*4.5. Samples Irradiation*

The samples were irradiated with gamma rays in the installations of the CBRN Defense Institute of the Brazilian army in a research irradiator of the armored cavity type with a source of Cs137, projected and constructed in 1969 in the Brookhaven National Laboratories, in the USA. The source of gamma rays consisted of 28 cylinders of CsCl, with approximately 2.5 cm of length, disposed linearly along a metallic guiding structure. The plastic bags containing the ricin samples were placed over a tray and introduced in one of the two irradiation chambers of the equipment. Samples were irradiated at dosages of 10 kGy, 20 kGy and 30 kGy.

The time of exposure to the irradiation source needed to achieve the desired dosage was calculated through software developed based on the dosimetric mapping of the irradiator. The calculations considered the current activity of the source and the density and geometry of the sample, among other factors. Equation (1) calculates the activity (A) of the source, in kCi·h−1, related to the year of the irradiation (t) [45].

$$\mathbf{A} = 108 \mathbf{\bar{e}}^{-0.23(t - 1969)} \tag{1}$$

Based on Equation (1) the value of A for the irradiator in the year of the experiment was of 2.75 Ci·h−1. The value found for the dosage absorbed by the samples was of 1.2 kGy·h−1. Table 8 lists the time of irradiation necessary for achieving the dosage desired for each sample.


**Table 8.** Time needed for each sample.
