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Radiation dosimetry with TAMU beams

Radiation dosimetry with TAMU beams. M.E. Brandan Instituto de Física UNAM brandan@fisica.unam.mx. About thermoluminescence. Thermoluminescence (TL) is the emission of light - induced by heating - from a material previosuly exposed to ionizing radiation

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Radiation dosimetry with TAMU beams

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  1. Radiationdosimetrywith TAMU beams M.E. Brandan Instituto de Física UNAM brandan@fisica.unam.mx

  2. Aboutthermoluminescence • Thermoluminescence (TL) istheemission of light -inducedbyheating- from a material previosulyexposedtoionizingradiation • TL materials are dielectriccrystalscontainingactivators • Trapsforchargecarriers • Luminescence centers whichemit light

  3. TL materials • TL materials are used a dosemeters (TLD) because the emitted light is (almost) proportional to deposited energy. • A linear response is observed over a limited dose interval (few microGy to tens of Gy). • The best known properties are those associated to their use as X- or g • LiF:Ti,Mg (TLD-100) • LiF:Mg,Cu,P (TLD-100H) • CaF2:Mn (TLD-400) • CaSO4:Dy (TLD-900) • They come as disks, rods or chips, a few mm in size. • They are not absolute dosemeters, they require a calibration. • Their response (emitted light per imparted energy) depends on radiation type.

  4. Project at UNAM • Systematic study of the TLD response to • low- and intermediate- energy ions • Efficiency (as a function of the ion’s everything) • Linearity (as a function of fluence) • 3 MV Pelletron (IFUNAM) and TAMU cyclotron • (College St, TX) • TL dosimetry laboratory • Interpretation • Track Interaction Models (MC version MC) for supralinearity • Track Structure Models for efficiency

  5. TLD-100 glow curve (emitted light as function of heating) Gamma rays Ions

  6. ions X or g ion A B C D Ion irradiation • Non-uniform irradiation (spatially localized) • Non-uniform dose profile within each track • High ionization density (LET=DE/Dx) along the ion trajectory Avila et al., J. Phys. D: Appl. Phys. 32 (1999) 1175-1181

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  8. When a charged particle traverses a medium, • it deposits energia via secondary electrons. • The energy tranfer is quantified by • the lineal energy transfer, LET, • LET= DE/Dx • LET a z2/v2 Ion high energy Ion low energy Low LET High LET

  9. DE1DE2DE3DE4DE5 E1 E2 E3 E4 E5 E6 Intermediate energy ions (TAMU cyclotron) • In-air rradiation 1H, 3He, 12C, 16O, 20Ne beams, up to 40 MeV/A incident energy • Average fluence determined by an independent detector • TLD-100 chips in “stacks” (i.e. various energies and LET simultaneously)

  10. Ion glow curve 200 mGy For similar doses, glow curves depend on LET

  11. LiF:Mg,Ti glow curve shape All ions Glow curve shape depends on the incident particle ionization density G Massillon, I Gamboa, MEB, J. Phys. D: Appl. Phys. 40 (2007)

  12. Efficiency (relative to gamma rays) for individual peaks h = TLsignal dose-1 mass-1)ion ion,g TLsignal dose-1 mass-1)g Models describe the general features of the data, not the detail G Massillon, I Gamboa, MEB, J. Appl. Phys. 100 (2006)

  13. The relative efficiency for high-temperature peaks displays a maximum as a function of LET This reminds us (the 70s…)the induction of damage in cells exposed to ions LET at themaximum, 100 keV/mm, impliesionizationseach~2 nm ~ the DNA helix diameter: Ifyouionize at therightdistance, bothstrands are broken, and therepairgetsverydifficult. LET(keV/mm)

  14. Someresults • Low- and high- temperaturepeaks in TLD-100 exposedtoionsdisplaydistinctbehavior in terms of • relativeefficiency, • dependence of efficiency as a function of LET and particletype. • Use of TLD-100 as a set of independentdetectors? • Modeldescriptionssuggest a muchstronger “two-hit” structure in thehigh-temperaturepeaks. Agreementbetween data and model do notpermit a quantitativeevaluation of target sizes, orthelike • Details in the data suggestthepossibility of correlation in theexcitation of peaks 6a, 6b and 7 • Presently, westudythe “high LET” features of the TL response tolow-energy X-rays

  15. JBN, corresponding member, Mexican Academy of Sciences, Nov 2009

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