Thermoluminescent glow curve of Gd1-xRExAlO3 (RE=Dy or Pr) beta irradiated phosphors.

Phosphors composed of Gd1-xRExAlO3 (0≤x ≤ 5 RE = Dy or Pr) stoichiometries were synthesized using the reverse coprecipitation pathway. The thermoluminescent responses of all phosphors were studied under beta radiation exposure. Doping the gadolinium aluminate host improved the thermoluminescent response of the phosphors, with the phosphors composed of Gd0.99Dy0.01AlO3 and Gd0.95Pr0.05AlO3 being the most sensitive. The Dy3+ ions produced a higher improvement of the thermoluminescent signal than the Pr3+ ions. Additionally, a proportional relationship between the similarity of the atomic numbers of the dopant and replaced ions and the sensitivity to thermoluminescence was confirmed. Besides, a slight shift of the thermoluminescent peaks toward lower temperatures was detected for doped phosphors. In the repeatability tests applied to the phosphor composed of Gd0.99Dy0.01AlO3, an anomalous increase in sensitization was observed. The observed sensitization was associated with the formation of electron trap clusters resulting from the continuous exposure to beta radiation. Furthermore, another sensitization phenomenon was detected in the phosphor with Gd0.95Pr0.05AlO3 stoichiometry when it was heated at low temperatures. The aforementioned striking behavior was related to quasi-continuous distributions of electron traps and the tunneling effect. In regard to linearity, the phosphor composed of Gd0.99Dy0.01AlO3 exhibited a linear response with the dose across the entire range of beta doses. However, the response of the Gd0.95Pr0.05AlO3 phosphor lost linearity beyond 26.4 Gy of beta dose. The results obtained through the use of the Tmax-Tstop method and deconvolutions suggested an enhancement in the efficiency of the thermoluminescent mechanisms due to the incorporation of activators.

Fluorescence intensity ratio for BaHfO3:Eu3+ temperature sensor.

We use 395 nm ultraviolet radiation to excite the matrix of barium hafnate doped with europium ions to develop an optical temperature sensor. Luminescent analysis as a function of temperature was performed in the physiological range. The Emission spectra showed significant variations in luminescent intensity at all transitions, obtaining a relative sensitivity of 1574.3/T2, when the temperature of the material increases from 289.7 to 323.8 K. The 5D0 -> 7F2 transition presented the better temperature resolution (1.1 × 102 K).

Thermoluminescence analysis of beta particle irradiated Gd1-xEuxAlO3 phosphors.

The suitable choice of an activator and host combination is essential for synthesizing very sensitive thermoluminescence phosphors. In addition, conspicuous synthesis variables must be optimized to achieve the maximal response. The research presented herein shows that the most recommendable conditions to improve the thermoluminescence response of beta irradiated Gd1-xEuxAlO3 phosphors were: x = 0.02 for europium stoichiometry and 1500 °C for the calcination temperature. The glow curve recorded for the most sensitive phosphor was partially erased by photo-bleaching, and thus, should yield optically stimulated luminescence.

Neutron H*(10) estimation and measurements around 18MV linac.

Thermoluminescent dosimetry, analytical techniques and Monte Carlo calculations were used to estimate the dose of neutron radiation in a treatment room with a linear electron accelerator of 18MV. Measurements were carried out through neutron ambient dose monitors which include pairs of thermoluminescent dosimeters TLD 600 (6LiF: Mg, Ti) and TLD 700 (7LiF: Mg, Ti), which were placed inside a paraffin spheres. The measurements has allowed to use NCRP 151 equations, these expressions are useful to find relevant dosimetric quantities. In addition, photoneutrons produced by linac head were calculated through MCNPX code taking into account the geometry and composition of the linac head principal parts.

Photon spectrum and absorbed dose in brain tumor.

Using Monte Carlo methods a BOMAB phantom inside a treatment hall with a brain tumor nearby the pituitary gland was treated with photons produced by a Varian 6MV linac. The photon spectrum and the absorbed dose were calculated in the tumor, pituitary gland and the head. The treatment beam was collimated to illuminate only the tumor volume; however photons were noticed in the gland. Photon fluence reaching the tumor is and 15.7 times larger than the fluence in the pituitary gland, on the other hand the absorbed dose in the tumor is 37.1 times larger than the dose in the gland because photons that reach the pituitary gland are scattered, by the head and the tumor, through Compton effect.