| dc.description | Introduction: Applications of ethylene-vinyl acetate
(EVA) have been reported in radiation physics research,
such as in electron beam irradiations, UV measurements
and microwave irradiations. Gamma radiation
is well known and presents several applications for radiation
dosimetry [1]. The evaluation of EVA and other
dosimeters can be undertaken by the Fourier Transform
Infrared (FTIR) spectrophotometry technique. The goal
of this work was to investigate the effect of gamma radiation
in green, white and black EVA dosimeter samples
for their sensitivity and linearity response, using the
PCR method, and evaluated with the FTIR spectrophotometry
technique.
Material and method: The EVA samples had dimensions
of 0.5 x 0.5 x 0.1 cm3, in colors green, white
and black. These samples were irradiated in triplicates,
with absorbed doses of 0.01 kGy, 0.05 kGy, 0.10 kGy,
0.25 kGy, 0.50 kGy, 1.0 kGy, 5.0 kGy and 10.0 kGy
using a 60Co Gamma Cell-220 system (dose rate of
1.089 kGy/h of the Radiation Technology Center of
IPEN); afterwards, the absorbance spectrum of each
sample was acquired on a Fourier Transform Infrared
(FTIR) spectrometer (Frontier/Perkin Elmer) from
400 cm-1 to 4000 cm-1, with 1 cm-1 spectral resolution.
The linearity of response was evaluated using the
Pearson correlation coefficient (R2). The sensitivity was
set as the linear coefficient from a simple linear
regression that was fitted using the Ordinary Least
Squares Method between the absorbed doses and
absorbance values for each wavenumber in the spectra
for all colors of EVA samples.
The PCR method combines all spectra from
absorbance measurements into a single matrix, called
here as Xnm, where n is the absorbed doses that varied
discreetly from n = 1 up to 8, matching the absorbed
doses of 0.01 kGy, 0.05 kGy, 0.10 kGy, 0.25 kGy,
0.50 kGy, 1.0 kGy, 5.0 kGy and 10.0 kGy, m is the
spectral resolution index, from m = 1 up to 3600,
equivalent to the range from 400 cm-1 to 4000 cm-1.
Results: Predicted absorbed dose versus absorbed
dose data are shown in Figure 1, for the PCR method,
for EVA samples of all colors. The R2 obtained was
1.000 for the PCR method. It can be inferred that these
methods are a good alternative, in the applications that
require assessing linearity response in dosimetry, since
the measurements from each kind of sample may be
transformed in linear results. Consequently, these methods
can be associated with other characteristics from radiation
dosimetry as: reproducibility, fading, spatial
resolution and others.
Conclusion: EVA samples can be considered as a
promising material for measurements of high doses of
gamma radiation. | |
