Physics and Engineering of Radiation Detection

6.3. Inorganic Scintillators 359

chemically stability,

high mechanical stability, and


temperature stability.

Because of its mechanical stability,LuAG:Cecan be used in imaging applications
and has shown good spatial resolution. It has also been successfully used in PET
scanners.

C.9 Cerium Doped Yttrium Aluminum Perovskite (YAP:Ce)

YAlO 3 :Ceor simplyYAP:Ceis one of the few scintillators that have properties
desired for imaging applications, such as

fast response,

high mechanical stability,


chemical stability, and

low secondary emission.

The high mechanical stability of this material has been exploited by many re-
searchers to design and develop high precision imaging detectors.

C.10LiquidXenon..........................

Xenon is an inert gas having good scintillation properties. It is one of the few liquid
scintillation materials that have been successfully used in detectors. Some of its
properties relevant to its use in radiation detectors are listed below.

High density and high atomic weight: Liquid xenon has much higher

density (2.98gcm−^3 than the organic liquid scintillators. Its atomic weight

is also much higher (54) than the effective atomic weight of the organic liquid

scintillators. These two factors make it more aggressive in terms of stopping

the incident radiation quickly, thus generating more scintillation light.


Light Yield:The light yield of liquid xenon approaches that ofNaIscintil-

lator.

Response: The response of xenon to radiation is quite fast which makes it

suitable for use in timing applications.

Transparency:Most of the scintillation photons emitted by liquid xenon are
in the ultraviolet region. For these photons the liquid is highly transparent
because the energy of such a photon lies well below the excitation energy of
xenon.
The main disadvantage associated with using liquid xenon as scintillation medium
is the dramatic degradation of its optical properties due to dissolved contaminants.
During the discussion on organic liquid scintillators we saw that small amounts of
water and oxygen can deteriorate their optical properties considerably. The same is
true for liquid xenon. It has been observed that water or oxygen contamination at a