How can X-Rays ionize air? (or other molecules)

[mahela007]

How can X-Rays ionize air? (or other molecules)

[insane_alien]

simple, they hit the other molecule. specifically the electrons of said molecule/atom.

 

the xray photon has sufficient energy to eject the electron from its orbital, much like if i stuck a cattleprod into you you'd jump out of your comfy chair.

 

this is ionization.

[mahela007]

That would be a positive ion right?

The whole problem occurred to me when I was reading about Millikans famous oil drop experiment. I read that he used X-Rays to charge some of the oil drops.. (they way I understood it the oil drops got a negative charge.. ) So how could the X-rays give the oil droplets a negative charge?

[insane_alien]

i'm not sure, i've done that experiment and x-rays were not used at all. the charge came from friction with the atomizer like how you can charge a plastic rod using a cloth.

 

i have never actually heard of it being done with x-rays.

[swansont]

That would be a positive ion right?

The whole problem occurred to me when I was reading about Millikans famous oil drop experiment. I read that he used X-Rays to charge some of the oil drops.. (they way I understood it the oil drops got a negative charge.. ) So how could the X-rays give the oil droplets a negative charge?

 

If you ionized the air, you have liberated electrons. They become attached to the oil drops.

 

And apparently he did do it this way

http://www.juliantrubin.com/bigten/millikanoildrop.html

http://chem.ch.huji.ac.il/history/millikan.html

[mahela007]

sorry to be so persistent .... but how do electrons "stick" to oil?

[swansont]

sorry to be so persistent .... but how do electrons "stick" to oil?

 

Like they'd stick to any other molecule — electromagnetically. Molecules can attract extra electrons; some do this better than others.

[mahela007]

whoops... I forgot my chemistry classes.

[Liquid Nitrogen]

How can X-Rays ionize air? (or other molecules)

 

The source ionizes the air and remove electric charges on the material.

[insane_alien]

bit late t the party aren't you?

 

also, when answering try to answer the question rather than just defining part of the question which presumably the poster already knew.

[McCrunchy]

Just to give you some numbers, a photon in the X-ray domain has an energy typically around 8000 eV, whereas an electron's binding energy can be at most -13.6 eV, level 1s 's energy in hydrogen. So you have plenty of energy to pick it from the atom.

 

This effect is put to practical use in X-ray gas detectors : they're filled with a neutral gas, typically xenon (which won't oxidize you're device once ionized), at a given pressure. When an X-ray goes through the gas chamber, it ionizes the gas. The released electrons are accelerated by an electric field to a cathode, where they read out as a small current.

 

McCrunchy

[insane_alien]

whereas an electron's binding energy can be at most -13.6 eV, level 1s 's energy in hydrogen. So you have plenty of energy to pick it from the atom.

 

its only -13.6 eV in hydrogen. helium is more like -25eV

[McCrunchy]

oops, indeed. Somehow I had imagined the electron-electron repulsion would make the ionization potential smaller than that of hydrogen ... but it's true we can almost neglect this repulsion to compute the energy levels [ and why is that again ? drifting from the initial subject ...]