
248 Nuclear Forensic Analysis
are chronometric pairs that can be measured with great precision and are based
o
n
t
he
c
hemical
p
roperties
o
f
d
ifferent
e
lements,
i
t
i
s
a
ssumed
t
hat
t
he
s
ample
w
as
c
ompletely
p
uried
a
t
t
he
t
ime
o
f
s
eparation.
H
owever,
f
or
U
S
w
eapons-grade
P
u,
241
Am/
241
Pu often gives a signicantly larger value for the age than do the U
i
sotopes.
T
he
o
nly
r
easonable
e
xplanation
f
or
t
his
o
bservation
i
s
t
hat,
w
hen
t
he
U
i
sotopes
w
ere
r
emoved
f
rom
t
he
P
u
s
ample
f
or
t
he
l
ast
t
ime,
s
ome
A
m
w
as
l
eft
i
n
t
he
m
aterial.
T
his
m
eans
t
hat
a
t
a
ny
s
ubsequent
t
ime,
t
here
w
ill
b
e
m
ore
241
Am in
t
he
P
u
s
ample
t
han
c
an
b
e
e
xplained
b
y
i