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Author Topic: A burning question .....  (Read 2717 times)

Offline antonymous

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A burning question .....
« on: 19 March, 2013, 04:08:04 PM »
.....that has just crossed my mind.
Stars such as our own sun are powered by thermo-nuclear fusion. At the end of their lives we are told that they collapse and eventually explode and all the material that exists at the core is discharged into space as debris which then goes on to form planets, meteors, asteroids - whatever, in fact we are told that we humans are made up of mass created thus. Given the thermo-nuclear origins of this material how come we are not radio-active?
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Offline seacommander

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Re: A burning question .....
« Reply #1 on: 19 March, 2013, 05:16:32 PM »
I am no nuclear physicist Ant but I can only offer the notion that the vast majority of the erstwhile radioactive material ends up as non-radioactive isotopes of elements after releasing alpha, beta gamma etc radiation. Perhaps in a similar way that Uranium can eventually end up as stable Lead. The timescales involved in which changes take place in the universe are immense - so we are told - and probably considerably exceed the half life and even total decay of many if not all known radioactive isotopes.

A rough 'back of fag packet' calculation indicates to me that even the longest half lives for radioactive isotopes are in the region of 2 billion years which I believe is within the timescales of the unverse as we know it - sorry as eminent scientists think they know it!!
« Last Edit: 19 March, 2013, 05:25:41 PM by seacommander »

Offline antonymous

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Re: A burning question .....
« Reply #2 on: 19 March, 2013, 11:06:02 PM »
 I take your point about half-lives  but there is still some radio-active uranium within the earth and it should be well beyond its half-life span given the age of the planet. ??
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Offline seacommander

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Re: A burning question .....
« Reply #3 on: 19 March, 2013, 11:20:48 PM »
As I said Ant, I am not a nuclear physicist so can't take this any further. Except, that your point raises an interesting question about the age of the earth given the fact that there are still naturally occuring deposits of radioactive isotopes that should have long since decayed if they originated from the postulated Big Bang. Uhm.

Offline antonymous

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Re: A burning question .....
« Reply #4 on: 19 March, 2013, 11:38:02 PM »
Not necessarily right back to the big bang - our solar system could have formed from the debris of a later dying star which means a shorter period for the Uranium to turn in to Pb. But still a mighty long time ago.
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imfeduptoo

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Re: A burning question .....
« Reply #5 on: 20 March, 2013, 08:11:43 AM »
what a good question.

According to this we are slightly radioactive.

http://hps.org/publicinformation/ate/faqs/faqradbods.html

Offline antonymous

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Re: A burning question .....
« Reply #6 on: 20 March, 2013, 08:56:44 AM »
what a good question.

According to this we are slightly radioactive.

http://hps.org/publicinformation/ate/faqs/faqradbods.html

Well I'll be jiggered MrsToo - whoever would have thought it - it adds new meaning to the expression " having a glowing future"!  ;D
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Offline P-Kasso2

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Re: A burning question .....
« Reply #7 on: 20 March, 2013, 09:01:10 AM »
So we are all slightly radioactive? That explains why Mrs P-K glows in the dark when she comes home after a session with the ladies in the Brewers Arms.
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Offline antonymous

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Re: A burning question .....
« Reply #8 on: 20 March, 2013, 09:05:48 AM »
So we are all slightly radioactive? That explains why Mrs P-K glows in the dark when she comes home after a session with the ladies in the Brewers Arms.
Facepalm
Is it true that she is banned from The Elephant & Castle? Or is it just a vicious rumour I just started?
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Offline P-Kasso2

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Re: A burning question .....
« Reply #9 on: 20 March, 2013, 09:11:49 AM »
She was banned but only because her radioactive level kept setting off the smoke detectors and activating the sprinkler system in the main bar annoyed the other regulars who moaned that their beer was already watered down quite enough. ;)
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Offline antonymous

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Re: A burning question .....
« Reply #10 on: 20 March, 2013, 03:31:31 PM »
As I said Ant, I am not a nuclear physicist so can't take this any further. Except, that your point raises an interesting question about the age of the earth given the fact that there are still naturally occuring deposits of radioactive isotopes that should have long since decayed if they originated from the postulated Big Bang. Uhm.

Having thought about this apparent anomaly - if you think about it mathematically - if you reduce any quantity by half over a period of time, followed by another halving over the same period and continue the process ad infinitum you never reach zero! 1/2,1/4,1/8, .........1/10^20 etc i.e. there will always be an infinitely small amount left after any multiple of periods of time.
PHEW! my brain hurts now- I'll have to have a lie down. rolls eyes
« Last Edit: 20 March, 2013, 03:37:15 PM by antonymous »
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Offline siasl

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Re: A burning question .....
« Reply #11 on: 20 March, 2013, 04:49:59 PM »
Uranium (U-238) has a half life in the billions of years, so is quite useful in working out the age of the earth (I think the consensus is somewhere around 16billion years old).

It gets more complicated, too, as there are things called "decay chains" whereby an atom of one element decays into an atom of another element which decays into an atom of another element and so on :-)

Note that decay is a probabilistic term - so if an atom has a half life of a minute, then one minute later there isn't half an atom, merely a 50% chance that it has decayed (and there are different ways of decaying)

Offline antonymous

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Re: A burning question .....
« Reply #12 on: 20 March, 2013, 05:26:45 PM »
Ah! Yes - its all becoming clear now.
"The nuclides found [on earth] naturally comprise not only the 288 primordials, but also include about 51 more short-lived isotopes (defined by a half-life less than 80 million years, too short to have survived from the formation of the Earth) that are daughters of primordial isotopes (such as radium from uranium); or else are made by energetic natural processes, such as carbon-14 made from atmospheric nitrogen by bombardment from cosmic rays."

Nuclides: "A nuclide (from nucleus) is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state.[1]"
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