TWO MAIN TYPES OF DATA:
WAVEFORM AND RADIONUCLIDE
Three of the technologies employed by
the IMS - seismology, hydroacoustics and
infrasound – are called waveform. Waveform
stations monitor and record the movement
of energy that is generated by certain events
and propagates as seismic waves or acoustic
waves through the Earth, the oceans or the
atmosphere. As of 16 May 2011, almost 80
percent of these stations were operational
and sending data to the IDC. Waveform
data can help identify the location of an
event and determine whether it was natural
or manmade. Natural phenomena include
earthquakes, submarine volcanic eruptions,
meteorites, explosive volcanoes and storms,
while manmade events can include mining
and chemical explosions, aircraft, re-entering
space debris, oil exploration, and military
exercises.
The fourth technology employed by the
IMS is radionuclide monitoring, which can
confirm whether an event detected and located
by the other technologies is indicative of a
nuclear test. Radionuclide stations measure the
abundance of radionuclides in the air. These
include radioactive particles and noble gases
such as xenon. As of 16 May 2011, 75 percent
of the radionuclide stations were operational.
Each radionuclide monitoring station sends
a preliminary gamma ray spectrum to the
IDC every two hours. The final spectrum
which undergoes analysis at the IDC is a
two-dimensional plot showing the type and
number of radionuclides observed in a sample
obtained from a filter that has been exposed to
air for about 24 hours.
DATA PRODUCTS FOR
MEMBER STATES
A number of products containing
information about events recorded by
IMS facilities are made available to CTBTO
Member States in the form of automatically
generated lists of all the events that have
been detected followed by more refined lists
that have undergone meticulous analysis.
1. S T ANDARD EVENT LISTS AND
AUTOMATIC RADIONUCLIDE REPORTS
The first data processing occurs as soon as
waveform data arrive at the IDC, resulting in
the production of Standard Event Lists (SELs).
These lists are generated automatically every
20 minutes throughout the year by specially
designed computer programmes. SELs include
location estimates for events formed from
signals recorded at IMS waveform stations.
Improvements to the initial bulletin
are made as more data arrive in Vienna and
are processed. The IDC issues three SELs at
different time intervals in order to provide
progressively improved location estimates.
The first list – SEL1 – is issued within two
hours of ‘real time’, followed by SEL2 after
about four hours and SEL3 after six hours.
The initial processing of radionuclide
data is also automatic and the results are listed
in the Automatic Radionuclide Report. After
automatic analysis, the results are refined by
IDC analysts during interactive review.
2. R EVIEWED EVENT BULLETIN AND REVIEWED
RADIONUCLIDE REPORT
In order to provide reliable and
comprehensive information to Member
States, every single event listed in SEL3
is reviewed by IDC analysts. During this
process, analysts discard just over one-third
of the automatically produced events. The
confirmed and corrected events and signal
measurements at each station that detected
an event are listed in the Reviewed Event
Bulletin (REB). The REB is produced daily and
contains an average of 160 events.
Radionuclide data take much longer to
be collected and analyzed so data analysis
takes place on a different timescale. After
reviewing the Automatic Radionuclide
Report, analysts produce the Reviewed
Radionuclide Report.
3. S T ANDARD SCREENED EVENT BULLETIN
The next bulletin is the result of an automatic
screening process in which natural events
such as earthquakes are discarded and
manmade events remain. The Standard
Screened Event Bulletin thus contains
all events that are considered potentially
suspicious in the CTBT verification context.
The findings of the screening
process for radionuclide data are
presented in the Standard Screened
Radionuclide Event Bulletin.
ANALYZING DATA AT THE INTERNATIONAL DATA CENTRE
SOME OF THE KEY
RADIONUCLIDES
BARIUM-140 (Ba-140)
has a half-life of 12.8 days. The
half-life is the time for half of the
radionuclide's material to decay. Ba-
140 decays into lanthanum-140 (La-
140), which has a half life of 1.7 days.
By analyzing the activity ratio of
these two radionuclides, the time of a
nuclear explosion can be established.
CAESIUM-134 (Cs-134)
has a half-life of 2.1 years. Only a
small amount of Cs-134 is produced by
nuclear weapon testing but it
accumulates in nuclear reactors. It can
therefore be used to distinguish
between releases from nuclear weapon
testing and nuclear power plants.
CAESIUM-137 (Cs-137):
has a half-life of 30.1 years. This is the
most common radioactive form of
caesium and is produced by nuclear
fission. Cs-137 is one of the major
radionuclides in spent nuclear fuel and
radioactive wastes associated with the
operation of nuclear reactors and fuel
reprocessing plants. Large amounts of
Cs-137 and other radioactive isotopes
were released into the environment by
atmospheric nuclear weapon tests
between 1945 and 1980. Cs-137 did not
occur in nature before nuclear weapon
testing began.
IODINE-131 (I-131):
has a half-life of 8.0 days. I-131 is a
radioactive isotope released into the
environment mostly in gaseous form
as a result of the atmospheric testing
of nuclear weapons and accidents
that have occurred at nuclear power
plants (e.g. the Chernobyl nuclear
power plant in 1986 and the
Fukushima power plant in March
2011). It was a significant contributor
to the effects on human health from
atmospheric nuclear weapon testing
and from the Chernobyl disaster.
TELLURIUM-132 (Te-132):
has a half life of 76 hours. It is
produced by nuclear fission and is
released in gaseous form in hot
conditions after a nuclear power plant
accident or nuclear test. It decays to
iodine-132 (I-132), which has a half-
life of 2.3 hours. I-132 contributes
significantly to the effects on human
health during the first few days after
the nuclear reaction has stopped.
XENON-133 (Xe-133):
has a half-life of 5.2 days. It does not
occur in nature but is released from
nuclear power plants and nuclear
weapon testing. As a noble gas,
xenon-133 does not react with other
materials and only poses a very small
risk to human health when released
into the atmosphere.
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CTBTO SPECTRUM 16 | MAY 2011