I keep on hearing on the news stuff like: "scientists are studying the background radiation left over from the big bang.." Wouldn't the radiation of dissapated by now? Or does the radiation that was produced have a extreemly long half life? (just to make a point i am not a creationist (as seen from my other posts) and i believe in a old age of the universe. I am just wondering how come we still have backgroujd radiation from soemthing that happened 20 bya. )

Also i uderstand the principleof half life, but it still makes no sense. Say a particle has a half life of 4 years. So in 4 years you will have half of that particle left. But in 4 more years wouldn't not be all gone? Or as the particle gets smaller does it decay slower? So in 4 years only half of the half is decaysed and so on. (but with the half of a half model, it is impossible to tottaly dissolve a particle of something, it will just get down to a infinitesimally small number and contine halving.) So the nuclear waste will always be there and will be radioactive forever, so there really is no safe place to keep it for the time being.

Am i right or tottaly on the wrong track?

__________________
GIYUL :-)
"It takes Thousands to fight a battle for a mile, Millions to hold an election for a nation, but it only takes One to change the world." - Dan Sandler 2002

Your confusion arises from the two different uses of the word 'radiation'. You're thinking of the kind of radiation emitted in nuclear decay - alpha and beta particles.

But 'radiation' also refers to electromagnetic waves -- that is, light in its many forms (radio, infrared, visible, UV, X-ray, and gamma). That's the kind of radiation that you should be thinking about. Think of the aftermath of the Big Bang as being very hot and bright, slowly dimming and cooling over the time scale of the universe.

Beskeptical is right about the radiation thing, but there is another point.
That is essentially the case--except that it is not half of the particle that decays, it is half of all of the particles. So, if you start with 8 billion particles, after a half life, there will be 4 billion particles. After another half life, there will be 2 billion particles.

Since there is half as many particles, they should give off half as much radiation--but often the results of the decay are more radioactive elements that have a different half life! You need those details to determine exactly what would happen.

So i am correct in saying that the rate of radiation changes with the amount of material present. For example: I have a box with 1 million radioactive particles and another box with 500,000 of the same radioctive particle. Would they have the same half live or would the 1st box decay to its half life faster that the 2nd box (or vice versa)?

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GIYUL :-)
"It takes Thousands to fight a battle for a mile, Millions to hold an election for a nation, but it only takes One to change the world." - Dan Sandler 2002

Thanks!! It makes sense now!! I forgot that radiation encompases x-rays, ect. also. (It has been 3 years since my last astronomy class) [img]/phpBB/images/smiles/icon_smile.gif[/img] It goes to show that you easily forget stuff that you learned. Plus having to memorize facts for 4 other classes does not help either.

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GIYUL :-)
"It takes Thousands to fight a battle for a mile, Millions to hold an election for a nation, but it only takes One to change the world." - Dan Sandler 2002

The half life for a particular material is fixed absolutely. That is why half lives are useful for dating stuff.

If the two boxes held the same material then the time taken for the material to half would be the same. ie if the half life was ten years then after ten years one box would have 500,000 undecayed particles and the other would have 250,000 undecayed particles.

The amount of radiation depends on the amount and type of particles present as stated above, as decayed particles are often still radioactive themselves.

Half life is statistics. Given an element with a half life of one year. If you have only one atom of this element, there is no way to predict when that atom will decay. It could decay now or it could last the life of the universe. If you have a kilogram of it you can state with certainty that half a kilo will have decayed in a year. After two years, another 1/4 kilo will have decayed, etc, etc. This relation will hold true as long as there is a statistically significant number of atoms present. Once you get down to a few atoms, the accuracy starts to break down.

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Be alert! The world needs more lerts.

<font size=-1>[ This Message was edited by: Kaptain K on 2002-10-14 15:13 ]</font>

Here's what the Great Detective had to say about this:

"You can, for example, never foretell what any one man will do, but you can say with precision what an average number will be up to." (Sherlock Holmes, The Sign of the Four)

Ah, the wonders of probability . . . check this out for a little snicker.

[img]/phpBB/images/smiles/icon_smile.gif[/img]

__________________
SeanF

"Ask to understand, but don't challenge unless you have the knowledge."--NEOWatcher

The contents of this post are ©2008 by SeanF and may not be copied or retransmitted in any form without the express written consent of SeanF

I thought a half-life meant how long a particular atom took to decay into a different atom. Wouldn't you still have the same amount of matter, only different types?

Yes, except for a very slight loss of mass due to the energy released with the decay. If you have a kilogram of uranium-238, after 4.5 billion years, you'll have half a kilo of uranium and half a kilo of lead. (Actually, there are some intermediate products, too, but those are comparatively short-lived.)

Don't try this at home. [img]/phpBB/images/smiles/icon_wink.gif[/img]

__________________
Everything I need to know I learned through Googling.

*hides 4.49999 billion year old stache of uranium-238* Try what at home?

<font size=-1>[ This Message was edited by: Jetmech0417 on 2002-10-16 01:38 ]</font>

I know we've all but exhausted this topic, but I was making lunch today and came up with yet another way to describe the half-life, quantum indeterminacy, etc.

Consider a bag of popcorn. We know that if we stick it in the microwave for 3 to 5 minutes, most of the kernels will be popped (or in the case of my microwave, most will be unpopped or charred, but that's beside the point). The "3 to 5 minutes" part is a better-documented time for radioisotopes that for popcorn, but anyway...
We can say with a high degree of certainty that after 5 minutes of thorough nuking, most of the kernels will have popped. The point is that if we choose one particular kernel we have no way of knowing whether it will pop after 1 minute, 2.5 minutes, or never. Now that I think of it, this may be a direct result of indeterminancy, the same as our decaying atoms, but don't quote me on it. Anyway, the metaphor is solid.

--BM

<font size=-1>[ This Message was edited by: BlueMan137 on 2002-10-16 18:47 ]</font>

Too late. [img]/phpBB/images/smiles/icon_smile.gif[/img]

The Copenhagen interpretation of quantum mechanics says that it has true indeterminancy, that there is no underlying physical cause of the decay. In your popcorn example, though, if we had more information, we could probably tell which kernels were going to pop first--maybe the ones with a higher water content, for instance.

That's kinda like a hidden variable. So, I'm liking that metaphor more and more. Can I use it?

Grapes,
The fundamental indeterminacy exists in solving the effect for cause starting from a three-body problem. So, "flow of time" equals "indeterminacy" in real world.

Three-body problem? Are we still talking about popcorn? [img]/phpBB/images/smiles/icon_smile.gif[/img]

That would be very little popcorn. [img]/phpBB/images/smiles/icon_wink.gif[/img]

JayUtah gave a very tasty description of radioactive decay at Apollohoax:

http://www.apollohoax.com/forums/vie...c=293&forum=17

Look for his 2001-07-09 Skittles post. It doesn't really deal with why certain elements decay, but it is an interesting approach.