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Old 12-02-2020, 09:07 AM   #11
DataPacRat
 
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Originally Posted by Anthony View Post
The regular radiation rules assume gamma rays; low energy nuclei have much worse penetration. 0.2c is only 19 MeV/nucleon, even 0.5c is only 145.
Is this the source of 'solar flares and planetary radiation belts' getting a rPF*20, due to being 'mostly free electrons and alpha particles' (pB436)?

If so, a factor of 20 doesn't reduce a total accumulated dose of 95B rem by all that much...


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Originally Posted by Say, it isn't that bad! View Post
Plus, at higher tech levels, radiation shielding can be combined with both radiation medication, and genetic engineering for radiation resistance, tolerance, and recovery.

Resisting +10% more Rems; tolerating a Rem dose +10% higher; and being able to recover from 0.5 Rems per year; would (calculated simply) combine into being able to handle +33.1% more Rems per year. And, if dosage remains below 6.05 Rems per year, you could also slowly recover from Rem overdoses.
This particular probe is unmanned. It contains a fairly complete genetic library of Earth, and a small robofac that could theoretically eventually build gizmos to build cells from scratch, but during the interstellar voyage proper nothing living needs to be protected.
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Old 12-02-2020, 10:11 AM   #12
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Originally Posted by DataPacRat View Post
Is this the source of 'solar flares and planetary radiation belts' getting a rPF*20, due to being 'mostly free electrons and alpha particles' (pB436)?

If so, a factor of 20 doesn't reduce a total accumulated dose of 95B rem by all that much...
Well, that's also the GURPS radiation rules being wrong. Assume it counts as 20 layers, not 20 PF.
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Old 12-02-2020, 10:15 AM   #13
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Well, that's also the GURPS radiation rules being wrong. Assume it counts as 20 layers, not 20 PF.
I'm not quite sure what you mean by that; could you elaborate?
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Old 12-02-2020, 10:27 AM   #14
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Default Re: [Spaceships] Magnetic Shielding above TL8

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I'm not quite sure what you mean by that; could you elaborate?
Basically, the way it works is:

High energy particles and gamma rays have an average penetration, and undergo exponential decay (reduce intensity by a factor of e for every multiple of the average, or by a factor of 2 for ever 0.69* that average, or by a factor of 10 for every 2.3* that average). This value depends somewhat on energy.

Moderate energy charged particles do not undergo exponential decay -- they just lose energy at a fairly consistent rate and eventually stop. In the process they produce secondary radiation, which works the same way as gamma rays, but if you choose your shielding material properly the secondary radiation doesn't have a lot of penetration.

If you have 100g/cm^2 of shielding and the stuff you're shielding against is gamma with a tenth-value-thickness of 50g/cm^2, you have PF 100. If it has a TVT of 20 g/cm^2 you have PF 100,000. If it has a TVT of 10g/cm^2 you have PF 10,000,000,000.
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Old 12-02-2020, 10:43 AM   #15
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Originally Posted by Anthony View Post
Basically, the way it works is:

High energy particles and gamma rays have an average penetration, and undergo exponential decay (reduce intensity by a factor of e for every multiple of the average, or by a factor of 2 for ever 0.69* that average, or by a factor of 10 for every 2.3* that average). This value depends somewhat on energy.

Moderate energy charged particles do not undergo exponential decay -- they just lose energy at a fairly consistent rate and eventually stop. In the process they produce secondary radiation, which works the same way as gamma rays, but if you choose your shielding material properly the secondary radiation doesn't have a lot of penetration.

If you have 100g/cm^2 of shielding and the stuff you're shielding against is gamma with a tenth-value-thickness of 50g/cm^2, you have PF 100. If it has a TVT of 20 g/cm^2 you have PF 100,000. If it has a TVT of 10g/cm^2 you have PF 10,000,000,000.
Ah, I know what you're referring to, now. I was still thinking in terms of EM deflection rather than physical materials, which is why I was confused.


My current notes are that this probe's front is covered with some 80 lb/cf wood (geneered from Australian Buloke), a layer 85 cm thick, a total of around 109 g/cm^2. I don't have any notes on the TVT of the particles I'm interested in - in fact, I'm not completely sure it's relevant, as the main purpose of the wood is less to shield the probe, and more to break up the neutral atoms into charged particles for the magshield to fend off. But my instincts there might be wrong; any chance you know the TVT for dissociated protons and electrons with a speed on the order of 0.01c?
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Old 12-02-2020, 10:48 AM   #16
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Default Re: [Spaceships] Magnetic Shielding above TL8

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But my instincts there might be wrong; any chance you know the TVT for dissociated protons and electrons with a speed on the order of 0.01c?
They're charged particles, don't have a TVT, and are stopped by tissue paper.
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Old 12-02-2020, 10:56 AM   #17
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Default Re: [Spaceships] Magnetic Shielding above TL8

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They're charged particles, don't have a TVT, and are stopped by tissue paper.
That... doesn't seem to match what my reference material describes.

Just dug up the URL; https://arxiv.org/ftp/physics/papers/0610/0610030.pdf is what I'm drawing most of my approach form. It mostly focuses on 0.1c and above, a bit faster than what I'm looking at, so I've been trying to extrapolate downwards.
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Old 12-02-2020, 11:08 AM   #18
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Default Re: [Spaceships] Magnetic Shielding above TL8

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That... doesn't seem to match what my reference material describes.

Just dug up the URL; https://arxiv.org/ftp/physics/papers/0610/0610030.pdf is what I'm drawing most of my approach form. It mostly focuses on 0.1c and above, a bit faster than what I'm looking at, so I've been trying to extrapolate downwards.
Take a look at page 4, table c. That shows penetration in tissue and titanium (penetration appears to be the logarithm of penetration, in centimeters). The curve for penetration depth in titanium appears to hit the bottom of the chart (-2, or 0.1mm) at about 0.1c.
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Old 12-02-2020, 12:44 PM   #19
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Take a look at page 4, table c. That shows penetration in tissue and titanium (penetration appears to be the logarithm of penetration, in centimeters). The curve for penetration depth in titanium appears to hit the bottom of the chart (-2, or 0.1mm) at about 0.1c.
... That makes my life ridiculously simpler. I can reduce the magshield down to a token, mostly for a bit extra rPF while at a star system instead of during the long voyage.

My attention was focused on table b, the rem/s, extrapolating that down to 0.01c and working from there. I completely missed the one you just described.

That also implies that the radiation dose is mostly from uncharged cosmic rays, and at 0.01c those are pretty much the same as while stationary - 104 rad/year. A lot better than 0.5/second, but 104,000 (minus whatever's blocked by rPF) over a trip still needs some mitigation; if nothing else, keeping the probe's minifac busy melting down and rebuilding every component multiple times. pB436 mentions that every 100 rads a piece of electronics experiences needs a HT roll,so an effective rPF of 1,000 would be nice, but that would need a main rPF of 100,000 because of cosmic rays' penetration, which is kind of infeasible for any probe on this scale.

Unless I'm missing a trick - which I think we've established I'm rather prone to.

The setting's technobabble includes some new understandings of some basic physics, such as how photons and neutrinos work; if need be, I can nudge the details to include a new trick that counts as superscience, though I'd prefer keeping any such gizmo as low-key as possible.
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Old 12-02-2020, 12:56 PM   #20
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Default Re: [Spaceships] Magnetic Shielding above TL8

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That also implies that the radiation dose is mostly from uncharged cosmic rays.
Cosmic rays are usually charged (they're heavy nuclei) though they can be very high energy, you want shielding sufficient for multi-gigavolt particles.
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