Радиоактивность (5 эксперименты)
внесение
We can find many technical, industrial or diagnostic applications, where ionizing devices are used, such as smoke detectors in fire detectors, x-ray devices for industrial or medical diagnosis, sterilization of food and medical instruments. Ionizing radiation can have healing effects (eg. meet with Leksell gama knife, which is situated at Hospital Na Homolce in Prague), but it can also have devastating effects. That is reason why everyone should know well about elemetary ways how to protect against ionizing radiation and recognize types of radiation.
We distinguish several types of ionizing radiation, which differ by their penetration through materials.
- Alfa radiation consists of so called alpha particles. Alpha particle is helium nuclueus, a helium atom without electrons (so it is charged). They can be shielded very easily, eg. by paper of thickness 1 mm. Sometimes there is not needed to shield this radiation, because the stopping range in air is only few centimeters, by higher energy maximally few decimeters. Because of the charge of alpha particle it interacts in electromagnetic field.
- Beta radiation is created by stream of light electrons (β−), or by stream of positrons (β+). It can be also easily shileded with light materials (plastic, eg. plexiglass of thickness between 5–10 mm). Curiosity: lead (Pb) is not eligible shielding material, since when passing through this material, there is intensive bremsstrahlung created . Beta radiation interacts in electromagnetic field, too, because it consists of charged particles.
- Gama radiation consists of high energy quantum of elektromagnetic field – which is called photon. It is shielded best by dense materials , such as lead, concrete. Lead curtains, lead panellings are often used pharmacy – see pic. 1. Emitters are stored in lead wraps. To shield gamma radiation of energi cca 100 keV it is needed lead layer thick 2 mm. Gamma radiation can't be influenced by electromagnetic field.
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| Pic. 1: Shielding wall made of lead. (Picture taken from website of corporation Plehaso, KG) |
Basic and intuitive ways of protection against ionizing radiation are:
- Protection with distance – to be as far from emitter as possible.
- Protection by exposure time – try to minimalise time of presence nearby emitter of ionizing radiation.
- Protection with shielding – if we move near radioactive emitters, we can effectively protect with layer of appropriate material.
In the first and second case there is no need of special eqipment. Also we don't need to protect against natural radioactive background. Live forms on earth are well adapted; eg. in cells there are self-repair mechanisms of DNA double helix (which carries genetic informaton), which are effective up to certain damage. On the contrary radioactivity participated on rich biodiversity on earth.
Radioactivity - spontaneous transformation of nuclei of unstable chemical elements, which is accompanied by creation of ionizing radiation, is random physical phenomenon, that is unable to predict. However, it is well described by means of statistical physics. In this experiment you will be learn something about statistics, therefore you will be able to check simple relations, which are used in radioactive shielding.