Alpha Decay

[soby10]

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This quest is in examkrackers phys book.

When a 224Ra undergoes alpha decay an alpha particle is emitted at 1.0 x 107 m/s. What is the velocity of the other particle?

The answer states it's 1.8 x 105 m/s. I understand you are to use p=mv and solve for v and initial p=0 and final p=0 and the mass is from the atomic mass of Ra minus a alpha particle (220Rn).... but how is momentum found? They said it's 4 x 107?

 

[Handinhand]

You're right, moment will be equal for each particle. They give you the velocity at which the Alpha particle is ejected. Knowing what we do about Alpha particles (at least I hope you know what an alpha particle is), we know it weights ~4amu. 4amu * 10^7m/s = 4.0 * 10^7amu*m/s.

Then, because momentum is equal for both particles, and we know that mass of the other daughter particle of 224Ra (224 - 4), we just divide our momentum by 220, to find the other velocity.

 

[soby10]

ok thanks so the mass of a alpha particle is needed 4 amu that makes sense.