FAS Note: The "Sigma categories" are subsets of nuclear weapons information classified under the Atomic Energy Act that are grouped by subject matter. The only Sigma categories that are currently in effect are Sigma 14, Sigma 15, Sigma 18, and Sigma 20. Sigma categories 1-13 are no longer in use.
SIGMA CATEGORY DEFINITIONS
Sigma categories: Restricted Data and/or Formerly Restricted Data in the following categories which concern the design, manufacture, or utilization of atomic weapons, or utilization of atomic weapons or nuclear explosive devices.
SIGMA DEFINITION Sigma 1 Theory of operation (hydrodynamic and nuclear) or complete design of thermonuclear weapons or their unique components.
Sigma 2 Theory of operation or complete design of fission weapons or their unique components. This includes the high explosive system with its detonators and firing unit, pit system, and nuclear initiation system as they pertain to weapon design and theory.
Sigma 3 Manufacturing and utilization information not comprehensively revealing the theory of operation or design of the physics package. Complete design and operation of nonnuclear components but only information as prescribed below for nuclear components. Utilization information necessary to support the stockpile to target sequence. Information includes:
(a) General external weapon configuration, including size, weight, and shape.
(b) Environmental behavior, fuzing, ballistics, yields, and effects.
(c) Nuclear components or subassemblies which do not reveal theory of operation or significant design features.
(d) Production and manufacturing techniques relating to nuclear components or subassemblies.
(e) Anticipated and actual strike operations.
Sigma 4 Information inherent in preshot and postshot activities necessary in the testing of atomic weapons or devices. Specifically excluded are the theory of operation and the design of such items. Information includes:
(a) Logistics, administration, other agency participation.
(b) Special construction and equipment.
(c) Effects, safety.
Production rate and/or stockpile quantities of nuclear weapons and their components.
Purpose of tests, general nature of nuclear explosive tested including expected or actual yields and conclusions derived from tests not to include design features.
Category of sensitive information concerning the design and function of nuclear weapon transportation and nuclear weapon facility physical security design that significantly enhances an adversary's ability to obtain an unauthorized nuclear detonation from a nuclear weapon or device. This includes physical security design information for all facilities, in which nuclear explosive operations are performed.
The category of sensitive information concerning physical security operations and tactics used for the protection of nuclear weapons during transportation and nuclear explosive operations that significantly enhances an adversary's ability to obtain an unauthorized nuclear detonation from a nuclear weapon or device.
Sigma 9 General studies not directly related to the design or performance of specific weapons or weapon systems, e.g., reliability studies, fuzing studies, damage studies, aerodynamic studies, etc.
Sigma 10 Chemistry, metallurgy, and processing of materials peculiar to the field of atomic weapons or nuclear explosive devices.
Sigma 11 Information concerning inertial confinement fusion which reveals or is indicative of weapons data.
Sigma 11 Subcategories Eight (8) additional subcategories of Sigma 11 not included in this list are Secret Restricted Data and refer to laser fusion.
Complete theory of operation, complete design, or partial design information revealing either sensitive design features or how the energy conversion takes place for the nuclear energy converter, energy director or other nuclear directed energy weapon systems or components outside the envelope of the nuclear source but within the envelope of the nuclear directed energy weapon.
Sigma 13 Manufacturing and utilization information and output characteristics for nuclear energy converters, directors or other nuclear directed energy weapon systems or components outside the envelope of the nuclear source, not comprehensively revealing the theory of operation, sensitive design features of the nuclear directed energy weapon or how the energy conversion takes place. Information includes:
(a) General, external weapon configuration and weapon environmental behavior characteristics, yields, and effects.
(b) Component or subassembly design that does not reveal theory of operation or sensitive design features of nuclear directed energy weapon systems categorized as Sigmas 1, 2, or 12.
(c) Production and manufacturing techniques for components or subassemblies of nuclear directed energy weapons that do not reveal information categorized as Sigmas 1, 2, or 12.
Sigma 14 Category of sensitive information, including bypass scenarios, concerning the vulnerability of nuclear weapons to a deliberate, unauthorized nuclear detonation or to the denial of authorized use.
Sigma 15 Category of sensitive information concerning the design and function of nuclear weapon use control systems, features, and components. This includes use control for passive and active systems and may include security verification features or weapon design features not specifically part of a use control system.
Sigma 18 Category of NWD including information that allows or significantly facilitates a nation or entity to fabricate a credible nuclear weapon or nuclear explosive device based on a proven, certified, or endorsed U.S. nuclear weapon or device. This information would enable the establishment or improvement of nuclear capability without nuclear testing or with minimal research and development. DOE determines the information placed in the Sigma 18 category, which includes: complete design of a gun-assembled weapon; complete design of a primary or single stage implosion-assembled weapon; complete design of a secondary stage; weapon design codes with one-dimensional hydrodynamics and radiation transport with fission and/or thermonuclear burn; and weapon design codes with two- and three-dimensional capabilities. Sigma 20
Specific category of NWD that pertains to "crude, simple, or innovative" improvised nuclear device (IND) designs, concepts, and related manufacturing or processing pathways. Not all INDs fall within the Sigma 20 category.