Angular Distributions forC12(α, p)N15at 16.1-19.0 Mev andF19(α, p)Ne22at 18.9 Mev

Abstract

Angular distributions have been measured for the reactions ${\mathrm{C}}^{12}(\alpha , p)N^{15}$ and ${\mathrm{F}}^{19}(\alpha , p){\mathrm{Ne}}^{22}$ using the cyclotron 19-Mev alpha-particle beam. The ${\mathrm{C}}^{12}(\alpha , p_0){\mathrm{N}}^{15}$ data at 18.0, 17.1, and 16.1 Mev differ markedly from the 19.0-, 18.7-, and 18.3-Mev data; the latter three are very similar to each other. The differential excitation function at 31.8° (lab) shows a resonance at 17.5 Mev with a width at half-maximum of ∼2 Mev. Steep backward peaking is observed in the 16.1-Mev data. Some of the features of the 17.1- and 18.0-Mev data can be represented by Butler's formula for ($\alpha , p$) reactions using $l=1\mathrm{}$ and $r_0=5.9\mathrm{} \mathrm{and} 5.5$f, respectively. For the ${\mathrm{F}}^{19}(\alpha , p){\mathrm{Ne}}^{22}$ data the cross sections for the transition to the ground state of ${\mathrm{Ne}}^{22}$ are factors of 10 to 20 less than the cross sections for the transition to the first excited state of ${\mathrm{Ne}}^{22}$. This inhibition, together with the ${\mathrm{F}}^{19}(n, d){\mathrm{O}}^{18}$ data, may be explained by assuming that the two last neutrons of ${\mathrm{F}}^{19}$ are not disturbed in the direct interactions and that they are in a ${\left({d_{\frac{5}{2}}}^2\right)}_0$ configuration in ${\mathrm{Ne}}^{22}$, in a ${\left({d_{\frac{5}{2}}}^2\right)}_2$, or ${\left({s_{\frac{1}{2}}}^2\right)}_0$ configuration in ${\mathrm{F}}^{19}$. Using $r_0=5.1\mathrm{}$f, Butler's formula accounts reasonably well for the forward peak and the location of the minima of all three angular distributions for the region of angles less than 90°. The angular distributions are all peaked in the backward angles.