Experiments on the transmutation of fluorine by deuterons

Abstract

The radioactive effects induced in fluorine by deuteron bombardment are supposed to be due to the formation of 20 F in accordance with the process 19 F + 2 H → 20 F + 1 H, (1) the radioactive body 20 F transforming into 20 Ne as a result of β -ray emission. Crane, Delsasso, Fowler and Lauritsen (1935, 1936) found the value 12 sec. for the half-period of the radioactive decay and the value 5.2 x 10 6 eV for the upper energy limit of the β -ray spectrum. Protons emitted during the bombardment of fluorine by deuterons have been detected by Burcham and Smith (1938) using an ionization chamber and linear amplifier. In these experiments an inhomogeneous group of protons of mean range 11.6 cm. was observed, and this proton emission was attributed to the formation of 20 F according to the process (1). The intensity of this proton group was found to be insufficient to account for the amount of radioactive 20 F which was observed. No proton group having a range greater than 11.6 cm. was detected but the emission of shorter range groups could not be excluded and it was thought that such shorter range groups might be sufficiently intense to account for the amount of radioactive fluorine produced in the transmutation. On the assumption that the total energy release in reaction (1) could be obtained from the energy of the 11.6 cm. group, a mass of 20.0087 was deduced for 20 F in its ground state. This led to the conclusion that the 20 Ne nucleus formed in accordance with the process 20 F → 20 Ne + β (2) must be left with an excitation energy of 4.1 x 10 6 eV which it might subsequently lose as a γ -ray, so that every β particle from 20 F should be followed by a γ -ray from 20 Ne. Some support for this view was obtained by the detection of a γ -ray activity decaying with a period of about 12 sec. from fluoride targets after deuteron bombardment. Measurements of the energy of these γ -rays are described and discussed in this paper.