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# Simple Atomic Mass Unit question

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1. Simple Atomic Mass Unit question
The uranium isotope 235U captures a neutron and undergoes fission to produce 93Rb and 141Cs. Calculate the energy released in this process.

The nuclear masses of the relevant isotopes are
235U 235.0439u,
93Rb 92.9217u,
141Cs 140.9195u

n + 235U → 93Rb + 141Cs + 2n

LHS 235.0439 + 1.0087
RHS 92.921712 + 140.91949 + 2.10087

Difference is 0.1943u = 181 MeV

In the answer, how is it known that 2n should be added? Why 2?
Last edited by little pixie; 06-05-2012 at 18:06.
2. Re: Simple Atomic Mass Unit question
The nucleon number (mass number) has to be conserved. On the left hand side of the equation the total nucleon number is 236. The isotopes of Rubidium and Caesium have a total nucleon number of 234, hence 2 neutrons.
3. Re: Simple Atomic Mass Unit question
That's great! Thanks very much for that ASaunders!

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Last updated: May 6, 2012
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