Speaker
Mr
Pablo Vasquez
(Nuclear and Energy Research Institute – IPEN/CNEN, Brazil)
Description
Disinfection by $\gamma$-radiation of cultural heritage artefacts and
archived materials has been successfully applied in recent years.
Radiation processing used for cultural heritage disinfection has
several advantages when compared to conventional methods (e.g.,
chemical gases) mainly related to the safety, efficiency, reliability,
capacity, process time and safety for users and the environment.
However, more research is still required to study undesirable effects
(side-effects) which may appear in sensitive materials as a function
of the absorbed radiation dose. Some conservators and restorers are
frequently worried about possible long-term effects in irradiated
materials (post-effects). During the irradiation process, some
energetic and unstable chemical species called free radicals appear in
the treated matter. They disappear in different ways, interacting
either with each other or with the artefact compounds thus becoming
responsible for disinfestation and irradiation side-effects.
The kinetics of free radical decay reactions depend on the absorbed
dose, the properties of irradiated material among others. In this
study, contemporary paper samples were irradiated using
$\gamma$-radiation from $^{60}$Co with different absorbed
doses. The absorbed dose range was chosen taking into account the
effective values to promote insect eradication, fungal disinfection
and sterilization. The decay kinetics of the cellulose free
radicals induced by irradiation was analyzed using electron
paramagnetic resonance. Several spectra were obtained at room
temperature for each applied absorbed dose immediately after
irradiation as reference measurements. To understand the
free radical decay process, additional spectra were obtained for
different decay times up to almost $50$ days after irradiation.
De-noising treatment of the original obtained spectra signals were
performed using wavelets.
Free radical populations, proportional to the spin concentrations, were
found by integrating the electron paramagnetic resonance signal curves.
Comparison of spectra was done by normalizing the calculated area
corresponding to cellulose spin concentration, taking first
measurement after irradiation as $100\%$. Further analyses and
calculations were made to study the half-life and the kinetics models
of the free radicals created. diffraction was carried out to
identify crystalline phases and the effect of ionizing radiation on
the crystalline structure of cellulose in paper. Scanning electron
microscopy and scanning electron microscopy energy dispersive
spectrometry were performed to analyze structure modifications induced
by ionizing radiation, identifying cellulose fibre agglomeration zones
and to quantify chemical elements.
Results show that for the sterilization dose, $80\%$ of the cellulose
free radicals induced by ionizing radiation disappear in almost
$40$ days and for disinfection dose in $8$ days. It can be concluded
that if no modifications (side-effects) appear in the irradiated
material after the radical decay time, the material will stay stable
for the remaining lifetime. Results showed that the proposed method
using electron paramagnetic resonance is suitably to study the
behaviour of radicals on cellulosic-based cultural heritage materials.
| Country/Organization invited to participate | Brazil |
|---|
Primary author
Mr
Pablo Vasquez
(Nuclear and Energy Research Institute – IPEN/CNEN, Brazil)
Co-authors
Mr
Larissa Otubo
(Nuclear and Energy Research Institute – IPEN/CNEN, Brazil)
Mr
Paulo Souza Santos
(Nuclear and Energy Research Institute – IPEN/CNEN, Brazil)
Mr
Rafael Henrique Lazzari Garcia
(Nuclear and Energy Research Institute – IPEN/CNEN, Brazil)
Mr
Rodrigues Jr. Orlando
(Nuclear and Energy Research Institute – IPEN/CNEN, Brazil)
Ms
Yasko Kodama
(Nuclear and Energy Research Institute – IPEN/CNEN, Brazil)
