A nucleus in a transition from an excited state emits a gamma-ray photon with an energy of 2.5 MeV. (a)
What is the photon frequency? (b) What is the photon wavelength? (c) How does the wavelength compare
with typical nuclear radii (of the order 10−15 m)?

Respuesta :

a) The frequency of the photon is [tex]7.16\cdot 10^{20}Hz[/tex]

b) The wavelength of the photon is [tex]4.19\cdot 10^{-13} m[/tex]

c) The wavelength of the photon is about 100 times larger than the nuclear radius

Explanation:

a)

The energy of a photon is given by

[tex]E=hf[/tex] (1)

where:

[tex]h=6.63\cdot 10^{-34} Js[/tex] is the Planck constant

f is the frequency of the photon

The photon in this problem has an energy of

[tex]E=2.5 MeV = 2.5\cdot 10^6 eV[/tex]

And keeping in mind that

[tex]1eV = 1.6\cdot 10^{-19} J[/tex]

we can convert to Joules:

[tex]E=(2.5\cdot 10^6)(1.9\cdot 10^{-19})=4.75\cdot 10^{-13} J[/tex]

And now we can use eq.(1) to find the frequency of the photon:

[tex]f=\frac{E}{h}=\frac{4.75\cdot 10^{-13}}{6.63\cdot 10^{-34}}=7.16\cdot 10^{20}Hz[/tex]

b)

The wavelength of a photon is related to its frequency by the equation

[tex]c=f\lambda[/tex]

where

[tex]c=3.0\cdot 10^8 m/s[/tex] is the speed of light

f is the frequency

[tex]\lambda[/tex] is the wavelength

For the photon in this problem,

[tex]f=7.16\cdot 10^{20}Hz[/tex]

Re-arranging the equation, we find its wavelength:

[tex]\lambda=\frac{c}{f}=\frac{3\cdot 10^8}{7.16\cdot 10^{20}}=4.19\cdot 10^{-13} m[/tex]

c)

The size of the nuclear radius is approximately

[tex]d \sim 10^{-15} m[/tex]

While we see that the wavelength of this photon is

[tex]\lambda=4.19\cdot 10^{-13} m[/tex]

Therefore, the ratio between the wavelength of the photon and the nuclear radius is

[tex]\frac{\lambda}{d}=\frac{\sim 10^{-13}}{\sim \cdot 10^{-15}}=100[/tex]

So, the wavelength of the photon is approximately a factor 100 times larger than the nuclear radius.

Learn more about photons:

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