The disintegration of boron by slow neutrons

Abstract

Photometrical measurements of the photographic images of cloud tracks of the disintegration of boron by slow neutrons,have enabled the ranges of both the He and the Li particle to be determined. We find that the He particle has a range of 7·0 ± 0·3 mm. and the Li particle a range of 4·3 ± 0·2 mm. in standard air.We deduce that the 7Li nucleus is usually formed in an excited state, with energy of excitation of either 0·5 or 0·8 M.e.V. The wide latitude in excitation energy is due to the uncertain state of our knowledge of the energy-range relation for α-particles.

The disintegration of boron by slow neutrons. II

“…Another advantage of using a gas of high atomic number was that it increased the chance of scattering at the end of a track and so made more pronounced the characteristic 'curl' at the end. This generally enabled a boron disintegration to be distinguished for certain from a proton * An account of the earlier work on this disintegration by other authors is contained in the paper by Bower, Bretscher and Gilbert (1). recoil, for the disintegration, resulting in the emission of two particles travelling in opposite directions, will show a curl at each end of the combined track, whilst a proton cannot have a curl at the beginning.…”

Range-energy relations

“…Any such effects should be noticeable in the comparison at low energies of the stopping powers of different gases containing the same type of atoms. However, it was noticed very early that, for gases, the stopping power was the sum of the stopping powers of their constituents (Bragg and Kleeman 1905). Recent work has confirmed this and it has been used to deduce the atomic stopping power of other elements.…”

“…More accurate relations were sought by finding correction curves to this relation (Rutherford, Wynn-Williams, Lewis and Bowden 1933) or by altering the exponent of the velocity. For instance, the relation R = kV3 26 was found to be better for ranges greater than 5 cm (Briggs 1933). Convenient as these empirical relations were, P S P R 4 successful attempts have been made since then to extend the range-energy relation beyond these limits by theoretical predictions for the rate of energy loss, and these have been based on classical and quantum mechanical models of the atom.…”

Variation of ionization with range of α-particles, protons, deuterons and 3H particles

“…Since the above investigation was completed the method has been applied to combined 'Li and 4 He tracks produced in the slow neutron disintegration of boron (8). It was found possible to detect a pronounced density change in the track corresponding to the change in the rate of ionization at the common point of origin of the oppositely directed 7 Li and 4 He particles.…”