253Chronometry
the U chronometers that give a consistent, smaller age. It is perhaps possible that the
A
m
w
as
c
ompletely
r
emoved,
b
ut
at
a
n
e
arlier
t
ime
t
han
w
as
t
he
U
.
H
owever,
w
e
h
ave
o
bserved
t
race
a
mounts
o
f
243
Am in Pu samples, and
243
Am is not a product of
t
he
r
adioactive
d
ecay
o
f
m
ixed
P
u
i
sotopes,
c
ooled
f
or
at
l
east
1
d
ay
a
fter
d
ischarge
f
rom
a
r
eactor
b
efore
b
eing
s
eparated.
T
he
e
mpirical
243
Am can be present only if it
w
as
r
esidual
f
rom
t
he
o
riginal
r
eactor
f
uel.
T
herefore,
t
he
A
m
w
as
n
ever
c
ompletely
i
solated
f
rom
P
u
i
n
t
he
P
UREX
p
rocess.
P
UREX
i
s
m
uch
m
ore
e
ffective
at
r
emov-
ing
ssion
p
roducts,
a
nd
w
e
h
ave
p
erformed
g
ood
c
hronometric
me
asurements
o
f
137
Cs/
240
Pu and
125
Sb/
240
Pu ratios in several samples.
The
r
elationship
o
f
c
h