Neutron Health Dictionary

This is a form of a chemical element with the same chemical properties as other forms, but which has a di?erent atomic mass. It contains an identical number of positively charged particles called protons, in the nucleus, giving it the same atomic number, but the numbers of neutrons di?er. A radioactive isotope, or radionuclide, is one that decays into other isotopes, and in doing so emits alpha, beta or gamma radiation.

Applications of radionuclides to diagnosis The use of radionuclides in diagnosis is based on the fact that it is possible to tag many of the substances normally present in the body with a radioactive label. Certain synthetic radioactive elements, such as technetium, can also be used. Because it is possible to detect minute quantities of radioactive material, only very small doses are needed, making the procedure a safe one. Furthermore the body pool of the material is therefore not appreciably altered, and metabolism is not disturbed. Thus in studies of iodine metabolism the ratio of radioactive atoms administered to stable atoms in the body pool is of the order of 1:1,000 million. By measuring radioactivity in the body, in blood samples, or in the excreta it is possible to gain information about the fate of the labelled substance, and hence of the chemically identical inactive material. Therefore it is theoretically possible to trace the absorption, distribution and excretion of any substance normally present in the body, provided that it can be tagged with a suitable radioactive label.

If the investigation necessitates tracing the path of the material through the body by means of external counting over the body surface, it is obviously essential to use an isotope that emits gamma radiation or positrons. If, however, only measurements on blood sample or excreta are required, it is possible to use pure beta emitters. Whole-body counters measure the total radioactivity in the body, and these are of great value in absorption studies.

Moving images can provide information on body functions such as the movements of the heart, blood ?ow, bile ?ow in the liver, and urine in the kidneys. The development of COMPUTED TOMOGRAPHY or CT scanning has replaced radionuclide scanning for some imaging procedures.

Five main groups of diagnostic uses may be de?ned:

(1) METABOLIC STUDIES The use of radioactive materials in metabolic studies is based on the fundamental property that all isotopes of an element are chemically identical. The radioactive isotope is used as a true isotope tracer – that is, when introduced into the body (in whatever form) it behaves in the same way as the inactive element. For example, isotopes of iodine are used to measure thyroid function (see THYROID GLAND), and isotopes of calcium enable kinetic studies of bone formation and destruction to be performed.... isotope

A machine in which positively charged atomic particles are so accelerated that they acquire energies equivalent to those produced by millions of volts. From the medical point of view, its interest is that it is a source of neutrons. (See RADIOTHERAPY.)... cyclotron

The central core, structure, or focal point of an object.

The nucleus of a living cell is a roughly spherical unit at the centre of the cell. It contains the chromosomes (composed mainly of nucleic acid), which are responsible for directing the cell’s activities, and is surrounded by a membrane. The membrane has small pores through which various substances can pass between the nucleus and the cytoplasm, a thick fluid that forms the bulk of the cell. Usually, the nucleus has 1 nucleolus, a smaller dense region with no membrane that is concerned with protein manufacture.

A nerve nucleus is a group of neurons (nerve cells) within the brain and spinal cord that work together to perform a particular function.

The nucleus of an atom, composed of protons and neutrons, accounts for almost the total mass of the atom but only a tiny proportion of its volume. Nuclear energy is produced through changes in atomic nuclei.... nucleus

n. an *isotope of an element that emits alpha, beta, or gamma radiation during its decay into another element. Artificial radioisotopes, produced by bombarding elements with beams of neutrons, are widely used in medicine as *tracers and as sources of radiation for the different techniques of *radiotherapy.... radioisotope