An International Monitoring System (IMS) is nearing completion to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty.

What is the Comprehensive Nuclear-Test-Ban Treaty?

A Comprehensive Nuclear-Test-Ban Treaty (CTBT) to ban all nuclear explosion tests was opened for signature in New York on 24 September 1996. The Treaty aims to eliminate nuclear weapons by restricting the development and qualitative improvement of new types of nuclear weapons, playing a critical role in working towards a safer and more secure world. Australia signed the Treaty on the same day and ratified it on 9 July 1998. As of June 2020, 184 countries have signed and 153 have ratified. To see the latest country to sign or ratify and to find more information on the CTBT Organization visit their website at

How can nuclear tests be detected?

The CTBT provides a comprehensive global verification regime, which includes an International Monitoring System (IMS). By analysing, integrating and comparing data from the IMS, the time, location and nature of a possible nuclear event can be determined. The network, which is located all over the world, will consist of 337 IMS monitoring facilities and 16 radionuclide laboratories that monitor the earth for evidence of nuclear explosions in all environments. The IMS is nearing completion with over 90% of stations installed, certified and operational.

These monitoring facilities use a variety of methods to detect evidence of nuclear testing. Seismic, hydroacoustic and infrasound stations are employed to monitor the underground, underwater and atmosphere environments, respectively. The fourth technology detects radiation from atmospheric sampling.

Monitoring technologies

Seismic (170 stations)

Seismic monitors detect vibrations in the earth’s crust. The principal use of the seismic data in the verification system is to locate seismic events and to distinguish between an underground nuclear explosion and the numerous earthquakes that occur around the globe.

Hydroacoustic (11 stations)

Hydroacoustic monitoring detects acoustic waves produced by natural and artificial phenomena in the oceans. The data from the hydroacoustic stations are used in the verification system to distinguish between underwater explosions and other phenomena, such as sub-sea volcanoes and earthquakes, which also propagate acoustic energy into the oceans.

Infrasound (60 stations)

The infrasound network uses microbarometers (acoustic pressure sensors) to detect very low-frequency sound waves in the atmosphere produced by natural and artificial events.  The data collected is used to distinguish between atmospheric explosions and natural phenomena such as meteorites, explosive volcanoes, meteorological events and artificial phenomena such as re-entering space debris, rocket launches and supersonic aircraft.

Radionuclide (80 stations)

The 80 radionuclide stations can detect radioactive debris from atmospheric explosions or vented by underground or underwater nuclear explosions. The presence of specific radionuclides provides unambiguous evidence of a nuclear explosion. Forty of these stations will be capable of measuring for the presence of the relevant noble gases. See below for more on how these stations work.

Radionuclide laboratories (16 stations)

The 16 Radionuclide Laboratories are used to verify samples that are suspected of containing radionuclide materials that may have been produced by a nuclear explosion.

What is ARPANSA's involvement with the Treaty?

ARPANSA is responsible for carrying out Australia's radionuclide monitoring obligations to the Comprehensive Nuclear-Test-Ban Treaty. In this capacity, ARPANSA has worked to establish the IMS systems required to monitor treaty compliance through the installation, implementation and operation of seven stations within Australia and its Territories. The CTBT team within ARPANSA has also expanded to include operational responsibility for the radionuclide stations situated in Fiji and Kiribati. 

To see further information on the CTBT technologies across the world, visit the CTBTO Facilities Map

The station operators who perform daily check and filter changes are required to undertake basic training which is supported by ARPANSA’s technical specialists. This ensures the radionuclide sites continue to operate to the highest standards through maintenance, repair and continual improvement. ARPANSA also contributes to the global network via formal channels, to assist with policy recommendations to the CTBTO in matters of regulations, developing technical standards and improving data quality within the IMS.

In addition, ARPANSA’s experts work closely with colleagues in the Australian Safeguards and Non-Proliferation Office (ASNO) to ensure that Australia’s international obligations are met through the CTBT.

What are the locations of the Australian monitoring stations?

Australia hosts all four technologies totalling 21 facilities within Australia and its territories. ARPANSA is responsible for the following radionuclide laboratory and stations. 

Radionuclide stationNoble Gas stationRadionuclide laboratory
Melbourne, VictoriaAUP04AUX04AUL02
Mawson Station, AntarcticaAUP05  
Townsville, QueenslandAUP06  
Macquarie Island, Southern OceanAUP07  
Cocos Keeling Island, Indian OceanAUP08  
Darwin, Northern TerritoryAUP09AUX09 
Perth, Western AustraliaAUP10  
Fiji, South Pacific OceanFJP26  
Kiribati, Central Pacific OceanKIP39  

Geoscience Australia is responsible for operating the other three technologies with some stations co-located with the radionuclide. 

A typical radionuclide monitoring station process

A typical radionuclide particulate monitoring station contains an air sampler, detection equipment, computers and a communication set-up. 

Roof-top high volume air sampler
The radionuclide monitoring process involves collecting particulate matter from air onto a piece of filter material on a high volume air sampler for about 24 hours.
Press used to compress the filter before analysis
After this time the filter is taken from the air sampler, compressed into a disk.
Decay chamber where natural radionuclides are allowed to decay
The disk is then placed in a chamber to allow natural radionuclides to decay for about 24 hours.
A gamma detector is used to measure radionuclides
Finally, the filter sample is placed on a gamma detector for about 24 hours to be analysed.
A computer monitors the workflow and collects data
A computer monitors the workflow and collects data.
Data is forwarded by satellite to the International Data Centre

The data relating to the sampling conditions and radionuclides measured is then forwarded by satellite to the International Data Centre in Vienna where it is compiled and released to countries participating in the Treaty.

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