Radioactives-Isotopes- general data

[Richard Hull]

There are only three natural elements, which are radioactive to the casual geiger counter and they are uranium,thorium and radon. (Natural elements end at atomic number 92, uranium)

There are other radioactive natural elements which are not extant on earth due to either short half life or near zero relative abundance. These are radium, polonium, astatine, francium, actinium, protactinium, technicium, and promethium.

There are regular, non-radioactive elements which have naturally occuring isotopes as part of their makup which are radioactive due to nearly infinite half lives up to 10e16 years! (vastly beyond the age of the universe.) To name prime examples...Potassium 40 (1.3 billion years), Rubidium 87 (49 billion years) and Samarium 148 (7 quadrillion years or 7000 trillion years). Of these, only potassium's isotope (K40) is readily detected (gamma spectrometer) for even in a massive sample, the decay is slow as it has over a billion years before even half is gone and normal potassium contains only a tiny amount at that (1/100ths of 1%). It throws off a ~1.5 mev gamma particle which will cruise through a decent chunk of lead. I can detect the K40 gamma peak on my Canberra gamma spectrograph from a one pound tin of potassium nitrate placed near the scintillator head.

There are decay products of the uranium, thorium and actinium families which are extant on earth which are, themselves, radioactive, but are found only as part of the uranium and thorium ores. Most have half lives so short that extraction and refining is, effectively, impossible. Therefore, radioactive isotopes of most nautral elements are produced in reactors by neutron bombardment.

Needless to say, there are literally hundreds of isotopes of all of the elements from hydrogen to uranium and many are radioactive with only a few, naturally occuring either by original deposition on earth or in decay chains of other elements. There are an amazing number of non-radioactive (stable) isotopes known which do not occur in nature and must be created by man in reactors or accelerators.

Tin (Sn) is an example of an element that has many isotopes (10) occuring naturally in every sample extant on earth. None are radioactive, but there are a large number of tin isotopes not found in nature which are both radioactive and non-radioactive.

Due to our isolation, and being totally marooned on this particular slag heap in the universe, it is totally unknown if the observed local relative abundance of isotopes in the "natural" elements is common to the enitre universe or just the birthing of our particular solar neighborhood. It seems rather bizarre that there are so many stable, happy isotopes of so many elements of which there is absolutely zero atoms found on earth or in nearby stellar atmospheres.

Remember, the word isotope doesn't necessarily mean radioactivity, but instead, a different atomic weight of a given atomic number element. Basically more or less neutrons in a nucleus of any given element.

An element is identified by the number of protons ONLY! (the atomic number) For a given atomic number (element) there can be many different atomic weights.(isotopes) Throwing an extra neutron in any element may or may not make it unstable (radioactive) but will always make it heavier (increase its atomic weight.) It is nearly impossible to separate the isotopes out of any given element into bulk, pure quantities of each.

Chemically, (gaseuos diffusion), the separation process is extremely costly and requires huge assemblies. Atomically, (mass separation), it is unbelievably slow producing micro amounts over weeks of vast electrical expenditures. We did it at great cost during WWII to get U235, making the per gram quantity price outrageous.

Transuranics are those elements above atomic number 92 beginning with neptunium. All are man made, none are found in nature and all have half lives which are microscopic compared to geologic time. Some have half lives short relative to rifle bullet flight times in the barrel of a gun!

Many of the transuranics are fissile but are far too expensive to produce to displace good old natural U235. Only plutonium can compete in this transuranic class as it is a quantity byproduct of normal nuclear fission. It is easily separated chemically from all the other nuclear debris but, of course, the whole process is a nastey radioactive gloppy mess not only as a worker health hazard, but as a waste disposal rad-hazard as well. By comparison, the U235 separation process is a non-hazardous activity producing only DU (depleted uranium) waste product which is good for bomb casings, neutron shields, modern artillery sabo-penetrator rounds and internal aircraft counter and balance weights.

Richard Hull

[ChrisSmolinski]

I can get a reasonable reading from a small bit if salt substitute (KCl) using my GM-10 detector, and much better results using the GM-45. In my case I am mostly picking up the betas.

I've often thought it would be humorous to take a geiger counter to the supermarket (clicker at full volume) and check out the shelf of No-Salt. Well, it would be have been fun pre 9/11 anyway.

Your comments on nuclide distributions are interesting. It is a bit presumptious of us to assume that the rest of the universe has the same distributions as here on Earth. Since theory has it that the heavy elements were all formed from a supernova explosion (or possibly several explosions), I suppose that the mass of the star might have an influence on the distribution of nuclides. Maybe each neck of the galaxy has a different distribution? Maybe there's some planet that got a lot more U235, very little U238, and developed intelligent life much earlier, resulting in natural uranium being suitable for nuclear weapons? For that matter, we could be one of the few that got any U235 at all. Either case would certainly have changed history here.

I have read the article about the natural reactor that operated in Africa several billion? years ago. Interesting reading.

[Richard Hull]

There are now two suspected natural reactors with only the African one verified to a scientific degree. There are, I am sure, many more and some of them cookin' away deep down in the crust or mantle.

I have a mineral collector friend who recently presented me with an amazing specimen of North Carolina pitchblend for my mineral collection. It is absolutely pitchblack and ultra dense. On splitting it in half I could detect no other mineral content within. This means the thing is effectively pure oxide.

A count with my NIM based counter using a special holder for the 2" pancake detector yielded an alpha-beta combined count of 115,000 cpm on one side of the larger irregular piece. This would mean about 375 kilocounts per minute isotropically in this golf ball sized lump THAT ESCAPED! Vastly more particles never see the light of day due to internal self absorption. Remember, the Gammas are just not counted for the most part either!

I can easily see how a natural reactor could crank up in a vein of this stuff.

The old Chicago squash court pile was just the oxide for the most part and not much metal at all. All of it at 0% enrichment.

Incidentally, U238 metal or its compounds all spontaneously fission! About 14-20 fissions/second in a mass of about 3kg. Some old aircraft counterwieghts in DU far exceeded this figure. So the stuff, especially the ore with the natural U235, is fissioning all the time. Of course it presents no real hazard in small mineral samples like collectors hold in their collections.

Richard Hull

[guest]

I saw the most amazing pictures on the BBC last night.
It seems the Russian navy under the old USSR regime
used Cobalt 60 and Strontium 90 in metallic form to
power sonar buoys and Warning lights for coastal use.
The IAEA is now running like mad to pick up the 12 - 15 kg hot hunks of metal off the ground in Ukraine.
I watched as a team picked up this stuff with a hot pole
at a length of 15 feet and the working time was like 30 seconds per worker. The filmed rescue of this loose
hot stuff was in the winter. Steam was visible at two hundred yards where the film crew was positioned.
These hot cores were just tossed out like trash all over
the area near the major military port. They estimate about 200 missing cores they have found about 20 so far.

Larry Leins
Physics Teacher

[Richard Hull]

Not that we haven't used our share of Sr90 RTGs either.

We have used them in the artic and antarctic. Some few were used by NSA and other spook apps for behind the lines power sources for automatic listening posts, etc. Plus NASA sent a gang o' those puppies out into space on probes as the ubiquitous SNAP series of RTGs in the 60's, 70' and 80's. They were out on the end of long booms to keep the hot stuff from cookin' off the electronics. I am not sure if they are using them now or not.

Richard Hull