11Introduction
events during 2006 and 2009 were perhaps consistent with explosive yields of ≤1 kt
a
nd
1
–10
k
t,
r
espectively.
A
nother
ca
ndidate
l
ow-yield
u
nderground
t
est
i
n
2
010
p
ro-
vided
n
o
s
eismic
s
ignal,
b
ut
d
id
r
elease
s
uggestive
r
adioactive
X
e.
T
he
i
sotopic
r
atios
o
f
t
he
X
e
[
6]
w
ere
u
nusual,
t
hough,
p
erhaps
i
ndicative
o
f
a
m
ixed
s
ource-term,
a
nd
t
he
p
ossibility
o
f
r
eprocessing
a
ctivities
c
ould
n
ot
b
e
d
ismissed
b
y
s
ome
a
nalysts.
However, a recent publication [7] attributes the measurement discrepancies to under-
ground
f
ractionation
d
uring
me
lt
c
ooling
(
see
S
ection
5
.4.2).
A
2
013
t
est
i
nduced
a
s
eismic
e
vent
o
f
m
agnitude
5
.1,
c
onsistent
w
ith
a
n
u
nderground
n
uclear
e
xplosion
o
f
s
everal
k
t.
T
able
1
.2
l
ists
i
nitial
w
eapons
t
ests
a
nd
S
NM
p