The Controversy of a Potential Hafnium Bomb

deglr6328 writes "Physics Today has a report detailing the surprisingly heated controversy surrounding the usually sober science of nuclear isomers (the Washington Post has run a less scientifically rigorous version). Since the 70's it has been known that the specific "m2" isomer of Hafnium-178 has an extraordinarily long half life of 31 years (nuclear isomers usually have half-lives on orders of pico or nanoseconds) and on decaying, emits high energy gamma rays at ~2.5 Mev. The prospect of energy storage and rapid release in Hf-178 for the puropse of creating large energy stores, bombs and even exotic gamma ray lasers did not escape the interest of Reagan era Star Wars researchers and was seriously studied for a time during SDI's heyday, but was eventually abandoned after being considered unfeasible. Then, in 1999, Carl Collins at the Univ. of Texas Center for Quantum Electronics reported inducing energy release from Hf-178 by bombarding a sample with X-rays (from a dental machine no less). Immediately, comments about the article were submitted, pointing out inconsistencies with basic nuclear theory and the controversy has only grown since then, with claims and counter-claims of flawed experimental design, incompetence and irrational theories in feuds reminiscent of the cold fusion debacle of the late 80's. It's seeming more unlikely as the arguments drag on, but if a Hafnium bomb could be built, it is thought that a golf ball sized chunk could produce the energy equivalent of 10 tons of conventional explosives."

Comments

What is Hafnium?

[Anonymous Coward]

Find out here!

isotope vs isomer

[frankie]

For those of us non-nuclear scientists (like me) who thought isomer meant a molecule with different bond orientations (e.g. trans vs cis), here's an explanation: A nuclear isomer is a metastable state of an atom caused by the excitation of a proton or neutron in its nucleus so that it requires a change in spin before it can release its extra energy.

Next question: how the heck do you control the spin of individual baryons in a nucleus?

Re:isotope vs isomer

[Christopher Thomas]

Next question: how the heck do you control the spin of individual baryons in a nucleus?

You fire something at the nucleus and isolate the ones where one of the outer-shell nucleons was bumped up to the energy state you want.

If you fire X or gamma rays at the nucleus, you should only be able to excite very short-lived isomers (if it is boosted by absorbing a photon, it can decay by emitting a photon). Firing things like electrons or protons at the nucleus can excite states that don't have a single-photon decay path. These can be metastable.

We do the same thing in HeNe lasers. Helium atoms are excited to a metastable state by electric discharge, and after a while interact with neon atoms, putting them in a state suitable for lasing (target state of neon has almost exactly the same energy as the metastable helium state, so the exchange happens easily).

I hope this helps :).

Experiments not reproducible

[starbuzz]

American Physical Society columnist Bob Park reports in his What's New column that the Hf-experiments were found by several groups to be not reproducible. That puts the claim squarely in the category of Bogus Science.

• April 2004
• August 2003

Atomic Weight

[kcdoodle]

This research is flawed.

Hafnium is like phoshorus. It spontaneously combusts on contact with air. Adding gamma or xrays isn't going to activate the nucleus of the Hafnium atom somehow.

Elements that offer nuclear energy are either at the low end or high end of the periodic table. Low-end atomic weight element hydrogen and helium (1 and 4) can be made to fuse (fusion) to create middlish weight elements and energy (look at the sun). High-end atomic weight elements like uranium and plutonium (235 and 238) can be made ti split (fission) and create middlish weight atoms.

So there is NO WAY you will get a energy-yielding atomic reaction with hafnium and gamma/xrays.

Hafnium is used in many reactor control rods and are constantly exposed to a barrage of neutrons, gamma rays, fission fragment particles, etc. If this reasearch were true, nearly every nuclear reactor on the planet would be blowing up right now.

Hafnium might be used in weapons, but it is no more dangerous than phosphorus.

I live the greatest adventure anyone could want. - Tosk the Hunted

Re:Atomic Weight

[SEE]

Who modded this up? Obviously no one who understood the physics of the story. So let's explain.

The process described is neither fission nor fusion. Instead, it's analogous to how a light bulb works.

(What? Yes, a light bulb. Bear with me.)

In a lightbulb, you add energy to a fillament. The electrons (mostly) in the fillament are placed into excited states by the energy, then very quickly release the energy in the form of photons (visible light) and fall from the excited state into a ground state.

A similar thing can be done to particles other than electrons -- such as neutrons. In most cases, the neutrons fall from the excited state very quickly and release photons (gamma rays and the like).

In hafnium, however, the excited state of the neutrons is metastable -- which is just a fancy way of saying they stay excited for a long time between when they're excited and when they release photons.

If a way could be developed to induce the grounding, then hafnium could be used to store large amounts of energy in the metastable state, and then induced to release it all at once, resulting in much larger discharges than ordinary chemical reactions can store/release.

It doesn't yield energy; at best you get from the grounding the energy you put in to get the neutrons excited. It isn't fission, and it isn't fusion; not what we typically call a "nuclear" reaction. However, it is a beyond-chemical-bond-capacity energy release based on the nucleus.

Oh, and by the way, there are middlish-weight elements that are unstable, and thus can provide nuclear energy through ordinary radioactive decay. The classic example is Technetium, number 43 on the Periodic Table, atomic mass 98.

Ten TONS, not ten KILOTONS.

[tukkayoot]

When I read the summary, I thought "10 tons of TNT... kind of weak". Because really it is, compared to nukes. I browsed the article, so for those who didn't bother to RTFA, the contraversy here is not that the stuff is so powerful, but that it is a lot more powerful than conventional explosives but not as powerful as nuclear weapons... so they don't fall under the domain of most non-proliferation treaties.

On a side note, this kind of makes the terrorist thing a moot point. I mean, I have to think it'd be very tricky to make a weapon out of these things, since there is so much debate on whether or not it's even possible to unlock the energy (hence the "Cold Fusion" reference). If it's a more difficult to weaponize this stuff than uranium and plutonium, as well as having less destructive power, I doubt we'll see any terrorists using this kind of thing as a weapon for a long, long time.

I'm not particularly worried. Seems we've already let a much more horrible genie out of the bottle.

Even if Hafnium emits X-rays, still no Bomb!

[Salis]

Like the end of the report (linked in the slashdot article) mentions, even if Hafnium does indeed emit 2.5MeV X-rays when hit by a 20 keV X-ray then it still could not be used to make a bomb.

A bomb requires that a chain reaction occur so that the energy released from the initial X-ray emission propogates and hits other Hafnium atoms, making them emit more X-rays. There are two reasons why the bomb will never 'explode':

1) The possibily bogus research report stated that only a 20 KeV (or a 10 KeV, whatever) would trigger Hafnium emissions. So there would be no propogation from one Hafnium emission to the next.

2) The 2.5 MeV photons would interact with other particles (electrons, itself, etc) and sap away that energy before it came into contact with another Hafnium atom.

So, don't worry about a bomb, it's all vaporware.

Re:How much energy?

[Glock27]

Gamma photons are not heat. The heat radiation is in the infrared. VERY different part of the spectrum there. (X-ray patients don't warm up when they're being examined. They might get cancer though, through the ionization effects though.)

When atomic weapons explode, most of the energy is released in the soft X-ray region. This is simply a consequence of the black body curve and the (extremely high) temperature of a nuke blast.

In the atmosphere (note emphasis) these soft X-rays are quickly absorbed (average free path is something like 9 in. if I remember correctly) and then re-emitted as thermal radiation. That is why there's a "fireball" from a nuclear bomb.

If the bomb were to explode in space, there would be much less thermal effect.

Why do you think nuclear reactors work through heating water instead of X-ray absorption? Hint: It's not just because it's easier.

No, it's because the reactor materials become hot. Note that in a fission reactor the temperature never reaches several million degrees, where the X-rays would be produced, as they are in a nuclear explosion.

I hope this cleared things up for you. If not, read more at TutorGig. Read the part about 2/3 of the way down under "Effects of a Nuclear Explosion".

Re:Power, Science and Death

[tiger99]

Yes, but these guys had virtually no computers to support their work. Nowadays anyone can build a Beowulf cluster, but I suspect that if you are not in too much of a hurry, a standard PC is capable of simulating lots of things that the Manhattan Project team could only guess at, or measure by a series of tedious experiments. Also, much more is known about explosives nowadays, "simple" shaped charge theory should be sufficient to get a spherical implosion, the rest apart from the neutron source to ensure efficent explosion, is fairly straightforward using published information.

One evil genius and a small team of good technicians could do it, given the plutonium. A basic weapon would not need to be all that much bigger than the plutonium core, depending on how fast the detonation velocity of the conventional explosive is. The yield-enhancement features which make the thing much bigger would not be too important to a terrorist. In fact, a low explosive yield, tons rather than kilotons, of TNT equivalent, might be of more use to a terrorist, AFAIK the fall-out from unreacted plutonium etc would be very much worse, and the area might be uninhabitable for a very long time. Apparently there was minimal fallout in either Hiroshima or Nagasaki, people were mostly injured or killed by radiation absorbed by their bodies in the few microseconds of the blast, although the horrific deaths are probably continuing to this day. I strongly suspect that a low-yield weapon in a modern city would kill a lot more people, maybe a few hundred by blast and direct radiation, but a million might inhale plutonium dust before they could be evacuated, all of them would die, mostly of lung cancer.

However,if you want to get it past radiation detectors, you have to do a lot more, although AFAIK most of the output from the plutonium, and probably the polonium in the initiator, is alpha and easily stopped.

But, my guess is that an inexperienced team who could get sufficient plutonium might try a cylindrical configuration, it might be even easier to get the simulations correct, and it might fit more easily in a briefcase, but it would use more material.

As computers are widespread, and everything you need to know to build a weapon is published (why that was ever allowed, I don't understand!), the only means of control is to restrict the circulation of plutonium. It makes me sick to think that enough for maybe 50 or 100 weapons has simply been allowed to go missing over the years. Much of it might simply be lost, not in the hands of the wrong people, but where is it, and who is it polluting?

I would be even more worried if large amounts of U235 went missing, an idiot could make a uranium bomb using published information, nothing remotely high-tech is required, but that one would be heavy. Even worse, a suicidal maniac with 2 pieces of U235 could create a "fizzle" with no extra hardware, it would kill a lot of people if used in a crowded place such as a city. Note that the Hiroshima bomb was untested, they knew it must work, even in 1945, with no simulation. The test at Alamogordo was for the plutonium bomb used on Nagasaki.

BTW you are right about the silver in Fort Knox, but it got recycled afterwards, and was used because of a wartime shortage of copper. I don't think a terrorist would go that route, they would not need a uranium enrichment plant for a plutonium weapon, AFAIK plutonium is "relatively" easily separated from used reactor fuel rods by a chemical process. But, stealing used fuel rods would be suicidal, and it would need very elaborate robotic handling to be able to do the processing. I think that any makeshift processing facility would leak so much radiation that it would soon be discovered.

I think that society as a whole needs to think about installing many more radiation detectors (they can be cheap and unobtrusive) so that unauthorised movements of radioactive materials will be spotted. They will also help prevent accidents such as the one in the US some years ago when a cobalt source was melted d