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Topic: ?- and ?-  (Read 14851 times)

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Offline constant thinker

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?- and ?-
« on: May 10, 2005, 09:51:50 PM »
I see ?- and ?- all the time. The problem is I don't know what they mean. Can someone please help.
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Offline Mitch

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Re:?- and ?-
« Reply #1 on: May 10, 2005, 11:06:23 PM »
very vague question
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Re:?- and ?-
« Reply #2 on: May 11, 2005, 01:41:45 AM »
I think you might be referring to alpha and beta particles.

a is an 42He nucleus. it is emitted during radioactive decay and is able to be stopped by a sheet of paper & it travels at 10% of the speed of light. it only travles a few centimetres in the air.

? is a 0-1e i.e. a highly charged electron that travels at 90% of the speed of light. and can be stopped be aluminium a few centimetres thick. These can travel up to 30cm in the air.

I hope this is what you were after. The question wasnt very clear...
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Offline Borek

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Re:?- and ?-
« Reply #3 on: May 11, 2005, 03:52:39 AM »
In what context do you see them?
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Offline xiankai

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Re:?- and ?-
« Reply #4 on: May 11, 2005, 06:09:30 AM »
 i thought alpha particles were the equalivent of a helium nucleus, but NOT a helium nucleus itself?

same goes for beta, i also thought it was just an equalivent of an electron :/ and do electrons really travel that fast? i heard soemwhere that elctrons move slow, like a few cm per sec.
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Offline Borek

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Re:?- and ?-
« Reply #5 on: May 11, 2005, 06:58:48 AM »
Quote from: xiankai on May 11, 2005, 06:09:30 AM
i thought alpha particles were the equalivent of a helium nucleus, but NOT a helium nucleus itself?

That's exatcly the same particle - two neutrons and two protons.

Quote
same goes for beta, i also thought it was just an equalivent of an electron

As above - it is just an electron.

Quote
and do electrons really travel that fast? i heard soemwhere that elctrons move slow, like a few cm per sec.

It depends. cm/s is a translational speed of electron in the wire in the lamp on your desk. Electron in accelerator can be accelerated almost to speed of light.
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Corvettaholic

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Re:?- and ?-
« Reply #6 on: May 11, 2005, 01:02:17 PM »
About the beta particles, I thought it was more than just an electron. Read somewhere that its an electron AND an anti-neutrino? But as I understand it, neutrino's will just zip right through anything and they're good for nothing particles currently. Just kinda neat to watch them exist.
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Offline Donaldson Tan

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Re:?- and ?-
« Reply #7 on: May 11, 2005, 03:08:58 PM »
beta particles also refer to positrons, ie. anti-electrons

in organic chemistry, alpha and beta are carbon positions.
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Offline movies

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Re:?- and ?-
« Reply #8 on: May 11, 2005, 03:30:32 PM »
Some other places alpha and beta show up:

- Sign of electron spin in quantum mechanics
- proximity to a certain atom or functionality (e.g. the alpha carbon of a carbonyl group, alpha,beta-unsaturated carbonyls, beta-hydride elimination in organometallic chemistry)
- antiquated method of describing stereochemistry at a chiral center (If the structure is drawn such that the functionality in question goes back into the page, it is alpha, if the functionality comes out of the page, it is beta.  Note that this descriptor depends entirely on how the structure is drawn.)
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Offline Borek

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Re:?- and ?-
« Reply #9 on: May 11, 2005, 04:34:29 PM »
Quote from: Corvettaholic on May 11, 2005, 01:02:17 PM
About the beta particles, I thought it was more than just an electron. Read somewhere that its an electron AND an anti-neutrino?

Beta particle is just electron. Some kind of neutrino is a byproduct of beta decay.
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Offline constant thinker

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Re:?- and ?-
« Reply #10 on: May 11, 2005, 08:04:55 PM »
I can't find the website that triggered me to ask the question. It was talking about nuclear decay though so it probably refers to the alpha and beta particles. I realized it was vague and apoligize. I should have quoted the website when I started this. Thanks.

Would anyone happen to know what gamma radiation is made of? I've only read it was energy released during the realignment of the nucleus not what it was made of.
« Last Edit: May 11, 2005, 08:06:27 PM by constant thinker »
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Offline jdurg

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Re:?- and ?-
« Reply #11 on: May 11, 2005, 08:27:57 PM »
Gamma rays are basically high energy photons.  The nucleus emitting a gamma ray is akin to an excited electron emitting a wavelength of light when it falls back down into the ground state.  In a nuclear reaction, the nucleus winds up in an excited state when a decay occurs, so it will shoot off a gamma ray as it settles back into a ground state.  Thinks of a gamma ray as a VERY high energy, VERY short wavelength of light.
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Offline constant thinker

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Re:?- and ?-
« Reply #12 on: May 12, 2005, 03:36:02 PM »
Ok. Cool thanks for the help.
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"The nine most terrifying words in the English language are, 'I'm from the government and I'm here to help.' " -Ronald Reagan

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