After months of exchanging fire, Russia and Ukraine are now exchanging claims that the other side is preparing to detonate a 'dirty bomb' – possibly under a 'false flag' attack attempting to pin the blame on their opponents.

Although no 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 two decades ago.

But what is a dirty bomb?

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Dirty bombs have long been feared as a potential weapon of terrorists because their main objective is to sow panic, confusion and anxiety by hurling radioactive dust and smoke into the atmosphere.

Technically known as radiological dispersion devices, dirty bombs are relatively primitive, imprecise weapons. Although considered far less dangerous than a standard nuclear device, they are much easier and cheaper to build.

The central idea is simple: Dirty bombs use conventional explosives, such as dynamite, placed alongside radioactive material, which is then flung outward by the force of the blast. 

The material used in the bomb could have been obtained from radioactive sources used in medicine and industry or from research facilities.

"A dirty bomb is really easy to make," says Scott Roecker, vice president for the nuclear materials security program at The Nuclear Threat Initiative, a non-profit based in Washington. "It's a crude device."

Low-level radiation exposure

The number of casualties and the extent of damage from a dirty bomb depends on many variables. The amount of radioactive material dispersed, while dangerous, is not necessarily lethal. 

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.

Most dirty bombs would not discharge enough radiation to cause death or even severe illness. 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.

'Weapon of mass disruption'

A dirty bomb would likely cause a limited number of deaths, but its main impact is psychological, which is why such devices are often referred to as "weapons of mass disruption."

Dirty bombs are not for battlefield use, says Roecker, being deployed more obviously in urban areas,.

"They're more of a psychological weapon," he explains. "When you're trying to scare people, intimidate people, you'd use a weapon like this."

The radioactive dust and smoke can become widespread and can be dangerous if inhaled near the blast's epicenter. 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.

Specialized 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.