Radiation Measurements 43 (2008) 467 – 470 www.elsevier.com/locate/radmeas Enhanced sensitivity of alanine dosimeters to low-energy X-rays: Preliminary results Felipe Chen, Patrícia Nicolucci, Oswaldo Baffa ∗ Departamento de Física e Matemática, FFCLRP – Universidade de São Paulo, 14040-901 Ribeirão Preto, SP, Brazil Abstract In this work, the response or sensitivity of L-alanine minidosimeters to low-energy photons was enhanced through the addition of iodine atoms in the form of KI, which is considered as a dopant. L-alanine minidosimeters with four different content of dopant (0%, 5%, 10%, 15%) were produced and irradiated with 30 Gy to X-ray beams of 80, 120, 250 kV and 10 MV. A 60 Co beam was also used for the normalization of the energy response. The EPR measurements were carried out using a K-Band (24GHz) spectrometer. The results showed a maximum response around 40–50 keV for the doped minidosimeters. This maximum increases with the dopant content 2.2, 3.4 and 4.5 times for 5%, 10% and 15% KI, respectively, with respect to the response of the 60 Co irradiated undoped minidosimeter. This result can be explained by the presence of the iodine atom that would increase the probability of photoelectric absorption due to its K-absorption edge (∼33 keV). © 2007 Elsevier Ltd. All rights reserved. Keywords: L-alanine minidosimeter; K-band EPR; Dopant; KI; Low-energy photons; Photoelectron 1. Introduction The effect of ionizing radiation after its interaction with the L-alanine molecule is the production of stable free radicals. Because the free radical is a paramagnetic species, it is suscep- tible to be detected by electron paramagnetic resonance (EPR) spectroscopy. The number of these radicals in irradiated ala- nine is directly correlated with its EPR signal intensity that in turn is proportional to the radiation dose and is taken as the dosimeter reading h (Fig. 1)(Regulla and Deffner, 1982). The amount of free radicals produced will depend on the type of radiation (photons, electrons, protons, neutrons, alpha particles, heavy ions, etc.), the energy and the dose (Ebert et al., 1965). In addition, it is well known that the number N of radicals formed in alanine is expressed by (Rotblat and Simmons, 1962; Nelson, 2005) N = N ∞ (1 - e -KE ), (1) where N ∞ represents a saturation level, K is a constant related with the saturation behaviour and E is the total energy deposited ∗ Corresponding author. E-mail address: baffa@ffclrp.usp.br (O. Baffa). 1350-4487/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2007.11.066 by radiation in alanine. On the other hand, the radiation yield (radical production due to radiation) G is defined as the num- ber of radicals produced per unit of absorbed energy (Nelson, 2005): G = dN dE . (2) The inverse of G (1/G) will give the necessary energy to pro- duce one free radical. It was found in different reports that the G value for ala- nine varies between 0.9 and 7.7 depending on type and energy of radiation (Regulla and Deffner, 1982; Koizumi et al., 2003; Köhnlein and Müller, 1962; Sharaf and Hassan, 2004). We believe that this difference between the G values reported is due to the difficulty to accurately perform EPR quantitative mea- surements of the number of spins N in the sample (Poole, 1983; Mazur, 2006). The EPR signal intensity depends on several parameters, such as the cavity quality factor Q, filling factor, dielectric constant, humidity, effective microwave power in the sample, among others, and it is difficult to control all of them. Additionally, these measurements were performed at different laboratories with no intercomparison calibration among these spectrometers.