277Techniques forSmall Signatures
a larger band gap than Ge and is not as susceptible to the promotion of electrons
t
o
t
he
c
onductance
b
and
b
y
t
hermal
i
nteractions.
S
ilicon
d
etectors
c
an
t
herefore
o
perate
a
t
r
oom
t
emperature,
w
hereas
G
e
d
etectors
m
ust
b
e
c
ooled,
u
sually
w
ith
l
iquid
n
itrogen.
I
n
c
ontrast,
t
he
a
tomic
n
umber
o
f
g
ermanium
(Z = 3
2)
i
s
s
igni-
cantly
l
arger
t
han
t
hat
o
f
s
ilicon
(Z = 1
4),
m
aking
i
t
a m
uch
m
ore
e
fcient
m
aterial
for γ-ray detection.
Silicon
d
etectors
a
re
o
ften
us
ed
f
or
t
he
me
asurement
o
f
α
s
pectra.
T
he
a
verage
e
nergy
n
eeded
t
o
p
roduce
a
c
harge–carrier
p
air
i
n
S
i
i
s
3
.65
e
V,
c
ompared
w
ith
a
pproximately
3
0
e
V
i
n
t
he
n
oble
g
ases.
T
hus,
t
he
a
vailable
c
harge
t
hat
i
s
p
ropor-
tional
t
o
t
he
e
nergy
o
f
t
he
α
p
article
i
s
a
lmost ...