1) Calculate the mass defect (in amu) for bismuth-209 if the exact mass of this
ID: 867158 • Letter: 1
Question
1) Calculate the mass defect (in amu) for bismuth-209 if the exact mass of this atom is 208.980383 amu? The exact mass of a proton is 1.007276467 amu and the exact mass of a neutron is 1.008664916 amu. Give the answer as a POSITIVE value in units of amu. Answer must be within 5% of the actual answer so carry at least 6 significant digits.
2) How much energy is released when 0.783 g of uranium-235 (exact mass = 235.043922 amu) fissions into two neutrons (1.008664916 amu each), cesium-137 (136.907085 amu) and rubidium-96 (95.93427 amu). The units are giga-joules where one GJ equals a billion joules (1.0E+9 J). Carry many significant digits in your calculations.
Explanation / Answer
1) Bismuth Z = 83
Dm = Mass deffect = [Z*mp+(A-Z)*mn]-Ma
= [83*1.007276467+(209-83)*1.008664916]-208.980383
= 1.71534 amu
2) mass defect = 235.043922-[2*1.008664916+136.907085+95.93427]
= 0.185237168 amu
Energy = Dm*931 Mev
= 0.185237168*931
= 172.455803408 Mev
= 1.72455803408*10^-11 joule
1 U-235 atom releases = 1.72455803408*10^-11 joule
total no of atoms = 0.783/235*6.023*10^23 = 2.0068123*10^21 atoms
energy released = 2.0068123*10^21*1.72455803408*10^-11
= 3.460864275*10^10 joule
= 34.60864275 GJ
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