Question

Pure silicon (EBG = 1.1 eV) is used as a photon detector. An incoming photon can strike the surface and excite electrons from the valence band to the conduction band, where they can be counted.

Answer 1

Answer:

Explanation:

Complete Question:

A.Compute no of electrons you expect to count if silicon detector is struck with a 1.04 Mev gamma ray produced in a decay of  136 Cs nucleus.

b.Explain counting of electrons is more precise as the detector is cooled well below room temperature

Answer:

a.

Gamma ray energy =$Cs^{135}=1.04 Mev$

photon strikes the surface excite the electrons to move from valence band to conduction band where then counted by detector.

energy gap between valence band and conduction band in case of silicon = 1.1 eV

The minimum amount of energy required is 1.1 ev

minimum number of electron counted is = $\frac{1.04 Mev}{1.1eV/electrom}$

=$0.945\times10^{6}$

b.

In the case of semi conductors

forbidden energy gap in inversely proportional to temperature

with decrease in temperature forbidden energy gap increases,hence electrons jumping from valence band to conduction band decreases and hence counting by detector decreases