Gamma-ray shielding against bursters

[stevebowers]

Centauri Dreams has an interesting article about shielding, suggesting that simply burying your civilisation underground would not be enough
http://www.centauri-dreams.org/?p=36591
This is based on a paper by M. Ćirković and B. Vukotić: Long-term prospects: Mitigation of supernova and gamma-ray burst threat to intelligent beings

I disagree that burying your civilisation underground would be of little value, since the shields described would be useless at stopping cosmic rays - but they could act to protect the biosphere of a planet from the worst effects, making recovery more certain.

Note that we have at least one event in OA that required the use of hi-tech biosphere shields- the Verifex Event was countered by large scale Emple-DokCetic shielding, which is described as being an array of smart matter very like the one described by Ćirković. if and when I get hold of the preprint I'll post it here, and perhaps we can incorporate some hard data into the Emple-DokCetic article.

[Rynn]

One possible solution with OA-level technology would be to upload the entire biosphere. Take the most detailed recording possible, bury a whole bunch of crashcaches with fabs and use the industry and data to regrow after the event. A massive undertaking sure, but for a terragen civ it costs little more than time and inconvenience given that the processes of terraformation are largely automated (like everything else).

[selden]

Wouldn't the caches have to be protected, too?
Could adequate shielding be produced before the wavefront hits?

Gamma rays are photons and travel at c, so there wouldn't be much, if any, warning that such an event was about to happen if you're depending only on direct observation. When you see that it's blowing up, it's too late: the photons have already arrived.

Presumably substantial predictive capability would be needed to determine where such caches would be needed (i.e. to determine where and when a GRB is going to happen) and they'd have to be implemented well in advance. I'm sure the local modosophonts would strenuously object to their lives being interrupted "unnecessarily". Preventing colonization in threatened regions might or might not be particularly effective. People live on active volcanoes, after all.

[stevebowers]

Note that the Verifex event was set up rather cleverly by Anders so that the wavefront from the supernovas was first detected by a nearby system connected to the Wormhole Nexus, which allowed some warning to travel to more distant systems before the wavefront arrived. OA wormholes do allow a certain amount of information to travel faster than light, but they do not allow reversal of causality (the worlds affected by the wavefront could get advanced warning, but they could not act upon that information to prevent the explosion).

[Cray]

I'm a little dubious about the figure "need to burrow up to 3 kilometers below the surface before the incoming flux would drop to 1% of its initial value. "

Earth's atmosphere cuts cosmic ray and gamma ray fluxes to just about 0. Or, specifically, background ionizing radiation dose on Earth at sea level is about .000001 R/hour.

Unless you're delivering so much energy as to ablate and move the shielding material (like a weapons-grade laser), the number of gamma rays and cosmic rays doesn't matter when determining shielding thickness requirements. What matters is the energy of the individual rays.

Gamma ray bursts don't generate rays particularly more energetic than the ones that hammer Earth every day. Frankly, distant gamma ray bursts are probably the source of some of the stuff pounding Earth every day. Water cuts their dose in half for every 7cm of water; a 7-meter water shield reduces that by a factor of 2^100. The atmosphere does the same as about 2.8m of water.

It's just bloody weird to say "1% will still get through 3km of rock."

[stevebowers]

I think it is the cosmic ray flux that Circovic is talking about, but the paper may explain that. If, on the other hand, they have a reasonable configuration in mind for the shield, then it may be worth adapting to OA. Any shield would necessarily be quite thin, even if it only just covered each inhabited planet. Such a thin shield would not stop cosmic ray photons - but a magnetic shield could deflect charged particles.

[Cray]

but a magnetic shield could deflect charged particles.

A lot of cosmic rays are protons and heavier atomic nuclei, so magnetic fields will help with them. It's why ISS astronauts don't rack up much of a radiation dose.

[stevebowers]

We have megascale magnetic shields in OA, often in the Lagrange position.
http://www.orionsarm.com/eg-article/4851d85e0791b
If the direction of a GRB were known then the same technology could be used to protect against them. Alternately a Bussard ramscoop could be used, with the focus situated safely away from the planet.

[selden]

Don't forget that magnetic fields don't provide any protection against photons, i.e. no protection against gamma rays. Most of the articles I've seen discuss the damage done by gamma rays. e.g. https://arxiv.org/pdf/astro-ph/0503625

[Cray]

Don't forget that magnetic fields don't provide any protection against photons, i.e. no protection against gamma rays. Most of the articles I've seen discuss the damage done by gamma rays. e.g. https://arxiv.org/pdf/astro-ph/0503625

Yep. They blitz the ozone layer and may deliver some dangerous rads at ground level. But they're not going to punch through 3km of rock.