S.G. Tims

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.

Cross sections of proton induced reactions on 61Ni

Abstract Excitation functions have been measured for the reactions 61 Ni(p, γ) 62 Cu and 61 Ni(p, pγ) 61 Ni over the bombarding energy range 1.05–3.98 MeV, and for the reaction 61 Ni(p, n) 61 Cu over the bombarding energy range 3.08–4.66 MeV. Cross sections for 61 Ni(p, γ) 62 Cu, 61 Ni(p, n) 61 Cu, and 61 Ni(p, p) 61 Ni leading to 8 excited states of 61 Ni, were extracted from the data, and compared with the results of statistical-model calculations. The agreement is good. Thermonuclear reaction rates for the (p, γ) and (p, n) reactions are calculated for the temperature range 5 × 10 8 –10 10 K, which includes the range of temperatures of interest in stellar nucleosynthesis calculations.

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.

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.

Cross sections and thermonuclear reaction rates for 51(α, n)54Mn and 51(α, p)54Cr

Abstract The cross sections of 51 V(α, n) 54 Mn and 51 V(α, p) 54 Cr have been measured in the bombarding-energy ranges of 2.00–9.49 MeV and 5.755–9.590 MeV, respectively. The cross sections, together with cross sections of 54 Cr(p, γ) 55 Mn and 54 Cr(p, n) 54 Mn taken from the literature, have been compared with the results of statistical-model calculations. Thermonuclear reaction rates at temperatures appropriate to silicon burning in massive stars and supernovae have been calculated for both reactions.

Cross sections and thermonuclear reaction rates for 41K(α, n)44Sc and 41K(α, p)44Ca☆

Abstract The cross sections of 41 K(α, n) 44 Sc and 41 K(α, p) 44 Ca have been measured in the bombarding energy ranges 3.0–8.0 MeV and 4.5–9.0 MeV, respectively. The cross sections have been compared with the results of statistical-model calculations made with global optical-model parameters, and also with a set of modified parameters. Thermonuclear reaction rates at temperatures important in silicon burning in evolving stars and supernovae have been calculated.

The 54Fe(α, n)57Ni and 54Fe(α, p)57Co cross sections☆

Abstract The cross sections of 54 Fe(α, n) 57 Ni and 54 Fe(α, p) 57 Co have been measured over bombarding energy ranges of 6.35–9.50 MeV and 5.31–9.59 MeV, respectively. The 54 Fe(α, n) 57 Ni measurements were based on observation of neutrons by means of a 4π detector and also on observation of 57 Co γ-rays associated with the β-decay of 57 Ni. The 54 Fe(α, p) 57 Co measurements were made with a surface barrier detector at 125°. The cross sections have been compared with the predictions of statistical-model calculations made with a number of different optical-model parameter sets. Thermonuclear reaction rates at temperatures representative of those encountered in freeze-out from nuclear statistical equilibrium in supernovae have been calculated.

The 60Ni(p, γ)61Cu AND 62Ni(p, γ)63 Cu cross sections

Abstract The cross sections of 60 Ni(p, γ) 61 Cu and 60 Ni(p, pγ) 60 Ni have been measured over the bombarding-energy range 1.0–4.0 MeV, and of 62 Ni(p, γ) 63 Cu and 62 Ni(p, pγ) 62 Ni over the bombarding-energy range 1.02–4.42 MeV. The measurements were based on observation of the yields of 61,63 Cu and 60,62 Ni de-excitation γ-rays. The cross sections, and those for proton induced reactions on all other stable nickel isotopes, have been compared with the predictions of statistical- model calculations. A new prescription for the optical-model proton imaginary well depth, for use with nickel isotopes only, is presented, leading to agreement between theory and experiment at the factor of 1.5 level. Thermonuclear reaction rates at temperatures representative of those encountered in freeze-out from nuclear statistical equilibrium in supernovae have been calculated from the data and the significance of these for stellar nucleosynthesis calculations is discussed. The excitation energies and (p, γ) resonance strengths of fifty-four resonances in 60 Ni(p, γ) 61 Cu, which feature significant resonance to ground-state transitions, have been measured.

The 45Sc(α, p)48Ti and 45Sc(α, n)48V cross sections

Abstract The cross sections of 45 Sc(α, p) 48 Ti and 45 Sc(α, n) 48 V have been measured in the bombarding energy ranges of 4.45–9.15 MeV and 3.76–9.98 MeV, respectively. The cross sections have been compared with the results of statistical-model calculations made with global optical-model parameters, and also with a set of modified parameters. Thermonuclear reaction rates at temperatures appropriate to silicon burning in massive stars and supernovae have been calculated for both reactions and also for 48 V(n, p) 48 Ti.