Christa
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Physics Atom Question

Mon Mar 14, 2005 6:52 am

Just a quick question. What happens inside an atom when radiation is emitted?

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Chris
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flybyguy
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RE: Physics Atom Question

Mon Mar 14, 2005 7:02 am

Simple... It turns out that an atom, when it emits radiation loses an electron (or many electrons) These jettisoned electrons cause radiation. This is also the reason why sodium burns yellow. Because it emits electrons (radiation ) within the visible electromagnetic spectrum at a wavelength around yellow (don't remember the exact number).

Nuclear fission is just a step above that. All we do is start shooting heavy particles at the nucleus of an atom (neutrons etc.) and if our momentum is great enough we bust the atom open and cause neutrons from that "busted atom" to strike the nuclei of other atoms, causing a chain reaction.
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aloges
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RE: Physics Atom Question

Mon Mar 14, 2005 7:06 am

What radiation? Alpha, Beta, Gamma?

Alpha rays are Helium nuclei, so I assume each atom that emits Alpha "rays" loses two protons and two neutrons; I don't know what happens to the electrons.

Beta rays are electrons, so the atoms lose those. Again, no idea what happens to the then surplus protons.

Gamma rays are similar to light; at least they don't consist of relatively large particles like Alpha and Beta rays do.
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aloges
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RE: Physics Atom Question

Mon Mar 14, 2005 7:10 am

Quoting Flybyguy (Reply 1):
This is also the reason why sodium burns yellow. Because it emits electrons (radiation )

Sorry, but Sodium doesn't become radioactive once you put it in a flame. It colours the flame because the energy absorbed by the Sodium atoms puts electrons to higher levels, which then "fall down" again. The energy set free by that "falling" is then visible in the form of light.
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backfire
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RE: Physics Atom Question

Mon Mar 14, 2005 7:17 am

Quoting Flybyguy (Reply 1):
Simple... It turns out that an atom, when it emits radiation loses an electron (or many electrons) These jettisoned electrons cause radiation.

Flybyguy - I think you need to go back to physics class.

A sodium atom emits radiation when it is releasing energy in order to attain a more stable energetic state.

When the atom is in an excited state its electrons are occupying energy levels than normal. In order to drop back to their normal energy levels, the excess energy has to be released - and it's released in the form of photons. The electrons are NOT ejected.

[Edited 2005-03-13 23:19:02]
 
MD11Engineer
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RE: Physics Atom Question

Mon Mar 14, 2005 7:36 am

Again: what kind of radiation? Electromagnetic radiation from the visible spectrum up to x-rays is being emitted by the electrons "surrounding" the nucleus.
Typicaly electrons get kicked to higher energy levels (get excited) and emit the excess energy when "falling" back to their original level.
Infrared radiation is usually the result of oscillations of atoms in molecules, around interatom (chemical) bonds.
Alpha radiation occurs when a certain instable nucleus breaks up and emits an Alpha particle, consisting of two neutrons and two protons each (a helium nucleus, positively charged). The resulting nucleus will be more stable, but will be excited as well, usually loosing the excess energy via a gamma photon.
Beta minus radiation occurs if a neutron breaks up into an electron, a proton and a neutrino. The proton will form part of the resulting new nucleus (an element one position further up the periodic table), while the electron will be emitted from the nucleus with high energy, as will be the neutrino. Since neutrinos rarely interact with matter, in most cases it will not be detected. Again, excess energy will be emitted via a Gamma quantum.
Another source of gamma radiation is to excite a nucleus e.g. through absorbtion of gamma radiation of resonant frequency and then letting it be emitted, similar to flourescence. This is used in Mössbauer spectroscopy (the resonace frequency of a nucleus is dependend on the chemical bond of the atom and will vary slightly).
Neutron radiation usualy gets emitted by breaking up nuclei, e.g. in a nuclear fission reactor U235 gets bombarded with slow (thermic) neutrons, the impact of a neutron on a U235 nucleus will cause the new compound nucleus ( U236, very instable) to oscillate and break up into Y96, I139 and 3 neutrons. These, being instable themselves, will again break up, emitting mostly beta radiation until they reach the stable nuclei of Ba138 and Mo 95. Another source would be to bombard Be 9 with Alpha particles, causing it to emit neutrons ( a neutron source we used during our basic experimental physics lab class in university to irradiate other elements, e.g. silver, with the neutrons to cause them to change. We then measured the resulting halflifes and gamma spectra of the resulting new elements).

Jan
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flybyguy
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RE: Physics Atom Question

Mon Mar 14, 2005 7:38 am

Quoting Backfire (Reply 4):
A sodium atom emits radiation when it is releasing energy in order to attain a more stable energetic state.

My bad... in my rush to answer the question I confused the term "emitting light" with emitting electrons.

It is true that the light emitted is electromagnetic radiation, but that the radiation is released due to falling to lower energy states, not jetissoning electrons.

My apologies for the confusion, Christa.
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MD11Engineer
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RE: Physics Atom Question

Mon Mar 14, 2005 7:45 am

Another thing: Most of what goes on at atomic level can´t be described with macroscopic everyday terms. Most of the stuff is very abstract and ideas like electrons being little spheres circling the nucleus are very coarse and inaccurate. Many aspects of quantum mechanics go against human intuition, but prove to be physically accurate and measurable

Jan
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aloges
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RE: Physics Atom Question

Mon Mar 14, 2005 7:54 am

Quoting MD11Engineer (Reply 7):
Most of the stuff is very abstract and ideas like electrons being little spheres circling the nucleus are very coarse and inaccurate.

Correct, a better description than Bohr's Model would be the Orbital Model which essentially says that only spaces inside of which the electrons are most likely to be found can be defined. It's difficult at first, but when you begin to understand it, it explains nicely how e.g. double bonds between carbon atoms influence molecules.
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MD11Engineer
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RE: Physics Atom Question

Mon Mar 14, 2005 8:00 am

Yes, but try to explain to a layperson why an electron can be at the same time WITHIN the nucleus and 20 km away, while still belonging to the same atom, being everywhere and nowwhere at the same time. Or the Fermi gas of electrons within a cristal, a electron wave function spread over the whole cristal. Get into probability functions and Heisenberg´s principle of uncertainity and by then you´ve lost most people.

Jan
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aloges
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RE: Physics Atom Question

Mon Mar 14, 2005 8:05 am

Quoting MD11Engineer (Reply 9):
and by then you´ve lost most people.

including myself...

However, I think I'd be able to understand that stuff if I really cared enough and needed to. I love chemistry, which most people I know hate, and there isn't much that motivates me as much as a chemistry problem does.
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MD11Engineer
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RE: Physics Atom Question

Mon Mar 14, 2005 8:11 am

I studied Chemistry almost to BS level (ran out of money unfortunately), and I loved the quantum mechanics class.... I also did Physics for a few years.

Jan
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Christa
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RE: Physics Atom Question

Mon Mar 14, 2005 8:31 am

Thanks for your help.. but..nobody has answered my question. It does not actually ask for any specific type of radiation.

So.. the answer is?

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Chris
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aloges
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RE: Physics Atom Question

Mon Mar 14, 2005 8:35 am

Quoting Christa (Reply 12):
So.. the answer is?

...not that simple at all. If you take the battery out of a car, are the same things going to happen inside that car that happen inside one without tyres?

It depends on the type of radiation and cannot be generalised.
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Christa
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RE: Physics Atom Question

Mon Mar 14, 2005 8:47 am

I think that the question is looking for a general answer. It is the first question on my Physics paper. I've finished the rest of the paper. However, as usual it is classed as a very easy question or so they say but they normally have a stupid or silly answer that in a way is incorrect.

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Chris
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Klaus
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RE: Physics Atom Question

Mon Mar 14, 2005 8:52 am

Well, in the most general terms, the atom loses energy; In some cases it also loses mass (depending on the kind of radiation).

[Edited 2005-03-14 00:53:40]
 
MD11Engineer
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RE: Physics Atom Question

Mon Mar 14, 2005 8:57 am

Klaus,

Don´t forget Einstein.... if it looses mass, it also looses energy E=mc²  Wink

Jan
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Klaus
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RE: Physics Atom Question

Mon Mar 14, 2005 9:03 am

I knew someone would have to nitpick here... Big grin
But I´m still not entirely certain you´re exactly right: Mass has an energy equivalent, but it is not energy (under "normal" circumstances). You´d still need a conversion to switch between the two sides of the equation, don´t you?
 
aloges
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RE: Physics Atom Question

Mon Mar 14, 2005 9:11 am

Quoting Klaus (Reply 17):
You´d still need a conversion to switch between the two sides of the equation, don´t you?

You mean the one called "BOOOOOOOOOOOOMMM"?  Wink
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Klaus
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RE: Physics Atom Question

Mon Mar 14, 2005 9:14 am

...being the most "popular" one, yes. Big grin
 
MD11Engineer
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RE: Physics Atom Question

Mon Mar 14, 2005 10:57 am

Seriously, on nuclear level and below almost all energy changes give a noticable change of mass.

Jan

[Edited 2005-03-14 02:57:46]
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MD11Engineer
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RE: Physics Atom Question

Mon Mar 14, 2005 11:02 am

Klaus,

You know the basic formula of quantum physics:

E=h*nu (sorry, can´t get Greek characters on my ´puter)

h= Planck´s constant
nu= frequency of the radiation.

so you can say:

E= h*nu=mc²
every photon leaving a nucleus reduces it´s mass, except when energy was previously added (e.g. through nuclear resonance).

Jan
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