<s>
An	O
atomic	B-Application
battery	I-Application
,	O
nuclear	B-Application
battery	I-Application
,	O
radioisotope	B-Application
battery	I-Application
or	O
radioisotope	B-Application
generator	I-Application
is	O
a	O
device	O
which	O
uses	O
energy	O
from	O
the	O
decay	O
of	O
a	O
radioactive	O
isotope	O
to	O
generate	O
electricity	O
.	O
</s>
<s>
They	O
are	O
very	O
costly	O
,	O
but	O
have	O
an	O
extremely	O
long	O
life	O
and	O
high	O
energy	O
density	O
,	O
and	O
so	O
they	O
are	O
typically	O
used	O
as	O
power	O
sources	O
for	O
equipment	O
that	O
must	O
operate	O
unattended	O
for	O
long	O
periods	O
of	O
time	O
,	O
such	O
as	O
spacecraft	O
,	O
pacemakers	B-Device
,	O
underwater	O
systems	O
and	O
automated	O
scientific	O
stations	O
in	O
remote	O
parts	O
of	O
the	O
world	O
.	O
</s>
<s>
Nuclear	B-Application
battery	I-Application
technology	O
began	O
in	O
1913	O
,	O
when	O
Henry	O
Moseley	O
first	O
demonstrated	O
a	O
current	O
generated	O
by	O
charged	O
particle	O
radiation	O
.	O
</s>
<s>
In	O
1954	O
RCA	O
researched	O
a	O
small	O
atomic	B-Application
battery	I-Application
for	O
small	O
radio	O
receivers	O
and	O
hearing	O
aids	O
.	O
</s>
<s>
Nuclear	B-Application
batteries	I-Application
can	O
be	O
classified	O
by	O
energy	O
conversion	O
technology	O
into	O
two	O
main	O
groups	O
:	O
thermal	O
converters	O
and	O
non-thermal	O
converters	O
.	O
</s>
<s>
The	O
most	O
notable	O
example	O
is	O
the	O
radioisotope	B-Application
thermoelectric	I-Application
generator	I-Application
(	O
RTG	O
)	O
,	O
often	O
used	O
in	O
spacecraft	O
.	O
</s>
<s>
The	O
most	O
notable	O
example	O
is	O
the	O
betavoltaic	B-Algorithm
cell	I-Algorithm
.	O
</s>
<s>
Atomic	B-Application
batteries	I-Application
usually	O
have	O
an	O
efficiency	O
of	O
0.1	O
–	O
5%	O
.	O
</s>
<s>
High-efficiency	O
betavoltaic	B-Algorithm
devices	I-Algorithm
can	O
reach	O
6	O
–	O
8%	O
efficiency	O
.	O
</s>
<s>
A	O
thermionic	B-Algorithm
converter	I-Algorithm
consists	O
of	O
a	O
hot	O
electrode	O
,	O
which	O
thermionically	O
emits	O
electrons	O
over	O
a	O
space-charge	O
barrier	O
to	O
a	O
cooler	O
electrode	O
,	O
producing	O
a	O
useful	O
power	O
output	O
.	O
</s>
<s>
Caesium	O
vapor	O
is	O
used	O
to	O
optimize	O
the	O
electrode	O
work	O
functions	O
and	O
provide	O
an	O
ion	O
supply	O
(	O
by	O
surface	B-Algorithm
ionization	I-Algorithm
)	O
to	O
neutralize	O
the	O
electron	O
space	O
charge	O
.	O
</s>
<s>
A	O
radioisotope	B-Application
thermoelectric	I-Application
generator	I-Application
(	O
RTG	O
)	O
uses	O
thermocouples	O
.	O
</s>
<s>
The	O
University	O
of	O
Houston	O
TPV	O
Radioisotope	O
Power	O
Conversion	O
Technology	O
development	O
effort	O
is	O
aiming	O
at	O
combining	O
thermophotovoltaic	O
cells	O
concurrently	O
with	O
thermocouples	O
to	O
provide	O
a	O
3	O
-	O
to	O
4-fold	O
improvement	O
in	O
system	O
efficiency	O
over	O
current	O
thermoelectric	O
radioisotope	B-Application
generators	I-Application
.	O
</s>
<s>
A	O
Stirling	O
radioisotope	B-Application
generator	I-Application
is	O
a	O
Stirling	O
engine	O
driven	O
by	O
the	O
temperature	O
difference	O
produced	O
by	O
a	O
radioisotope	O
.	O
</s>
<s>
A	O
more	O
efficient	O
version	O
,	O
the	O
advanced	B-Algorithm
Stirling	I-Algorithm
radioisotope	I-Algorithm
generator	I-Algorithm
,	O
was	O
under	O
development	O
by	O
NASA	O
,	O
but	O
was	O
cancelled	O
in	O
2013	O
due	O
to	O
large-scale	O
cost	O
overruns	O
.	O
</s>
<s>
Unlike	O
thermoelectric	O
and	O
thermionic	B-Algorithm
converters	I-Algorithm
their	O
output	O
does	O
not	O
depend	O
on	O
the	O
temperature	O
difference	O
.	O
</s>
<s>
Electromechanical	O
atomic	B-Application
batteries	I-Application
use	O
the	O
buildup	O
of	O
charge	O
between	O
two	O
plates	O
to	O
pull	O
one	O
bendable	O
plate	O
towards	O
the	O
other	O
,	O
until	O
the	O
two	O
plates	O
touch	O
,	O
discharge	O
,	O
equalizing	O
the	O
electrostatic	O
buildup	O
,	O
and	O
spring	O
back	O
.	O
</s>
<s>
A	O
radiovoltaic	O
(	O
RV	O
)	O
device	O
converts	O
the	O
energy	O
of	O
ionizing	O
radiation	O
directly	O
into	O
electricity	O
using	O
a	O
semiconductor	O
junction	O
,	O
similar	O
to	O
the	O
conversion	O
of	O
photons	B-Application
into	O
electricity	O
in	O
a	O
photovoltaic	O
cell	O
.	O
</s>
<s>
Depending	O
on	O
the	O
type	O
of	O
radiation	O
targeted	O
,	O
these	O
devices	O
are	O
called	O
alphavoltaic	O
(	O
AV	O
,	O
αV	O
)	O
,	O
betavoltaic	B-Algorithm
(	O
BV	O
,	O
βV	O
)	O
and/or	O
gammavoltaic	O
(	O
GV	O
,	O
γV	O
)	O
.	O
</s>
<s>
Betavoltaics	B-Algorithm
have	O
traditionally	O
received	O
the	O
most	O
attention	O
since	O
(	O
low-energy	O
)	O
beta	O
emitters	O
cause	O
the	O
least	O
amount	O
of	O
radiative	O
damage	O
,	O
thus	O
allowing	O
a	O
longer	O
operating	O
life	O
and	O
less	O
shielding	O
.	O
</s>
<s>
Betavoltaic	B-Algorithm
devices	I-Algorithm
use	O
a	O
semiconductor	O
junction	O
to	O
produce	O
electrical	O
energy	O
from	O
energetic	O
beta	O
particles	O
(	O
electrons	O
)	O
.	O
</s>
<s>
A	O
commonly	O
used	O
source	O
is	O
the	O
hydrogen	O
isotope	O
tritium	B-Language
.	O
</s>
<s>
Betavoltaic	B-Algorithm
devices	I-Algorithm
are	O
particularly	O
well-suited	O
to	O
low-power	O
electrical	O
applications	O
where	O
long	O
life	O
of	O
the	O
energy	O
source	O
is	O
needed	O
,	O
such	O
as	O
implantable	O
medical	O
devices	O
or	O
military	O
and	O
space	O
applications	O
.	O
</s>
<s>
Gammavoltaic	O
devices	O
use	O
a	O
semiconductor	O
junction	O
to	O
produce	O
electrical	O
energy	O
from	O
energetic	O
gamma	O
particles	O
(	O
high-energy	O
photons	B-Application
)	O
.	O
</s>
<s>
Medtronic	O
and	O
Alcatel	O
developed	O
a	O
plutonium-powered	O
pacemaker	B-Device
,	O
the	O
Numec	O
NU-5	O
,	O
powered	O
by	O
a	O
2.5	O
Ci	O
slug	O
of	O
plutonium	O
238	O
,	O
first	O
implanted	O
in	O
a	O
human	O
patient	O
in	O
1970	O
.	O
</s>
<s>
The	O
139	O
Numec	O
NU-5	O
nuclear	O
pacemakers	B-Device
implanted	O
in	O
the	O
1970s	O
are	O
expected	O
to	O
never	O
need	O
replacing	O
,	O
an	O
advantage	O
over	O
non-nuclear	O
pacemakers	B-Device
,	O
which	O
require	O
surgical	O
replacement	O
of	O
their	O
batteries	O
every	O
5	O
to	O
10	O
years	O
.	O
</s>
<s>
Atomic	B-Application
batteries	I-Application
use	O
radioisotopes	O
that	O
produce	O
low	O
energy	O
beta	O
particles	O
or	O
sometimes	O
alpha	O
particles	O
of	O
varying	O
energies	O
.	O
</s>
<s>
Radioisotopes	O
such	O
as	O
tritium	B-Language
,	O
nickel-63	O
,	O
promethium-147	O
,	O
and	O
technetium-99	O
have	O
been	O
tested	O
.	O
</s>
<s>
Caesium-137	O
,	O
another	O
high	O
yield	O
nuclear	O
fission	O
product	O
,	O
is	O
rarely	O
used	O
in	O
atomic	B-Application
batteries	I-Application
because	O
it	O
is	O
difficult	O
to	O
convert	O
into	O
chemically	O
inert	O
substances	O
.	O
</s>
<s>
In	O
the	O
field	O
of	O
microelectromechanical	B-Architecture
systems	I-Architecture
(	O
MEMS	B-Architecture
)	O
,	O
nuclear	O
engineers	O
at	O
the	O
University	O
of	O
Wisconsin	O
,	O
Madison	O
have	O
explored	O
the	O
possibilities	O
of	O
producing	O
minuscule	O
batteries	O
which	O
exploit	O
radioactive	O
nuclei	O
of	O
substances	O
such	O
as	O
polonium	O
or	O
curium	O
to	O
produce	O
electric	O
energy	O
.	O
</s>
<s>
Ongoing	O
work	O
demonstrate	O
that	O
this	O
cantilever	O
is	O
capable	O
of	O
radio	O
frequency	O
transmission	O
,	O
allowing	O
MEMS	B-Architecture
devices	O
to	O
communicate	O
with	O
one	O
another	O
wirelessly	O
.	O
</s>
<s>
These	O
micro-batteries	O
are	O
very	O
light	O
and	O
deliver	O
enough	O
energy	O
to	O
function	O
as	O
power	O
supply	O
for	O
use	O
in	O
MEMS	B-Architecture
devices	O
and	O
further	O
for	O
supply	O
for	O
nanodevices	O
.	O
</s>
<s>
The	O
radiation	O
energy	O
released	O
is	O
transformed	O
into	O
electric	O
energy	O
,	O
which	O
is	O
restricted	O
to	O
the	O
area	O
of	O
the	O
device	O
that	O
contains	O
the	O
processor	B-Architecture
and	O
the	O
micro-battery	O
that	O
supplies	O
it	O
with	O
energy	O
.	O
</s>
