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Question #43706

Difficulty: 8/10 | 🟢 Free

The Question

In a theoretical statistical model of beta decay, the probability density of emitting a non-relativistic beta particle of mass mm with kinetic energy EE is given by ρc(E)=AE(1−EQ)n\rho_c(E) = A E \left(1 - \frac{E}{Q}\right)^n, where QQ is the endpoint kinetic energy, AA is a normalization constant, and nn is a very large integer (n≫1n \gg 1) representing the phase space degrees of freedom.

To account for the wave nature of the beta particle, a quantum suppression factor S(E)S(E) is introduced. S(E)S(E) is defined as the ratio of the nuclear volume V0V_0 to the spherical volume VλV_\lambda associated with the electron's de Broglie wavelength λe\lambda_e (i.e., Vλ=43πλe3V_\lambda = \frac{4}{3}\pi \lambda_e^3).

The modified quantum probability density is ρq(E)=Bρc(E)S(E)\rho_q(E) = B \rho_c(E) S(E), where BB is another normalization constant. Let EcE_c and EqE_q be the most probable kinetic energies of the beta particle in the classical and quantum models, respectively. What is the limiting value of the ratio EqEc\frac{E_q}{E_c} for n→∞n \to \infty?

Options

  • A.

    1.5

  • B.

    2.5

  • C.

    3.5

  • D.

    4.0

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Energy Distribution in Beta Decay|De Broglie Wavelength Scaling|Approximation (Binomial)

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to integrate quantum mechanical wave properties into a classical statistical mechanics phase-space distribution.

The primary trap lies in the De Broglie wavelength scaling: students often incorrectly assume λ∝E−1\lambda \propto E^{-1} (relativistic) instead of E−1/2E^{-1/2} (non-relativistic), which leads to an incorrect suppression factor S(E)∝E3S(E) \propto E^3 and a wrong ratio of 4.0.

Furthermore, the problem forces the use of the exponential limit approximation (1−E/Q)n≈e−nE/Q(1 - E/Q)^n \approx e^{-nE/Q} (derived from the binomial expansion).

Students who fail to recognize this will be bogged down in heavy algebraic differentiation (math bloat), increasing the likelihood of calculation errors.

Finally, a common structural mistake is applying S(E)S(E) but forgetting to multiply it by the original classical density prefactor EE, leading to an incorrect ratio of 1.5.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterNuclei - Class 12
ConceptEnergy Distribution in Beta Decay
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree