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# A levels Physics Nuclear physics! Help!! Watch

1. Hi people!
I was reading through my textbook and got this really confusing point in it!
Well..its about The GM tube and stuff... A GM tube connected to a scaler or rate meter cannot be used to detect Alpha particles because they cannot pentrate the thin mica window.. BUT .... why in experiments to determine half lives of alpha emmiters do they use a GM tube?
2. "The wavelength of the incident light must be less than a maximum value equal to the speed of light divided by the threshold frequency." I have no idea what this means. Can someone explain what this maximum value is?
3. (Original post by Mathsismylife)
Hi people!
I was reading through my textbook and got this really confusing point in it!
Well..its about The GM tube and stuff... A GM tube connected to a scaler or rate meter cannot be used to detect Alpha particles because they cannot pentrate the thin mica window.. BUT .... why in experiments to determine half lives of alpha emmiters do they use a GM tube?
You can get a 'windowless' GM tube, or one with a very thin window which alphas can penetrate. These devices are very fragile so are not used except for specialised purposes. A normal GM tube has a relatively thick window and is robust enough for widespread use
4. (Original post by yajman)
"The wavelength of the incident light must be less than a maximum value equal to the speed of light divided by the threshold frequency." I have no idea what this means. Can someone explain what this maximum value is?
We know that
V is equal to f*lambda. So lambda is equal to v divided by f. In case the speed of light is v, which is a maximum, the value of lambda will be high. It will correspond to the threshold frequency required to knock out electrons, so we say that. I assume youre considering the photoelectric effect?

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5. Thank you!

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