Glossary

Acquisition Path Analysis – A structured method used to analyse the plausible paths by which, from a technical point of view, nuclear material suitable for use in a nuclear weapon or other nuclear explosive device could be acquired.

Annex II States – The 44 countries that participated in the negotiations of the CTBT from 1994-1996 and that possessed nuclear power reactors or research reactors at that time. All of these countries must sign and ratify the CTBT before it can enter into force.

Atoms for Peace – A U.S. programme announced by President Dwight D. Eisenhower at the United Nations on 8 December 1953 to share nuclear materials and technology for peaceful purposes with other countries. This programme required countries receiving nuclear materials to agree to inspections of the transferred technology to ensure it was not used for military purposes. The programme was formally established in 1954, following the pa ssage of the Atomic Energy Act, and ended abruptly in 1974 following India’s first nuclear test.

Australia Group – An informal forum of countries which, through the harmonisation of export controls, seeks to ensure that exports do not contribute to the development of chemical or biological weapons.

Ballistic Missile – A delivery vehicle powered by a liquid or solid-fuelled rocket that primarily travels in a ballistic (free-fall) trajectory. The flight of a ballistic missile includes three phases: (1) boost phase, where the rocket generates thrust to launch the missile into flight; (2) midcourse phase, where the missile coasts in an arc under the influence of gravity; and (3) terminal phase, in which the missile descends towards its target. Ballistic missiles are primarily intended for use against ground targets.

Baruch Plan – A 1946 U.S. initiative to: (1) implement control of nuclear power to the extent necessary to ensure its use only for peaceful purposes; (2) eliminate from national armaments nuclear weapons and all other major weapons adaptable to mass destruction; (3) establish effective safeguards by way of inspection and other means to protect complying States against the hazards of violations and evasions. After Bernard Baruch proposed the plan in 1946 at the United Nations, the United States and the Soviet Union held negotiations on the programme but never reached agreement.

Chain Reaction – A process in which neutrons are absorbed by fissionable material and the neutrons released as a result of fission go on to cause more fissions. A self-sustaining chain reaction is one where the number of neutrons released from fission in one period of time (or generation) is enough to cause the same number of fissions in the following generation, taking into account that some neutrons will be absorbed by non-fissionable material or escape the region of fissionable material. A chain reaction can be thought of a run-away series of fissions. Nuclear reactors, as well as nuclear weapons, utilize chain reactions.

Comprehensive Nuclear-Test-Ban Treaty (CTBT) – This international Treaty prohibits all nuclear explosions on Earth.

Comprehensive Nuclear-Test-Ban Treaty Organization (Preparatory Commission and Provisional Technical Secretariat) – An organization established pursuant to the CTBT to help implement the treaty and monitor States parties’ compliance. Pending the CTBT’s entry into force, Provisional Technical Secretariat (PTS) assists the CTBTO Preparatory Commission in the establishment of a global verification regime to monitor compliance with the comprehensive ban on explosive nuclear testing.

Conference (Committee) on Disarmament (CD) – Known as the world’s single multilateral disarmament negotiating body, the CD is an international negotiating forum based in Geneva. Although it reports to the UN General Assembly and has a relationship with the United Nations, it adopts its own rules of procedure and agenda, giving it some degree of independence. The CD has a permanent agenda devoted to the negotiation of disarmament issues. The CD and its predecessors have negotiated major non-proliferation and disarmament agreements such as the NPT, the Biological and Toxin Weapons Convention, the Chemical Weapons Convention, and the CTBT. Since 1996, the CD has not been able to begin negotiations on any new instrument.  During this time, deliberations at the CD have focused on a proposed treaty banning the production of fissile material for nuclear weapons or other nuclear explosive devices (FMCT); the prevention of an arms race in outer space; and negative security assurances.

Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency – Adopted in 1986, it sets out an international framework for cooperation among States parties and with the IAEA to facilitate prompt assistance and support in the event of nuclear accidents or radiological emergencies. It requires States to notify the IAEA of their available experts, equipment and materials for providing assistance. In case of a request, each State party decides whether it can render the requested assistance as well as its scope and terms.

Convention on Early Notification of a Nuclear Accident – In force since 27 October 1986, it establishes a notification system for nuclear accidents from which a release of radioactive material occurs or is likely to occur and which has resulted or may result in an international transboundary release that could be of radiological safety significance for another State. It requires States to report the accident’s time, location, nature and other data essential for assessing the situation. Notification is to be made to affected States directly or through the IAEA, and to the IAEA itself.

Convention on the Physical Protection of Nuclear Material (CPPNM) – In force since 8 February 1987, it obliges parties to ensure that during international transport across their territory, or on ships or aircraft under their jurisdiction, civil nuclear materials are protected according to agreed standards. The convention also provides a framework for international cooperation on the protection, recovery and return of stolen nuclear material, and on the application of criminal sanctions against persons who commit crimes involving nuclear material. The Amendment to the CPPNM extended the convention’s scope to also cover the physical protection of nuclear material in domestic use, in storage, and during transport, and of nuclear facilities used for peaceful purposes, and provided for additional cooperation between states.

Cruise Missile – An unmanned, self-propelled, guided vehicle that sustains flight through aerodynamic lift for most of its flight path. There are subsonic and supersonic cruise missiles currently deployed in conventional and nuclear arsenals, while conventional hypersonic cruise missiles are currently in development. These can be launched from the air, submarines or the ground. Although they carry smaller payloads, travel at slower speeds, and cover lesser ranges than ballistic missiles, cruise missiles can be programmed to travel along customized flight paths and to evade missile defence systems.

Diversion of Nuclear Material – (1) The undeclared removal of declared nuclear material from a safeguarded facility; or the use of a safeguarded facility for the introduction, production or processing of undeclared nuclear material (INFCIRC/153-type agreements); (2) The use of the nuclear material specified and placed under safeguards in such a way as to further any military purpose (INFCIRC/66-type agreements).

Environmental Sampling – In the context of IAEA safeguards, the collection of samples from the environment with a view to analysing them for traces of materials that can reveal information about nuclear material handled or activities conducted.

Euratom (or the European Atomic Energy Community) – An international organization established by one of the Treaties of Rome in 1958 to form a common market for the development of the peaceful uses of atomic energy. In 1993 Euratom and the other two communities (European Economic Community and the European Coal and Steel Community) were subsumed under the European Union.

Export Controls – National laws or international arrangements established to restrict the sale of certain goods to certain countries, or to ensure that safeguards or end-use guarantees are applied to the export and sale of sensitive and dual-use technologies and materials.

Fissile Material Cut-Off Treaty (FMCT) – A proposed multilateral treaty to end the production of fissile material (highly enriched uranium and plutonium) for nuclear weapons.

Fissile Material – A type of fissionable material capable of sustaining a chain reaction by undergoing fission upon the absorption of low-energy (or thermal) neutrons.  Uranium-235, Plutonium-239, and Uranium-233 are the most prominently discussed fissile materials for peaceful and nuclear weapons purposes.

Fission – The splitting of the nucleus of a heavy atom into two lighter nuclei (called fission fragments). It is accompanied by the release of neutrons, gamma rays and fission fragments with large amounts of kinetic energy.  It is usually triggered by absorption of a neutron, but in some cases may be induced by protons, gamma rays or other particles.

Fissionable Material – A material whose nuclei can undergo fission, but requires the absorption of high-energy neutrons. Uranium-238 is an example of a fissionable isotope.

Fusion – Nuclear fusion is a type of nuclear reaction in which two atomic nuclei combine to form a heavier nucleus, releasing energy. For a fusion reaction to take place, the nuclei, which are positively charged, must have enough kinetic energy to overcome their electrostatic force of repulsion (also called the Coulomb Barrier). Thermonuclear fusion of deuterium and tritium will produce a helium nucleus and an energetic neutron. This is one basis of the hydrogen bomb, which employs a brief, uncontrolled thermonuclear fusion reaction. A great effort is now underway to harness thermonuclear fusion as a source of power.

Gromyko Plan – A Soviet Union’s proposal for nuclear disarmament and control of nuclear energy made in 1946. The plan included the following: (1) elaboration and conclusion of a convention to prohibit the production, storage and use of nuclear weapons and to require the destruction of all such weapons; and (2) the creation of two committees of the Atomic Energy Commission, including a committee for the exchange of scientific information and a committee for the prevention of the use of atomic energy to the detriment of mankind.

Humanitarian Initiative – A movement of states and civil society advancing an approach to nuclear disarmament that focuses on the humanitarian impact of nuclear weapons. The beginnings of the initiative and the shift in the discourse can be traced to the 2010 NPT Review Conference, the Final Document of which for the first time expressed deep concern over catastrophic humanitarian consequence of the use of nuclear weapons.

IAEA – International Atomic Energy Agency – Founded as a result of Dwight D. Eisenhower’s 1953 “Atoms for Peace” speech, the IAEA is the international centre for cooperation in the nuclear field. The IAEA works with its Member States and multiple partners worldwide to promote the safe, secure and peaceful use of nuclear technologies.

IAEA Board of Governors – The Board of Governors is one of the two policy-making bodies of the International Atomic Energy Agency (IAEA), along with the annual General Conference of IAEA Member States. The Board examines and makes recommendations to the General Conference on the IAEA’s financial statements, programme and budget. It considers applications for membership, approves safeguards agreements and the publication of the IAEA’s safety standards. It also appoints the Director General of the IAEA, with the approval of the General Conference. The Board generally meets five times per year: in March and June, twice in September (before and after the General Conference) and in November.

IAEA General Conference – The General Conference consisting of representatives of the IAEA Member States meets in a regular annual session, usually in September, to consider and approve the IAEA’s  budget and to decide on other issues raised by the Board of Governors, the Director General and Member States.

IAEA Safeguards – A set of technical measures through which the IAEA verifies that States are honouring their international legal obligations to use nuclear material and technology only for declared purposes.

IAEA Safeguards, Additional Protocol (AP) – A protocol to a safeguards agreement that provides for measures for strengthening the effectiveness and improving the efficiency of IAEA safeguards which could not be implemented under the legal authority of the existing safeguards agreement. Based on INFCIRC/540 (Corrected).

IAEA Safeguards, Broader Conclusion – For each State with a comprehensive safeguards agreement and an additional protocol in force, a broader conclusion can be drawn for the year concerned that all of the nuclear material in the State had been placed under safeguards and remained in peaceful nuclear activities or was otherwise adequately accounted for.

IAEA Safeguards, Complementary Access – Access provided by the State to IAEA inspectors in accordance with the provisions of an additional protocol.

IAEA Safeguards, Comprehensive Safeguards Agreement (CSA) – An agreement that applies safeguards on all nuclear material in all nuclear activities in a State. Also called full-scope safeguards. Based on document INFCIRC/153 (Corrected).

IAEA Safeguards, Inspections – Under an INFCIRC/153-type safeguards agreement, a set of activities carried out by IAEA inspectors at a facility or a location outside facilities to verify that the nuclear material declared and placed under safeguards remains in peaceful nuclear activities or is otherwise adequately accounted for. Three types of inspection may be performed under these agreements: ad hoc, routine and special inspections.

IAEA Safeguards, Integrated Safeguards – The optimum combination of all safeguards measures available to the IAEA under CSAs and Aps to achieve maximum effectiveness and efficiency in meeting the IAEA’s safeguards obligations within available resources.

IAEA Safeguards, Item-Specific Safeguards Agreement – An agreement based on guidelines contained in IAEA information circular INFCIRC/66/Rev. 2. The agreement defines what nuclear material, non-nuclear material (e.g. heavy water, zirconium tubes), facilities and/or equipment must be safeguarded, and prohibits the use of the specified items in such a way as to further any military purpose.

IAEA Safeguards, Safeguards by Design – A process of including the consideration of international safeguards throughout all phases of a nuclear facility project, from the initial conceptual design to facility construction and into operations, including design modifications and decommissioning.

IAEA Safeguards, Small Quantities Protocol (SQP) – A protocol to a CSA concluded between the IAEA and a State on the basis that the State has less than specified minimal quantities of nuclear material and no nuclear material in a facility. This protocol suspends, or “holds in abeyance”, the implementation of most of the detailed provisions of Part II of a comprehensive safeguards agreement until such time as the quantity of nuclear material in the State exceeds the prescribed limits or the State has nuclear material in a facility as defined in INFCIRC/153 (Corrected).

IAEA Safeguards, State-Level Approach – A safeguards approach developed for a specific State, encompassing all nuclear material, nuclear installations, activities related to the nuclear and safeguards-relevant information in that State.

IAEA Safeguards, State-Level Concept (SLC) – The process by which the IAEA takes into account State-specific characteristics and all available safeguards-related information about a State in order to create a customized approach to safeguards implementation for that State. The SLC conceptual framework is used to develop a State-level approach (SLA) in consultation with the State in question.

IAEA Safeguards, Voluntary Offer Agreement (VOA) – An agreement concluded between the IAEA and a nuclear-weapon State which, under the NPT, is not required to accept safeguards but which has voluntarily offered to do so on select materials and activities, among other things, to address concerns that the application of safeguards could lead to commercial disadvantages for the nuclear industries of non-nuclear-weapon States. Based on document INFCIRC/153 (Corrected).

Improvised Nuclear Device – A device incorporating radioactive materials designed to result in the formation of a nuclear-yield reaction. Such devices may be fabricated in a completely improvised manner or may be an improvised modification to a nuclear weapon.

INFCIRC – IAEA Information Circulars Information Circulars (INFCIRCs) are published by the IAEA to bring matters of general interest to the attention of its Member States. Commonly referenced INFCIRCs include INFCIRC/153 and INFCIRC/540.

Intermediate-Range Nuclear Forces (INF) Treaty – A treaty between the United States and the former Soviet Union, signed on 8 December 1987, which entered into force on 1 June 1988. It aimed to eliminate and ban all ground-launched ballistic and cruise missiles with a range of between 500 to 5,500 kilometres (300 and 3,400 miles). The treaty required the United States and the Soviet Union to conduct inspections at each other’s sites during the elimination of treaty-limited items. By May 1991, all intermediate-range and shorter-range missiles, launchers, related support equipment, and support structures were eliminated. For additional information, see the INF Treaty. The United States affected its withdrawal from the INF Treaty on 2 August 2019.

International Data Centre (IDC) – The CTBTO’s IDC processes and analyses the data registered at the monitoring stations and produces data bulletins that are submitted to the Member States for their evaluation and judgement.

International Monitoring System (IMS) – The CTBTO’s IMS consists of monitoring stations (seismic, hydro-acoustic, infrasound and radionuclide) and radionuclide laboratories built worldwide.

International Physical Protection Advisory Service (IPPAS) – Created by the IAEA in 1995, it provides peer advice on implementing international instruments and IAEA guidance on the protection of nuclear and other radioactive material, associated facilities and associated activities.

Isotope – Isotopes are variants of a particular chemical element, such as uranium or plutonium, which differ in neutron number, and consequently in mass number (e.g., ²³⁸Pu and ²³⁹Pu).

JCPOA – Joint Comprehensive Plan of Action – The  JCPOA is an agreement between Iran and the E3/EU+3 (China, France, Germany, Russia, the United Kingdom and the United States) that establishes a range of limitations on Iran’s nuclear programme along with extensive monitoring and verification measures in return for sanctions relief and economic cooperation. It was concluded in July 2015 and endorsed by UN Security Council Resolution 2231 (2015).

Missile Technology Control Regime – An informal and voluntary association of countries which share the goals of non-proliferation of unmanned delivery systems capable of delivering weapons of mass destruction, and which seek to coordinate national export licensing efforts aimed at preventing their proliferation. Established in 1987.

Mixed Oxide (MOX) – A mixture of the oxides of uranium and plutonium used as reactor fuel for the recycling of plutonium in thermal nuclear reactors (‘thermal recycling’) and for fast reactors.

Negative Security Assurances – A type of pledge by a nuclear-weapon State that it will not use nuclear weapons against a non-nuclear-weapon State.

New Agenda Coalition (NAC) – In June 1998, the foreign ministers of Brazil, Egypt, Ireland, Mexico, New Zealand, Slovenia, South Africa and Sweden issued a statement calling for a new nuclear disarmament agenda. Slovenia withdrew from NAC shortly after its creation, while Sweden left the group in early 2014. The NAC called for the five nuclear-weapon States and the then-three nuclear-armed States to make an unequivocal commitment to eliminate their nuclear arsenals and to begin negotiations on practical steps to accomplish this goal.

New Strategic Arms Reduction Treaty (New START) – A treaty between the United States and Russia on further limitations and reductions of strategic offensive weapons, signed on 8 April 2010, which entered into force on 5 February 2011. Under the New START provisions, the two sides have to reduce the number of deployed strategic warheads and the number of deployed strategic delivery vehicles within seven years of the treaty’s entry into force. The Treaty’s verification measures are based on the earlier verification system created under START I. New START supersedes the Moscow Treaty, and its duration is 10 years, with an option of extension for up to five years. US and Russian Presidents may decide to extend New START by a simple exchange of letters, without legislative approval. If it is not extended, New START will expire on 5 February 2021.

Non-Aligned Movement (NAM) – Formed in the 1960s during the Cold War, NAM is a group of States that did not formally align themselves with either the United States or the Soviet Union and sought to remain independent or neutral. NAM identifies the right of independent judgment, the struggle against imperialism and neo-colonialism and the use of moderation in relations with all big powers as the three basic elements that have influenced its approach. NAM is the largest grouping of states in the NPT.

Non-Nuclear-Weapon State (NNWS) – Under the NPT, NNWSs are States that had not detonated a nuclear device prior to 1 January 1967 and who agree in joining the NPT to refrain from pursuing nuclear weapons. NNWSs include all States Parties to the NPT other than China, France, the Soviet Union/Russia, the United Kingdom and the United States.

Non-Proliferation and Disarmament Initiative (NPDI) – NPDI is a ministerial-level group of States within the framework of the NPT, formed in September 2010 with a view to focussing on practical steps to forward the consensus outcomes of the 2010 NPT Review Conference. Initiated by Japan and Australia, as of 2019 the group includes Australia, Canada, Chile, Germany, Japan, Mexico, the Netherlands, Nigeria, the Philippines, Poland, Turkey and the United Arab Emirates.

NPT – Treaty on the Non-Proliferation of Nuclear Weapons – Open for signature in 1968 and in force as of 1970, the NPT is the second most widely adhered-to international security agreement (191 States parties as of 2019). The three pillars of the NPT are nuclear disarmament, non-proliferation and peaceful uses of nuclear energy. The Treaty stipulates that non-nuclear-weapon States will not seek to acquire nuclear weapons and will accept International Atomic Energy Agency safeguards on their nuclear activities, while nuclear-weapon States commit not to transfer nuclear weapons to “any recipient whatsoever”. All States parties to the NPT also commit to pursue good-faith negotiations on the cessation of nuclear arms race, nuclear disarmament and general and complete disarmament.

Nuclear Forensics – The examination of nuclear and other radioactive materials using analytical techniques to determine the origin and history of this material in the context of law enforcement investigations or the assessment of nuclear security vulnerabilities.

Nuclear Fuel Cycle – A term for the full spectrum of processes associated with utilizing nuclear fission reactions for peaceful or military purposes. The “front-end” of the uranium-plutonium nuclear fuel cycle includes mining uranium, milling to a powder form (also called yellowcake uranium), conversion into gas form, enrichment to increase the ratio of the 235 isotope, conversion back to solid form and fabrication into fuel. The fuel is used in a nuclear reactor to produce neutrons that can, for example, produce thermal reactions to generate electricity or propulsion. The “back-end” of the nuclear fuel cycle refers to the temporary storage of spent fuel in pools of water after irradiation in a reactor, possible reprocessing of the spent fuel, and ultimately long-term storage.

Nuclear Reactors, Common Components:

• Core – The central part of a nuclear reactor where nuclear fission occurs. It contains the fuel, control rods, moderator, coolant and support structures.
• Control Rods – Technology in a nuclear reactor that controls the state of fission reactions in real time, both in order to keep the reaction going and to prevent it from accelerating out of control. Control rods are often made of boron.
• Moderator – A material that encases fuel in rods nuclear reactors that is in place to slow down chain reactions. Graphite is a common moderator.
• Coolant – The heat released by fission in nuclear reactors must be captured and transferred to generate electricity. Coolants remove heat from the core and carry it to electrical generators. Coolants also serve to maintain manageable pressures within the core.
• Containment vessel – surrounds the reactor core like a shield, absorbing neutrons and ionising radiation, and can be as thick as 5.5 meters.

Nuclear-Related Dual-Use Item – An item which has a technical use in both civilian and military applications and is subject to certain conditions of supply because such items could make a major contribution to a nuclear explosive activity. A list of dual-use items is incorporated in the Nuclear Suppliers Group Guidelines and published in INFCIRC/254, Part 2.

Nuclear Security – The prevention and detection of, and response to, theft, sabotage, unauthorized access, illegal transfer or other malicious acts involving nuclear material, other radioactive substances or their associated facilities.

Nuclear Security Culture – The assembly of characteristics, attitudes and behaviour of individuals, organizations and institutions which serves as a means to support and enhance nuclear security.

Nuclear Security Summits – A high-level initiative started by US President Barack Obama to consolidate and enhance efforts to reduce the risk of nuclear and radiological terrorism by strengthening national laws, bolstering international cooperation and minimizing weapons-usable materials. The process brought together more than 50 world leaders at four summits—Washington, D.C. (2010), Seoul (2012), The Hague (2014), and Washington D.C. (2016).

Nuclear Suppliers Group – A group of nuclear supplier countries that seeks to contribute to the non-proliferation of nuclear weapons through the implementation of two sets of Guidelines for nuclear exports and nuclear-related exports. Established in 1975.

Nuclear Weapon Design Basics: gun-type and implosion-type

In a gun-type device, two or more pieces of fissionable material, each smaller than a critical mass, are brought together very rapidly so as to form a supercritical mass which can explode as the result of a rapidly expanding fission chain reaction.

In an implosion-type device, a subcritical mass of fissile material (typically plutonium) is compressed by a chemical high explosive into a denser critical mass.

Nuclear Weapon, Thermonuclear Device – A nuclear weapon in which the fusion of light nuclei, such as deuterium and tritium, leads to a significantly higher explosive yield than in a regular fission weapon. Thermonuclear weapons are sometimes referred to as staged weapons, because the initial fission reaction (the first stage) creates the condition under which the thermonuclear reaction can occur (the second stage). Also archaically referred to as a hydrogen bomb.

Nuclear-Weapon State (NWS) – As defined by Article IX, paragraph 3 of the NPT, a nuclear-weapon State is a State that had detonated a nuclear device prior to 1 January 1967. Five States fit this definition: China, France, the Soviet Union (succeeded by Russia), the United Kingdom and the United States. Coincidentally, these five States are also permanent members of the UN Security Council, though this is related to their victory in World War II. States that acquired and/or tested nuclear weapons subsequently are not legally recognized as nuclear-weapon States.

NPT Review Conference (RevCon) – The NPT provides for conferences of States parties to review treaty implementation at five-year intervals. At the 1995 Review and Extension Conference, States parties decided to “strengthen” the review process and to convene 10-day Preparatory Committee (PrepCom) meetings in each of the three years preceding a Review Conference.

Nuclear-Weapon-Free Zone (NWFZ) – A zone created through a legally binding treaty among a group of States that establishes complete absence of nuclear weapons within the identified geographical area. NWFZ treaties typically prohibit the acquisition, possession, transfer, deployment and testing of nuclear weapons by the States parties or anywhere within the zone. All zonal agreements also require their States parties to accept safeguards on their nuclear activities.

On-Site Inspection – Inspectors collect information directly at an alleged (or suspected) site of an explosion. This might help to confirm whether or not a nuclear explosion has been carried out in violation of the Treaty. Part of the Verification Regime of the CTBT, on-site inspections constitute the final verification measure of the CTBT.

Outer Space Treaty – The Treaty on Principles Governing the Activities of States in the Exploration and use of Outer Space, Including the Moon and other Celestial Bodies prohibits the placement of weapons of mass destruction in orbit around the earth, on the moon or any other celestial body, or otherwise in outer space. It does not otherwise prohibit the conventional weaponisation of outer space.  It was opened for signature on 27 January 1967 and entered into force on 10 October 1967.

Plutonium – A transuranic element with atomic number 94, produced when uranium is irradiated in a reactor. It is used primarily in nuclear weapons and, along with uranium, in mixed-oxide (MOX) fuel. The fissile isotope ²³⁹Pu, is the most suitable isotope for use in nuclear weapons. Plutonium that is concentrated in 93 percent or more in ²³⁹Pu is considered to be weapon-grade, while the reactor-grade plutonium has a lower concentration, roughly 76 percent or less. Both weapon-grade and reactor-grade plutonium can be used for the production of nuclear weapons.

Proliferation Security Initiative (PSI) – A U.S.-led effort to prevent the proliferation of WMD, their delivery systems, and related materials through the use of information sharing and coordination of diplomatic and military efforts. Members of the initiative share a set of 13 common principles, which guide PSI efforts.

Radiological dispersal device (RDD) – Any device that causes the purposeful dissemination of radioactive material without a nuclear detonation. A particular case is a “dirty bomb” that uses conventional explosives to disperse radioactive material.

Radiation exposure device (RED) – A device with radioactive material designed to intentionally expose members of the public to radiation. It uses partially or fully unshielded radioactive material and could be hidden from sight in a public place (e.g., under a subway seat, in a food court, or in a busy hallway), exposing those who sit or pass close by.

Radioactivity – The spontaneous emission of radiation, generally alpha or beta particles, often accompanied by gamma rays, from the nucleus of an unstable isotope. Ionizing radiation is radiation that has sufficient energy to remove electrons from substances that it passes through, forming ions. May include alpha particles, beta particles, gamma rays, x-rays, neutrons, high-speed electrons, high-speed protons, and other particles capable of producing ions. Excess exposure to ionizing radiation causes acute radiation syndrome or radiation sickness.

Significant Quantity of Nuclear Material (SQ) – The approximate amount of nuclear material for which the possibility of manufacturing a nuclear explosive device cannot be excluded (e.g., for high enriched uranium – 25 kg, for plutonium – 8 kg). Significant quantities take into account unavoidable losses due to conversion and manufacturing processes and should not be confused with critical masses.

Source Material – As defined in Article XX.3 of the IAEA Statute: Uranium containing the mixture of isotopes occurring in nature; uranium depleted in the isotope 235; thorium; any of the foregoing in the form of metal, alloy, chemical compound or concentrate; any other material containing one or more of the foregoing in such concentration as the Board of Governors shall from time to time determine; and such other material as the Board of Governors shall from time to time determine. Under comprehensive safeguards agreements, the term source material shall not be interpreted as applying to ore or ore residue.

Special Fissionable Material – As defined in Article XX.1 of the IAEA Statute: ²³⁹Pu; ²³³U; uranium enriched in the isotopes 235 or 233; any material containing one or more of the foregoing; and such other fissionable material as the Board of Governors shall from time to time determine; the term ‘special fissionable material’ does not include source material.

State System of Accounting for and Control of Nuclear Material (SSAC) – Organisational  arrangements  at  the  national  level  which  may  have  both  a  national objective to account for and control nuclear material in the State and an international objective  to  provide  the  basis  for  the  application  of  IAEA  safeguards  under  an agreement  between  the  State  and  the  IAEA.

Treaty on the Prohibition of Nuclear Weapons (TPNW) – An international treaty that includes a comprehensive set of prohibitions on participating in any nuclear weapon activities, such as to develop, test, produce, acquire, possess, stockpile, use or threaten to use nuclear weapons. The Treaty also prohibits the deployment of nuclear weapons on a State party’s territory and the provision of assistance to any State in the conduct of prohibited activities. States parties will be obliged to prevent and suppress any activity prohibited under the TPNW undertaken by persons or on territory under its jurisdiction or control.

Trigger List – A control list of the specific types of nuclear-related material, equipment, technology and software to which particular conditions of supply apply. For the the Nuclear Suppliers Group, a trigger list is published in INFCIRC/254, Part 1.

United Nations Disarmament Commission (UNDC) – UNDC was established in 1952 as a deliberative body with the purpose of examining and making recommendations on disarmament issues and following-up and evaluating decisions made within special sessions.

United Nations, First Committee of the General Assembly – Debates disarmament, non-proliferation, arms control and international security issues, recommending resolutions and decisions for adoption by the plenary session of the UN General Assembly.

United Nations, Security Council Resolution 1540 – Adopted in 2004, the Resolution prohibits States from providing any form of support to non-State actors that attempt to develop, acquire, manufacture, possess, transport, transfer or use nuclear, chemical or biological weapons or their means of delivery, in particular for terrorist purposes. The resolution requires all States to adopt and enforce appropriate laws to this effect as well as other effective measures to prevent the proliferation of WMD and their means of delivery to non-State actors.

Uranium, natural – Uranium as it occurs in nature, having an atomic weight of approximately 238 and containing minute quantities of ²³⁴U, about 0.7% ²³⁵U and 99.3% ²³⁸U.

Uranium, High Enriched (HEU) – Uranium containing 20% or more of the isotope ²³⁵U, a key ingredient for nuclear weapons manufacturing. HEU that is enriched at or above 90% in ²³⁵U is considered weapon-grade uranium.

Uranium, Low Enriched (LEU) – Enriched uranium containing less than 20% of the isotope ²³⁵U.

Wassenaar Arrangement – Established in order to contribute to regional and international security and stability, by promoting transparency and greater responsibility in transfers of conventional arms and dual-use goods and technologies, thus preventing destabilising accumulations.

Yellowcake – Concentrated powder of uranium ore, most commonly the concentrated crude oxide U₃O₈.

Zangger Committee – A group of 35 nuclear exporting states established in 1971 under the chairmanship of Claude Zangger of Switzerland. The purpose of the committee is to maintain a “trigger list” of: (1) source or special fissionable materials, and (2) equipment or materials especially designed or prepared for the processing, use or production of special fissionable materials. Additionally, the committee has identified certain dual-use technologies as requiring safeguarding when they are supplied to non-nuclear weapon states.