1 research outputs found
Organic-Gelatin-Free Nanocomposite Fricke Gel Dosimeter
We report a nanocomposite Fricke
gel (NC-FG) dosimeter prepared
using only Fe<sup>2+</sup> and nanoclay in water, without any organic
gelling agents. This dosimeter gels due to its thixotropic properties
and exhibits linear energy transfer (LET)-independent radiological
properties under carbon ion beam irradiation. The radiation sensitivity
of this dosimeter was 1.8 [s<sup>–1</sup> kGy<sup>–1</sup>], which is three times higher than that reported previously (0.6
[s<sup>–1</sup> kGy<sup>–1</sup>]) for a similar dosimeter
containing gelatin. The Fe<sup>3+</sup> yield was determined to be
0.19 μmol/J by evaluating the difference in spin–lattice
relaxivity between Fe<sup>3+</sup> and Fe<sup>2+</sup>. A further
increase in the radiation sensitivity was observed upon addition of
the hydrated electron scavenger N<sub>2</sub>O, suggesting the reduction
of Fe<sup>3+</sup> by a hydrated electron. LET-dependent variations
of the contributions of OH radicals and hydrated electrons compensate
each other in the oxidation yield of NC-FG. This is the main mechanism
of the suppression of LET effects in the Bragg peak compared to conventional
Fricke dosimeters. The radiation-induced oxidation yield <i>G</i>(Fe<sup>3+</sup>) can be described by the stoichiometric equation
{<i>G</i>(Fe<sup>3+</sup>) = <i>G</i>(OH) – <i>G</i>(e<sub>aq</sub><sup>–</sup>) + 2<i>G</i>(H<sub>2</sub>O<sub>2</sub>) + <i>G</i>(H)} with the reported
LET dependence of the primary yield of water decomposition radicals.
The calculated results are in approximate agreement with the absolute
value of the experimental oxidation yield of NC-FG. The effects of
the addition of small amounts of radical scavengers (nitrate, selenate,
or cadmium) are also evaluated. The sensitivity was divided into two
types, and influences of intermediate radicals after scavenging reaction
are indicated