Physics and Engineering of Radiation Detection

4.1. Properties of Liquids 223

Table 4.1.1: WandGvalues of several liquids used in radiation detectors (25; 9).

Liquid W(eV) G

Liquid Argon 23.7 4.2

Liquid Krypton 20.5 4.9

Liquid Xenon 16.4 6.1

Tetramethylsilane (TMS) 33.3 3.0

Tetramethylgermanium (TMG) 33.3 3.0

Tetramethyltin (TMT) 25.6 3.9

Hexamethyldisilane (HMDS) 50 2.0

V 0

Iliquid

Igas

Forbidden Gap

Forbidden Gap

Conduction Band

Valence Band

Valence

Levels

Conduction Level

Gaseous State Liquid State

Figure 4.1.1: Comparison of energy levels in a gas and a

liquid. HereIrepresents the ionization potential.

susceptible to each other’s electromagnetic fields. The existence of energy bands is
actually the result of this physical nearness. Hence, to understand the creation of a
charge pair in a liquid, we must consider the whole liquid as an entity and not its
individual molecules. Now let us suppose that we supply the liquid enough energy
that it elevates one of its electrons from the valence band to the conduction band
(see Fig.4.1.2). This process creates a vacancy in the valence band, which effectively
produces a positive charge. This effective charge is generally referred to as ahole
to signify the fact that it represents a vacancy in the valence band. The quantum
mechanical treatment of this hole has shown that it can be regarded as a particle