According to IAEA “TRS 398” protocol for R₅₀ < 4 gm/cm² phantom material will water or plastic. Finally, assured that the phantom is stable and won’t move during measurements. The ionization chamber was inserted into the water phantom holder and ensured the chamber is aligned perpendicular to the beam direction. Laser and marker were used to verify the chamber’s positioned and stably within the water phantom. For plane parallel chamber the reference point is on the inner surface of the window at its center and for cylindrical chamber the reference point on the central axis at the center of the cavity.

Based on the data presented in Figure 6 and Figure 7 , the half-value depths (R₅₀) (in Table 2 ) for 6 MeV and 9 MeV electron energies were determined. These values were then substituted into Equation (2) to calculate the reference depths (z_ref), resulting in values of 1.27 cm for 6 MeV and 2.00 cm for 9 MeV. Subsequently, both the PPC-40 (plane-parallel) and FC65-P (cylindrical) ionization chambers were placed in the water phantom at their respective reference depths. Then the PPC-40 and FC65-P ionization chambers were connected to the electrometer and applying bias voltage for ion collection. In accordance with the “TRS-398” protocol, bias voltages of +300 V, −300 V, and +150 V were applied during the measurements. For each bias voltage setting, three sets of data were recorded to ensure consistency and reliability of the readings ( Figures 1-3 ).

The beam quality index for electron beams is the half-value depth in water R₅₀. This is the depth in water (g/cm²) at which the absorbed dose is 50% of its value at the absorbed dose maximum, measured with a constant SSD of 100 cm and a field size at the phantom surface of at least 10 cm × 10 cm for R₅₀ < 7 g/cm² (E₀ ≤ 16 MeV) [8] . From relative ionization data we have got the value of R_{50, ion} and then the reference conditions for the determination of R₅₀ are given below for electron beam qualities [9] ,

$R_{50}=1.029R_{50,ion}-0.06g/c{m}^2\left(R_{50,ion}\le 10g/c{m}^2\right)$ (1)

To determine the value from equation (1) and from absorbed dose versus depth curve we have got the value of $R_{50}\text{and}$ the reference depth z_ref is [10] .

$z_{ref}=0.6R_{50}-0.1g/c{m}^2\left(R_{50}ing/c{m}^2\right)$ (2)

This depth is close to the depth of the absorbed-dose maximum z_max at beam qualities R₅₀ < 4 g/cm² (E_o ≤ 10 MeV), but at higher beam qualities is deeper than z_max.

As all chambers recommended in TRS 398 are open to the ambient air, the mass of air in the cavity volume is subject to atmospheric variations. The correction factor:

$\text{KTP}=\frac{\left(273.2+T\right)P_0}{\left(273.2+T_0\right)P}$ (3)

Should be utilized to convert the mass of air in the cavity to reference conditions. Here, P and T represent the cavity air pressure and temperature during the measurements, while P_o and T_o denote the reference values (typically 1013.25 hPa and 20˚C) [9] .

Polarity effect can be particularly significant in charged particle beams, especially electrons. The influence of using polarizing potentials of opposite polarity for each user beam quality Q can be accounted for by applying a correction factor:

$k_{pol}=\frac{\left|M_{+}\right|+\left|M_{-}\right|}{2M}$ (4)

where, M₊ and M₋ are the electrometer readings obtained at positive and negative polarity, respectively, and M is the electrometer reading obtained with the polarity used routinely [9] .

The incomplete collection of charge in an ionization chamber cavity due to the recombination of ions necessitates the application of a correction factor (k_s). For pulsed beams, “TRS 398” deriving the correction factor (k_s) using the two-voltage method [11] . This method assumes a linear relationship between 1/M and 1/V, utilizing the measured values of collected charges M₁ and M₂ at polarizing voltages V₁ and V₂, respectively, under the same irradiation conditions. Here, V₁ represents the normal operating voltage, while V₂ is a lower voltage; ideally, the ratio V₁/V₂ should be equal to 2 or greater than 3. The recombination correction factor k_s at the normal operating voltage V₁ is obtained from

$k_s=a_0+a_1\left(\frac{M_1}{M_2}\right)+a_2\left(\frac{M_1}{M_2}\right)\times \left(\frac{M_1}{M_2}\right)$ (5)

where, the constants a_i are given for pulsed scan radiation ( Table 1 ).

The correction factor k_s evaluated using the two voltages method in pulsed beams corrects for both general and initial recombination [9] [12] .

Corrected dosimeter reading at the voltage V₁:

$M_Q=M_1.h_{pl}.k_{TP}.k_{ele}.k_{pol}.k_s$ (6)

In our experiment we used a water phantom so the fluence scaling factor, $h_{pl}=1$. The electrometer is not calibrated separately so the value of electrometer calibration factor, $k_{ele}$ = 1 [9] .

Clinical normalization most often takes place at the depth of the dose maximum z_max which, in the present Code of Practice, does not always coincide with z_ref. To determine the absorbed dose to water at the depth of dose maximum z_max: [9] [13]

$D_{w,Q}\left(z_{\max }\right)=\frac{100D_{w,Q}\left(z_{ref}\right)}{PDD\left(z_{ref}\right)}$ (7)

Cross-calibration of an ionization chamber is the process of comparing the response of a field or clinical chamber to that of a wellcharacterized reference chamber under identical radiation beam conditions. The ratio of their readings is used to derive a calibration coefficient for the field chamber, ensuring its dose measurements remain traceable and accurate. The calibration factor

$N_F=\frac{M_R}{M_F}$ (8)

$N_F$ = Calibration factor of the field chamber in the electron beam;

$M_R$ = Dose measured by the reference chamber (PPC-40);

$M_F$ = Charge (or dose) measured by the field chamber (FC65-P).

There are several potential sources of error in dosimetric measurements. A common issue arises from the improper recording of ambient conditions, such as temperature and pressure, which must be measured with precision and consistency. The majority of errors typically occur during the setup of the ionization chamber, including its positioning and alignment. Furthermore, inaccuracies can be introduced during ion collection by the electrometer and throughout the dose calculation process. These errors can be minimized by ensuring meticulous chamber setup, verifying the accuracy and calibration of the thermometer, barometer, and electrometer, and maintaining the correct bias voltage throughout the measurement procedure.