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Radiating materials processing

X-ray dose measurements on laser materials processing machines

PTBnews 1.2019
Especially interesting for

manufacturers and users of lasers for materials processing

radiation protection

In the laser materials processing of workpieces unwanted X-rays can occur. Their dose rate and spectral distribution have now been accurately determined for the first time.

Sketch of the TLD-based spectrometer. Basic principle: The deeper the radiation penetrates the spectrometer, the higher its energy.

Materials processing by means of laser radiation is a long-used technique. More recently, ultrashort pulsed laser radiation has been increasingly used for this purpose. By using the high peak intensities of up to more than 1014 W/cm² in the laser focus, unwanted X-rays are generated which were measured for the first time in an application environment of industrial laser materials processing.

For this purpose, a thermoluminescence detection (TLD) based spectrometer was used. The penetration depth of the X-ray radiation in the spectrometer depends on the energy, so that the energy- resolved spectrum of the radiation can be calculated from the dose values in the TLD layers by means of mathematical methods (Bayesian deconvolution).

The resulting dose rate depends on the processed material and its nature and was in the order of 1600 mSv/h to 7300 mSv/h in terms of the radiation protection quantity '(0,07), 16 mSv/h to 71 mSv/h in terms of the quantity '(3) and 1 mSv/h to 4 mSv/h in terms of the quantity *(10), in each case per materials processing time. Such high dose rates would exceed legal dose limits within a few minutes to one hour (for the local skin dose, as estimated by '(0,07), and the eye-lens dose estimated by '(3)) or a few hours (for the effective dose of the whole body, estimated by *(10)). The spectral distribution was in the range of a few keV up to 30 keV. The dose contribution of photons above 30 keV was negligible.

These measurements, traceable for the first time, not only provided manufacturers and users of ultrashort pulse lasers with important information for the design of the machines with regard to radiation protection, but already influenced the current legislative procedure in the field of radiation protection. At the same time, machines with even higher laser intensities are already being developed. Therefore, the presented measuring method will become even more important in the future.


R. Behrens
Department 6.3
Radiation protection dosimetry
Phone: +49 531 592-6340
Opens window for sending emailrolf.behrens(at)ptb.de

Scientific publication

R. Behrens, B. Pullner, M. Reginatto: X-ray emission from materials processing lasers. Radiat. Prot. Dosim. (2018) Opens external link in new windowDOI: 10.1093/rpd/ncy126