Page 231 - Radiochemistry and nuclear chemistry

Detection and Measurement Techniques 215

I0000 -
5486

---" "-- 11.2 keY FIIHIt
5443 9 9
--I000
e~
ca
1' * ] 9
o
= 5389
o ,e *:
o 100
; 5513
9 ~ 554~
;o ~
9 ,~..~ :,r, i,
9 o 0"~."
*A,, V
, .
I0 ~'-" t
5400 5500 56O0
g(keV)
FIG. 8.12. (a) Surface barrier detector; S detector wafer, H gold surface layer, M
connector. (b) c~-spectrum of :41Am measured with a high resolution detector (Ace. to
ORTEC.)

8.4.2. Lithium-drifted detectors

The probability of 'y-interaction is so small in the small depletion depth of the surface
barrier detectors that they are not very useful for -y-spectroscopy. Large depleted volumes
can be created by drifting lithium atoms into a silicon or germanium crystal. Lithium does
not occupy a crystal site in the crystal, but is small enough to go into interstitial sites. The
ease of ionization of Li to Li + makes it a donor impurity. The lithium is drifted from one
side of the crystal using an electric field. Its concentration at the "entrance" side becomes
high and then decreases towards the other end of the crystal. The amount of lithium in the

>. H D

1 2 3
EdEIdx = A Z 2
FIG. 8.13. Plot of relative particle intensities for H, D, and T versus EdE/dx in a two-
detector telescope, where the first detector records dE/dx and the second E.