Modelling of the thermoluminescence response of LiF:Mg,Cu,P (MCP-N) detectors after doses of low energy photons

A simple numerical approach has been developed to predict the relative (to Cs-137 gamma rays) response of LiF:Mg,Cu P (MCP-N) thermoluminescence detectors after doses of photons in the energy range from 4 to 1000 keV. The following major factors influencing the TL detector response were taken into account: (i) mass energy absorption coefficients for LiF:Mg,Cu,P and air; (ii) attenuation of low energy X rays in a thick TL detector; (iii) self-absorption of thermoluminescence light in a thick detector; and (iv) the relative TL efficiency (intrinsic luminous efficiency), eta, of MCP-N detectors, which depends strongly on the photon energy via radiation ionisation density. The values of eta were calculated using the microdosimetric one-hit detector model and fitted with the function eta = 0.794 - exp [-(E[keV]-4.663)/9.69] over the range of photon energies, 4 keV < E < 40 keV. The results of model calculations agree well with experimental values of eta measured in the energy range 6-18 keV at SLAG using monoenergetic synchrotron radiation and with literature data for higher energies. This approach may be useful in practical applications of MCP-N detectors in X ray dosimetry, such as TL dosimetry of mammography units.