Page 213 - 00. Complete Version - Progress Report IPEN 2014-2016

Nuclear Science and Technology | Progress Report 213

Figure 16 – Alanine/EPR dosimetric system: (a) alanine encapsulated in polyethylene tube and build-
up cap in polymethylmethacrylate; (b) Bruker ESR spectrometer (X-band).

(EPR) dosimetric system provides a second- dose study by the EPR technique. These items
ary standard for routine radiation dosimetry included nails, plastics, clothes, glasses, sugar,
in gamma rays, X-rays and electron beams ceramic and pharmaceuticals.
sources (Fig. 16a).
Radioprotection Level
The amino acid alanine is tissue-equivalent
material with several features for dosimet- An improvement on the calibration procedure
ric applications: low fading, low uncertainty in high exposure rate field was implement-
(<3%), no dose rate dependence and non-de- ed for portable survey meters used in radio-
structive EPR signal readout. protection routines. These equipments were
tested in relation to their response as: repeat-
For therapeutic dose range, the High Dose Do- ability, reproducibility, and exposure rate mea-
simetry Laboratory of IPEN developed a dosi- surements. According to the calibration re-
metric system based on alanine/EPR. The de- sults obtained in a 137Cs gamma radiation
tector is encapsulated in special polyethylene field, the procedure for portable survey meters
tube that reduces the humidity problems and used in a high exposure rates was established
improves the mechanical resistance. A com- at Calibration Laboratory of IPEN-CNEN/SP.
puter program to extract signals from noise It was also introduced an improved test pro-
spectra based on the wavelet transform was gram to be applied before the calibration proce-
developed in order to allow the use of the do- dure starts in a gamma radiation field. Several
simetric system at radiotherapy dose ranges problems related to the equipment operation
(1 to 20 Gy). as: check of the battery voltage, display mal-
function, could be avoided with these actions.
For industrial applications, the dosimetric sys- About 15% of the equipments have shown this
tem is based in commercial alanine pellets type of problems during the calibration pro-
which offer wide dose range from 10 to 105 cedures. The qualification test was made with
Gy (Fig. 16b). Geiger-Müller detectors, from different man-
ufacturers and models, according to energy
EPR spectrometry is powerful instrument for dependence in standard field of gamma radi-
radiation dosimetry accident evaluation. Inor- ation. The qualification results obtained from
ganic or organic substances present in the acci- two hundred detectors agree with the nation-
dent scenario are candidates for retrospective al and international standard recommenda-