Direct radiation doses

It is often useful to have an idea of the possible radiation fields caused by a point source. The approximate formula to remember is the following (see Note 1)  

Remember that a-rays are stopped by the thickness of a simple sheet of paper, while -rays can penetrate several centimetres into human body tissue. 

As can be seen, there is a certain inverse proportionality to the material density. 

ICRP (1991) Recommendations of the International Commission on Radiological Protection. ICRP Publication 60, Pergamon Press. 

1 Relaxation moment Concerning the use of obsolete units of measure, the subtle truth contained in a popular joke comes to mind. It concerns a professor, very popular with his students, who, answering a question about the reason why he taught so many incorrect notions in his lessons, replied, This way they understand better . 

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The target for direct radiation dose during normal operation and incidents is 0.1 m Sv year . The target is independent from plant rated power. 

The dose from direct radiation needs also to be added. Section 12.4.2 of the EDCD (Reference 12.1) states that the direct radiation dose at the site boundary is negligible. To provide an estimate, the doses experienced from the closest comparable design currently in operation in the UK have been used, i.e., the Sizewell B PWR, which is based on an older Westinghouse design. The direct shine dose at the Sizewell B perimeter fence was 4 pSv in 2007, taken from Appendix 4 of Radioactivity in Food and the Environment Report, 2007 (Reference 12.7). 

Hemispherical total quantities combine the radiation over all wavelengths and from all directions. They do not provide information on the spectral distribution and the directional dependence of the radiation but are frequently sufficient to provide the solution to radiative heat transfer problems. 

Power excursions (transients) may lead to comparatively high power levels and consequent high levels of direct radiation if the core is not well shielded. Power excursions may be of particular importance for research reactors or critical assemblies of low power level, which in normal operating conditions do not require significant shielding. In the design of the irradiation facilities (e.g. beam tubes), the direct radiation caused by transients should be considered. 

A Geiger counter monitors radiation by detecting the ionization of a low-pressure gas, as shown in the illustration. The radiation ionizes atoms of the gas inside a cylinder and allows a brief flow of current between the electrodes. The resulting electrical signal can be recorded directly or converted into an audible click. The frequency of the clicks indicates the intensity of the radiation. A limitation of Geiger counters is that they do not respond well to 7 rays. Only about 1% of the 7-ray photons are detected, whereas all the (3 particles incident on the counter are detected. Because the efficiency of a Geiger counter depends on the size of the tube, a counter used to monitor a wide range of activities usually contains two tubes of different sizes. 

How do we know the composition of the sun and other stars How can we measure the temperature inside a flame so hot that any thermometer would melt How can we explore chemical reactions among molecules that are much too tiny to see directly Light allows us to do all these things. The study of matter with electromagnetic radiation is called spectroscopy. 

By using NFS, information on both rotational and translational dynamics can be extracted. In many cases, it would be favorable to obtain separate information about either rotational or translational mobility of the sensor molecule. In this respect, two other nuclear scattering techniques using synchrotron radiation are of advantage. Synchrotron radiation-based perturbed angular correlations (SRPAC) yields direct and quantitative evidence for rotational dynamics (see Sect. 9.8). NIS monitors the relative influence of intra- and inter-molecular forces via the vibrational density of states (DOS) which can be influenced by the onset of molecular rotation (see Sect. 9.9.5). 

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