Simple Alpha Particle Spectroscopy Question

[~Sam~]

Homework Statement

When detecting alpha decay with a spectrometer, why is it important to evacuate the chamber to create a adequate vacuum for where the source is place? Why is it better to place a radioactive source underneath a detector facing up rather than above the detector and facing down?

Homework Equations

None.

The Attempt at a Solution

I'm guessing the pump will evacuate any particles in the air that would absorbed the alpha particles. For the second part, I'm not so sure because radiation emits out evenly, so how would it make a difference?

 

[gneill]

When it rains, why is it better to be under the umbrella than on on top of it?

 

[~Sam~]

When it rains, why is it better to be under the umbrella than on on top of it?

Well because rain is approaching from the top, and being under it prevents rain from hitting the person. Not sure I quite understand the comparison here. It sounds like you're saying something along the lines that it is ideal for the source to be under the detector because then the detector covers it. But I'm not sure how that explains it. Since radioactive sources radiates outwards in even directions, how would this affect it? Unless you mean to say that it prevents interference from the environment.

 

[gneill]

Since radioactive sources radiates outwards in even directions, how would this affect it? Unless you mean to say that it prevents interference from the environment.

Bingo. What's the biggest source of interference? What's the biggest "umbrella" you can think of? (consider that the counter is "looking" directionally).

 

[~Sam~]

Bingo. What's the biggest source of interference? What's the biggest "umbrella" you can think of? (consider that the counter is "looking" directionally).

ahhh, other than excess particles in the air due to imperfect vacuum, it must be background radiation? The detector is placed so it looks down towards the emitting source, preventing interference from background radiation coming from above to enter the detector.