He3- andHe4-Induced Coulomb Excitation

Abstract

In order to examine the characteristics of the ${\mathrm{He}}^3$-induced Coulomb excitation process and the validity of the cross-section ratio technique for the identification of both $E1\mathrm{}$ and $E2\mathrm{}$ transitions, thick-target radiation yield ratios have been measured for ${\mathrm{He}}^3$-and ${\mathrm{He}}^4$-induced Coulomb excitation of each of the 110- and 197-kev levels of ${\mathrm{F}}^{19}$, the 446-kev level of ${\mathrm{Na}}^{23}$, the 160-kev level of ${\mathrm{Ti}}^{47}$, and the 126-kev level of ${\mathrm{Mn}}^{55}$ at corresponding (equal $\xi$) energies. For the $E2\mathrm{}$ transitions a mean ratio of the ${\mathrm{He}}^3$- to ${\mathrm{He}}^4$-induced yields of 0.63±0.02 was found, independent of incident energy in the range 1.0 to 2.5 Mev, in agreement with the calculated value of 0.64 for ${\mathrm{F}}^{19}$ and ${\mathrm{Na}}^{23}$ and of 0.63 for ${\mathrm{Ti}}^{47}$ and ${\mathrm{Mn}}^{55}$. In the single $E1\mathrm{}$ transition (110 kev in ${\mathrm{F}}^{19}$) studied, the experimental ratios range from 0.76±0.07 at $E_{{\mathrm{He}}^3}=1.00\mathrm{} \mathrm{Mev} \mathrm{to} 0.59\pm 0.11$ at $E_{{\mathrm{He}}^3}=1.75\mathrm{}$ Mev. While in accord with the theoretical prediction of 0.76 at the lower energies, the indicated energy dependence of the ratio is suggestive of contributions due to nuclear inelastic scattering of alpha particles. It has been demonstrated that the ratio technique, using ${\mathrm{He}}^3$ and ${\mathrm{He}}^4$ ions, provides an unambiguous multipolarity determination provided that inelastic-scattering contributions can be excluded.