Doubt regarding X-rays

[bananakicker456]

Hello everyone. My question is that can an electron if incident (on say, a metal ) with enough energy knockout another electron (of the metal atom)?. I know that atomic excitation can occur causing atomic electron to jump to higher energy level (bohr s model), but staright up knockout and then later form x rays? if yes, then is there a formula to derive the minimum amout of energy needed to do it, and is my claim even correct?

 

[Baluncore]

Welcome to PF.

My question is that can an electron if incident (on say, a metal ) with enough energy knockout another electron (of the metal atom)?.

Easily, when an electron hits a target it may be absorbed, produce a photon of light, or another electron with a similar energy.

If you remove an electron from the surface of a metal, and then accelerate it through a voltage difference of 1 volt, it will gain an energy of 1 eV, (one electron volt). When that electron impacts a metal target, it may release that energy as a photon. The wavelength (colour) of that photon is inversely proportional to its energy.

but straight up knockout and then later form x rays? if yes, then is there a formula to derive the minimum amount of energy needed to do it,...

If you specify the required wavelength, λ, you can work out the voltage difference needed to accelerate the electron to get a photon of that wavelength.
Energy; eV = 1239.84 / λ nm

X-rays have a wavelength of about 30 pm = 0.03 nm, so the required energy is 1239.84 / 0.03 = 41.3 keV, which will require a voltage of 41.3 kV. X-ray machines operate between about 20 kV and 80 kV.

To produce red light, λ = 700 nm. V = 1239.84 / 700 = 1.77 volts.
That is the voltage needed to light a red LED.

 

[A.T.]

.... but staright up knockout and then later form x rays? if yes, then is there a formula to derive the minimum amout of energy needed to do it, and is my claim even correct?

Aren't the energy levels of electrons in an atom usually given relative to an electron outside of the atom (or at infinity)? Those would be the energies that you need to kick the electron out of the atom.

 

[bananakicker456]

Aren't the energy levels of electrons in an atom usually given relative to an electron outside of the atom (or at infinity)? Those would be the energies that you need to kick the electron out of the atom.

i mean yeah. energy values are the amount of energy needed to free the electron (take it to infinity).

 

[bananakicker456]

Welcome to PF.


Easily, when an electron hits a target it may be absorbed, produce a photon of light, or another electron with a similar energy.

If you remove an electron from the surface of a metal, and then accelerate it through a voltage difference of 1 volt, it will gain an energy of 1 eV, (one electron volt). When that electron impacts a metal target, it may release that energy as a photon. The wavelength (colour) of that photon is inversely proportional to its energy.


If you specify the required wavelength, λ, you can work out the voltage difference needed to accelerate the electron to get a photon of that wavelength.
Energy; eV = 1239.84 / λ nm

X-rays have a wavelength of about 30 pm = 0.03 nm, so the required energy is 1239.84 / 0.03 = 41.3 keV, which will require a voltage of 41.3 kV. X-ray machines operate between about 20 kV and 80 kV.

To produce red light, λ = 700 nm. V = 1239.84 / 700 = 1.77 volts.
That is the voltage needed to light a red LED.

alright thank you so much

 

[A.T.]

i mean yeah. energy values are the amount of energy needed to free the electron (take it to infinity).

Exactly. So for the minimum energy needed to kick an electron out of the atom, look up the highest electron energy level (negative number closest to zero) for the specific element. When this hole is filled again by a slow electron, the photon emitted will have that energy.

 

[bananakicker456]

Exactly. So for the minimum energy needed to kick an electron out of the atom, look up the highest electron energy level (negative number closest to zero) for the specific element. When this hole is filled again by a slow electron, the photon emitted will have that energy.

yes i know that. my core question was that, " can an electron actually do that?" and i have got my answer. thank you

 

[A.T.]

my core question was that, " can an electron actually do that?"

Sure, there is no upper limit on the energy an electron can have.

 

[Rive]

..staright up knockout ...

Actually, it can be very useful when that happens. As the other electrons are jumping around to fill up the hole the emitted radiation is highly specific to that atom. Look up 'XRF spectrometer' if you are interested.

a metal ... is there a formula to derive the minimum amount of energy

That also has it's own tricks. If you ask for metals (and some other materials) instead of atoms then the energy needed to make electrons depart can be very low (even some heating can do the trick).
You need x-rays only to reach deeper into the atoms.