**6. Methods to increase dose uniformity in the objects irradiated with accelerated electrons**

Sterilization of biological and non-biological objects using accelerated electrons involves the reduction of microbial growth to the required level due to high energy values absorbed by microorganisms. As electrons penetrate biological objects, they

lose energy in direct interaction with atomic electrons of bacteria cell structures, which results in DNA breaks and the destruction of cell membrane [1, 3]. Reactive oxygen species appearing during radiolysis of water in biological objects destroy chemical bonds in cell molecules causing inactivation of microorganisms. Moreover, the higher the dose absorbed by the object, the greater number of microorganisms inhibited during irradiation. However, the increase in irradiation dose is limited by the irreversible physical and chemical changes occurring in the biological object. Considering that each object has its specific chemical composition and physical properties, it is necessary to select the dose range individually to ensure that effective irradiation dose does not lead to irreversible changes in the object. The dose range for the treatment of biological objects is narrower compared to non-biological objects due to a great complexity of biochemical composition of such objects, and even a small change in the dose can lead to a significant alteration in the structure and functionality of cells.

Treatment of biological objects with accelerated electrons is characterized by the non-uniformity of dose distribution over the volume of irradiated objects due to the nature of dose distribution, non-homogeneous density of biological objects, complex geometry, and chemical composition. The distribution of radiation effect on both microbiological parameters and properties of the object is non-homogeneous, which reduces the efficiency of irradiation treatment and makes it difficult to maintain the microbial values throughout the object at the required level. Thus, it is highly important to develop feasible methods to increase uniformity of absorbed dose distribution over the volume of irradiated objects.

Currently, the following methods are used in industrial irradiation facilities to increase the uniformity of dose distribution:


When the thickness of the object exceeds the maximum path of electrons with energies up to 10 MeV, it is reasonable to carry out double-side irradiation [17]. However, this is not applicable to objects with a shape different from that of a parallelepiped because it does not provide consistent irradiation uniformity.

The second way to improve the uniformity of irradiation is the use of polymer absorbers designed to fill the empty space in the package or irregularities of the irradiated object, imitating the shape of a parallelepiped to enable the use of the previous method [17]. However, this way of tackling the problem of irradiation nonuniformity is not cost-effective since it requires the replacement of polymers that are destroyed during irradiation.

Another way to increase the irradiation uniformity is to vary the energy of accelerated electrons during several irradiation sessions. **Figure 6** shows the dependencies of the absorbed dose on the depth of a parallelepiped irradiated with 3 MeV and 10 MeV electrons, as well as the distribution of the absorbed dose when the

**Figure 6.**

*Distribution of absorbed dose in the water parallelepiped during irradiation with 3 MeV (blue line) and 10 MeV (red line) electrons, as well as irradiation with the combination of 3 MeV and 10 MeV electron beams (yellow line).*

parallelepiped is irradiated by a combination of 3 MeV and 10 MeV electron, beams with weighted coefficients 0.1 and 0.9, respectively.

As can be seen from **Figure 6**, the combination of two irradiation energies allows to increase the dose uniformity. However, the use of multiple sessions increases treatment time, which makes it difficult to apply to a wide range of categories of biological objects.
