Energy of Cosmic Rays

E. Regener

Editor’s Note

Physicists had obtained increasingly accurate measurements of the ionisation created in the upper atmosphere by cosmic rays. Using this data, Erich Regener here estimates the energy flux of the cosmic rays impinging upon the Earth. He estimates that 108 pairs of ions are created per second in each square cm. As impinging cosmic rays need an energy of 32 electron-volts to trigger ionisation, this led to an estimate for the total energy flux of 5.2 × 10－3 erg. cm.－2 sec.－1 As Regener notes, a body in thermal equilibrium under illumination from this flux would bear a temperature of 3.1 K, similar to Arthur Eddington’s result for a body in equilibrium with the ordinary radiation coming from stars.ft　　中文

IN Nature for September 3, 1932, p. 364, I published the curve of the intensity of cosmic radiation in the high atmosphere, deduced from measurements made with a self-registering electrometer. It was possible by extrapolation to find the intensity I∞ of radiation at its entrance in the atmosphere. The preliminary value given has now been corrected by the experimental determination of the factor which reduces the measurements with the ionisation chamber at 5 atmospheres to 1 atmosphere. Now the value I∞ is found corresponding to a production of 333 pairs of ions cm.–3 sec.–1 in air at 0° and 760 mm. mercury pressure.ft　　中文

The graphical integration of the curve, giving the ionisation as a function of the height, makes it possible to calculate the total number of ions, produced by total absorption of cosmic rays by a column of air of 1 sq. cm. section. The high value of 1.02 × 108 pairs of ions is found. Some time ago, Millikan and Cameron1 made a similar calculation, which gave a value of only 1.28 × 107 pairs of ions, due to an insufficient knowledge of the intensity in the high atmosphere. Taking the energy required to produce a pair of ions in air2 as 32 electron-volts the flux S of energy coming to the earth from the cosmic rays is found to be 5.2 × 10–3 erg. cm.–2 sec.–1.ft　　中文

From an astrophysical point of view, the great energy of cosmic rays is remarkable. A body which absorbs all the cosmic rays would be heated by them. Equilibrium will be attained when the absorbed flux S of cosmic rays is equal to the heat radiation σ T4 of that body. T works out as 3.1° Kelvin. The value is equal to the temperature (3.18°) which Eddington3 finds for a black body heated only by the heat and light radiation of stars. Eddington’s calculation relates to a point in our local system of stars, but not in the neighbourhood of one of them. If at such a point the flux of energy of cosmic radiation is equal to that on the earth, the temperature of a black body, absorbing entirely the two radiations, rises only to 3.7° Kelvin, according to the T4 law. But at a point in space among the spiral nebulae, the ordinary radiation is very small and causes only a very small rise of temperature. Supposing that cosmic rays originate in such intergalactic space, they would produce an elevation of temperature corresponding to the flux of cosmic rays.ft　　中文

A more detailed report will be published shortly in the Zeitschrift für Physik.ft　　中文

(131, 130; 1933)

E. Regener: Physik. Inst. d. Techn. Hochschule, Stuttgart, Dec. 31.

References:

  1. Phys. Rev., 31, 930 (1928).

  2. Kulenkampff, H., Phys. Z., 30, 777 (1929).

  3. Internal Constitution of the Stars, German edition, 468 (1928).