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Question: Obtain equation (6.18) from(6.16) and (6.17).

Short Answer

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Answer

The equationT=16E1U01-E1U0e-2L2mU0-E1/ is derived from L=2m(U0-E)L1andT=4E/U01-E/U0sinh2(L)+4E/U01-E/U0

Step by step solution

01

Definition of transmission probability

The transmission or tunneling probability can be calculated using transmitted intensity and the incident intensity.

In the case of tunneling barriers being wide, it can be found as follows.

T16EU0(1-EU0)e-2L2m(U0-E1)/

Here E is the jump energy, U0is barrier energy, L is the length of the tunnel, and m is the mass of the particle.

02

Given quantities 

The given values are L=2m(U0-E)L1and T=4E/U01-E/U0sinh2(L)+4E/U01-E/U0.

03

Imposing the limiting value in the equation of transmission probability.

We know that,

.=2mU0-E

Use the hyperbolic relation ofSinh(L)=eL2 for L1in the transmission formula as:

T=4E/U01-E/U0sinh2(L)+4E/U01-E/U0=4E/U01-E/U0e2L4+4E/U01-E/U0=16E/U01-E/U0e2L=16E/U01-E/U0e-2L=16EU01-EU0e-2L2mU0-E/

Therefore, the equation is obtained fromT=16E1U01-E1U0e-2L2mU0-E1/

L=2m(U0-E)L1and T=4E/U01-E/U0sinh2(L)+4E/U01-E/U0.

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Most popular questions from this chapter

Given the situation of exercise 25, show that

(a) as Uo, reflection probability approaches 1 and

(b) as L0, the reflection probability approaches 0.

(c) Consider the limit in which the well becomes infinitely deep and infinitesimally narrow--- that is Uoand data-custom-editor="chemistry" L0but the product U0L is constant. (This delta well model approximates the effect of a narrow but strong attractive potential, such as that experienced by a free electron encountering a positive ion.) Show that reflection probability becomes:

R=[1+2h2EmUoL2]-1

To obtain a rough estimate of the mean time required for uranium-238 to alpha-decay, let us approximate the combined electrostatic and strong nuclear potential energies by rectangular potential barrier half as high as the actual 35 Mev maximum potential energy. Alpha particles (mass 4 u) of 4.3 Mev kinetic energy are incident. Let us also assume that the barrier extends from the radius of nucleus, 7.4 fm to the point where the electrostatic potential drops to 4.3 Mev (i.e., the classically forbidden region). Because U(1/r), this point is 35/4.3 times the radius of the nucleus, the point at which U(r) is 35 Mev. (a) Use these crude approximations, the method suggested in Section 6.3, and the wide-barrier approximation to obtain a value for the time it takes to decay. (b) To gain some appreciation of the difficulties in a theoretical prediction, work the exercise 鈥渂ackward鈥 Rather than assuming a value for U0, use the known value of the mean time to decay for uranium-238 and infer the corresponding value of U0, Retain all other assumptions. (c) Comment on the sensitivity of the decay time to the height of the potential barrier.

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Your friend has just finished classical physics and can鈥檛 wait to know what lies ahead. Keeping extraneous ideas and postulates to a minimum, Explain the process of Quantum-mechanical tunneling.

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