Date | November 2020 | Marks available | 1 | Reference code | 20N.2.SL.TZ0.6 |
Level | Standard level | Paper | Paper 2 | Time zone | 0 - no time zone |
Command term | State | Question number | 6 | Adapted from | N/A |
Question
One possible fission reaction of uranium-235 (U-235) is
U23592+n10→Xe14054+Sr9438+2n10
Mass of one atom of U-235 =235 u
Binding energy per nucleon for U-235 =7.59 MeV
Binding energy per nucleon for Xe-140 =8.29 MeV
Binding energy per nucleon for Sr-94 =8.59 MeV
A nuclear power station uses U-235 as fuel. Assume that every fission reaction of U-235 gives rise to 180 MeV of energy.
A sample of waste produced by the reactor contains 1.0 kg of strontium-94 (Sr-94). Sr-94 is radioactive and undergoes beta-minus (β-) decay into a daughter nuclide X. The reaction for this decay is
Sr9438→X+ˉve+e.
The graph shows the variation with time of the mass of Sr-94 remaining in the sample.
State what is meant by binding energy of a nucleus.
Outline why quantities such as atomic mass and nuclear binding energy are often expressed in non-SI units.
Show that the energy released in the reaction is about 180 MeV.
Estimate, in J kg-1, the specific energy of U-235.
The power station has a useful power output of 1.2 GW and an efficiency of 36 %. Determine the mass of U-235 that undergoes fission in one day.
Write down the proton number of nuclide X.
State the half-life of Sr-94.
Calculate the mass of Sr-94 remaining in the sample after 10 minutes.
Markscheme
energy required to «completely» separate the nucleons
OR
energy released when a nucleus is formed from its constituent nucleons ✓
Allow protons AND neutrons.
the values «in SI units» would be very small ✓
140×8.29+94×8.59-235×7.59 OR 184 «MeV» ✓
see «energy=» 180×106×1.60×10-19 AND «mass=» 235×1.66×10-27 ✓
7.4×1013 «J kg-1» ✓
energy produced in one day =1.2×109×24×36000.36=2.9×1014 «J» ✓
mass =2.9×10147.4×1013=3.9 «kg» ✓
39 ✓
Do not allow X9439 unless the proton number is indicated.
75 «s» ✓
ALTERNATIVE 1
10 min=8 t1/2 ✓
mass remaining=1.0×(12)8=3.9×10-3«kg» ✓
ALTERNATIVE 2
decay constant =«ln275=»9.24×10-3 «s-1» ✓
mass remaining =1.0×e-9.24×10-3×600=3.9×10-3 «kg» ✓