[Q] Why is technitium radioactive?

[Moontanman]

Why is technetium radioactive? It is well with int the stable elements of the periodic table but no stable isotope exists.

[belovelife]

technetium Is a byproduct of uranium fission

buy if it is the first unstable element

does it correlate to the other unstable elements

through periodic number

43, 61, Etc

if there is a function that relates

[Moontanman]

there are other byproducts of fission that have stable isotopes, technetium has no stable isotope, why? It's smaller than other elements that have stable isotopes, why is it always radioactive?

[Karnuvap]

It is to do with the arrangement of the protons and neutrons in the nucleus.

They just cannot seem to get comfy and are always wriggling around with the upshot being that one of the protons has to be ejected before the rest of them can settle down.

In reality, a proton doesn't get ejected - instead a neutron spits out an electron thus increasing the number of protons by one which makes the arrangement a happier one for the remaining nucleons or a proton grabs hold of one of the low flying electrons thus neutralising itself into a neutron making one fewer proton and one more neutron which, I think we can all agree, is a much more convivial arrangement for a nucleus to have.

 

There is just no easy way to arrange 43 protons together (no matter how many neutrons you let them have) and so something bad always happens.

 

42 protons = peace, 44 protons = harmony but 43 protons always arguments in the nuclear household.

 

Hope this helps.

 

The Vap.

[Pyrotex]

The Vap pretty much got it right.

 

It all has to do with potential energy levels within the nucleus. All the bosons (protons, neutrons) inside the nucleus arrange themselves in sub-groups. This allows the bosons to achieve lower energy states. If I remember correctly from the book, Particle Physics, which I read when I was 17 years old, bosons group themselves into 2-proton-2-neutron clusters inside the nucleus. Such a cluster would the be the equivalent of a Helium nucleus or an Alpha particle. Any nucleus that can fully arrange its bosons into Alpha particles is an exceptionally stable nucleus, with a very low potential energy state.

 

Even back in the 1960's it was also known that certain groupings of Alpha particles inside the nucleus would also confer extra stability. Apparently the Alpha particles themselves liked to cluster into set groups of 4 (I think). This gave the group-of-4 a lower overall energy state than four unassociated Alpha particles.

 

Poor Technetium, atomic number 43. It can make 21 Alpha particles with one proton left over. The 21 Alphas can make 5 groups-of-4, with one Alpha left over. 5 happens to be an inconvenient number because groups-of-4 ALSO cluster in tetrahedrons, so you got one group-of-4 left over.

 

The upshot of all this is: the extra group-of-4 bumps the nucleus energy level up; the extra Alpha particle bumps it up even more; the extra proton bumps it way up even more.

 

Add a proton or subtract a proton and you have a muchly-much lower energy state. If you graph the energy levels of all the atoms, Technetium sits on an energy spike in the middle of a line that gently slopes upward toward the heavier atoms. Protons jostle around; neutrons swap electrons with protons; Alpha particles jostle around; groups-of-4 jostle around. The Technetium spike is so high that it's just a matter of time before the game of Musical Chairs causes an electron to be kicked outside the nucleus (or an electron to be sucked in).

 

Now, other atoms also have this trouble with odd numbers of protons, Alphas, groups-of-4, etcetera, but they solve the problem by having more neutrons in the mix. This serves to either increase the binding energy, or to keep the various clusters further apart, but the end result is to lower the overall energy level so that the nucleus is stable.

 

But for Technetium, no matter how many neutrons are added, it just (barely) happens that there are always too few or too many neutrons. At its most stable Tc(98) has a half-life of 4 million years. Other isotopes have half-lives from a few hundred thousand years down to a few hours.

[Pyrotex]

Technetium is very interesting for other reasons. One is nuclear isomers which is defined as "metastable states of an atomic nucleus caused by the excitation of one or more of its nucleons."

 

Now, an isotope of an element has the same number of protons (the Atomic Number, which defines what element it is), but a different number of neutrons (which changes the Atomic Weight, but not the Atomic Number).

 

A nuclear isomer has the SAME numbers of protons and neutrons as its fellow isotope! But its nucleus has an "excited" energy state. This is typically because the nucleus has a nucleon (or several nucleons) with a spin different from the ground state. This means that simply spitting out an electron or positron (Beta Decay) won't work. A different mode of "decay" is necessary so that the funky spin state can be reversed. Isomers typically decay to their ground state isotope by emitting a gamma ray, which carries no charge.

 

Only one long-lived nuclear isomer is found in nature, 180mTa(73), an isomer of Tantalum. 180mTa(73) has the unusual property that the excited state decays with a half life longer than 10^15 years* while the lower-energy ground state 180Ta(73) undergoes beta decay with a half-life of only 8 hours.

*[that's right, ten-to-the-fifteen. longer than the age of the universe.]

 

Technetium is blessed with scores of different nuclear configurations, including several isomers. Ordinary 97Tc(43) has a half-life of 2.6 million years. Isomer 97mTc(43) has a half-life of 91 days. More often than not, an excited isomer has a longer half-life because the usual transformation decay path is "blocked" by the odd spin state. But sometimes, as here, the excited isomer has a different decay path that is even more unstable.

 

Another reasonably stable nuclear isomer (with a half-life of 31 years) is Hafnium, 178m2Hf(72), which has the highest excitation energy of any comparably long-lived isomer. (The "m2" means that this is a second excitation level above the ground state.) One gram of pure 178m2Hf contains approximately 1330 megajoules of energy, the equivalent of exploding about 317 kilograms (700 pounds) of TNT. Further, in the natural decay of 178m2Hf, the energy is released as gamma rays with a total energy of 2.45 MeV. As with 180mTa, there are disputed reports that 178m2Hf can be stimulated into releasing its energy, and as a result the substance is being studied as a possible source for gamma ray lasers.

 

This has all led the military to look for some way to create "Hafnium bombs", whereby a small amount of the metal can be irradiated with precisely the right frequency of X-rays, causing the stored nuclear excitation energy to be released from all atoms at the same time. Can you say "atomic handgrenade" boys and girls??? :lol:

 

See, S. Weinberger (28 March 2004). "Scary things come in small packages". Sunday Supplement Magazine. Washington Post. Hafnium bomb. Retrieved 2009-05-03.

[Pyrotex]

...This has all led the military to look for some way to create "Hafnium bombs", whereby a small amount of the metal can be irradiated with precisely the right frequency of X-rays, causing the stored nuclear excitation energy to be released from all atoms at the same time....

 

Y'know, there's a lot of buzz going around about how to build better batteries. Trouble is, at some point you are dealing with energy densities so high that the battery could explode.

 

It just occurred to me---what about a Hafnium Nuclear Battery? (HNB)

 

An HNB would not store energy chemically, but would store it... [we need a new word here] in the nuclei of the Hafnium atoms---rather, in isomers of Hafnium. 700 PE of TNT per gram is a LOOOOT of energy.

 

How it would work: internal klystron cell in the HNB would generate finely tuned beam of Xrays which would bathe a tiny section of a Hafnium wire, wound on a spool. This would trigger 2.5 Mev Gamma rays from the Hafnium, which would be absorbed chemically or thermally and converted to electricity. When the HNB was "empty" (all the isomers decayed to ground states), it would be returned to the manufacturer who would place the Hafnium wire in a specially designed nuclear reactor where it would be bombarded by 2.5 Mev Gamma rays. The Gammas would transform the nuclei back into isomers.

 

In Science Fiction, several authors use "batteries" like these to power cars and spaceships. A commonly used name for them is "shipstones".

[Yoron]

Pyrotex and Karnuvap, thanks. Didn't know that, a very strange matter, but we don't have it naturally then? Or do we?

[Pyrotex]

Technetium does not occur naturally on Earth. It HAS been found in the outer atmospheres of some cool stars (class M, R, N). And there is evidence that once it WAS created in a naturally occurring "nuclear pile" that has been found deep underground in the Congo.

 

The only long-lived isomer that occurs naturally on Earth is one for Tantalum. All the others are created in the lab.

 

All the Technitium isotopes we study are created