|  | G |
SECTION G — PHYSICS

|  | G |
Note(s) In this section, the following term is used with the meaning indicated: "variable" (as a noun) means a feature or property (e.g., a dimension, a physical condition such as temperature, a quality such as density or colour) which, in respect of a particular entity (e.g., an object, a quantity of a substance, a beam of light) and at a particular instant, is capable of being measured; the variable may change, so that its numerical expression may assume different values at different times, in different conditions or in individual cases, but may be constant in respect of a particular entity in certain conditions or for practical purposes (e.g., the length of a bar may be regarded as constant for many purposes). Attention is drawn to the definitions of terms or expressions used, appearing in the notes of several of the classes in this section, in particular those of "measuring" in class Fulltext... Hierarchy... Expanded...G01 and "control" and "regulation" in class Fulltext... Hierarchy... Expanded...G05. Classification in this section may present more difficulty than in other sections, because the distinction between different fields of use rests to a considerable extent on differences in the intention of the user rather than on any constructional differences or differences in the manner of use, and because the subjects dealt with are often in effect systems or combinations, which have features or parts in common, rather than "things", which are readily distinguishable as a whole. For example, information (e.g., a set of figures) may be displayed for the purpose of education or advertising (Fulltext... Hierarchy... Expanded...G09), for enabling the result of a measurement to be known (Fulltext... Hierarchy... Expanded...G01), for signalling the information to a distant point or for giving information which has been signalled from a distant point (Fulltext... Hierarchy... Expanded...G08). The words used to describe the purpose depend on features that may be irrelevant to the form of the apparatus concerned, for example, such features as the desired effect on the person who sees the display, or whether the display is controlled from a remote point. Again, a device which responds to some change in a condition, e.g., in the pressure of a fluid, may be used, without modification of the device itself, to give information about the pressure (Fulltext... Hierarchy... Expanded...G01L) or about some other condition linked to the pressure (another subclass of class Fulltext... Hierarchy... Expanded...G01, e.g., Fulltext... Hierarchy... Expanded...G01K for temperature), to make a record of the pressure or of its occurrence (Fulltext... Hierarchy... Expanded...G07C), to give an alarm (Fulltext... Hierarchy... Expanded...G08B), or to control another apparatus (Fulltext... Hierarchy... Expanded...G05). The classification scheme is intended to enable things of a similar nature (as indicated above) to be classified together. It is therefore particularly necessary for the real nature of any technical subject to be decided before it can be properly classified.

NUCLEONICS

|  | G21 |
NUCLEAR PHYSICS; NUCLEAR ENGINEERING

|  | G21B |
FUSION REACTORS (uncontrolled reactors Fulltext... Hierarchy... Expanded...G21J)

|  | G21B |
Subclass index
THERMONUCLEAR FUSION REACTORS | 1/00
LOW-TEMPERATURE NUCLEAR FUSION REACTORS | 3/00

|  | G21C |
NUCLEAR REACTORS (analogue computers therefor Fulltext... Hierarchy... Expanded...G06G 7/54; fusion reactors, hybrid fission-fusion reactors Fulltext... Hierarchy... Expanded...G21B; nuclear explosives Fulltext... Hierarchy... Expanded...G21J)

|  | G21C |
Subclass index
REACTORS | 1/00
REACTOR ELEMENTS |
Fuel; moderator; cooling; containment; shielding | 3/00; 5/00; 15/00; 13/00; 11/00
Handling fuel and other materials | 19/00
CONTROL; MONITORING, TESTING | 7/00; 17/00
EMERGENCY PROTECTION | 9/00
MANUFACTURE | 21/00
ADAPTATIONS OF REACTORS FOR EXPERIMENTATION OR IRRADIATION | 23/00

|  | G21D |
NUCLEAR POWER PLANT (electric or magnetic analogue computers, e.g. simulators, for nuclear physics Fulltext... Hierarchy... Expanded...G06G 7/54)

|  | G21F |
PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR (radiation protection by pharmaceutical means Fulltext... Hierarchy... Expanded...A61K 8/00, Fulltext... Hierarchy... Expanded...A61Q 17/00; in cosmonautic vehicles Fulltext... Hierarchy... Expanded...B64G; combined with a reactor Fulltext... Hierarchy... Expanded...G21C 11/00; combined with X-ray tubes Fulltext... Hierarchy... Expanded...H01J 35/16; combined with X-ray apparatus Fulltext... Hierarchy... Expanded...H05G 1/02)

|  | G21G |
CONVERSION OF CHEMICAL ELEMENTS; RADIOACTIVE SOURCES (applications of radiation in general Fulltext... Hierarchy... Expanded...G21H 5/00; handling particles, e.g. neutrons, or electromagnetic radiation not otherwise provided for Fulltext... Hierarchy... Expanded...G21K) [2]

|  | G21H |
OBTAINING ENERGY FROM RADIOACTIVE SOURCES; APPLICATIONS OF RADIATION FROM RADIOACTIVE SOURCES; UTILISING COSMIC RADIATION (measurement of nuclear or X-radiation Fulltext... Hierarchy... Expanded...G01T; fusion reactors Fulltext... Hierarchy... Expanded...G21B; nuclear reactors Fulltext... Hierarchy... Expanded...G21C; semiconductor devices sensitive to electromagnetic or corpuscular radiation Fulltext... Hierarchy... Expanded...H01L 31/00)

|  | G21J |
NUCLEAR EXPLOSIVES; APPLICATIONS THEREOF (electric or magnetic analogue computers, e.g. simulators, for nuclear physics Fulltext... Hierarchy... Expanded...G06G 7/54)

|  | G21J |
Note(s) This subclass covers uncontrollable fission or fusion reactions.

|  | G21K |
TECHNIQUES FOR HANDLING PARTICLES OR ELECTROMAGNETIC RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA- OR X-RAY MICROSCOPES (X-ray technique Fulltext... Hierarchy... Expanded...H05G; plasma technique Fulltext... Hierarchy... Expanded...H05H) [2]