Production and use of isomeric nuclear beams.

Abstract

An intense secondary beam of excited isomeric nuclei, $\sp{18}$F$\sp{m}$ (J$\sp\pi = 5\sp+,$ E$\sb{\rm x}$ = 1.1 MeV, T$\sb{1/2}$ = 162 ns), has been produced using the direct transfer reaction $\sp{12}$C($\sp{17}$O,$\sp{18}$F$\sp{m})\sp{11}$B. Three different magnetic devices have been tested as fragment separators, for refocusing the secondary beam. The relative merits of these devices are considered. The uses of isomeric nuclear beams in astrophysics and medical physics are discussed. A scattering experiment, $\sp{18}$F$\sp{m}$(p,p)$\sp{18}$F$\sp{m}$ was performed using a 412 MeV beam of $\sp{18}$F$\sp{m}$ incident on a polyethylene foil, (CH$\sb2)\sb{\rm n},$ at angles between 30$\sp\circ$ and 120$\sp\circ$ in the center of mass. A novel "$\gamma$-tagging" technique was used to identify the isomer, by its unique $\gamma$-decays. These results are compared to predictions based on $\sp{18}$O optical model parameters. In addition, using a limited data set from beam diagnostics, the total reaction cross section for $\sp{18}$F$\sp{m}$ + $\sp{28}$Si was measured and an average cross section of 2400 $\pm$ 700 mb was extracted.