Solving the Mystery of X Nucleus Binding Energy

[Darkmisc]

Homework Statement

I have a multichoice past exam that does not come with answers. Please help with the following:

The binding energy of the X nucleus is 38.4MeV. Which of the following statements is FALSE?

a) The binding energy of 38.4MeV represents the mass deficit between the assembled nucleus and its constituents.
b) The energy required to disassemble the nucleus to its constituent parts is 38.4MeV
c) A photon of energy 45MeV will cause the component nucleons to move apart with kinetic energy of 6.6MeV.
d) The concept of binding energy cannot be applied to the assembly of a proton and an electron to form a hydrogen atom.

Homework Equations

none.

The Attempt at a Solution

I chose C. I have not come across fission caused by a photon. That said, I'm not sure what is supposed to happen when high energy photons strike nuclei.

I think D is true, but binding energy in that case is referred to as ionisation energy.

 

[cepheid]

If b is true, than c has to be true, wouldn't you think? You've supplied enough energy to break apart the nucleus, so why wouldn't it break apart?

By the way, a photon with energy of 45 MeV has a wavelength of 0.00002755 nm (compare to 400 nm - 700 nm for visible light) That's a hard gamma ray (i.e. a very energetic photon).

You may not have come across this, but it does have applications. For instance, in the early universe, big bang nucleosynthesis (the formation of light elements, mainly helium, from protons and neutrons through nuclear reactions) could not occur until the universe had expanded and cooled enough that very few photons were left in the radiation field that were more energetic than the binding energy of deuterium. That's because you have to make deuterium first, and build helium-4 out of it. That's called the deuterium bottleneck.

You might want to re-examine answer choice d.

 

[Darkmisc]

Thanks.

 

[Redbelly98]

[STRIKE]I have a different opinion. Think about this: what affect does a photon have on the constituent neutrons?[/STRIKE]

EDIT: Never mind, I was thinking about things backwards.

 

[rwisz]

I would like to confirm that the correct answer is indeed C. The statement that a photon of energy 45MeV will cause the component nucleons to move apart with kinetic energy of 6.6MeV is false. This is because the energy required to disassemble the nucleus is not solely dependent on the energy of the photon, but also on the binding energy of the nucleus itself. Therefore, the kinetic energy of the nucleons will not always be the same as the energy of the photon.

Additionally, I would like to clarify that the concept of binding energy can be applied to the assembly of a proton and an electron to form a hydrogen atom. In this case, the binding energy is known as the ionization energy, which is the energy required to remove the electron from the atom. However, this is a different concept from the binding energy of a nucleus, which is the energy required to disassemble the nucleus into its constituent parts.