A. Azhari

Tests of transfer reaction determinations of astrophysical {bold {ital S}} factors

The {sup 16}O({sup 3}He,d){sup 17}F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of {sup 17}F. The coefficients provide the normalization for the tails of the overlap functions for {sup 17}F{r_arrow}{sup 16}O+p and allow us to calculate the {ital S} factors for {sup 16}O(p,{gamma}){sup 17}F at astrophysical energies. The calculated {ital S} factors are compared to measurements and found to be in very good agreement. This provides a test of this indirect method to determine astrophysical direct capture rates using transfer reactions. In addition, our results yield S(0) for capture to the ground and first excited states in {sup 17}F, without the uncertainty associated with extrapolation from higher energies. {copyright} {ital 1999} {ital The American Physical Society}

Evolution of the giant dipole resonance in excited 120Sn and 208Pb nuclei populated by inelastic alpha scattering

Abstract The evolution of the giant dipole resonance (GDR) in 120 Sn and 208 Pb nuclei at excitation energies in the range of 30–130 MeV and 40–110 MeV, respectively, were studied by measuring high energy γ rays from the decay of the resonance. The excited states were populated by inelastic scattering of α particles at beam energies of 40 and 50 MeV/nucleon for 120 Sn and 40 MeV/nucleon for 208 Pb. A systematic increase of the resonance width with increasing excitation energy was observed for both nuclei. The observed width evolution was compared to calculations employing a model that adiabatically couples the collective excitation to the nuclear shape, and to a model based on the collisional damping of nucleons. The adiabatic coupling model described the width evolution in both nuclei well, whereas the collisional damping calculation could describe the width evolution only in 208 Pb. Light-particle inelastic scattering populates low angular momentum states in the target nucleus. The observed width increase is therefore interpreted to be predominantly due to fluctuations in the nuclear shape induced by temperature. This interpretation is consistent with the adiabatic model calculations and with recent angular momentum-gated measurements of the GDR in excited Sn isotopes.

Temperature dependence of the giant dipole resonance width in 208Pb

Abstract The evolution of the giant dipole resonance (GDR) in hot 208Pb nuclei was studied by measuring high energy γ-rays from the decay of the resonance built on excited states. Nuclei in the excitation energy range of 40–110 MeV were populated by inelastic scattering of 40 MeV/nucleon α-particles. The GDR width was observed to increase systematically from 4 MeV at the ground state to ∼8 MeV at the highest excitation energy.

Efficiency of a BaF2 scintillator detector for 15–150 MeV neutrons

Abstract The neutron detection efficiency of a BaF 2 scintillator detector was measured relative to a NE213 detector for neutron energies between 15 and 150 MeV. The efficiency for the BaF 2 detector is found to be higher than a comparable NE213 detector for neutrons above 70 MeV.

Asymptotic Normalization Coefficients in nuclear astrophysics

Abstract The technique of Asymptotic Normalization Coefficients (ANC) provides an effective method of indirect determination of S-factors for the synthesis in astrophysically important reactions. These coefficients can be extracted from the differential cross sections of the peripheral particle transfer reactions. Recent applications include measurements of ANCs for determining of stellar reaction rates of 9 Be( p , γ) 10 B, 13 C( p , γ) 14 N, 11 C( p , γ) 12 N and 14 N( p , γ) 15 O.

Elastic and inelastic scattering of protons on 38S in inverse kinematics

Abstract Elastic and inelastic scattering of protons on unstable 38 S nuclei has been measured in inverse kinematics by using a 38 S secondary beam at 39 MeV/nucleon. The excitation energy spectrum is measured up to 5 MeV. The first 2 + state is seen at 1.2 MeV excitation energy, and strength at around 3–5 MeV is also observed. Angular distributions for inelastic and elastic scattering are shown and compared to optical potential and folding model calculations. The preliminary β 2 value extracted for the first 2 + state is 0.38±0.05.

Giant dipole resonance in excited 120Sn and 208Pb nuclei populated by inelastic alpha scattering

Abstract The evolution of the giant dipole resonance (GDR) in hot 120 Sn and 208 Pb nuclei was studied by measuring high energy γ-rays from the decay of the resonance. The excited nuclei were populated by inelastic scattering of α-particles at 40 and 50 MeV/nucleon. The resonance width was observed to increase systematically with excitation energy in both systems. Inelastic scattering populates low angular momentum states in the target. The observed width increase is thus attributed to fluctuations in the nuclear shape induced by temperature.

Studies of light nuclei beyond the particle driplines: the two-proton emitter 12O

Abstract The decay dynamics of the ground state two proton emitter 12O, which lies beyond the proton dripline, were investigated following the population of 12O via single-neutron stripping of an 13O projectile. The decay products, two protons and 10C, were detected in coincidence and correlations among these particles were studied. No evidence was seen for 2He emission in the decay. This appears consistent with direct breakup or possibly sequential decay through 11N.

The14N(7Be,8B)13Creaction and the7Be(p,γ)8BSfactor

The {sup 14}N({sup 7}Be,{sup 8}B){sup 13}C reaction was studied using an 85 MeV {sup 7}Be radioactive beam. The asymptotic normalization coefficients for the virtual transitions {sup 7}Be+p{leftrightarrow}{sup 8}B were determined from the measured cross section. These coefficients specify the amplitude of the tail of the {sup 8}B overlap function in the {sup 7}Be+p channel, and were used to calculate the astrophysical {ital S} factor for the direct capture reaction {sup 7}Be(p,{gamma}){sup 8}B at solar energies S{sub 17}(0). We find that S{sub 17}(0)=16.6{plus_minus}1.9 eVhb. {copyright} {ital 1999} {ital The American Physical Society}

The {sup 14}N({sup 7}Be,{sup 8}B){sup 13}C reaction and the {sup 7}Be(p,{gamma}){sup 8}B S factor

The {sup 14}N({sup 7}Be,{sup 8}B){sup 13}C reaction was studied using an 85 MeV {sup 7}Be radioactive beam. The asymptotic normalization coefficients for the virtual transitions {sup 7}Be+p{leftrightarrow}{sup 8}B were determined from the measured cross section. These coefficients specify the amplitude of the tail of the {sup 8}B overlap function in the {sup 7}Be+p channel, and were used to calculate the astrophysical {ital S} factor for the direct capture reaction {sup 7}Be(p,{gamma}){sup 8}B at solar energies S{sub 17}(0). We find that S{sub 17}(0)=16.6{plus_minus}1.9 eVhb. {copyright} {ital 1999} {ital The American Physical Society}