Construction of a pressure Van de Graaff generator and its application to nuclear physics

摘要

An electrostatic generator of the Van de Graaff type has been constructed in a pressure tank in combination with an accelerating tube designed to produce one to two million volt ions. Tests with the high potential terminal negative have indicated that the installation might be a practical compact source of high voltage x-radiation for possible therapeutic application. With the terminal positive, it is possible to obtain and to focus on a target five to ten microamperes of positive ion current with proton or deuteron currents of the order of 5-10% of the total, homogeneous in energy to one percent, or better.ududThe machine has been used to study the resonance reactions of Fluorine under proton bombardment at two energies, 0.334 and 0.927 Mev., by measuring the gamma ray energies in a cloud chamber at both values. From the fact that the energy difference of nearly 0.6 Mev. does not appear in the gamma ray, it is concluded that it results from a transition in O16, from a level excited to 6.3 Mev. to the ground state, and that the triplet state of (Ne20)* formed by the capture of the resonant protons must drop to (O16)* with emission of a short range alpha particle. The possibility that the gamma ray may result from the transition to a level in Ne20 preceding the emission of the alpha particle is considered to be ruled out by this evidence. Some indication for an additional gamma ray line at about 10 Mev., amounting to two or three percent of the total radiation is found at the higher resonance, but is not considered as established, and the general character of the reaction at the high resonances is certainly the same as that of the lowest one. The experimental facts are found to be not inconsistent with theoretical expectations, but the theory is still far from giving a complete picture of the situation. Further work, both experimental and theoretical, is indicated on the problem.ud