|WikiProject Physics||(Rated Start-class, High-importance)|
Alpha Penetration and Detection
I was recently reading a discussion on a Yahoo group which led me here due to difficulty reconciling what Geiger-Müller tubes can detect vs. what alpha particles can penetrate. According to the GM tube article, "The usual form of tube is an end-window tube. [...] The mica window type will detect alpha radiation but is more fragile." But, according to this article, "Because of their charge and large mass, alpha particles are easily absorbed by materials and can travel only a few centimeters in air. They can be absorbed by tissue paper or the outer layers of human skin (about 40 micrometres, equivalent to a few cells deep)". If alphas are stopped by tissue paper, how can they possibly penetrate mica? One poster in the Yahoo discussion asserts that since alpha emitters are also gamma emitters, that what GM tubes detect from alpha sources is really only the gamma radiation. Another theory is that they can detect alphas only indirectly, if an alpha impact happens to knock loose an electron (beta particle) from the inside surface of the window. If either of these assertions is true, then I believe a correction to the GM tube article is in order.
- The mica window is very thin and for this reason very expensive. In the literature, sectional densities of 1.0 to 1.5 mg/cm^2 are given. For simplicity, if you figure mica has density 2.8 g/cm^3, and use a sectional density of 1.4 mg/cm^2 (half that), then the thickness is 1/2000th of a cm = 5 micrometers. If (epidermal) skin is 50 micrometers (st the thinnest-- over the eyelids) and tissue paper 30 microns thick, then it's not completely crazy that they might stop alphas, but a mica window of 3 times the density that is 1/6th or 1/10th as thick, will not. Air has a density of roughly 1.3 kg/m^3 = 1/2000th that of mica. A stopping power of 2 cm in air corresponds then to 1/1000 cm = 10 micrometers in mica. I would suppose that's how they picked 5 microns. SBHarris 18:18, 19 August 2009 (UTC)
- Alpha particles leave very small holes upon collision with mica. This is a fact. In fact, if you don't believe me, get some radium, put it near some mica and then boil the mica in NaOH. The holes will get bigger. It's a plain, simple fact. Bochum 08:53, 6 August 2007 (UTC)
- OK - got a reference for that plain, simple fact? Vsmith 14:23, 6 August 2007
He just DID--an experiment can be proof. Try it Yourself before armchair-slashing... Bochum: Perhaps you should do a control experiment: Take some of the same mica, but don't expose it to alpha. Then pickle the same way in NaOh. Look and see if the holes are already there or not.126.96.36.199 (talk) 01:53, 27 December 2009 (UTC).188.8.131.52 (talk) 17:03, 21 December 2009 (UTC)
I'm posting this here because I don't know where such a suggestion should be posted in relation to the GM tube article, because the discussion page there just says something about "This article is within the scope of WikiProject Physics..." with nothing about how/where to go about posting a message such as this one.
- Will someone please clarify the last part about alpha particles in computer engineering?
Perhaps the definition should be separated from various subtopics such as hisotircal references and reasoning for the nomenclature. Perhaps using subheadings whereby the concept is defined before it's history is described.
As from studied alpha particles have a charge of +2 but the beta particle has a charge of -1, but respectively the gamma particle has a charge of 0.58.107.129.188 08:25, 16 April 2007 (UTC) Dr Mena(MBS) cambridge press
The article has now been updated with additional diagrams and text. Alpha particles do penetrate the end window, but end window tubes are not the only ones in common use. The article has been expanded to cover the many types of tube and the different particle interactions. The article on the G-M counter has a link to the UK HSE site which describes the uses that GM tubes can be put to. The article on alpha particles contains much useful information including the Bragg curve and peak for alpha. Dougsim (talk) 12:08, 10 November 2012 (UTC)
please, add Tub Geiger-Müller as a interwiki. Thanks!
Mistake needs correction (original source needed)
Hi everyone. The paragraph "Quenching and dead time" features the sentence: "This effectively causes a loss of counts at sufficiently high count rates and limits the G-M tube to a count rate of between 10^4 to 10^5 counts, depending on its characteristic."
A rate is counts per time. I can't just add "1/s" without consultion a source. (Hope i'm using the discussion feature the right way - doing this the first time) Regards, Martin — Preceding unsigned comment added by Orby1 (talk • contribs) 12:32, 27 September 2013 (UTC)