P.S. Freier

The low energy end of the cosmic ray spectrum of alpha-particles

Abstract An experiment has been carried out at Saskatoon, Canada, at a nominal geomagnetic latitude of 60.5°N, which shows the form of the low energy end of the cosmic ray alpha particle spectrum independent of the earths magnetic field. The differential spectrum shows a maximum at about 300 mev per nucleon. The number of particles on the low energy side of the maximum is too great to be accounted for by secondary production, and it is believed that this spectrum represents the differential spectrum of primary alpha particles outside the earths magnetic field. A re-analysis of previous experiments at a lower geomagnetic latitude, 56°N, in the American continent, gives a spectrum very similar to the one obtained in Saskatoon. As a consequence of this it appears that the cutoff energies experienced by cosmic ray particles over the American continent are probably lower than those predicted by geomagnetic theory.

The primary alpha particle spectrum over North America and geomagnetic cut-off energies

The series of flights made in North America have shown that cosmic ray cut-off energies cannot be computed with conventional geomagnetic co-ordinates. The measured cut-off indicates that the effective cosmic ray latitudes in the United States are 4° higher than would be obtained from conventional geomagnetic co-ordinates. This effect is opposite to the effect observed in England where Waddington found that cosmic ray cut-off energies indicated effective cosmic ray co-ordinates 4° lower than those given by geomagnetic co-ordinates. The measurements reported here, taken together with the English measurements, appear to be consistent with the suggestion of Rothwell that cosmic ray co-ordinates more nearly resemble the magnetic dip co-ordinates of the earth than they do the geomagnetic co-ordinates of the earth. Over the period of the sunspot cycle which these measurements cover, there appears to be no evidence within the statistics of our experiments (i.e. ± 10 % for individual absolute flux measurements) of a correlation between the α-particle fluxes and the solar activity.

A cosmic ray jet in the 1012 electron volt energy range

SummaryA 22.4 litre stack of emulsions was exposed in Minnesota during Septemper 1956 in a balloon flight at 116000 feet. The emulsion stack, which was flown in a cooperative experiment with University of Bristol, weighed 200 lbs and had dimensions of 16 in. × 12 in. × 7 in. The largest jet so far found by naked-eye scanning traversed the entire Minnesota half of the stack with a total lenght of 26 cm. The primary interaction is a 6 + 1α star. In the nine radiation lengths of the Minnesota portion of the stack, the jet multiplied from nine particles, mainly in two cores, to 8 000 particles. The electromagnetic, cascade appeared to be initiated by several γ rays probably from the decay of two neutral mesons. The electromagnetic cascade was still increasing in numbers after nine radiation lengths. At approximately 23 cm from the primary interaction, the primary particle produced a meson jet in the core of the electromagnetic cascade. The meson star was classified as 4 + 80p. The angle containing half of the 80 minimum ionization particles was 3.10-4 rad. The energy of the primary α-particle is estimated to be ⩾ 1015 eV. The energy in this event which appeared in electronic component is approximately 1014 eV.