The primary objective of a dirty bomb is to sow fear, panic and confusion by hurling radioactive dust and smoke into the atmosphere.
The Kremlin alleges that Ukraine is preparing to detonate a dirty bomb in order to blame it on Russia and force an escalation of the war that has entered its ninth month.
Western countries have dismissed Moscow’s claim as “transparently false”.
Although no successful dirty bomb attack has ever been recorded, two failed attempts to detonate such a device were reported in the southern Russian province of Chechnya more than 20 years ago. Investigators also found nuclear material capable of being used in a dirty bomb in an abandoned factory in Chechnya.
Here’s a look at what experts mean by the term “dirty bomb”:
How does a dirty bomb work?
Technically known as radiological dispersal devices, dirty bombs are relatively primitive, imprecise weapons. They are much easier and cheaper to build than a nuclear device and also far less dangerous.
Dirty bombs use conventional explosives, such as dynamite, placed alongside radioactive material, which is then flung outward by the force of the blast. The amount of radioactive material dispersed, while dangerous, is not necessarily lethal.
The material used in a dirty bomb could be obtained from radioactive sources used in medicine and industry or from research facilities.
“A dirty bomb is really easy to make,” said Scott Roecker, vice president for the nuclear materials security programme at The Nuclear Threat Initiative, a non-profit organisation based in Washington.
“It’s a crude device.”
Richard Giragosian, founding director of the Regional Studies Centre, an independent think-tank in Yerevan, Armenia, said in a 2016 op-ed for Al Jazeera that following the September 11, 2001 attacks on the United States by al-Qaeda, fears multiplied in the West of the dangers posed by radiological “dirty” bombs.
Giragosian said that while there had been significant efforts in Russia and Ukraine to dispose of radioactive materials left over from the former Soviet Union, safely disposing of such material in the Caucasus had been “a lower priority”.
Soviet-era facilities in the Caucasus had once had “ample supplies of caesium, strontium and other related radiological materials”. But since the collapse of the Soviet Union, “most of these facilities have been only minimally protected, with meagre security precautions or safeguards”, he said.
Giragosian had also said at the time of writing that the arrests of three suspects in Georgia for attempting to sell radioactive material should remind the world that it cannot remain complacent to dirty bombs.
The same year, then-US President Barack Obama hosted world leaders at a Nuclear Security Summit focused on preventing assailants from using radioactive material to “outdo” the 9/11 attacks.
What damage can a dirty bomb cause?
The number of casualties and the extent of damage from a dirty bomb depends on many variables.
A key factor is the amount and type of conventional explosives that are used, which determine the magnitude of the blast.
The quantity and type of radioactive materials released are other factors, as are weather conditions – and especially the wind – at the time of the blast. A potentially wide area could be contaminated.
Low levels of radiation exposure usually do not cause any symptoms. People may not know whether they have been exposed because radiation cannot be seen, smelled or tasted.
How dangerous is a dirty bomb?
Experts say the main effect of a dirty bomb is psychological, which is why such devices are often referred to as “weapons of mass disruption” as against mass destruction.
Dirty bombs are not for battlefield use, being deployed more obviously in urban areas, Roecker said.
“They’re more of a psychological weapon. When you’re trying to scare people, intimidate people, you’d use a weapon like this,” he said.
The radioactive dust and smoke can spread far and are dangerous if inhaled near the blast’s epicentre.
The radioactive cloud would likely spread over several blocks, according to Roecker. But as radioactive material spreads through the atmosphere, it becomes less concentrated and less harmful.
Key factors in radiation exposure are what type of radiation it is, how long someone is exposed to it, and whether the radiation was absorbed through the skin, inhaled or consumed orally.
Specialised equipment is required to detect radiation.
Contaminated homes, businesses and public services could be placed off-limits for months and need an expensive clean-up operation.
In a 2002 testimony at a United States Senate hearing, Richard A. Meserve, then-chairman of the US Nuclear Regulatory Commission, said a dirty bomb “has to be sharply distinguished from a nuclear weapon, which itself relies upon the nuclear material to cause the propulsive force.
“A nuclear weapon … would have devastating effects. This is in contrast with a radiological dispersion device. Our evaluation… is that such devices are really not very effective as a means for causing fatalities,” he said.
“We have looked at a range of scenarios in which they might be used, and they could cause, certainly could cause death, but we are talking deaths on the order of tens of people in most scenarios, rather than hundreds or thousands, or tens of thousands.”