Emission of Neutrons from Argon, Chlorine, Aluminum and Some Heavier Elements Under Alpha-Particle Bombardment

Abstract
The emission of neutrons from chlorine, argon, scandium, titanium, manganese and iron under alpha-particle bombardment was established. The yield from argon is considerable and enabled a measurement of the energy of the neutrons to be made: the majority are associated with a group of energy change -5.6±1.0 Mev, but two groups must be present. The excitation curve for these neutrons was plotted for alpha-particle energies between 3.5 and 9.0 Mev and varies smoothly in agreement with penetration through a barrier of radius 7.6×1013 cm. This smooth variation means that the total neutron yield does not change rapidly as a new group is excited, from which it is deduced that observations on single groups would show apparent resonance effects. The excitation curve for chlorine fits a theoretically derived function for a nuclear radius of 6.0×1013 cm and a similarly plotted curve for aluminum agrees with a radius of 5.8×1013 cm. These last elements have radii approximately fitting the formula R=R0A13 with R0=1.94×1013, while argon has a radius which is definitely too large to fit the above relation. This abnormally large radius is linked with the large neutron content of the argon nucleus.

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