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The largest manmade explosion on record is Tsar Bomba, detonated at a yield of 50 megatons. There were other nuclear explosions that were given sensationalist names--Castle Bravo, the most powerful ever made by the United States; Mike, the first successful attempt at multi-megaton thermonuclear weaponry; and King, the largest nuclear explosion to be done via fission rather than fusion.

The real problem with these explosions is the problem that condemned the fates of Chernobyl and Fukushima--radiation poisoning.

This is not an issue to take lightly. Exposure to nuclear waste results in multitudes of health risks, including cancer. In Chernobyl, nuclear radiation has been preserving the Red Forest, preventing decomposition from renewing the soil. If a lightning bolt were to hit a tree and start a wildfire, the flames would carry the radiation to the air, threatening to plague nearby civilizations and ecosystems. To make this more worrying is that the radiation in the soil will be dangerous for millions and millions of years.

So are there any weapons that can detonate as powerfully as Tsar Bomba, Castle Bravo, Mike or King but without the resulting threat of radiation poisoning?

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  • $\begingroup$ I think those two instances were poor examples to describe as being dangerous for "millions of years", I probably would have said a hundred or two, but your point comes across. $\endgroup$ – Xandar The Zenon Jul 3 '16 at 3:48
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If the issue is to create a super powerful bomb without radioactivity, then your options are very limited. Nuclear energy is orders of magnitude more powerful than any conventional bomb using chemical energy. Consider that while the bombs which were used at the end of WWII released 20 kilotons of energy, they only fissioned a small percentage of the nuclear materials (@ 1.3% of the highly enriched Uranium in Little Boy and @ 15% of the Plutonium in Fat Man).

Much of the energy in thermonuclear weapons like Castle Bravo and the proposed "full power" version of the Tsar Bomba come from the energetic neutrons released by the fusion stage starting a fission chain reaction in the third stage Uranium "pusher". If the Tsar Bomba had use a Uranium pusher rather than the lead one provided, the yield would probably be well over 100 megatons. The carrying aircraft would not have been able to outrun the shockwave of that, which was one of the reasons the Soviets decided not to go that route.

Since we "want" the energy of nuclear reactions without the radioactivity issues the fission trigger and fission third stage of a thermonuclear weapon create, we will need to find a way to trigger nuclear fusion without the fission. This seems to be extremely difficult (peaceful fusion reactions in a commercial reactor have never been achieved, and even experimental reactors have yet to reach "break even" where fusion energy equals or is greater than the input energy). In thermonuclear weapons a "pusher" is irradiated by the energy of the fission trigger and is used to compress the Lithium fuel to pressures measured in thousands of bars, as well as energetic neutrons from the fission trigger and "spark plug" are used to trigger the fusion reaction, which is opposite of what we are looking for.

Irradiating the nuclear fuel with energetic gamma radiation from an antimatter reaction might serve to provide much of the energy to initiate a fusion reaction, but a heavy pusher is still needed to compress the lithium fuel. Electrons and positrons react to release gamma rays with a very distinct 512 KEV energy signature, so your super weapon might have electrons and positrons held in some sort of "capacitor" to be released into the hohlraum

For that matter, you might just dispense with the nuclear fuel altogether and simply have a matter antimatter reaction. A positron-electron reaction will be the "cleanest", creating a burst of highly energetic gamma rays, which are deadly on their own and will also convert air into plasma and create massive shockwaves. One milligram of matter + one milligram of antimatter releases 1.8 X 10^11J, or about the energy of 43 tons of TNT, so you see this is very energetic and quite compact. A device containing a kilogram of matter + a kilogram of antimatter would have almost the same yield of the Tsar Bomba (1.8 X 10^17J or @ 43 MT).

Depending on "how" apocalyptic you want to get, weapons using antimatter are probably the most compact and indiscriminate devices possible using known physics.

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  • $\begingroup$ How accessible is antimatter today? $\endgroup$ – JohnWDailey Jul 1 '16 at 21:34
  • $\begingroup$ Not very, which is why we don't have to worry too much about antimatter weapons in the wrong hands, There have been some ideas floated about harvesting antiprotons in the Van Allen belts (see NextBigFuture for ideas on how to do this: nextbigfuture.com/2013/09/…), but even space harvesting would only produce antimatter at a rate of grams per year. Some major breakthroughs in antimatter production are needed to become a serious threat. $\endgroup$ – Thucydides Jul 2 '16 at 1:00
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It's all about orbital mass drivers.

Just fire a suitably sized rock in from orbit, all of the destruction but none of the mess.

For hundreds of years the greatest siege weapon was simply the biggest rock you could throw. Take it to the next level and drop it from orbit.

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    $\begingroup$ Except that it's a natural bomb, not manmade. $\endgroup$ – JohnWDailey Jul 1 '16 at 16:56
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    $\begingroup$ @JohnWDailey Your question does not specify a need for artificial weapons. Of course, Separatrix, I don't think rods from heaven could be considered to detonate, as the OP asked. $\endgroup$ – Frostfyre Jul 1 '16 at 17:25
  • $\begingroup$ I think OP asked clearly for weapons which can be made or launched by us (humans). So are there any weapons that can detonate as powerfully as Tsar Bomba ... I don't think an asteroid is classified as a weapon and it cannot detonate. OP's question is clear and discrete. $\endgroup$ – Youstay Igo Jul 1 '16 at 18:04
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    $\begingroup$ Also, if the rock's trajectory was changed by man, doesn't that make it a man-made weapon. It is not like we made the lead in the bullets or the uranium in the atom-bomb. We put our man-made label on a lot of things that aren't entirely made by man. +1 for man-made meteors! $\endgroup$ – Henry Taylor Jul 1 '16 at 18:59
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    $\begingroup$ +1 For me, pulling an asteroid down to earth makes for a very big man-made explosion indeed. $\endgroup$ – Bookeater Jul 1 '16 at 21:48
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You are radioactive...

The real problem with these explosions is the problem that condemned the fates of Chernobyl and Fukushima--radiation poisoning.

No. No, no and no. I am sorry but Greenpeace and every other anti-nuclear organisation has been lying to you. Radiation is not a the Super Villain Deluxe™ that kills everything "for millions of years".

You are radioactive. The food you eat is radioactive. The ocean you take a swim in is radioactive. The ground you stand on is radioactive. The sky above your head; the deep space you look into at night is shining radiation at you.

Did you know that in the Gulf of Mexico alone there is 3 million tons of Uranium? And that is not even near the most radioactive part of that water.

You live with, breathe, eat and — pardon the profanity — shit radioactive substances your entire life.

It is with radiation as with everything else: the dose makes the poison.

enter image description here

And - yes - it is true that about half of those that did die from the atomic bombings of the two Japanese cities in 1945 died from radiation. But the vast majority of those were from the direct radiation at the moment of detonation. The fallout was small, and made for very few residual cases that died of long-term effects. The notion that a nuclear bomb must cause dangerous amounts of radiation to linger, is false.

As proof... this is Hiroshima today:

enter image description here

Ground zero is at the domed structure to the left

enter image description here

enter image description here

Fallout after a nuclear explosion depends on two things:

  1. The yield of the bomb.
  2. The proximity to the ground.

A ground burst will produce intense fallout, as was for instance fatally found at the Castle Bravo test. But an air burst, where the fireball only lightly touches the ground... while intensely devastating and causing acute radiation sickness in those caught out in the open by the blast of radiation at the moment of detonation, leave relatively little fallout.

And yes... the "radioactive wasteland" trope is so over-used it sickens me. But in reality you can use use nuclear explosions without turning everything into an irradiated desert where nothing can live. The key is air bursts. About half will die from the heat and blast effects, about half die from the direct radiation at the moment of detonation... and less than 10% die later from the residual radiation.

To answer the letter to your question and not just kill your faulty premise: what Separatrix said: projectiles from space at speed of Mach 10 or more will make some big booms.

Chelyabinsk meteor... Damage starts at 1m 45s ...and this was just a relatively "light" touch.

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  • $\begingroup$ +1 again, because how often can I +2 a really good answer! $\endgroup$ – Henry Taylor Jul 1 '16 at 19:06
  • $\begingroup$ 1) Is there a point in repeating your own answer? 2) Then explain why the Red Forest is not a safe place to visit. 3) This does not really answer the question. $\endgroup$ – JohnWDailey Jul 1 '16 at 19:41
  • $\begingroup$ Oopsie... accidental double-post... my bad. $\endgroup$ – MichaelK Jul 1 '16 at 20:20
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    $\begingroup$ Chernobyl was dangerous exactly because the reactor products were not a bomb. A bomb produces the most destruction when its radionuclides are fully fissioned and/or fused. The radiation is mostly released on detonation, and the remainder is due to fast neutrons bombarding whatever is nearby. A damaged nuclear power plant, on the other hand, has massive quantities of radionuclides remaining to be fissioned, releasing neutrons and gamma rays continuously. This is far more damaging to the environment than a bomb explosion. $\endgroup$ – Lawnmower Man Jul 1 '16 at 22:41
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    $\begingroup$ @LawnmowerMan Your logic falters in that it is not the unspent fuel that poses a hazard. It is always the waste products that are bothersome. But a nuclear plant has tens of tons of fuel and waste products. A bomb has only a few kilograms. $\endgroup$ – MichaelK Jul 2 '16 at 4:50

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