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In health physics, whole-body counting refers to the measurement of radioactivity ''within'' the human body. The technique is primarily applicable to radioactive material that emits gamma rays. Alpha particle decays can also be detected indirectly by their coincident gamma radiation. In certain circumstances, beta emitters can be measured, but with degraded sensitivity. This must not be confused with whole body ''personnel exit monitoring'', which is the term used in Radiation protection for checking of external contamination of a whole body leaving a contamination controlled area. 〔''Operational Monitoring Good Practice Guide - The Selection of Alarm Levels for Personnel Exit Monitors.'' Industry Radiological Protection Coordination Group, NPL, UK, Dec 2009.〕 == Principles == If a gamma ray is emitted from a radioactive element within the human body due to radioactive decay, and its energy is sufficient to escape then it can be detected. This would be by means of either a scintillation detector or a semiconductor detector, placed in close proximity to the body. Radioactive decay may give rise to gamma radiation which cannot escape the body due to being absorbed or other interaction whereby it can lose energy; so account must be taken of this in any measurement analysis. There are many ways a person can be positioned for this measurement: sitting, lying, standing. The detectors can be single or multiple and can either be stationary or moving. The advantages of whole body counting are that it measures body contents directly, does not rely on indirect methods (such as urinalysis) and that it can measure insoluble radionuclides in the lungs. On the other hand, disadvantages of whole body counting are that it can only be used for gamma emitters, except in special circumstances, and it can misinterpret external contamination as an internal contamination. On its own, it may be unable to distinguish between radioisotopes that have similar gamma energies. Alpha and beta radiation is largely shielded by the body and will not be detected externally, but the coincident gamma from alpha decay may be detected, as well as radiation from the parent or daughter nuclides. Image:Stand-up_WBC.JPG|A stand-up whole-body counter with phantom (mannequin) for calibration. Image:Scanning Bed WBC.JPG|A scanning-bed whole-body counter. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「whole body counting」の詳細全文を読む スポンサード リンク
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