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Atoms and Nuclei question

2019 · 10 Jan · Shift 2 · Q72
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Atoms and Nuclei question

2019 · 10 Jan · Shift 2 · Q72

JEE MainPhysicsAtoms and NucleiMCQ+4 / −1
Consider the nuclear fission Ne20 →\to→ 2He4 + C12 Given that the binding energy/ nucleon of Ne20, He4 and C12 are, respectively, 8.03 MeV, 7.07 MeV and 7.86 MeV, identify the correct statement -
  1. A
    8.3 MeV energy will be released
  2. B
    energy of 11.9 MeV has to be supplied
  3. C
    energy of 12.4 MeV will be supplied
  4. D
    energy of 3.6 MeV will be released
View written solutionFree

Correct answer: NONE OF THE GIVEN OPTIONS IS CORRECT., IF THE INTENDED REACTION/DATA WERE DIFFERENT, THE QUESTION LIKELY CONTAINS A TYPO. FOR THE REACTION AS WRITTEN AND THE GIVEN BINDING ENERGIES, THE REQUIRED SUPPLIED ENERGY IS 38.0 MEV.

  1. Use binding energies to find total binding energy of reactants and products

Given binding energy per nucleon:

  • For 20Ne\mathrm{^{20}Ne}20Ne: 8.03 MeV/nucleon8.03\,\text{MeV/nucleon}8.03MeV/nucleon
  • For 4He\mathrm{^{4}He}4He: 7.07 MeV/nucleon7.07\,\text{MeV/nucleon}7.07MeV/nucleon
  • For 12C\mathrm{^{12}C}12C: 7.86 MeV/nucleon7.86\,\text{MeV/nucleon}7.86MeV/nucleon

So total binding energies are:

B(20Ne)=20×8.03=160.6 MeVB(\mathrm{^{20}Ne}) = 20 \times 8.03 = 160.6\,\text{MeV}B(20Ne)=20×8.03=160.6MeV B(4He)=4×7.07=28.28 MeVB(\mathrm{^{4}He}) = 4 \times 7.07 = 28.28\,\text{MeV}B(4He)=4×7.07=28.28MeV B(12C)=12×7.86=94.32 MeVB(\mathrm{^{12}C}) = 12 \times 7.86 = 94.32\,\text{MeV}B(12C)=12×7.86=94.32MeV
  1. Find total binding energy of products

Reaction:

20Ne→ 4He+ 12C\mathrm{^{20}Ne \rightarrow \, ^4He + \, ^{12}C}20Ne→4He+12C

Total binding energy of products:

Bproducts=28.28+94.32=122.60 MeVB_{\text{products}} = 28.28 + 94.32 = 122.60\,\text{MeV}Bproducts​=28.28+94.32=122.60MeV
  1. Compare initial and final binding energies

Initial binding energy:

Binitial=160.6 MeVB_{\text{initial}} = 160.6\,\text{MeV}Binitial​=160.6MeV

Final binding energy:

Bfinal=122.6 MeVB_{\text{final}} = 122.6\,\text{MeV}Bfinal​=122.6MeV

Change in binding energy:

ΔB=Bfinal−Binitial=122.6−160.6=−38.0 MeV\Delta B = B_{\text{final}} - B_{\text{initial}} = 122.6 - 160.6 = -38.0\,\text{MeV}ΔB=Bfinal​−Binitial​=122.6−160.6=−38.0MeV

Since the products have less total binding energy, the reaction is less stable after fission. Therefore, energy must be supplied.

Amount of energy required:

Erequired=160.6−122.6=38.0 MeVE_{\text{required}} = 160.6 - 122.6 = 38.0\,\text{MeV}Erequired​=160.6−122.6=38.0MeV
  1. Check options
  • A: 8.3 MeV8.3\,\text{MeV}8.3MeV released — incorrect
  • B: 11.9 MeV11.9\,\text{MeV}11.9MeV supplied — incorrect
  • C: 12.4 MeV12.4\,\text{MeV}12.4MeV supplied — incorrect
  • D: 3.6 MeV3.6\,\text{MeV}3.6MeV released — incorrect

So, based on the given data, none of the options matches.

  1. Conclusion

The correct physical result is:

38.0 MeV must be supplied\boxed{38.0\,\text{MeV} \text{ must be supplied}}38.0MeV must be supplied​

Hence the stored answer B\mathbf{B}B does not agree with the calculation. The reaction as written also appears nucleon-number inconsistent because 4+12=16≠204 + 12 = 16 \neq 204+12=16=20, suggesting there may be a typo in the question.

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