X and gamma photon spectrometry

Study of continuous spectra produced by X-ray generators

International standards define the characteristics and methods of radiation beam production for testing and calibration of measuring equipment (e.g. ISO 4037-1 standard for X-ray and gamma-reference radiation for calibration of dosimeters and flowmeters). Radiation field quality indices are mainly based on the measurement of radiation attenuation in a given material (e.g. half-value layer – HVL).

Stricter control measures for irradiation systems in industrial and medical applications are accompanied by increased demands for calibration and accuracy. As the energy range expands towards low energies, the establishment of reference beams becomes increasingly challenging due to attenuation phenomena that significantly alter the photon spectra emitted by X-ray generators. It is therefore important to be able to qualify the spectra at the measuring point in order to better control the dosimetry of the beams with, in particular, a better estimation of the correction factors to be applied for the determination of the reference values of the dosimetric quantities.

The LNHB is developing spectrometry systems for continuous wide-spectrum beams equipped with semiconductor detectors that can be used in multiple configurations to meet its own needs and those of external users. The measured spectra are corrected for artifacts created as a result of photon interactions in the detectors (pile-up, escape peaks, Compton scattering) using algorithms developed at the LNHB. These allow a more accurate estimation of the spectra emitted by X-ray generators compared to those obtained using deterministic calculations or simulations using Monte-Carlo codes. In particular, they make it possible to take into account the possible effect of ageing of X-generators.

This better knowledge of the spectra makes it possible to better characterize dosimetric quantities in various fields of application such as contact therapy, radiodiagnosis, but also industrial applications using X-rays.

– J. Plagnard, Comparison of measured and calculated spectra emitted by the x-ray tube used at the Gustave Roussy radiobiological service, (2014), X-ray Spectrometry, 43, 298-304
DOI: 10.1002/xrs.2554
– J. Plagnard, Mesure de spectres en énergie de l’émission de tubes à rayons X au LNE-LNHB/LMD , Revue Française de métrologie, n°43, volume 2016-3, 37-47
DOI : 10.1051/rfm/2016014