Solid state simeconductor

It is main advantage is that it has much better resolution than NaI(Tl)
It is main disadvantages are that it is not available in large sizes and it is much more expensive.

The principle of operation :its acts as a solid ionization chamber so it acts as an  insulator and dose not allow current to flow until ionization has taken place in its volume. It kept very cold to minimize the current produced by thermal activation of electrons.

Collimator: it is used on the scintillation detector to limit its counting volume. It is a specially designed lead shield with one or more holes in

It has two types:
1 – The open flat field collimator: it is useful for detecting gamma rays from a relatively large volume such as the thyroid or kidney.
2- The focused collimator : it has a number of trapped holes oriented to point at a small volume  7.5 to 12.5 cm from it , it is often used in nuclear medicine