Proton-induced direct capture on 21Ne and 22Ne

The direct capture process in the reactions ²¹Ne(p, γ)²²Na and ²²Ne(p, γ)²³Na has been investigated at E_p = 0.3–1.6 MeV using neon gas enriched to 91 % in ²¹Ne and to 99 % in ²²Ne, respectively. The gas was recirculated in a differentially pumped gas target system of the extended-static and quasi-point supersonic jet type. For ²²Ne(p, γ)²³Na, the direct capture process has been observed to several final states in ²³Na up to E_x = 8.83 MeV excitation energy. The deduced spectroscopic factors C²S are in fair agreement with the corresponding values from stripping reactions. The capture transition into the ²³Na ground state exhibits broad structures, which resemble Ericson fluctuations. The data remove the previously reported discrepancies in C²S for the ²³Na ground state. The excitation functions for the ²¹Ne(p, γ)²²Na reaction are dominated by broad and intense resonances, which hampered the measurement of the direct capture process. The nuclear and astrophysical aspects of the results are discussed.     

Photoabsorption resonances of Na20, Na21Cl and Na22Cl2 clusters

Plasma resonance profiles in the visible part of the spectrum were measured by photoabsorption spectroscopy for the clusters Na₂₀, Na₂₁Cl and Na₂₂Cl₂ in a beam. The resonance positions in Na₂₀ and Na₂₁Cl are close, suggesting that the Cl^- ion does not locate at the center of the metallic droplet and does not strongly modify the effective valence electron density. The spectrum of Na₂₂Cl₂ is noticeably dissimilar to the other two, raising the possibility of structural differences and/or incomplete charge transfer.     

Coulomb dissociation studies for reactions in steady and explosive hydrogen burning

Radiative capture processes in steady and explosive hydrogen burning sometimes involve unstable nuclei. The Coulomb dissociation method has been used to determine the cross-sections of such reactions indirectly with intermediate-energy RI beams. Recent studies on reactions in the pp chain, hot pp chain and CNO cycle are discussed. Received: 1 May 2001 / Accepted: 4 December 2001     

Eikonal approximation for single-electron capture from hydrogen molecules by proton impact

A four-body eikonal approximation is developed to study the single-electron capture process in collision of the fast protons with the hydrogen molecular targets. For a fixed orientation of the molecular axis, the double-differential cross sections are evaluated for electron capture. Interference patterns originated from the two atomic centres are obtained for different orientations of the molecular target. Equal-weighted average of the differential capture cross sections over all the possible orientations of the molecular target is calculated for various impact energies. Angular distributions of the differential cross sections for single charge transfer at various impact energies as a function of the angle between the axis of the molecule and the incident beam direction are calculated and compared with their corresponding experimental values as well as the results obtained from other theories. Integrated cross sections are calculated and compared with available experimental data and other theoretical calculations.     

The electron capture to positron emission ratios in the decay of22Na and65Zn

The electron capture to positron emission ratios for allowed Gamow-Teller transitions from the decay of²²Na and⁶⁵Zn were measured. The values ?/gb⁺=0.1128±0.0057 andK/Β ⁺= 31.3±2.0 were obtained for²²Na and⁶⁵Zn, respectively. A detailed comparison with previous data is made. Theoretical ratios were calculated using the most recent Fermi and Coulomb functions. It was found an excellent agreement between our experimental data and the theoretical results evaluated without including contributions due to induced interactions.     

Electron capture in the collision of a proton with a hydrogen atom

Electron capture in the collision of a proton with a hydrogen atom is investigated. The probability of electron capture is calculated from first principles by the direct solving of the three-dimensional nonstationary Schr?dinger equation. The dependence of the probability of electron capture by a proton on the proton??s velocity and impact parameter is obtained and analyzed thanks to highly efficient computations with the use of graphic processing units.     

Muon capture on the proton and deuteron

By measuring the lifetime of the negative muon in pure protium (¹H), the MuCap experiment determines the rate of muon capture on the proton, from which the proton’s pseudoscalar coupling g _p may be inferred. A precision of 15% for g _p has been published; this is a step along the way to a goal of 7%. This coupling can be calculated precisely from heavy baryon chiral perturbation theory and therefore permits a test of QCD’s chiral symmetry. Meanwhile, the MuSun experiment is in its final design stage; it will measure the rate of muon capture on the deuteron using a similar technique. This process can be related through pionless effective field theory and chiral perturbation theory to other two-nucleon reactions of astrophysical interest, including proton-proton fusion and deuteron breakup. for the MuCap [1] and MuSun [2] Collaborations     

A study of the proton resonant property in 22Mg by elastic scattering of 21Na + p and its astrophysical implication in the 18Ne(α, p)21Na reaction rate

Proton resonances in ²²Mg have been investigated by the resonant elastic scattering of ²¹ Na + p . The ²¹Na beam with a mean energy of 4.00 MeV/nucleon was separated by the CNS radioactive-ion-beam separator (CRIB) and bombarded a thick ( CH_{2 n} target. The energy spectra of recoiled protons were measured at scattering angles of θ_c.m. ≈ 172^° , 146^° , respectively. Several excited states observed before have been confirmed including two states (at 6.616, 6.796 MeV) observed at TRIUMF. A new state at 7.06 MeV has been observed, and another new one at 7.28 MeV is tentatively identified due to its low statistics. The proton resonant parameters were deduced from an R -matrix analysis of the differential cross-section data with a SAMMY-M6-BETA code. The astrophysical implication for the ¹⁸ Ne(α, p)²¹ Na reaction has been briefly discussed.     

Radiative muon capture on hydrogen

The radiative capture of negative muons by protons can be used to measure the weak induced pseudoscalar form factor. Brief arguments why this method is preferable to ordinary muon capture are given followed by a discussion of the experimental difficulties. The solution to these problems as attempted by experiment #452 at TRIUMF is presented together with preliminary results from the first run in August 1990. An outlook on the expected final precision and the experimental schedule is also given. Talk presented by W. Bertl at the Symposium “The Future of Muon Physics” in Heidelberg, Germany, May 7–9, 1991     

21Na(p,gamma)22Mg reaction and oxygen-neon novae

The 21Na(p,gamma)22Mg reaction is expected to play an important role in the nucleosynthesis of 22Na in oxygen-neon novae. The decay of 22Na leads to the emission of a characteristic 1.275 MeV gamma-ray line. This report provides the first direct measurement of the rate of this reaction using a radioactive 21Na beam, and discusses its astrophysical implications. The energy of the important state was measured to be E(c.m.)=205.7+/-0.5 keV with a resonance strength omegagamma=1.03+/-0.16(stat)+/-0.14(sys) meV.     

Molecular dynamics of reactions between (4,0) zigzag carbon nanotube and hydrogen peroxide under extreme conditions

ABSTRACT

Single-wall carbon nanotubes (CNTs) have been suggested as potential materials for use in next-generation gas sensors. The sidewall functionalisation of CNTs facilitates gas molecule adsorption. In this study, density functional theory (DFT)-based ab initio molecular dynamics simulations are performed for a periodic zigzag single-wall (4,0) CNT surrounded by a monolayer of hydrogen peroxide molecules in an attempt to find conditions that favour sidewall functionalisation. The dependency of dynamics on charge states of the system is examined. It is found negative charges favour reactions that result in the functionalisation of the CNT. First principles molecular dynamics of defect formation yields chemically reasonable structure of stable defects, which can be reproduced in CNTs of any diameter and chirality. The explored hydroxyl and hydroperoxyl defects increase conductivity in a large diameter (10,0) CNT, while decrease conductivities in a small diameter (4,0) CNT.     

Search for low-energy resonances in 21Ne(p, γ)22Na and 22Ne(p, γ)23Na

The reactions ²¹Ne(p, γ)²²Na and ²²Ne(p, γ)²³Na have been investigated at E_p(lab) = 70–355keV. Neon gas enriched to 91% in ²¹Ne and to 99% in ²²Ne was recirculated in a differentially pumped gas target system of the extended-static and quasi-point supersonic jet type. For ²¹Ne(p, γ)²²Na, new resonances were found at E_p = 126, 272, 291 and 352 keV. The 291 keV resonance corresponds to a new unbound state in ²²Na. Excitation energies, γ-ray decay schemes, resonance widths and strengths as well as J^π assignments are reported for all the resonances. Information on low-lying states in ²²Na is also obtained. Of the 9 expected resonances in ²²Ne(p, γ)²³Na none has been observed. Upper limits on their ωγy strengths are presented. The astrophysical as well as the nulcear structure aspects of the results are discussed.     

Remeasurement of capture to positron decay ratios in22Na and65Zn and comparison with theory

In the decay of²²Na theEC/β ⁺ ratio for theβ-transition to the 1275 keV-level was measured to beEC/β ⁺=0.1050 (29). Single and coincidence counting was performed using a 16% Ge(Li) and an NaI well-type detector. For⁶⁵Zn theK/β ⁺ ratio for the ground state transitionK ₁/β ⁺=30.3 (10) was obtained using the same apparatus and in addition a 10 mm diam. × 5.4 mm Si(Li) detector. The results are compared with earlier experiments and with theory.     

Low-energy resonance strengths for proton capture on Mg and Al nuclei

Absolute strengths of selected low-energy resonances for proton captures on the nuclei ²⁴Mg, ²⁵Mg, ²⁶Mg and ²⁷Al have been determined. The experiments were carried out by measuring the number of resonant γ-rays, integrated over the yield curve, simultaneously with the number of Rutherford scattered protons. The method applied in the present work is independent of target stoichiometries and uniformities, stopping powers, beam straggling and current integration. The ratio of charged-particle and γ-ray detection efficiencies was measured by using the ¹⁹F(p,α₂γ)¹⁶O reaction at E_R=340 keV. A new set of reliable resonance strength standards at low bombarding energies is presented and our results are compared with previous work.     

Determination of the parton distributions and structure functions of the proton from neutrino and antineutrino reactions on hydrogen and deuterium

The analytic expressions for the production cross sections of polarized bottom and top quarks ine ^* e ^– annihilation are explicitly derived at the one-loop order of strong interactions. Chirality-violating mass effects will reduce the longitudinal spin polarization for the light quark pairs by an amount of 3%, when one properly considers the massless limit for the final quarks. Numerical estimates of longitudinal spin polarization effects in the processese ^* e ^–b (g) ande ^* e ^–t (g) are presented.supported in part by the BMFT, Germany under contract 06MZ730     

Effect of nuclear deformation on direct capture reactions

Direct radiative capture processes are well described by a spherical potential model. Since most nuclei are not spherical, and in order for the model to explain direct radiative captures more accurately, the effect of nuclear deformation has been analyzed with q-deformed Woods-Saxon potential in this work. The results imply that nuclear deformation largely affects the direct radiative capture, and it should be taken into account when discussing direct capture reactions.