Direct-Capture Model for the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mo>(</mml:mo><mml:mi>α</mml:mi><mml:mo>,</mml:mo><mml:mi> </mml:mi><mml:mi>γ</mml:mi><mml:mo>)</mml:mo><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Be</mml:mi></mml:mrow><mml:mrow><mml:mn>7</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">T</mml:mi><mml:mo>(</mml:mo><mml:mi>α</mml:mi><mml:mo>,</mml:mo><mml:mi> </mml:mi><mml:mi>γ</mml:mi><mml:mo>)</mml:mo><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">Li</mml:mi></mml:mrow><mml:mrow><mml:mn>7</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Reactions

Using the ${\mathrm{He}}^{3}$+${\mathrm{He}}^{4}$ scattering phase shifts, the cross section for the ${\mathrm{He}}^{3}(\ensuremath{\alpha}, \ensuremath{\gamma}){\mathrm{Be}}^{7}$ reaction is calculated on the basis of a ${\mathrm{He}}^{3}$+${\mathrm{He}}^{4}$ model for the ground state and first excited state of ${\mathrm{Be}}^{7}$. Capture of particles from the $S$, $P$, $D$, and $F$ partial waves by means of $E1$, $M1$, and $E2$ transitions is considered. The results are in excellent agreement with the experimental data presented in the preceding paper and indicate that the reaction proceeds chiefly by means of $E1$ capture from the $S$ and $D$ waves. It is a surprising consequence that the $D$ wave contributes an appreciable fraction of the total capture cross section for alpha-particle energies as low as 1 MeV. Using the same values for the reduced widths of the final states that were determined for the ${\mathrm{He}}^{3}(\ensuremath{\alpha}, \ensuremath{\gamma}){\mathrm{Be}}^{7}$ reaction, similar calculations have also yielded excellent agreement with the experimental data for both the branching ratio and the total cross section of the mirror reaction $\mathrm{T}(\ensuremath{\alpha}, \ensuremath{\gamma}){\mathrm{Li}}^{7}$.

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