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Short-range, high-LET recoil tracks in CR-39 plastic nuclear track detector. E. R. Benton 1 , C. E. Johnson 1 , J. DeWitt 1 , N. Yasuda 2 , and E. V. Benton 3 1 Dept. of Physics, Oklahoma State University, Stillwater, OK 74078 USA 2 National Institute of Radiological Sciences, Chiba, Japan
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Short-range, high-LET recoil tracks in CR-39 plastic nuclear track detector E. R. Benton1, C. E. Johnson1, J. DeWitt1, N. Yasuda2, and E. V. Benton3 1Dept. of Physics, Oklahoma State University, Stillwater, OK 74078 USA 2National Institute of Radiological Sciences, Chiba, Japan 3Dept. of Physics, University of San Francisco, San Francisco, CA 94117 USA
Integral LET Fluence Spectra60, 230, & 1000 MeV Protons on CR-39 PNTD CR-39 PNTD: 36 hr etch in 50°C, 6.25 N NaOH, B =~8 mm
Proton- & Neutron-Induced Target Fragment Reactions
Contribution to Dose and Dose Equivalent from Proton-Induced Target Fragmentation LLUMC Proton Therapy Beam, Bragg Plateau • Contribution of high LET (5 keV/m) particles to dose ranges from 3 to 4.5% • The contribution of high LET particles to the dose equivalent ranges from ~25 to ~35% • Only includes fragments with range >8 mm... shorter range fragments are not included.
CR-39 PNTD Exposures for AFM Analysis 10 µm x 10 µm • CR-39 PNTD: 2-4 hr etch in 50°C, 6.25 N NaOH B = 0.5-1.0 mm • Primary Proton Fluence: ~1010 cm-2
31010 cm-2 1 GeV Protons on CR-39 PNTD 4 hr etch, 1 mm removed, 103 ´ 79 mm2
Short-Range, High-LET Recoil Tracks in CR-39 PNTD Light Microscopy Exposure: 108 cm-2 230 MeV Protons 36 hr etch, 8 mm removed 328 ´ 253 mm2 AFM Exposure: 1.5 ´ 1012 cm-2 1 GeV Protons 4 hr etch, 1 mm removed 103 ´ 79 mm2 No track >100 keV/ mm For Comparison: 108 cm-2 1 GeV/n Ti 4 hr etch, 1 mm removed 103 ´ 79 mm2 (~100 keV/ mm)
1.51010 cm-2 230 MeV Protons on CR-39 PNTD 4 hr etch, 1 mm removed, 103 ´ 79 mm2
Stopping Particles, Low Enery Scattering1 GeV Protons on Au Target
Proton-induced Target Fragmentation as functions of Target Z and Energy CR-39 (12C &16O) 27Al 28Si 64Cu 108Ag 197Au 60 MeV (LLUMC) 230 MeV (LLUMC) 1 GeV (NSRL)
Target Fragment Fluence as functions of Proton Energy and Target
Fragment Distribution as a Function of Angle230 MeV Protons (LLUMC)
Integral LET Fluence Spectra230 MeV Protons on CR-39 PNTD AFM CR-39 PNTD: 2 hr etch in 50°C, 6.25 N NaOH, B = 0.5 mm
Integral LET Fluence Spectra1 GeV Protons on CR-39 PNTD AFM CR-39 PNTD: 2 hr etch in 50°C, 6.25 N NaOH, B = 0.5 mm
Conclusions from Light Microscopy Analysis of CR-39 PNTD AFM Exposures • The heavy recoil tracks often take the form of long tubes, not short cones. Tube-shaped tracks are characteristic of extremely high LET (>1000 keV/m) particles near the end of their ranges. • Some tracks “zig zag” toward their ends, illustrating range straggling. • Some tracks are “forked”, illustrating low-energy Rutherford scattering. • The size of the tracks (width and length) scales with Z of the target material. • Fluence (and production cross section) scales with proton energy. • Preliminary measurements appear to show that the angular distribution of high Z recoil fragments is isotropic.
Relevance/Applications • Nuclear Physics: Validate Nuclear Reaction Models • Provide Data to Extend Radiation Transport Codes • Proton and Heavy Ion Therapy • Radiation Effects on Electronic Circuits • Space Radiation Dosimetry • Study of Neutron Interactions with Heavy Nuclei
Conclusions • Tracks from proton- and neutron-induced short-range (<20 mm), high-LET recoil fragments in CR-39 PNTD are visible through a standard optical microscope for Bulk Etch of 0.5-1.0 mm. • New method to quantify heavy recoil nuclear processes previously not accessible due to short range of fragments. • LET spectra measured by AFM consistent with previous LET measurements made by standard light microscopy. • Extend work to other targets, different proton energies, heavy ions, and medium and high energy neutrons.
