Breckow, J.

Fehrenbacher, G.

Horst, F.

Kozlova, E.

Radon, T.

Zink, K.

GSI Repository

Radiation protection related x-ray spectrometry at PHELIXF. Horst1,2, G. Fehrenbacher1, T. Radon1, E. Kozlova1, K. Zink2, and J. Breckow21GSI, Darmstadt, Germany; 2Technische Hochschule Mittelhessen, Gießen, GermanyIntroductionIn the context of a bachelor thesis [1], a thermolumines-cence dosimetry (TLD) based method has been developedfor the measurement of photon spectra in ultrashort-pulsedradiation fields as generated e.g. during operation of thePHELIX-laser at GSI [2]. The method is a further develop-ment of a work from Behrens et al. [3] and has been val-idated at a clinical electron-linac (Elekta Synergy: 6 and18 MeV) by comparing spectra measured by the developedmethod with spectra obtained by detailed Monte Carlo sim-ulations of the linac. It has been first applied at PHELIXduring a beamtime in December 2013. The following ar-ticle presents the principle of the method of measurementand first results from the measurements at PHELIX.Method of measurementAs a result of the sub-picosecond time scale of the laserpulses at PHELIX, an active measurement is quite diffi-cult to implement. For that reason, TLD’s are used. 10TLD-cards (Harshaw TLD-700H) are placed into a stackof absorbers, made of various materials and thicknesses,surrounded by a shielding stepped from lower to higher Zmaterials. The prototype is shown on Figure 1.Figure 1: Schematic view of the TLD-spectrometerThe response functions of the 10 TLD’s to monoener-getic photon- and electron-radiation were simulated by theuse of the Monte Carlo code FLUKA [4]. The differentgradients and thresholds of these response-functions (Fig-ure 2) allow the reconstruction (unfolding) of photon spec-tra from the readings of the 10 TLD’s. An algorithm for thepurpose of unfolding bremsstrahlung spectra in the range of30 keV to 100 MeV, resolved in 10 different energy bins,was developed (written in SCILAB [5]).Figure 2: Simulated response-functions of the 10 TLD’s tomonochromatic photon radiationFirst resultsFigure 3 shows an x-ray spectrum, measured by this pro-totype at the PHELIX petawatt target area from the outsideof the target chamber behind a 2 cm steel window duringexperiments in December 2013. The laser intensity de-posited on the Ti-foil target was about 1019 W/cm2. Thedistance between the target and the spectrometer was 80cm. The presented x-ray spectrum is equivalent to an am-bient dose of 80± 20 µSv/shot.0.01 0.1 1 10106107108Photon Energie E / MeV            Fluence ΦPh    /                      cm−2  ⋅ MeV−1  ⋅ shot−1        Figure 3: X-ray spectrum: measured at PHELIXRepeated measurements with a variation of the windowmaterials and thicknesses provided evidence, that the wallof the target chamber is the main x-ray source.References[1] F. Horst, “Ro¨ntgenspektrometrie am Petawattlaser PHELIX”,bachelor thesis, Technische Hochschule Mittelhessen, 2014[2] S. Go¨tte et al., this report[3] R. Behrens et al., “A thermoluminescence detector-basedfew-channel spectrometer for simultaneous detection of elec-trons and photons from relativistic laser-produced plasmas”,Review of Scientific Instruments Vol. 74, 961, Feb 2003[4] http://www.fluka.org/[5] http://www.scilab.org/PNI-PP-19 GSI SCIENTIFIC REPORT 2013200 doi:10.15120/GR-2014-1-PNI-PP-19

Radiation protection related x-ray spectrometry at PHELIX

http://repository.gsi.de/record/67905/files/PNI-PP-19.pdf

Radiation protection related x-ray spectrometry at PHELIX

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