Contents lists available at ScienceDirect Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem Measurement of photoelectron generation in a gold coated glass slide K.S. Almugren a , S.F. Abdul Sani b,∗ , E.H. Uguru b , N.H. Amiera Narissa b , R. Zakaria b , F.H. Alkallas a , D.A. Bradley c,d a Department of Physics, Princess Nourah Bint Abdulrahman University, Riyadh, Saudi Arabia b Department of Physics, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia c Sunway University, Centre for Biomedical Physics, Jalan Universiti, 46150, PJ, Malaysia d Department of Physics, University of Surrey, Guildford, GU2 7XH, UK ARTICLEINFO Keywords: Glass slides High-Z dose enhancement Thermoluminescence Dosimetry ABSTRACT In thin low-Z media irradiated by photon energies of several tens of keV, the presence of a high-Z additive can result in manifest locally modifed secondary electron dose. Present study analyses the photoelectron dose en- hancement resulting from nanometre thickness gold (atomic number Z = 78) coated on commercial borosilicate (B 2 O 3 ) glass microscope cover-slips. Two thicknesses of B 2 O 3 cover-slip have been utilized, 0.13 ± 0.02 mm and 1.00 ± 0.01 mm, with single-sided Au coatings of 20, 40, 60, 80 and 100 nm. An additional uncoated glass slide has been kept as a comparator. The samples have been exposed to X-rays generated at kVp potentials, delivering a fxed dose of 2 Gy. Dose enhancement resulting from the 1.00 mm glass has been observed to be ~1.32 × that of the 0.13 mm thickness glass. The elemental composition of the samples has been obtained via Electron Dispersive X-ray (EDX), elemental content diferences between the two thicknesses of glass leading to a diference in efective atomic number of less than 0.3%. The infuence on photon yield of the gold coating and variations in elemental content has been modelled using Monte Carlo simulation, allowing comparison with the measured values of enhanced TL yield. 1. Introduction The interaction of low-energy X-rays with high-Z materials results in increase of photoelectron production, the limited path-length of sec- ondary electrons resulting in additional dose deposition in the low-Z microscopic volumes adjacent to the high Z material. The earliest re- cognition of such enhancement of dose would appear to be that due to Spiers (1949). The underpinning mechanism concerns the marked de- pendence of the photoelectric cross-section on the atomic number of the high-Z medium, most prominently at photon energies around the binding of electrons to the nucleus (the jump or so-called edge energies, K, L etc). This results in electron ejection from the atom (ionization), for present purposes interest being in the K and L-shell electrons given that these carry the photoelectron energies of major dose consequence. As such, in the specifc case of keV photon radiotherapy, if a tumour could be preferentially infused with an appropriate high-Z substance, then this would result in a greater fraction of the incident photon energy being delivered within the tumour in the absence of escalation of da- mage to surrounding normal tissues. This is explained in terms of the completely slowing down approximation (CSDA) for electron tracks, with relatively small initial change in the linear energy transfer (LET) but with marked increase in LET towards the end of the electron track (with values of LET ranging from an initial low fraction of a keV μm −1 through to several tens of keV μm −1 at the very end of the electron range). The overall result in respect of the photoelectric interaction products (photoelectrons, characteristic X-rays and Auger electrons) is that these are of rather short range (a few mm at most in tissue), as previously alluded to. This produces increased overall damage to tu- mour cells. The latter can lead to benefcial employment in superfcial radiotherapy treatments, via for instance radiation synovectomy, syn- chrotron stereotactic radiotherapy (SSR) and intraoperative radio- therapy (e.g. utilizing 50 kVp X-rays). As a dose enhancer gold nanoparticles ofer an attractive option, due in good part to the chemical properties of gold (with potentially negligible toxicity for tissues and molecular stability), also potentially ofering high tumour uptake specifcity for appropriately sized nano- particles. Experimental evidence has demonstrated dose escalation during various in vitro treatment phases (Mello et al., 1983; Herold et al., 2000; Corde et al., 2004; Hainfeld et al., 2004). For low energy photon irradiation of gold nanoparticle radiosensitizers, Jones et al. (2010) and Lechtman and Pignol (2017) reported dose enhancement to be most efective at energies around the gold K-edge i.e. 80.75 keV, a https://doi.org/10.1016/j.radphyschem.2020.108913 Received 10 February 2020; Received in revised form 1 April 2020; Accepted 3 April 2020 ∗ Corresponding author. E-mail address: s.fairus@um.edu.my (S.F. Abdul Sani). Radiation Physics and Chemistry xxx (xxxx) xxxx Available online 14 April 2020 0969-806X/ © 2020 Elsevier Ltd. All rights reserved. Please cite this article as: K.S. Almugren, et al., Radiation Physics and Chemistry, https://doi.org/10.1016/j.radphyschem.2020.108913