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PTSideshow
03-31-2009, 06:39 AM
Here is a long video of a guy making vacuum tubes, valves what ever you prefer. He also built the equipment to make them. The spot welder is pretty cool. But over all a pretty hard way to make an AM radio! :D
http://news.cnet.com/8301-13645_3-9843011-47.html

rotate
03-31-2009, 08:38 AM
I saw this video before but watching it for the second time was just as enjoyable.

Something that I didn't think about the first time, which is that if for some reason all our silicon fabs were destroyed (may be war), then the likely hood of humanity being able to make a transistor in their bunker is very low, however as the video shows making a vacuum tube is well within the reaches of many university labs.

Just as we bank seeds for posterity, some technological know-how should be preserved.

lazlo
03-31-2009, 08:56 AM
if for some reason all our silicon fabs were destroyed (may be war), then the likely hood of humanity being able to make a transistor in their bunker is very low, however as the video shows making a vacuum tube is well within the reaches of many university labs.

That's an interesting point. There's a massive infrastructure required to design, test, and fab, and mass-produce modern silicon. Intel's new 32nm Fabs in Beaverton and Chandler are $7 Billion each.

But also consider that, as part of the march of Moore's Law, all the Majors are constantly building new fabs, so Intel and IBM, in particular, are already designing their 28nm Fabs.

So if a fab were wiped out, it'd be a financial catastrophe, but we wouldn't lose the technology and/or expertise to build a new one.

Now, if you're talking about a Mad Max apocalypse, then yes -- people aren't going to be building semiconductors in their basements. But a lot of universities have mini-fabs. Old technology, for sure (they don't have the funds or the infrastructure/chemical purity necessary for ultra fine feature sizes), but group of say 20 engineers and process physicists could probably build a mini-fab if worse came to worse.

Duffy
03-31-2009, 09:57 AM
Russia is still manufacturing vacuum tubes, I believe. Up until a few years ago, our Defence Department was buying them for some ancient but essential equipment. It is amazing to see an individual doing what once, in our lifetime, was a standard manufacturing procedure. But then again, at "historic villages" people will stand and watch a dirty guy in a leather apron beat a bar of iron into nails, one at a time, (you know-those little things that you load in sticks into an air-supplied gun!)

Evan
03-31-2009, 10:04 AM
Now, if you're talking about a Mad Max apocalypse, then yes -- people aren't going to be building semiconductors in their basements. But a lot of universities have mini-fabs. Old technology, for sure (they don't have the funds or the infrastructure/chemical purity necessary for ultra fine feature sizes), but group of say 20 engineers and process physicists could probably build a mini-fab if worse came to worse.


Easily. I have a kit that was given out to science teachers by Bell Labs in the 60s. It's a "Make Your Own Solar Cell" kit. The only thing you don't do is grow your own 1" silicon ingot, slice it and polish it. They supplied that. The rest is according to the book and they supply tiny vials of dopants, arsenic and boron and instructions on how to do all the diffusion steps in your own micro furnace that you build from a few firebricks over an electric hot plate. They include solutions for masking and metallizing the chip and and special solder for tinning and attaching leads.

The kit is in new condition, I wonder if it is worth anything?

oldtiffie
03-31-2009, 10:11 AM
I thought they still make and use "vacuum tubes" aka thermionics - for some quality audio platforms.

sch
03-31-2009, 10:21 AM
There are lots of boutique audio equipment made in US, China, Japan and
Europe using tubes. You can buy a CD player with tube analog sections.
They like to use tubes designed in the '20s and '30s for a lot of this. Pentodes are too modern. All of the tubes are sourced from Russian or Chinese tube makers. Costs are going way up because the demand is so
low that the few production factories are also a boutique setup but afficionados will pay whatever is asked for the beloved tubes. For awhile in
the '80s east european sources were available but the economics didn't make
sense and they gradually evaporated. There is a smidgeon of NOS US and
European tubes but manufacture of these stopped in the '60s or early '70s.

Evan
03-31-2009, 10:35 AM
I have boxes of tubes. I wonder what they might be worth?

In particular I have a good collection of military peanut tubes. If anybody is restoring old aircraft radios and needs some just ask.

Just Bob Again
03-31-2009, 11:24 AM
Easily. I have a kit that was given out to science teachers by Bell Labs in the 60s. It's a "Make Your Own Solar Cell" kit. .....

I had one of those and actually made solar cells. As I recall, they included a fluoride compound to make dilute HF acid for etching. I doubt anybody would risk distributing a kit like that these days. Too bad. I learned a lot from those kits. Used the optics and speech synthesis and solar cell kit at least and maybe some others. These days, somebody probably makes a semiconductor fab video game and one for machine shop.

Liger Zero
03-31-2009, 12:12 PM
I have boxes of tubes. I wonder what they might be worth?

In particular I have a good collection of military peanut tubes. If anybody is restoring old aircraft radios and needs some just ask.

I have THOUSANDS of tubes and vintage electronic things in storage. Grandfather Smith was a WW2 radio R&D person who owned his own high-end repair-shop after the war.

Are there services that identify and buy these things?

Seastar
03-31-2009, 03:01 PM
Liger
If you weren't so far from me I would come help identify your collection.
Don't throw anything away. Most of it is worth something to restorers like myself.

Evan
I am sure that your tubes would be welcome some place.
Try ebay and see what happens.

I graduated from Purdue the year the transistor was invented so my professional career has bridged both vacuum tube and semiconductor technology.

It's suprising how many vacuum tubes are available on line.
Perhaps some of the on line suppliers would like to buy your tubes.
Bill

Your Old Dog
03-31-2009, 08:03 PM
There is still a tube manufacture here in the states but I can't remember who it is. My fairly new Fender HotRod amp has tubes in the final stage. You can still buy several models of RF amps for hams that have the 4-400A, 3-500, 572B's and a few others. The hams don't favor the russian tubes as their specs are supposedly all over the place and hard to match up pairs.

lazlo
03-31-2009, 09:00 PM
Now, if you're talking about a Mad Max apocalypse, then yes -- people aren't going to be building semiconductors in their basements. But a lot of universities have mini-fabs. Old technology, for sure (they don't have the funds or the infrastructure/chemical purity necessary for ultra fine feature sizes), but group of say 20 engineers and process physicists could probably build a mini-fab if worse came to worse.Easily. I have a kit that was given out to science teachers by Bell Labs in the 60s. It's a "Make Your Own Solar Cell" kit.

Sadly, optical lithography is a little more complicated than growing a solar cell from a children's kit. For one thing, semiconductors use mononcrystalline silicon - the entire 1,000 lb boule is one giant, ultra-pure crystal. But more importantly you have to master optical lithography, and make a set of masks, learn how to sputter. Then there's plasma etch...


The kit is in new condition, I wonder if it is worth anything?

Probably not. They sell them at Fry's in the children's science section.

Evan
03-31-2009, 09:36 PM
Sadly, optical lithography is a little more complicated than growing a solar cell from a children's kit. For one thing, semiconductors use mononcrystalline silicon - the entire 1,000 lb boule is one giant, ultra-pure crystal. But more importantly you have to master optical lithography, and make a set of masks, learn how to sputter. Then there's plasma etch...


I am entirely familiar with the process Robert. I have examples of all the steps in my collection. I also know that the original ICs were a rather simple affairs with a component density less than current surface mount devices. You don't need 12" wafers to make an IC. Incidentally, the Bell kit contains a monocrystalline slice of silicon. They weren't using polycrystalline silicon at the time that kit came out. Poly xtal was developed later as a way to cut cost. You don't need plasma etch, UV lithography or electron beam or lasers to make an IC. The workhorse ICs like the 555 timer are simple chips and can be made with simple equipment. The original wafers were cut from a slug the size of a dildo, not half a ton of silicon.

Funny thing about digital electronics, the most simple processor and the most complex can both be built using the exact same logic. You only need two functions. In principle and even in practice you can build a CPU using the AND boolean logic operation and the NOT operation. That's all you need.


They sell them at Fry's in the children's science section.


Complete with arsenic, boron and hydrofluoric acid? I doubt it.

nheng
03-31-2009, 09:50 PM
It's funny that no matter how fine the geometry gets or how many millions or billions of transistors can be placed, Microsoft continues to apply the inverse Moore's law to keep applications running at the same speed :D I'm not joking. Thanks to the massive bloat of dot net and the sluggish speed of JIT compiled languages like C#, your 3.2GHz dual core machine now runs just like your old 1GHz model. Top it off with several AV and other protection packages and you're almost back to the good ole original PC for speed :D

back to tubes ...
Just finished studying some old WWII artillery fuzes and related items and its amazing (for someone involved in modern electronics) to think about the tiny tubes that were used in airborne weapons at the time.

Den

gunbuilder
03-31-2009, 10:40 PM
Russia is still manufacturing vacuum tubes, I believe. Up until a few years ago, our Defence Department was buying them for some ancient but essential equipment.
I heard the "old" Russian tube type military equipment is less susceptible to EMP, so they use tubes.

All our "modern" electronics will be up in smoke if we get hit with an EMP.

EMP, you know H-Bomb burst at high altitude.

Thanks,
Paul

lazlo
03-31-2009, 10:47 PM
I heard the "old" Russian tube type military equipment is less susceptible to EMP, so they use tubes.

That's an Urban Legend :) I was fortunate enough to work with Boris Babaian, the "Seymour Cray of Russia," when Intel bought his company, Elbrus, in 2004.

Boris spent 40 years with the Russian "Institute of Precision Mechanics and Computer Technology" building the Elbrus supercomputers used on the Russian missile defense system. They used conventional bulk CMOS semiconductors, just like their brethren in the West, although their process technology was several process generations behind:

http://www.thocp.net/biographies/babaian_boris.htm

Bart may have met Boris as well -- Boris' company did a lot of VLIW work for Sun Microsystems in the 90's.

Boris is in his late 70's, but he's a friggin' whipper-snapper. And never, ever, agree to go out drinking with a Russian :D

Carld
04-01-2009, 12:06 AM
My son was in the Navy and told me that in the event of an atomic blast all solid state equipment was toast and the military has tube radios as backup. I would think it would be the same with the computers that power the ships and aircraft. Does that mean that if the aircraft went through a high radiation area it would fail?

Evan
04-01-2009, 01:44 AM
Does that mean that if the aircraft went through a high radiation area it would fail?

Those are two different problems. EMP stands for ElectroMagnetic Pulse. When a nuclear weapon explodes it ionizes a huge volume of air in the immeadiate area of the blast. That is cause by the sudden intense release of very high energy x-rays in the initial part of the reaction. The atmosphere of the Earth acts as the dielectric in a giant capacitor with the ground being one plate and the ionosphere the other. The standing potential on an average day with no T-storm activity is around a couple of hundred volts per meter in free air. When a cubic kilometer of air is suddenly turned conductive enormous currents flow through the air as those potentials try to equalize.

Any time a current flows it generates a magnetic field. Then, a few milliseconds later the ultrasonic blast wave compresses that air and those currents and the fields they produce are magnified by millions of times as they are forced to occupy a much smaller volume. At the speed of light an intense electromagnetic field spreads out in all directions. It is a multi gigawatt burst of wide spectrum radio energy. Anything that is conductive will act as an antenna for that signal as it goes past. In the near vicinity of the blast voltages in the millions can be induced in most any conductor which will destroy electronics and even electromechanical devices as well as any bolt of lightning.

Even a ranges of tens of miles the pulse is still strong enough to destroy all but the best hardened electrical and electronic system.

Even worse by far is if the explosion takes place in or just above the ionosphere at an altitude of several hundred to a 1000 miles depending on time of day. Then the ionosphere is compressed and the intensity of the EMP is magnified by huindreds of times. Back in the early 60s the US conducted several test blasts in space over the Pacific Ocean. One in particular called Starfish Prime was exploded hundreds of miles up and about 800 miles from Hawaii. Remember that at that time there were no solid state devices in widespread use, just plain old vacuum tubes and electromechanical systems.

The EMP from Starfish Prime knocked out the power throughout the Islands and damaged the telephone system. It blew out lighting such as street lamps and many other types of lighting that were attached to the grid.

There is no general defense possible against such effects. The only way to protect equipment is to surround it entirely within a metal container or a correctly bonded metal cage with a fine mesh. Any wires that lead in or out must have very effective surge supression on them.

Worst of all is that the entire continent of North America could be bombed back to the stone age by exploding three or four nuclear weapons at the same time several hundred miles up. There would be no radiation or blast damage but the death toll would be horrendous as all aircraft in flight would lose all electrical systems and modern cars and trucks would suddenly stop functioning. All communications would be destroyed in one second. Nuclear plants would lose all control systems including all backup systems. The entire electrical grid would fail at once.

The matter of radiation is entirely different. High levels of radiation can cause improper operation of high density integrated circuits. This is a particular problem for systems that operate in space. When a high energy particle passes through a ram or CPU chip it may cause what is called a Single Event Upset. It can flip just one bit to the wrong value causing a program to fail.

The higher the density and the smaller the feature size of a chip the more likely it will experience such failures. It also depends on the logic family with Bipolar logic followed by CMOS operating at high voltages being the most resistant. For that reason NASA still uses the CMOS version of the 486 CPU in space applications.

Weston Bye
04-01-2009, 05:55 AM
Evan,
Your scenario suggests an explanation for the previous and current North Korean activity with nukes and missiles. Maybe Iran also. Perhaps a means of "leveling the playing field", no matter how irrational.

Circlip
04-01-2009, 08:24 AM
So "Sunburn" hasn't been counteracted yet then??

Evan
04-01-2009, 08:46 AM
It's a very real scenario and one the government and military really don't like to talk about. It's the reason that the US and USSR agreed so readily to ban nuclear weapons in space early in the cold war. Since a weapon in orbit could be exploded at any moment there would be zero chance to retaliate and no warning time at all. It's also the reason why nuclear missle submarines operate under what is called "Negative Control". On a regular basis they are instructed not to fire their missiles. If they don't receive those orders for a set period of time, perhaps a month, then they fire at predetermined targets. Thats another little "secret" that they don't like to talk about.

Evan
04-01-2009, 08:51 AM
"Sunburn" is a sea skimming cruise missile, a completely different scenario.

mofugly13
04-01-2009, 09:43 AM
I have THOUSANDS of tubes and vintage electronic things in storage. Grandfather Smith was a WW2 radio R&D person who owned his own high-end repair-shop after the war.

Are there services that identify and buy these things?

Boutique guitar amp builders buy up the right tubes like crazy.

These guys buy UOS and NOS tubes.

www.tubesandmore.com

there are others....

Swarf&Sparks
04-01-2009, 12:57 PM
Yeah, check the price of Sovtek valves for a Marshall or Fender guitar amp! :eek:

Liger Zero
04-01-2009, 01:30 PM
Nuclear plants would lose all control systems including all backup systems. The entire electrical grid would fail at once.



Not just nuclear plants. Pumped storage scheme hydroplants would lose valve control, so would conventional hydroplants, coal and oil fired plants would lose control there would be massive steam explosions and fires at these plants. Gas plants as well.

Don't just push the "nuclear scare," other forms of power generation can be just as dangerous if not more so than nuclear.

Ever wonder what would happen if an enormous hydroelectric dam let go? :)

Evan
04-01-2009, 03:23 PM
An interesting thing about hydroelectric dams is the control systems. They are normally fully mechanical systems that may be operated by hand if need be. They may have the capability for remote operation but they are designed to fail safe if anything goes wrong. A total failure of the control system at a major dam would simply result in the shutdown of the generators and probably the closing of the penstock gates.

digger_doug
04-01-2009, 03:29 PM
"A total failure of the control system at a major dam would simply result in the shutdown of the generators and probably the closing of the penstock gates. "

Yes, Joe Micheals over at P.M. did a nice write up on his workplace
(a pumped hydro installation), and how he worked to build
black start tools. (portable hydraulic units and such)

I believe in 90 seconds he can be at full power, and
synchronized to the grid, ready to deliver.

hoof
04-01-2009, 05:20 PM
Really enjoyed the video, thanks alot. As for tube sources I have a small box of them from Radio Shack I got back in the 70's. They are lifetime gaurenteed. I suppose that would mean I'm set for life. :D

Liger Zero
04-01-2009, 05:33 PM
An interesting thing about hydroelectric dams is the control systems. They are normally fully mechanical systems that may be operated by hand if need be. They may have the capability for remote operation but they are designed to fail safe if anything goes wrong. A total failure of the control system at a major dam would simply result in the shutdown of the generators and probably the closing of the penstock gates.


Now apply that logic to a nuclear power plant. Nuclear power plants have the same number of fail-safes and redundancy likely more than a hydro plant. Control rods are driven by hydraulic pressure and by design they "drop on loss of signal." BWR style plans have enormous springs that drive the rods up into the reactor upon loss of control signal. The rods are on the bottom unlike a PWR type.

Browns Ferry lost control of both operating reactors due to a fire under the control room in the cable tunnel. The reactor did what it was supposed to do upon a loss of control signal... it shut down.

TMI shows even with a boiloff the damage caused by a post-shutdown loss of coolant is manageable and containable.

Not poking at you Evan, but I get tired of the "OMG NUCLEAR SH*T IS DANGEROUS OMG OMG OMG" rants. 99.99% of the nonsense circulating out there can be debunked with facts and operating experience. It's only because the TV and Media in general spend so much time harping up the dangers of "Nuklear" for drama that the public can't overcome it's fear.

A huge portion of that is paid for by various lobbies that want to see nuclear fail... Nuclear energy has the potential to displace a huge amount of petro and coal energy across many applications... not just huge steam plants like Ginna or Nine Mile Point, but in small contained portable generators as well.

Look up some of the designs for radioisotope thermoelectric generators out there, do research on nuclear photocell batteries. A nuclear battery, designed properly, could propell a car for 20 years and it would be sealed in such a way that your worst-case car-wreck wouldn't breach it.

Same thing with small plug-in community power-plant cells like they want to place in Alaska. That would take a huge load off the grid and reduce the need for central plants and an enormous complex interconnected grid.

Think the dinosaur-piss lobby wants that to happen?

The one in my town is 40 years old... hasn't killed anyone yet nor will it over the next 20 years. :)

(rant over ya'll come out now continue with the discussion)

topct
04-01-2009, 06:15 PM
We are sitting on a source of heat that could be used for power that can be used very cheaply.

It is the earth itself.

Nuclear power does nothing but create filth. Those that propose its use are simpletons.

Liger Zero
04-01-2009, 06:24 PM
We are sitting on a source of heat that could be used for power that can be used very cheaply.

It is the earth itself.

Nuclear power does nothing but create filth. Those that propose its use are simpletons.

Except the technology to access geothermal on demand just doesn't exist in a practical mode yet.

Nuclear power does. :)

And just want to point out most pro-nuclear folk are highly educated. It's the anti-nukes that get pre-digested opinions from a talking box on the wall who are simpletons. :)

topct
04-01-2009, 06:45 PM
Except the technology to access geothermal on demand just doesn't exist in a practical mode yet.

Nuclear power does. :)

And just want to point out most pro-nuclear folk are highly educated. It's the anti-nukes that get pre-digested opinions from a talking box on the wall who are simpletons. :)

It does exist.

Who are these pro-nuclear folk? I would rather follow the money. If they were as truly educated as they claimed they would know what I am saying.

The science of the approach does not rely on pre-digested opinions. It is pure fact.

It is the most dirtiest of things.

Liger Zero
04-01-2009, 06:52 PM
Ok I see the geothermal plants that are currently running. Very nice.

But what about my town? We don't have any vents, volcanic activity or anything of the sort. Just how deep would we have to drill to access the heat? And how many of these injection-wells would we need to replace the 500+ megawatts we get out of our local nuclear thing?

Not practical... yet.

sansbury
04-01-2009, 09:21 PM
It is the most dirtiest of things.

Think so? Read this--"Coal Ash is more radioactive than nuclear waste."
http://www.sciam.com/article.cfm?id=coal-ash-is-more-radioactive-than-nuclear-waste

Geothermal systems drink a lot of water and do ugly stuff with it--there's a lot of heavy metals and other nasties down there under the crust. The way things are going it won't be long before water becomes as precious as oil.

There are good techniques out there for reprocessing spent fuel, glassification, and other ways to reduce the waste problem. Public perception and the regulation it drives is a big reason why fission power hasn't made much headway in a few decades.

OTOH, there's been a big uptick in positive news from fusion lately. The key thing I see is that we're seeing some progress on designs other than the giant tokamaks, which have soaked up incredible amounts of money relative to the energy produced. It's not a sure thing yet, but if one of these architectures works, you're looking at the generation capacity of fission with none of the waste or catastrophic failure modes.

Evan
04-01-2009, 09:50 PM
Not poking at you Evan, but I get tired of the "OMG NUCLEAR SH*T IS DANGEROUS OMG OMG OMG" rants.

I don't recall me or anybody else ranting or anything similar about nuclear power. I happen to be in favor of utilizing nuclear energy sources as long as an end to end solution to waste disposal is included in the plan.

Scramming a reactor is not a particularly safe procedure. It can cause serious problems in the cooling systems of LBW reactors if all systems shut down at once. It may even damage core components making it impossible to restart. Of course, that is a moot point if all your controls are destroyed. You then have a hot pile with no long term cooling sytems. The chance of venting happening is very good.

That wasn't my point anyway. It came to mind because it is one of the more obvious type of systems where manual control is not an option.

Evan
04-01-2009, 10:01 PM
It's not a sure thing yet, but if one of these architectures works, you're looking at the generation capacity of fission with none of the waste or catastrophic failure modes.


That is one of the biggest fairy tales ever foisted on the public.

As an example, the ITER experimental fusion reactor will generate 60 million pounds of radioactive waste during it's planned lifetime. 20 percent of that will be high level waste including the reactor vessel itself. The reactor vessel will be so "hot" that it will have to be entombed for at least 100 years before it can be dismantled and transported somewhere for disposal. These numbers are from ITER but they are less than forthcoming with the real data. In their accounting of waste disposal they include a tiny footnote that says "excluding removed components/materials". Those are by far the most radioactive parts in a fusion reactor and require the same treatment as high level waste such as used fuel rods.

Liger Zero
04-02-2009, 10:57 AM
Scramming a reactor is not a particularly safe procedure. It can cause serious problems in the cooling systems of LBW reactors if all systems shut down at once. It may even damage core components making it impossible to restart. Of course, that is a moot point if all your controls are destroyed. You then have a hot pile with no long term cooling sytems. The chance of venting happening is very good.


They've come a long way with "SCRAM" mode shutdowns since TMI. Also, they've come a very long way in eliminating the need to use that shutdown mode by developing preventive and predictive maintenance programs.

One of the things they look at for re-licensing is the number of full on SCRAMs a plant has experienced in it's life. Nuclear-components aside that's an enormous thermal transient over a very short period and it takes its toll on welds,mounting brackets, pipe-straps and the very infrastructure of the plant.

I sort of lost track over the years but apparently they wanted to block the licensing of Oyster Creek in New Jersey because of it's piss poor availability recor... JCP&L (the original operators) used "Reactive Mantainance" (fix it after it breaks) resulting in hundreds of forced shutdowns over the years resulting in them exceeding the recommended number of thermal cycles.

sansbury
04-02-2009, 05:11 PM
That is one of the biggest fairy tales ever foisted on the public.

As an example, the ITER experimental fusion reactor will generate 60 million pounds of radioactive waste during it's planned lifetime. 20 percent of that will be high level waste including the reactor vessel itself. The reactor vessel will be so "hot" that it will have to be entombed for at least 100 years before it can be dismantled and transported somewhere for disposal.

OK, fair enough, any process that emits neutrons is going to produce hot stuff. ITER looks, as expected, to be the worst design in this regard, though I haven't seen a model of what the waste stream from something like the National Ignition Facility-derived plant would look like. Bussard/Polywell looks a lot more efficient in this regard.

Well, we don't have to worry too much about that since ITER will probably never be more than a giant science-fair project.

My understanding (which could be wrong) was also that while fusion waste starts out as hot as fission waste, the half-life is also a lot shorter, so the disposal problem is not as extreme.

Liger Zero
04-02-2009, 06:11 PM
Depends on what they build it out of. As we go forward and gain understanding of the process we'll know which materials to avoid.

For example some %&*&tard thought high-cobalt steel was a good idea on some nuclear power plant valves and systems. IIRC Indian Point spent $$$$ to eliminate as much of it as possible because it becomes active and generates a nice low-level buzz.

Operating experience. TMI had to happen so we could improve the next generation of plants.

Chernobyl... exists as an example of "when we tell you it's a piss poor design LISTEN TO US" and "seniority/political reliablity cannot change the laws of physics!" :D

Evan
04-02-2009, 07:10 PM
My understanding (which could be wrong) was also that while fusion waste starts out as hot as fission waste, the half-life is also a lot shorter, so the disposal problem is not as extreme.


It very much depends on the materials. Unfortunately some of the most desirable materials also have the greatest activation potential, tungsten carbide being an example. The way I see it is if the lifetime during which the material is dangerous to be around is longer than a human lifetime then the requirement for dedicated autonomous containment facilities becomes the same regardless of whether the half life is 500 years or 50,000 years. We cannot depend on future generations to take care of our messes with the necessary caution they demand.