The magic nature of (132)Sn explored through the single-particle states of (133)Sn.

Atomic nuclei have a shell structure in which nuclei with 'magic numbers' of neutrons and protons are analogous to the noble gases in atomic physics. Only ten nuclei with the standard magic numbers of both neutrons and protons have so far been observed. The nuclear shell model is founded on the precept that neutrons and protons can move as independent particles in orbitals with discrete quantum numbers, subject to a mean field generated by all the other nucleons. Knowledge of the properties of single-particle states outside nuclear shell closures in exotic nuclei is important for a fundamental understanding of nuclear structure and nucleosynthesis (for example the r-process, which is responsible for the production of about half of the heavy elements). However, as a result of their short lifetimes, there is a paucity of knowledge about the nature of single-particle states outside exotic doubly magic nuclei. Here we measure the single-particle character of the levels in (133)Sn that lie outside the double shell closure present at the short-lived nucleus (132)Sn. We use an inverse kinematics technique that involves the transfer of a single nucleon to the nucleus. The purity of the measured single-particle states clearly illustrates the magic nature of (132)Sn.

Mass Measurement of 56Sc Reveals a Small A = 56 Odd-Even Mass Staggering, Implying a Cooler Accreted Neutron Star Crust.

We present the mass excesses of (52-57)Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)((-54)(+0)) MeV and -21.0(1.3) MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We find that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in A≈56 nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-A nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.

Constraint of the astrophysical

The Galactic 1.809-MeV γ-ray signature from the ß decay of ^{26g}Al is a dominant target of γ-ray astronomy, of which a significant component is understood to originate from massive stars. The ^{26g}Al(p,γ)^{27}Si reaction is a major destruction pathway for ^{26g}Al at stellar temperatures, but the reaction rate is poorly constrained due to uncertainties in the strengths of low-lying resonances in ^{27}Si. The ^{26g}Al(d,p)^{27}Al reaction has been employed in inverse kinematics to determine the spectroscopic factors, and hence resonance strengths, of proton resonances in ^{27}Si via mirror symmetry. The strength of the 127-keV resonance is found to be a factor of 4 higher than the previously adopted upper limit, and the upper limit for the 68-keV resonance has been reduced by an order of magnitude, considerably constraining the ^{26g}Al destruction rate at stellar temperatures.

Mass measurements demonstrate a strong N=28 shell gap in argon.

We present results from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. We report the first mass measurements of ^{48}Ar and ^{49}Ar and find atomic mass excesses of -22.28(31) MeV and -17.8(1.1) MeV, respectively. These masses provide strong evidence for the closed shell nature of neutron number N=28 in argon, which is therefore the lowest even-Z element exhibiting the N=28 closed shell. The resulting trend in binding-energy differences, which probes the strength of the N=28 shell, compares favorably with shell-model calculations in the sd-pf shell using SDPF-U and SDPF-MU Hamiltonians.

Double-magic nature of 132Sn and 208Pb through lifetime and cross-section measurements.

Single-neutron states in (133)Sn and (209)Pb, which are analogous to single-electron states outside of closed atomic shells in alkali metals, were populated by the ((9)Be, (8)Be) one-neutron transfer reaction in inverse kinematics using particle-γ coincidence spectroscopy. In addition, the s(1/2) single-neutron hole-state candidate in (131)Sn was populated by ((9)Be, (10)Be). Doubly closed-shell (132)Sn (radioactive) and (208)Pb (stable) beams were used at sub-Coulomb barrier energies of 3 MeV per nucleon. Level energies, γ-ray transitions, absolute cross sections, spectroscopic factors, asymptotic normalization coefficients, and excited-state lifetimes are reported and compared with shell-model expectations. The results include a new transition and precise level energy for the 3p(1/2) candidate in (133)Sn, new absolute cross sections for the 1h(9/2) candidate in (133)Sn and 3s(1/2) candidate in (131)Sn, and new lifetimes for excited states in (133)Sn and (209)Pb. This is the first report on excited-state lifetimes of (133)Sn, which allow for a unique test of the nuclear shell model and (132)Sn double-shell closure.

Neutron single particle structure in 131Sn and direct neutron capture cross sections.

Recent calculations suggest that the rate of neutron capture by (130)Sn has a significant impact on late-time nucleosynthesis in the r process. Direct capture into low-lying bound states is expected to be significant in neutron capture near the N=82 closed shell, so r-process reaction rates may be strongly impacted by the properties of neutron single particle states in this region. In order to investigate these properties, the (d,p) reaction has been studied in inverse kinematics using a 630 MeV beam of (130)Sn (4.8 MeV/u) and a (CD(2))(n) target. An array of Si strip detectors, including the Silicon Detector Array and an early implementation of the Oak Ridge Rutgers University Barrel Array, was used to detect reaction products. Results for the (130)Sn(d, p)(131)Sn reaction are found to be very similar to those from the previously reported (132)Sn(d, p)(133)Sn reaction. Direct-semidirect (n,γ) cross section calculations, based for the first time on experimental data, are presented. The uncertainties in these cross sections are thus reduced by orders of magnitude from previous estimates.

Halo nucleus 11Be: a spectroscopic study via neutron transfer.

The best examples of halo nuclei, exotic systems with a diffuse nuclear cloud surrounding a tightly bound core, are found in the light, neutron-rich region, where the halo neutrons experience only weak binding and a weak, or no, potential barrier. Modern direct-reaction measurement techniques provide powerful probes of the structure of exotic nuclei. Despite more than four decades of these studies on the benchmark one-neutron halo nucleus 11Be, the spectroscopic factors for the two bound states remain poorly constrained. In the present work, the 10Be(d,​p) reaction has been used in inverse kinematics at four beam energies to study the structure of 11Be. The spectroscopic factors extracted using the adiabatic model were found to be consistent across the four measurements and were largely insensitive to the optical potential used. The extracted spectroscopic factor for a neutron in an nℓj=2s(1/2) state coupled to the ground state of 10Be is 0.71(5). For the first excited state at 0.32 MeV, a spectroscopic factor of 0.62(4) is found for the halo neutron in a 1p(1/2) state.

Near-barrier fusion of Sn + Ni and Te + Ni systems: examining the correlation between nucleon transfer and fusion enhancement.

The fusion excitation functions for radioactive (132)Sn + (58)Ni and stable (130)Te + (58,64)Ni were measured at energies near the Coulomb barrier. The coupling of transfer channels in heavy-ion fusion was examined through a comparison of Sn + Ni and Te + Ni systems, which have large variations in the number of positive Q-value nucleon transfer channels. In contrast with previous experimental comparisons, where increased sub-barrier fusion cross sections were observed in systems with positive Q-value neutron transfer channels, the reduced excitation functions were equivalent for the different Sn + Ni and Te + Ni systems. The present results suggest a dramatically different influence of positive Q-value transfer channels on the fusion process for the Sn + Ni and Te + Ni systems.

Ground-state proton decay of 69Br and implications for the 68Se astrophysical rapid proton-capture process waiting point.

We report on the first direct measurement of the proton separation energy for the proton-unbound nucleus (69)Br. Bypassing the (68)Se waiting point in the rp process is directly related to the 2p-capture rate through (69)Br, which depends exponentially on the proton separation energy. We find a proton separation energy for (69)Br of Sp((69)Br )= -785(-40)(+34) keV; this is less bound compared to previous predictions which have relied on uncertain theoretical calculations. The influence of the extracted proton separation energy on the rp process occurring in type I x-ray bursts is examined within the context of a one-zone burst model.

Time-of-flight mass measurements for nuclear processes in neutron star crusts.

We present results from time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory that are relevant for neutron star crust models. The masses of 16 neutron-rich nuclei in the scandium-nickel range were determined simultaneously, with the masses of (61)V, (63)Cr, (66)Mn, and (74)Ni measured for the first time with mass excesses of -30.510(890) MeV, -35.280(650) MeV, -36.900(790) MeV, and -49.210(990) MeV, respectively. With these results the locations of the dominant electron capture heat sources in the outer crust of accreting neutron stars that exhibit super bursts are now experimentally constrained. We find the experimental Q value for the (66)Fe→(66)Mn electron capture to be 2.1 MeV (2.6σ) smaller than predicted, resulting in the transition occurring significantly closer to the neutron star surface.

Neutron-proton asymmetry dependence of spectroscopic factors in ar isotopes.

Spectroscopic factors have been extracted for proton-rich 34Ar and neutron-rich 46Ar using the (p, d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton-rich nucleus 34Ar compared to that of 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements.

Decay of a Resonance in 18Ne by the Simultaneous Emission of Two Protons.

Radioactive ion beams of 17F were used to study several resonance states in 18Ne. Clear evidence for simultaneous two-proton emission from the 6.15 MeV state (Jpi = 1(-)) in 18Ne has been observed with the reaction 17F+1H. Because of limited angular coverage, the data did not differentiate between the two possible mechanisms of simultaneous decay, diproton (2He) emission or direct three-body decay. The two-proton partial width was found to be 21+/-3 eV assuming 2He emission and 57+/-6 eV assuming three-body decay. The total width of the 1(-) state was measured to be 50+/-5 keV. Several additional resonances that decay by single proton emission were also studied.

Trapeziometacarpal joint osteoarthritis and carpal tunnel syndrome: a new surgical approach for concomitant treatment.

A new approach for the concomitant surgical treatment of trapeziometacarpal joint osteoarthritis and carpal tunnel syndrome through the same incision is described. The technique was used in 25 patients (20 women, five men; mean age, 56 years). At a mean follow-up of 27 months, there was complete disappearance of the symptoms of carpal tunnel syndrome in 20 of the 25 patients, incomplete but substantial relief in four patients, and no improvement in one patient. One patient had scar tenderness and another had a superficial wound infection. The surgical technique is simple, safe and cost-effective as it avoids separate operations for both pathologies. The procedure is not suitable for severe carpal tunnel syndrome or when direct visualization of the median nerve and the carpal tunnel is necessary.

Amino acid substitutions in the D1 protein of photosystem II affect QB- stabilization and accelerate turnover of D1.

Isogenic strains of Synechococcus PCC7942 were genetically engineered so that copy I of the gene psb A was mutated at specific sites. These mutations resulted in replacements of Ser 264 by Gly or Ala and of Phe 255 by Tyr or Leu in the D1 protein. The mutants were resistant to herbicides inhibiting electron transfer in photosystem II. All mutants exhibited alterations in the stability of QB- as demonstrated by a temperature downshift, to various extents, of the in vivo thermoluminescence emission. Measurements of the light-dependent turnover of D1 showed a marked decrease in the t 1/2 of this protein in the mutants as compared to wild-type, under low to medium light intensities. A correlation was found between the degree of perturbation in the QB- stability and the rate of acceleration in the turnover of D1. These data provide a direct evidence for the overlapping binding sites for the plastoquinone B and herbicides in the D1 protein. In addition these data indicate a close link between QB- destabilization in reaction center II and the mechanism controlling the light-dependent turnover of D1. Based on these results and previous work we suggest that destabilization of the semireduced quinone, facilitates a light-induced damage in D1 which triggers its degradation.

[The liver in juvenile rheumatoid arthritis].

Hepatic involvement in juvenile rheumatoid arthritis of the systemic type (JRA) is a diagnostic challenge because of the varied clinical picture it presents. We describe a 21-year-old woman in whom JRA had started at the age of 4 years as an illness resembling familial Mediterranean fever. This long-standing illness was complicated by liver damage and needle biopsy showed massive hepatic deposition of amyloid. It is possible that this patient may have developed JRA as a complication of familial Mediterranean fever.

[Sulfasalazine in rheumatoid arthritis].

Sulfasalazine (SLZ) is now a second-line treatment in rheumatoid arthritis (RA), as well as in psoriatic arthritis and ankylosing spondylitis. 54 patients with active RA were treated with enteric coated SLZ (2 g daily) in a 24-week open study. Clinical and laboratory parameters of disease activity were monitored initially and thereafter at 2-week intervals for the first 2 months, and then at 4-week intervals until the end of the 24-week study. There was significant clinical improvement at the end, as shown by scores for joint pain (Ritchie), grip strength and morning stiffness (p less than 0.0001, less than 0.0001 and less than 0.01, respectively, by paired t test). Clinical improvement was accompanied by significant decrease in erythrocyte sedimentation rate and increase in hemoglobin (p less than 0.002 and less than 0.016, respectively). There was improvement in some cases as early as 3 weeks after starting therapy. The drop-out rate was significant: 19/54 (35%), most (13) due to side-effects, mainly gastrointestinal; none of the side-effects were serious. Our results, similar to those of other studies, indicate that despite the high rate of side effects, SLZ is an effective, second-line drug for RA.

Musculoskeletal manifestations of Crohn's disease.

The prevalence of musculoskeletal system complaint and involvement in a group of 54 Crohn's disease patients, with a follow-up of 2 to 40 years, was studied and compared to that of a control group of patients with a similar distribution of sex and age. Twenty-four (44%) with Crohn's disease complained of arthralgia in various joints, but only 7.4% had objective findings compatible with joint pathology such as swelling, tenderness, and decreased range of motion. None of them had any serological or radiological evidences of joint damage. No significant correlation was found between patients' complaints/physical signs and age, sex, duration, or severity of Crohn's disease or mode of medical or surgical treatment. In the control group, 46% complained of arthralgia in various joint. The differences in the percentages of arthralgia between the two groups was not significant, although they differed in location of the affected joint. In the Crohn's disease group, a significantly higher proportion of knee, hip, and wrist involvement was observed, while backache was very common in the control group. It is suggested that arthritis in patients with Crohn's disease is an uncommon finding and that arthralgia is just as prevalent as in a matched control group. The pathogenesis of arthralgia in such a condition may be caused by soft tissue involvement.