<s>
A	O
semiconductor	B-Algorithm
detector	I-Algorithm
in	O
ionizing	O
radiation	O
detection	O
physics	O
is	O
a	O
device	O
that	O
uses	O
a	O
semiconductor	O
(	O
usually	O
silicon	O
or	O
germanium	O
)	O
to	O
measure	O
the	O
effect	O
of	O
incident	O
charged	O
particles	O
or	O
photons	O
.	O
</s>
<s>
Semiconductor	B-Algorithm
detectors	I-Algorithm
find	O
broad	O
application	O
for	O
radiation	O
protection	O
,	O
gamma	O
and	O
X-ray	O
spectrometry	O
,	O
and	O
as	O
particle	B-Algorithm
detectors	I-Algorithm
.	O
</s>
<s>
In	O
semiconductor	B-Algorithm
detectors	I-Algorithm
,	O
ionizing	O
radiation	O
is	O
measured	O
by	O
the	O
number	O
of	O
charge	O
carriers	O
set	O
free	O
in	O
the	O
detector	B-Algorithm
material	O
which	O
is	O
arranged	O
between	O
two	O
electrodes	O
,	O
by	O
the	O
radiation	O
.	O
</s>
<s>
The	O
energy	O
required	O
to	O
produce	O
electron-hole-pairs	O
is	O
very	O
low	O
compared	O
to	O
the	O
energy	O
required	O
to	O
produce	O
paired	O
ions	O
in	O
a	O
gas	O
detector	B-Algorithm
.	O
</s>
<s>
Consequently	O
,	O
in	O
semiconductor	B-Algorithm
detectors	I-Algorithm
the	O
statistical	O
variation	O
of	O
the	O
pulse	O
height	O
is	O
smaller	O
and	O
the	O
energy	O
resolution	O
is	O
higher	O
.	O
</s>
<s>
Compared	O
with	O
gaseous	B-Algorithm
ionization	I-Algorithm
detectors	I-Algorithm
,	O
the	O
density	O
of	O
a	O
semiconductor	B-Algorithm
detector	I-Algorithm
is	O
very	O
high	O
,	O
and	O
charged	O
particles	O
of	O
high	O
energy	O
can	O
give	O
off	O
their	O
energy	O
in	O
a	O
semiconductor	O
of	O
relatively	O
small	O
dimensions	O
.	O
</s>
<s>
Most	O
silicon	O
particle	B-Algorithm
detectors	I-Algorithm
work	O
,	O
in	O
principle	O
,	O
by	O
doping	B-Algorithm
narrow	O
(	O
usually	O
around	O
100	O
micrometers	O
wide	O
)	O
silicon	B-Algorithm
strips	I-Algorithm
to	O
turn	O
them	O
into	O
diodes	O
,	O
which	O
are	O
then	O
reverse	O
biased	O
.	O
</s>
<s>
Arranging	O
thousands	O
of	O
these	O
detectors	B-Algorithm
around	O
a	O
collision	O
point	O
in	O
a	O
particle	O
accelerator	O
can	O
yield	O
an	O
accurate	O
picture	O
of	O
what	O
paths	O
particles	O
take	O
.	O
</s>
<s>
Silicon	B-Algorithm
detectors	I-Algorithm
have	O
a	O
much	O
higher	O
resolution	O
in	O
tracking	O
charged	O
particles	O
than	O
older	O
technologies	O
such	O
as	O
cloud	O
chambers	O
or	O
wire	O
chambers	O
.	O
</s>
<s>
The	O
drawback	O
is	O
that	O
silicon	B-Algorithm
detectors	I-Algorithm
are	O
much	O
more	O
expensive	O
than	O
these	O
older	O
technologies	O
and	O
require	O
sophisticated	O
cooling	O
to	O
reduce	O
leakage	O
currents	O
(	O
noise	O
source	O
)	O
.	O
</s>
<s>
They	O
also	O
suffer	O
degradation	O
over	O
time	O
from	O
radiation	O
,	O
however	O
,	O
this	O
can	O
be	O
greatly	O
reduced	O
thanks	O
to	O
the	O
Lazarus	B-Algorithm
effect	I-Algorithm
.	O
</s>
<s>
Diamond	O
detectors	B-Algorithm
have	O
many	O
similarities	O
with	O
silicon	B-Algorithm
detectors	I-Algorithm
,	O
but	O
are	O
expected	O
to	O
offer	O
significant	O
advantages	O
,	O
in	O
particular	O
a	O
high	O
radiation	O
hardness	O
and	O
very	O
low	O
drift	O
currents	O
.	O
</s>
<s>
Germanium	B-Algorithm
detectors	I-Algorithm
are	O
mostly	O
used	O
for	O
gamma	O
spectroscopy	O
in	O
nuclear	O
physics	O
,	O
as	O
well	O
as	O
x-ray	O
spectroscopy	O
.	O
</s>
<s>
While	O
silicon	B-Algorithm
detectors	I-Algorithm
cannot	O
be	O
thicker	O
than	O
a	O
few	O
millimeters	O
,	O
germanium	O
can	O
have	O
a	O
depleted	O
,	O
sensitive	O
thickness	O
of	O
centimeters	O
,	O
and	O
therefore	O
can	O
be	O
used	O
as	O
a	O
total	O
absorption	O
detector	B-Algorithm
for	O
gamma	O
rays	O
up	O
to	O
a	O
few	O
MeV	O
.	O
</s>
<s>
These	O
detectors	B-Algorithm
are	O
also	O
called	O
high-purity	O
germanium	B-Algorithm
detectors	I-Algorithm
(	O
HPGe	B-Algorithm
)	O
or	O
hyperpure	O
germanium	B-Algorithm
detectors	I-Algorithm
.	O
</s>
<s>
Before	O
current	O
purification	O
techniques	O
were	O
refined	O
,	O
germanium	O
crystals	O
could	O
not	O
be	O
produced	O
with	O
purity	O
sufficient	O
to	O
enable	O
their	O
use	O
as	O
spectroscopy	O
detectors	B-Algorithm
.	O
</s>
<s>
Impurities	O
in	O
the	O
crystals	O
trap	O
electrons	O
and	O
holes	O
,	O
ruining	O
the	O
performance	O
of	O
the	O
detectors	B-Algorithm
.	O
</s>
<s>
Consequently	O
,	O
germanium	O
crystals	O
were	O
doped	O
with	O
lithium	B-Language
ions	O
(Ge(Li )	O
)	O
,	O
in	O
order	O
to	O
produce	O
an	O
intrinsic	O
region	O
in	O
which	O
the	O
electrons	O
and	O
holes	O
would	O
be	O
able	O
to	O
reach	O
the	O
contacts	O
and	O
produce	O
a	O
signal	O
.	O
</s>
<s>
When	O
germanium	B-Algorithm
detectors	I-Algorithm
were	O
first	O
developed	O
,	O
only	O
very	O
small	O
crystals	O
were	O
available	O
.	O
</s>
<s>
Low	O
efficiency	O
was	O
the	O
result	O
,	O
and	O
germanium	B-Algorithm
detector	I-Algorithm
efficiency	O
is	O
still	O
often	O
quoted	O
in	O
relative	O
terms	O
to	O
a	O
"	O
standard	O
"	O
3″	O
x	O
3″	O
NaI(Tl )	O
scintillation	O
detector	B-Algorithm
.	O
</s>
<s>
Crystal	O
growth	O
techniques	O
have	O
since	O
improved	O
,	O
allowing	O
detectors	B-Algorithm
to	O
be	O
manufactured	O
that	O
are	O
as	O
large	O
as	O
or	O
larger	O
than	O
commonly	O
available	O
NaI	O
crystals	O
,	O
although	O
such	O
detectors	B-Algorithm
cost	O
more	O
than	O
€	O
100,000	O
(	O
US$	O
113,000	O
)	O
.	O
</s>
<s>
,	O
HPGe	B-Algorithm
detectors	B-Algorithm
commonly	O
use	O
lithium	B-Language
diffusion	O
to	O
make	O
an	O
n+	O
ohmic	O
contact	O
,	O
and	O
boron	O
implantation	O
to	O
make	O
a	O
p+	O
contact	O
.	O
</s>
<s>
Coaxial	O
detectors	B-Algorithm
with	O
a	O
central	O
n+	O
contact	O
are	O
referred	O
to	O
as	O
n-type	O
detectors	B-Algorithm
,	O
while	O
p-type	O
detectors	B-Algorithm
have	O
a	O
p+	O
central	O
contact	O
.	O
</s>
<s>
The	O
thickness	O
of	O
these	O
contacts	O
represents	O
a	O
dead	O
layer	O
around	O
the	O
surface	O
of	O
the	O
crystal	O
within	O
which	O
energy	O
depositions	O
do	O
not	O
result	O
in	O
detector	B-Algorithm
signals	O
.	O
</s>
<s>
The	O
central	O
contact	O
in	O
these	O
detectors	B-Algorithm
is	O
opposite	O
to	O
the	O
surface	O
contact	O
,	O
making	O
the	O
dead	O
layer	O
in	O
n-type	O
detectors	B-Algorithm
smaller	O
than	O
the	O
dead	O
layer	O
in	O
p-type	O
detectors	B-Algorithm
.	O
</s>
<s>
The	O
major	O
drawback	O
of	O
germanium	B-Algorithm
detectors	I-Algorithm
is	O
that	O
they	O
must	O
be	O
cooled	O
to	O
liquid	O
nitrogen	O
temperatures	O
to	O
produce	O
spectroscopic	O
data	O
.	O
</s>
<s>
Cooling	O
with	O
liquid	O
nitrogen	O
is	O
inconvenient	O
,	O
as	O
the	O
detector	B-Algorithm
requires	O
hours	O
to	O
cool	O
down	O
to	O
operating	O
temperature	O
before	O
it	O
can	O
be	O
used	O
,	O
and	O
cannot	O
be	O
allowed	O
to	O
warm	O
up	O
during	O
use	O
.	O
</s>
<s>
Ge(Li )	O
crystals	O
could	O
never	O
be	O
allowed	O
to	O
warm	O
up	O
,	O
as	O
the	O
lithium	B-Language
would	O
drift	O
out	O
of	O
the	O
crystal	O
,	O
ruining	O
the	O
detector	B-Algorithm
.	O
</s>
<s>
HPGe	B-Algorithm
detectors	B-Algorithm
can	O
be	O
allowed	O
to	O
warm	O
up	O
to	O
room	O
temperature	O
when	O
not	O
in	O
use	O
.	O
</s>
<s>
Germanium	B-Algorithm
detectors	I-Algorithm
with	O
multi-strip	O
electrodes	O
,	O
orthogonal	O
on	O
opposing	O
faces	O
,	O
can	O
indicate	O
the	O
2-D	O
location	O
of	O
the	O
ionization	O
trail	O
within	O
a	O
large	O
single	O
crystal	O
of	O
Ge	O
.	O
</s>
<s>
Detectors	B-Algorithm
like	O
this	O
have	O
been	O
used	O
in	O
COSI	O
balloon-born	O
astronomy	O
missions	O
(	O
NASA	O
,	O
2016	O
)	O
and	O
will	O
be	O
used	O
in	O
an	O
orbital	O
observatory	O
(	O
NASA	O
,	O
2025	O
)	O
Compton	O
Spectrometer	O
and	O
Imager	O
(	O
COSI	O
)	O
.	O
</s>
<s>
Cadmium	O
telluride	O
(	O
CdTe	O
)	O
and	O
cadmium	O
zinc	O
telluride	O
(	O
CZT	O
)	O
detectors	B-Algorithm
have	O
been	O
developed	O
for	O
use	O
in	O
X-ray	O
spectroscopy	O
and	O
gamma	O
spectroscopy	O
.	O
</s>
<s>
These	O
detector	B-Algorithm
materials	O
can	O
be	O
used	O
to	O
produce	O
sensors	O
with	O
different	O
electrode	O
structures	O
for	O
imaging	B-Algorithm
and	O
high-resolution	O
spectroscopy	O
.	O
</s>
<s>
However	O
,	O
CZT	O
detectors	B-Algorithm
are	O
generally	O
unable	O
to	O
match	O
the	O
resolution	O
of	O
germanium	B-Algorithm
detectors	I-Algorithm
,	O
with	O
some	O
of	O
this	O
difference	O
being	O
attributable	O
to	O
poor	O
positive	O
charge-carrier	O
transport	O
to	O
the	O
electrode	O
.	O
</s>
<s>
Semiconductor	B-Algorithm
detectors	I-Algorithm
are	O
often	O
commercially	O
integrated	O
into	O
larger	O
systems	O
for	O
various	O
radiation	O
measurement	O
applications	O
.	O
</s>
<s>
Gamma	O
spectrometers	O
using	O
HPGe	B-Algorithm
detectors	B-Algorithm
are	O
often	O
used	O
for	O
measurement	O
of	O
low	O
levels	O
of	O
gamma-emitting	O
radionuclides	O
in	O
environmental	O
samples	O
,	O
which	O
requires	O
a	O
low	O
background	O
environment	O
,	O
usually	O
achieved	O
by	O
enclosing	O
the	O
sample	O
and	O
detector	B-Algorithm
in	O
a	O
lead	O
shield	O
known	O
as	O
a	O
'	O
lead	O
castle	O
 '	O
.	O
</s>
<s>
Semiconductor	B-Algorithm
detectors	I-Algorithm
especially	O
HPGe	B-Algorithm
are	O
often	O
integrated	O
into	O
devices	O
for	O
characterising	O
packaged	O
radioactive	O
waste	O
.	O
</s>
<s>
This	O
can	O
be	O
as	O
simple	O
as	O
detectors	B-Algorithm
being	O
mounted	O
on	O
a	O
moveable	O
platform	O
to	O
be	O
brought	O
to	O
an	O
area	O
for	O
in-situ	O
measurements	O
and	O
paired	O
with	O
shielding	O
to	O
restrict	O
the	O
field-of-view	O
of	O
the	O
detector	B-Algorithm
to	O
the	O
area	O
of	O
interest	O
for	O
one-shot	O
"	O
open	O
detector	B-Algorithm
geometry	O
"	O
measurements	O
,	O
or	O
for	O
waste	O
in	O
drums	O
,	O
systems	O
such	O
as	O
the	O
Segmented	O
Gamma	O
Scanner	O
(	O
SGS	O
)	O
combine	O
a	O
semiconductor	B-Algorithm
detector	I-Algorithm
with	O
integrated	O
mechatronics	O
to	O
rotate	O
the	O
item	O
and	O
scan	O
the	O
detector	B-Algorithm
across	O
different	O
sections	O
.	O
</s>
<s>
If	O
the	O
detector	B-Algorithm
field	O
of	O
view	O
is	O
scanned	O
across	O
small	O
areas	O
of	O
the	O
item	O
in	O
multiple	O
axes	O
as	O
is	O
done	O
with	O
a	O
Tomographic	B-Algorithm
Gamma	O
Scanner	O
(	O
TGS	O
)	O
,	O
Tomography	B-Algorithm
can	O
be	O
used	O
to	O
extract	O
3D	O
information	O
about	O
the	O
density	O
and	O
gamma	O
emissions	O
of	O
the	O
item	O
.	O
</s>
