What is a significant reason why plane parallel chambers are recommended for dosimetry of low-energy electron beams?

Plane parallel chambers are specifically recommended for dosimetry of low-energy electron beams primarily due to their design and how they interact with low-energy radiation. In the case of low-energy electrons, the depth of maximum dose is relatively shallow compared to higher energy beams, and the electron fluence can be significantly perturbed by the geometry of the chamber used for measurement.

Farmer-type chambers, while commonly used for higher energy photon beams, can introduce significant electron fluence perturbation when exposed to low-energy electrons, primarily because of their cylindrical shape and the surrounding wall, which can affect the scattering of electrons and lead to inaccuracies in dose measurement. The plane parallel configuration, on the other hand, minimizes these perturbations due to its design, which allows for a more uniform response to the incident electron fluence.

Using plane parallel chambers therefore provides more accurate and reliable dosimetry for low-energy electron beams, making them the preferred choice in these scenarios. Their design helps in obtaining more accurate measurements of dose distribution without the influence of wall perturbations that are common with cylindrical chambers.