Investigation of dose rate effects in radiation chemistry with laser-driven pulsed sources at ELI Beamlines

Transcription

1 Investigation of dose rate effects in radiation chemistry with laser-driven pulsed sources at ELI Beamlines Martin PŘEČEK, Ph.D. ELI Beamlines Research program 4 Applications Institute of Physics (FZÚ), Czech Academy of Sciences martin.precek@eli-beams.eu ELIMEDICS Conference, Dolní Břežany, Czechia March 3-4, 2016

2 Outline of the talk pulse radiolysis with ultrashort electron pulses in the world plans for ELI Beamlines pulse radiolysis with protons and other ions overview of main past studies study on dose rate effects in fluorescence dosimeters for on-line dosimetry

3 Radiolysis (=radiation induced breakup) of water

4 Current state-of-the-art electron accelerators for pulse radiolysis

5 ELYSE accelerator Univ. Paris Sud RF LINAC with fs-laser-activated Cs 2 Te photocathode, capable of producing 5-15 ps electron pulses at up to 8 nc charge magnitudes, 4-9 MeV

6 Osaka University fs-accelerator (Yoshida group) laser photocathode LINAC, S-band (2856 MHz), 10 Hz rep. rate, Cu photocathode, capable of ~100 fs electron pulses at 200 pc charge magnitudes, electron energy up to 30 MeV jitter is an issue below 1 ps

7 7

8 Time resolved absorption with electrons classical pulse radiolysis approach with ~10 MeV energy electrons higher efficiency in conversion of the primary laser light into radiation Malka et al. (2002) 30fs 30TW Ti:Sa ( 1 J) converted 1% of the incident laser energy into an electron bunch electrons with energy above 1.25 MeV totalling 0.6 nc in charge and 6 mj in total kinetic energy higher dose should be possible species of interest hydrated electron ε(782 nm)= M -1 cm -1 pre-hydrated electrons (spectrum red-shifted) OH radical ε(263 nm)= 460 M -1 cm -1 small sample to avoid pulse velocity difference small absorption length small sensitivity to low dose

9 Possible advantages of laser-accelerated electrons for pulse radiolysis shorter electron pulse (~down to several femtoseconds) elimination of the issue of timing jitter between the radiofrequency field of the LINAC acceleration stage and the probing laser availability of extensive probing laser light and spectroscopic opportunities (technologies and know-how) > multi-beam time-resolved spectroscopy e.g., femtosecond stimulated Raman spectroscopy

10 Femtosecond Stimulated Raman Spectroscopy eliminates issue with fluorescence lifetime (~ ns) time resolution ~ 10 fs requires multiple beam approach up to x Raman response sensitivity uncertain possible species for study: solv. electron OH radical?, H 2 O +. super-excited H 2 O? provides vibrational structural information about transient species

11 As a result of the reduced velocity v light of probing light in liquid solutions compared to the speed of light in vacuum c, during the traversal of a sample of thickness L a time delay δt GVM arises between the arrival of the pump radiation pulse (X-ray photons/ relativistic electrons) and the probing light pulse. For water (refractive index n = 1.33) v light = c / n 0.75 c Problem: group velocity mismatch between electrons and probing light δt GVM / L = (c v light )/v light c -1 1/3 c -1 1 ps delay per 1 mm of sample To achieve 100 fs time resolution, water sample thickness may not exceed 100 microns. VIS-NIR laser pulse v laser = v electron v laser = 0.75 v electron 5 MeV electron pulse

12 NIST ESTAR : Stopping Power and Range Tables for Electrons 12

13 Target sample delivery liquid jet (1-100 µm) liquid droplets (>10 µm) flat jets? liquid in cuvettes (>1000 µm) gas-puff (?) particles (µm) surface-enhanced Raman spectroscopy fs processes in radiation damaged biol. molecules 20 micron diameter 2-3mm laminar flow (on air)

14 Why? Laser driven pulses may be larger than from conventional accelerators higher dose rate effects of elevated dose rate may be observable in chemical systems impacts: Radiation chemistry with laser accelerated protons and other ions effects on chemical dosimetry radiobiological effects radiotherapy

15 NIST PSTAR : Stopping Power and Range Tables for Protons 15

16 Past studies on proton/ion pulse radiolysis 1) 5 MeV proton accelerator (Van de Graaf) ordinary conditions: mean current 8-10 µa, ns pulses at 10 MHz modified to give 12 µs single pulse with 500 µa peak current (6 nc = 3.7 x p) proton energy 4.6 MeV after window total pulse energy = 30 mj proton range in water approx cm range in gases approx. 30 cm gas phase studies

17 2) Past studies on proton/ion pulse radiolysis small charge

18 3) 18

19 4) 19

20 5) 20

21 STUDY OF CHEMICAL DOSIMETRY WITH SHORT PULSES Fyzikální ústav AV ČR, v. v. i. Na Slovance Praha 8 info@eli-beams.eu

22 On-line fluorescent dosimetry for pulse radiolysis Expected liquid jet velocity approx. 10 m/s = 10 µm/µs Visualization of the concept of on-line fluorescent chemical dosimetry

23 Fluorescence chemical dosimetry high sensitivity for low dose in thin samples on-line/off-line evaluation mechanism example: terephthalate (TA) dosimeter Very fast reaction with OH radical k = M -1 s -1 τ OH = 3 [TA] 0 = 10-4 M formation of hydroxy-terephthalate anion (HTA), multi-step produced fluorescence linear within Gy

24 Main challenge: Dosimeter yield changes at elevated dose rates Fricke dosimeter: change of yield (G) with dose rate (dose per short pulse) ev/l/sec 16 Gy/µs = 16 MGy/s

25 Experiments with trimesic acid dosimeter at the ELYSE picosecond radiolysis facility in Orsay, France ELYSE LINAC accelerator: electrons energy: 4-10 MeV charge: nc pulse width: 4-10 ps Ce:YAG Cherenkov

26 Results 1 Trimesic acid, Terephthalate: no dose rate effect Dose-rate: Cobalt-60, gamma: 1-2 mgy/s Elyse, 4.5 MeV electrons: TGy/s 26

27 Results 2 C3CA (coumarin): significant dose rate dependence 27

28 Effect of LET Co-60 gamma rays LET 2 MeV/cm 20 kvp Mo X-rays LET 40 MeV/cm* *F.Verhaegen and J.Seuntjen, Radiation Research 137,11-17 (1994) 28

29 Agreement with literature data for C3CA 29

30 Mechanism of C3CA hydroxylation 30

31 Libor Juha group at the Institute of Physics (FZÚ) Department of Nuclear Chemistry - CTU (ČVUT) in Prague Václav Čuba, Aleš Vetešník Acknowledgment ELYSE / Laboratoire de Chimie Physique Université Paris- Sud Mehran Mostafavi, Uli Schmidthammer, Ma Jun, Jean-Philippe Larbre, Alexandre Demarque, Pierre Jeunesse This project has been suported from the project Strengthening the capacity of research teams in the field of physical sciences CZ.1.07/2.3.00/ of the Operational Program Education for Competitivness (OPVK).

32 Thank you for your attention