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Author: Subject: What are half-lives in MeV and unknown ones? Are they short?
radioboy
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[*] posted on 19-4-2016 at 14:01
What are half-lives in MeV and unknown ones? Are they short?


Can I consider them simply short (less than second at least)? Is it the reason why some are unknown (no value given)? Also how can I convert MeV to time? Using e=mc2 formula, correct? Why are they given in MeV?
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[*] posted on 19-4-2016 at 14:19


You can convert between energy and mass. This is entirely valid in some contexts.
You can convert between time and distance -- also valid in some contexts, but the conversion is not symmetrical. Time has some properties that distance does not -- namely that it appears to go in one direction only. Second law of thermodynamics and all that.

You cannot convert between energy and time. They have different units and even in relativity are quite different quantities.




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MrHomeScientist
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[*] posted on 20-4-2016 at 10:22


I've never seen a half life given in MeV. Can you give an example link?
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[*] posted on 20-4-2016 at 12:40


Empirically, there is a strong relationship between half life and alpha emission energy
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/alptun.ht...

but that's not the same as saying they can be interconverted.
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radioboy
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[*] posted on 20-4-2016 at 12:50


Some are given in both units (MeV and normal) like He7 https://en.m.wikipedia.org/wiki/Isotopes_of_helium (in tables) or Li4, Li5, Li10 https://en.m.wikipedia.org/wiki/Isotopes_of_lithium. Just check for other elements, there are more. Or check here www.nndc.bnl.gov/chart/ or here nrv.jinr.ru/nrv/webnrv/map/nucleus.php?q=C8

There are many more. And some like first example He2 are unknown. It means short?
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radioboy
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[*] posted on 20-4-2016 at 13:11


Quote: Originally posted by unionised  
Empirically, there is a strong relationship between half life and alpha emission energy
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/alptun.ht...

but that's not the same as saying they can be interconverted.


That is all I could find also, here: https://en.m.wikipedia.org/wiki/Geiger–Nuttall_law

But maybe when they say that half-life is independant of temperature, they only think about low temperatures. But what if I heat (accelerate) proton (H1) to energy of 782.38 keV or 1804.38 keV. Will it become neutron? And fuse it with proton to get deuterium, or fuse it with anything else to get any isotope? Isn't just one of these energies enough to make neutron stable (if we could hold it isolated to not react with anything)? I mean neutron has half-life few minutes and has exactly same energy as above (just opposite sign) where it becomes proton (782.38 keV)!
www.nndc.bnl.gov/chart/decaysearchdirect.jsp?nuc=1NN&unc=nds
nrv.jinr.ru/nrv/webnrv/map/nucleus.php?q=H1

[Edited on 20-4-2016 by radioboy]
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[*] posted on 20-4-2016 at 23:43


Quote: Originally posted by radioboy  

But maybe when they say that half-life is independant of temperature, they only think about low temperatures. But what if I heat (accelerate) proton (H1) to energy of 782.38 keV or 1804.38 keV. Will it become neutron? And fuse it with proton to get deuterium, or fuse it with anything else to get any isotope?

When two protons fuse in the proton-proton reaction inside the sun, then the energy released from their attraction by the strong nuclear force, does transform one of the protons into a neutron. And the result is a deuterium nucleus, as you say :)
And in decays of some nuclei, the proton does either capture an electron from one of the atoms electron shells, *or* decays and emits a positron, in both cases turning into a neutron.
One can even drive this process purposely, and bombard nuclei with electrons of a specific energy; which both supplies the necessary energy, and the electron to react with the proton, and create a neutron; thus creating a different isotope.

[Edited on 21-4-2016 by Theoretic]




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radioboy
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[*] posted on 21-4-2016 at 03:05


I also realized that electron capture (not beta+) is opposite of beta- decay. Just can't figure half-life of any induced decay by energy (as proton to neutron conversion, and does high temperature really affects it). Also, it seems much more simple and faster to simply fuse proton with something because coulomb barrier is the lowest for hydrogen isotopes. Even lower than energy for making neutron from proton. And probably fast.

[Edited on 21-4-2016 by radioboy]
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[*] posted on 21-4-2016 at 04:35


Quote: Originally posted by radioboy  
I also realized that electron capture (not beta+) is opposite of beta- decay. Just can't figure half-life of any induced decay by energy (as proton to neutron conversion, and does high temperature really affects it). Also, it seems much more simple and faster to simply fuse proton with something because coulomb barrier is the lowest for hydrogen isotopes. Even lower than energy for making neutron from proton. And probably fast.

[Edited on 21-4-2016 by radioboy]

And there is *no*coulomb barrier for electrons.
When there's a half life is listed together with an energy, that's probably just the decay energy




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[*] posted on 21-4-2016 at 05:36


Agree with Theoretic. It's certainly the decay energy. You can't convert between energy and time, it's nonsensical.
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[*] posted on 9-6-2016 at 00:29


Quote: Originally posted by MrHomeScientist  
Agree with Theoretic. It's certainly the decay energy. You can't convert between energy and time, it's nonsensical.


In CRC Handbook of Chemistry and Physics it says "Half-Life/Resonance Width: Half-life in decimal notation, microseconds, milliseconds, seconds, minutes, hours, days, years. For quasi-stable nuclides, the measured width at half-maximum of the energy resonance is given."

And they gave half-life in MeV, keV, and eV for some nuclides (H4, H5, H6, H7...) for which I believe have extremely short half-lives (am I right?). What means "resonance width" and "quasi-stable nuclide"?
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[*] posted on 9-6-2016 at 12:48


I too have noticed exotic isotopes with half-lives given in energy units. One example is beryllium 6, half life given as 92 keV +- 6 keV: http://www.nndc.bnl.gov/chart/reCenter.jsp?z=4&n=2.

The book Be Beryllium: The Element. Production, Atom, Molecules, Chemical Behavior, Toxicology says that

Beryllium 6 is particle unstable with respect to helium 4 + 2 protium by 1371 +- 5 keV. The width of the ground state for this decay is 92 +- 6 keV in the center-of-mass system. (My emphasis).

These half-lives reported in energy units are really reporting "the width of the ground state" for the decay? I don't know what that means with respect to time units. But presumably there is some relationship to conventional time units since reputable data sources keep reporting half-lives in these energy units.

The primary source for the beryllium 6 data is Energy Levels of Light Nuclei A=5-10, Nuclear Physics A 413 1/214, by F. Ajzenberg-Selove.




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[*] posted on 10-6-2016 at 01:42


This is something I've come across in NMR and Fourier theory, but not nuclear physics. It's to do with uncertainty.
http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/parlif.ht...


[Edited on 10-6-2016 by Marvin]
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[*] posted on 21-6-2016 at 03:07


You cannot convert between time and energy in classical relativity, but you can in quantum mechanics - even in nonrelativistic quantum mechanics. Heisenberg uncertainty principle and Planck constant.

The practicably measurable lifetimes span over 50 orders of magnitude, from 10-23 seconds to 1030 seconds or so.

For short lifetimes, decay width is a useful measurement. It also is distinct from decay energy. For example, beryllium 8 undergoes alpha decay. Decay energy 188 keV (94 per each alpha particle), devay width about 7 eV. Meaning halflife about 10-16 seconds.


Not sure which lifetimes are left unknown.
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