Lightweight Radiation-proof Fabric?

kramer writes "New Scientist is reporting the creation of a lighweight radiation-proof fabric called Demron. Demron is being touted by its inventors as comparable to lead shielding at a fraction of the weight. Could be very useful for any future interplanetary space missions where the amount of radiation absorbed by the crew is a significant concern."

Comments

Re:Imaginary Particles?

[Ann Coulter]

The electron clouds give an "illusion" of large atoms when viewed with gamma or X-rays. These electron configurations are just as effective for providing radiation obstruction as any heavy element such as lead or bismuth. Illusions can beget real effects if used correctly.

No, weight

[Grotus]

Weight might not be a big issue once you are actually in space, however, it is a huge issue when it comes to getting there. The currently used number for launch price is around $10000 a pound to get into low earth orbit.

Testing

[justanyone]

It seems reasonable that that gamma radiation (high energy photons) could be intercepted by a 'cloud of electrons' in the polymer in this material.

However, high energy neutrons would not interact with the electrons due to their high velocities. The relativistic effect of width/length contraction applies to these neutrons. This was the fundamental problem of early fission reactors - they had to moderate (reduce the speed of) the neutrons in order for them to appear big enough to interact with a nucleus. An electron is 1,836 times less massive than a proton. Thus you'd need 1836 electrons to equal one proton-with of neutron blocking power. I doubt they have that many electrons in the polymer's cloud!

However, any material that more effectively screens high energy photons is a welcome material. It would also be highly useful in creating X-Ray and Gamma-ray telescopes, methinks! NASA, you listening?

The article should have gone into which radiation types besides Alpha particles that it would block (Alphas I think are just Hydrogen nucleii - or is it Helium...).

Cosmic ray shielding would be useful on the ISS as well, but it would not stop relativistic particles, and it might break down under repeated insults of high energy collisions occurring regularly in space.

Any nuclear engineers out there who can comment better? go Navy?!?

Re:Testing

[Anonymous Coward]

Alpha particles are Helium nuclei. Hydrogen nuclei on the other hand, are commonly referred to as protons :)

Re:Testing

[Imabug]

anybody who's studied radiation interactions with matter will tell you that for gamma/X rays, it's not the density (g/cm^3) of the material but the electron density (electrons/cm^3) that determines the attenuation properties of a material. Generally, metals with a higher atomic number (Z) have more electrons, so they usually have better attenuation properties.

As it turns out, sometimes you can pack lighter weight nuclei close enough together that you get a similar electron density to metals (or even higher sometimes). this is probably what they've done with this 'polymer'. Althogh on a mailing list I'm on, someone mentioned that the material was just fabric that had been soaked in a barium solution and dried. Whether that was true or not was never establised though.

There is one incorrect statement in the article though.

"The helium nuclei that make up alpha radiation have so little energy that almost any physical barrier can stop them."

Alpha particles can be emitted with extremely high energies, upwards of 10 MeV. What makes alpha particles so non-penetrating is their charge. Their +2 charge causes them to interact very strongly with neighbouring electrons, which causes them to lose energy quickly. That's also the reason why there isn't any special shielding necessary for alpha particles. Most alpha particles will be stopped in the dead layer of your skin, and therefore pose little external hazard. What makes alpha particles dangerous is if they become internalized (inhaled or ingested). The fact they lose energy quickly means that energy is transferred to whatever material it happens to collied with, causing much damage in the process.

Re:Testing

[esonik]

With respect to gamma/X-ray shielding who depend on electron number, I don't think that large improvements in total weight of shielding can be made. The reason is of course that for charge neutrality reasons each electron has to be balanced by one proton in a core plus some amount of neutrons. It is only the amount of additional neutrons that can be varied by chosing different materials and as it happens to be the percentage of neutrons in nuclei increases with Z, with the extreme being the hydrogen 1H atom that has no proton at all. From this reasoning it would be best to use materials with high hydrogen amount (polymers for example) to reduce weight. But then volume is a concern too, esp. with polymers who have a low density (compared to high Z metals).

radiation suits is a misnomer

[weglian]

I was a Navy nuke, so I know a thing or two about radiation. What people think of as "radiation suits" are not designed to shield radiation. They are used to prevent contamination. The suit prevents radioactive material from getting on your skin and clothes, so that you don't take it home with you. There are several kinds of radiation. Alpha particles are helium nuclei (He4). These particles are not dangerous unless you ingest or breathe them into your lungs. The dead layer of skin on your hand is enough to stop them. If they get into your body, they cause serious harm, as there is no "dead layer" of anything to stop them. Beta particles are electrons. They are light and fast, so they penetrate more. They will give you a dose to your skin, but not much deeper than that. A contamination suit can probably stop Betas. Even the old ones. Gammas are photons/electromagnetic radiation. Whatever you want to call them. X-Rays, microwaves, and radio waves all fall into this general category. The real biological hazard comes from the high energy particles/waves. These will pass right through your skin and can affect your internal organs. A contamination suit is not expected to reduce the dose from gammas. neutrons are produced in fission and some rare decay events, mostly shortly after a fission event. Neutrons are the only thing that can make something ELSE radioactive. Neutrons have no charge, so shielding them is difficult. It takes LOTS of lead or iron or water, etc. I don't care what their material is made of, if it's light enough to wear, it will not shield neutrons well. The web site said that it shileds low energy gammas, alphas, and betas. Low energy gammas don't cause much harm. Unless you work with a low energy gamma source on a routine basis, this material is not going to change your life. Or your life expectancy. This is my first post. Is it WAY too long? Sorry. -John

Secondary emissions?

[dpilot]

The article doesn't mention anything about the secondary emission characteristics of this fabric.

Secondary emissions are a very real bane of shielding for interplanetary travel, due to the extremely high energies of cosmic rays. Even if you could launch lead shielding for a spacecraft, manageable thicknesses would cause secondary emissions that were even more dangerous to the occupants than the original cosmic rays.

They've tried a new type of radiation shielding on the ISS made of polyethylene that is supposed to block without creating secondaries, and I see that's part of this fabric. Unfortunately the new shields don't seem to be as effective as hoped.

Radiation is anticipated to be a big problem on a Mars mission. IIRC, the radiation exposure will have a cancer risk equivalent to a lifetime of smoking.

But you really know to be scared of cosmic rays if they make rapping noises on your spacecraft, and upon return to Earth you start stretching, bursting into flame, become invisible, or turn into a pile of muscular orange bricks.

Some Additional Information

[ljhiller]

I checked out their website a few days ago and as you've noticed, it has no details. You can get an idea of the technology from their granted patent (amended) 6,459,091 here. The idea in the patent is to impregnate cloth with a heavy metal such as barium salt, with a metal film layer or cloth woven from metal thread for additional protection. The technology mentioned in the New Scientist article sounds like a newer version that is still pat. pending. There's still no hard information about how well the suits actually work for the different radiation sources, e.g. Medical x-rays, airline cosmic rays, nuclear warfare. It's all marketing.

Re:Underwear

[theedge318]

If you are worried about radiation, you might want to kick your wife out of bed, b/c she is exposing you to 0.1 millirems of radiation per year. Which incidentily is the same amount of radiation you experience by living within 50 miles of a nuclear power plant. Before you kick your wife out of bed, which will have its own adverse affect on having children, try doing the following to reduce your radiation exposure:

• Throw away your alarm clocks and wrist watch, the glowing hands give you 0.6 mrem/year.
• Or try giving up bananas, most people recieve about 40 mrems/year per year in Potassium-40 radiation
• But the absolute worst source of radiation, cigarettes- 1.5 packs per day = 8000 mrem/year
• And move away from coal fired plants; Uranium occurs naturally in coal, which when burned exposes you to 1-4 mrems/year

All thanks to having a girlfriend at a national lab (which probably means she radiates more than your wife ... so I am going out and buying lead blankets) For more radiation doses: Lawrence Berkeley Labs

This is bullshit and I can PROVE it.

[Peter T Ermit]

I'm not even going to talk about the ludicrous "science" behind the fabric, and I'm not going to talk about how it tends to be heavy nuclei, not electrons, that stops ionizing radiation. Even without using those arguments, I can still show that they're full of shit.

Check out their "test results." (PDF file) Go to page 3 to see the blocking power of their fabric.

Error #1: There is no such unit as a Kv. They mean KeV, as in Po-210 emits an alpha particle with 5,300 KeV of energy. But this is minor.

Error #2: X-rays and gamma rays are both photons; they're only distinguished by their energies. But the X-ray results and gamma ray results (which overlap in energy, which, in itself, makes no sense) contradict each other. For example, why does the fabric block only 52% of 60KeV gamma rays, but 82% and 72% of 50 and 70KeV X-rays respectively? Makes no sense, but this is nothing compared to...

Error #3: The real killer, and what makes me suspect this is fraud, rather than mere incompetence. They use 0.5 mm of lead as the comparison for their gamma emitter tests. The radiation-absorbing properties of lead are well known, and easily accessible in handy-dandy tables. For example, the half-value layer (the amount of material needed to block 50% of incoming radiation) for a Co-57 source is 0.15 mm of lead (ref here ), so 0.5 mm of lead should block more than 90% of the radiation, not just 52%. Proof positive that they're full of shit.

Fuck them, and fuck New Scientist. (Pardon my French.)