# Elastic collision between an unknown mass and an alpha particle

1. Jan 21, 2009

### pentazoid

1. The problem statement, all variables and given/known data

In an elastic collision between an alpha particle and an unknown nucleus at rest, the alpha particle was deflected through a right angle and lost 40 percent of its energy . Identify the mysterious nucleus.

2. Relevant equations

(E2)/(E0)=[4*gamma/(gamma+1)^2]*(sin(phi/2))^2

$$\theta$$2=.5*(pi-phi)

gamma is the ratio between the alpha mass particle and the unknown mass
3. The attempt at a solution

Is the deflected angle the recoil angle? If so then I can use the recoil angle to find phi. Then I can use phi to find gamma and with gamma since I know the mass of an alpha particle, I can find the unknown mass. When the problem says the recoil angle loses 40 % of its energy , doesn't that mean E2=.4E0

2. Jan 22, 2009

### tiny-tim

Hi pentazoid!

Yes, the deflected angle is the recoil angle …

but no, E2=.6E0

3. Jan 22, 2009

### pentazoid

if my deflected angle is 90 degrees that means my phi is zero. which means sin(phi/2) is zero, which means then that there is no way to determine what the unknown mass is

4. Jan 23, 2009

### tiny-tim

I'm confused

isn't φ = π/2?

5. Jan 24, 2009

### turin

Not if you mean the angle that the nucleas recoils. Conservation of energy and momentum determine this recoil angle.