A.E. Buenfil

Thermoluminescent response and relative efficiency of TLD-100 exposed to low-energy x-rays.

The dose-response of LiF:Mg,Ti (TLD-100) exposed to 15 and 35 kVp (8.0 +/- 0.1 and 8.1 +/- 0.1 keV effective energy respectively) x-rays and 60Co gamma-rays has been measured in the dose interval from (1.2-5.4) x 10(3) Gy for x-rays, and from 0.14 to 850 Gy for gamma-rays. In both cases the total TL signal and glow curve peaks 3 to 9 show supralinearity. The supralinearity function f(D) is similar for both x-ray beams, except for peak 8, where a 30% difference is observed. The maxima of f(D) for the total TL signal and peaks 5 to 8 are 2.1, 1.7, 6.4, 3.3 and 7.5 respectively for 8.1 keV x-rays and 3.7, 3.1, 13.6, 9.9 and 11.0 for gamma-rays. The measured relative efficiencies for x-rays with respect to 60Co, for the total TL signal and peaks 5 and 7, were 1.04, 0.97 and 3.2 respectively.

Response of radiochromic dye films to low energy heavy charged particles

Abstract We have studied the possible use of radiochromic dye films (RCF) as heavy charged particle dosemeters. We present the results of irradiating two commercial RCF (GafChromic HD-810 and MD-55-1) with 1.5, 2.9 and 4.4 MeV protons, 1.4, 2.8, 4.7, 5.9, 6.8 MeV 4He ions and 8.5 and 12.4 MeV 12C ions, at proton doses from about 1 Gy up to 3 kGy, helium ions doses from 3 Gy to 5 kGy and carbon ion doses from 30 Gy to 20 kGy. The films were scanned and digitized using commercial equipment. For a given particle, the response per unit dose at different energies indicates an energy dependence of the sensitivity, which is discussed. Comparison was made for the use of a standard spectrophotometer to obtain optical density readings versus a white light scanner.

Supralinear response and efficiency of LiF:Mg,Ti to 0.7, 1.5 and 3 MeV protons

Abstract The thermoluminescent (TL) response, supralinearity function, and relative efficiency with respect to 60 Co γ-rays, of TLD-100 exposed to 0.7, 1.5 and 3 MeV protons have been measured. The TL response of the glow curve peaks using two different deconvolutions, separating in either 7 (3–9) or 9 peaks (3–10 and peaks 6a and 6b), was investigated. Results for the supralinearity function of peaks 5 and 7–9 and the relative response of peaks 5 and 7 are insensitive to the chosen deconvolution scheme. At all energies we observe that peak 5 is slightly supralinear and that supralinearity increases as a function of the peak temperature. The relative efficiencies, measured for the total TL signal (area under the glow curve) and peaks 5 and 7, decrease with the proton energy having values of 0.33, 0.46 and 0.70 (total TL signal), 0.22, 0.32 and 0.53 (peak 5) and 1.4, 2.6 and 3.6 (peak 7) at 0.7, 1.5 and 3 MeV, respectively. These data agree with the systematics reported in the literature. The measurements of the supralinearity function are compared with Monte Carlo track interaction model calculations. The analysis suggests that the model ion track effective radius and the saturation radius are independent of the incident ion energy.

Thermoluminescent characteristics of KBr:Eu and KBr:Eu,Mg irradiated with UV light

The TL response of KBr:Eu (0.1% Eu) and KBr:Eu,Mg (0.1% Eu, 0.01 and 0.001% Mg) to 254 nm UV light has been studied. Crystals were subjected to different thermal treatments. The Mg concentration and the thermal treatment that produced the best glow curve reproducibility and sensitivity increase were identified. The sensitivity to UV radiation increased by about three times after the optimum thermal treatment. The addition of Mg (0.001%) was responsible for improvements in the reproducibility of the glow curve characteristics for different samples. The glow curves showed two high-temperature peaks above , similar to those observed after exposure to rays, and the TL response was linear for fluences between 15 and .

A novel method to use radiochromic dye films to determine dose under proton irradiation

The response of commercial radiochromic dye films exposed to 0.7, 1.5 and 3.0 MeV protons, in the dose interval between 1−103 Gy, has been studied. The response of the plastics (MD-55 and HD-810 from Gafchromic) to the radiation was evaluated by digitalizing and analyzing the films with commercial computer systems. Curves of response as a function of dose show an approximately linear behaviour followed by saturation. The response in the lower dose interval suggests a possible use of these methods in heavy charged particle medical applications. To verify consistency with the traditional spectrophotometer reading procedure, the films were also irradiated and evaluated with 60Co gamma rays.

Dosimetric Quantities for Computed Tomography Examinations of Paediatric Patients on the Thoracic and Abdominal Regions

Computed Tomography (CT) is a high dose X ray imaging procedure and its use has rapidly increased in the last two decades fueled by the development of helical CT. The aim of this study is to present values of the dosimetric quantities for CT paediatric examinations of thoracic and abdominal regions. The protocols studied were those of chest, lung‐mediastine, chest‐abdomen, pulmonary high resolution and mediastine‐abdomen, which are the more common examinations performed at “Hospital Infantil de Mexico Federico Gomez” in the thoracic‐abdominal region. The measurements were performed on a Siemens SOMATOM Sensation 16 CT Scanner and the equipment used was a CT pencil ionization chamber, connected to an electrometer. This system was calibrated for RQT9 CT beam quality. A PMMA head phantom with diameter of 16 cm and length of 15 cm was also used. The dosimetric quantities measured were the weighted air kerma index (Cw), the volumetric dose index (Cvol) and the CT air kerma–length product. It was found that the...

Computed Tomography: Image and Dose Assessment

In this work an experimental evaluation of image quality and dose imparted during a computed tomography study in a Public Hospital in Mexico City is presented; The measurements required the design and construction of two phantoms at the Institute of Physics, UNAM, according to the recommendations of American Association of Physicists in Medicine (AAPM). Image assessment was performed in terms the spatial resolution and image contrast. Dose measurements were carried out using LiF: Mg,Ti (TLD‐100) dosemeters and pencil‐shaped ionisation chamber; The results for a computed tomography head study in single and multiple detector modes are presented.

Thermoluminescent response of TLD-100 exposed to low energy protons

The fluence response curve of LiF:Mg,Ti (TLD-100) exposed to 0.7, 1.5 and 3 MeV proton beams has been measured. In all cases, the total TL signal and glow curve peaks 5 to 9 show a linear-supralinear response for fluences between 107 and 1012 protons/cm2. The supralinearity increases with the energy of the incident beam. The measured relative efficiencies for protons with respect to 60Co γ-rays, for the total TL signal and peaks 5 and 7 indicate that the efficiency increases with energy, that is, decreases with the linear energy transfer. The efficiencies are lower than unity for the total TL signal and peak 5 and greater than unity for peak 7.