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A NEW TYPE OF NUCLEAR REACTIONS OBSERVED IN PHOTOEMULSIONS
Recently, photographic plates with thick emulsion layers have come to be used especially successfully for the study of nuclear reactions. Their use has made it possible to discover new types of nuclear disintegrations. Fowler, Burrows, and Curry*) report an interesting reaction observed by them when photographic plates were irradiated with deuterons of energy 9 MeV.
The deuterons, obtained from a cyclotron, fell on the photographic plate at angles close to the grazing angle. With an exposure of the photographic plates of 0.01 sec, a sufficient number of tracks was produced in the emulsion. Along with other tracks, 5 cases were observed in which 5 tracks emerged from a single point of the photographic plate. One of them should be ascribed to the incident deuteron, which causes the disintegration of the nucleus with the emission of four charged particles. The authors put forward the hypothesis that in this case the reaction leads to the complete disintegration of the nitrogen nucleus into \(\alpha\)-particles, namely:
\[ \mathrm{N}^{14} + \mathrm{H}^{2} \to 4\mathrm{He}^{4}. \]
Indeed, the character of the tracks makes it possible to assert that the four denser tracks belong to \(\alpha\)-particles (the thinner track belongs to the incident deuteron, which produces less ionization in comparison with the \(\alpha\)-particles). The photographic-plate method makes it possible to register both the energy of the \(\alpha\)-particles and their momentum. This made it possible for the authors to verify the validity of the assumption they had made by comparing the experimental results with the requirements of the conservation laws. Obviously, the component of the total momentum of the \(\alpha\)-particles in the plane perpendicular to the direction of the deuteron must be equal to 0. In the three cases studied this holds to within the experimental error. If the direction of the deuteron is taken as the \(x\)-axis, then, according to the law of conservation of momentum,
\[ P_x^d = \sum P_x^\alpha, \]
where \(P_x^d\) is the momentum of the deuteron, and \(P_x^\alpha\) is the component of the momentum of the \(\alpha\)-particle in the direction of the \(x\)-axis. If the momentum is measured by the formula
\[ P = \sqrt{2mE}, \]
where \(E\) is the energy of the particle in MeV, and \(m\) is the mass number, then the results of the observations can be reduced to the following table:
) P. H. Fowler, H. B. Burrows, W. J. J. Curry, Nature, 159*, 569 (1947).
| $N$ | $P_x^d$ | $\sum P_x^a$ | $\sum E_{\text{(in MeV)}}^a$ | $E^d$ | $Q$ |
|---|---|---|---|---|---|
| 1 | 5.61 | 5.75 | 14.20 | 8.29 | 5.91 |
| 2 | 5.49 | 5.69 | 14.33 | 8.10 | 6.23 |
| 3 | 5.80 | 5.52 | 13.19 | 7.58 | 5.61 |
Here $Q$ denotes the energy released in the disintegration of the nitrogen nucleus, equal to the difference between the energy of the $\alpha$-particles and the energy of the deuteron. The mean value of $Q$ differs from that calculated from the mass defects of $N^{14}$, $He^4$, and $H^2$ by only 0.4 MeV. Thus, verification by means of the conservation laws proves the validity of the authors’ proposed course of the nuclear reaction.
P. Nemirovsky