Sunday, December 27, 2009

Nuclear Radioactivity : Types of ionizing radiation

Types of ionizing radiation

Alpha radiation (), that can be deflected by electric and magnetic fields, is a positively charged helium nucleus emitted by a larger unstable nucleus. It is a rela­tively massive particle. but it only has a short range in air (1-2 cm) and can be absorbed completely by paper or skin.

Alpha radiation can, however, be hazard­ous if it enters the body by inhalation or ingestion, because large exposures can result in nearby tissues, such as the lining of the lung or stomach

­Beta radiation (β) is an electron emitted by an unstable nucleus. Beta particles are much smaller than alpha particles and therefore are strongly deflected by electric and magnetic fields can penetrate further into materials or tissue. Beta radiation can be absorbed completely by sheets of plastic, glass, or metal. It does not normally penetrate beyond the top layer of skin. However large exposures to high-energy beta emitters can . cause skin burns. Such emitters can also be hazardous if inhaled or ingested.

Gamma radiation (γ) is a very high energy photon (a form of electromagnetic radiation like light) emitted from an unstable nucleus that is often emitting a beta particle at the same time. Gamma radiation causes ionization in atoms when it passes through matter, primarily due to interactions with electrons. It can be very penetrating and only a substantial thickness of dense materials such as steel or lead can provide good shielding.

Gamma radiation can therefore deliver significant doses to internal organs without inhalation or ingestion.

Cosmic radiation comes from deep space. It is a mixture of many different types of radiation, including pro­tons, alpha particles, electrons and other various exotic (high energy) particles . All these energetic particles interact strongly with the atmosphere and, as a result, cosmic radiation at ground level becomes primarily muons, neutrons, electrons, positrons and photons. Most of the dose at ground level comes from muons and electrons.

X rays are high-energy photons, like gamma radiation, and are produced artificially by the rapid slowing down of an electron beam. X rays are similarly penetrating and, in the absence of shielding by dense materials, can deliver significant doses to internal organs. Most of the common types of radiation come from .radioactive materials, but some types of radiation are produced in other ways. The most important example is that of X rays that are normally produced by firing a beam of electrons at a metal target (usually tungsten). The electrons in the metal atoms absorb energy from the electron beam, the metal atoms become 'excited', and then release the energy in the form of X rays as they 'relax'. The radiation, therefore, comes from the metal atoms but, unlike radioactivity, it is-not from the nucleus. Because of how they are produced, there is no half-life for an X ray. Once the beam is switched off, the X rays disappear.

Neutron radiation (n) is a neu­tron emitted by an unstable nucleus, in particular during atomic fission and nuclear fusion. Apart from a component in cosmic rays, neutrons are usually produced artificially. Because they are electrically neutral particles, neutrons can be very penetrating and when they interact with matter or tissue, they cause the emission of beta and gamma radia­tion. Neutron radiation therefore requires heavy shielding such as concrete to reduce exposures.

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