**6.1 Electron beam modification method for improving dose uniformity**

This study proposes a method of modifying the beam spectrum using aluminum plates, which allows to increase the dose uniformity during irradiation with accelerated electrons with the energy up to 10 MeV [44]. The main idea of increasing the uniformity of irradiation consists in additional placement of modifier plates between the beam output and the irradiated object. The energy and angular distributions of the directed monoenergetic electron beam are blurred after passing through the plate, which leads to the appearance of electrons with lower energies in the beam, improving the dose uniformity throughout the object during one irradiation session.

**Figure 7** shows that the addition of aluminum modifier plates changes the dose distribution throughout the irradiated object. The dose value increases in the surface layers at a distance ranging from 0 to 1.5 g/cm2 , while the maximum electron path in the substance decreases. **Figure 8** shows that the uniformity coefficient *K* grows linearly with increasing thickness of the aluminum modifier plate *d*.

For mass thicknesses of the object *L* ranging from 1.025 to 3.125 g/cm<sup>2</sup> with an error of no more than 5% it is possible to select the thickness of the aluminum modifier plate d in the range from 0.5 to 5 mm, at which the thickness of the object

### **Figure 7.**

*Dependency of the relative absorbed dose on the depth in water phantom irradiated with 6 MeV (a) and 10 MeV (b) electron beams with the aluminum modifier plates with thicknesses ranging from 1 mm to 5 mm.*

### **Figure 8.**

*Dependency of irradiation uniformity* K *of a water parallelepiped on the thickness of the aluminum modifier plate after irradiation with 4 MeV, 6 MeV, 8 MeV, and 10 MeV electron beams [44].*

corresponds to the optimal distance when the object is irradiated with electron beams with the energy ranging from 4 MeV to 10 MeV using the following formula:

$$d[\text{cm}] = -0.060[\text{cm}] - 0.199\left[\frac{\text{cm}^3}{\text{g}}\right] \times L\left[\frac{\text{g}}{\text{cm}^2}\right] + 0.093\left[\frac{\text{cm}}{\text{MeV}}\right] \times E\_0[\text{MeV}] \quad \text{(13)}$$

$$- -0.002\left[\frac{\text{cm}^3}{\text{MeV}\cdot\text{g}}\right] \times E\_0[\text{MeV}] \times L\left[\frac{\text{g}}{\text{cm}^2}\right],$$

and to calculate with an error not exceeding 5% the irradiation uniformity *K* for different combinations of modifier thicknesses *d* in the range from 0.5 mm to 5 mm and initial electron energies *E*0:

*Electron Beam Processing of Biological Objects and Materials DOI: http://dx.doi.org/10.5772/intechopen.112699*

$$K = 0.603 - 1.830 \left[ \frac{1}{\text{cm}} \right] \times d[\text{cm}] + 0.012 \left[ \frac{1}{\text{MeV}} \right] \times E\_0[\text{MeV}] - -0.135 \left[ \frac{1}{\text{MeV} \cdot \text{cm}} \right]$$

$$\times E\_0[\text{MeV}] \times d[\text{cm}].\tag{14}$$

Thus, knowing the required minimum value of the coefficient *Kmin*, it is possible to select combinations of electron beam energies and thicknesses of modifier plates, at which for a parallelepiped-shaped object the irradiation uniformity is achieved at a level that is not less than the required *K* ≥ *Kmin* over its volume.

The proposed method allows to increase the irradiation uniformity up to 0.97 in parallelepiped-shaped objects irradiated with electron beam energy between 4 MeV and 10 MeV when using aluminum modifier plates with a thickness ranging from 0.5 mm to 5.5 mm. The optimal distance from the surface of the object at which the dose value is equal to the surface dose ranges from 1.025 g/cm<sup>2</sup> to 3.125 g/cm<sup>2</sup> and decreases with an increase in modifier plate thickness [65].
