For Questions That Don't Merit Their Own Thread

[KG3]

9 hours ago, ARS said:

If we replace the fragment grooves on frag grenade casing with diamonds to make it sprays diamond fragments everywhere when it explodes, does it make the grenade more effective in dealing with armored infantry?

Yes, I believe these are standard issue in the army of cloned Marilyn Monroe.  

https://www.youtube.com/watch?v=hEyWqVfY4vo

 

[magnemoe]

9 hours ago, DerekL1963 said:

Probably not.  For all it's hardness, diamonds are extremely brittle - the explosion alone would probably turn them into dust from the shock.

Yes, you would get dust who would slow down fast, you would in fact want larger fragments to have better chance to penetrate armor, however you can also go for more and smaller ones because just head and torso has amor. 

Some bombs and other weapons is design to not give large fragments to limit effect, the coke box on stick grenades is just explosives to not generate fragments. 
An shotgun slug police uses to shoot up doors will turn into dust on impact so if it penetrate the door if would not be very dangerous for people in the room. 
 

[YNM]

4 hours ago, p1t1o said:

Was a practical, physical question. With possibly a bit of a crossover into semantics.

Digital information is an encoded information. Without the necessary means of decoding, it is not intelligible.

In Japan, before Unicode came along, there used to be multiple means of encoding text characters. If you send files from one encoding into another, they'd clash and produce garbled results (they even had a name for it, mojibake).

Analog means of reproduction however, means that regardless of how it is preserved (say, with microfilms), the text remains intelligible as it retains the information of what the physical object was, and not an instruction to recreate the physical object.

Same goes to music (bytes in .mp3 vs. the grooves in a vinyl record or magnetization of magnetic tapes), videos (bytes in MPEG vs. the capacitance of disks or the magnetization in magnetic tapes or the grooves on an optical disk).

Digital data can even be encoded further for physical storage, such as the various rainbow books for CD.

[tater]

 

 

[p1t1o]

2 hours ago, magnemoe said:

Yes, you would get dust who would slow down fast, you would in fact want larger fragments to have better chance to penetrate armor, however you can also go for more and smaller ones because just head and torso has amor. 

Some bombs and other weapons is design to not give large fragments to limit effect, the coke box on stick grenades is just explosives to not generate fragments. 
An shotgun slug police uses to shoot up doors will turn into dust on impact so if it penetrate the door if would not be very dangerous for people in the room. 
 

There is such a thing as a "Dense Inert Metal Explosive" warhead, packed with metal dust and with a carbon fibre (instead of steel) casing.

https://en.wikipedia.org/wiki/Dense_Inert_Metal_Explosive

This is intended to limit the collateral damage by drastically limiting the shrapnel range, whilst preserving intense destruction in the target region.

All-in-all, it works exactly as advertised with one unusual effect - they tend to generate a much larger proportion of amputations in the blast zone. There are also concerns that survivors injuries can be complicated by multiple micro-shrapnel wounds, introducing particulate heavy metals into their bodies with unknown long term effects.

[magnemoe]

38 minutes ago, p1t1o said:

There is such a thing as a "Dense Inert Metal Explosive" warhead, packed with metal dust and with a carbon fibre (instead of steel) casing.

https://en.wikipedia.org/wiki/Dense_Inert_Metal_Explosive

This is intended to limit the collateral damage by drastically limiting the shrapnel range, whilst preserving intense destruction in the target region.

All-in-all, it works exactly as advertised with one unusual effect - they tend to generate a much larger proportion of amputations in the blast zone. There are also concerns that survivors injuries can be complicated by multiple micro-shrapnel wounds, introducing particulate heavy metals into their bodies with unknown long term effects.

Did not know, who would it differentiate from just explosives in an fiber casing? One effect is that the overpressure wave would be faster and therefor have higher risk of blasting derbies in all directions

Two reasons to use this bomb, one is that you can have your own forces much closer so they can charge in just after the bomb hit and maximize on the shock and confusion.
Other is then enemy is hugging close to civilians in an dense city.  

[p1t1o]

1 hour ago, magnemoe said:

Did not know, who would it differentiate from just explosives in an fiber casing? One effect is that the overpressure wave would be faster and therefor have higher risk of blasting derbies in all directions

Two reasons to use this bomb, one is that you can have your own forces much closer so they can charge in just after the bomb hit and maximize on the shock and confusion.
Other is then enemy is hugging close to civilians in an dense city.  

 

Approx half the mass of an iron bomb is the heavy steel casing. This doesnt just produce fragments, but also serves to contain the detonation for a fraction of a second before bursting. This has the effect of increasing blast yield, by allowing pressure to spike the reaction progresses much faster and to a higher completion than otherwise.

DIME explosions are not safe to be around, they are still bombs after all, but due to shrapnel, the minimum safe (exposed) distance from a standard iron bomb is measured in kilometres. With a DIME it might be a few hundred metres (blast-driven debris has much less energy than a casing fragment.)

It would be wrong to assume that it would, say, destroy one house and leave the people next door safe and sound.

 

I also really love this design, the CBU-107 "Passive Attack Weapon":

https://en.wikipedia.org/wiki/CBU-107_Passive_Attack_Weapon

In a nutshell, its a standard cluster bomb casing, but instead of bomblets, it contains a large number of heavy tungsten rods, ranging in size from a few inches to a foot or so long. These have the effect of absolutely obliterating structures, with zero shrapnel or blast of any kind. Deployed differently to a regular CBU, the footprint can be made quite small.

There is another version which is packed with conductive carbon filament, specifically designed to attack power substations and similar, the cloud of filaments drapes over electrical cables and equipment shorting everything out.

https://en.wikipedia.org/wiki/Graphite_bomb

 

 

 

 

 

Edited October 23, 2018 by p1t1o

[K^2]

7 hours ago, p1t1o said:

Approx half the mass of an iron bomb is the heavy steel casing. This doesnt just produce fragments, but also serves to contain the detonation for a fraction of a second before bursting. This has the effect of increasing blast yield, by allowing pressure to spike the reaction progresses much faster and to a higher completion than otherwise.

Point of clarification for anyone that might miss this, it's the mass of the casing that provides brief confinement, not structural strength. No material is strong enough to make an iota of difference to a detonation wave, but inertia is a big factor on these time scales. Hence, while lighter, stronger materials are certainly available, they aren't helpful. Steel is a good compromise between providing enough mass, giving the bomb sufficient strength in transportation and handling, and being relatively cheap as casing material.

[kerbiloid]

On 10/19/2018 at 6:57 PM, p1t1o said:

What is the maximum physical size of a "bit" before it becomes a "dot"?

You could try this as a rough approximation.
https://en.wikipedia.org/wiki/Planck_length.

On 10/22/2018 at 2:36 PM, KG3 said:

If an altimeter works by measuring barometric pressure at what altitude does it stop working?  Same with pitot tubes.  Is there an altitude that pitot tubes stop reading air speed because there just isn't enough air?

It works everywhere. Though the less dense is density, the worse is accuracy, until the measurement error exceeds the value itself,
And the higher you get, the more volatile is the atmosphere.

So, if it worked at 100 km, the satellites would have it.

On 10/23/2018 at 5:35 AM, ARS said:

If we replace the fragment grooves on frag grenade casing with diamonds to make it sprays diamond fragments everywhere when it explodes, does it make the grenade more effective in dealing with armored infantry?

Yes, but against yours own.
The more diamonds in grenades - they less money for anything else.

Diamonds are 3.5 g/cm3, while steel or cast iron is 7.8, so energy per cross-section area is twice lower for a diamond (if take equal mass of both per grenade).
And all of them are still harder than bones, vest or helmet.

19 hours ago, p1t1o said:

There is such a thing as a "Dense Inert Metal Explosive" warhead, packed with metal dust and with a carbon fibre (instead of steel) casing.

https://en.wikipedia.org/wiki/Dense_Inert_Metal_Explosive

This is intended to limit the collateral damage by drastically limiting the shrapnel range, whilst preserving intense destruction in the target region.

Now I understand what were those hand grenades in Duke Nuk'em 3d.

Edited October 24, 2018 by kerbiloid

[raxo2222]

How close you can stand behind 1 kt - 1 Mt nuclear bomb in space?

Assuming you have normal space suit and you are behind 1 meter of lead block.

In space there is no shockwave and all energy from explosion is dissipated instantly.

[p1t1o]

1 hour ago, raxo2222 said:

How close you can stand behind 1 kt - 1 Mt nuclear bomb in space?

Assuming you have normal space suit and you are behind 1 meter of lead block.

In space there is no shockwave and all energy from explosion is dissipated instantly.

I know that all of the necessary maths is probably on projectrho somewhere, I might get back to you, depending on how far down the rabbit hole is required.

Or if you want:

http://www.projectrho.com/public_html/rocket/radiation.php

http://www.projectrho.com/public_html/rocket/spacegunconvent.php

 

The attenuation of radiation by 1m of lead will not necessarily be a trivial calculation. Different radiation types are stopped differently, and have different effects on the body. But probably a broad idea can be gotten. Not all bombs are the same either, but again, a general idea can be gained from the known amounts of energy involved.

 

Exceedingly rough estimate (without lead shield):

A "lethal dose" of radiation is not a fixed amount and varies wildly but generally starts around 1-5 Greys. (A "Grey" is a unit of ionising radiation dose. Joules absorbed per kilo of body mass. Radiation that passes straight through is harmless).

Lets assume a 100kg person, large, but easy to calculate for.

Lets assume 10% absorption for all radiation types (horribly inaccurate, but we are going for broad strokes here)

Lets assume, ooh, lets say 1 square metre cross section?

 

So, very roughly, a "lethal" dose of 5 Greys would be absorbed when 5000joules of ionising radiation passes through your 1m2 person. 

5000joules passes

500joules absorbed

5joules per kilo body mass

 

So now we have a "lethal" flux of 5kJ per m2

Using spherical trigonometry, it will now be easy to estimate the distance for any particular size of weapon for which this occurs.

100kt = 4184e11 joules total

Of which roughly (VERY roughly) half of which is ionising radiation.

2042e11 joules ionising radiation in all directions.

 

Area of sphere = 4pi r2

Area of 1km radius sphere = 12566370m2

Flux at 1km = roughly 16MJ per m2

 

Using the inverse-square law, we can find the distance where flux = 5kj/m2

 

Which works out to be about 57km for an unprotected person with the characteristics mentioned above. Which seems about the right ballpark, 100kt is not a small nuke.

Remember that there is no atmospheric attenuation in space. On Earth, the safe distance (ionising radiation) would be much, much less.

Also remember that the above calc is EXCEEDINGLY rough.

 

You can extrapolate the same figure for different yield by using the inverse-square law again.

Multiply yield by x

Multiply lethal distance by square route of x

 

So for a 1Mt device, the lethal distance (with above caveats) would work out to 180km

 

 

These are super quick calcs, if anyone can see a problem with them, shout out.

I would say that the error bars are in excess of +/-30-50% based on the simplified assumptions I made about radiation spectrum, absorbance and various other things that have been left out.

 

NB: for an almost-certainly-lethal-to-anyone dose of 50Gr, divide all distances by about 3. Lethal doses are explained at length on the links provided, amongst other things.

 

Edited October 24, 2018 by p1t1o

[DerekL1963]

1 hour ago, raxo2222 said:

How close you can stand behind 1 kt - 1 Mt nuclear bomb in space?

Assuming you have normal space suit and you are behind 1 meter of lead block.

In space there is no shockwave and all energy from explosion is dissipated instantly.

There's no shockwave in space because the shockwave is a product of the energy of the bomb interacting with matter (in this case, the atmosphere) around the bomb.  However, you provide matter in the form of a lead block...

[raxo2222]

13 minutes ago, DerekL1963 said:

There's no shockwave in space because the shockwave is a product of the energy of the bomb interacting with matter (in this case, the atmosphere) around the bomb.  However, you provide matter in the form of a lead block...

So I guess it would partially vaporize lead block and shoot it away :p

Farther out it just might melt surface.

[kerbiloid]

Spoiler

41 minutes ago, p1t1o said:

Lets assume a 100kg person

 

41 minutes ago, p1t1o said:

lets say 1 square metre cross section

The 1 m thick lead block had fallen on him.

 

41 minutes ago, p1t1o said:

Of which roughly (VERY roughly) half of which is ionising radiation.

In vacuum it would be ~100% X-ray + some gamma.

No air to make shockwave, light, and most part of gamma.

(Though, this twice dose compensates the twice cross-section area.)

***

OP should make clear: how long is he going to stay alive after/during the experiment.

5 Sv (= 5 Gr for photons) are ~LD50 (with medical assistance).
The distance should be multiplied by :
sqrt(5) = 2.2 = to just get the acute radiation syndrome (1 Sv).
sqrt(10) = 3.2 = to just get the clear symptomes (0.5 Sv)
sqrt(20) = 4.5 = to just get the appropriate dose for apocalyptic warriors (0.25 Sv)

But if you have a protection, it will provide you with 13/density (g/cm3) up to 23/density half-value layer (cm) for gamma and hard X-ray.

So, for the lead (11.3 g/cm3) ~1.5 cm.

As you have 100 cm of it, it will decrease the dose for 2^(100/1.5)= 2^(66.66666).... oops almost totally.

(At this place I have been ninja'd by @raxo2222)

Edited October 24, 2018 by kerbiloid

[p1t1o]

1 hour ago, raxo2222 said:

So I guess it would partially vaporize lead block and shoot it away :p

Farther out it just might melt surface.

Strongly dependant on conditions. If your lead block is being actually propelled by the detonation, Id say you dont have to worry about safe distances anymore.

It makes sense, it takes a lot less energy to kill a human than it does to move a 1m thick slab of lead.

 

1 hour ago, kerbiloid said:

  Reveal hidden contents

 

The 1 m thick lead block had fallen on him.

 

In vacuum it would be ~100% X-ray + some gamma.

No air to make shockwave, light, and most part of gamma.

(Though, this twice dose compensates the twice cross-section area.)

Depending on the nature of the weapon, neutrons can be a significant contributor, and not all X/gamma rays are the same. There will be a spread across the spectrum, with various peaks, depending on the exact makeup of the weapon.

It is possible to build a warhead that will emit huge amounts of neutrons and much less Xray, and also the reverse is possible. Rumour has it that it is possible to tailor the radiation emission quite finely by engineering the case and components in various ways.

Interestingly, since gamma and hard Xray are the same thing, which term you use seems to depend more on which field you are in than anything else (though it is usually the source which decides) but generally Xrays are used in nuclear weapon physics because of how they are formed (mostly from electrons - gamma mostly refers to emission from a nucleus).

 

@raxo2222 for extra credit, google the word "bremsstrahlung" - this is a thing which complicates the calculation of radiation shielding.

Which is already complicated - for example, to get an idea of how much lead you need, or the effects of a certain amount of lead (or whatever element) you need to be able to digest this:

https://physics.nist.gov/PhysRefData/XrayMassCoef/chap3.html

 

Edited October 24, 2018 by p1t1o

[kerbiloid]

18 minutes ago, p1t1o said:

It is possible to build a warhead that will emit huge amounts of neutrons and much less Xray

Neutron bombs are usually presumed to be of <10 kt yield range.
So, 1 Mt would clearly be a dull normal bignuke with most part of energy emitted as X-rays.

Also if take a neutron bomb (85% of energy in neutrons iirc) we should multiply the dose (i.e. divide the required energy) by 5..20 (depending on the neutron energy).
So, the safety distance for 1 kt neutron bomb should be multiplied by 2..4.

P.S.
Mars nuking is also an interesting question.
The "air" is thin, so no sphere, no significant aerial shockwave, no light emission, no bremsstrahlung, just Xray and original gamma.

On another hand if detonate it right at the surface, then a half of energy will hit the ground like on Earth, and make a cloud of vaporized ground.

On the third hand, as the air is thin you can hit the Martian base from orbit with an Xray/gamma-laser, unlike on Earth.

Edited October 24, 2018 by kerbiloid

[magnemoe]

1 hour ago, kerbiloid said:

 Neutron bombs are usually presumed to be of <10 kt yield range.
So, 1 Mt would clearly be a dull normal bignuke with most part of energy emitted as X-rays.

Also if take a neutron bomb (85% of energy in neutrons iirc) we should multiply the dose (i.e. divide the required energy) by 5..20 (depending on the neutron energy).
So, the safety distance for 1 kt neutron bomb should be multiplied by 2..4.

P.S.
Mars nuking is also an interesting question.
The "air" is thin, so no sphere, no significant aerial shockwave, no light emission, no bremsstrahlung, just Xray and original gamma.

On another hand if detonate it right at the surface, then a half of energy will hit the ground like on Earth, and make a cloud of vaporized ground.

On the third hand, as the air is thin you can hit the Martian base from orbit with an Xray/gamma-laser, unlike on Earth.

Think neutron bombs was though of as anti tank weapons, inside an tank you can handle high over-pressure and derbies very well.
During WW2 tanks survived close misses from battleship fire, tank was more likely to roll over than crew getting killed. 
You are also well protected against nuclear fallout in more modern tanks. 
However the steel / composite armor don't shield well against direct radiation. 

On the other hand project orion was about blowing up nukes right behind your ship. Yes they used liquid as radiation shielding during burn. Liquid was fuel for escape system
So direct radiation is pretty easy to shield against if you have mass and distance. 

[kerbiloid]

21 minutes ago, magnemoe said:

anti tank

and anti-warhead and anti-aircraft

21 minutes ago, magnemoe said:

However the steel / composite armor don't shield well against direct radiation. 

Half-value layer of steel: gamma ~3 cm, neutrons ~11 cm.
So, it stops gamma better than neutrons. A polymer layer inside weakens the neutrons twice or so.
As a result a tank weakens a common nuke radiation by ~10 times, but a neutronuke radiation, say, 3 times.

21 minutes ago, magnemoe said:

On the other hand project orion was about blowing up nukes right behind your ship. Yes they used liquid as radiation shielding during burn. Liquid was fuel for escape system
So direct radiation is pretty easy to shield against if you have mass and distance. 

According to the open sources, an Orion/Casaba round had also a polymer filler between the charge and the membrane, and also there was a ~1 meter thick main plate, bottom, and machinery.
As the charge purpose was to evaporate the membrane with Xrays they were interested to make neutrons production as low as possible.
So, they were withstanding gamma/Xrays with thick and dense metal, extinguishing the neutrons with fuel, oil and so.

A thing which they lack in Orion to make its atompunk perfectness complete is a reactor inside

Edited October 24, 2018 by kerbiloid

[Gargamel]

On 10/22/2018 at 10:35 PM, ARS said:

If we replace the fragment grooves on frag grenade casing with diamonds to make it sprays diamond fragments everywhere when it explodes, does it make the grenade more effective in dealing with armored infantry?

F=MA.

Big chunks of steel have more force to them than little shards of diamonds, at the same speed.   You would need sizable diamonds to make a difference, and even then, the same volume of steel may have more mass than a diamond. 

[YNM]

Make the casing of spiky tungsten rods.

[StrandedonEarth]

A nuke will make a shockwave in space, from the vaporized bomb itself, but it will fade quickly with distance. 

[kerbiloid]

Very-very quickly.

Say, a Hiroshima-like sphere of 150 m radius contains (4*pi/3 * 150³ * 1.225) / 1000 = 17 000 t of gas.
While the bomb itself is tens thousands times lighter.

[Eric S]

I think someone is pulling my leg in a discussion on physics, and just wanted to get another opinion, if anyone cares to check my understanding.

I've read Newton's Principia, and while I don't doubt that we've refined things since then, even disregarding relativity and QM. However, someone's insisting that according to Principia, a forming planet couldn't pull itself into a sphere because Newton's concepts at that time didn't allow a mass to affect itself.  He claimed something about Newtonian mass having the concept of identity.  I think that's BS since Newton himself said that all parts of the 'Earth are attracted to each other.

 

[kerbiloid]

But the planet particles do not pull themselves, they pull each other.

[Eric S]

Right, the particles affect the other particles, he's saying that the entire mass of the planet has no effect on any part of the planet according to Newtonian gravitation as described in Principia.  Another reason that I think this is BS is that one of the masses Newton used in his experiment was grain (or was it rice?), and at that point, any "identity" would have to be strictly conceptual.  I can see what's wrong with that logic and I really doubt Newton wouldn't have seen it, but while I've read Principia, I haven't actually studied it in depth, so it's possible I missed something.

 

 

Edited October 25, 2018 by Eric S
clairification