Page 66 - PR 2014 2016 07 Nuclear Science and Technology

208 Nuclear Science and Technology | Progress Report

Figure 46 – Alanine/EPR dosimetric system: (a) Bruker ESR spectrometer (X-band); (b) alanine en-
capsulated in polyethylene tube and buildup cap in polymethylmethacrylate.

in gamma rays, X-rays and electron beams glasses, sugar, ceramic and pharmaceuticals.
sources (Fig. 46a).
Radioprotection Level
The amino acid alanine is tissue-equivalent
material with several features for dosimetric An improvement on the calibration proce-
applications: low fading, low uncertainty dure in high exposure rate field was imple-
(<3%), no dose rate dependence and non-de- mented for portable survey meters used in
structive EPR signal readout. radioprotection routines. These equipments
were tested in relation to their response as:
For therapeutic dose range, the High Dose repeatability, reproducibility, and exposure
Dosimetry Laboratory of IPEN developed a rate measurements. According to the cali-
dosimetric system based on alanine/EPR. The bration results obtained in a Cs-137 gamma
detector is encapsulated in special polyeth- radiation field, the procedure for portable
ylene tube that reduces the humidity prob- survey meters used in a high exposure rates
lems and improves the mechanical resistance. was established at Calibration Laboratory
A computer program to extract signals from of IPEN-CNEN/SP. It was also introduced an
noise spectra based on the wavelet transform improved test program to be applied before
was developed in order to allow the use of the calibration procedure starts in a gamma
the dosimetric system at radiotherapy dose radiation field. Several problems related to
ranges (1 to 20 Gy). the equipment operation as: check of the
battery voltage, display malfunction, could
For industrial applications, the dosimetric be avoided with these actions. About 15%
system is based in commercial alanine pellets of the equipments have shown this type
which offer wide dose range from 0,01 to 100 of problems during the calibration pro -
kGy (Fig. 46b). cedures. The qualification test was made
with Geiger-Müller detectors, from differ-
EPR spectrometry is powerful instrument ent manufacturers and models, according
for radiation dosimetry accident evaluation. to energy dependence in standard field of
Inorganic or organic substances present in gamma radiation. The qualification results
the accident scenario are candidates for ret- obtained from two hundred detectors agree
rospective dose study by the EPR technique. with the national and international standard
These items included nails, plastics, clothes, recommendations. The data sheets and all

Instituto de Pesquisas Energéticas e Nucleares