User:Tmckeage/sandbox

ALARA, an acronym for As Low As Reasonably Achievable, is a term used in risk management of radiation exposure using all reasonable methods. It is both a basic philosophy as well as a regulatory requirement in the US. It is based on the general theory that radiation exposure at any level can be harmful to biological tissue and should always be kept to a certain minimum level while taking into consideration both technological and economic limitations. ALARA is separated into two broad categories, minimizing dose from external sources and minimizing dose from internal sources.

JUSTFICATION

ALARA requires the assumption that there is no safe level of radiation exposure because if a safe level existed there would be no need to minimize dose beyond this level. This idea is called the linear non-threshold hypothesis. While the majority of evidence supports this hypothesis it may be impossible to demonstrate beyond reasonable doubt. This is because while it is easy to see the dose relationship at high levels it becomes difficult to draw accurate conclusions at low levels due to natural variations in background radiation exposure. For this reason regulatory and advising bodies in the US have chosen the better supported and more conservative linear non-threshold dose response relationship.

IMPLEMENTATION

The implementation of ALARA is divided into three primary categories: Maximizing the distance from the radiation source, minimizing the amount of time exposed, and shielding between the subject and source.

Distance

Distance is a particularly effective way to minimize dose. This is because the level of exposure is inversely proportional to the square of the distance to the source. For example if the subject moves three times as far away from the source they will only receive 1/9th the dose.

Time

The amount of time exposed is directly proportional to the dose from a given source. Also included with time is the idea of protracted dose. A protracted dose is a series of short exposures given over an extended period of time and has a lower health risk than a single dose given all at once.

Shielding

Shielding is more complicated than either distance or time. The type of material, type of radiation, and thickness of the shielding all have different effects on the reduction of dose.

SUBJECTIVITY

ALARA can be subjective to a certain degree. What is considered a safe distance or safe exposure time while still being able to adequately do the task at hand can vary depending on the individual performing the task and the nature of the task being performed. On the other hand a certain minimum safe distance, time, or shielding my be required.