Stanton D. answered • 07/03/21
Tutor to Pique Your Sciences Interest
Hi Again Mishal M.,
It would appear that you are stuck in a course that you don't much like(?), so it doesn't make sense to you, and you don't want to put time into it. That may be the case, but Wyzant really can't solve the bigger problem there, even if we may help you with an occasional concept. Just sayin'.
Geiger-Mueller tubes detect ionizing radiation, that which ionizes air along its path within the detection tube. A detection tube consists of a central wire at a large voltage vs. the surrounding wall at the large opposite voltage. The voltage gradient set up radially inside the detection tube is so great, that every time one ionizing particle zips through, all the air ions in its path jump towards the counter-electrode, so vigorously that they in turn smash electrons from any neutral air molecules they hit. Then all the various ions continue to move and bump into more neutral molecules, ionizing them also, and so on. The result is a whole mess of ions arriving at about the same time to the counterelectrode, from just one ionizing particle passing through. That is detected as a "count". In order to discriminate between counts, there must be some time between arrival of each. That is called "dead time". It's the time the counting circuit mechanism needs to get ready to detect the next count. If there are very high rates of counting, the counter will miss some of them, because that pulse will arrive either together with another pulse, or so close in time that the counting circuit mechanism just only thinks there was one pulse. Thus, the GM-counter will UNDERCOUNT at high radiation rates.
Also, the GM-counter can only detect ionizing radiation that traverses its chamber. If radiation is stopped by air or by the entrance window (e.g., alpha rays), the GM won't count it at all. But many radioactive elements decay with alpha emission, and if you didn't know they were around, you *might* get careless and get them on you, bad news...
