 24Si was carried out in order to investigate the behavior of a weakly‐bound s‐wave proton. We observed two β transitions to low‐lying bound states in 24Al for the first time. The Gamow‐Teller transition strengths B(GT) to the 11+ and 12+ states were deduced to be 0.13(2) and 0.14(1), which were smaller than that of mirror nucleus 24Ne by 22% and 10%, respectively. These mirror asymmetries of B(GT) indicate the configuration change in the wave function. By comparing with theoretical shell‐model calculations, it is implied that the configuration change is attributed to the lowering of the 1s1/2 orbital.

Absolute and relative measurements of the beta asymmetry parameter in the decays of mirror nuclei are examined as a means of detecting the possible existence of a right-handed contribution to the weak interaction, or of providing further restrictions on it. The constraints to be obtained from these measurements on the parameters of the manifest left-right symmetric model are shown to be complementary among mirror transitions. The limitations of recent experiments and the requirements to improve the present limits are discussed.

Mean lifetimes of levels in the mirror nuclei {sup 25}Mg and {sup 25}Al have been measured using the Doppler-shift-attenuation (DSA) method and the reactions {sup 12}C({sup 15}N,{ital pn}){sup 25}Mg and {sup 24}Mg({ital p},{gamma}){sup 25}Al, respectively. The lifetime values or limits were determined for 13 bound levels in {sup 25}Mg below the excitation energy of 7 MeV and for the 1.61- and 1.79-MeV bound levels in {sup 25}Al. The lifetime values or limits of the 7.79, 8.02, and 9.00 MeV neutron unbound states in {sup 25}Mg, and the 2.72-, 3.42-, and 4.03-MeV proton unbound states in {sup 25}Al were also determined. The lifetimes of four levels in {sup 25}Mg are reported for the first time. The targets were prepared by implanting {sup 12}C and {sup 24}Mg into Ta substrates, to ensure effective slowing down of the recoils. Computer simulations with the Monte Carlo method and experimental stopping power were used in the DSA analysis. Experimental transition matrix elements, based on the measured mean lifetime values, are compared with predictions of the universal {ital sd}-shell model.

The use of the tilted-foil interaction in conjunction with separated reaction-product beams has been demonstrated to be a powerful method for polarizing short-lived nuclei. Such polarization can in turn be utilized for diverse measurements of electromag- netic properties of nuclei such as signs and magnitudes of quadrupole moments of isomeric high spin levels, magnetic moments of ground states of mirror nuclei and parity violation effects. These activities, as well as the possible use of the tilted-foil polarization of radioactive beams for surface physics studies, will be summarized and discussed with regard to future prospects.

We investigate a recent suggestion that the Nolen-Schiffer anomaly can be resolved if the {ital in}{minus}{ital medium} proton-neutron mass difference is substantially changed from its free space value. In a number of hadronic models, such an effect is a natural consequence of partial chiral restoration in the nuclear medium. This suggestion is meaningful in the context of a local-density approximation, which has strong implications for the {ital systematics} of the Nolen-Schiffer anomaly over a range of nuclei. We show that such a mechanism predicts both noticeable shell effects and modest variations in the anomaly as the nuclear size is changed.

A new systematic shift of the single-particle spectra of nuclei under the Coulomb interaction is considered. This shift results from the interplay between the Coulomb interaction and strong interaction, being greatly enhanced by the presence of the nuclear surface. This shift affects the position of the calculated proton drip line decreasing the maximal Z of a nucleus near the drip line by several units. The same mechanism is responsible for significant corrections to the mass difference of the mirror nuclei and to the effective proton mass.

The low-energy structures of the mirror nuclei {sup 21}Ne and radioactive {sup 21}Na have been examined by using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. Beams of {approx}5x10{sup 6} ions/s were accelerated to 1.7 MeV/A and Coulomb excited in a 0.5 mg/cm{sup 2} {sup nat}Ti target. Scattered beam and target particles were detected by the segmented Si detector BAMBINO, while {gamma} rays were observed by using two TIGRESS HPGe clover detectors perpendicular to the beam axis. For each isobar, Coulomb excitation from the (3/2){sup +} ground state to the first excited (5/2){sup +} state was observed and B(E2) values were determined by using the 2{sup +}{yields}0{sup +} de-excitation in {sup 48}Ti as a reference. The {phi} segmentation of BAMBINO was used to deduce tentative assignments for the signs of the mixing ratios between the E2 and M1 components of the transitions. The resulting B(E2){up_arrow} values are 131{+-}9 e{sup 2} fm{sup 4} (25.4{+-}1.7 W.u.) for {sup 21}Ne and 205{+-}14 e{sup 2} fm{sup 4} (39.7{+-}2.7 W.u.) for {sup 21}Na. The fit to the present data and the known lifetimes determined E2/M1 mixing ratios and B(M1){down_arrow} values of {delta}=(-)0.0767{+-}0.0027 and 0.1274{+-}0.0025 {mu}{sub N}{sup 2} and {delta}=(+)0.0832{+-}0.0028 and 0.1513{+-}0.0017 {mu}{sub N}{sup 2} more » for {sup 21}Ne and {sup 21}Na, respectively (with Krane and Steffen sign convention). By using the effective charges e{sub p}=1.5e and e{sub n}=0.5e, the B(E2) values produced by the p-sd shell model are 30.7 and 36.4 W.u. for {sup 21}Ne and {sup 21}Na, respectively. This analysis resolves a significant discrepancy between a previous experimental result for {sup 21}Na and shell-model calculations. « less

International audience; Precision correlation measurements in nuclear beta decay using atom and ion traps have made significant progress since the last ENAM2004 Conference. We review here the achievements and plans of different projects and discuss for each of them their potential to contribute to the determination of the Vud element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. This matrix element has traditionally been determined from the analysis of data in nuclear superallowed 0+ → 0+ transitions, neutron decay and pion beta decay but can also independently be determined from data in nuclear mirror transitions. This requires the measurement of correlation parameters in such decays to determine the Gamow-Teller to Fermi mixing ratio which, in most cases, dominates the error on the extracted value of |Vud|.

Coulomb excitation of the proton-rich nucleus {sup 20}Mg was studied using a radioactive {sup 20}Mg beam at 58A MeV impinging on a lead target. The reduced transition probability B(E2;0{sub g.s.}{sup +}{yields}2{sub 1}{sup +}) was extracted to be 177(32) e{sup 2} fm{sup 4}, which agrees with the theoretical predictions by a cluster model assuming {sup 16}O + 2p + 2p structure, a mean-field approach based on the angular momentum projected generator coordinate method, and the USD shell model. The ratio of the neutron-to-proton multipole matrix elements M{sub n}/M{sub p} in the mirror nucleus {sup 20}O was deduced to be 2.51(25) with the M{sub n} value evaluated from the measured B(E2) value for {sup 20}Mg with the help of isospin symmetry. The results confirm the large M{sub n}/M{sub p} value previously reported in {sup 20}O, leading to the dominant role of the four valence nucleons in the 2{sub 1}{sup +} excitation and persistence of the {sup 16}O core in {sup 20}O and {sup 20}Mg.

One of the key uncertainties in our understanding of the astrophysical $\mathit{rp}$ process is the extent to which even-even $N=Z$ nuclei such as $^{68}\mathrm{Se}$ and $^{72}\mathrm{Kr}$ act as waiting points in the process because of the next nucleus in the proton-capture chain being proton unbound. For these specific cases, much of the argument is based on the nonobservation of $^{69}\mathrm{Br}$ and $^{73}\mathrm{Rb}$ following projectile fragmentation. An examination of the nuclear structure involved, and the high population of low-lying isomers in the mirror nuclei, $^{69}\mathrm{Se}$ and $^{73}\mathrm{Kr}$ in fragmentation, suggests that this nonobservation may be down to a shadowing mechanism where the majority of the population goes to the isomer that proton decays before the ground state can be reached. Strong conclusions on the extent to which the $^{69}\mathrm{Br}$ and $^{73}\mathrm{Rb}$ are unbound may therefore be unsafe. The possible astrophysical implications of this are discussed along with the relevance of this shadowing mechanism to the search for exotic nuclei in fragmentation.

We examine the magnetic moments and $\ensuremath{\beta}$-decay lifetimes of light $T=\frac{1}{2}$ mirror nuclei and obtain very tight correlations between these quantities by making use of shell-model estimates for small quantities. Using the information thus obtained, we predict values for some unknown magnetic moments of heavier $T=\frac{1}{2}$ mirror nuclei. Correlations for the magnetic moments of some $T=\frac{3}{2}$ mirror nuclei are also included. The effective operators required to reproduce the data are discussed and compared to those obtained with other methods.

6 pags., 3 figs. -- 9th International Conference on Clustering Aspects of Nuclear Structure and Dynamics (CLUSTERS'07) 3–7 September 2007, Stratford upon Avon, UK, The β-decays of the mirror nuclei 12B and 12N both populate states in 12C and they are therefore a precious source of information about this nucleus. Due to the selection rules of β-decay only 0+, 1+ and 2+ states are populated. This allows a very clean study of unbound states just above the 3α-threshold with those spin and parities. This probe has been applied in two experiments using two complementary experimental techniques: in the first the three α-particles emitted after β-decay are measured in coincidence in separate detectors using the ISOL method, while in the second method 12B and 12N are implanted in a detector and the summed energy of the three α-particles is measured directly. Preliminary results from the two approaches are presented. © 2008 IOP Publishing Ltd.

Following suggestions that the energy associated with Coulomb correlations and a possible charge-symmetry breaking of nuclear forces might largely cancel the Coulomb-exchange term, we refit the HFB-14 mass model without the Coulomb-exchange term to essentially all the mass data. The resulting mass model, HFB-15, gives a better fit to the 2149 mass data, ${\ensuremath{\sigma}}_{\mathrm{rms}}$ falling from 0.729 to 0.678 MeV. The improvement in the energy differences between mirror nuclei is particularly striking: the Nolen-Schiffer anomaly, which is strong for HFB-14, is essentially eliminated. As for the extrapolation to highly neutron-rich nuclei, the HFB-15 model differs significantly from HFB-14, with up to 15 MeV less binding being predicted. However, the differences in the predicted values of differential quantities such as the neutron-separation energies, \ensuremath{\beta}-decay energies and fission barriers are very much smaller.