Improvement of Mass Resolution for Iron Isotopes in CR-39 Track Detector

Abstract

The capability of the CR-39 track detector for isotope identification was verified using 56Fe and 55Fe beams from the heavy ion accelerator HIMAC at NIRS. A CR-39 stack was exposed to 56Fe and 55Fe beams with the energies of 460 MeV/nucleon. Drastic improvements in the accuracies of microscopic image analysis and detector thickness measurement enabled us to identify those iron isotopes with high mass resolution using the CR-39 track detector. As a consequence of the reduction of systematic errors, the mass resolution for iron isotopes in the CR-39 detector was obtained to be 0.22±0.03 amu in rms. The mass resolution newly obtained by the CR-39 detector was compared with the former result and found to be 66% better than the former value of mass resolution as a result of reducing the systematic errors of mass dispersion. Moreover, the ultimate mass resolution of the CR-39 detector was estimated by calculation using those experimental results. As a consequence of reducing the random error, it is expected that the mass resolution for iron isotopes can ultimately approach to ∼0.10 amu in the CR-39 detector.

Track detector of CR-39-DAP-copolymer with variable threshold to detect trans-iron nuclei in galactic cosmic rays

“…A solidstate track detector (SSTD) such as CR-39 track detector is very promising for the large-scale observation of such nuclei in GCRs. It is known that CR-39 track detector has a good mass resolution for iron nuclei (Kodaira et al, 2004(Kodaira et al, , 2007. However, a large number of background tracks produced by iron nuclei and other particles lighter than iron will cover up the tracks of trans-iron nuclei in GCRs during exposure in space.…”

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

“…Fig. 6 shows a part of the previously obtained relationship between the sensitivity, S, and residual range, R, in a logarithmic scale for Fe ions in CR-39 detectors [2]. The stopping behavior of heavy ions in a uniform media is identical to each isotope from the view of the end points is strongly dependent on its charge and also affected by its mass.…”

“…In the oblique incidence, the cone length was obtained by analyzing the two different microscopic images of focal plane on the etched surface and the cone-tip for an etch pit, taking incident angle into account. The detail procedure is described elsewhere [2]. The track registration sensitivity, S, was obtained using the following relation:…”

“…In recent studies, we experimentally demonstrated that the adjacent isotope (A = 55 and 56) of iron nuclei (Z = 26) are clearly resolved with mass resolution of <0.22 amu (atomic mass unit) [1,2] and individual nuclear charge of trans-iron nuclei (Z>30) is separated with the charge resolution of <0.21 cu (charge unit) [3]. These results were obtained using highly purified CR-39 detectors (BARYOTRAK) combined with high speed and precise measuring systems [4][5][6].…”

Mass spectrometry analysis of etch products from CR-39 plastic irradiated by heavy ions

“…remains without clear explanation. A fundamental understanding of the physical and chemical processes of nuclear track formation from track registration and latent track formation through the chemical etching process is important to the design of new polymers nuclear track detectors bearing novel properties such as variable LET detection threshold [8,9], improved charge and mass resolutions [10,11], etc.…”