Final state interaction and direct features of the 9Be(τ, α)αα and 10B(d, α)αα reactions

doi:10.1016/0375-9474(75)90083-4

Nuclear Physics A

Volume 245, Issue 1, 23 June 1975, Pages 87-106

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Abstract

Alpha-particle spectra and α-α correlations have been measured from the ⁹Be(τ, α)αα and ¹⁰B(d, α)αα reactions at several energies between 2.9 and 10.0 MeV. Significant difierences in the spectra from the reactions were observed at equal c.m. energies and momentum transfer values. However the continuous energy spectra have been successfully analyzed with two-body interactions as obtained from elastic α-α scattering, within a formalism adequate for a three-body state. DWBA fits have also been obtained for both reactions but they are satisfactory only for the ⁹Be(τ, α)⁸Be reaction.

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The three-body reaction ⁹Be + d → t + α + α has been investigated in kinematically complete experiments at E_d = 7.0 MeV for θ_t = −40° and θ_t = 40°, θ_α = −72.5° to −162.5. The experimental spectra are dominated by sequential processes via intermediate excited states of ⁸Be and ⁷Li. R-matrix theory was employed to describe the line shape of the first excited state and the ghost anomaly of the ground state of ⁸Be. Use was made of the αα phase shifts. The best fits were obtained assuming a channel radius of a_αα = 4.5 fm. The average intensity of the ghost anomaly for E_αα = 0.35–1.0 MeV is 4.3%/MeV (θ_t = 40°) and 8%/MeV (θ_t = 100°). For the first excited state of ⁸Be we find E_x = 3.00 MeV and Γ_x = 1.23 MeV(FWHM).
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In order to study the intrinsic line shape of the broad first excited 2⁺ state of ⁸Be, the radiative capture reaction ⁷Li(p,γ)⁸Be has been investigated in an energy range close to the center of the giant dipole resonance built upon this state. A large NaI(Tl) spectrometer with a well-known response function is employed. The data are fitted with spectral density functions derived from αα phase shifts in the framework of the R- matrix theory. The optimum value of the channel radius obtained from the fits, a = 4.5 fm, is in agreement with the value deduced from a similar analysis of a kinematically complete coincidence study of the ⁹Be(d,tα)⁴He reaction. The calculated spectral density function for a = 4.5 fm reaches its maximum at E_x = 2.91 MeV, the width (FWHM) is 1.23 MeV.
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Various light- and heavy-ion reactions, 20 < E < 100 MeV, have been used to study the reaction dependence of α-decay widths for ⁸Be^∗(2 ⁺ , 2.9 MeV) and ¹⁶O^∗(1⁻, 9.6 MeV). Although slight differences (< 20 %) are found for the observed line shapes (Γ), the resonance widths inferred (Γ_R) are self-consistent and indicate little if any reaction dependence (< 10 %). Near a decay threshold one may expect Γ < Γ_R by 20 % or more, however, and thus care must be taken in comparing decay widths inferred from nuclear reactions with those from scattering resonances. Reduced formal α-decay widths of γ_λ² = 680 ± 100 keV (s = 4.8 fm) and γ_λ² = 350 ± 50 keV(s = 5.4 fm), corresponding to θ_λ² = 0.50 and θ_λ² = 0.49 are deduced for ⁸Be^∗(2 ⁺ , 2.9 MeV) and ¹⁶O^∗(1⁻, 9.6 MeV) using the nuclear-reaction Γ_R values and a particular set of α-nucleus potentials.
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^†: Present address: Lawrence Berkeley Laboratory, Berkeley, Ca 94720, USA.

^††: Present address: Service de Physique Nucléaire á Haute Energie, CEN Saclay B.P. No. 2, 91190 Gif-sur-Yvette, France.

^†††: Present address: IASR Kernforschungszentrum, 75 Karlsruhe, Postfach 3640, West Germany.

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Final state interaction and direct features of the 9Be(τ, α)αα and 10B(d, α)αα reactions

Abstract

Phys. Rev.

Phil. Mag.

Comp. Rend.

Comp. Rend.

Phys. Rev.

Nucl. Phys.

J. de Phys.

J. de Phys.

Nucl. Phys.

Phys. Rev.

Phys. Rev.

Nucl. Phys.

Phil. Mag.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Phys. Rev.

Phys. Rev. Lett.

Nucl. Phys.

Nucl. Phys.

Rev. Mod. Phys.

Phys. Rev.

Phys. Lett.

Rep. Prog. Phys.

Phys. Rev.

Phys. Rev.

Nucl. Phys.

Final state interaction and direct features of the ⁹Be(τ, α)αα and ¹⁰B(d, α)αα reactions