The Nuclear Security Summit which has just ended in Washington included the usual assertions about the danger of nuclear proliferation whether to rogue states or terrorists. It is interesting, however, that despite a vast number of nuclear weapons being produced by a large number of countries and many weapons tested not one since 1945 has been used in anger.
Essentially now four potential nuclear scenarios cause concern. The least talked about currently is the most lethal: a nuclear war between nuclear armed states or states. Whilst this has the potential to cause immense, even apocalyptic destruction, it seems less likely than it did from the 1950s to the 1980s. The scenarios which usually cause concern are the development and use of nuclear weapons by terrorists or their use of so called “dirty bombs”.
The failure of terrorists over the last 70 years to develop nuclear weapons is interesting (as well as deeply gratifying). It is worth remembering that many terrorist organisations existed long before current pseudo Islamic terrorists and many of them might have found nuclear weapons very useful.
This failure to develop nuclear devices speaks to the difficulty of so doing rather than any altruism on the part of the terrorists.
The fundamental physics of a simple nuclear fission device as used over both Hiroshima and Nagasaki is actually quite straightforward. It can be found on any one of a number of websites but essentially involves the fact that Uranium 235 and Plutonium 239 both undergo spontaneous fission to form Barium and Krypton in the case of Uranium and Zirconium and Tellurium in the case of Plutonium.
Normally these reactions do not produce a chain reaction as there is not enough U238 or Pu239. However, if one manages to create a mass of the respective metals large enough then a chain reaction will occur. In the case of a nuclear bomb one wants to make significant supra criticality (a mass greater than the critical mass for a chain reaction) very suddenly and very quickly. This is achieved by one of two strategies: either firing a “cannonball” of uranium into a “cup” of the same material as was done in the Little Boy Hiroshima bomb (the gun method). The alternative used in the Fat Man bomb at Nagasaki is to use conventional explosives to force “lenses” of the metal onto a central ball of the same material. Either of these strategies can be used with either metal – Little Boy used uranium and Fat Man used Plutonium. Almost everyone who has created a nuclear weapon since 1945 has used implosion apart form the South Africans who apparently used the gun method and interestingly may well have developed the only gun method thermonuclear bomb.
The nuclear physics of these reactions is fairly simple: the engineering is not that complex either. The problem arises in getting an adequate quantity of fissile material. Uranium is common for a rare earth mineral and is mined in many countries. However, the vast majority of uranium is the initially pretty useless for bomb making Uranium 238. Only 0.72% of naturally occurring Uranium is U235. As anyone who did chemistry to any level will remember different isotopes exhibit identical chemical properties. As such using chemical reactions to split U235 and U238 is ineffective. The original technique was to use centrifuges to spin and separate the isotopes based on their weight. This works but is slow and requires major manufacturing processes. Prior to the First Gulf War the Iraqis were in the process of doing this but it is laborious, requires very complex equipment and is very expensive.
As such it is essentially outwith the capabilities of a terrorist organisation, even one like IS, which controls large amounts of territory. Plutonium 239 is better as, being a different element to uranium it can be separated by chemical reactions. However, it occurs in only tiny amounts in nature. It can be manufactured from U238 in a nuclear reactor. However, for that one again needs a large industrial process and if starting from scratch without outside help, the U235, in the first place.
As such a terrorist organisation would find making a nuclear bomb very challenging. Furthermore the initial nuclear bombs were physically very large and although massively powerful as compared to conventional explosives, not powerful as compared to modern military nuclear weapons. To obtain such levels of destruction one needs a thermonuclear bomb. The physics of this is extremely complex. Several states have made these and although their techniques are classified it is accepted that all are variants on the Tellar Ulam configuration. This requires a the initial nuclear explosion to be boosted by a small amount of hydrogen fusion which then bombards U238 with neutrons which undergoes fission and emits vast amounts of destructive power.
The initial thermonuclear bombs were physically enormous and although current ones can be quite small, the miniaturisation process is very difficult. In addition those countries which have tried to make thermonuclear bombs have all had failures where the explosions were very small. This may well have been what happened in the recent North Korean thermonuclear test that was considered very small for a thermonuclear explosion.
Once one has made a nuclear weapon one then needs a delivery mechanism and again that can be simple of complex. Whilst theoretically a terrorist organisation could bring a bomb to a city in a lorry or such like that would require assembling it on the continent of choice and transporting it. Arguably the best method for terrorists would be to use a ship to transport a bomb as it would allow them to forego the miniaturisation process. That they have not done so again, however, speaks to the difficulties of making a bomb in the first place.
The assorted “rogue states” have tried to develop delivery systems but again that is difficult. As I mentioned previously planes are not as good a method as they were 40 years ago. The Iraqi’s tried missiles and superguns to fire missiles but again that requires massive investment. The North Koreans seem to be trying the traditional missile method and seem to have got satellites into orbit (remember the space race was really the nuclear missile race by proxy) but the process of getting the bombs back to target from low earth orbit is far from straightforward.
Since the production of a viable nuclear weapon and its delivery are so clearly technically challenging the alternative of acquiring a “pre owned” version seems attractive. Although this has been the proposition behind assorted James Bond films and other literature the reality is that no terrorist organisation nor rogue state has so far as we know obtained a nuclear weapon from one of the nuclear weapon states. A small number of nuclear weapons have been lost either when nuclear armed bombers crashed or else when nuclear armed submarines sank. Thus far, however, although not all the weapons have been accounted for, none has been (nor now realistically will be) recovered by third parties in a functional state.
The break up of the Soviet Union and the parlous state of its armed forces in the 1990s offered states or terrorists intent on obtaining thermonuclear weapons an apparently golden opportunity. Again, however, this appears not to have happened and that window of opportunity for them seems to have closed.
The next option for terrorists or rogue states would be to take over a state with nuclear weapons and hence, obtain a nuclear weapon. That might have happened had South Africa’s whites tried to declare some sort of counter revolutionary UDI. The Apartheid regime had some form of viable nuclear arsenal and the means to deliver it (probably missiles but also Buccaneer bombers) but abandoned the attempt. It has been alleged that the Americans insisted that the South Africans hand over their nuclear weapons before the regime fell.
Pakistan has for some time been one of the countries considered most likely to collapse and hence, give a terrorist group access to ready made nuclear weapons. However, despite its ongoing internal security problems and the continued lethality of the Pakistani Taliban the Pakistani state has remained and even over the last few years appears to have strengthened to the extent that no longer do people suggest that it is likely to become a failed state and in the anarchy which follows allow a terrorist organisation to acquire for itself ready made fission weapons and viable delivery systems (Pakistan like Israel and North Korea and are felt unlikely currently to possess practically functional thermonuclear weapons).
If then terrorists have had no success in acquiring nuclear weapons their last and weakest option would be to manufacture a “Dirty Bomb”. This is not a poor man’s nuclear weapon but rather a pretend nuclear bomb. It is a conventional explosive that rather than initiate nuclear fission let alone fission followed by fusion and fission of Teller Ulam, simply scatters radioactive material from the conventional explosion. As such its only danger beyond the conventional explosive would be radioactivity from the scattered material.
Obtaining such material would be extremely simple as compared to getting fissile Uranium or Plutonium; assembling it would require no physics at all. Many health care and industrial processes use radioactive sources. One could steal waste materials from hospitals or if one had the patience take apart fire alarms or even the luminous dials of diving watches. The mundane nature of these sources, however, hints at their uselessness as dangerous weapons. Although they might create initial panic the actual amount of radiation produced might be equivalent to people in the immediate vicinity having some X rays or at worst a CT scan. They might increase the statistical rate of cancer but not by much.
It is worth remembering that the Chernobyl explosion was essentially a giant dirty bomb with a conventional explosion in a nuclear reactor liberating many tonnes of radioactive material. Despite this the actual number of deaths caused by Chernobyl was 56 and it is suggested by the UN that increased cancer rates will kill 4,00 people. Those estimates are considered by some highly conservative but by others alarmist. What is clear is that despite high levels of radiation wildlife has thrived in the evacuated areas around Chernobyl.
A similar controversy now also surrounds Fukushima with some suggesting the exclusion zone is unnecessary. Whatever the amounts of radiation and its dangerousness the reality is that a dirty bomb would release orders of magnitude less radioactivity than the nuclear power plant disasters A dirty bomb would create panic, a clean up operation but rapidly a realisation that it was not a huge issue. Remember that people have lived at Hiroshima and Nagasaki ever since vastly greater releases of radioactive material.
One of the strongest arguments against the utility to terrorists of a Dirty Bomb has been the simple fact that terrorists have not tried it. They likely have realised that it is better as a threat than a reality: once utilised the threat would rapidly be seen for the phantasm it is.
Despite all the talk about nuclear terrorism in all its various forms the reality is that many thousands of people have been killed by terrorists since the Second World War and none of them by nuclear weapons. The most effective weapons of mass destruction thus far obtained by terrorists, which completely blind sided those fighting terrorism, have been the two Boeing 767s which destroyed the World Trade Centre’s twin towers. In contrast the most effective terrorist weapons overall have been the Improvised Explosive Device and the AK47 Kalashnikov. Interestingly Einstein is said to have stated after Hiroshima: “If I had only known, I would have been a locksmith” whilst Robert Oppenheimer quoted the Hindu scripture: “Now I am become Death, the destroyer of worlds.” Meanwhile Mikhail Kalashnikov wrote to the Patriarch of Moscow regarding his spiritual pain at the deaths his AK 47 rifle had caused. The Patriarch’s reply bears repetition: “He designed this rifle to defend his country, not so terrorists could use it in Saudi Arabia.” An explanation of the nature of personal responsibility which many would do well to remember.