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Abstract: Single-particle properties of low-lying resonance levels in 14O have been studied efficiently by utilizing a technique of proton elastic resonance scattering with a 13N secondary beam and a thick proton target. The excitation functions for the elastic scattering were measured over a wide energy range of and fitted with an R-matrix calculation. A clear assignment of has been made for the level at in 14O for the first time. The excitation functions show a signature of a new level at with . The excitation energies and widths of the 14O levels are discussed in conjunction with the spectroscopic structure of nuclei with . [Copyright &y& Elsevier]

Resonance states in 12N were studied by using the resonance elastic scattering of 11C+p with a low-energy radioactive ion beam of 11C at 3.5 MeV/nucleon and a thick (CH2)n target. The 11C beam was separated by a newly installed CNS radioactive ion beam separator (CRIB). The energy spectrum of recoil protons was measured at laboratory scattering angles around θLAB=0° to identify resonance states in 12N. The spin-parity values of Jπ=3− and (2)+ have been determined for the levels at the excitation energies of Ex=3.1 and 3.6 MeV in 12N, respectively, suggesting a small contribution of the 3.1-MeV level to the 11C(p, γ)12N stellar reaction. [Copyright &y& Elsevier]

Abstract: A new measurement of proton resonance scattering on 7Be was performed up to the center-of-mass energy of 6.7 MeV using the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator) at the Center for Nuclear Study of the University of Tokyo. The excitation function of elastic scattering above 3.5 MeV was measured successfully for the first time, providing important information about the resonance structure of the 8B nucleus. The resonances are related to the reaction rate of 7Be()8B, which is the key reaction in solar 8B neutrino production. Evidence for the presence of two negative parity states is presented. One of them is a state observed as a broad s-wave resonance, the existence of which had been questionable. Its possible effects on the determination of the astrophysical S-factor of 7Be()8B at solar energy are discussed. The other state had not been observed in previous measurements, and its spin and parity were determined as . [Copyright &y& Elsevier]

Background: Type I x-ray bursts are the most frequently observed thermonuclear explosions in the galaxy, resulting from thermonuclear runaway on the surface of an accreting neutron star. The 30S(α,p) reaction plays a critical role in burst models, yet insufficient experimental information is available to calculate a reliable, precise rate for this reaction. Purpose: Our measurement was conducted to search for states in 34Ar and determine their quantum properties. In particular, natural-parity states with large α-decay partial widths should dominate the stellar reaction rate. Method: We performed the first measurement of 30S+α resonant elastic scattering up to a center-of-mass energy of 5.5 MeV using a radioactive ion beam. The experiment utilized a thick gaseous active target system and silicon detector array in inverse kinematics. Results: We obtained an excitation function for 30S(α,α) near 150° in the center-of-mass frame. The experimental data were analyzed with R-matrix calculations, and we observed three new resonant patterns between 11.1 and 12.1 MeV, extracting their properties of resonance energy, widths, spin, and parity. Conclusions: We calculated the resonant thermonuclear reaction rate of 30S(α,p) based on all available experimental data of 34Ar and found an upper limit about one order of magnitude larger than a rate determined using a statistical model. The astrophysical impact of these two rates has been investigated through one-zone postprocessing type I x-ray burst calculations. We find that our new upper limit for the 30S(α,p)33Cl rate significantly affects the predicted nuclear energy generation rate during the burst. [ABSTRACT FROM AUTHOR]

Background: The properties of resonances in 26Si are important to better constrain the 25Al(p,γ)26Si reaction rate relevant to the synthesis of galactic 26Algs and energy generation in explosive stellar environment at higher temperature. Purpose: 21Al + p elastic scattering was measured to further constrain and investigate disagreements in resonance parameters for the high-lying excited states of 26Si with high statistics and without background contamination within the target. Methods: The experiment was performed by bombarding a thick H2 target with an 25Al radioactive ion beam. The resonances at excitation energies of 6.6-8.3 MeV in the 26Si compound nucleus were studied at the low-energy radioactive-ion beam facility CRIB (Center for Nuclear Study Radioactive Ion Beam separator) at the University of Tokyo. Results: Six resonant states were observed and their resonance parameters were extracted by an R-matrix analysis. Our resonance parameters for two levels are in good agreement with the results of previous studies, while for four others, excitation energy, proton partial width, and spin-parity assignment disagree with the results of recent study via elastic scattering of 25Al + p. Conclusion: The parameters of resonant states in 26Si determined in the present work for the 25Al(p,γ)26Si reaction rate are consistent with that of the previous result, solving spin-parity assignment discrepancies between experiments, relevant at higher temperatures. [ABSTRACT FROM AUTHOR]

The 14O(αp)17F reaction is one of the key reactions involved in the breakout from the hot-CNO cycle to the rp-process in type-I x-ray bursts (XRBs). The resonant properties in the compound nucleus 18Ne have been investigated through resonant elastic scattering of 17F+p. The radioactive 17F beam was separated by the Center for Nuclear Study radioactive ion beam separator (CRIB) and bombarded a thick H2 gas target at 3.6 MeV/nucleon. The recoiling hght particles were measured by three Δ E-E silicon telescopes at laboratory angles of Θ1ab ≈3°, 10°, and 18°. Five resonances at Ex = 6.15, 6.28, 6.35, 6.85, and 7.05 MeV were observed in the excitation functions, and their spin-parities have been determined based on an R-matrix analysis. In particular, Jπ = 1- was hrmly assigned to the 6.15-MeV state which dominates the thermonuclear 140 (αp)17F rate below 2 GK. As well, a possible new excited state in 18Ne was observed at Ex = 6.85 ± 0 .1 1 MeV with tentative 7 = 0 assignment. This state could be the analog state of the 6.880 MeV (0-) level in the mirror nucleus 180, or a bandhead state (0+) of the six-particle four-hole (6p-4h) band. A new thermonuclear 140 (α,p)17F rate has been determined, and the astrophysical impact of multiple recent rates has been examined using an XRB model. Contrary to previous expectations, we find only a modest impact on predicted nuclear energy generation rates from using reaction rates differing by up to several orders of magnitude. [ABSTRACT FROM AUTHOR]

The 18Ne(α,p)21Na reaction is thought to be one of the key breakout reactions from the hot CNO cycles to the rp process in type I x-ray bursts. In this work, the resonant properties of the compound nucleus 22Mg have been investigated by measuring the resonant elastic scattering of 21Na + p. An 89-MeV 21Na radioactive beam delivered from the CNS Radioactive Ion Beam Separator bombarded an 8.8 mg/cm² thick polyethylene (CH2)n target. The 21Na beam intensity was about 2 × 105 pps, with a purity of about 70% on target. The recoiled protons were measured at the center-of-mass scattering angles of θc.m. ≈ 175.2°, 152.2°, and 150.5° by three sets of ΔE-E telescopes, respectively. The excitation function was obtained with the thick-target method over energies Ex(22Mg) = 5.5-9.2 MeV. In total, 23 states above the proton-threshold in 22Mg were observed, and their resonant parameters were determined via an R-matrix analysis of the excitation functions. We have made several new Jα assignments and confirmed some tentative assignments made in previous work. The thermonuclear 18Ne(α,p)21Na rate has been recalculated based on our recommended spin-parity assignments. The astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the 18Ne(α,p)21Na rate significantly affects the peak nuclear energy generation rate, reaction fluxes, and onset temperature of this breakout reaction in these astrophysical phenomena. [ABSTRACT FROM AUTHOR]

The 18Ne(a,p)21Na reaction provides a pathway for breakout from the hot CNO cycles to the rp process in type-I x-ray bursts. To better determine this astrophysical reaction rate, the resonance parameters of the compound nucleus 22Mg have been investigated by measuring the resonant elastic scattering of 21Na+p. An 89 MeV 21Na radioactive ion beam was produced at the CNS Radioactive Ion Beam Separator and bombarded an 8.8 mg/cm2 thick polyethylene target. The recoiled protons were measured at scattering angles of θc.m.~175° and 152¯ by three θE-E silicon telescopes. The excitation function was obtained with a thick-target method over energies Ex(22Mg) = 5.5-9.2 MeV. The resonance parameters have been determined through an R-matrix analysis. For the first time, the Jπ values for ten states above the a threshold in 22Mg have been experimentally determined in a single consistent measurement. We have made three new Jπ assignments and confirmed seven of the ten tentative assignments in the previous work. The 18Ne(a,p)21Na reaction rate has been recalculated, and the astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the 18Ne(a,p)21Na rate significantly affects the peak nuclear energy generation rate and the onset temperature of this breakout reaction in these phenomena. [ABSTRACT FROM AUTHOR]

Neutron single-particle states in the neutron-rich nucleus 35Si, which is located beside the N = 20 shell breaking nucleus 32Mg, were investigated through their isobaric analog resonances. The excitation function for 34Si+p elastic scattering was measured around 0d in the laboratory frame by the thick target inverse kinematics method with a 34Si beam around 5 MeV/nucleon and a thick polyethylene target. Eight resonances were successfully observed. Angular momenta and proton and total widths of the resonances were assigned using R-matrix analysis. With the help of information of the β decay study, six isobaric analog resonances were identified. Spectroscopic factors and spin-parities of the corresponding parent states in 35Si are presented. [ABSTRACT FROM AUTHOR]

25A1 + p elastic scattering in inverse kinematics was measured to explore the level structure of 26Si above its proton threshold. The 2H(24Mg, n) 25A1 reaction was used to produce a 3.4 MeV/nucleon 25A1 radioactive beam with intensities of about 106 ions per second on target. By using a thick target of (CH2)n, a center-of-mass energy range of 3 MeV was scanned, reaching up to about 8.5 MeV in excitation energy in 26Si. This energy range covered the region of importance for the 25Al(p, &ggr;)26Si at temperatures characteristic of explosive nucleosynthesis. Level parameters of six strong s-wave 25Al + p resonances in 26Si were extracted from fits to the measured excitation functions using the R-matrix formalism. Two new levels have been discovered, while for two others, our spin-parity assignments disagree with the results of some previous studies. Lastly, our resonance parameters for the remaining two levels are in good agreement with past experimental work, and with recent shell-model calculations. [ABSTRACT FROM AUTHOR]

Abstract: The astrophysically important states in 26Si have been studied with different reactions because of their dominant contribution to the 25Al(p,γ)26Si reaction rate at nova temperatures. We performed two different experiments to study the states of interest in 26Si, with the aim of reducing the main uncertainty in the current 25Al(p,γ)26Si rate by determining the level parameters of the dominant states more accurately. One is the p(27Si,26Si*)d experiment at NSCL, in which we measured the gamma-ray decays from the excited states in 26Si. The other one is the 25Al+p elastic scattering experiment with CRIB at RIKEN. [Copyright &y& Elsevier]