<s>
A	O
betavoltaic	B-Algorithm
device	I-Algorithm
(	O
betavoltaic	B-Algorithm
cell	I-Algorithm
or	O
betavoltaic	B-Algorithm
battery	O
)	O
is	O
a	O
type	O
of	O
nuclear	B-Application
battery	I-Application
which	O
generates	O
electric	O
current	O
from	O
beta	O
particles	O
(	O
electrons	O
)	O
emitted	O
from	O
a	O
radioactive	O
source	O
,	O
using	O
semiconductor	O
junctions	O
.	O
</s>
<s>
A	O
common	O
source	O
used	O
is	O
the	O
hydrogen	O
isotope	O
tritium	B-Language
.	O
</s>
<s>
Unlike	O
most	B-Application
nuclear	I-Application
power	I-Application
sources	I-Application
which	O
use	O
nuclear	O
radiation	O
to	O
generate	O
heat	O
which	O
then	O
is	O
used	O
to	O
generate	O
electricity	O
,	O
betavoltaic	B-Algorithm
devices	I-Algorithm
use	O
a	O
non-thermal	O
conversion	O
process	O
,	O
converting	O
the	O
electron-hole	O
pairs	O
produced	O
by	O
the	O
ionization	O
trail	O
of	O
beta	O
particles	O
traversing	O
a	O
semiconductor	O
.	O
</s>
<s>
Betavoltaic	B-Algorithm
power	O
sources	O
(	O
and	O
the	O
related	O
technology	O
of	O
alphavoltaic	O
power	O
sources	O
)	O
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>
Betavoltaics	B-Algorithm
were	O
invented	O
in	O
the	O
1970s	O
.	O
</s>
<s>
Some	O
pacemakers	B-Device
in	O
the	O
1970s	O
used	O
betavoltaics	B-Algorithm
based	O
on	O
promethium	O
,	O
but	O
were	O
phased	O
out	O
as	O
cheaper	O
lithium	B-Language
batteries	O
were	O
developed	O
.	O
</s>
<s>
The	O
more	O
efficient	O
semiconducting	O
materials	O
used	O
today	O
can	O
be	O
paired	O
with	O
relatively	O
benign	O
isotopes	O
such	O
as	O
tritium	B-Language
,	O
which	O
produce	O
less	O
radiation	O
.	O
</s>
<s>
The	O
Betacel	B-Algorithm
was	O
considered	O
the	O
first	O
successfully	O
commercialized	O
betavoltaic	B-Algorithm
battery	O
.	O
</s>
<s>
The	O
primary	O
use	O
for	O
betavoltaics	B-Algorithm
is	O
for	O
remote	O
and	O
long-term	O
use	O
,	O
such	O
as	O
spacecraft	O
requiring	O
electrical	O
power	O
for	O
a	O
decade	O
or	O
two	O
.	O
</s>
<s>
Recent	O
progress	O
has	O
prompted	O
some	O
to	O
suggest	O
using	O
betavoltaics	B-Algorithm
to	O
trickle-charge	B-Algorithm
conventional	O
batteries	O
in	O
consumer	O
devices	O
,	O
such	O
as	O
cell	O
phones	O
and	O
laptop	B-Device
computers	I-Device
.	O
</s>
<s>
As	O
early	O
as	O
1973	O
,	O
betavoltaics	B-Algorithm
were	O
suggested	O
for	O
use	O
in	O
long-term	O
medical	O
devices	O
such	O
as	O
pacemakers	B-Device
.	O
</s>
<s>
The	O
half-life	B-Application
of	O
nickel-63	O
is	O
100	O
years	O
.	O
</s>
<s>
Recent	O
work	O
has	O
indicated	O
the	O
viability	O
of	O
betavoltaic	B-Algorithm
devices	I-Algorithm
in	O
high-temperature	O
environments	O
in	O
excess	O
of	O
like	O
the	O
surface	O
of	O
Venus	B-Application
.	O
</s>
<s>
As	O
radioactive	O
material	O
emits	O
,	O
it	O
slowly	O
decreases	O
in	O
activity	O
(	O
refer	O
to	O
half-life	B-Application
)	O
.	O
</s>
<s>
Thus	O
,	O
over	O
time	O
a	O
betavoltaic	B-Algorithm
device	I-Algorithm
will	O
provide	O
less	O
power	O
.	O
</s>
<s>
For	O
tritium	B-Language
devices	O
,	O
the	O
half-life	B-Application
is	O
12.32	O
years	O
.	O
</s>
<s>
Liability	O
connected	O
with	O
environmental	O
laws	O
and	O
human	O
exposure	O
to	O
tritium	B-Language
and	O
its	O
beta	O
decay	O
must	O
also	O
be	O
taken	O
into	O
consideration	O
in	O
risk	O
assessment	O
and	O
product	O
development	O
.	O
</s>
<s>
Naturally	O
,	O
this	O
increases	O
both	O
time-to-market	O
and	O
the	O
already	O
high	O
cost	O
associated	O
with	O
tritium	B-Language
.	O
</s>
<s>
A	O
2007	O
report	O
by	O
the	O
UK	O
government	O
's	O
Health	O
Protection	O
Agency	O
Advisory	O
Group	O
on	O
Ionizing	O
Radiation	O
declared	O
the	O
health	O
risks	O
of	O
tritium	B-Language
exposure	O
to	O
be	O
double	O
those	O
previously	O
set	O
by	O
the	O
International	O
Commission	O
on	O
Radiological	O
Protection	O
located	O
in	O
Sweden	O
.	O
</s>
<s>
Betavoltaic	B-Algorithm
nuclear	B-Application
batteries	I-Application
can	O
be	O
purchased	O
commercially	O
.	O
</s>
<s>
Available	O
devices	O
include	O
a	O
100	O
μW	O
tritium-powered	O
device	O
weighing	O
20	O
grams	O
.	O
</s>
<s>
Although	O
betavoltaics	B-Algorithm
use	O
a	O
radioactive	O
material	O
as	O
a	O
power	O
source	O
,	O
the	O
beta	O
particles	O
used	O
are	O
low	O
energy	O
and	O
easily	O
stopped	O
by	O
a	O
few	O
millimetres	O
of	O
shielding	O
.	O
</s>
<s>
With	O
proper	O
device	O
construction	O
(	O
that	O
is	O
,	O
proper	O
shielding	O
and	O
containment	O
)	O
,	O
a	O
betavoltaic	B-Algorithm
device	I-Algorithm
would	O
not	O
emit	O
dangerous	O
radiation	O
.	O
</s>
<s>
Leakage	O
of	O
the	O
enclosed	O
material	O
would	O
engender	O
health	O
risks	O
,	O
just	O
as	O
leakage	O
of	O
the	O
materials	O
in	O
other	O
types	B-Algorithm
of	I-Algorithm
batteries	I-Algorithm
(	O
such	O
as	O
lithium	B-Language
,	O
cadmium	O
and	O
lead	O
)	O
leads	O
to	O
significant	O
health	O
and	O
environmental	O
concerns	O
.	O
</s>
<s>
Due	O
to	O
the	O
high	O
power	O
density	O
of	O
radioisotopes	O
and	O
the	O
need	O
for	O
reliability	O
above	O
all	O
else	O
in	O
many	O
applications	O
of	O
betavoltaics	B-Algorithm
,	O
comparatively	O
low	O
efficiencies	O
are	O
acceptable	O
.	O
</s>
<s>
If	O
the	O
betavoltaic	B-Algorithm
device	I-Algorithm
doubles	O
as	O
a	O
radioisotope	O
heater	O
unit	O
it	O
is	O
in	O
effect	O
a	O
cogeneration	O
plant	O
and	O
achieves	O
much	O
higher	O
total	O
efficiencies	O
as	O
much	O
of	O
the	O
waste	O
heat	O
is	O
used	O
for	O
useful	O
purposes	O
.	O
</s>
<s>
Similar	O
to	O
photovoltaics	O
,	O
the	O
Shockley	O
–	O
Queisser	O
limit	O
also	O
imposes	O
an	O
absolute	O
limit	O
for	O
a	O
single	O
bandgap	O
betavoltaic	B-Algorithm
device	I-Algorithm
.	O
</s>
