New Nuclear Reactions Induced by 2-Mev Lithium Ions; the Masses ofB13andC15

A lithium ion source has been developed which can be used in a standard 2-Mev van de Graaff generator, producing a focussed beam of 1-2 microamperes of magnetically separated ${\mathrm{Li}}^7$. Above 1.4 Mev the beam produced disintegration particles from lithium targets, and above 1.8 Mev disintegrations from beryllium were observed. The reaction ${\mathrm{Li}}^7({\mathrm{Li}}^7, p){\mathrm{B}}^{13}$ was studied by observing the protons at 90° from the lithium beam. The $Q$ value is 5.97±0.05 Mev and the $M-A$ of ${\mathrm{B}}^{13}$ is 20.39±0.05 Mev, corresponding to a physical atomic weight of 13.02190±0.00005. The cross section for the ejection of ${\mathrm{B}}^{13}$ protons into unit solid angle at 90° rises monotonically and exponentially from 1.2 to 22 microbarns between 1.4 and 2.0-Mev bombarding energy.