D.G. Sargood

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

Abstract The strengths of selected resonances in the range E p = 0.5–2.0 MeV in the (p, γ) reactions on Mg, 30 Si, 34 S, 37 C1, 39 K and 40 Ca have been found relative to the E p = 632 and 992 keV resonances in 27 Al(p, γ) 28 Si 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 27 A1(p, γ) 28 Si and 30 Si(p, γ) 31 P 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 23 Na, 31 P and 35 Cl, reported in a previous paper, were deduced by normalizing to the absolute measurements on the Al(p, γ) 28 Si resonances.

Cross-section measurements and thermonuclear reaction rates for 52Cr(p, γ)53Mn and 54Fe(p, γ)55Co☆

Abstract The yields of γ-rays from the reactions 52 Cr(p, γ) 53 Mn and 52 Cr(p, p′ γ) 52 Cr have been measured as a function of bombarding energy over the range 0.84–4.00 MeV, and from the reactions 54 Fe(p, γ) 55 Co and 54 Fe(p, p′γ) 54 Fe over the range 1.05–3.69 MeV. All γ-ray yields were lower by factors of order of 2 than those predicted by statistical model calculations based on global parameter sets. Data are taken from the literature for proton induced reactions on 48 Ca, 50 Ti, and 51 V, which like 52 Cr and 54 Fe contain a closed shell of 28 neutrons, and for which statistical model calculations were also high by factors of order of 2 or more. A new prescription for obtaining the imaginary well depth for the proton channel is proposed for N = 28 nuclei and it is shown to result in a striking improvement in the agreement between experimental and calculated cross sections. Thermonuclear reaction rates for the (p, γ) reactions on 52 Cr and 54 Fe are calculated for the temperature range (0.6−10) × 10 9 K.

Cross section of the reaction 6Li(p, γ)7Be

Abstract The cross section of the reaction 6 Li(p, γ ) 7 Be has been measured using Ge(Li) γ-ray spectrometers for proton bombarding energies E p from 200 keV to 1200 keV. At E p = 800 keV, the total (p, γ) integrated cross section is found to be 3.1 ± 0.4 μ b. The cross section adopted from consideration of this and previous measurements is in good agreement with that predicted from the known thermal neutron cross section for 6 Li(n, γ ) 7 Li on the assumption that properties of mirror direct capture reactions can be well described by optical potentials that use the same parmeter values for the two reactions.

The 48Ti(α, n)51Cr and 48Ti(α, p)51V cross sections☆

Abstract The cross sections of the reactions 48 Ti(α, n) 51 Cr and 48 Ti(α, p) 51 V have been measured over bombarding-energy ranges of 4.98–9.52 MeV and 5.52–8.98 MeV, respectively. The data, together with those for all other N = 28 compound nucleus reactions reported in the literature, have been compared with the results of statistical-model calculations. New formulae prescribing optical-model parameters for use exclusively with N = 28 compound nucleus reactions are presented. Thermonuclear reaction rates for 48 Ti(α, n), (α, p) have been calculated for temperatures appropriate for stellar nucleosynthesis, and have been compared with published rates derived both from experimental measurements and from statistical-model calculations.

Resonance strength measurements and thermonuclear reaction rates for 25Mg(p, γ)26Al☆

Abstract The strengths of resonances in 25 Mg(p, γ) 26 Al in the energy range E p = 317–591 keV have been obtained. Resonance strengths at E p = 317, 387, 433 and 591 keV have been measured absolutely. The strengths of resonances at E p = 591 and 433 keV were also deduced by comparison with the strength of the resonance at E p = 620 keV in 30 Si(p, γ) 31 P. Relative measurements of 10 resonances in the range E p = 317–591 keV were made. A search for (p, γ) strengths below E p = 300 keV was undertaken and an upper limit for the sum of all possible strengths is given. Thermonuclear reaction rates are calculated for the reaction 25 Mg(p, γ) 26 Al leading to both the ground state and isomeric first excited state of 26 Al in the temperature range T = 5 × 10 7 −5 × 10 8 K and are compared with rates determined from cross sections obtained from statistical-model calculations. The superelastic and inelastic scattering of protons is investigated as a mechanism by which the 26 Al nucleus may attain a thermal distribution of excited states and is shown to be ineffective.

Cross sections of the reactions 58Fe(p, γ)59Co, 58Fe(p, n)58Co, 55Mn(α, n)58Co, 55Mn(α, p)58Fe and 57Fe(p, n)57Co

Abstract The cross sections of the reactions 58 Fe(p, γ) 59 Co, 58 Fe(p, n) 58 Co, 55 Mn(α, n) 58 Co, 55 Mn(α, p) 58 Fe and 57 Fe(p, n) 57 Co have been measured over bombarding energy ranges of 0.785–4.650, 3.155–4.925, 2.700–9.995, 5.145–10.045 and 1.645–3.155 rmMeV, respectively. The data have been compared with statistical-model predictions, with the first four reactions being treated as a single unit. Thermonuclear reaction rates have been calculated for temperatures appropriate for stellar nucleosynthesis and compared with published rates, both experimental and theoretical.

The 59Co(α, p)62Ni and 59Co(α, n)62Cu cross sections☆

Abstract The cross sections of 59Co(α, p)62Ni and 59Co(α, n)62Cu have been measured over bombarding energy ranges of 5.18–9.40 MeV and 5.07–9.80 MeV, respectively. The 59Co(α, p)62Ni measurements were made with a charged-particle detector at 125° c.m., and the 59Co(α, n)62Cu measurements were based on observation of neutrons by means of a 4π detector and also on observation of the yield of annihilation γ-rays associated with the positron decay of 62Cu. The cross sections have been compared with the predictions of statistical-model calculations made with global optical-model parameters, and a set of modified parameters has been found which gives a better overall fit. Thermonuclear reaction rates at temperature representative of those encountered in freeze-out from nuclear statistical equilibrium in supernovae have been calculated.

25Mg (α, n)28Si and 26Mg(α, n)29Si as neutron sources in explosive neon burning

Abstract The yields of neutrons from the reaction 25 Mg(α, n) 28 Si and of γ-rays from the reaction 25 Mg(α, nγ) 28 Si have been measured as a function of bombarding energy over the range 1.8–6.3 MeV, and the yield of neutrons from 26 Mg(α, n) 29 Si has been measured over the range 1.8–6.0 MeV. Cross sections for 25, 26 Mg(α, n) 28, 29 Si were extracted from the data and compared with global statistical-model calculations. The agreement is very good. Thermonuclear reaction rates under stellar conditions appropriate for explosive neon burning are calculated and their significance for the nucleosynthesis of rare neutron-rich nuclei is discussed.

Cross-section measurements and thermonuclear reaction rates for 49Ti(p, γ)50V and 49Ti(p, n)49V

Abstract The yield of γ-rays from the reaction 49 Ti(p, γ) 50 V has been measured as a function of bombarding energy over the range 0.74–2.27 MeV and the yield of neutrons from the reaction 49 Ti(p, n) 49 V has been measured from threshold to a bombarding energy of 3.25 MeV. Strong competition effects were observed in the γ-ray yield at the opening of the neutron channel. The energy dependence of these cross sections is compared with statistical-model calculations, and good agreement is achieved. Thermonuclear reaction rates are calculated for the temperature range 5 × 10 8 –5 × 10 9 K which includes the range of temperatures of interest in nucleosysnthesis calculations. The effect of a strong isobaric analogue resonance on the (p, γ) thermonuclear reaction rate is identified and its importance is discussed.

The 34S(α, γ)38Ar, 34S(α, n)37Ar and 34S(α, p)37Cl cross sections☆

Abstract The cross sections of the reactions 34 S(α, γ) 38 Ar, 34 S(α, n) 37 Ar and 34 S(α, p) 37 Cl have been measured over bombarding-energy ranges of 2.79–5.87 MeV, 5.26–9.88 MeV and 5.70–9.33 MeV, respectively. The data, together with those for proton-induced reactions on 37 Cl, have been compared with statistical-model calculations. Thermonuclear reaction rates for 34 S(α, γ), (α, n), (α, p) have been calculated for temperatures appropriate for stellar nucleosynthesis.