A Program for the Precise Observations of Ultra Heavy Nuclei in Galactic Cosmic Rays

Abstract

The origin of galactic cosmic rays (GCRs) nuclei is still unknown. Precise observation of ultra heavy GCRs would be an important step in resolving their origin including the remaining problems in cosmic ray astrophysics. A program to observe UH nuclei in GCRs is proposed which involves the use of a high performance solid-state track detector on board a long-duration balloon. The program focuses measuring the elemental and isotopic compositions of UH nuclei up to the actinides. The observation of nuclear composition covers a wide range of scientific themes including studies of nucleosynthesis in cosmic ray sources, chemical evolution of galactic material, the characteristic time of cosmic rays, and heating and acceleration mechanisms of cosmic ray particles.

Temperature and pressure conditions for the appropriate performance of charge and mass resolutions in balloon-borne CR-39 track detector for the heavy cosmic rays

“…Fe ion was selected for the benchmark of balloonborne measurement of charge compositions heavier than Fe nuclei in galactic cosmic rays [7]. The irradiations were made at Heavy Ion Medical Accelerator in Chiba, HIMAC, at the National Institute of Radiological Science, NIRS, Japan.…”

“…These results were obtained using highly purified CR-39 detectors (BARYOTRAK) combined with high speed and precise measuring systems [4][5][6]. Precise measurements of ultra heavy nuclei and isotopes in galactic cosmic rays are planned using CR-39 detectors in a long-duration balloon experiment [7]. The registration stability of latent tracks in SSNTD is known to be influenced by environmental factors [8].…”

Applicability of Polyimide Films as Etched-Track Detectors for Ultra-Heavy Cosmic Ray Components

“…7) On the other hand, information of a certain abundance ratio in the ultra-heavy cosmic ray composition spectra, including the ratio of Th to U, can be used to evaluate the validity of modern theories on the origin, acceleration, and propagation of galactic cosmic rays. [8][9][10][11] In these artificial satellite experiments, etched nuclear track detectors with relatively high detection thresholds have been applied in order to avoid the disturbance by an enormous amount of etch pits by proton and other lighter ions. 9,10) In our recent study, we found that the threshold of Kapton was around 2500 keV/m for Ne and Fe ions at energies less than 6 MeV/n.…”

“…Therefore, it is possible to identify the charge of heavy ions from the total length of recorded tracks and the etch pit size or form on each film. 11) Tracks of Fe ions are easily excluded because they cannot produce etch pits on both sides of the Kapton films of 125 m thickness. The total track lengths of relativistic Bi, Th, and U ions are 5.64, 8.02, and 8.40 mm, respectively, provided that the detection threshold was Z= ¼ 150 for them.…”