| Zugriffsnummer | 19040 |
| Dokumenttyp | Buchartikel |
| Sprache | Englisch |
| Titel | X-ray safety and protection |
| Autor(in); Institution |
Ambrosi, Peter; 6.3, Strahlenschutzdosimetrie, PTB-Braunschweig
|
| Quelle/Jahr | Handbook of practical X-ray fluorescence analysis:(2006), 835 - 845 |
| Herausgeber(in) |
Beckhoff, Burkhard; 7.1, Photonenradiometrie, PTB-Berlin
|
| ISBN | 3-540-28603-9 ; 978-3-540-28603-5 |
| Verlag | Berlin [u.a.]: Springer |
| Zusammenfassung | X-rays are photons of sufficient energy to ionise atoms or molecules. Such radiation is called ionising radiation. Ionisation is a process to (partially) separate charges, e.g., by separating an electron. The atoms or molecules can be gaseous (e.g., air) liquid (e.g., water), solid (e.g., semiconductors) or a mixture of these (e.g., tissue in the human body). For air, the required energy to procedure one ionisation, the ionisation energy, is about 34 eV. Therefore, visible light is not an ionising radiation, because its energy is about 2.5 eV per photon. In liquids and solids the ionisation energy is lower. Photons are uncharged particles which have long pathways through matter without energy deposition and in each energy deposition process they lose large amounts of energy. The main part of this energy is converted into kinetic energy of secondary particles, mainly electrons. These electrons will lose their energy by secondary ionisation processes very close to their location of generation. These processes will occur with defined probability, resulting in an exponential attenuation law. Such radiation is called indirect ionising radiation. The opposite is direct ionising radiation, e.g., electrons, which have short pathways from one energy depositions to the other and in each of the frequent energy deposition processes they lose small but constant amounts of energy. These “quasi” continuous energy deposition processes result in a maximum range of radiation. In the last few decades, tow main developments have taken place in the dosimetry of ionising radiation: the redefinition of the measurands and the lowering of the dose limits. The measurands are now equally defined for all kinds of radiation and in any case with respect to the human body. Therefore, an area dose value is always a good estimate for the individual dose value for a person at the same place, and dose values due to neutron and photon radiation can be added without any difficulty. Another important consequence is that individual dosemeters and area dosimeters must be of different design, whereas for the former quantities such dual use has been possible. The “new” measurands are now used in most countries worldwide. In all countries the dose limits are prescribed by law and all values are based on recommendations of the ICRP. For all EU Member States, Directive 96/29 forms the basis for any national regulations. In most countries the dose limits have been lowered in the last few years. This paper will deal only with the dosimetry of external radiation. Other topics such as dosimetry at light altitudes and internal dosimetry will not be considered. |
