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Author Topic: Why do we add elements to the periodic table that decay instantly?  (Read 1778 times)

Offline thedoc

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Luke Pullar asked the Naked Scientists:
   It seems odd that new elements can be created and added to the periodic table even though they decay in a vanishingly small increment of time. They're not useful in any way, and they cannot exist outside of a minuscule fraction of a second under laboratory conditions. Why add them?
What do you think?
« Last Edit: 27/09/2016 09:53:02 by _system »


 

Offline evan_au

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You could say the same about the Olympics. Someone ran (or swam or jumped) a teeny bit better than someone else. It's not useful in any way, and it doesn't exist outside the Olympic stadium. Why give them a gold medal??

It's mostly human competitiveness - my particle accelerator (or gamma ray spectrometer or biceps) are bigger than yours...

But there is some use in it - there is some debate about the energy levels inside a nucleus, and how many protons and neutrons will fill an energy shell. This affects the energy of the nucleus and its lifetime. There is a hypothesis that if you could create an atom with a filled shell of both protons and neutrons, it might be exceptionally stable.

In theory, some such atoms could be left behind on Earth after a neutron star collision, but careful searches have failed to find any. So people are trying to make them in the lab.
 

Offline William McC

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Luke Pullar asked the Naked Scientists:
   It seems odd that new elements can be created and added to the periodic table even though they decay in a vanishingly small increment of time. They're not useful in any way, and they cannot exist outside of a minuscule fraction of a second under laboratory conditions. Why add them?
What do you think?

Years back universal scientists declared that the earths proximity to the sun, causes the higher elements to become unstable. Even when cooled the radiation that passes right through the earth, is just too much for those larger elements to deal with. They are too unstable to positively identify. Scientists from different areas of earth testing these substances found that they could not get similar results. That is when they declared them too unstable to be safely used. Back then radiation that was detectable was considered slow moving or not at natural undetectable normal super high velocity ambient radiation.

The universal scientists stopped declaring elements at Uranium. They declared the rest radio active isotopes. Because crazy fools ran the world and the dark ages were announced, most never understood how important it is to keep radio active materials from getting into everything.

Sincerely,

William McCormick
 

Offline evan_au

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I heard an interview with a researcher who was studying Nobelium.
It's half-life is around 2.5 seconds, and they can produce about 10 atoms per second.

They were using lasers to study the electron energy levels. Apparently, the intense electric fields around these very positive nuclei are expected to produce some unusual electron behaviors which are not seen with lighter elements.

See: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature19345.html
 
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Offline zx16

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Do these new "elements" which last only for seconds or microseconds, exist anywhere else in the Universe, except in laboratories on Earth?

If not, I agree with Luke, they're not real "elements" at all. Just something we've fiddled about with, and cooked up locally.  Surely the fact that they disappear so quickly, rules them out as real elements. How can something that vanishes in a split-second, be regarded as anything more than a terrestrial artefact.

Shouldn't a real element stay around for the duration of the Universe, so that it could always be found in the Universe, without relying on a terrestrial source?

 

Offline Janus

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Do these new "elements" which last only for seconds or microseconds, exist anywhere else in the Universe, except in laboratories on Earth?

If not, I agree with Luke, they're not real "elements" at all. Just something we've fiddled about with, and cooked up locally.  Surely the fact that they disappear so quickly, rules them out as real elements. How can something that vanishes in a split-second, be regarded as anything more than a terrestrial artefact.

Shouldn't a real element stay around for the duration of the Universe, so that it could always be found in the Universe, without relying on a terrestrial source?

Many "Natural" elements do not have infinite lifetimes.  Carbon 14 is constantly forming being formed in our atmosphere and decaying, Uranium is also a "naturally" occurring element which decays, and in doing so creates other short-lived elements. I don't think it makes much sense to say that naturally occurring Radium is not a "real element" just because its most stable isotope has a half-life of just 1600 years.   
As far as these other element existing elsewhere in the universe, If we can make them here on the Earth, then surely they are formed in the supernovae that forged all the other elements including the Uranium we still find in our own crust.   
That's one reason for trying to make these elements on Earth; to learn the rules that determine just what is possible in terms of element formation and to verify whether or not our understanding of what these rules are stand up to experiment.
 
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Offline chiralSPO

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Do these new "elements" which last only for seconds or microseconds, exist anywhere else in the Universe, except in laboratories on Earth?

If not, I agree with Luke, they're not real "elements" at all. Just something we've fiddled about with, and cooked up locally.  Surely the fact that they disappear so quickly, rules them out as real elements. How can something that vanishes in a split-second, be regarded as anything more than a terrestrial artefact.

Shouldn't a real element stay around for the duration of the Universe, so that it could always be found in the Universe, without relying on a terrestrial source?

It is not obvious to me why natural occurrence is necessary for something to be an element. We can synthesize molecules that have never before existed anywhere in the universe, but that doesn't mean that they aren't molecules (some of these are also delicate, and decompose quickly.)

Certainly there is something less "fundamental" about elements that exist only on Earth, but these synthetic atoms have unique numbers of protons and neutrons, and are therefore new elements.
 
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Offline evan_au

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Quote from: zx16
Do these new "elements" which last only for seconds or microseconds, exist anywhere else in the Universe, except in laboratories on Earth?
Supernovas are thought to cast elements up to iron and cobalt into space.
- Measurement of the light output of supernovas shows a reduction in intensity over time which is related to the radioactive decay of Cobalt 56 (half-life: 77 days).
- Trace amounts of Iron 60 are found on Earth. With a half life of around 2.6 million years, it is thought that this must have originated in a supernova that occurred in the vicinity of the Sun
- Elements much heavier than iron, like gold, uranium and Nobelium are though to be cast into space during the collision of neutron stars. Nobelium doesn't last very long, but the gold is a valuable commodity on Earth.

Quote
Shouldn't a real element stay around for the duration of the Universe, so that it could always be found in the Universe, without relying on a terrestrial source?
It is thought that elements produced in the big bang included Hydrogen, Helium and trace amounts of Lithium.

All the rest have not been around for the age of the universe, but were formed in later stars, supernovas, neutron star collisions and physics labs.
« Last Edit: 22/10/2016 08:18:58 by evan_au »
 

Offline zx16

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Thanks to evan, janus and chiral for all your valuable comments.

The point that "heavy" elements are always getting created in supernovae, is one that I realised with a head-smack after posting.  But I didn't to bother to edit, as it was obviously bound to get picked up.

However, going back to the original question, about whether very transient, swiftly-decaying elements should be added to the Periodic Table.  I would say not, because it would make the list of "elements" too long.

If I might cite a comparable example from Astronomy.  The list of "planets" in the Solar System was eight, until the year 1930.  In that year, a new "planet", Pluto, was discovered.  Right from the time of its discovery, there were doubts whether "Pluto", should properly be added as a planet, as it's very small.  However it got accepted until 2006, when the IAU threw it out. 

This was because a lot of new objects were being discovered, like Eris, which is bigger than Pluto. So if you accept Pluto as a planet, you'd have to accept Eris too. And there were more objects of comparable size.  You could eventually end up with a list of 40 or 50 "planets".  Which is far too long.

So the IAU demoted Pluto to dwarf status.  Now astronomers (well, most of them), only acknowledge eight planets on the list. Pluto and the rest are regarded as interesting, but not genuine.

Couldn't this approach be adopted with the Periodic list of elements?  That's to say,  physicists and chemists, should only recognise 92 genuine elements, the rest being merely interesting?


 

Offline Janus

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Thanks to evan, janus and chiral for all your valuable comments.

The point that "heavy" elements are always getting created in supernovae, is one that I realised with a head-smack after posting.  But I didn't to bother to edit, as it was obviously bound to get picked up.

However, going back to the original question, about whether very transient, swiftly-decaying elements should be added to the Periodic Table.  I would say not, because it would make the list of "elements" too long.

If I might cite a comparable example from Astronomy.  The list of "planets" in the Solar System was eight, until the year 1930.  In that year, a new "planet", Pluto, was discovered.  Right from the time of its discovery, there were doubts whether "Pluto", should properly be added as a planet, as it's very small.  However it got accepted until 2006, when the IAU threw it out. 

This was because a lot of new objects were being discovered, like Eris, which is bigger than Pluto. So if you accept Pluto as a planet, you'd have to accept Eris too. And there were more objects of comparable size.  You could eventually end up with a list of 40 or 50 "planets".  Which is far too long.

So the IAU demoted Pluto to dwarf status.  Now astronomers (well, most of them), only acknowledge eight planets on the list. Pluto and the rest are regarded as interesting, but not genuine.

Couldn't this approach be adopted with the Periodic list of elements?  That's to say,  physicists and chemists, should only recognise 92 genuine elements, the rest being merely interesting?

Because half-life doesn't make a good parameter by which to judge whether something is an element or not.  With Pluto, we didn't have a clear cut definition for what a planet was until the IAU decided on the most recent definition.

We do have a good definition for element.

Besides, using half-life would not be consistent with a cut off at element 92.   Neptunium, Plutonium, and Americium all have Isotopes with half-lives that are longer than the longest lived isotopes of a number of elements with atomic numbers less than 92, the shortest being Americium at 7270 yrs. Compare this to Actinium, Radium, Francium, Radon, astatine and Polonium, The longest lived isotope in this group belongs to Radium at 1600 yrs, and the longest lived isotope of Francium (atomic number 87) is a mere 22 min.
Why include it as a "real" element while rejecting higher numbered elements with more stable isotopes?
 
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Offline zx16

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OK Janus, many thanks for your post - you've (almost) persuaded me.

Especially when you cite Francium, whose longest-lasting isotope , -223, has a half-life of only 22 minutes!  That did surprise me.  Is there much Francium in the Universe?
But if it's accepted as an entry in the Periodic Table, then I suppose there's not much more to say.

Except I still feel that "elements" with a far shorter half-life, measured in mere milliseconds, don't really belong in a practical Periodic Table.

Thanks again for your post, which I appreciate.

 

Offline chiralSPO

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Let us also not forget Technetium, which is smack dab in the middles of the periodic table. There are no stable isotopes, and the longest lived has a half life of 4 million years (other isotopes have half lives in the days to weeks range, and some decay even more swiftly). https://en.wikipedia.org/wiki/Technetium
 

Offline chiralSPO

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Now, there are some "exotic" elements that I am unsure of whether to include or not. These are atoms that contain particles other than protons, neutrons and electrons (sometime in addition to these standard particles, sometimes without any). Many examples include muons substituted for electrons. These decay after only a few microseconds, but that is an eternity for some physical processes that occur on the atomic scale (for instance we can do spectroscopy on these to measure the energy levels, and this is even a tactic for performing "cold" fusion).

https://en.wikipedia.org/wiki/Exotic_atom
 

Offline Bored chemist

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Let us also not forget Technetium, which is smack dab in the middles of the periodic table. There are no stable isotopes, and the longest lived has a half life of 4 million years (other isotopes have half lives in the days to weeks range, and some decay even more swiftly). https://en.wikipedia.org/wiki/Technetium

Promethium is similar. The longest lives isotope is 145Pm with a half life of about 18 years.
If we didn't put the radioactive elements in the table, it would have holes in it.
 

Offline zx16

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How far could the Periodic Table be extended, if we allowed all possible combinations of protons, electrons and neutrons to be included?

Would it have hundreds of "elements"?
 

Offline chiralSPO

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If we define elements as atoms with unique numbers of protons, then there are already 118 known elements. If we include all isotopes (unique numbers of protons and neutrons), then there are already several hundred. unique nuclei known. I'm sure there are all kinds of crazy elements formed during catastrophic events involving neutron stars, even if they are only short-lived.
 
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Offline zx16

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If we define elements as atoms with unique numbers of protons, then there are already 118 known elements. If we include all isotopes (unique numbers of protons and neutrons), then there are already several hundred. unique nuclei known. I'm sure there are all kinds of crazy elements formed during catastrophic events involving neutron stars, even if they are only short-lived.

Thanks chiral, when you mention "crazy elements", I take it you're envisaging that such elements, even if short-lived and formed in catastrophic events, would still have nuclei containing only particles of "standard matter", ie protons and neutrons.

Might there be elements whose nuclei are made of particles of "Dark Matter".  I mean, can Dark Matter form atoms, and "elements", which could be arranged into a kind of "Dark Matter Periodic Table".

Is there any way we can find out?

 

Offline evan_au

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Quote from: zx16
Might there be elements whose nuclei are made of particles of "Dark Matter"?
That is a bit difficult to say, since we don't know what Dark Matter is!
Or, more accurately, it is definitely made up of a variety of different things, but we haven't positively identified the majority of it.

For example, the observed effects of Dark Matter has contributions from:
- Thinly-spread normal stars: These may have been ejected by galaxies during collisions, and be spread so thinly through space that they don't show up in astronomical telescopes behind the glow of Earth's atmosphere. These are made up of regular nuclei.
- Free-floating planets or the dark cinders of small burnt-out stars: These are made up of regular atoms, made of standard matter.
- Neutron stars: These are like a single huge nucleus, with the mass of the Sun
- Black holes: Our equations don't work at the center of a black hole. But it is safe to say that it can't form a stable nucleus, as it will swallow the rest of the nucleus.
- Relic Neutrinos from the Big Bang: These interact only with the weak nuclear force. They ignore the strong nuclear force that holds the nucleus together, so they can't form a stable part of a nucleus (and even if they did, they would be so light that they would not affect its properties in any measurable way). They can be emitted by normal matter during nuclear decay, and they can (infrequently) be absorbed or scattered by normal matter, making them (slightly) detectable. They even ignore the electromagnetic force that holds the atom together. Unbound, they fly straight through matter at enormous velocities.
- Unknown particles that don't even interact via the weak nuclear force (this is the theory that most particle physicists think is most likely at present): These would be even more ghostly than neutrinos, even less likely to form part of a nucleus with standard matter, and even less likely to be detected. 
- Small deviations from Einstein's gravity on large scales (this theory is not very popular): This theory has no need for Dark Matter particles.

Quote
"Dark Matter Periodic Table"
If Dark Matter is primarily made of unknown/hard-to-detect particles (as many cosmologists expect), there is nothing preventing these (unknown) particles from experiencing an (unknown) 5th force which would bind them together in a periodic table of their own, forming the equivalent of a Dark Matter periodic table.

And if these unknown particles have antiparticles, they may annihilate, perhaps releasing energy in the form of gamma rays. Several searches of the gamma-ray spectrum are underway at present, in an attempt to detect such events.

See: https://en.wikipedia.org/wiki/Dark_matter#Composition
« Last Edit: 29/10/2016 22:42:45 by evan_au »
 
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Offline syhprum

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Is not the reason for the hunt for elements with ever shorter lives the dream that past 118 there maybe at 126 "an island of stability" with a relatively long life and interesting properties. 
 

Offline Bored chemist

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We don't add things to the periodic table; it's already there. We just make the things that are in it.
 

Offline zx16

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Is not the reason for the hunt for elements with ever shorter lives the dream that past 118 there maybe at 126 "an island of stability" with a relatively long life and interesting properties.

Yes, and perhaps this "dream" as you call it, is a true intuitive reaction against the very idea of so-called "Dark Matter".

What if "Dark Matter" isn't some alien thing made of weird particles, but consists of ordinary proton/neutron elements in the "island of stability"  -  at 126, and possibly other "islands" beyond.  Elements like these, would probably have long-lives and "interesting properties", as you say. 

Such properties might account for observations such as anomalous galactic rotations. These are currently ascribed to the presence of "Dark Matter". Couldn't they be due to the presence of "super-heavy" elements which are higher in the Periodic Table than we've yet discovered?



 

Offline zx16

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We don't add things to the periodic table; it's already there. We just make the things that are in it.

I salute you sir, as an apparent true "Aristotelian"!   Aristotle said the very same thing -  that the idea of a "table", is already there.  It exists as an eternal, pure, thought-form : "tableness".  All we do, when we make an actual dining-room table, is make the wooden bits, nails, glue etc, that are in it.

Mind you, you can't really be an Aristotelian if you're a chemist, as his chemical ideas about there being just "four elements" - Earth, Air, Fire and Water, are unsound.

 

Offline chiralSPO

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Is not the reason for the hunt for elements with ever shorter lives the dream that past 118 there maybe at 126 "an island of stability" with a relatively long life and interesting properties.

Yes, and perhaps this "dream" as you call it, is a true intuitive reaction against the very idea of so-called "Dark Matter".

What if "Dark Matter" isn't some alien thing made of weird particles, but consists of ordinary proton/neutron elements in the "island of stability"  -  at 126, and possibly other "islands" beyond.  Elements like these, would probably have long-lives and "interesting properties", as you say. 

Such properties might account for observations such as anomalous galactic rotations. These are currently ascribed to the presence of "Dark Matter". Couldn't they be due to the presence of "super-heavy" elements which are higher in the Periodic Table than we've yet discovered?

I think this is highly unlikely. Dark matter is invisible to the entire electromagnetic spectrum to the extent that we have probed it (between 1012 and 103 meter wavelengths). Atomic or molecular matter made of such heavy atoms would surely absorb somewhere within this region. This apparent non-interaction with electromagnetic energy is why people have posited particles such as neutrinos as explanations of dark matter.
 
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Offline zx16

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Thanks chiral,. You say we've "probed" and found Dark Matter to be invisible in the electro-magnetic spectrum. Therefore it must be made of some exotic stuff, like neutrinos

I suppose Russian radar-operators could "probe" US B-2 stealth-bombers, find them to be invisible on radar, and report that B-2's therefore must be made of neutrinos.
But the B-2's are only made of metal, just shaped and coated in a way that absorbs and deflects the probing radar emissions, so the B-2's don't show up.

Perhaps "superheavy elements" have a similar effect when we try to probe them?



 

Offline Bored chemist

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We don't add things to the periodic table; it's already there. We just make the things that are in it.

I salute you sir, as an apparent true "Aristotelian"!   Aristotle said the very same thing -  that the idea of a "table", is already there.  It exists as an eternal, pure, thought-form : "tableness".  All we do, when we make an actual dining-room table, is make the wooden bits, nails, glue etc, that are in it.

Mind you, you can't really be an Aristotelian if you're a chemist, as his chemical ideas about there being just "four elements" - Earth, Air, Fire and Water, are unsound.
I'm not sure about Aristotle's periodic table.
More importantly, I'm not absolutely sure about mine.
Until the elements were synthesised and characterised by their chemistry, we were not sure of the "shape" of that bit of the periodic table.
It's not clear if we put the elements in their places.
Maybe, they put us in our place.
 

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