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Question #43693

Difficulty: 8/10 | 🟢 Free

The Question

A sample contains N0N_0 identical hypothetical heavy nuclei, each initially having a mass number A0A_0. These nuclei undergo a continuous decay process by emitting neutrons. The binding energy per nucleon for these nuclei is given by the functional approximation B(A)=α−βAB(A) = \alpha - \beta A, where α\alpha and β\beta are positive constants, and AA is the instantaneous mass number. The energy released per unit decrease in mass number is defined as the instantaneous Q-value, Q(A)Q(A). The decay process is statistical but can be modeled continuously such that the rate of decrease of mass number for each nucleus is directly proportional to its instantaneous Q-value, given by dAdt=−kQ(A)\frac{dA}{dt} = -k Q(A) (where kk is a positive constant). Assuming A0>α2βA_0 > \frac{\alpha}{2\beta}, which of the following expressions represents the total power P(t)P(t) released by the sample as a function of time tt?

Options

  • A.

    N0k(2βA0−α)2e−4βktN_0 k (2\beta A_0 - \alpha)^2 e^{-4\beta k t}

  • B.

    N0k(2βA0−α)2N_0 k (2\beta A_0 - \alpha)^2

  • C.

    N0k(α−βA0)2e2βktN_0 k (\alpha - \beta A_0)^2 e^{2\beta k t}

  • D.

    N0k(2βA0−α)e−2βktN_0 k (2\beta A_0 - \alpha) e^{-2\beta k t}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Multi-Concept_Bridge

Master problems that require linking physics and math concepts to solve complex competitive questions.

Concepts Behind This Question

Statistical Nature of Decay|Binding Energy per Nucleon Curve|Variable Force Integration

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to link macroscopic decay power to the microscopic, continuously varying mass defect.

The primary trap (Option B) catches students who treat the Q-value as a global constant calculated only at A0A_0, failing to recognize that as the nucleus decays, its position on the Binding Energy curve shifts, altering the instantaneous Q-value.

Another common error (Option D) is calculating the rate of decay dAdt\frac{dA}{dt} but forgetting that power requires multiplying this rate by the Q-value again, leading to a missing square and incorrect exponential factor.

Option C traps students who incorrectly differentiate the binding energy per nucleon B(A)B(A) instead of the total binding energy EB(A)E_B(A).

The problem enforces the application of energy conservation in a nuclear context via localized differentials.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterNuclei - Class 12
ConceptStatistical Nature of Decay
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree