Proton capture reaction of ³³S in nova V1065 Centauri

Previous studies have shown that 33 S(p, γ) 34 Cl is the most important reaction that affects the abundance of 33 S in the product of nova nucleosynthesis. In this paper, a more accurate thermonuclear reaction rate of 33 S(p, γ) 34 Cl in the nova is calculated based on the newly measured 34 Cl nuclear resonance levels. The electron screening correction and the non-resonance and narrow-resonance contributions are considered. The calculations are also combined with the recent observational data of nova V1065 Centauri and show that the thermonuclear reaction rates of 33 S(p, γ) 34 Cl are significantly different in the improved method. Because these results can affect the isotopic ratio of sulfur in the nova ejecta significantly, we make an estimate of the values of 32 S/ 33 S and 33 S/ 33 S ⊙ , which can be used as a diagnostic tool for the novae.     

Cross sections and thermonuclear reaction rates of proton-induced reactions on 37Cl

The yields of γ-rays from the reactions ³⁷Cl(p, γ)³⁸Ar and ³⁷Cl(p, αγ)³⁴S have been measured as a function of bombarding energy over the ranges 0.65–2.15 MeV and 1.25–2.15 MeV respectively, and the yield of neutrons from ³⁷Cl(p, n)³⁷Ar from threshold to 2.50 MeV. The results are compared with global statistical-model calculations and thermonuclear reaction rates are calculated for the temperature range 5 × 10⁸–10¹⁰ K. The significance of these thermonuclear reaction rates for stellar nucleosynthesis calculations is discussed.     

Étude des états excités du noyau 34Cl: (I). Courbe d'excitation de la réaction 33S(p, γ)34Cl, énergies,rapports d'embranchement et vies moyennes des niveaux du 34Cl

Resonance energies and strengths are reported for forty-five ³³S(p, γ)³⁴Cl resonances in the range E_p = 1.0–2.0 MeV. Analysis of the γ-ray spectra by means of two Ge(Li) detectors leads to precise excitation energies of bound states and branching ratios of resonant levels and bound states. New bound levels are found. The reaction Q-value is 5140.3 ± 1.5 keV. Mean lives (or limits) of twelve bound states of ³⁴Cl have been obtained from DSA measurements at seven of the studied ³³S(p, γ)³⁴Cl resonances.     

Nuclear structure study of37Cl

Properties of levels up to 5 MeV excitation in³⁷Cl were studied with³⁷Cl(p, p′ γ)³⁷Cl,³⁷Cl(α, α′ γ)³⁷Cl and³⁴S(α, pγ)³⁷Cl reactions. Results are discussed with reference to the many-particle shell model with an effective surface delta interaction.     

Investigation of 38Ar levels by 37Cl+p reactions: (I). Yield curves,excitation energies and branching ratios

Yield measurements have been performed on the reactions ³⁷Cl(p, p₀)³⁷Cl, ³⁷Cl(p, α₀)³⁴S (E_p = 1.17–1.70 MeV) and ³⁷Cl(p, n₀)³⁷Ar, ³⁷Cl(p.γ)³⁸Ar (E_p = 0.64–2.92 MeV); detailed investigations are restricted to resonances below E_p = 1.79 MeV. Resonance energies, strengths and (some) widths are reported for 12, 26 and 247 resonances in the reactions (p, p₀), (p, n₀) and (p, γ), respectively.Simultaneous (p, α₀) and (p, γ) yield measurements over selected E_p intervals in the E_p = 0.88–1.64 MeV range established the existence of 42 resonances decaying by both γ and α₀ emission. Analysis of the γ-ray spectra of 100 ³⁷Cl(p, γ)³⁸Ar resonances leads to precision excitation energies (ΔE_x = 0.1–2 keV) of 57 bound states (E_x < 8 MeV) and branching ratios of the resonances and of 50 bound states.     

Strengths of (p, γ) resonances in 33Cl, 35Cl and 28Si

Absolute strength measurements have been performed for the E_p = 580 and 588 keV ³²S(p,γ)³³Cl, E_p = 1214keV³⁴S(p,γ)³⁵Cl and E_p = 633 and 744 keV²⁷Al(p,γ)²⁸Si resonances with a Ge(Li) detector. Results are discussed with regard to the decay of isobaric analog resonances in ³⁵Cl and ³⁷Cl.     

Study of the36Cl(n,p)36S reaction in the neutron energy range up to 10 keV

The³⁶Cl(n,p)³⁶S reaction cross-section was measured by the time-of-flight method in the IBR-30 pulsed reactor of the JINR. The measured cross-section shows three not previously observed neutron resonances with energies E_n = 1.3; 3.5 and 8.2 keV for which the parameters A_p=gΓ_nΓ_p/Γ: 0.07 ±0.01; 0.08 + 0.03 and 1.7 + 0.3 eV were determined, respectively. Comparison of these results with the excited states obtained by the³⁶S(p, γ)³⁷Cl reaction made possible a more exact determination of the scale energy of the³⁷Cl nucleus excited states.     

Structure and total strength of the magnetic dipole resonance in <Superscript>35</Superscript>Cl nuclei

The γ-decay of the resonance-like structure observed in the ³⁴S(pγ)³⁵Cl reaction in the energy range E _p = 1.0–3.0 MeV of accelerated protons was investigated. The M1 resonance on the ground and excited states of ³⁵Cl with E* = 1219 and 1763 keV was identified. The position of the center of gravity and total strength of the M1 resonance on ground state ³⁵Cl nucleus are determined. The position and total strength of the M1 resonance on the ground state in ³⁵Cl are explained taking into account pairing forces.     

Study of the reactions31P(α,p)34S and29Si(α,n)32S

The (α,p) reaction on³¹P in the energy rangeE _α=3.25 to 5.25 MeV and the (α,n) reaction on²⁹Si in the energy rangeE _α=3 to 4.8 MeV, have been used to determine nuclear properties of³⁵Cl and³³S respectively. Resonance energies, strengths and partial widths are reported. The analysis of angular distribution measurements yields spin values for 23 resonance levels in³⁵Cl and 14 levels in³³S.     

The reaction 35Cl(n,γ)36Cl studied with non-polarized and polarized thermal neutrons

The γ-radiation following capture of non-polarized and polarized thermal neutrons in ³⁵Cl has been investigated. Of the 420 γ-rays ascribed to the ³⁵Cl(n,γ)³⁶Cl reaction, 236 have been placed in a ³⁶Cl decay scheme. The branching ratios and the excitation energies (with 0.04–0.9 keV errors) of 72 bound states have been determined. Unambiguous spin assignments are given for 11 levels. The multipole mixing ratios for some primary γ-ray transitions have been determined. There exists a significant correlation between (d, p) stripping strengths and (n, γ) reduced primary transition probabilities for transitions to l_n(d, p) = 0 levels.     

Étude des États excités du 33Cl à l′aide de la réaction 32S(p, γ)33Cl

Energies and strengths of resonances of the ³²S(p, γ)³³Cl reaction were determined in the range E_p = 0.4 ? 2.6 MeV. Three new resonances were observed respectively at E_p = 1588, 1748, 1880 keV and the doublet of resonances at E_p ≈ 1900 keV was clearly shown. The (p, γ) strengths of resonances at E_p = 422, 580, 588, 721 and 2577 keV were measured with a 80 cm³ Ge(li) detector. The Q-value of this reaction and the energies, γ-ray branchings and mean lifetimes of levels were determined. The spins and parities of the E_x = 2.35, 3.82, 3.97, 3.98, 4.78 MeV levels have been measured. A comparison of γ-ray transition strengths with mirror transitions and with model predictions is made.     

Allowed electron-capture branches in the decay of 34mCl

The decay of ^34mCl has been studied with 36 and 100 cm³ Ge(Li) detectors and with a high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer. The ^34mCl activity was produced with the reaction ²⁴Mg(¹²C, pn)³⁴Cl at $\text{E(}{}^{12}\text{C}\text{) = 35}\text{MeV}$ by bombarding thick natural Mg targets. The half-life was measured to be $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 32.06 ± 0.08}\text{min}$. Nine γ-ray transitions were observed including four γ-rays not seen previously. The measured γ-ray intensities determine new electron-capture branches of (0.030 ± 0.006) % and (0.032 ± 0.003) % to ³⁴S levels at 4.69 and 4.88 MeV with log ft values of 5.48 ± 0.08 and 5.26 ±0.04, respectively. These log ft values imply allowed transitions and are consistent with the known J_π values of J_π = 4⁺ and 3⁺ of the 4.69 and 4.88 MeV levels, respectively. A lower limit of log ft ? 6.9 is obtained for the allowed electron-capture branch to the J^π = 2⁺, 4.89 MeV level. Other previously observed decay branches have been confirmed. Since the decay of ^34mCl proceeds (46.9 ± 1.0)% to the ³⁴Cl ground state, the latter decay was studied concurrently; ³⁴Cl(0)with J^π = 0⁺, T = 1 decays exclusively to its analog ³⁴S(0) and the sum of the intensities of four other allowed branches is less than 1.2 × 10^?4 of the intensity of the ground-state branch. The experimental results are compared with recent shell-model calculations performed in a large configuration space.     

New low-energy measurement of the 18F(p,α)15O reaction

The ¹⁸F, produced during nova explosions, is the main responsible for the 511 keV γ-ray emitted during the outburst that could be detected with satellite missions or future γ-ray telescopes. In spite of many experimental efforts, the amount of ¹⁸F synthesized still suffers from large uncertainties concerning mainly the ¹⁸F(p,α)¹⁵O reaction. We report here on a new direct measurement of the ¹⁸F(p,α)¹⁵O cross section recently carried out at the RIB facility at Louvain-la-Neuve. Cross section data down to a center-of-mass energy of 400 keV have been obtained using an isobarically pure ¹⁸F beam (averaged intensity of the order of 10⁶ pps) and a thin polyethylene target. The reaction products were detected using the multi-strip detector array LEDA. The cross section data are analysed in the framework of the R-matrix model. Our main aim is to determine the interference sign between three 3/2⁺ resonances above threshold that can significantly affect the extrapolation of the ¹⁸F(p,α)¹⁵O cross section to the energies relevant for novae, and thus, the modeling of nova explosions.     

Radiative thermal neutron capture by natural sulfur

A high precision study of the gamma ray spectrum following neutron capture by a target of natural sulfur is reported. The energy precision obtained has permitted construction of decay schemes for³³S and³⁵S. In the case of the former isotope a total of 22 levels have been identified while for the latter and much weaker reaction 7 states have been observed. While some transitions attributable to capture by³³S are observed, their weakness prohibited detailed analysis. The neutron separation energies, based upon the¹⁴N(n, γ)¹⁵N standard are found to be 8,641.60 (3) keV and 6,985.84 (5) keV for³³S and³⁵S respectively.     

51(p,n)51Cr reaction from E p 1.9 to 4.5 MeV

The total cross-section for the reaction⁵¹V(p, n)⁵¹Cr has been measured fromE _p 1.9 to 4.5 MeV by using two different techniques: (i) by detecting the neutron using the 4π neutron counter and (ii) by measuring the activity of the residual nucleus⁵¹Cr. The two measurements are consistent with each other and together they are in good agreement with the data of Zyskindet al. The thermonuclear reaction rates have also been extracted starting from these cross-sections.     

Explosive hydrogen burning of 17O in classical novae

We report on the observation of a new resonance at E(lab)(R)=190 keV in the 17O(p,gamma)18F reaction. The measured resonance strength amounts to omegagamma(pgamma)=(1.2+/-0.2)x10(-6) eV. With this new value, the uncertainties in the 17O(p,gamma)18F and 17O(p,alpha)14N thermonuclear reaction rates are reduced by orders of magnitude at nova temperatures. Our significantly improved reaction rates have major implications for the galactic synthesis of 17O, the stellar production of the radioisotope 18F, and the predicted oxygen isotopic ratios in nova ejecta.     

Nuclear clustering aspects in astrophysics

Atomic nuclear clusters play a crucial role in nucleosynthesis in the universe, especially in the main sequence of heavy element synthesis. Cluster aspects in nucleosynthesis are briefly discussed based on a Cluster-Nucleosynthesis Diagram proposed here. Two recent topics on critical α-induced thermonuclear reactions are reviewed; the first one is the¹²C(α, γ)¹⁶O reaction for the He burning stage and the other one is the⁶ Li(α, n) ¹¹B reaction for the big bang nucleosynthesis. A new field of nuclear astrophysics using radioactive nuclear beams is also discussed.     

(p, γ) Resonance strengths in the s-d shell

The strengths of selected resonances in the range E_p = 0.5–2.0 MeV in the (p, γ) reactions on Mg, ³⁰Si, ³⁴S, ³⁷C1, ³⁹K and ⁴⁰Ca have been found relative to the E_p = 632 and 992 keV resonances in ²⁷Al(p, γ)²⁸Si by relative yield measurements. Targets were made from mixtures or chemical compounds such that each contained at least two of the isotopes of interest and their chemical composition was determined by Rutherford back-scattering of α-particles. Absolute measurements were conducted on the selected resonances in ²⁷A1(p, γ)²⁸Si and ³⁰Si(p, γ)³¹P by semi-thick target and thin target techniques with the target thickness, needed for the latter technique, found by Rutherford back-scattering of protons. Absolute strengths for all of the resonances treated, together with one from each of ²³Na, ³¹P and ³⁵Cl, reported in a previous paper, were deduced by normalizing to the absolute measurements on the Al(p, γ)²⁸Si resonances.     

High-spin states in 34CI

High-spin yrast states in ³⁴Cl have been studied with the reactions ³¹P(α, nγ)³⁴Cl at E_α = 11.7?16.3 MeV and ²⁴Mg(¹²C, pnγ)³⁴Cl at E(¹²C) = 32–35 MeV. Ambiguities in the ³⁴Cl level scheme for levels at E_x = 4.82 and 5.32 MeV have been resolved through combination of threshold measurements with the ³¹P + α reaction and gamma-gamma coincidence and E_γ-measurements with the ²⁴Mg + ¹²C reaction. Gamma-gamma coincidence and in-beam γ-γ angular correlation experiments have been performed employing a Compton-suppression spectrometer with a solid angle of 120 msr.Unambiguous spin-parity assignments of J^π = 6^?, 5⁺ and 7⁺ to the ³⁴Cl levels at E_x = 4.74, 4.82 and 5.32 MeV, respectively, are obtained.Previously unreported levels of high spin are found at E_x = 7.25 and 7.80 MeV with J^π = (9⁺) and (8⁺); τ_m = 200 ± 70 fs and 100 ± 70 fs, respectively. Excitation energies, mean lives, branching ratios and multipole mixing ratios are reported. The experimental results are compared with large-scale shell-model calculations. The high-spin yrast levels can be characterized by a rather simple shell-model structure.     

Investigation of the reaction 37Cl(n, γ)38Cl

With Ge(Li) detectors the γ-radiation following thermal-neutron capture in natural and in ³⁷Cl enriched targets was studied. A total of 79 γ-lines has been assigned to the ³⁷Cl(n, γ) reaction and 64 of these lines have been placed in a decay scheme of ³⁸Cl. The excitation energies of 24 bound states of ³⁸Cl have been determined with 0.09–1.2 keV errors. The neutron separation energy of ³⁸Cl is 6107.7 ± 0.4 keV. A strong correlation between reduced stripping widths and (n, γ) primary reduced widths was found for the l_n(d, p) = 1 states if, instead of the Weisskopf reduction factor E_γ^?3, a factor E_γ^?1.2 was used.