Alen.m
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Hi guys.
Does anyone know why it is important for the electrons to have same amount of kinetic energy in the beam when they aim to determine the radius of a nucleus using high energy electron diffraction?
your help would be greatly appreciated .
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katieMCR
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I do biology -- I don't know what the f*ck this means
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Alen.m
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anyone else?
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JoshDawg
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I do product design and I don't know what this means.
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lerjj
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I don't know the experiment. It would help if you posted some details.

At a guess, the kinetic energy is related to the momentum and then in turn to the wavelength of the electrons. If you want to do diffraction calculations then I imagine it would be very unhelpful to have lots of different wavelengths going on, but I can't give you a more precise answer at the moment.

equations
:  T = \dfrac{p^2}{2m} ,  p=\hbar k , \rightarrow T = \dfrac{\hbar ^2 k^2}{2m} Where k is the wave number (2pi/wavelength).
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Absent Agent
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(Original post by Alen.m)
Hi guys.
Does anyone know why it is important for the electrons to have same amount of kinetic energy in the beam when they aim to determine the radius of a nucleus using high energy electron diffraction?
your help would be greatly appreciated .
How do you think the electron diffraction would be different if electrons of different kinetic energy were to be fired towards a positive nucleus?
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Kallisto
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(Original post by Alen.m)
Hi guys.
Does anyone know why it is important for the electrons to have same amount of kinetic energy in the beam when they aim to determine the radius of a nucleus using high energy electron diffraction?
your help would be greatly appreciated .
Is there an experiment which refers to the question? it would be easier by far to give an answer to you, if I know the closer relation.
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Alen.m
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(Original post by lerjj)
I don't know the experiment. It would help if you posted some details.

At a guess, the kinetic energy is related to the momentum and then in turn to the wavelength of the electrons. If you want to do diffraction calculations then I imagine it would be very unhelpful to have lots of different wavelengths going on, but I can't give you a more precise answer at the moment.

equations
:  T = \dfrac{p^2}{2m} ,  p=\hbar k , \rightarrow T = \dfrac{\hbar ^2 k^2}{2m} Where k is the wave number (2pi/wavelength).
Full question : The radius of a nucleus can be determined from high energy electron diffraction experiment ( which is involve directing a beam of high energy electrons at a thin solid sample of an element , the incident electrons are diffracted by the nuclei of the atom in the foil). explain why it is important that the electrons the beam have the same kinetic energy.
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Alen.m
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(Original post by Kallisto)
Is there an experiment which refers to the question? it would be easier by far to give an answer to you, if I know the closer relation.
Full question : The radius of a nucleus can be determined from high energy electron diffraction experiment ( which is involve directing a beam of high energy electrons at a thin solid sample of an element , the incident electrons are diffracted by the nuclei of the atom in the foil). explain why it is important that the electrons the beam have the same kinetic energy.
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Alen.m
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(Original post by Mehrdad jafari)
How do you think the electron diffraction would be different if electrons of different kinetic energy were to be fired towards a positive nucleus?
i think electrons of high kinetic energy would be diffracted more than the electrons with less kinetic energy and if we say this the case, the radius of nucleus can not be determined using electrons with different kinetic energy. am i in the right path ?
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Absent Agent
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(Original post by Alen.m)
i think electrons of high kinetic energy would be diffracted more than the electrons with less kinetic energy and if we say this the case, the radius of nucleus can not be determined using electrons with different kinetic energy. am i in the right path ?
That's correct but why do you think the electrons with a higher kinetic energy would be diffracted more?
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Kallisto
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(Original post by Alen.m)
Full question : The radius of a nucleus can be determined from high energy electron diffraction experiment ( which is involve directing a beam of high energy electrons at a thin solid sample of an element , the incident electrons are diffracted by the nuclei of the atom in the foil). explain why it is important that the electrons the beam have the same kinetic energy.
Is that the diffraction experiment? which you are talking about?

(Original post by Alen.m)
i think electrons of high kinetic energy would be diffracted more than the electrons with less kinetic energy and if we say this the case, the radius of nucleus can not be determined using electrons with different kinetic energy. am i in the right path ?
Sounds plausible, but based on the picture in the link, but does the diffraction not also depend on position, so where the electron is diffracted?
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Alen.m
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(Original post by Mehrdad jafari)
That's correct but why do you think the electrons with a higher kinetic energy would be diffracted more?
Is this because they have less De broglie wavelength so the diffraction would be more?
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Alen.m
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(Original post by Kallisto)
Is that the diffraction experiment? which you are talking about?



Sounds plausible, but based on the picture in the link, but does the diffraction not also depend on position, so where the electron is diffracted?
well it's the one that you determine radius of nucleus using a beam of high energy electrons directed at the nucleus. that's actually what the experiment is
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Absent Agent
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(Original post by Alen.m)
Is this because they have higher velocity which will cause more diffraction?
Electron beams in electron diffraction experiments have almost reached the maximum speed attainable (the speed of light), so their velocity hardly increases. It is the mass of the electron that increases, increasing their kinetic energy and so their wavelength

Edit; the wavelength of the electrons would have to be equal or greater than the nuclei spacing for diffraction to be greater
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Joinedup
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It's not asking you whether high energy is better than low energy... it's asking you why all electrons having the same energy as each other is ideal

which is to do with having a monochromatic source / all the same wavelength.

we call it monochromatic even though there isn't really any visible colour in an electron beam.
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(Original post by Joinedup)
It's not asking you whether high energy is better than low energy... it's asking you why all electrons having the same energy as each other is ideal

which is to do with having a monochromatic source / all the same wavelength.

we call it monochromatic even though there isn't really any visible colour in an electron beam.
That's true! Although at A level they just want us to suggest why it is ideal (because electrons would be diffracted at different angles and so not allowing us to determine the nuclear radius accurately [using the formula]), I was only explaining why there would a a change in wavelength
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Alen.m
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(Original post by Joinedup)
It's not asking you whether high energy is better than low energy... it's asking you why all electrons having the same energy as each other is ideal

which is to do with having a monochromatic source / all the same wavelength.

we call it monochromatic even though there isn't really any visible colour in an electron beam.
so should i come to the conclusion that the reason behind it is because diffraction of electrons withought the same kinetic energy wouldn't be possible so it's ideal that electrons have the same kinetic energy. Mehrdad jafari
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(Original post by Alen.m)
so should i come to the conclusion that the reason behind it is because diffraction of electrons withought the same kinetic energy wouldn't be possible so it's ideal that electrons have the same kinetic energy. Mehrdad jafari
Electrons with different kinetic energies would still be diffracted, but the angle at which they are be diffracted would be different ( electrons of higher kinetic energy would be diffracted at a greater angle than the electrons with lower kinetic energy).
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Alen.m
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(Original post by Mehrdad jafari)
Electrons with different kinetic energies would still be diffracted, but the angle at which they are be diffracted would be different ( electrons of higher kinetic energy would be diffracted at a greater angle than the electrons with lower kinetic energy).
ok i guess I'm really **** at this but suddenly realised that the de Broglie wavelength of high energy electrons is comparable to nuclear radii, they can therefore be diffracted by nuclei [or not subject to the strong nuclear force] so that's why electrons of same kinetic energy needed so their wavelength would be the same which can determine the nucleus radius .
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