A calculation of the density of electron-trapping defects in neutron-irradiated graphite from measurements of the temperature variation of the hall coefficient

✍ Scribed by D.F. Johnston

• Publisher: Elsevier Science
• Year: 1955
• Weight: 568 KB
• Volume: 1
• Category: Article
• ISSN: 0891-3919
• DOI: 10.1016/0891-3919(54)90033-9

✦ Synopsis

model for the Hall effect in graphite is described. Theoretical curves are given for 200 and 300°K relating the Hall coefficient for a single crystal to the number of electrons trapped. The density of electrons (n/cm") trapped in irradiated graphite is deduced from the observed Hall coefficient, and found to be about 2.8 x 1018 per cm3 at 2OO"K, and about 3.4 x lOI per cm' at 300°K after a dose of 5 x LO'@ thermal neutrons per cm2.

The chemical potential E, for a single crystal is calculated in terms of the temperature, and the density of trapped electrons.

The effect of spin and orbital degeneracy w on the occupation of the trapping sites is considered. The density of electron-trapping defects N is first discussed, assuming a single trapping energy level ~~ in terms of a relation of the form where et is found empirically from the temperature variation of n. The effect of more than one kind of trapping site is then considered. The various sources of error in an estimate of N are reviewed.

Finally the probable value of N after a dose of 5 x lo'* thermal neutrons/cm* is estimated to be about 1 x 10zo electron-trapping defects per cm3.