I am also grateful for the willing cooperation of the many officers and men of the U. This describes a study of the energy spectrum of cosmic rays at an altitude of 30,000 feet (9200 rn) above sea level. The construction and operation of the device was carried out under the direction of Professor Carl D.
For the work described here, only the electromagnet and the basic mechanical parts of the cloud chamber were used, the. The cloud chamber, with a diameter of 17 meters and a depth of 2 meters, is of the type with reciprocating pistons. The expansion of the cloud chamber is completed in about 4 milliseconds after passing the beam, creating very sharp trails.
The room temperature is determined by that of the iron and copper in the center of the magnet. The water temperature can be controlled so that the chamber temperature remains constant at ~1°C throughout the flight.
ENERGY SPECTRUM -- THE EXPERIMENTAL DATA
Due to its large mass, the latter follows the ambient temperature only very slowly; therefore, the temperature balance must be established by cooling or heating the cabin several hours before the flight. During flight, the temperature of the magnet and thus the temperature of the chamber is determined by the temperature of the cooling water circulating through the magnet coils. The curvatures of all tracks with radii less than 140 em were measured by direct comparison of the projected tracks with a family of circular arcs.
For low-momentum tracks, the accuracy of the measurements is limited by the inhomogeneity of the magnetic field, while for high-momentum tracks, the measurement accuracy is limited by the distortions produced by the mass motion of the gas inside the cloud chamber. Of the 245 runways, 206 are classified as counter-controlled runways and 39 as random runways. are the ones that couldn't have obstructed the room either because the positions of their footprints in the room rule it out. the possibility of their passage through both com1tors or because their extreme sharpness indicates that they passed through the chamber after the expansion had taken place. The charge sign of a cosmic ray particle is uniquely determined by its direction of curvature in a magnetic field, provided the direction of motion of the particle is known.
For the traces reported here, the direction of the magnetic field is such that positive traces curve clockwise, while negative traces curve counterclockwise. Because it is impossible to indicate the direction of motion of the particles, but since most cosmic ray particles are known to be traveling downward, it is assumed for classification purposes. Fig. l and 2 show representative traces of the same momentum, one of which has ionization greater than the minimum while the other has the ionization minimum.
Because the magnetic curvature measures the momentum and not the energy of the particle, the 11energy11 distributions are given in terms of the magnetic curvature, Hp, in gauss-em.
DISCUSSION OF RESULTS
An examination of the primary proton hypothesis may perhaps be valuable in forming more definite conclusions. The rest of the discussion can apply equally well to any high-energy proton left over from the first impacts of the primary. Those protons having energies in the 1 to 2.5 Bev range survive to the 30,000 ft level and make up a fraction of the protons observed there.
It will be recalled that the data show that as many as 30 percent of the particles at 30,000 feet are protons. It seems difficult to explain such a large fraction of particles assuming that they are all primary protons. We thus come to the likely conclusion that at least three-quarters of the protons found at 10,000 meters above sea level are of secondary origin.
In 1934, Anderson and Neddermeyer(3) reported a determination of the sea-level spectrum for counter-controlled tracks only. All beams were assumed to be directed downwards to determine the charge sign of the particles. Since the discovery of the mesotron, single particles at the surface of the sea are assumed to be mesotrons.
Blackett discusses in some detail the noticeable significance of the "fine-structure" visible in the curves. Arrangement C resulted in similar positive and negative spectra, the main difference between the results of arrangements B and C being a shift of some of the very high energy particles (non-deflected rays) to the negative spectrum. A positive excess of about ten percent of the total number of particles is found whether the lead is present or not.
The corresponding x-axis zoom to be used depends on the degree of curvature of the track. The new curve is seen to be just a different segment of the same parabolic curve. VVhen the parabola has been found which fits the plotted track points, the magnetic curvature, Hp, can be calculated.
For sharp tracks, the accuracy of ma6~etic curvature measurements is limited primarily by the distortion created in the tracks by gas movement within the cloud chamber. Examination of many trace plots is necessary to determine the type and magnitude of distortion. Misinterpretation of such data is avoided by a final inspection of the projected track photograph.
By looking obliquely across the trace image, it can be determined whether the apparent distortions shown in the drawn trace are real.
