# Current from Alpha Particles

1. Jul 10, 2009

### typeinnocent

1. The problem statement, all variables and given/known data
Assume a steady stream of α particles travels with a constant energy of 20 MeV and carries a current of 2.5 μA.

a) If the beam is directed perpendicular to a plane target, how many α's will strike this target in 8 seconds?
b) At any given instant, how many α's are in a 20 cm length of the beam?
c) Through what electrical potential diffence is it necessary to accelerate each α from rest to bring it to the energy of 20 MeV?

2. Relevant equations
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3. The attempt at a solution
I have absolutely no idea how to solve any of these questions. The only thing I could think to do was find how many protons were in the current by multiplying 2.5E-6 by 8 seconds to give me the amount of Coulombs. I then multiplied that by 6.2415E18 e/C to get the number of elementary charges. I thought this solution may be the answer to part a) but it wasn't. So now I'm lost.

Any help will be greatly appreciated.

2. Jul 10, 2009

### turin

How many elementary charges are there per alpha?

3. Jul 10, 2009

### typeinnocent

There's two protons per alpha particle.

4. Jul 10, 2009

### turin

It was a hint.

5. Jul 10, 2009

### typeinnocent

I don't want to be rude, but that really doesn't help me... I still don't know what to do.

6. Jul 10, 2009

### turin

If you know how many elementary charges hit the surface, and you know how many elementary charges there are per alpha particle, then ...

7. Jul 10, 2009

### typeinnocent

Oh, wow. See, I had thought my entire methodology was incorrect... I didn't realize I was actually close to the answer for part a). Thanks! Now I at least have part a) correct.