The Radioactivity Induced in Oxygen by Deuteron Bombardment

Abstract

An induced radioactivity of half-life 1.16 minutes has been observed after the bombardment of oxygen or its compounds by 3 MV deuterons. The disintegration particles were observed to be positrons. Chemical tests showed that the active substance was an isotope of fluorine. The probable reactions are therefore: ${\mathrm{O}}^{16}+{\mathrm{D}}^2={\mathrm{F}}^{17}+n^1; {\mathrm{F}}^{17}={\mathrm{O}}^{17}+e^{+}.$ A product of the same properties was already known to be induced in nitrogen under $\alpha -\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{l}\mathrm{e}$ bombardment. The activation function of oxygen has been measured by collecting radioactive recoil atoms at several points along the path of the deuteron beam when it is passing through an atmosphere of oxygen. The excitation curve drops very rapidly and goes to zero at about 2 MV deuteron energy. This is best accounted for by assuming that energy disappears in this reaction, and that the energy of reaction is the negative of the threshold energy. By correcting for recoil, $Q=-1.8\mathrm{}$ MV. To confirm this estimate of the energy of reaction, the maximum angle between the direction of the deuteron beam and the paths of the radioactive recoil atoms has been measured. A piece of optical quartz (Si${\mathrm{O}}_2$) was bombarded at a glancing angle by a narrow beam of deuterons, and radioactive recoil atoms were collected on a cylindrical strip of copper which was placed about the target. The maximum angle of recoil was found to be about 30° which corresponds to $Q=-1.3\mathrm{}$ MV. The agreement with the value, -1.8 MV found previously, is within the errors of the measurements. In order to check the method the same experiment was performed with a graphite target; the longer half-life of the active material made possible a more accurate measurement. The maximum angle of recoil was found to be 42° for the activation of carbon; this corresponds to $Q=-0.1\mathrm{}$ MV for the reaction ${\mathrm{C}}^{12}+{\mathrm{D}}^2={\mathrm{N}}^{13}+n^1$. This agrees reasonably well with the experimental value of $Q$ found by Tuve and Hafstad and with the value of $Q$ which is deduced from maximum energy of the positrons from ${\mathrm{N}}^{13}$ and the range of the protons which are emitted when carbon is bombarded by deuterons.