<s>
In	O
experimental	O
and	O
applied	O
particle	O
physics	O
,	O
nuclear	O
physics	O
,	O
and	O
nuclear	O
engineering	O
,	O
a	O
particle	B-Algorithm
detector	I-Algorithm
,	O
also	O
known	O
as	O
a	O
radiation	B-Algorithm
detector	I-Algorithm
,	O
is	O
a	O
device	O
used	O
to	O
detect	O
,	O
track	O
,	O
and/or	O
identify	O
ionizing	O
particles	O
,	O
such	O
as	O
those	O
produced	O
by	O
nuclear	O
decay	O
,	O
cosmic	O
radiation	O
,	O
or	O
reactions	O
in	O
a	O
particle	O
accelerator	O
.	O
</s>
<s>
Many	O
of	O
the	O
detectors	O
invented	O
and	O
used	O
so	O
far	O
are	O
ionization	O
detectors	O
(	O
of	O
which	O
gaseous	B-Algorithm
ionization	I-Algorithm
detectors	I-Algorithm
and	O
semiconductor	B-Algorithm
detectors	I-Algorithm
are	O
most	O
typical	O
)	O
and	O
scintillation	O
detectors	O
;	O
but	O
other	O
,	O
completely	O
different	O
principles	O
have	O
also	O
been	O
applied	O
,	O
like	O
Čerenkov	O
light	O
and	O
transition	O
radiation	O
.	O
</s>
<s>
The	O
following	O
types	O
of	O
particle	B-Algorithm
detector	I-Algorithm
are	O
widely	O
used	O
for	O
radiation	O
protection	O
,	O
and	O
are	O
commercially	O
produced	O
in	O
large	O
quantities	O
for	O
general	O
use	O
within	O
the	O
nuclear	O
,	O
medical	O
,	O
and	O
environmental	O
fields	O
.	O
</s>
<s>
Solid-state	B-Algorithm
detectors	I-Algorithm
:	O
</s>
<s>
Particle	B-Algorithm
detectors	I-Algorithm
can	O
also	O
usually	O
track	O
ionizing	O
radiation	O
(	O
high	O
energy	O
photons	B-Application
or	O
even	O
visible	O
light	O
)	O
.	O
</s>
<s>
If	O
their	O
main	O
purpose	O
is	O
radiation	O
measurement	O
,	O
they	O
are	O
called	O
radiation	B-Algorithm
detectors	I-Algorithm
,	O
but	O
as	O
photons	B-Application
are	O
also	O
(	O
massless	O
)	O
particles	O
,	O
the	O
term	O
particle	B-Algorithm
detector	I-Algorithm
is	O
still	O
correct	O
.	O
</s>
<s>
Beyond	O
their	O
experimental	O
implementations	O
,	O
theoretical	O
models	O
of	O
particle	B-Algorithm
detectors	I-Algorithm
are	O
also	O
of	O
great	O
importance	O
to	O
theoretical	O
physics	O
.	O
</s>
<s>
They	O
receive	O
the	O
name	O
of	O
particle	B-Algorithm
detectors	I-Algorithm
because	O
when	O
the	O
non-relativistic	O
quantum	O
system	O
is	O
measured	O
in	O
an	O
excited	O
state	O
,	O
one	O
can	O
claim	O
to	O
have	O
detected	O
a	O
particle	O
.	O
</s>
<s>
The	O
first	O
instance	O
of	O
particle	B-Algorithm
detector	I-Algorithm
models	O
in	O
the	O
literature	O
dates	O
from	O
the	O
80	O
's	O
,	O
where	O
a	O
particle	O
in	O
a	O
box	O
was	O
introduced	O
by	O
W	O
.	O
G	O
.	O
Unruh	O
in	O
order	O
to	O
probe	O
a	O
quantum	O
field	O
around	O
a	O
black	O
hole	O
.	O
</s>
<s>
Beyond	O
their	O
applications	O
to	O
theoretical	O
physics	O
,	O
particle	B-Algorithm
detector	I-Algorithm
models	O
are	O
related	O
to	O
experimental	O
fields	O
such	O
as	O
quantum	O
optics	O
,	O
where	O
atoms	O
can	O
be	O
used	O
as	O
detectors	O
for	O
the	O
quantum	O
electromagnetic	O
field	O
via	O
the	O
light-matter	O
interaction	O
.	O
</s>
<s>
From	O
a	O
conceptual	O
side	O
,	O
particle	B-Algorithm
detectors	I-Algorithm
also	O
allow	O
one	O
to	O
formally	O
define	O
the	O
concept	O
of	O
particles	O
without	O
relying	O
on	O
asymptotic	O
states	O
,	O
or	O
representations	O
of	O
a	O
quantum	O
field	O
theory	O
.	O
</s>
<s>
As	O
M	O
.	O
Scully	O
puts	O
it	O
,	O
from	O
an	O
operational	O
viewpoint	O
one	O
can	O
state	O
that	O
"	O
a	O
particle	O
is	O
what	O
a	O
particle	B-Algorithm
detector	I-Algorithm
detects	O
"	O
,	O
which	O
in	O
essence	O
defines	O
a	O
particle	O
as	O
the	O
detection	O
of	O
excitations	O
of	O
a	O
quantum	O
field	O
.	O
</s>
