Branching ratio Γα/Γγ of the 4.033 MeV 3/2+ state in 19Ne

The branching ratio Γα/Γγ of the 4.033 MeV 3/2+ state in 19Ne plays a crucial role in the breakout from the hot CNO cycle into the rapid proton capture process. This ratio has been studied by making use of the advantages of inverse kinematics. The state was populated via the 3He(20Ne,α) 19Ne* reaction and its decay via γ or α emission was measured by detecting the heavy reaction products (19Ne or 15O) in coincidence in a magnetic spectrograph. An upper limit Γα/Γγ≤6×10-4 has been obtained. With these results, the astrophysical reaction rate for the 15O (α, γ) 19Ne reaction has been calculated. Its influence on the breakout at various astrophysical sites, novas, x-ray bursts, and supermassive stars, is discussed

Search for excited states in He7 with the (d,p) reaction

We have studied the properties of low-lying levels in He7 using the H2(He6,p)He7 reaction at 11.5 MeV/u. This reaction probes the He6g.s.+n character of states in He7. The ground state was populated with a spectroscopic factor comparable to that obtained from ab initio calculations, supporting the tentative spin-parity assignment of 3/2- in the literature. In addition to the ground state, a broad structure is observed between EX=2-3 MeV, the excitation-energy range expected for the 1/2- state in He7. No evidence was found for a lower-lying, first-excited state reported recently

Neutron spectroscopic factors in9Li from2H( 8Li, p)9Li

We have studied the 2H(8Li, p)9Li reaction to obtain information on the spins, parities, and single-neutron spectroscopic factors for states in 9Li, using a radioactive 8Li beam. The deduced properties of the lowest three states are compared to the predictions of a number of calculations for the structure of 9Li. The results of ab initio quantum Monte Carlo calculations are in good agreement with the observed properties

Determination of the E1 component of the low-energy C12(α,γ)O16 cross section

A measurement of the β-delayed α decay of N16 using a set of twin ionization chambers is described. Sources were made by implantation, using a N16 beam produced via the In-Flight Technique. The energies and emission angles of the C12 and α particles were measured in coincidence and very clean α spectra, down to energies of 450 keV, were obtained. The structure of the spectra from this experiment is in good agreement with results from previous measurements. An analysis of our data with the same input parameters as used in earlier studies gives SE1(300)=86±22 keVb for the E1 component of the S-factor. This value is in excellent agreement with results obtained from various direct and indirect measurements. In addition, the influence of new measurements including the phase shift data from Tischhauser on the value of SE1(300) is discussed

First evidence of fusion hindrance for a small Q-value system

The excitation function for the fusion-evaporation reaction 28Si + 64Ni has been measured down to a cross section of 25 nb. This is the first observation of fusion hindrance at extreme sub-barrier energies for a system with a small, negative Q-value (- 1.78 MeV). This result is further proof that heavy-ion fusion hindrance, reported earlier only for systems with large, negative Q-values, is a general phenomenon. The measured behavior can be reproduced by coupled-channels calculations with a modified ion-ion potential incorporating the effects of nuclear incompressibility

New determination of the astrophysical S factor SE1 of the C12(α,γ)O16 reaction

A new measurement of the β-delayed α decay of N16 has been performed using a set of high efficiency ionization chambers. Sources were made by implantation of a N16 beam, yielding very clean α spectra down to energies as low as 400 keV. Our data are in good agreement with earlier results. For the S factor SE1, we obtain a value of 74±21keVb. In spite of improvements in the measurement, the error in SE1 remains relatively large because of the correlations among the fit parameters and the uncertainties inherent to the extrapolation

Forensic analysis of tempered sheet glass by particle induced X-ray emission (PIXE)

The elemental concentrations of five trace elements in tempered sheet glass fragments were determined using particle-induced X-ray emission (PIXE) spectrometry. The trace element concentrations for calcium, iron, manganese, strontium, and titanium are compared to those obtained by inductively-coupled plasma-atomic emission spectrometry (ICP-AES) following complete digestion by hydrofluoric acid. For these five elements, the absolute concentrations obtained by both methods are shown to agree well over a wide range of concentrations. The limits of detection for trace elements are typically lower for the ICP-AES method. However, we show that the concentrations of these five elements can be accurately measured by the PIXE method. Since PIXE is an entirely non-destructive method, there exists a niche for this technique to be used as a complement to the more sensitive ICP-AES technique in the forensic analysis of sheet glass

First studies of the (8)B(alpha,p)(11)C reaction

The (8)B(alpha,p)(11)C reaction is part of the network that can bypass the triple a process leading to the production of (12)C. We have measured the astrophysical reaction rate for this reaction by studying the inverse (11)C(p,alpha)(8)B process. The radioactive (11)C beam was produced via the p((11)B,(11)C)n reaction using the in-flight facility at the ATLAS accelerator. The astrophysical reaction rate obtained from the excitation function measured in the energy range E(x)=8.8-10 MeV was found to be a factor of 10-50 higher than previous estimates

Structure of He7 by proton removal from Li8 with the (d,3He) reaction

We report on a study of the structure of the unbound nucleus He7 utilizing the proton-removal reaction 2H(8Li,3He)7He. Combining the present results with those of our prior measurements of the neutron-adding reaction 2H(6He,p)7He, a consistent picture emerges for the low-lying excitations in He7. Specifically, the negative-parity sequence of resonances, in order of excitation energies, is consistent with 3/2-,1/2-, and 5/2-. The stable-beam reactions 2H(7Li,t)6Li and 2H(7Li,3He)6He were also measured. The results are compared with the predictions of nuclear structure models, including those of ab initio quantum Monte Carlo calculations. © 2008 The American Physical Society