PROTONS IN COSMIC RADIATION AT SEA LEVEL

The paper under review1 consisted of measuring the spectrum of the proton component at sea level. The arrangement of the apparatus, consisting of two Wilson chambers controlled by Geiger counters, is shown in Fig. 1. The upper chamber, placed in a magnetic field, served to measure the momentum of charged particles stopped in 14 lead and copper absorbers located inside the second, lower, chamber. The total thickness of these 14 plates, expressed as the equivalent thickness of lead in stopping power, was 10 cm. Measurements were made with the placement, above the entire setup, of lead blocks of thickness 2, 7, 17, or 48 cm. The masses of the particles that stopped in the absorbers of the lower chamber were determined from their range, which was determined by the number of the plate that absorbed the particle (lower chamber), and from the momentum measured in the upper chamber. During the entire measurement period, 161 mesons and 72 protons were recorded that stopped in the absorbers of the lower chamber.

Fig. 1.

The range spectrum of these protons and mesons is shown in Fig. 2, where along the abscissa is plotted the thickness of the upper lead absorber \(P\),

Fig. 2.

placed above the entire system, and along the ordinates—the number of particles that stopped in the absorbers of the lower chamber.

This spectrum also includes data reported earlier in paper2. The proton spectrum is described fairly well by the formula

\[ N(R)=Cl^{-\frac{R}{tL}}, \]

where \(L=12\) cm, and \(l\) is the range in 1 cm of lead. If one calculates the total number of protons in this spectrum, it turns out that they constitute about 25% of the meson intensity in the range interval 2–48 cm of lead. Such an intensity of the proton component is in sharp contradiction with all data on protons at sea level, according to which their number should be an order of magnitude smaller. The authors suppose that, under the conditions of their experiment, processes leading to the generation of protons in the absorber located above the instrument take place. The main process of this kind may be the generation of protons by fast neutrons. It is known that even at sea level there is an appreciable number of neutrons whose energy is sufficient for them to be able to generate fast protons either in nuclear disintegrations or in a charge-exchange process with a neutron. Such a phenomenon of proton generation by neutrons was observed at an altitude of 3250 m by A. I. Alikhanian, M. I. Daion, and V. M. Kharitonov[^3].

Fig. 3.

To check the correctness of this assumption about the generation of protons by the neutral component, the authors measured the absorption of the proton beam in an absorber placed in the lower chamber. In this case, generation phenomena from the neutral component are completely excluded. The measured absorption curve on a semilogarithmic scale is given in Fig. 3, where, for comparison, the proton spectrum from Fig. 2 is also shown. We see that the spectrum of protons for which generation phenomena are excluded (1) falls considerably more rapidly than spectrum 2. If, however, the intensity of protons is calculated from spectrum 1, it turns out that the number of such protons is approximately 7% of the meson intensity, which is considerably superior in magnitude to all available experimental data on the intensity of protons at sea level. The difference between the two spectra in Fig. 3 gives an idea of the intensity of the process of generation of fast protons by neutrons at sea level.

A. V.

References Cited

1. E. L. Goldwasser, T. C. Merkle, Phys. Rev. 83, 43 (1951).
2. T. C. Merkle, E. L. Goldwasser and R. B. Brode, Phys. Rev. 79, 926 (1950).
3. A. I. Alikhanian, M. I. Daion, V. M. Kharitonov, ZhETF 19, 739 (1949).