[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

A dose of 4 gy to fingers or the hand may lead to

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A dose of 4 Gy to fingers or the hand may lead to changes in skin pigmentation, blistering and ulceration, but would certainly not be fatal. The hands, fore- arms, feet and ankles are about 100 times less sensitive to radiation, therefore, the limits given in Table 8.3 are much larger for these extremities. Other possible late effects of radiation include cataract formation in the lens of the eye. There appears to be a threshold limit of about 15 Gy below which cataracts are not induced. The dose limit for the eye is set so that this value will not be exceeded over a whole working lifetime. 8.1.4 Measuring Instruments Detectors Several detection principles are being used, the most important one being the direct detection of ionisation which is the mostly used principle for direct reading instruments: 1. The ion chamber is a fixed volume surrounded by walls and filled with gas (mainly air). The charge induced in the gas is measured without any amplification within the detector. 2. The proportional counter also consists of a fixed gas-filled volume but due to the higher high voltage applied, the charge pulses generated in the detector are amplified by a fixed factor. Therefore, the charge pulses are proportional to the energy stemming from the radiation particle in the volume. 3. The Geiger-M¨uller counter (GM-counter) also consists of a fixed gas-filled volume but due to the kind of gas and the high voltage applied, the charge pulses generated in the detector are amplified until saturation. Therefore, the charge pulses cannot be used to get information about the energy stemming from the radiation particle in the volume. 4. The semiconductor detector consists of a piece of semiconducting material. Similar to an ion chamber, the radiation induces charges which are a measure of the dose. There is no amplification in the detector. Another detection principle is the indirect detection of ionisation, i.e., the detection of the physical effects occurring during the discharge after ionisation. 1. The scintillation detector generates light when exposed to ionising radiation. 2. The thermoluminescence detector (TL detector) exhibits light generation when the detector is heated after exposure to ionising radiation.
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842 P. Ambrosi 3. The radio photoluminescence detector (RPL detector) exhibits visual light generation when the detector is illuminated with UV-light after exposure to ionising radiation. 4. The film detector shows a blackening of the exposed film after develop- ment. This is similar to a photographic film. 5. The radiochromic dye film detector exhibits colouring (blackening) of the exposed film directly after exposure without development. A special detection principle is the direct measurement of the energy absorbed in matter. Such a detector is called a calorimeter because the increase in temperature (of only a few 1/1,000 K) is measured.
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  • Spring '14
  • MichaelDudley

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