# Scintillator size

## Scintillator size

iMetry's scintillator is 20×10×10mm according to the site, I tried to consider its size.

When a γ-ray that is a photon of higher energy enters the scintillator, the γ-ray interacts with atoms constituting the scintillator inside the scintillator.The probability to cause interaction is 1 - Exp(-μ x) when a γ-ray ran some distance x (cm). Here, μ is called the linear attenuation coefficient, with the unit of 1/cm, and shows the probability of causing an interaction when a γ ray runs 1 cm in the scintillator. Specifically this means that the probability of causing an interaction increases as x increases, so the scintillator size becomes larger, the sensitivity becomes higher.

But there is also a problem of pricing issues in addition to the size issue when the distance that a γ-ray runs becomes longer and the scintillator size becomes bigger. Therefore the scintillator should be the prism shape rather than the regular hexahedron(cube) shape. However, the sensitivity, i.e. cpm value also varies for stroke γ rays running through the scintillator is changed in the case where it is incident from the side as if the γ-ray is incident from the bottom surface, cpm value changes each time changing the orientation of the scintillator there is a problem to measure the dose space. However, if there in relation 2:1 height and width of the prism, for example, the scintillator 2 cm 1 cm X 1 cm X 2 cm, stroke from the side entrance area is 1 sqcm and when it is incident from the bottom surface stroke becomes 1 cm incident area is 2 sqcm and when it is incident from the size.

In this case, around 660keV that is the γ-ray energy of a Cs137, the probability of the photoelectric effect when the γ-ray enters from the bottom of the cintillator is about the same as that when the γ-ray enters from the size. This giger counter is able to measure from 300keV to 1MeV with sufficient accuracy.

- 最終更新:2013-05-22 18:28:15