[Vehicles] How big should a self-destruct be?

[Anthony]

Originally Posted by DataPacRat

By the by, does anyone know offhand how much conventional explosive is used in a typical A-bomb, to compress the fissionables to criticality?

Probably classified, though it's going to depend on what you're trying to do with it (technically, you can get a criticality without any explosives, it just disassembles itself before producing much of an explosion).

Originally Posted by DataPacRat

Also, while I'm thinking about it, how about how much gamma-emitting metastable isomer do you need to have before throwing in some tritium or other fusables would start adding to the explosive force?

The problem with using it for a super tiny fusion weapon is that the explosive product is 2.5 MeV gamma rays, which will not be efficiently absorbed by a compact fusion target (this also limits the minimum practical size, as you need to wrap it in enough shielding to efficiently absorb gamma; a couple centimeters of lead is adequate. Of course, if you're just interested in destroying electronics, just expose it directly, you can wipe electronics with much less radiation than it takes to melt or vaporize the chips).

[DataPacRat]

Originally Posted by Anthony

The problem with using it for a super tiny fusion weapon is that the explosive product is 2.5 MeV gamma rays

Actually, my reading suggests that if I use niobium instead of hafnium, the emitted photons are only around 30.77 keV (7.44 EHz, 40.3 picometres), more in the hard x-ray range than gamma. (Still probably not all that easy to convert into fusion, though.)

Of course, if you're just interested in destroying electronics, just expose it directly, you can wipe electronics with much less radiation than it takes to melt or vaporize the chips).

Indeed; I came across an optional GURPS rule - I forget which edition - that a target with built-in physical contact with a carefully-placed explosive automatically takes full damage. Implying that a single gram of isomer-in-carrier-plastic would dump 32 rads straight onto whatever chip it was built into, before even counting explosive damage. Even rad-hardened chips have their limits.

[Anthony]

Originally Posted by DataPacRat

Indeed; I came across an optional GURPS rule - I forget which edition - that a target with built-in physical contact with a carefully-placed explosive automatically takes full damage. Implying that a single gram of isomer-in-carrier-plastic would dump 32 rads straight onto whatever chip it was built into, before even counting explosive damage. Even rad-hardened chips have their limits.

Not appropriate to radioactive weapons, but also 32 rads is ... multiple orders of magnitude wrong.

[DataPacRat]

Originally Posted by Anthony

Not appropriate to radioactive weapons, but also 32 rads is ... multiple orders of magnitude wrong.

My figuring:
Pyramid 51, page 9; isomers have a REF of 100 (presumably from tiny amounts of actual isomer embedded in whatever clay/plastic/etc carrier substance is chosen), and refers to the rad modifier on pB105, which inflicts "1 rad per point of basic damage rolled". pB415 offers the damage formula of 6d * ((lbs * 4 * REF)^.5), so 1/500th of a pound of REF 100 material does about 5.3d6 damage, which maxes out at 32 points. 0.01 lbs is 12d6, 0.1 lbs 38d6, 1 lb 120d6, 6 lbs 294d6, etc.

Where did my numbers go wrong?

[Anthony]

Originally Posted by DataPacRat

Where did my numbers go wrong?

At the point you started using GURPS rules. 1/500lb at REF 100 is about 400 kJ, assuming a distance of 10 cm and a 1/e penetration of 10 g/cm^2, absorbed dose is about 30 kJ/kg (enough to get the chips hot but nowhere near melting) or 3,000,000 rads. Which is around twenty times what the best rad hardened chips can survive.

[DataPacRat]

Originally Posted by Anthony

At the point you started using GURPS rules. 1/500lb at REF 100 is about 400 kJ, assuming a distance of 10 cm and a 1/e penetration of 10 g/cm^2, absorbed dose is about 30 kJ/kg (enough to get the chips hot but nowhere near melting) or 3,000,000 rads. Which is around twenty times what the best rad hardened chips can survive.

These are some fascinating numbers; do you have a reference handy where I can learn more about them, so I can figure out such quantities for myself in the future? (Or, failing that, a quickie equation or two which I could refer to?) Eg, for larger amounts, would I linearly scale by mass of the isomer-explosive (x10 stuff, x10 radiation), or by GURPS' explosive damage-scaling (x10 for each x100 increase in mass), or some other factor? And for radiation dose, do I simply apply inverse-square, with a base of 3M rads at 10cm, or another approach?


(3M rads for 1/500th of a lb puts a whole new complexion on using 1/500th of a modified pollinator cyberswarm to carry that much isomer-explosive to a target... But I've gotta admit, I enjoy learning new things in this forum that make me have to completely rethink my earlier ideas.)

[Fred Brackin]

Originally Posted by DataPacRat

By the by, does anyone know offhand how much conventional explosive is used in a typical A-bomb, to compress the fissionables to criticality?


Also, while I'm thinking about it, how about how much gamma-emitting metastable isomer do you need to have before throwing in some tritium or other fusables would start adding to the explosive force?

The thing with TL7-8 plutonium core bombs is that what you're doing with the explosives is changing the shape of the plutonium from a hollow sphere to a non-hollow sphere as quickly as possible. The average density of the hollow spehre wasn't high enough for neutron chain reactions but the non-hollow sphere is-until the energy released blows the sphere apart.

I'm being very cautious about using the word "solid" because after the explosives go off the sphere is a liquid metal until it's a rapidly spreading plasma. Indeed, I think the last componets of a nuclear bomb to do their job in a solid form are the wires that lead to the detonating caps.

In Gurps terms the explosion probably does more damage than the plutonium's HP but less than -10 x that HP. It's my interpretation that at -10xHP you've pslattered the plutonium rather than neatly compressed it. For the masses traditionally used for critical mass of Plutonium (5 to 6 kilos or 11 to 13 lbs) that's 18-20 HP. That would mean we''re talking about the equivalents of 0.75 lbs of TNT something around 25 lbs.

I warn you that this is all Gurps theory. No real nuclear secrets were divulged.

That's fission but you need neutrons to initiate fission. That's why you had to use plutonium which is a natural source of neutron radiation. To intiate fusion you have to have heat. So schemes to initiate fusion with gamma (or even x-rays) have problems. You need that high energy EM radiation to be absorbed by something and turned into heat that way.

The reason contemporary fission-fusion-fission bombs work as well as they do is that neutrons->fission->heat->fusion thing and the fact fusion (the D--T and De-De reactions specifically) puts out 80% of its' energy in the form of neutrons and those neutrons then ignite another fission stage.

Pure fusion devices.with no fission have problems. see the "National Ignition facility" for an example of the scale you have to work on.

[DataPacRat]

Originally Posted by DataPacRat

These are some fascinating numbers; do you have a reference handy where I can learn more about them, so I can figure out such quantities for myself in the future? (Or, failing that, a quickie equation or two which I could refer to?) Eg, for larger amounts, would I linearly scale by mass of the isomer-explosive (x10 stuff, x10 radiation), or by GURPS' explosive damage-scaling (x10 for each x100 increase in mass), or some other factor? And for radiation dose, do I simply apply inverse-square, with a base of 3M rads at 10cm, or another approach?


(3M rads for 1/500th of a lb puts a whole new complexion on using 1/500th of a modified pollinator cyberswarm to carry that much isomer-explosive to a target... But I've gotta admit, I enjoy learning new things in this forum that make me have to completely rethink my earlier ideas.)

After some further reading myself, the simple equation for explosive force is 4 kg per gram of TNT; so it looks like I can simply multiply the total radiation by the mass of the isomer.

Temporarily sticking with $1 worth of isomers, 1/500 lb, sticking to inverse square, if we have 3M rads at 10cm, that'd be 30k rads at 1 metre, 300 rads at 10 metres, and 3 rads at 100 metres. Or, if we go up to 1 lb, worth $500, it's 1,500 rads at 100 metres, and 15 rads at 1 km.

... Anyone know offhand how much air absorbs hard x-rays of around 30.77 keV / 7.44 EHz / 40.3 picometres? I know that the overall atmosphere absorbs pretty much all cosmic x-rays before they reach the ground, and I've been able to dig up the occasional reference such as https://www.exul.ru/education/1/30.pdf that seems to imply the process takes on the order of a few 10s of metres of air. (I've also found tables such as https://physics.nist.gov/PhysRefData...omTab/air.html , but I don't yet understand what things like "μ/ρ" or "μen/ρ" mean.) On the other hand, if x-rays of this energy level are reasonably penetrating, then I don't see too many governments allowing the production, storage, or use of such isomers anywhere near a biosphere.

[Plane]

Originally Posted by DataPacRat

A particular space-borne cybershell has around 100 hp
..
According to Vehicles, 100 micrograms of antimatter should do around 0.00125 kilotons of boomage, or 15d*2000 damage, an average of 105,000 points.

One idea that came to mind to model a self-destruct would be taking B136-7's Fragile: Explosive as a "Controllable Disadvantage" perk.

6DxHP/10 would be 6Dx10 for something with 100 HP though so that would fall way short of what you want.

Makes me wonder if it could be bought as a leveled perk though...

Like if you take Self Destruct [100] you get 100x the damage from your explosion?

6Dx1000 is only an average of 21,000 so I think you'd actually have to take 500 levels of it.

I wonder if a cheaper approach might be to design a one-use-ever innate attack (this is -80% or 1/5 cost depending on where you look) which is also powered by character points (may as well: you'll have no use for them!)

You could design this as an "Internal Advantage" to cut costs further, I think? 1/5 there

I don't think there's anything stopping you from defining an internal advantage as AE and having that AE damage things outside you, but your own body HP would probably count as "cover DR" for anything outside of you, so that would limit your ability to damage external foes without destroying yourself...

Except of course if you took "Injury Tolerance" because unlike buying DR that won't add to your cover DR...

Kind of a neat trick there, potentially. Hard to exploit for low-cost characters due to the high cost of injury tolerance, of course.

[DataPacRat]

Originally Posted by DataPacRat

After some further reading myself, the simple equation for explosive force is 4 kg per gram of TNT; so it looks like I can simply multiply the total radiation by the mass of the isomer.

Temporarily sticking with $1 worth of isomers, 1/500 lb, sticking to inverse square, if we have 3M rads at 10cm, that'd be 30k rads at 1 metre, 300 rads at 10 metres, and 3 rads at 100 metres. Or, if we go up to 1 lb, worth $500, it's 1,500 rads at 100 metres, and 15 rads at 1 km.

... Anyone know offhand how much air absorbs hard x-rays of around 30.77 keV / 7.44 EHz / 40.3 picometres? I know that the overall atmosphere absorbs pretty much all cosmic x-rays before they reach the ground, and I've been able to dig up the occasional reference such as https://www.exul.ru/education/1/30.pdf that seems to imply the process takes on the order of a few 10s of metres of air. (I've also found tables such as https://physics.nist.gov/PhysRefData...omTab/air.html , but I don't yet understand what things like "μ/ρ" or "μen/ρ" mean.) On the other hand, if x-rays of this energy level are reasonably penetrating, then I don't see too many governments allowing the production, storage, or use of such isomers anywhere near a biosphere.

After eyeballing some more charts, I finally got an estimate that about 15 metres of air absorbs half of the X-rays of this wavelength. Based on that, I was able to throw together a quick spreadsheet to estimate concussion damage and whole-body rads received, in vacuum and in air, at https://docs.google.com/spreadsheets...n-8/edit#gid=0 . (The one thing I haven't figured out how to turn into an equation is 3e's rules on explosive damage range, which doubles for every so many dice of damage.)
For 1 lb of isomers and carrier goop, I end up with in-atmosphere numbers of:
0-12 metres: >50,000 rads, death in 0-1 hours
14-30 metres, >3,000 rads, death in 1-2 days
35-40 metres, >1,000 rads, death in 1-2 weeks
45-50 metres, >400 rads, 50% chance of death
55-70 metres, >100 rads, acute radiation sickness
75-135 metres, >1 rad, little immediate effect
150+ metres, <1 rad, no immediate effect.
... all of which compare to average concussion damage, which in 3e terms is around 200 (blown to smithereens) at 9 metres, 10 (50% death for unprotected person) at about 17 metres, and around 0 at 30 metres. In vacuum, there's at least 400 rads out to 150 metres, and 100 rads out to 350 metres.

... All of which adds up to some fairly strong reasons that this stuff isn't used as an everyday explosive, and is likely LC1. And the only reason I'm not dropping it to LC0 is that it's a fairly self-contained zone of death without much risk of spreading uncontrollably, the way fallout or bioweapons (the standard examples for LC0) can. But I might change my mind; maybe I'll peg it around an average of LC0.5, depending on jurisdiction.