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Hydrogen has a higher diffusivity than helium. Seems to be about 25% higher.[PDF]

That seems to be about diffusion of gaseous things within H2, not diffusion of H2 through solids.

Since I've never heard of such a thing, please provide a link.

https://en.wikipedia.org/wiki/...
http://energy.gov/sites/prod/f...
http://www.google.co.uk/search...

Note: given that hydrogen, even when diatomic, is smaller than Helium,

Really? The atomic radius of Helium is 31pm http://periodictable.com/Prope... whereas the bond length for H2 is 74 pm http://www.wiredchemist.com/ch...

Helium, it doesn't need to be "soluble" in metal to diffuse better.

I like hopw you've never heard of it, can't be arsed to google, then use disparaging scare quotes because you want to be a consescending. Turns out you should have googled. It's a real thing.

That isn't correct. While in a reactor Plutonium, or Uranium (fission) will produce more energy than fusion per nucleon, that is the average energy over the life of all of the decay products:

http://periodictable.com/Isoto...

The majority of the decay products takes far longer than a full second to be produced, so they aren't relevant to the detonation, or the brisance of the device.

http://www.kayelaby.npl.co.uk/...

In the environment of a reactor, you can simply wait long enough, and extract the full energy as Plutonium is converted between a dozen different elements, but in a bomb, speed is king, so the slow fission products don't add meaningful amounts of force, or power to the explosion. Fusion boosters don't have a critical mass, so you can pack in as much of them as you want.

Oh yeah, in case you haven't read it in my previous posts, see the neutron cross section data at http://periodictable.com/Prope... where you can also find boiling point, melting point, density, neutron mass absorption and the like data, per elements. Elements stable to nuclear neutron bombardment are important in nuclear applications, because compounds are wrecked to elemental pieces from the high speed neutrons, and all you get is a bunch of free radicals that might be very corrosive, unless the recombination rate is faster than the chance to corrode anything, as it might be in a molten salt. Fluorine moderates, and chlorine is very neutron absorbing, but I don't have individual isotopical data for chlorine, but bromine and iodine are better than chlorine regarding absorption, also less moderating, however their nonmoderating barium, strontium, rubidium and even calcium and potassium compounds might be more volatile at extreme temperatures than chlorides or fluorides would be. None of the salts though have the neutron economy of pure bismuth, or even lead, or the very high boiling tin (which might be added for safety to even bismuth running at 1500C, whose boiling point is 1564C, compared to lead at 1749C, compared to tin boiling at 2602C, or even gallium boiling at 2204C, in case of a thermal runaway the higher boilers stay liquid longer with good thermal cooling contact, and they, tin and gallium, have decent neutron cross sections, and low melting points. That's the other problem with molten salts, the getting stuck frozen hard pipes of salt, which take forever to dissolve out with water (maybe hours or days for a couple ten yard pipe segment, so a very high dissolution rate salt should be considered, possibly anhydrous baked rubidium iodide, or calcium iodide might be such a thing), and impossibility to melt with an external torch, compared to low melting bismuth, lead, tin, and even gallium and especially germanium (boiling pt. 2820), and their alloys, all being low neutron absorbers, also indium dumped as shortstop into such molten alloys in case of a sudden need for reactor shutdown, which is also low melting, high boiling, and an excellent neutron absorber (at least one of its isotopes got to be.)

http://periodictable.com/Prope...

Shows that bismuth excels at neutron economy, while having a 271C mp/1560C bp. In case you can enclose the whole reactor into an electric oven, it may be an economic option, but all I can say is that it's not possible to do manual labor maintenance on 271C pipes and fittings that have been plugged and freshly thawed, but gallium melting at 30C, as a eutectic with zinc (or perhaps magnesium, or perhaps, but much more worse with sodium and potassium) even lower, so even pure cadmium is a joy to work with as far a maintenance personnel applying steam heat to thaw a frozen pipe goes, compared to all the other fast neutron breeder coolant options of sodium, lead, bismuth, NaK, and the like. The only question is whether neutron bombardment of cadmium generates serial neutron poisons, as neutron bombardment of sodium gives magnesium and aluminum, all low cross section, so cadmium giving germanium and arsenic, also low cross section, is that the case?

The issue with gas coolant is the low thermal capacity and conductivity and requiring fast flows - just think of your car radiator, what it looks like, and why it needs a fan. And with fast flows you can get uneven velocity distribution, and pockets of local overheating or local meltdown - something that does not happen in a car radiator because you have a maximum highest incoming temperature, but in a gas cooled reactor, such as stacked balls, temperatures can get locally very high to where the whole stack shifts and moves and makes flow distribution even worse. Such a shift in an advanced gas reactor was what prompted the Germans to completely cancel their nuclear research. Now there might be ways to help the issue, I just thought of it yesterday. Instead of a pyramid of stack balls dependent on all others to be in place, and not move, you could have heat exchanger like tube-banks or fuel rod banks that are securely fastened at the two ends, fighting any kind of shift of the whole mass, even if one bar individually overheats a lot, it does not push the other ones out of their position, even if it melts, because of the clearance gap between them being large enough to allow a lot of flexure. Now as something overheats locally, because of uneven flow and heat exhcange rate, it should have lower density, but when you're dealing with light helium (which is not an idea coolant for breeder or fast neutron reactors because it moderates), the variation in density, and buoyant force from that density is very low. So you need something that's very high molecular weight yet has good neutron cross section, for both non-moderation reasons and for buoyancy reasons. For the available options on neutron cross section, see
http://periodictable.com/Prope...
http://periodictable.com/Prope...
and also the note, the picture on how U235 cross section varies with neutron temperature or velocity, and fast neutronss are not as effective at splitting it as moderated slow neutrons, cross section depends on velocity, for reasons that we do not understand, or at least I don't. These cross section numbers are all experimental because we don't have a good understanding of the atomic nucleus, for instance there is probably no theory of the atomic nucleus that would explain why (gadolinium, promethium, samarium) cadmium, boron, silicon and hafnium would have a high cross section, but oxygen, beryllium, magnesium, bismuth, lead, zirconium(best construction material if hafnium free), aluminum and iron have low or decent cross section.
In this respect CO2 looks like an ideal candidate, however it's a molecule, a combination of elemental atoms, not just atoms, and when you get a fast neutron coming at it at high velocity, it may form CO + O, and C + O2, and it may char, however if the temperature is high enough, say over 800C in the reaction zone, this would automatically combust back to CO2, so it might take the beating. However the C at 12 molecular weight is still a moderator, somewhat, not as good as helium 4 or water with hydrogen at 1, but better than sodium coolant for instance. For a fast neutron breeder reactor you want a really bad moderator, that keeps the neutrons unmoderated, and fast, able to attack and breed from fertile but otherwise nonfissile materials, like depleted U238, or thorium(which is realtively abundant and cheap.) Not too many things are gaseous at high temperature, yet have a huge molecular weight, and noble gases pretty much top the cake at gaseousness, inertness, and high molecular or atomic weight and nonmoderation. But the heavier gases like Krypton and Xenon, also have a bad high cross section, but Argon, silimar in molecular weight to sodium, is similar to cross section to sodium, and it's relatively abundant and cheap. Sulfur hexafluoride might be even better, as the sulfur is about the same as sodium and argon, but the fluoride is really awe

The issue with gas coolant is the low thermal capacity and conductivity and requiring fast flows - just think of your car radiator, what it looks like, and why it needs a fan. And with fast flows you can get uneven velocity distribution, and pockets of local overheating or local meltdown - something that does not happen in a car radiator because you have a maximum highest incoming temperature, but in a gas cooled reactor, such as stacked balls, temperatures can get locally very high to where the whole stack shifts and moves and makes flow distribution even worse. Such a shift in an advanced gas reactor was what prompted the Germans to completely cancel their nuclear research. Now there might be ways to help the issue, I just thought of it yesterday. Instead of a pyramid of stack balls dependent on all others to be in place, and not move, you could have heat exchanger like tube-banks or fuel rod banks that are securely fastened at the two ends, fighting any kind of shift of the whole mass, even if one bar individually overheats a lot, it does not push the other ones out of their position, even if it melts, because of the clearance gap between them being large enough to allow a lot of flexure. Now as something overheats locally, because of uneven flow and heat exhcange rate, it should have lower density, but when you're dealing with light helium (which is not an idea coolant for breeder or fast neutron reactors because it moderates), the variation in density, and buoyant force from that density is very low. So you need something that's very high molecular weight yet has good neutron cross section, for both non-moderation reasons and for buoyancy reasons. For the available options on neutron cross section, see
http://periodictable.com/Prope...
http://periodictable.com/Prope...
and also the note, the picture on how U235 cross section varies with neutron temperature or velocity, and fast neutronss are not as effective at splitting it as moderated slow neutrons, cross section depends on velocity, for reasons that we do not understand, or at least I don't. These cross section numbers are all experimental because we don't have a good understanding of the atomic nucleus, for instance there is probably no theory of the atomic nucleus that would explain why (gadolinium, promethium, samarium) cadmium, boron, silicon and hafnium would have a high cross section, but oxygen, beryllium, magnesium, bismuth, lead, zirconium(best construction material if hafnium free), aluminum and iron have low or decent cross section.
In this respect CO2 looks like an ideal candidate, however it's a molecule, a combination of elemental atoms, not just atoms, and when you get a fast neutron coming at it at high velocity, it may form CO + O, and C + O2, and it may char, however if the temperature is high enough, say over 800C in the reaction zone, this would automatically combust back to CO2, so it might take the beating. However the C at 12 molecular weight is still a moderator, somewhat, not as good as helium 4 or water with hydrogen at 1, but better than sodium coolant for instance. For a fast neutron breeder reactor you want a really bad moderator, that keeps the neutrons unmoderated, and fast, able to attack and breed from fertile but otherwise nonfissile materials, like depleted U238, or thorium(which is realtively abundant and cheap.) Not too many things are gaseous at high temperature, yet have a huge molecular weight, and noble gases pretty much top the cake at gaseousness, inertness, and high molecular or atomic weight and nonmoderation. But the heavier gases like Krypton and Xenon, also have a bad high cross section, but Argon, silimar in molecular weight to sodium, is similar to cross section to sodium, and it's relatively abundant and cheap. Sulfur hexafluoride might be even better, as the sulfur is about the same as sodium and argon, but the fluoride is really awe

It's possible you meant Thallium 208 (Historic Name: Thorium C, Half-Life: 3 minutes)?

There are two observationally stable byproducts at Tl203 and Tl205.
The most stable of the remaining isotopes has a half-life of just under 4 years. Most of the rest are measured in hours, seconds and in some cases, milliseconds.
So yes, it's very "hot". But it's extremely short-lived.

Thanks for pointing that out and also much appreciated about not being a dick about it.

No problem. I know how it is with "stream of consciousness typing".

I checked my notes at home and they were about Thallium 208. I agree, I want to learn more so I can have a reasoned and measured response. Unfortunately I see the nuclear mod trolls are out in force again.

Screw 'em.

I have nothing against this type of reactor technology, in principle however I'd like to know more about it's spent fuel byproducts and operational effluents. It is important to understand that if the halflife is three minutes and it's an energetic emmiter, how many daughter product iterations does it got through before it becomes stable an what is the rate of decay? That in itself may pose an even greater threat *because* if it is continually changing just how many micro-nutrient analogues does it present to biology? I'm not going to pretend I know the answer because I am still learning myself, however at least I know that's a question to ask. Another question about a Thorium fuel cycle to uncover is are we just making a new problem. Regardless of that, we still have problems with the Uranium based cycle and they all lead back to the same thing.

At least for Thallium 208, it looks like it decays directly to Lead 208, also known, historically as Thorium D.

Up to this point, I've seen nothing really reported other "useful waste", like the aforementioned P238.
Other by products are: xenon, neodymium (high-strength magnets), medical molybdenum-99, radiostrontium, zirconium, rhodium, ruthenium, and palladium.
http://liquidfluoridethoriumre...

On the decay. I've seen it reported that around 83% of all radioactive by products from LFTR are stable within 10 years with the remaining 17% stable within 350 with no uranium or plutonium waste.
http://liquidfluoridethoriumre...

The bottom line is that because this whole debate is so polarized, no one talks sense about it anymore. The irony is that if you took a rational look at both sides of the debate you would see that what the anti- and pro- nuclear lobby need is exactly the same thing.

I wouldn't say NOBODY talks any sense. But the ones who are get drowned out by the two rabid poles.

So let's get to the bottom of this whole pro- anti- nuclear bullshit right here.

Pro-Nuclears: want to have new reactor technology developed and deployed, old reactors desposed of responsibly. Is that a fair call?

Anti-nuclear: wants no Nuclear industry at all, but if it has to be there clean it up an make it safer. Is that a fair call?

The problem is, this is an over-simplification. And, thus, ROUNDLY incorrect.

It's a giant sliding scale with a nebulous median point.

On the pro nuke side, you have all manners of partisans. Each looking to push their own horse in the race. And LFTR (and myself for that matter) are little different.

On the anti-nuke side, you have groups of people with varying oppositions to nuclear. Anywhere from those who simply want a cleaner solution than today's mess, to those who'd rather see us go back to shivering and starving in caves than allow nuclear for ANYTHING (basically the ones who equate nuclear wi

They stored their plutonium stockpile carefully (also because packing it too tight is a very bad idea), but they were not aware that it was made of Pu-233. This explains why the stockpile they bought was sold at such a bargain price on the market...

Some type of triggered fission in the heavy elements of the meteorite? And gamma emitter with a short half life of minutes is being created and left in the trail, such as Barium-137?

uranium 233 has been created, and 96 kilograms of the stuff (enough to fuel 12 nuclear weapons) is now missing from the US national inventory

In addition, they have about 96 kilograms of lead that they don't remember ordering. And the situation gets worse every day!

If they started with 192kg of U-233, there'd be a lot more than 96kg of U-233 and a lot less than 96 kg of Pb around at this point.

A link for anyone who feels the AC has some kind of point.

http://www.periodictable.com/Properties/A/UniverseAbundance.html

The Possum Lodge Institute of Science and Technology would upgrade the super conductor to handle more current and be DIY by using Duct Tape and lantern batteries. http://periodictable.com/Stories/006.2/index.html

I can visualize Red Green demonstrating the project as I type this. Sure miss that show...

There are non-mercury, liquid metal thermometers available. http://periodictable.com/Items/031.6/index.html It's gallium, indium, and tin.

Yes, it seemed a bit strange to me as well when i found out too.

But what astounded me is that a similar thing applies to websites. One of the apps that people keep holding up as an example of how powerful the ipad is and apple even features in their ads, is an animated periodic table...

but instead of paying quite a lot of cash for it http://itunes.apple.com/us/app/the-elements-a-visual-exploration/id364147847?mt=8# you could just visit the website http://periodictable.com/; its almost exactly the same and completely free. When you consider that the app is 2 gigabytes and apparently crashes quite a bit (from the reviews) it seems even more strange...?

Easy enough to say that the product isn't aimed at me, but still, magical is not the word that springs to my mind.

It's not a microbe, but look at what happens when Mercury and Aluminum meet...

http://periodictable.com/PopSci/2004/10/1/index.html

Like the other replies to this post, I completely agree -- I wish more teachers thought like this (and not *just* in chemistry). Teaching chemistry using "theory only" is like teaching programming using pen and paper (which I'm old enough to remember, and greatly resent).

This is about mnemonics. Associate formulas, tables, ratios and reactions with visual memory -- seeing is remembering. Sometimes you don't even have to do the experiment in class -- if something is either dangerous or expensive, there's probably plenty of videos online of the process. This is actually a subject matter in which youtube is a "good resource" (for the visuals, anyway).

Here are a few sites that either give examples of practical/cheap experiments or provide videos of all sorts of chemistry-related material:
thenakedscientists.com
http://www.rsc.org/education/teachers/learnnet/videoclips.htm
http://www.planet-scicast.com/experiments.cfm

Here are a few additional online chemistry resources (the more visual information, the better):
webelements.com
chemicool.com
periodictable.com
periodicvideos.com
practicalchemistry.org
mindat.org

It's like any other subject -- get the students *interested* in _topic_, and they'll teach themselves.

So, thorium fluoride melts at 1110C, boils at 1680C, so it's a high pressure gas at 3000C.
Thorium dioxide melts at 3390C, and boils at 4400C. At 3000C one could still have thorium dioxide pebbles, though they might react with a graphite vessel to form thorium carbide and carbon monoxide, or some thorium-carbido-oxide. How fast this happens and how physically stable it would be, I don't know. With a tungsten vessel, there may be no reaction at all. The problem with tungsten is a relatively high neutron capture cross section.
Thorium nitride melts at 2820C, so it is probably liquid at 3000C, but it may be sufficiently metallic to react with graphite, and form some kind of thorium-carbido-nitride, with evolution of nitrogen gas.
Graphite melts, or more exactly sublimates at around 3600C. Next is tungsten melting near 3400C, boiling at near 5500C.
I just found http://www.periodictable.com/Properties/A/NeutronCrossSection.ssp.log.html
At least for thermal neutrons, graphite is one of the best neutron resistant materials at neutron cross section b 0.0035 , and I had no idea that oxygen is by far the most resistant, at 0.00028. Helium is third at 0.007, but this gives me the idea of using carbon monoxide as the heat exchange gas medium, in case helium's moderating power is too high. Carbon monoxide may behave like an inert gas in presence of graphite and thorium dioxide, unless C2O type materials might form, but that's very entropically unlikely. Beryllium and fluoride are next, at b=0.0092 and 0.0096, then bismuth at 0.034. Neon(0.04), lithium(0.045), magnesium (0.063), lead(0.171), and the first structural metal with sufficient strength, high enough melting point, other than graphite is zirconium with neutron cross section b=0.184 for thermal neutrons. But Zirconium's melting point is 1855C, and thorium's 1752C. Argon is 0.65, the cheapest noble gas, but much more absorbing than helium, neon or carbon monoxide.

High melting materials near tungsten are high absorbing some more than others. Thorium itself is 7.4 so the materials themselves should beat thorium dioxide 3400mp in nonabsorbing neutron capacity. Here are some top melting materials

Tungsten is b=18.4 /mp 3400C, rhenium is 90/3200C , osmium 3030/15, tantalum 20.5/3020C, niobium 1.15/2477, molybdenum 2.6/2350C, thorium 7.4/1842, etc

Tantalum carbide Ta11C mp 3880, Ta1.0C0.89 4000C, niobium carbide 3490C, thorium carbide 2630C.

Besides niobium carbide, that leaves graphite as the only cheap, nonreactive and truly high temperature nuclear material far beyond 2000C, together with thorium dioxide as the fuel, with carbon monoxide and helium as the heat exchange fluids with direct contact with the fuel. The heat exchange fluid might still have to go through a graphite heat exchanger external to the core, so that nuclear decay outgassing contaminants from thorium, such as lead oxides are contained, and the 2nd heat exchange fluid as it goes through the decompression cycle in a graphite piston or other mechanical device, does not contaminate up the wall surfaces from such nonvolatiles dropping out on cooling. Graphite pistons are self lubricating, but they are very weak mechanically. One could still build a humongous heat engine graphite piston that operates at 3100C to 100C temperature drop, and a pressure drop of 3 atm to near vacuum exhaust pressure, with very slow motion, with the high pressure gases introduced on alternating sides during a decompression cycle that might take 2 minutes to complete. Imagine a 10m x 10m diameter graphite piston, with a travel length of 30 meters. Such sizes are necessary at low pressures. It's very hard to find something that will provide containment to 100 bars at 3000C, but that very high temperature to exhaust temperature ratio, and initial pressure to final pressure ratio is what's critical to energy harvesting efficiency.

With the piston construction however, hi

This is exactly what I thought of when I read the summary. In fact I just saw the episode of Modern Marvels: Engineering Disasters that covers this topic last night.

My favorite: the Revigator!

That sounds right. According to Wikipedia, the natural abundance of Si28 is 92%.

Googling got me an interesting paper:
http://www.crystalresearch.com/crt/ab35/1023_a.pdf

Not really related, but pretty pictures of silicon:
http://www.periodictable.com/Elements/014/index.html

The author of this Popular Science article, Theo Gray, also recently relaunched http://www.periodictable.com/ Thousands of elemental pictures and videos are available there, all linked in with his Popular Science series.

Indeed, I can't see any practicing engineer or scientist finding any use for this thing. It's also a bad idea for instruction, because it's a gross oversimplification of the distribution of the elements in the universe. The periodic table is useful, because it's complete and accurate, but this is not. There are already several other period tables with more instructional or historical value.

By adulthood, Mendeleev's periodic table of the elements is firmly planted in a typical mind either as a tool for study or proof of mystical forces at work in nature. There are alternative structures: some clever and others using alternate media, extensions to the table providing nuclear structure, fermi surfaces, and line spectra.

Still others are extraordinarily cross-thematic, merging chemistry with comic books, poetry or haiku. But only the grouping-nature of the columns is retained in rejected elements, condiments and beer. Eventually the elements and the periodic qualities have been lost entirely, reducing the periodic table to a design template for topical lists of funk and rock music, comedy and TV shows, famous mathematicians and presidents, even SGI products. Soon a complete breakdown of the scientific aspect yields no similarity to the original, becoming a glorified table, a marketing tool, or hype itself. There is mounting evidence of a conspiracy.