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Ch
apte
r 5
5.1
–N
atur
al R
adio
acti
vity
5.2
–N
ucle
ar R
eac
tio
ns
5.3
–R
adia
tio
n M
eas
ure
me
nt
5.4
–H
alf-
Life
of a
Rad
iois
oto
pe
5.5
–M
ed
ical
Ap
pli
cati
on
s us
ing
Rad
ioac
tivi
ty
5.6
–N
ucle
ar F
issi
on
an
d F
usio
n
Go
al: D
esc
rib
e a
lph
a, b
eta
, po
sitr
on
, an
d g
amm
a ra
dia
tio
n.
Mo
st n
atur
ally
occ
urri
ng
iso
top
es
of e
lem
en
ts u
p to
ato
mic
num
be
r 19
hav
e s
tab
le
nucl
ei (
plu
ral o
f nuc
leus
).
In s
tab
le n
ucle
i, th
e n
ucle
ar fo
rce
s b
alan
ce th
e r
ep
ulsi
on
s b
etw
ee
n th
e p
osi
tive
pro
ton
s.
Ele
me
nts
ab
ove
ato
mic
num
be
r 19
ge
ne
rally
hav
e o
ne
or
mo
re is
oto
pe
s w
ith
un
stab
le n
ucle
i.T
he
nuc
lear
forc
es
can
no
t off
set t
he
re
pul
sio
ns
fro
m th
e g
reat
er
num
be
r o
f pro
ton
s.
Th
e n
ucle
i be
com
e u
nst
able
an
d s
po
nta
ne
ous
ly e
mit
s sm
all p
arti
cle
s o
f en
erg
y (r
adia
tion
)to
be
com
e m
ore
sta
ble
.
Un
stab
le n
ucle
i are
cal
led
rad
iois
otop
esan
d a
re s
aid
to b
e r
adio
acti
ve.
Rad
iati
on
can
be
em
itte
d fr
om
a r
adio
iso
top
e in
the
form
of:
Alp
ha
(α)p
arti
cle
sB
eta
(β)
par
ticl
es
Posi
tro
ns
(β+)
Pur
e e
ne
rgy
(exa
mp
le:
gam
ma
(γ) r
ays)
A r
adio
isot
ope
Is a
n is
oto
pe
of a
n e
lem
en
t th
at e
mit
s ra
dia
tio
n.
Can
be
on
e o
r m
ore
iso
top
es
of a
n e
lem
en
t.In
clud
es
the
mas
s nu
mb
er
in it
s n
ame.
Th
e a
tom
ic n
umb
er
of i
od
ine
-131
has
a m
ass
num
be
r o
f 131
an
d a
n
ato
mic
num
be
r o
f 53.
By
em
itti
ng
rad
iati
on
, an
un
stab
le n
ucle
us fo
rms
a m
ore
sta
ble
, low
er
en
erg
y nu
cle
us.
Alp
ha
par
ticl
esar
e id
en
tica
l to
a h
eli
um n
ucle
us (
2 p
roto
ns,
2 n
eut
ron
s).
Mas
s nu
mb
er
= 4
(2
pro
ton
s +
2 n
eut
ron
s)
Ato
mic
num
be
r =
2
(2 p
roto
ns)
Ch
arg
e =
+2
or
By
em
itti
ng
rad
iati
on
, an
un
stab
le n
ucle
us fo
rms
a m
ore
sta
ble
, low
er
en
erg
y nu
cle
us.
Bet
a p
arti
cles
are
hig
h e
ne
rgy
ele
ctro
ns
Mas
s nu
mb
er
= 0
Ato
mic
num
be
r =
0
Ch
arg
e =
-1
(or
1-)
A b
eta
par
ticl
e is
form
ed
wh
en
a n
eut
ron
in a
nun
stab
le n
ucle
us c
han
ge
s in
to a
pro
ton
.
By
em
itti
ng
rad
iati
on
, an
un
stab
le n
ucle
us fo
rms
a m
ore
sta
ble
, low
er
en
erg
y nu
cle
us.
Pos
itro
ns
are
hig
h e
ne
rgy
ele
ctro
ns
wit
h a
pos
itiv
e ch
arge
Mas
s nu
mb
er
= 0
Ato
mic
num
be
r =
0
Ch
arg
e =
+1
(or
1+)
A p
osi
tro
n is
pro
duc
ed
by
an u
nst
able
nuc
leus
wh
en
a
pro
ton
is tr
ansf
orm
ed
into
a n
eut
ron
an
d a
po
sitr
on
.
By
em
itti
ng
rad
iati
on
, an
un
stab
le n
ucle
us fo
rms
a m
ore
sta
ble
, low
er
en
erg
y nu
cle
us.
Pur
e e
ne
rgy
call
ed
gam
ma
ray
Mas
s nu
mb
er
= 0
Ato
mic
num
be
r =
0
Ch
arg
e =
0
Re
leas
ed
wh
en
an
un
stab
le n
ucle
us u
nd
erg
oe
s a
rear
ran
ge
men
t of i
ts p
arti
cle
s to
giv
e
a m
ore
sta
ble
, low
er
en
erg
y nu
cle
us.
Gam
ma
rays
are
oft
en
em
itte
d a
lon
g w
ith
oth
er
typ
es
of r
adia
tio
n a
t th
e s
ame
tim
e.
Ide
nti
fy th
e ty
pe
of r
adia
tio
n fr
om
the
foll
owin
g d
esc
rip
tio
ns:
A. C
on
tain
s 2
pro
ton
s an
d 2
ne
utro
ns
B. H
as a
mas
s nu
mb
er
of 0
an
d a
1-
char
ge
Ion
izin
g r
adia
tio
n s
trik
es
mo
lecu
les
in
its
pat
h a
nd
K
no
cks
away
the
ele
ctro
ns
in
mo
lecu
les,
form
ing
un
stab
le io
ns
such
as
H2O
+.
Cau
ses
und
esi
rab
le c
he
mic
al
reac
tio
ns.
Dam
age
s th
e c
ell
s w
hic
h m
ay lo
se
the
ir a
bil
ity
to p
rod
uce
ne
cess
ary
mat
eri
als.
Can
cer.
Dif
fere
nt t
ype
s o
f ra
dia
tio
n p
en
etr
ate
the
b
od
y to
dif
fere
nt d
ep
ths.
Mo
st s
usce
pti
ble
ce
lls
are
tho
se th
at u
nd
erg
o r
apid
ce
ll
div
isio
n (
reg
en
era
tio
n):
ado
lesc
en
t ce
lls
bo
ne
mar
row
skin
rep
rod
ucti
ve o
rgan
s
inte
stin
al li
nin
gFi
gh
t fir
e w
ith
fire
!
Man
y p
rofe
ssio
ns
exp
eri
en
ce w
ork
wit
h r
adio
acti
ve
iso
top
es:
Nuc
lear
me
dic
ine
tech
no
log
ists
, ch
em
ists
, do
cto
rs, a
nd
nur
ses
MR
I (m
agn
eti
c re
son
ance
imag
ing
), X
-ray
s, C
T s
can
s (c
om
put
ed
to
mo
gra
phy
), P
ET
(p
osi
tro
n e
mis
sio
n to
mo
gra
phy
),ca
nce
r tr
eat
me
nt,
etc
.
Pro
pe
r sh
ield
ing
is n
ee
de
d to
pro
tect
yo
urse
lf fr
om
ra
dia
tio
n.
Rad
iati
on
pro
tect
ion
re
qui
rem
en
ts d
ep
en
d o
n th
e ty
pe
of
rad
iati
on
:A
lpha
par
ticle
s ar
e s
low
an
d la
rge
an
d o
nly
trav
el a
few
ce
nti
me
ters
b
efo
re c
oll
idin
g w
ith
air
mo
lecu
les,
acq
uire
ele
ctro
ns,
an
d b
eco
me
st
able
he
lium
ato
ms.
Pap
er
and
clo
thin
g b
lock
s al
ph
a p
arti
cle
s.
Beta
par
ticle
s ar
e v
ery
sm
all a
nd
mov
e m
uch
fast
er
and
fart
he
r th
an
alp
ha
par
ticl
es.
Th
ey c
an tr
ave
l sev
era
l me
ters
. Th
ey c
an p
ass
thro
ugh
p
ape
r an
d p
en
etr
ate
4-5
mm
into
the
bo
dy.
T
hre
at: s
kin
can
cer
He
avy
clo
thin
g (
lab
co
ats
and
glo
ves)
pro
tect
ag
ain
st b
eta
par
ticl
es.
Gam
ma
rays
trav
el g
reat
dis
tan
ces
thro
ugh
the
air
an
d p
ass
thro
ugh
m
any
mat
eri
als
(in
clud
ing
bo
dy
tiss
ues)
Incr
ed
ibly
dan
ge
rous
.O
nly
ve
ry d
en
se s
hie
ldin
g (
lead
or
con
cre
te)
wil
l sto
p g
amm
a ra
ys.
Dif
fere
nt t
ype
s o
f ra
dia
tio
n p
en
etr
ate
the
b
od
y to
dif
fere
nt d
ep
ths.
For
tho
se w
ork
ing
in a
n e
nvir
on
me
nt w
he
re r
adio
acti
ve m
ate
rial
s ar
e p
rese
nt,
lim
it
your
exp
osu
re b
yM
inim
izin
g th
e a
mo
unt o
f tim
e s
pe
nt n
ear
a r
adio
acti
ve s
our
ce.
Incr
eas
ing
the
dis
tan
ce fr
om
the
so
urce
.
Ind
icat
e w
hat
typ
e o
f rad
iati
on
(al
ph
a, b
eta
, an
d/o
r g
amm
a) th
at is
p
rote
cte
d fo
r e
ach
typ
e o
f sh
ield
ing
.
A.
He
avy
clo
thin
g
B.
Pap
er
C.
Lead
D.
Th
ick
co
ncr
ete
5.1
–N
atur
al R
adio
acti
vity
5.2
–N
ucle
ar R
eac
tio
ns
5.3
–R
adia
tio
n M
eas
ure
me
nt
5.4
–H
alf-
Life
of a
Rad
iois
oto
pe
5.5
–M
ed
ical
Ap
pli
cati
on
s us
ing
Rad
ioac
tivi
ty
5.6
–N
ucle
ar F
issi
on
an
d F
usio
n
Go
al: W
rite
a b
alan
ced
nuc
lear
eq
uati
on
sh
owin
g m
ass
num
be
rs fo
r ra
dio
acti
ve d
eca
y.
In a
pro
cess
cal
led
rad
ioac
tive
dec
ay, a
nuc
leus
sp
on
tan
eo
usly
bre
aks
dow
n b
y e
mit
tin
g
rad
iati
on
. T
his
can
be
sh
own
wit
h a
nuc
lear
eq
uatio
n:
Rad
ioac
tive
nuc
leus
n
ew n
ucle
us +
rad
iati
on
(α,
β, β
+, o
r γ)
Cf→Cm+
HeT
he
mas
s nu
mb
er
and
ato
mic
num
be
r m
ay c
han
ge.
Th
e s
um o
f th
e m
ass
num
be
rs a
nd
the
ato
mic
num
be
rs m
ust b
e e
qua
l fo
r th
e r
eac
tan
ts (
left
si
de
) an
d th
e p
rod
ucts
(ri
gh
t sid
e).
Alp
ha
dec
ayo
ccur
s w
he
n a
ra
dio
acti
ve n
ucle
us e
mit
s an
al
ph
a p
arti
cle,
form
ing
a n
ew
nucl
eus
wit
h:
Th
e m
ass
nu
mb
er d
ecre
ased
by
4T
he
atom
ic n
um
ber
dec
reas
ed
by 2
Co
mp
lete
the
foll
owin
g n
ucle
ar e
qua
tio
n fo
r th
e d
eca
y o
f am
eri
cium
-241
:
In th
e n
ucle
ar e
qua
tio
n fo
r b
eta
dec
ay, a
bet
a p
arti
cle,
(an
ele
ctro
n),
is
em
itte
d fr
om
the
nuc
leus
w
he
n a
ne
utro
n in
the
nu
cle
us b
reak
s d
own
, fo
rmin
g a
pro
ton
an
d a
be
ta
par
ticl
e a
nd
incr
eas
ing
the
at
om
ic n
umb
er
by
1.
Wri
te a
n e
qua
tio
n fo
r th
e d
eca
y o
f 42K
, a b
eta
em
itte
r.W
rite
the
nuc
lear
eq
uati
on
for
the
be
ta d
eca
y o
f 60C
o.
In p
osit
ron
em
issi
on,
A p
roto
n is
co
nve
rte
d to
a n
eut
ron
an
d a
po
sitr
on
Th
e m
ass
num
be
r o
f th
e n
ew n
ucle
us is
the
sam
e, b
ut th
e a
tom
ic
num
be
r d
ecr
eas
es
by
1.
Wri
te th
e n
ucle
ar e
qua
tio
n fo
r th
e p
osi
tro
n e
mis
sio
n o
f 44K
In g
amm
a ra
dia
tion
En
erg
y is
em
itte
d fr
om
an
un
stab
le n
ucle
us, i
nd
icat
ed
by
mfo
llow
ing
the
mas
s nu
mb
er.
Th
e m
ass
num
be
r an
d th
e a
tom
ic n
umb
er
of t
he
new
nuc
leus
are
th
e s
ame.
Wh
en
the
nuc
lei o
f alp
ha,
b
eta
, po
sitr
on
, an
d g
amm
a e
mit
ters
em
it r
adia
tio
n,
new
an
d m
ore
sta
ble
nuc
lei
are
pro
duc
ed
.
Rad
ioac
tive
isot
opes
are
pro
duc
ed
Wh
en
a s
tab
le n
ucle
us is
co
nve
rte
d to
a r
adio
acti
ve n
ucle
us b
y b
om
bar
din
g it
wit
h a
sm
all p
arti
cle.
Th
is is
cal
led
tran
smu
tati
on.
Wri
te th
e b
alan
ced
nuc
leus
eq
uati
on
for
the
bo
mb
ard
me
nt o
f nic
kel-
58 b
y a
pro
ton
H, whic
h p
rod
uce
s a
rad
ioac
tive
iso
top
e a
nd
an
alp
ha
par
ticl
e.
Wh
at r
adio
acti
ve is
oto
pe
is p
rod
uce
d w
he
n a
ne
utro
n b
om
bar
ds
98T
c,
rele
asin
g a
alp
ha
par
ticl
e?
5.1
–N
atur
al R
adio
acti
vity
5.2
–N
ucle
ar R
eac
tio
ns
5.3
–R
adia
tio
n M
eas
ure
me
nt
5.4
–H
alf-
Life
of a
Rad
iois
oto
pe
5.5
–M
ed
ical
Ap
pli
cati
on
s us
ing
Rad
ioac
tivi
ty
5.6
–N
ucle
ar F
issi
on
an
d F
usio
n
Go
al: D
esc
rib
e th
e d
ete
ctio
n a
nd
me
asur
em
en
t of r
adia
tio
n.
A G
eige
r co
un
ter
is a
co
mm
on
inst
rum
en
t th
atD
ete
cts
be
ta a
nd
gam
ma
rad
iati
on
Use
s io
ns
pro
duc
ed
by
rad
iati
on
to c
reat
e a
n e
lect
ric
curr
en
t.
Ar
+ r
adia
tio
n
Ar+
+ e
-
Th
e a
ctiv
ity
of a
rad
iois
oto
pe
is d
efi
ne
d a
s th
e n
umb
er
of
dis
inte
gra
tio
ns
pe
r se
con
d.
Th
e C
uri
e (C
i): t
he
num
be
r o
f dis
inte
gra
tio
ns
that
occ
ur in
1 s
for
1 g
of r
adiu
m.
Nam
ed
aft
er
Mar
ie a
nd
Pie
rre
Cur
ie, w
ho
dis
cove
red
rad
ium
an
d p
olo
niu
m.
Th
e S
I un
it fo
r ac
tivi
ty is
the
bec
qu
erel
(Bq
): 1
dis
inte
gra
tio
n p
er
seco
nd
.
An
oth
er
way
to m
eas
ure
rad
iati
on
is b
y th
e a
mo
unt a
bso
rbe
d b
y a
mat
eri
al (
such
as
bo
dy
tiss
ue).
T
he
rad
(rad
iati
on a
bso
rbed
dos
e) is
a u
nit
that
me
asur
es
the
am
oun
t of
rad
iati
on
ab
sorb
ed
by
a g
ram
of m
ate
rial
.T
he
SI u
nit
for
rad
iati
on
ab
sorp
tio
n is
the
gra
y (G
y) –
the
joul
es
of e
ne
rgy
abso
rbe
d b
y 1k
g o
f bo
dy
tiss
ue. (
1 G
y=
100
rad
)
Co
nve
rt 2
.2 C
urie
to B
ecq
uere
l. (1
Ci =
3.7
x 1
010 B
q)
Co
nve
rt 3
20 G
yto
rad
. (1
Gy
= 1
00 r
ad)
An
oth
er
way
to m
eas
ure
rad
iati
on
is b
y th
e b
iolo
gic
al e
ffe
cts
of
dif
fere
nt k
ind
s o
f rad
iati
on
. Th
is is
cal
led
the
rem
(rad
iati
on
equ
ival
ent i
n h
um
ans)
.A
lpha
par
ticle
s ca
n’t
en
ter
the
bo
dy
thro
ugh
the
sk
in, b
ut if
it fi
nd
s an
oth
er
way
(m
out
h, e
yes,
inju
ry, e
tc)
it c
an c
ause
ext
en
sive
dam
age
w
ith
in a
sh
ort
dis
tan
ce in
tiss
ue.
Hig
h e
ne
rgy
rad
iati
on
(b
eta,
hig
h-en
erg
y p
roto
ns, h
igh-
ener
gy
neut
rons
) ca
n tr
ave
l far
the
r an
d b
y d
oin
g s
o c
ause
mo
re d
amag
e
than
alp
ha.
G
amm
a ra
ys a
re d
amag
ing
be
caus
e th
ey tr
ave
l a lo
ng
way
thro
ugh
th
e b
od
y ti
ssue
.
To d
ete
rmin
e th
e e
qu
ival
ent d
ose
or
rem
do
se, t
he
ab
sorb
ed
do
se
(rad
) is
mul
tip
lie
d b
y a
fact
or
that
ad
just
for
bio
log
ical
dam
age
cau
se
by
a p
arti
cula
r fo
rm o
f rad
iati
on
.
Bio
log
ical
dam
age
(rem
) = A
bso
rbed
dos
e (r
ad) x
Fac
tor
Be
ta a
nd
gam
ma
rad
iati
on
, th
e fa
cto
r is
1
Hig
h-e
ne
rgy
pro
ton
s an
d n
eut
ron
s, th
e fa
cto
r is
10
Alp
ha
par
ticl
es,
the
fact
or
is 2
0
A p
atie
nt r
ece
ive
s 34
00m
rad
s o
f I-1
31, w
hic
h e
mit
s b
eta
p
arti
cle
s. If
that
fact
or
that
ad
just
s fo
r b
iolo
gic
al d
amag
e is
1
for
be
ta p
arti
cle
s, h
ow m
any
rem
s d
id th
e p
atie
nt r
ece
ive
?
Oft
en
the
me
asur
em
en
t fo
r an
eq
uiva
len
t do
se w
ill b
e in
mil
lire
ms
(mre
m).
1 re
m =
100
0 m
rem
Th
e S
I un
it is
the
Sie
vert
(Sv)
. 1
Sv=
100
re
m
Foo
db
orn
e il
lne
sse
s ca
use
d b
y p
ath
og
en
ic b
acte
ria
such
as
Salm
onel
la, L
iste
ria,
and
E. C
olih
ave
be
com
e m
ajo
r h
eal
th c
on
cern
s in
the
Un
ite
d S
tate
s.
Th
e U
.S. F
oo
d a
nd
Dru
g A
dm
inis
trat
ion
(FD
A)
has
ap
pro
ved
the
do
se
of 0
.3 k
Gy
to 1
kG
yo
f rad
iati
on
pro
duc
ed
by
cob
alt-
60 o
r ce
sium
-137
fo
r tr
eat
me
nt o
f fo
od
s.
Wh
en
foo
d p
asse
s th
roug
h a
se
rie
s o
f rac
ks,
gam
ma
rays
pas
s th
roug
h th
e fo
od
an
d k
ill t
he
bac
teri
a w
ith
out
har
min
g th
e fo
od
.
Cur
ren
tly
tom
ato
es,
blu
ebe
rrie
s,
stra
wb
err
ies,
an
d m
ush
roo
ms
are
b
ein
g ir
rad
iate
d to
all
ow th
em
to b
e
har
vest
ed
wh
en
they
are
co
mp
lete
ly
rip
e to
ext
en
d th
eir
sh
elf
life
.
Th
e F
DA
re
qui
res
the
sym
bo
l (a)
to
app
ear
on
irra
dia
ted
foo
ds.
Aft
er
two
w
ee
ks,
the
irra
dia
ted
str
awb
err
ies
on
th
e r
igh
t sh
ow n
o d
amag
e. W
hil
e
tho
se n
ot i
rrad
iate
d g
row
mo
ld.
No
te th
at th
e fo
od
nev
er
com
es
into
co
nta
ct w
ith
the
rad
ioac
tive
iso
top
es
itse
lf. O
nly
the
gam
ma
rays
. So
the
fo
od
do
esn
’t b
eco
me
rad
ioac
tive
.
Peo
ple
wh
o w
ork
in r
adia
tio
n la
bo
rato
rie
s w
ear
d
osi
me
ters
att
ach
ed
to th
eir
clo
thin
g.
Do
sim
ete
rs d
ete
ct th
e a
mo
unt o
f rad
iati
on
ex
po
sure
fro
m th
e fo
llow
ing
:X
-ray
sG
amm
a ra
ysB
eta
par
ticl
es
It is
an
ad
de
d le
vel o
f se
curi
ty to
mak
e a
bso
lute
su
re th
at th
ey a
re s
afe.
Ave
rag
e a
nnu
al r
adia
tio
n r
ece
ive
d b
y a
pe
rso
n in
the
Un
ite
d S
tate
s:
Th
e a
vera
ge
pe
rso
n in
the
Un
ite
d S
tate
s is
exp
ose
d to
360
mre
m o
f rad
iati
on
an
nual
ly. E
xpo
sure
to r
adia
tio
n o
ccur
s ev
ery
day
fro
m n
atur
ally
occ
urri
ng
ra
dio
iso
top
es
in
Bui
ldin
gs
wh
ere
we
live
an
d w
ork
Foo
d a
nd
wat
er
Th
e a
ir w
e b
reat
he
Post
assi
um-4
0 in
all
po
tass
ium
-co
nta
inin
g fo
od
s (b
anan
as!)
Co
smic
rad
iati
on
fro
m th
e s
un
Th
e la
rge
r th
e d
ose
of r
adia
tio
n r
ece
ive
d
at o
ne
tim
e, th
e g
reat
er
the
eff
ect
on
the
b
od
y.
Exp
osu
re to
rad
iati
on
of 5
00 r
em
is
exp
ect
ed
to c
ause
de
ath
in 5
0% o
f th
e
pe
op
le r
ece
ivin
g th
e d
ose
. (ca
lle
d th
e
leth
al d
ose
for
one-
half
the
pop
ulat
ion,
or
LD50
.)
Mat
ch e
ach
pro
pe
rty
(1-3
) w
ith
its
unit
of m
eas
ure
me
nt (
A-D
).
1. a
ctiv
ity
A. m
rad
2. a
bso
rbe
d d
ose
B. m
rem
3. b
iolo
gic
al d
ose
C. b
ecq
uere
l
D. S
v
5.1
–N
atur
al R
adio
acti
vity
5.2
–N
ucle
ar R
eac
tio
ns
5.3
–R
adia
tio
n M
eas
ure
me
nt
5.4
–H
alf-
Life
of a
Rad
iois
oto
pe
5.5
–M
ed
ical
Ap
pli
cati
on
s us
ing
Rad
ioac
tivi
ty
5.6
–N
ucle
ar F
issi
on
an
d F
usio
nG
oal
: Giv
en
the
hal
f-li
fe o
f a r
adio
iso
top
e, c
alcu
late
the
am
oun
t o
f rad
iois
oto
pe
re
mai
nin
g a
fte
r o
ne
or
mo
re h
alf-
live
s.
Th
e h
alf l
ife
is th
e a
mo
unt o
f tim
e it
take
s h
alf o
f a r
adio
activ
e
sam
ple
to d
eca
y.
For
exam
ple
, I,has a
hal
f-li
fe o
f 8.0
day
s. A
s
Idecays
, it
pro
duc
es
the
no
n-r
adio
activ
e is
oto
pe
, Xeand
a b
eta
par
ticl
e.
IXe+
e
IXe+
eSu
pp
ose
we
hav
e a
sam
ple
that
init
ially
co
nta
ins
20. m
g o
f I.
In 8
.0 d
ays,
on
e-h
alf (
10 m
g)
of a
ll th
e
Inuclei i
n th
e s
amp
le w
ill h
ave
de
caye
d,
wh
ich
leav
es
10 m
g o
f I-1
31 le
ft.
You
now
hav
e 1
0mg
an
d a
fte
r an
oth
er
hal
f lif
e o
f 8 d
ays,
5 m
g w
ill h
ave
de
caye
d
and
yo
u w
ill h
ave
5 m
g le
ft…
etc
…
A d
ecay
cu
rve
is a
d
iag
ram
of t
he
de
cay
of a
ra
dio
acti
ve is
oto
pe.
Th
e d
eca
y cu
rve
for
I-13
1 sh
ows
that
on
e-h
alf t
he
sa
mp
le d
eca
ys e
very
8
day
s.
Th
e r
adio
iso
top
e s
tro
nti
um-9
0 h
as a
hal
f-li
fe o
f 38.
1 ye
ars.
If a
sam
ple
co
nta
ins
36 m
g o
f Sr-
90, h
ow m
any
mil
lig
ram
s w
ill r
em
ain
aft
er
152.
4 ye
ars.
Ge
olo
gis
t, ar
chae
olo
gis
ts, a
nd
his
tori
ans
use
kn
owle
dg
e o
f ra
dio
acti
ve is
oto
pe
s to
est
imat
e th
e a
ge
of a
nci
en
t ob
ject
s.
Th
e a
ge
of a
n o
bje
ct d
eri
ved
fro
m p
lan
ts o
r an
imal
s (s
uch
as
wo
od
, fib
er,
bo
ne,
wo
ol c
loth
ing
, etc
.) is
de
term
ine
d b
y m
eas
urin
g th
e a
mo
unt o
f car
bo
n-1
4 in
the
sam
ple
.C
arb
on
-14
is a
nat
ural
ly o
ccur
rin
g is
oto
pe
wh
ich
is
pro
duc
ed
in n
atur
e in
the
up
pe
r at
mo
sph
ere
.Li
vin
g p
lan
ts c
on
tinu
ous
ly a
bso
rb c
arb
on
-14
thro
ugh
re
spir
atio
n. O
nce
the
pla
nt d
ies,
it b
eg
ins
to lo
se th
e
carb
on
-14
as it
de
cays
. (ca
rbo
n-1
4s h
alf-
life
is 5
730
year
s.)
In c
arb
on
-dat
ing
, sci
en
tist
s us
e th
e le
vel o
f car
bo
n-1
4 in
an
ob
ject
to e
stim
ate
how
lon
g it
had
be
en
de
cayi
ng
an
d
gue
ss w
he
n it
die
d.
(Liv
ing
thin
gs
reac
h a
n a
mo
unt o
f car
bo
n-1
4 th
at s
tays
fa
irly
co
nst
ant d
urin
g li
fe.)
Car
bo
n d
atin
g w
as u
sed
to
de
term
ine
that
the
De
ad S
ea
Scro
lls
are
ab
out
200
0 ye
ars
old
.
A r
adio
log
ical
dat
ing
me
tho
d u
sed
be
ge
olo
gis
ts u
ses
the
sam
e
tech
niq
ue a
s ca
rbo
n d
atin
g, b
ut w
ith
ura
niu
m-2
38.
Ura
niu
m-2
38 h
as a
hal
f lif
e o
f 4.5
bil
lio
n y
ear
s an
d it
de
cays
to le
ad-
206.
By
me
asur
ing
the
U-2
38 a
nd
Pb
-206
am
oun
ts in
a r
ock
, th
e a
ge
can
b
e e
stim
ate
d. O
ver
tim
e th
e a
mo
unt o
f U-2
38 d
ecr
eas
es
and
Pb
-206
in
cre
ase
s.
Th
is m
eth
od
was
use
d to
dat
e m
oo
n r
ock
s re
turn
ed
by
the
Ap
ollo
mis
sio
ns.
Th
ey w
ere
foun
d to
be
ab
out
4 b
illi
on
ye
ars
old
, ap
pro
xim
ate
ly th
e s
ame
ag
e o
f th
e E
arth
.
Car
bo
n-1
4 w
as u
sed
to d
ete
rmin
e th
e a
ge
of t
he
De
ad
Sea
Scro
lls.
If th
e D
ead
Se
a Sc
roll
s w
ere
de
term
ine
d to
b
e 2
000
year
s o
ld a
nd
the
hal
f-li
fe o
f car
bo
n-1
4 is
573
0 ye
ars,
wh
at fr
acti
on
of t
his
hal
f-li
fe h
as p
asse
d?
Th
e h
alf-
life
of I
-123
is 1
3 h
our
s. H
ow m
uch
of a
64
mg
sam
ple
of I
-123
is le
ft a
fte
r 26
ho
urs?
5.1
–N
atur
al R
adio
acti
vity
5.2
–N
ucle
ar R
eac
tio
ns
5.3
–R
adia
tio
n M
eas
ure
me
nt
5.4
–H
alf-
Life
of a
Rad
iois
oto
pe
5.5
–M
ed
ical
Ap
pli
cati
on
s us
ing
Rad
ioac
tivi
ty
5.6
–N
ucle
ar F
issi
on
an
d F
usio
n
Go
al: D
esc
rib
e th
e u
se o
f rad
iois
oto
pe
s in
me
dic
ine.
Rad
iois
oto
pe
s w
ith
sh
ort
hal
f-liv
es
are
use
d in
nuc
lear
m
ed
icin
e b
eca
use
:T
he
ce
lls
in th
e b
od
y d
o n
ot d
iffe
ren
tiat
e b
etw
ee
n n
on
-rad
ioac
tive
at
om
s an
d r
adio
activ
e a
tom
s (t
hey
tre
at th
e r
adio
iso
top
es
as th
ey
wo
uld
the
re
gul
ar is
oto
pe
)O
nce
inco
rpo
rate
d in
to c
ell
s, th
e r
adio
activ
e a
tom
s ar
e d
ete
cte
d
be
caus
e th
ey e
mit
rad
iati
on
, giv
ing
an
imag
e o
f an
org
an.
Aft
er
a ra
dio
iso
top
e is
ing
est
ed
by
the
pat
ien
t, th
e b
od
y w
ill d
ire
ct th
e is
oto
pe
just
as
if it
was
the
typ
ical
no
n-
rad
ioac
tive
form
.
A s
can
ne
r is
the
n p
asse
d o
ver
the
bo
dy
abov
e th
e r
eg
ion
w
he
re th
e o
rgan
co
nta
inin
g th
e r
adio
iso
top
e is
loca
ted
.
Th
e s
can
ne
r d
ete
cts
the
gam
ma
rad
iati
on
giv
en
off
an
d
cre
ate
s an
imag
e b
ase
d o
n h
ow m
uch
rad
iati
on
is d
ete
cte
d
acro
ss th
e o
rgan
. A
n a
rea
of l
owe
r o
r h
igh
er
rad
iati
on
can
ind
icat
e c
on
dit
ion
s su
ch a
s a
dis
eas
e o
f th
e o
rgan
, a tu
mo
r, a
blo
od
clo
t, o
r e
de
ma.
To d
ete
rmin
e th
yro
id fu
nct
ion
, do
cto
rs u
se r
adio
activ
e io
din
e up
take
.
Take
n o
rally
, rad
ioac
tive
I-1
31 m
ixe
s w
ith
the
iod
ine
al
read
y in
the
thyr
oid
.
24 h
our
s la
ter,
the
am
oun
t of i
od
ine
take
n u
p b
y th
e
thyr
oid
is d
ete
rmin
ed
wit
h a
sca
nn
er.
A p
ers
on
wit
h h
ype
rthy
roid
ism
wil
l hav
e a
hig
he
r th
an
no
rmal
leve
l of r
adio
activ
e io
din
e. A
pe
rso
n w
ith
hy
po
thyr
oid
ism
wil
l hav
e a
low
er
than
no
rmal
leve
l.
On
e tr
eat
me
nt f
or
hyp
ert
hyro
idis
m is
to g
ive
a
“th
era
pe
utic
do
se”
of I
-131
(a
hig
he
r d
ose
than
for
the
sc
an).
Th
e r
adio
acti
ve io
din
e w
ill d
est
roy
som
e o
f th
e
cell
s in
the
thyr
oid
, low
eri
ng
the
am
oun
t of t
hyro
id
ho
rmo
ne
pro
duc
ed
.
Posi
tro
n e
mit
ters
wit
h s
ho
rt h
alf-
live
s:C
an b
e u
sed
to s
tud
y b
rain
fun
ctio
n, m
eta
bo
lism
, an
d b
loo
d fl
ow.
Mig
ht b
e c
arb
on
-11,
oxy
ge
n-1
5, n
itro
ge
n-1
3 o
r fl
uori
ne
-18.
Co
mb
ine
wit
h e
lect
ron
s af
ter
em
issi
on
to p
rod
uce
gam
ma
rays
, w
hic
h a
re th
en
de
tect
ed
by
com
put
ers
, cre
atin
g a
3-D
imag
e o
f th
e o
rgan
.
Th
ese
PE
T s
can
s o
f th
e b
rain
sh
ow a
no
rmal
bra
in o
n th
e le
ft
and
a b
rain
aff
ect
ed
by
Alz
he
ime
r’s
dis
eas
e o
n th
e r
igh
t.
An
imag
ing
me
tho
d u
sed
to s
can
org
ans
such
as
the
bra
in, l
ung
s, a
nd
he
art.
A c
om
put
er
mo
nit
ors
the
ab
sorp
tio
n o
f 30,
000
X-r
ay b
eam
s d
ire
cte
d a
t th
e o
rgan
in s
ucce
ssiv
e
laye
rs.
Dif
fere
nce
s in
ab
sorp
tio
n b
ase
d o
n ti
ssue
d
en
siti
es
and
flui
ds
pro
vid
e a
n im
age
of t
he
o
rgan
.
Th
e p
atie
nt d
oe
s n
ot i
ng
est
rad
ioac
tive
mat
eri
al.
Rat
he
r, ra
dio
activ
e m
ate
rial
was
use
d to
cre
ate
th
e X
-ray
s.
An
oth
er
nam
e fo
r th
is is
Co
mp
ute
rize
d A
xial
To
mo
gra
phy
(C
AT
sca
n)
CT
sca
n o
f a b
rain
sh
ows
a tu
mo
r (y
ell
ow).
An
MR
I is
a p
owe
rful
imag
ing
tech
niq
ue th
at is
the
le
ast i
nvas
ive
imag
ing
me
tho
d a
vail
able
.
MR
I is
bas
ed
on
the
ab
sorp
tio
n o
f en
erg
y w
he
n
pro
ton
s in
hyd
rog
en
ato
ms
are
exc
ite
d th
en
re
laxe
d b
y ra
dio
wav
es.
Wh
en
pla
ced
wit
hin
a m
agn
eti
c fi
eld
, th
e p
roto
ns
pre
vio
usly
ran
do
m o
rie
nta
tio
ns,
ali
gn
wit
h th
e fi
eld
.W
hil
e in
the
mag
ne
tic
fie
ld, r
adio
wav
es
are
pul
sed
at
dif
fere
nt f
req
uen
cie
s (w
ave
len
gth
s).
Pro
ton
s in
dif
fere
nt c
he
mic
al e
nvir
on
me
nts
re
son
ate
at
dif
fere
nt f
req
uen
cie
s (j
ump
to a
hig
he
r e
ne
rgy
stat
e)
and
the
n r
ela
x b
ack
to it
s o
rig
inal
wh
en
the
rad
io
wav
es
are
turn
ed
off
.E
ne
rgy
is r
ele
ase
d, c
orr
esp
on
din
g to
par
ticu
lar
colo
rs.
MR
Is a
re tu
ne
d to
hyd
rog
en
nuc
lei
be
caus
e th
ere
is s
uch
a la
rge
ab
und
ance
of h
ydro
ge
n in
the
bo
dy
(mo
stly
in w
ate
r).
MR
Is a
re p
arti
cula
rly
use
ful f
or
soft
b
od
y ti
ssue
wh
ich
co
nta
ins
larg
e
amo
unts
of w
ate
r.
Out
sid
e o
f th
e m
ed
ical
fie
ld, t
his
te
chn
ique
is c
alle
d N
ucle
ar M
agn
eti
c R
eso
nan
ce (
NM
R)
and
is u
sed
ex
ten
sive
ly in
ch
em
istr
y la
bs.
MR
I of h
ear
t an
d lu
ng
s.
Wh
ich
of t
he
foll
owin
g r
adio
iso
top
es
are
mo
st li
kely
to b
e
use
d in
nuc
lear
me
dic
ine
?
A. 40
Kh
alf-
life
1.3
x 1
09ye
ars
B. 42
K
hal
f-li
fe 1
2 h
our
s
C. 13
1 Ih
alf-
life
8 d
ays
Th
e p
roce
ss o
f bra
chyt
her
apy,
or
see
d im
pla
nta
tio
n, i
s an
in
tern
al fo
rm o
f rad
iati
on
the
rap
y fo
r ca
nce
r.
Th
e b
en
efi
t of b
rach
yth
era
py
ove
r tr
adit
ion
al e
xte
rnal
ca
nce
r tr
eat
me
nts
is th
at th
e r
adia
tio
n is
lim
ite
d to
a v
ery
sp
eci
fic
are
a (t
he
dir
ect
loca
tio
n o
f th
e tu
mo
r), w
he
re a
s tr
adit
ion
al tr
eat
me
nts
oft
en
eff
ect
an
en
tire
org
an.
Bra
chyt
he
rap
y is
als
o q
uick
er
than
trad
itio
nal
me
tho
ds.
B
eca
use
the
targ
et a
rea
is o
nly
the
can
cer,
larg
er
do
ses
can
b
e a
dm
inis
tere
d a
t a ti
me,
less
en
ing
how
man
y tr
eat
me
nts
ar
e r
eq
uire
d.
Per
man
ent b
rach
yth
erap
y is
a tr
eat
me
nt
op
tio
n fo
r p
rost
ate
can
cer.
Invo
lve
s im
pla
nti
ng
40+
tita
niu
m c
apsu
les
call
ed
se
ed
s in
the
can
cero
us a
rea.
Insi
de
the
tita
niu
m c
apsu
les
are
rad
ioac
tive
is
oto
pe
sI-
125,
Pd
-103
, or
Cs-
131
Th
e is
oto
pe
s d
eca
y b
y g
amm
a e
mis
sio
n w
hic
h
kil
ls th
e c
ance
r ce
lls’
ab
ilit
y to
re
pro
duc
e.If
the
rig
ht d
osa
ge
is u
sed
, th
e is
oto
pe
s w
ill e
mit
al
l its
rad
iati
on
into
the
can
cer
the
n s
top
be
fore
d
amag
ing
a la
rge
am
oun
t of b
od
y ti
ssue
.
Th
e “
see
ds”
are
inse
rte
d o
nce
an
d le
ft in
sid
e th
e b
od
y. (
On
ce
all t
he
rad
ioac
tive
de
cay
has
o
ccur
red
, th
e s
ee
ds
are
h
arm
less
.)
Tem
por
ary
bra
chyt
her
apy
is a
lso
a tr
eat
me
nt f
or
pro
stat
e
can
cer.
Lon
g n
ee
dle
s ar
e im
pla
nte
d in
to th
e tu
mo
r co
nta
inin
g Ir
-19
2.C
an b
e u
sed
to d
eliv
er
a h
igh
er
do
se o
f rad
iati
on
ove
r a
sho
rte
r ti
me
co
mp
are
d to
pe
rme
nan
tan
d m
ay b
e r
ep
eat
ed
in
a fe
w d
ays.
Th
e n
ee
dle
s ar
e r
em
ove
d a
fte
r 5-
10 m
inut
es.
Bra
chyt
he
rap
y is
als
o u
sed
foll
owin
g b
reas
t can
cer
lum
pe
cto
my
(tum
or
rem
oval
).
An
Ir-1
92 is
oto
pe
is in
sert
ed
into
a c
ath
ete
r im
pla
nte
d in
th
e s
pac
e le
ft b
y th
e r
em
oval
of t
he
tum
or.
Th
e is
oto
pe
is r
em
ove
d a
fte
r 5-
10 m
inut
es.
Th
e g
oal
is to
kil
l any
re
mai
nin
g c
ance
r ce
lls.
Th
e tr
eat
me
nt i
s re
pe
ate
d tw
ice
a d
ay fo
r 5
day
s. T
he
n th
e
cath
ete
r is
re
mov
ed
an
d n
o r
adio
acti
ve m
ate
rial
re
mai
ns
in
the
bo
dy.
5.1
–N
atur
al R
adio
acti
vity
5.2
–N
ucle
ar R
eac
tio
ns
5.3
–R
adia
tio
n M
eas
ure
me
nt
5.4
–H
alf-
Life
of a
Rad
iois
oto
pe
5.5
–M
ed
ical
Ap
pli
cati
on
s us
ing
Rad
ioac
tivi
ty
5.6
–N
ucle
ar F
issi
on
an
d F
usio
n
Go
al: D
esc
rib
e th
e p
roce
sse
s o
f nuc
lear
fiss
ion
an
d fu
sio
n.
Dur
ing
the
193
0s, s
cie
nti
sts
bo
mb
ard
ed
ura
niu
m-2
35 w
ith
n
eut
ron
s an
d d
isco
vere
d th
at th
e U
-23
5 nu
cle
us s
pli
ts in
to tw
o s
mal
ler
nucl
ei a
nd
pro
duc
es
a g
reat
amo
unt
of e
ne
rgy.
Nu
clea
r fi
ssio
n: s
pli
ttin
g a
n
ato
m in
to 2
+ p
arts
Ato
mic
en
erg
y: th
e e
ne
rgy
ge
ne
rate
d b
y fi
ssio
n.
n+U→
U→Kr+
Ba+ 3n+ en
erg
y
Od
dly
en
oug
h, i
f yo
u w
ere
ab
le to
we
igh
sta
rtin
g
mat
eri
als
(ne
utro
n a
nd
U-2
35)
and
the
n th
e p
rod
ucts
(K
r-91
, Ba-
142,
an
d 3
ne
utro
ns)
yo
u’d
fin
d th
ey d
idn
’t w
eig
h th
e s
ame.
Th
at is
be
caus
e s
om
e o
f th
e ‘m
ass’
was
co
nve
rte
d to
an
e
no
rmo
us a
mo
unt o
f en
erg
y.
E =
mc2
Ein
ste
in’s
fam
ous
eq
uati
on
. En
erg
y re
leas
ed
(E
), m
ass
lost
(m
), s
pe
ed
of l
igh
t (c)
= 3
x 1
08 m
/s.
Eve
n th
oug
h th
e m
ass
lost
is v
ery
ve
rysm
all,
wh
en
yo
u m
ulti
ply
that
by
the
sp
ee
d o
f lig
ht s
qua
red
, it b
eco
me
s a
hug
e a
mo
unt o
f en
erg
y.
Fiss
ion
be
gin
s w
he
n a
hig
h-e
ne
rgy
ne
utro
n c
oll
ide
s w
ith
a h
eav
y ra
dio
acti
ve
ato
m (
U-2
35 fo
r ex
amp
le).
T
he
ne
utro
n b
eco
me
s p
art o
f th
e a
tom
, h
owev
er
the
new
nuc
leus
is u
nst
able
an
d
spli
ts in
to s
mal
ler
nucl
ei.
Th
is a
lso
re
leas
es
seve
ral n
eut
ron
s th
at c
an
the
n c
oll
ide
wit
h o
the
r ra
dio
acti
ve a
tom
s an
d r
ep
eat
the
pro
cess
, cau
sin
g a
ch
ain
re
acti
on.
An
en
orm
ous
am
oun
t of e
ne
rgy
is r
ele
ase
d
as w
ell
.
To s
usta
in a
ch
ain
re
acti
on
, w
ith
out
ad
din
g a
ny
add
itio
nal
U-2
35 o
r n
eut
ron
s, th
e o
rig
inal
am
oun
t of U
-235
mus
t eq
ual
a cr
itica
l mas
s.
So m
uch
he
at a
nd
en
erg
y b
uild
up
that
an
ato
mic
ex
plo
sio
n c
an o
ccur
.
Hir
osh
ima,
Jap
anA
ugus
t 6, 1
945
Nag
asak
i, Ja
pan
Aug
ust 9
, 194
5
Dur
ing
WW
II, a
fte
r G
erm
any’
s d
efe
at, J
apan
re
fuse
d to
su
rre
nd
er.
It w
as c
lear
that
Ja
pan
wo
uld
no
t win
in th
e
lon
g r
un, w
hic
h a
pp
ear
ed
to
mak
e Ja
pan
eve
n m
ore
d
ead
ly. J
apan
ese
forc
es
infl
icte
d th
e s
ame
am
oun
t of
All
ied
forc
e c
asua
ltie
s in
3
mo
nth
s, a
s th
e fu
ll w
ar in
the
p
revi
ous
1.5
ye
ars.
Hir
osh
ima,
Jap
anA
ugus
t 6, 1
945
Nag
asak
i, Ja
pan
Aug
ust 9
, 194
5
Pre
sid
en
t Tru
man
’s w
ar c
oun
sel b
roug
ht h
im 2
o
pti
on
s.
1. T
o c
on
tinu
e c
urre
nt t
acti
cs o
f co
nve
nti
on
al
bo
mb
ing
foll
owe
d w
ith
a m
assi
ve in
vasi
on
. Tru
man
w
as a
dvi
sed
that
suc
h a
n in
vasi
on
wo
uld
re
sult
in
U.S
. cas
ualt
ies
of u
p to
mil
lio
n.
2. U
se th
e a
tom
ic b
om
b in
ho
pe
of b
rin
gin
g th
e w
ar
to a
qui
ck e
nd
.
Th
is w
as a
he
artb
reak
ing
an
d d
iffi
cult
de
cisi
on
to
mak
e. P
resi
de
nt T
rum
an c
ho
se to
use
an
ato
mic
b
om
b r
eg
ard
less
of t
he
mo
ral r
ese
rvat
ion
s m
any
in
his
war
co
unci
l vo
ice
d a
s w
ell
as
scie
nti
sts
wh
o
dev
elo
pe
d it
.
Th
e fi
rst a
tom
ic b
om
b, n
ame
d L
ittle
Boy
use
d
Ura
niu
m-2
35. I
t we
igh
ed
900
0 p
oun
ds.
It d
eto
nat
ed
200
0 fe
et a
bov
e H
iro
shim
a an
d
leve
led
5 s
qua
re m
ile
s o
f th
e c
ity.
Th
e b
last
was
the
eq
uiva
len
t of 1
2-15
,000
to
ns
of T
NT.
To A
me
rica
’s d
ism
ay, J
apan
ese
e
mp
ero
r, H
iro
hit
o, r
efu
sed
to
surr
en
de
r. H
e d
idn
’t b
eli
eve
th
e U
.S. c
oul
d p
oss
ibly
hav
e a
se
con
d b
om
b.
Pre
sid
en
t Tru
man
mad
e th
e
de
cisi
on
that
a s
eco
nd
bo
mb
w
as n
ece
ssar
y.
Th
e s
eco
nd
bo
mb
, nam
ed
Fat
Man
was
big
ge
r th
an th
e
firs
t.
It c
on
tain
ed
plu
ton
ium
(th
ere
was
no
t en
oug
h u
ran
ium
le
ft to
mak
e a
2n
db
om
b w
ith
).
Th
e b
om
b w
as d
rop
pe
d o
n N
agas
aki a
fte
r th
ick
clo
uds
pre
ven
ted
the
firs
t tar
ge
t, K
ok
ura,
fro
m b
ein
g a
n o
pti
on
.
Alt
ho
ugh
the
bo
mb
was
big
ge
r th
an th
e fi
rst,
Nag
asak
i w
as n
est
led
in n
arro
w v
alle
ys b
etw
ee
n m
oun
tain
s th
at
red
uce
d th
e b
last
rad
ius
to 2
.6 s
qua
re m
ile
s.
6 d
ays
late
r, o
n A
ugus
t 15,
194
5,
Em
pe
ror
Hir
oh
ito
an
no
unce
d Ja
pan
’s
surr
en
de
r in
a r
adio
bro
adca
st.
En
din
g W
WII
.
In o
rde
r to
re
ach
the
cri
tical
mas
s th
at e
nab
led
the
b
om
bs
to e
xplo
de,
the
ura
niu
m/p
luto
niu
m
mo
lecu
les
had
to b
e in
cred
ibly
clo
se to
ge
the
r.
In o
rde
r to
ach
ieve
this
, dyn
amit
e e
nci
rcle
d th
e
uran
ium
/plu
ton
ium
an
d w
as d
eto
nat
ed
.
Th
is c
ann
ot b
e a
chie
ved
in th
e s
ett
ing
of a
nuc
lear
re
acto
r.
In a
nuc
lear
pow
erp
lan
t, a
he
avy
ele
me
nt u
nd
erg
oe
s fi
ssio
n a
nd
the
en
erg
y g
en
era
ted
fro
m th
e r
eac
tio
n is
co
nve
rte
d to
ele
ctri
city
.U
ran
ium
-235
an
d p
luto
niu
m-2
39 a
re c
om
mo
n
Th
e a
mo
unt o
f en
erg
y h
arn
ess
ed
fro
m 1
gra
m o
f U-2
35 is
th
e e
qui
vale
nt o
f bur
nin
g 6
000
po
und
s o
f co
al.
Wit
hin
the
re
acto
r, th
ere
is a
sm
all b
ox (
14”
tall
, 20”
wid
e)
wh
ere
the
fiss
ion
take
s p
lace
.
Con
trol
rod
sca
n b
e in
sert
ed
into
the
box
or
rem
ove
d a
s n
ee
de
d.
U-2
35 (
or
wh
atev
er)
is a
dd
ed
in T
INY
am
oun
ts to
the
ch
amb
er
alo
ng
wit
h h
igh
-e
ne
rgy
ne
utro
ns.
Th
e e
ne
rgy
due
to fi
ssio
n is
in
the
form
of h
eat
.
n+U→
U→Kr+
Ba+ 3n+ en
erg
y
A s
yste
m
tran
sfe
rs th
e h
eat
o
ut o
f th
e r
eac
tor
into
a w
ate
r ta
nk
w
he
re it
he
ats
the
w
ate
r.
Th
e s
team
co
min
g o
ff th
e
wat
er
is fe
d
thro
ugh
a tu
rbin
e
wh
ich
ge
ne
rate
s e
lect
rici
ty a
nd
it
turn
s.
Nuc
lear
re
acto
rs r
eq
uire
sm
all
amo
unts
of f
uel t
o b
e a
dd
ed
ho
urly
b
y re
acto
r o
pe
rato
rs.
A r
eac
tor
nev
er
has
en
oug
h fu
el i
n it
to
re
ach
cri
tical
mas
san
d b
eco
me
ex
plo
sive
. In
fact
the
fue
l in
re
acto
rs
are
dif
fere
nt t
he
n th
ose
in b
om
bs,
an
d th
e te
chn
olo
gy
to a
chie
ve
“bo
mb
gra
de
mat
eri
al”
is h
igh
ly
clas
sifi
ed
. Ve
ry fe
w c
oun
trie
s in
the
w
orl
d h
ave
fig
ure
d it
out
.R
eac
tors
are
als
o b
uilt
wit
h g
ian
t co
ncr
ete
do
me
s w
ith
a th
ick
ne
ss
that
blo
cks
rad
iati
on
, sh
oul
d th
e
wo
rst e
ver
hap
pe
n.
Th
e “
wo
rst t
hat
co
uld
hap
pe
n”
is c
alle
d a
“r
eac
tor
me
ltd
own
.”
Gia
nt c
oo
lin
g ta
nk
s su
rro
und
the
re
acto
r an
d
mo
de
rate
it’s
tem
pe
ratu
re.
Pip
es
run
fro
m th
e c
oo
lin
g ta
nks,
thro
ugh
th
e r
eac
tor
box
, an
d b
ack
into
the
tan
ks.
If th
e r
eac
tor
is a
t a p
owe
r p
lan
t, th
e p
ipe
s w
ill
run
thro
ugh
wat
er
tan
ks
be
fore
re
turn
ing
to th
e
coo
lin
g ta
nk
s.T
he
se p
ipe
s ab
sorb
he
at fr
om
the
re
acto
r, co
oli
ng
the
re
acto
r.90
,000
gal
lon
s o
f liq
uid
so
diu
m p
asse
s th
roug
h
the
re
acto
r b
ox P
ER
MIN
UT
E. A
s th
e s
od
ium
e
nte
rs th
e b
ox, i
t is
700°
F an
d a
s it
leav
es
it is
820
°
F.
A r
eac
tor
me
ltd
own
occ
urs
wh
en
the
co
oli
ng
sys
tem
s fa
il.
Th
is h
app
en
ed
to 3
nuc
lear
pow
er
pla
nts
in M
arch
201
1 w
he
n a
9.0
m
agn
itud
e e
arth
qua
ke s
truc
k o
ff s
ho
re o
f Jap
an.
Th
e e
arth
qua
ke c
ut o
ff th
eir
pow
er
sup
ply
.T
he
15-
me
ter
tsun
ami f
loo
de
d th
e d
iese
l bac
k u
p g
en
era
tors
loca
ted
in th
e
bas
em
en
ts o
f th
e p
lan
ts.
Wit
ho
ut c
oo
lin
g s
yste
ms,
all
thre
e c
ore
s (r
eac
tor
box
es)
me
lte
d w
ith
in 3
d
ays.
Th
e d
ang
er
was
the
re
acto
r b
oxe
s b
ein
g c
rack
ed
fro
m th
e e
arth
qua
ke a
nd
ra
dio
activ
e m
ate
rial
leak
ing
out
an
d in
to g
roun
d w
ate
r.
Nuc
lear
pow
er
pla
nt f
uel i
s n
ot e
xplo
sive
.
Nuc
lear
pow
er
pla
nt f
uel i
s n
ot e
xplo
sive
.
Nuc
lear
pow
er
pla
nt f
uel i
s n
ot e
xplo
sive
.
Th
e th
reat
fro
m th
e fu
el i
s le
akin
g a
nd
en
teri
ng
the
gro
und
.
Th
ere
we
re 2
-3 e
xplo
sio
ns
at th
e F
ukus
him
a re
acto
rs o
ver
the
we
ek
aft
er
the
e
arth
qua
ke. T
hey
we
re d
ue to
op
era
tors
de
spe
rate
ly tr
yin
g to
co
ol t
he
re
acto
r d
own
. Due
to th
e in
san
e h
eat
(50
72°F
), p
ress
ure
was
bui
ldin
g in
all
the
pip
e w
ork
an
d to
avo
id a
wo
rse
dis
aste
r, th
ey le
t th
e p
ipe
s ve
nt.
Th
is r
ele
ase
d h
ydro
ge
n g
as
wh
ich
is fl
amm
able
wh
ich
pro
cee
de
d to
ign
ite.
100,
000
pe
op
le w
ere
eva
cuat
ed
fro
m th
eir
ho
me
s as
a p
reca
utio
n.
Th
ere
hav
e b
ee
n n
o d
eat
hs
or
case
s o
f rad
iati
on
sic
kn
ess
fro
m th
e
acci
de
nt.
Th
e F
ukus
him
a A
ccid
en
t was
a w
ake
up
cal
l to
the
nuc
lear
ind
ustr
y w
orl
d w
ide.
(an
d a
ho
rrif
yin
g e
mb
arra
ssm
en
t to
sci
en
tist
s.)
Th
e r
eac
tors
had
be
en
bui
lt to
wit
hsta
nd
tsun
amis
of 5
.7 m
ete
rs o
r le
ss b
ase
d o
ff a
tsun
ami i
n C
hil
e in
196
0. (
Jap
an w
as 1
5m)
Th
e
reac
tors
we
re a
lso
de
cad
es
out
of d
ate.
Foll
owin
g F
ukus
him
a, n
ucle
ar p
owe
r p
lan
ts a
ll o
ver
the
wo
rld
we
re s
hut
dow
n to
co
nd
uct m
ain
ten
ance
.
Nuc
lear
pow
er
pla
nts
are
bui
lt to
wit
hst
and
eve
ry p
oss
ible
dis
aste
r. B
ut m
ain
ten
ance
is
exp
en
sive
an
d c
an s
lip
be
twe
en
the
cra
cks.
Th
e U
.S. g
ove
rnm
en
t has
ve
ry s
tric
t re
gul
atio
ns
abo
ut m
ain
ten
ance
of b
oth
g
ove
rnm
en
t an
d in
dus
try
own
ed
pla
nts
. Tw
ice
a y
ear
, eve
ry r
eac
tor
is s
hut
dow
n a
nd
is
tho
roug
hly
insp
ect
ed
an
d m
ain
ten
ance
do
ne.
(T
his
ge
ne
rally
take
s 4-
8 w
ee
ks
pe
r re
acto
r.)
Man
y re
acto
rs a
re a
lso
bui
lt in
a w
ay th
at e
ven
if th
e p
owe
r fa
ils,
the
co
oli
ng
sys
tem
s co
nti
nue
to fu
nct
ion
we
ll e
no
ugh
to p
reve
nt m
elt
dow
ns.
In fu
sion
, tw
o s
mal
l nuc
lei c
om
bin
e to
form
a la
rge
r nu
cle
us.
Mas
s is
lost
, an
d a
tre
me
nd
ous
am
oun
t of e
ne
rgy
is r
ele
ase
d (
eve
n
mo
re th
an fr
om
fiss
ion
.)
A fu
sio
n r
eac
tio
n r
eq
uire
s 10
0 m
illi
on
°C
to o
verc
om
e th
e r
ep
ulsi
on
of
the
two
nuc
lei a
nd
cau
se th
em
to u
nd
erg
o fu
sio
n.
Fusi
on
re
acti
on
s o
ccur
co
nti
nuo
usly
on
the
Sun
an
d o
the
r st
ars,
p
rovi
din
g u
s w
ith
he
at a
nd
lig
ht.
If w
e c
oul
d a
chie
ve fu
sio
n r
eac
tors
, it w
oul
d b
e e
sse
nti
ally
cle
an e
ne
rgy.
H
owev
er
the
tem
pe
ratu
re to
ach
ieve
is d
aun
tin
g.
Re
sear
ch g
roup
s ar
oun
d th
e w
orl
d a
re a
tte
mp
tin
g to
dev
elo
p th
e te
chn
olo
gy
ne
ed
ed
wit
hin
our
life
tim
e.
5.1
–N
atur
al R
adio
acti
vity
5.2
–N
ucle
ar R
eac
tio
ns
5.3
–R
adia
tio
n M
eas
ure
me
nt
5.4
–H
alf-
Life
of a
Rad
iois
oto
pe
5.5
–M
ed
ical
Ap
pli
cati
on
s us
ing
Rad
ioac
tivi
ty
5.6
–N
ucle
ar F
issi
on
an
d F
usio
n
Recommended