| dc.description | Introduction: Plastic detectors represent an important
role in radiation dosimetry [1]. They have been
used in a variety of applications, such as portal monitors,
and for solar, cosmic, UV, thermal and gamma radiations.
Dosimetric evaluation is indicated for material
characterization seeking to identify possible applications;
proper preprocessing techniques are critical features
of this process. This work aimed to determine the
linearity response of plastic samples exposed to gamma
radiation, using the Fourier Transform Infrared (FTIR)
measurements technique.
Material and method: Plastic bottle caps were used
as sample detectors. They were composed of a hollow
cylindrical shape with a 14 mm radius, 0.05 mm thickness,
28 mm height and 3.1 g mass, and they were made
of polyethylene (F217). 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 at the Radiation Technology
Center of IPEN). Afterwards, each sample absorbance
spectrum 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 preprocessing was performed in the raw data
composed by the broadband source interferogram with
a +/- 0.04 cm-1 (2??) precision for each absorbed dose
profile. Subsequently, applying the Fast Fourier
Transform (FFT), FTIR was generated. Then, the
derivates in the frequency (wavenumber) space were
calculated seeking to assess high-order effects.
The complex FFT coefficients were explicitly
obtained for peak regions, which provided localized
information regarding the spectrum approximate shape
from the FTIR evaluations to obtain linearity
estimatives.
The resulting FTIR spectra for each peak was to
numerical differentiation at the 1st, 2nd and 3 rd orders
(D1, D2 and D3, respectively). The derivates obtained
were useful in achieving the spectra shapes and the
linearity of response.
Results: Figure 1 presents the results after the application
of the PCR method: Predicted absorbed dose versus
absorbed dose, for: I, II and III regions (from spectrum).
The results of the PCR method are the maximum
values for linearity, 1.000 for all regions. This result
demonstrates that the PCR method is more robust than
the linear method, and the preprocessing via PCA provides
the information pertinent to the evaluated plastic
detector.
Conclusion: The results on linearity of response
show that plastic bottle caps represent potential radiation
detectors for high gamma radiation doses. | |
