<s>
Scintillation	B-Algorithm
is	O
the	O
physical	O
process	O
where	O
a	O
material	O
,	O
called	O
a	O
scintillator	O
,	O
emits	O
UV	B-Application
or	O
visible	O
light	O
under	O
excitation	O
from	O
high	O
energy	O
photons	O
(	O
X-rays	B-Library
or	O
γ-rays	O
)	O
or	O
energetic	O
particles	O
(	O
such	O
as	O
electrons	O
,	O
alpha	O
particles	O
,	O
neutrons	O
or	O
ions	O
)	O
.	O
</s>
<s>
See	O
scintillator	O
and	O
scintillation	B-Algorithm
counter	O
for	O
practical	O
applications	O
.	O
</s>
<s>
Scintillation	B-Algorithm
is	O
an	O
example	O
of	O
luminescence	O
,	O
whereby	O
light	O
of	O
a	O
characteristic	O
spectrum	O
is	O
emitted	O
following	O
the	O
absorption	O
of	O
radiation	O
.	O
</s>
<s>
The	O
scintillation	B-Algorithm
process	O
can	O
be	O
summarized	O
in	O
three	O
main	O
stages	O
:	O
(	O
A	O
)	O
conversion	O
,	O
(	O
B	O
)	O
transport	O
and	O
energy	O
transfer	O
to	O
the	O
luminescence	O
center	O
,	O
and	O
(	O
C	O
)	O
luminescence	O
.	O
</s>
<s>
The	O
emitted	O
radiation	O
is	O
usually	O
less	O
energetic	O
than	O
the	O
absorbed	O
radiation	O
,	O
hence	O
scintillation	B-Algorithm
is	O
generally	O
a	O
down-conversion	O
process	O
.	O
</s>
<s>
The	O
first	O
stage	O
of	O
scintillation	B-Algorithm
,	O
conversion	O
,	O
is	O
the	O
process	O
where	O
the	O
energy	O
from	O
the	O
incident	O
radiation	O
is	O
absorbed	O
by	O
the	O
scintillator	O
and	O
highly	O
energetic	O
electrons	O
and	O
holes	O
are	O
created	O
in	O
the	O
material	O
.	O
</s>
<s>
For	O
highly	O
energetic	O
photons	O
such	O
as	O
X-rays	B-Library
(	O
0.1	O
keV	O
<  < 100 keV )  and γ-rays ( > 100 keV ) , three types of interactions are responsible for the energy conversion process in scintillation: photoelectric absorption, Compton scattering, and pair production, which only occurs when  >	O
1022	O
keV	O
,	O
i.e.	O
</s>
<s>
At	O
lower	O
X-ray	B-Library
energies	O
(	O
60	O
keV	O
)	O
,	O
the	O
most	O
dominant	O
process	O
is	O
the	O
photoelectric	O
effect	O
,	O
where	O
the	O
photons	O
are	O
fully	O
absorbed	O
by	O
bound	O
electrons	O
in	O
the	O
material	O
,	O
usually	O
core	O
electrons	O
in	O
the	O
K	O
-	O
or	O
L-shell	O
of	O
the	O
atom	O
,	O
and	O
then	O
ejected	O
,	O
leading	O
to	O
the	O
ionization	O
of	O
the	O
host	O
atom	O
.	O
</s>
<s>
At	O
low	O
X-ray	B-Library
energies	O
,	O
scintillator	O
materials	O
with	O
atoms	O
with	O
high	O
atomic	O
numbers	O
and	O
densities	O
are	O
favored	O
for	O
more	O
efficient	O
absorption	O
of	O
the	O
incident	O
radiation	O
.	O
</s>
<s>
After	O
the	O
energy	O
of	O
the	O
incident	O
radiation	O
is	O
absorbed	O
and	O
converted	O
into	O
so-called	O
hot	O
electrons	O
and	O
holes	O
in	O
the	O
material	O
,	O
these	O
energetic	O
charge	O
carriers	O
will	O
interact	O
with	O
other	O
particles	O
and	O
quasi-particles	O
in	O
the	O
scintillator	O
(	O
electrons	O
,	O
plasmons	O
,	O
phonons	B-Language
)	O
,	O
leading	O
to	O
an	O
"	O
avalanche	O
event	O
"	O
,	O
where	O
a	O
great	O
number	O
of	O
secondary	O
electron	O
–	O
hole	O
pairs	O
are	O
produced	O
until	O
the	O
hot	O
electrons	O
and	O
holes	O
have	O
lost	O
sufficient	O
energy	O
.	O
</s>
<s>
This	O
occurs	O
via	O
interaction	O
with	O
phonons	B-Language
for	O
electrons	O
and	O
Auger	O
processes	O
for	O
holes	O
.	O
</s>
<s>
The	O
average	O
timescale	O
for	O
conversion	O
,	O
including	O
energy	O
absorption	O
and	O
thermalization	O
has	O
been	O
estimated	O
to	O
be	O
in	O
the	O
order	O
of	O
1	O
ps	O
,	O
which	O
is	O
much	O
faster	O
than	O
the	O
average	O
decay	B-Algorithm
time	I-Algorithm
in	O
photoluminescence	O
.	O
</s>
<s>
The	O
second	O
stage	O
of	O
scintillation	B-Algorithm
is	O
the	O
charge	O
transport	O
of	O
thermalized	O
electrons	O
and	O
holes	O
towards	O
luminescence	O
centers	O
and	O
the	O
energy	O
transfer	O
to	O
the	O
atoms	O
involved	O
in	O
the	O
luminescence	O
process	O
.	O
</s>
<s>
This	O
is	O
probably	O
one	O
of	O
the	O
most	O
critical	O
phases	O
of	O
scintillation	B-Algorithm
,	O
since	O
it	O
's	O
generally	O
in	O
this	O
stage	O
where	O
most	O
loss	O
of	O
efficiency	O
occur	O
due	O
to	O
effects	O
such	O
as	O
trapping	O
or	O
non-radiative	O
recombination	O
.	O
</s>
<s>
The	O
charge	O
transport	O
can	O
also	O
become	O
a	O
bottleneck	O
for	O
the	O
timing	O
of	O
the	O
scintillation	B-Algorithm
process	O
.	O
</s>
<s>
The	O
charge	O
transport	O
phase	O
is	O
also	O
one	O
of	O
the	O
least	O
understood	O
parts	O
of	O
scintillation	B-Algorithm
and	O
depends	O
strongly	O
on	O
the	O
type	O
material	O
involved	O
and	O
its	O
intrinsic	O
charge	O
conduction	O
properties	O
.	O
</s>
<s>
Once	O
the	O
electrons	O
and	O
holes	O
reach	O
the	O
luminescence	O
centers	O
,	O
the	O
third	O
and	O
final	O
stage	O
of	O
scintillation	B-Algorithm
occurs	O
:	O
luminescence	O
.	O
</s>
<s>
The	O
exact	O
details	O
of	O
the	O
luminescence	O
phase	O
also	O
depend	O
on	O
the	O
type	O
of	O
material	O
used	O
for	O
scintillation	B-Algorithm
.	O
</s>
<s>
In	O
organic	O
molecules	O
scintillation	B-Algorithm
is	O
a	O
product	O
of	O
π-orbitals	O
.	O
</s>
<s>
The	O
triplet	O
states	O
decay	O
with	O
a	O
much	O
longer	O
decay	B-Algorithm
time	I-Algorithm
than	O
singlet	O
states	O
,	O
which	O
results	O
in	O
what	O
is	O
called	O
the	O
slow	O
component	O
of	O
the	O
decay	O
process	O
(	O
the	O
fluorescence	O
process	O
is	O
called	O
the	O
fast	O
component	O
)	O
.	O
</s>
