Control of the detection threshold of CR-39 track detector for the measurement of ultra heavy nuclei in galactic cosmic rays

1
Control of the detection threshold of CR-39 track
detector for the measurement of ultra heavy
nuclei in galactic cosmic rays
24th ICNTS _at_ Bologna (Italy) 04/09/2008

• S. Kodaira1, N. Yasuda1, N. Hasebe2,
  T. Doke2, S. Ota2, and K. Ogura5
• National Institute of Radiological Sciences
• Waseda University
• Nihon University

2
Goal of Cosmic Ray Research
? Origin Where and How are galactic cosmic
rays (GCRs) accelerated
? Are the Young or Old? ? Acceleration
Is the temperature at the
acceleration site Hot or Cold ? ?
Propagation How do GCRs propagate in the
Galaxy ?
3
Scientific Objectives
Precise observation of ultra-heavy nuclei (Zgt30)
in galactic cosmic rays (GCRs)

• Search for trans-Uranium nuclei predicted
  theoretically

4
Need SSTD with high threshold
Flux of Zlt30 nuclei gtgt Flux of
trans-iron nuclei Using high sensitive SSTD
such CR-39 Zlt30 nuclei are background tracks
for the observation of ultra heavy nuclei
Fe
Ultra heavy nuclei
HEAO-3-C3
Binns et al., (1989)
5
Objectives
PEW-x solution (15wtKOHxwtC2H5OH
(85-x)wtH2O) has a possibility to - Make to
desensitive the track registration sensitivity
of CR-39 track detector - Improve charge
resolution because of shrinking tracks of
rather lighter nuclei - Improve surface
condition after the etching
Somogyi Hunyadi, (1979) Ogura et al., (2001)

• Optimization of PEW-X etching condition using
  high purity CR-39 (BARYOTRAK)
• Verification of the performance of CR-39
  (BARYOTRAK) by PEW-x solution

6
Beam exposure Etching condition
-- Exposed heavy ion _at_ HIMAC---
Ion Fe, Kr, Xe
Energy lt 500 MeV/n (36 Z/b 115)
--- Etching condition ---
Solution 1) PEW-x x35, 50, 65wt for ethanol 2) 7N NaOH
Temp. 1) 50?C, 2) 70?C
Time 1240 min
7
Variation of response curve for PEW-x
concentration
70?C Temp.
PEW-50 (50wt for ethanol) is adequate to detect
heavy ion
8
Characteristics of bulk etch rate for PEW-50
min!
9
Response curve by PEW-50 etching
10
Surface condition after the PEW etching
PEW-50 70?C
PEW-50 50?C
Etching longer than roughly B30mm makes
extremely unclear edge of etch-pit
11
Charge resolution for Kr ion
PEW-50 70?C
PEW-50 50?C
Poor charge resolution is caused from 砥nclear
edge