1 U235 absorbs a neutron En0 and then fissions The products

1. U-235 absorbs a neutron (En=0) and then fissions. The products are 3 neutrons, an isotope with 36 protons and another isotope with 141 total protons plus neutrons. a. Find the two isotopes b. Calculate the Q-value of the fission reaction (Assume the masses of the two fission products are 140.914411 and 91.926156.).

Solution

Given:

92 U 235 + n0 = (36) X (m) + (A) Y (141) + 3n0

Where a X b means an element X with atomic number a and mass number b

now, 36 is Atomic Number of Kr -- (1)

Also, Net mass number should be constant,
so 235 + 1 = m + 141 + 3
m = 92 -- (2)

Also, Assuming Net atomic number should be constant,
so 92 = 36 + A
A = 56 -- (2)

now, 56 is Atomic Number of Ba -- (3)

92 U 235 + n0 = (36) Kr (92) + (56) Ba (141) + 3n0 -- (4)

Now for Q value,
Mass of products = 140.914411 + 91.926156 + 3 * 1.008701 = 235.86667
Mass of Reactants = 235 + 1.008701 = 236.008701
Mass deficit = 0.142031
Q value = m*c^2 = 0.142031 * c^2 = 1.2 * 10^16 amu m squared/second squared
Q value = 0.021J