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Nature 606(7915), 678 - 682 (2022). doi:10.1038/s41586-022-04827-6, Published by Nature Publ. Group, London [u.a.]

International audience; This work describes a silicon tracker system developed for experiments with proton-rich radioactive ion beams at the SAMURAI superconducting spectrometer of RIBF at RIKEN. The system is designed for accurate angular reconstruction and atomic number identification of relativistic heavy ions and protons which are simultaneously produced in reactions motivated by studies of proton capture reactions of interest for nuclear astrophysics. The technical characteristics of the tracking array are described in detail as are its performance in two pilot experiments. The physics justification for such a system is also presented.

A kinematically complete quasi-free $(p,pn)$ experiment in inverse kinematics was performed to study the structure of the Borromean nucleus $^{17}$B, which had long been considered to have neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for $1s_{1/2}$ and $0d_{5/2}$ orbitals, and a surprisingly small percentage of 9(2)$\%$ was determined for $1s_{1/2}$. Our finding of such a small $1s_{1/2}$ component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in $^{17}$B. The present work gives the smallest $s$- or $p$-orbital component among known nuclei exhibiting halo features, and implies that the dominant occupation of $s$ or $p$ orbitals is not a prerequisite for the occurrence of neutron halo., Accepted for publication in Physical Review Letters,8 pages, 4 figures

The sum-rule approach and the shell model are used to estimate the energies of Gamow-Teller (GT) giant resonances in high-spin isomeric (HSI) states in $N=Z$ nuclei. The newly derived energy-weighted sum rules show that the GT resonance energies of HSI states are related to the $\ensuremath{\sigma}\ensuremath{\sigma}\ensuremath{\tau}\ensuremath{\tau}$ and $\ensuremath{\sigma}\ensuremath{\sigma}$ interactions. Comparing the results of the sum-rule approach with those of large-scale shell-model calculations for the $^{52}\mathrm{Fe}({12}^{+})$ and $^{94}\mathrm{Ag}({21}^{+})\phantom{\rule{4pt}{0ex}}N=Z$ high-spin isomers, the deduced ${\ensuremath{\kappa}}_{\ensuremath{\sigma}}$, which is the strength of the $\ensuremath{\sigma}\ensuremath{\sigma}$ residual interaction in a simple residual-interaction model, is 2.5 MeV.

C.M. Shand et al. -- 6 pags., 3 figs., tab. --Open Access funded by Creative Commons Atribution Licence 4.0, We report on the measurement of new low-lying states in the neutron-rich Zn nuclei via in-beam γ-ray spectroscopy. These include the 4 →2 transition in Zn, the 2 →0 and 4 →2 transitions in Zn, and low-lying states in Zn were observed for the first time. The reduced E(2 ) energies and increased E(4 )/E(2 ) ratios at N=52, 54 compared to those in Zn attest that the magicity is confined to the neutron number N=50 only. The deduced level schemes are compared to three state-of-the-art shell model calculations and a good agreement is observed with all three calculations. The newly observed 2 and 4 levels in Zn suggest the onset of deformation towards heavier Zn isotopes, which has been incorporated by taking into account the upper sdg orbitals in the Ni78-II and the PFSDG-U models., All UK authors are supported by the Science and Technology Facilities Council (STFC). The development of MINOS and the core MINOS team have been supported by the European Research Council through the ERC Grant No. MINOS-258567. A. Jungclaus was supported by the Spanish Ministerio de Economía y Competitividad under contract FPA2014-57196-C5-4-P. Authors from Cologne were supported by German BMBF Grant No. 05P15PKFNA. Authors from TU Darmstadt were supported by German BMBF Grant No. 05P12RDFN8 and 05P15RDFN1. L.X. Chung and B.D. Linh would like to acknowledge Vietnam Ministry of Science and Technology for the support, and Radioactive Isotope Physics Laboratory of the RIKEN Nishina Center for supporting their stay during the experiments.

Fifty-five inclusive single nucleon-removal cross sections from medium mass neutron-rich nuclei impinging on a hydrogen target at ∼ 250 MeV / nucleon are measured at the RIKEN Radioactive Isotope Beam Factory. Systematically higher cross sections are found for proton removal from nuclei with an even number of protons as compared to odd-proton number projectiles for a given neutron separation energy. Neutron removal cross sections display no even-odd splitting, contrary to nuclear cascade model predictions. Both effects are understood through simple considerations of neutron separation energies and bound state level densities originating in pairing correlations in the daughter nuclei. These conclusions are supported by comparison with semimicroscopic model predictions, highlighting the enhanced role of low-lying level densities in nucleon-removal cross sections from loosely bound nuclei.

International audience; The 9C breakup was studied during the SAMURAI29R1 experiment through inclusive and exclusive measurements at energies around 160 AMeV for 9C, in order to evaluate the astrophysical S18 factor for the inverse process 8B(p,γ)9C at energies in the region of astrophysical interest. The radiative proton capture on 8B is important in the hot pp chains, in explosive Hydrogen burning (ppIV and rapI), at temperatures between 0.05 < T9 < 1 K, as possible alternative paths across the A = 8 mass gap. Another goal of this experiment was a detailed study of the breakup reaction mechanism. During the experiment the nuclear breakup process was studied using a natural C target with 425 µm thickness and the Coulomb dissociation by using a natural Pb target with 150 µm thickness. The reaction products were tracked simultaneously using a system of position sensitive Si detectors and in total 1024 output channels were read out by using new dual gain preamplifiers (DGP) specially designed for the experiments of the HI-p collaboration. The SAMURAI29R1 experiment was carried out during the SAMURAI 18Oxygen 2018 Spring campaign and it is part of the HI-p collaboration together with another three experiments. Performances of the setup used and first results of the analysis are presented.

The key parameter to discuss the possibility of the pion condensation in nuclear matter, i.e., the so-called Landau-Migdal parameter g^{'}, was extracted by measuring the double-differential cross sections for the (p,n) reaction at 216 MeV/u on a neutron-rich doubly magic unstable nucleus, ^{132}Sn with the quality comparable to data taken with stable nuclei. The extracted strengths for Gamow-Teller (GT) transitions from ^{132}Sn leading to ^{132}Sb exhibit the GT giant resonance (GTR) at the excitation energy of 16.3±0.4(stat)±0.4(syst) MeV with the width of Γ=4.7±0.8 MeV. The integrated GT strength up to E_{x}=25 MeV is S_{GT}^{-}=53±5(stat)_{-10}^{+11}(syst), corresponding to 56% of Ikeda's sum rule of 3(N-Z)=96. The present result accurately constrains the Landau-Migdal parameter as g^{'}=0.68±0.07, thanks to the high sensitivity of the GTR energy to g^{'}. In combination with previous studies on the GTR for ^{90}Zr and ^{208}Pb, the result of this work shows the constancy of this parameter in the nuclear chart region with (N-Z)/A=0.11 to 0.24 and A=90 to 208.

This corrects the article DOI: 10.1103/PhysRevLett.119.192501.

Background Methotrexate (MTX) is a well-known anchor drug for rheumatoid arthritis (RA); however, dose regimens vary. We previously reported in EULAR2015 that split dose weekly oral methotrexate induced elevation of AST and ALT in association with elevation of MTX with 2 glutamates (MTX-PG2) in a single-centre trial. Objectives We performed a multi-centre randomised controlled trial to compare the incidence of adverse events using single and split dose regimens. Methods Six hospitals and 2 rheumatology clinics participated in this study. Seventy-eight patients with insufficient control on MTX 8 mg/week were randomly assigned to 2 groups, i.e., a single weekly dose regimen with 39 patients and a 3 dose per week regimen with 39 patients. The MTX dose in all patients was gradually increased to 16 mg/week. The primary endpoint was the occurrence of liver dysfunction during the observation period (20 weeks). Other endpoints included the incidence of adverse events and the changes from baseline in the disease activity score (DAS28) based on ESR or CRP, the Simplified Disease Activity Index (SDAI), and MTX-PG at week 20. Results There were no differences between the groups in baseline data and MTX dose at 20 weeks (single dose: 10.2±0.8 vs. 3-dose: 10.2±0.9 mg/week). Liver dysfunction occurred in 3 patients (7.7%) receiving the single dose regimen and in 5 patients (13.2%) receiving the 3-dose regimen, but there was no significant difference in the incidence in both groups (p=0.455). There was a significant difference in the incidence of adverse events (gastrointestinal disorder was most common) between single dose (11 patients, 28.9%) and 3-dose (20 patients, 52.6%) regimens (p=0.036). There was no significant difference in the changes from baseline in DAS28-ESR (−1.55 vs. −1.36), DAS28-CRP (−1.31 vs. −1.26), or SDAI (−9.45 vs. −10.11). Compared to the single dose regimen, MTX-PG2 was significantly increased in the 3-dose regimen, and MTX-PG3, -PG4, and -PG5 were significantly increased in the single dose regimen (table 1). Conclusions There were no differences in the incidence of liver dysfunction and efficacy according to the oral MTX dose regimen; however, split weekly dosing compared with single weekly dosing reduced polyglutamylation and increased the risk of adverse events. Acknowledgements Clinical registration: UMIN000021157 Disclosure of Interest Y. Yoshioka: None declared, K. Katayama: None declared, T. Kasama: None declared, M. Sato: None declared, S. Ohno: None declared, Y. Amasaki: None declared, H. Kataoka: None declared, D. Kanai: None declared, A. Suda: None declared, M. Okamoto Employee of: AYUMI Pharmaceutical Corporation, M. Sasano: None declared, S. Nagaoka: None declared, A. Sagawa: None declared

Excited states in 63,65,67Mn were studied via in-beam γ-ray spectroscopy following knockout reactions from 68Fe. Similar level schemes, consisting of the 11/2−, 9/2−, 7/2− and 5/2g.s.− level sequence, connected by I→I−1 transitions, were established, the first time for 65,67Mn. Their level structures show features consistent with strongly-coupled rotational bands with K=5/2. State-of-the-art shell-model calculations with the modified LNPS effective interaction reproduce the observed levels remarkably well and suggest the dominance of 4-particle-4-hole neutron configurations for all the states. The data on the low-lying excited states of odd-mass 53−67Mn provide a textbook example of nuclear structure evolution from weak coupling through decoupling to strong coupling along a single isotopic chain on the n-rich side of the β stability line. These results help to deepen our understanding of the N=40 “island of inversion”. Keywords: In-beam γ-ray spectroscopy, “Island of inversion” around N=40, Strong coupling, Structure evolution

We report the local structure and the magnetic properties of a Co-doped TiO2 prepared by using the solid state reaction of milling with subsequent annealing. The Co-doped TiO2 shows a hysteresis behavior in the magnetization curve at room temperature, which maintains the same rutile-type structure as that of the starting material TiO2. The extended x-ray absorption fine structure measurement reveals that it contains some oxygen vacancies only around a Co atom which occupies a Ti site. This supports the oxygen vacancy mediated ferromagnetic exchange mechanism.

Gamow–Teller (GT) states in N = Z nuclei with the mass number A from 48 to 64 are studied by using Hartree–Fock–Bogoliubov + quasi-particle random phase approximation ( HFB + QRPA ) with Skyrme interactions. The isoscalar spin-triplet ( T = 0 , S = 1 ) pairing interaction is taken into account in QRPA calculations. It is found in the context of SU(4) symmetry in the spin–isospin space that the GT strength of lower energy excitations is largely enhanced by the T = 0 pairing interaction which works cooperatively with the T = 1 pairing interaction in the ground state. A two-peaked structure observed recently in ( p , n ) reaction on 56Ni can be considered as a manifestation of the role of T = 0 pairing in the GT collective states.

The spin magnetic dipole transitions and the neutron-proton spin-spin correlations in $sd\text{\ensuremath{-}}\mathrm{shell}$ even-even nuclei with $N=Z$ are investigated using shell-model wave functions. The isoscalar spin-triplet pairing correlation provides a substantial quenching effect on the spin magnetic dipole transitions, especially the isovector (IV) ones. Consequently, an enhanced isoscalar spin-triplet pairing interaction influences the proton-neutron spin-spin correlation deduced from the difference between the isoscalar (IS) and the IV sum rule strengths. The effect of the $\mathrm{\ensuremath{\Delta}}$ (${\mathrm{\ensuremath{\Delta}}}_{33}$ resonance)--hole coupling is examined in the IV spin transition and the spin-spin correlations of the ground states.

The Low Energy Neutron Detector Array (LENDA) is a neutron time-of-flight (TOF) spectrometer developed at the National Superconducting Cyclotron Lab- oratory (NSCL) for use in inverse kinematics experiments with rare isotope beams. Its design has been motivated by the need to study the spin-isospin response of unstable nuclei using (p, n) charge-exchange reactions at intermediate energies (> 100 MeV/u). It can be used, however, for any reaction study that involves emission of low energy neutrons (150 keV - 10 MeV). The array consists of 24 plastic scintillator bars and is capable of registering the recoiling neutron energy and angle with high detection efficiency. The neutron energy is determined by the time-of-flight technique, while the position of interaction is deduced using the timing and energy information from the two photomultipliers of each bar. A simple test setup utilizing radioactive sources has been used to characterize the array. Results of test measurements are compared with simulations. A neutron energy threshold of < 150 keV, an intrinsic time (position) resolution of \sim 400 ps (\sim 6 cm) and an efficiency > 20 % for neutrons below 4 MeV have been obtained., Version accepted for publication in Nucl. Instr. Methods A. Revised text, 2 new figures added (one in section 4 and one in section 7)

The composition and energy spectrum of primary cosmic rays (PCRs) are the only observables available at ultra-high energies to understand the nature of sources accelerating protons and other nuclei to 1000 TeV and beyond. These observables have been measured up to 1000 TeV, directly with detectors flown aboard balloons and satellites. The measurements at > 1000 TeV are obtained indirectly, from ground based observations of extensive air showers (EAS). However, their interpretation depends on rather inadequate knowledge of hadronic interactions at > 1000 TeV . The GRAPES-3 experiment has been designed to study the EAS at ∼ 30 TeV to provide a sizable overlap with the results from direct measurements, enabling selection of a suitable model of hadronic interactions. We present here the salient features of GRAPES-3 experiment and some details of muon multiplicity distributions (MMDs) observed with a 560 m2 muon detector as a function of shower size ( N e ) fro analysis of 560 days of data. A comparison of GRAPES-3 results with direct measurements over the energy region 100 – 1000 TeV is presented to show the suitability of hadronic interaction generator “SIBYLL” for the interpretation of EAS data. We presented the energy spectrum of five nuclear groups (H, He, N, Al and Fe) with good statistics for 100 – 10, 000 TeV.

We report on the measurement of the first 2(+) and 4(+) states of (66)Cr and (70,72)Fe via in-beam γ-ray spectroscopy. The nuclei of interest were produced by (p,2p) reactions at incident energies of 260 MeV/nucleon. The experiment was performed at the Radioactive Isotope Beam Factory, RIKEN, using the DALI 2γ-ray detector array and the novel MINOS device, a thick liquid hydrogen target combined with a vertex tracker. A low-energy plateau of 2(1)(+) and 4(1)(+) energies as a function of the neutron number was observed for N≥38 and N≥40 for even-even Cr and Fe isotopes, respectively. State-of-the-art shell model calculations with a modified Lenzi-Nowacki-Poves-Sieja (LNPS) interaction in the pfg(9/2)d(5/2) valence space reproduce the observations. Interpretation within the shell model shows an extension of the island of inversion at N=40 for more neutron-rich isotopes towards N=50.

A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction ^{4}He(^{8}He,^{8}Be) at 186 MeV/u. The energy of the state is 0.83±0.65(stat)±1.25(syst) MeV above the threshold of four-neutron decay with a significance level of 4.9σ. Utilizing the large positive Q value of the (^{8}He,^{8}Be) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently.

We report on the measurement of the first 2(+) and 4(+) states of (66)Cr and (70,72)Fe via in-beam γ-ray spectroscopy. The nuclei of interest were produced by (p,2p) reactions at incident energies of 260 MeV/nucleon. The experiment was performed at the Radioactive Isotope Beam Factory, RIKEN, using the DALI 2γ-ray detector array and the novel MINOS device, a thick liquid hydrogen target combined with a vertex tracker. A low-energy plateau of 2(1)(+) and 4(1)(+) energies as a function of the neutron number was observed for N≥38 and N≥40 for even-even Cr and Fe isotopes, respectively. State-of-the-art shell model calculations with a modified Lenzi-Nowacki-Poves-Sieja (LNPS) interaction in the pfg(9/2)d(5/2) valence space reproduce the observations. Interpretation within the shell model shows an extension of the island of inversion at N=40 for more neutron-rich isotopes towards N=50.

Certain aspects of ultra-high energy (UHE) cosmic ray astrophysics require correlated studies on the electron and muon components of air showers, namely, the search for cosmic ray sources through γ -ray astronomy and studies on the variation of the nuclear composition of primary cosmic rays with energy. While studies on the electron component provide basic information about the arrival direction and energy, it is the muon component that plays a crucial role in distinguishing primary γ -rays from charged cosmic ray particles and in determining the composition. A large area (560 m 2 ), tracking muon detector of the GRAPES-3 experiment, operating at Ooty in southern India, has been designed for detailed studies on both of these aspects of UHE cosmic ray astrophysics. We present here the details of the muon detector, associated electronics and the data acquisition system. A brief discussion of the potential of the muon detector is presented through simulation studies.

The high resolution Fly’s Eye (HiRes) detector in Dugway, Utah, is an air fluorescence detector designed for the measurement of the energy and arrival direction of cosmic ray particles with energy E >10 18 eV. HiRes monitors the night sky for fluorescence light from air shower cascades induced by cosmic ray primaries. The light is collected by mirrors and projected onto arrays of photomultiplier tubes that provide an image of the air shower. HiRes is an astronomical instrument, and the accuracy of the mirror pointing and understanding of the optical properties of the mirror–camera units is crucial. We present a method to cross-check and monitor the mirror pointing by using star light. A star crossing the field of view of a photomultiplier tube causes a temporary increase in the total light detected by the tube. Using UV bright stars, we analyze the pointing accuracy of the HiRes 2 detector, and evaluate the shape of a point-like object as a function of distance to the mirror axis.

The origin of the highest energy cosmic rays (≥1020 eV) is not well understood. Interesting models called "top-down" scenarios have been proposed to explain the origin. The γ-ray flux in ultra-high-energy cosmic rays is a key parameter for giving constraints on such models. To study the properties of γ-ray showers, we carry out simulation studies that take into account both the Landau-Pomeranchuk-Migdal effect and electromagnetic interactions in the geomagnetic field. Based on an analysis of muons in air showers observed by the Akeno Giant Air Shower Array, the upper limits on the γ-ray flux are estimated to be 28% above 1019 eV and 67% above 1019.5 eV in the observed air showers at a confidence level of 95%. Above 1020 eV, the primary composition is in agreement with an extrapolation from lower energies, and there is no indication that the observed events are mostly γ-ray showers. These results provide observational constraints for origin models up to the highest energies.

We have observed flares of TeV-gamma rays from Mrk501 in 1997 using three telescopes of the Utah Seven Telescope Array at Dugway, Utah. Determination of the energy spectrum from such Active Galactic Nuclei (AGN) is very important, because the gamma-ray spectrum is expected to steepen around 10 TeV from objects like Mrk501 by the interaction of the infrared photons. We have developed the method to estimate energies of the gamma rays by stereoscopic analysis using multiple telescopes. The differential index of the energy spectrum obtained is well expressed by −2.5 between 700 GeV and 3 TeV. This spectrum seems to become steeper above several TeV.

We will report the observations of TeV gamma ray flares from Markarian 501 using Telescope Array Prototype. The observation were carried out continuously from the end of March to the end of July in 1997. The energy spectrum, and the time variation of the gamma ray intensities are shown. The intensity has been changed by the order of magnitude in this period and the possible quasi periodic oscillation of 12.7days were discovered., 16 pages, 4 figures

Protein Fv (pFv) is a recently described 175-kD gut-associated sialoprotein with a potent capacity for augmentation of antibody-dependent immune functions. To investigate the molecular basis for Fab-mediated binding of pFv, we evaluated a panel of 52 monoclonal IgM and found that approximately 40% bound pFv. Whereas the majority (> or = 75%) of V H3 and V H6 IgM strongly bound pFv, only a small minority (< 20%) of IgM from other V H families bound pFv, and these antibodies had weaker binding interactions. Inhibition studies suggested that all binding occurred at the same (or overlapping) site(s) on pFv. Surface plasmon resonance studies demonstrated binding affinity constants up to 6.7 x 10(8) M-1 for pFv. Biopanning of IgM and IgG Fab phage-display libraries with pFv preferentially selected for V H3 and V H6 antibodies, but also obtained certain V H4 IgM. V H sequence analyses of 36 pFv-binding antibodies revealed that binding did not correlate with CDR sequence, JH, or L chain usage. However, there was preferential selection of pFv binders with V H CDR3 of small size. These studies demonstrate that a protein which enhances immune defense in the gut has structural and functional properties similar to known superantigens.

Background: Gamow-Teller (GT) transition strength distributions in stable and unstable $pf$-shell isotopes are key inputs for estimating electron-capture rates important for stellar evolution. Charge-exchange experiments at intermediate beam energies have long been used to test theoretical predictions for GT strengths, but previous experiments were largely restricted to stable nuclei. Since a large fraction of the nuclei relevant for astrophysical applications (including key nuclei such as ${}^{56}$Ni) are unstable, new methods are needed to perform charge-exchange experiments in inverse kinematics with unstable isotopes.Purpose: The ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were measured in inverse kinematics in order to extract GT strengths for transitions to ${}^{56}$Cu and ${}^{55}$Ni, respectively. The extracted strength distributions were compared with shell-model predictions in the $pf$ shell using the KB3G and GXPF1J interactions. By invoking isospin symmetry, these strength distributions are relevant for electron captures on the ground states of ${}^{56}$Ni and ${}^{55}$Ni to final states in ${}^{56}$Co and ${}^{55}$Co, respectively.Method: Differential cross sections and excitation energy spectra for the ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were determined by measuring neutrons recoiling from a liquid hydrogen target into the Low Energy Neutron Detector Array. GT contributions to the spectra were extracted by using a multipole decomposition analysis and were converted to strengths by employing the proportionality between GT strength and differential cross section at zero linear momentum transfer.Results: GT strengths from ${}^{56}$Ni and ${}^{55}$Co were extracted up to excitation energies of 8 and 15 MeV, respectively. Shell-model calculations performed in the $pf$ shell with the GXPF1J interaction reproduced the experimental GT strength distributions better than calculations with the KB3G interaction.Conclusions: A new technique for measuring ($p,n$) charge-exchange reactions on unstable nuclei was successfully developed. It can be used to study the isovector response of unstable nuclei in any mass region and for excitation energies beyond the particle decay threshold. In the first experiment, ${}^{56}$Ni($p,n$) and ${}^{55}$Co($p,n$) reactions were studied and GT transition strengths were extracted for the purpose of testing shell-model calculations used to estimate electron-capture rates in simulations of late stellar evolution. The calculation using the GXPF1J interaction was found to best reproduce the experimental strength distribution.

The double-differential cross sections for the (208)Pb and (90)Zr(t,(3)He) reactions at 300 MeV/u have been measured at the RI Beam Factory at RIKEN. This was the first physics experiment with the SHARAQ magnetic spectrometer. The combined analysis of the present (t,(3)He) data and previous (n,p) data provides the clearest identification for the β(+) isovector spin monopole resonance both in the (208)Tl and (90)Y nuclei, and puts the observations of this giant resonance on a firm foundation. The measured distributions of the (t,(3)He) monopole cross sections were well reproduced by the distorted-wave Born approximation calculation, where the target transition density was calculated with the self-consistent Hartree-Fock plus random-phase approximation using the T43 Skyrme interaction. A major part of the expected β(+) isovector spin monopole strength was found in the measured cross section spectra.

A new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate energies on unstable isotopes was successfully developed and used to study the (56)Ni(p,n) reaction at 110 MeV/u. Gamow-Teller transition strengths from (56)Ni leading to (56)Cu were obtained and compared with shell-model predictions in the pf shell using the KB3G and GXPF1A interactions. The calculations with the GXPF1A interaction reproduce the experimental strength distribution much better than the calculations that employed the KB3G interaction, indicating deficiencies in the spin-orbit and proton-neutron residual potentials for the latter. The results are important for improving the description of electron-capture rates on nuclei in the iron region, which are important for modeling the late evolution of core-collapse and thermonuclear supernovae.

A new technique to measure (p,n) charge-exchange reactions in inverse kinematics at intermediate energies on unstable isotopes was successfully developed and used to study the (56)Ni(p,n) reaction at 110 MeV/u. Gamow-Teller transition strengths from (56)Ni leading to (56)Cu were obtained and compared with shell-model predictions in the pf shell using the KB3G and GXPF1A interactions. The calculations with the GXPF1A interaction reproduce the experimental strength distribution much better than the calculations that employed the KB3G interaction, indicating deficiencies in the spin-orbit and proton-neutron residual potentials for the latter. The results are important for improving the description of electron-capture rates on nuclei in the iron region, which are important for modeling the late evolution of core-collapse and thermonuclear supernovae.

Unconventional Ag for B cells that are comparable to known superantigens for T lymphocytes have not been well characterized. However, the bacterial membrane protein, Staphylococcal protein A (SpA), has sites that interact with the Fab of many IgM, IgA, IgG, and IgE, and in recent reports we have provided evidence of VH restriction in Fab that bind SpA. To investigate the molecular basis for this Fab binding specificity, we have selected monoclonal Fab from a phage-display combinatorial Ig library, based on the ability to bind SpA. By this approach, in an unselected human polyclonal IgG Fab library, about 17% of antibody-expressing clones were found to bind SpA. SpA binding was completely restricted to Fab with VH3 H chains, and about 60% of VH3 Fab in the unselected library had SpA binding capacity. Analysis of 21 VH sequences and 6 VL sequences demonstrated that Fab that bind SpA use diverse VH3 genes, while the L chains derive from a variety of V kappa and V lambda gene families. By creation of antibodies with differential H-L chain pairing, the global capacity to bind SpA was shown to be dictated by VH3 usage, but different L chain usage could result in up to a fourfold change in binding affinity. The apparent KD of the SpA binding by different Fab ranged from 2.5 x 10(-7) to > 10(-5) M. Furthermore, repeated rounds of in vitro panning selected for antibodies based on higher binding affinity. These data indicate that the pattern of VH family restriction of Ig reactive with SpA is comparable to known superantigens, and there is a hierarchy within the binding affinities of VH3 Fab based on V gene usage.

We have recently demonstrated that there is a site on Staphylococcal protein A (SpA) that interacts with B cell Ig receptors in a manner comparable with known T cell superantigens, because this binding specificity is restricted to Fab with VH3 H chains and most VH3 Ig bind SpA. In the present studies, SpA was used as a phenotypic marker for VH3 expression by human lymphoid cells. As expected, this Fab-mediated binding specificity was completely inhibited by certain VH3 antibodies but not by antibodies from other VH families. In multiparameter flow cytometric analyses, this binding activity was demonstrated to be highly prevalent among B cells (14 to 54%), and was more common among IgM-bearing B cells compared with IgG-bearing B cells. In all studies, Fab-mediated binding of SpA was uniformly expressed by a greater proportion of CD5-positive B cells than CD5-negative B cells. The proportion of B lymphocytes with this VH3-restricted binding capacity was found to undergo age-associated changes, because a large proportion of the peripheral B cells of neonates (mean +/- SD, 46.0 +/- 2.9%) bind this site, but two 10-mo-old subjects and older children had significantly lower binding levels (29.0 +/- 3.5%) that were the same as binding levels by adult peripheral B lymphocytes (30.2 +/- 3.3%). In immunohistochemical studies, tonsilar B cells that bind this site on SpA were shown to be common in mantle zones and germinal centers of secondary follicles. We speculate that Fab-mediated SpA binding represents a fundamental and primitive binding capacity that is part of the human preimmune repertoire, and we discuss the implications for the observed age-dependent shift in Fab-mediated binding of SpA by peripheral blood B cells.