The gamma radiation itself doesn't cause immediate damage unless it is so dense that it transfers huge amounts of energy into nearby materials and vaporises it, but due to the penetrating properties of gamma radiation this would require quite a massive yield, and most of the energy would still escape.
Considering that the hulls are made to block cosmic radiation and withstand nuklear weapons (like the torpedoes) wouldn't that mean they aren't easily penetrated by gamma rays?
So unless they found a way to deflect radiation away from the hulls, wouldn't that mean instead of going through without causing harm, those gamma rays instead heat up the inside of those armor plates?
Apart from possibly making those plates softer till they can cool off again (depends on the material I guess) that should also raise the ships internal temperature causing the crew some discomfort and reducing the effectiveness of the cooling systems for beams and reactors.
Also antimatter tipped warheads sound like a shaped blast to me, so in front of the impact site there would be intense energy released, probably enough to vapourise the hull there. And if that material get's into the corridors of the ship, it'd be rather catastrophic I think.
Yes, that would work - for all the ships in close proximity. Would be interesting to do the math on how much gamma radiation would be needed for hull plating to absorb enough energy to start significantly heating up, though. It'll cause radiation sickness long before that happens, I would wager, but don't take my word for it, it's just my intuition.
The problem is, gamma rays spread evenly from a point source, and their effectiveness reduces in inverse square of distance. The even distribution means that at reasonably short distance, they won't be doing much damage at all (at least immediate damage - they may cause radiation sickness, but that doesn't immediately put a warship down like compromised hull structure will.
If you instead convert most of the energy from the reaction into kinetic energy (assumign you can do this) and send shrapnel from the blast site, you get a much more "coarse" distribution of possible damage - but at the same time, the damage delivery is more efficient. The
probability of getting hit by pieces of shrapnel will decrease in the inverse square of distance,
but individual pieces of shrapnel don't lose their initial kinetic energy, which means the individual pieces of shrapnel retain their effectiveness regardless if distance, unlike a free gamma burst.
Or, let me put it this way.
Let's say you have a free gamma burst of a 0.1 kg anti-hydrogen warhead. Assuming a clean conversion from energy to gamma rays, you will be getting 9x10
15 Joules of gamma radiation, spectrum spikes at 511 keV (electron-positron-annihilation spike) and 125, 307 and 530 MeV spikes for proton-antiproton annihilations. This is about 2.151 Megatons of TNT. This energy might sound like a lot (and it is, considering it's from 100 grams of antihydrogen), but let's break it up into what sort of effect it would actually have.
The higher the energy of photons, the more penetrating they are, which means their linear attenuation coefficient is reduced when they go through the same thickness of absorber. If you have,
d metres of hull plating at attenuation coefficient
α, you could relatively easily calculate the linear attenuation for each gamma spectrum spike and thus determine the percentage of absorption of pass-through gamma radiation:
I = I0 e-αdWhere
I0 is the intensity of radiation when it impacts the absorbing hull plate, which can be pretty trivially calculated if you know the distance from the annihilation site (and if you want, you can just deal with energies instead of power and intensity, since the time of annihilation reaction is pretty short).
I have no idea of the attenuation factors of spaceship hull material, but they'll be different for each gamma wave length. However, let us generously assume that the hull plating absorbs 80% of the gamma radiation.
The energy released in 0.1 kg antimatter warhead is, like said, about 9x10
15 Joules. At 1000 metres distance, the amount of energy passing through one square metre of space is
9x1015 J / 4 π (1000 m)2 = 716197244 J m-2Which is about 716 megajoules of energy per square metre.
For comparison, if you have a ton of water ice at 273.16 K temperature (solid form), it takes 333 megajoules to thaw it to 273.16 K temperature liquid. But if you had a cube of water ice with mass 1000 kg, at 1000 metres from the annihilation site, it would probably not melt all the way because the attenuation factor of water isn't too high; much of the gamma radiation would pass through.
So that's the practical effect of 0.1 kg annihilation warhead at one kilometre distance. If you replace the ice cube with humans, they'll heat up a bit and contract severe radiation sickness, but I doubt it would have radical effect on ship hull plating. Closer to the blast site, sure, but 1000 metres is relatively small distance even in FreeSpace.
Now, let's look at another scenario: let's say 80% of the annihilation energy is converted into kinetic energy of shrapnel pieces.
To be ambitious, let's make fragmentation shell with following configuration:
-Total mass 12566371 kg
-Mass of individual fragments on average 1 kg.
80% of 9x10
15 Joules is 7.2x10
15 Joules.
That as kinetic energy given to mass of 12 566 371 kg yields a velocity of 33.85 km/s.
Each fragment has thus velocity of 33.85 km/s and, unsurprisingly, kinetic energy of 572.9 MJ (which is 80% of the radiation of gamma rays passing through the one square meter area.
You might wonder why I picked such a random-looking value for the amount of shrapnel particles. Well, the reason is that the surface area of a sphere with radius of 1000 metres is 12 566 370.6 square metres, and when you evenly distribute 12566371 shrapnel particles on that area, you should get about one shrapnel piece per square metre, which is important in comparing the efficacy of this setup compared to the free gamma ray setup.
We've established that there will be about 12.5 million 1 kg pieces of shrapnel flying at almost 34 kilometres per second, and by average at distance of 1000 metres you will get one of them per one square metre of surface area.
Now you'll remember that the effect of gamma radiation on a block of ice was quite... lacking in destructive power. By contrast, I don't think anyone has any difficulties about what happens to a block of ice when it's impacted with one kilogram mass moving at 34 km/s.
Similarly, a projectile with 34 km/s is much more efficient against space ship hulls than an even spread of gamma radiation. Against organics, sure, you'll achieve a high mortality rate with induced radiation sickness, which may be an interesting way of acquiring ships relatively intact; gamma radiation does not irradiate materials like neutron radiation does, so in a way this would be much better way of dealing with space ship crews without causing excessive damage to the ship itself.
But, in open combat this would not work. The crew would stay operational for some while after the gamma burst. That's why as a pure weapon, the shrapnel based one would function better.
Any thoughts? Spot any calculation errors?
