[24th ICNTS @ Bologna (Italy) 04/09/2008] Control of the detection threshold of CR-39 track detector for the measurement of ultra heavy nuclei in galactic cosmic rays S. Kodaira1, N. Yasuda1, N. Hasebe2, T. Doke2, S. Ota2, and K. Ogura5 National Institute of Radiological Sciences Waseda University Nihon University
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 ?
Scientific Objectives Precise observation of ultra-heavy nuclei (Z>30) in galactic cosmic rays (GCRs) Origin: Primary compositions of elements and isotopes in GCRs. The freshly-synthesized material of R-process is enhanced in GCRs ? Injection mechanism: FIP or Volatility ? Life-time of GCRs: Mean-life time, Delay time between nucleosynthesis and acceleration Search for the nearby source History of Galactic materials Study of nucleosynthesis process and its site Search for trans-Uranium nuclei predicted theoretically
Need SSTD with high threshold Flux of Z<30 nuclei >> Flux of trans-iron nuclei Using high sensitive SSTD such CR-39 Z<30 nuclei are background tracks for the observation of ultra heavy nuclei Fe Ultra heavy nuclei HEAO-3-C3 Binns et al., (1989)
Objectives PEW-x solution (15wt%KOH+xwt%C2H5OH+ (85-x)wt%H2O) 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
Beam exposure & Etching condition -- Exposed heavy ion @ HIMAC--- Ion Fe, Kr, Xe Energy < 500 MeV/n (36 ≤ Z*/b ≤115) --- Etching condition --- Solution 1) PEW-x; x=35, 50, 65wt% for ethanol 2) 7N NaOH Temp. 1) 50C, 2) 70C Time 1~240 min
Variation of response curve for PEW-x concentration 70C Temp. PEW-50 (50wt% for ethanol) is adequate to detect heavy ion
Characteristics of bulk etch rate for PEW-50 Our normal etching condition: 7N NaOH 70C: Vb=2.1mm/hr Vb is ~22 times @ PEW-50 70C ~7 times @ PEW-50 50C min!
Response curve by PEW-50 etching
Surface condition after the PEW etching PEW-50 70C PEW-50 50C B=95.3mm B=33.2mm B=22.0mm B=84.0mm B=39.0mm B=33.2mm Etching longer than roughly B=30mm makes extremely unclear edge of etch-pit
Charge resolution for Kr ion PEW-50 70C PEW-50 50C Poor charge resolution is caused from “unclear edge“ of etch pit ?
Additional etching by 7N NaOH solution 7N NaOH 70C (8hr) etching after the post-etching of PEW-50 Only PEW-50 70C Recover very clear edge of etch pit by additional 7N NaOH etching ! PEW-50 70C+7N NaOH 70C
Drastic improvement of charge resolution PEW-50 70C + 7N NaOH addition sZ=0.30cu@Kr sZ=0.21cu@Kr Preliminary
PEW+NaOH hybrid etching is very useful technique for: Summary Verified the performance in CR-39 (BARYOTRAK) detector etched by PEW-x solution: ① Response curve - Suppress effectively light ion track and therefore inclination of response curve becomes steep - Variable response curve by changing ethanol concentration (xwt%) - Optimum ethanol concentration should be x=50wt% - Optimum temperature should be 70C - Threshold of Z/b~40 in case of PEW-50 70C ② Charge resolution - Drastic improvement of shape of etch pit and charge resolution by additional 7N NaOH - Charge resolution for Kr: 0.2cu (only single layer) PEW+NaOH hybrid etching is very useful technique for: - Observation of ultra heavy nuclei in galactic osmic rays - Measurement of nuclear interaction (charge changing cross section) of ultra heavy ion
Backup Chart
PEW-50 50C + 7N NaOH PEW-50 70C + 7N NaOH