High-Resolution Measurements of Slowing Cosmic Rays from Fe to U

Abstract

We have identified cosmic rays with Z = 40, 44, 52, 71, 77, 78, and 92 slowing in a balloon-borne stack. The values of Z assigned by both Lexan plastic detectors and nuclear emulsions were the same to within two units. Both low-and high-energy heavy cosmic rays are synthesized in the rapid neutron-capture process.We have found that nuclei with Z up to 92 are present in the low-energy cosmic radiation. Their abundance relative to Fe is similar to that previously observed at energies above ~1 GeV/ amu. 1,2 From their large rate of change of ionization as they slow down in a detector, their atomic number and energy can be much better determined than if they were relativistic. These observations are important as a basis for understanding the origin and propagation of the cosmic rays and as a standard of comparison with results obtained from the analysis of tracks of ancient cosmic rays left in meteorites 3 and moon rocks. 4

Theoretical and experimental aspects of the energy loss of relativistic heavily ionizing particles

“…Furthermore, it is well known that successful particle identification over a limited dynamic range is insensitive to the -129-response function used in the analysis (witness the good charge resolution obtained ~ith plastic scintillators which was referred to in the previous sub-section). However, the data presented by O 'Sullivan et. al.…”

“…(1971) are sufficiently good to rule out the REL model. These We plot the data of O' Sullivan et al (1971) in Fig. V1.5 and 6.…”

A database of charged cosmic rays

“…The presence of heavy Z < 30 (Freier et al 1948a,b) and extremely heavy Z ≥ 30 elements (Fowler et al 1967;Blanford et al 1969) in the cosmic radiation were among the main discoveries related to Galactic CR nuclei, which culminated with the discovery of a few Z > 90 events (Fowler et al 1970;O'Sullivan et al 1971;Price et al 1971). Isotopes and, in particular, the radioactive CR clocks were identified with more or less difficulties due to their decreasing abundance and mass separation with increasing atomic number:…”

Propagation of cosmic rays in the galaxy

“…are: (a) Price et al (1971) from a study of the abundance ratio of nuclei with Z>85 to those with 70<Z-83 conclude that the life time of cosmic rays is <107 yrs and possibly as low as 106 yrs; (b) since the nucleus 5 3 Mn decays only by K-capture with a mean life on two million years, Reames (1971) has concluded from an analysis of the observed ratio of Cr/Mn as a function of energy, that the cosmic ray age is consistent with the confinement of cosmic rays in the Disk rather than in the Halo.…”

“…Nevertheless, because of the large errors in the ratios (CRS/SS), it is difficult at present to distinguish between explosive nucleosynthesis with further The study of abundances of cosmic ray nuclei of charge >30 gives a clue to the process of nucleosynthesis. The abundance of ultra heavy nuclei at source given in Table 4.1 is based on the estimates of who made use of all the existing observations (Price et al, 1971b;O'Sullivan et al, 1971;Shirk et al, 1973;Blanford et al, 1973a,b;Binns et al, 1973;. These abundances seem to be in better agreement with r-process than with the total solar abundances relative to iron (Fowler et al, 1970;Price et al, 1971b); however, a more reliable distinction can be made only when individual abundances are measured, because in some of the charge groups used in Table 4.1 only a few elements,depending upon the process of nucleosynthesis, are expected to dominate the observed flux .…”