Angular Distribution of Alphas fromLi6(d,α)αandLi7(p,α)α

Abstract

The intensity of the reaction ${\mathrm{Li}}^6(d,\alpha )\alpha$ is observed to vary with angle as $1+A\left(E\right)\mathrm{}{cos}^2\theta +B\left(E\right)\mathrm{}{cos}^4\theta$, as expected from the Bose statistics of the product alphas, with $A\left(E\right)\mathrm{}$ rising gradually beginning just below 1 Mev to a broad maximum a little below unity at a bombarding energy $E$ in the neighborhood of 2 Mev. The coefficient $B\left(E\right)\mathrm{}$ remains zero up to almost 1.5 Mev and rises to a positive value of about 0.35 at higher energies. The yield curve observed at right angles to the beam displays a sharp maximum at 0.75 Mev and there is evidence of approach to another peak at or just beyond the highest bombarding energy employed, 3.75 Mev. The substitution of a proportional counter for the ionization chamber used in earlier work has made possible improvement over our earlier observations of the angular distribution of the reaction ${\mathrm{Li}}^7(p,\alpha )\alpha$ in the neighborhood of 3 Mev, where difficulty was experienced in the discrimination against pile-up of scattered protons, and the new results show a node in the curve for $A\left(E\right)\mathrm{}$ at 2.7 Mev. A peak in the yield curve of this reaction is found at 3 Mev, which is about 3 Mev lower in the compound nucleus ${\mathrm{Be}}^8$ than the lower peak observed in the reaction ${\mathrm{Li}}^6(d,\alpha )\alpha$. There is great similarity in the trends of the angular distributions of the two reactions, but their coefficients $B\left(E\right)\mathrm{}$ have opposite signs in the energy regions investigated, and both $A\left(E\right)\mathrm{}$ and $B\left(E\right)\mathrm{}$ rise from zero more gradually in ${\mathrm{Li}}^6(d,\alpha )\alpha$ than in ${\mathrm{Li}}^7(p,\alpha )\alpha$ as the bombarding energy increases from low values.