The Story (Literally)
Extract: First Draft, Third Person Limited.
"C'mon! We need the engines back, now!" Valerie yelped over the general channel. The interceptor floated adrift, otherwise without any radio-signature. The jellyfish-like leviathan of lashing tendrils that was the apex sparred with the main ship, leaving whips of PDC fire dashing over them.
Jayden floated idly in a cloud of debris and discarded tools, above the fusion reactor core. Kitsuki floated in a corner, wrestling the cargo bay door open. "I have a plan, and Val ain't gonna like it." Jayden muttered, only Kit on the channel.
He wrenched out the reactor's antimatter catalyst cylinder from its cooling system. Its magnets glowing idle blue. "No no n-n-no. This is going to get us killed." "Maybe, but we're all dead anyway. If we don't kill it."
He knocked his mag-boots together and they disengaged, floating up next to the canister. Getting himself in between the canister and the apex, he kicked off the ground, spun and kicked the canister with both legs, right at the leviathan. It lashed its tendrils to meat the canister, and just as he swung behind the tank, he swung the rifle off his back and leveled it.
There was a bright bolt of plasma and-
He came to. He noticed his ears hurt, a lot. They rung with deafening silence. Water floated everywhere, blobs freezing as they coalesced, in the shimmering cloud of shrapnel that used to be the starboard side of the engineering bay. He took a second to thank the nameless engineer who invented anti-spalling net, which was the only thing between the fiery debris of the tanks, and both of them being shredded.
"...What happened?" Valerie asked, dead calm.
It's quite simple, how much water and ship do you need to put between you and the gamma ray flash of a canister of antimatter exploding. Let's just say that it was a few miligrams of X kind of antimatter. I would like it to be full anti-hydrogen, to be consistent with most other antimatter in the book, but it would in all reality just be positronium. And only throw off gamma rays.
If you chucked it out and it managed to get a kilometer away from the ship before exploding, and you get behind seven inches of steel and ceramic shield plating, (possibly the drive cone of the ship, because it was facing the explosion), a nondescript tank of reaction mass (water), and a thick anti-spalling net, could you reasonably survive?
I can only get as far as figuring out the energy of such an explosion, and sort of attenuating it with distance, beyond that I have no clue as to whether my fluffy crew gets reduced to ashes.