The discovery that items containing depleted uranium and iridium-192 – both radioactive materials – had been dumped by thieves at the Seri Era Apartments in Desa Latania, Shah Alam, Selangor, has raised the spectre of radioactive exposure for residents and visitors to that area.
The materials, reportedly dismantled from two industrial radiographic exposure devices, were dumped in a rubbish bin at the Rukun Tetangga room in the apartment building.
The police believe that the projectors were stolen between 3am and 4am on Feb 9 from the nearby Kampung Sungai Kandis, and were only recovered on Feb 11 some 63 hours later.
So far, two residents of the building have been sent for blood tests to see if they have unusual radioactivity levels.
According to University Malaya Faculty of Medicine professor of Medical Physics Dr Ng Kwan Hoong, radioactivity is the spontaneous decay or disintegration of an unstable atomic nucleus, accompanied by the emission of radiation.
“An atomic nucleus consists of protons and neutrons.
“When the number of protons and neutrons is not balanced, the nucleus becomes unstable (i.e. has higher energy); thus, to achieve stability, it has to get rid of the excess energy in the form of electromagnetic radiation (gamma rays) and as particulate radiation (beta particles and alpha particles),” he ex-plains in an email interview with Fit for life.
These forms of radiation have a wide range of energy levels and different physical properties, he adds.
For example, alpha particles are only able to travel a few centimetres in the air and can be stopped by a sheet of paper; beta particles can travel tens of centimetres in the air and can be stopped by a sheet of aluminium; and gamma rays can travel many metres and can only be stopped by thick lead or concrete.
Depleted uranium emits all three forms of radiation, while iridium-192 emits beta particles and gamma rays.
Pros and cons
The hazards of being exposed to radioactive materials usually comes from beta particles and gamma rays as they can penetrate our skin and damage our DNA via ionisation.
Radiation with enough energy can remove the tightly-bound electrons from an atom, causing the atom to become ionised, and thus, unstable.
Prof Ng explains that radiation can cause ionisation to DNA both directly and indirectly.
In a direct hit, the radiation ionises the DNA atoms themselves, disrupting and damaging them.
In an indirect hit, it ionises the water molecules close to the DNA, creating free radicals. These unstable free radicals then interact with the DNA and damages it.
However, radiation can be put to good use as well. Prof Ng notes that gamma rays are used in medicine, industry and scientific research.
For example, radioisotopes that emit very low-energy gamma rays are used for medical imaging, while radioisotopes with high-energy gamma rays are used to target and destroy cancer cells.
Very high doses of gamma rays are also used to sterilise items like surgical gloves and drugs, ensuring that they are germ-free.
In addition, gamma rays are commonly used for non-destruct-ive testing, like checking for metal fatigue in planes, flaws in engines or welding, and cracks in pipes.
The stolen radiography project-ors were used for such testing, specifically for cracks in soldered pipe joints,
The depleted uranium in the stolen radiographic projectors was used as an inner casing in the device.
Depleted uranium has been used as containers for radioactive sources (in this case, iridium-192), radiation shielding in hospital radiotherapy units, in heavy industrial drilling equipment, and as a counterbalance in some aircraft and large sailboats, for decades.
Its most common use, however, is military; in tank armour and armour-piercing ammunition, for example.
According to the US Air Force’s centre for professional military training, Air University, depleted uranium is 40% less radioactive than natural uranium.
Its online fact sheet on depleted uranium states that “depleted uranium does not significantly add to the background radiation that we encounter every day”.
We receive an average of two to three millisieverts (mSv) of radiation a year from natural sources like the sun, granite rock, natural radon gas and others.
A sievert is the SI unit measuring the biological effect of radiation exposure by an ionising radiation source undergoing an energy loss of one joule per kilogram of body tissue.
While there is no definitive ma-ximum limit for safe exposure to radiation, 20mSv per year is often taken as the maximum limit of radiation exposure for those working with radioactive materials.
Porf Ng says that current radiation protection recommendations are based on the Linear No Threshold (NLT) hypothesis.
This hypothesis assumes that even the lowest, near-zero dose of radiation can be detrimental, that the risk per unit dose is constant and incremental, and that the risk can only increase with dose; thus, erring on the side of caution.
Because depleted uranium is not only radioactive, but also toxic, anyone who inhales, ingests or is penetrated by depleted uranium (for example, by a bullet encased with depleted uranium) faces a double whammy.
The kidney is usually the most affected organ as it helps to excrete depleted uranium from the body.
Ingesting depleted uranium is likely to result in more danger from radiation, with 1.5g of a moderately soluble compound containing depleted uranium and 8.8g of an insoluble compound respectively needed to expose the body to one mSv of radiation.
Meanwhile, inhaling depleted uranium will result in more danger from its toxicity, with 230mg of a moderately soluble aerosol containing depleted uranium and 7,400mg of an insoluble aerosol respectively needed to concentrate 3µg of depleted uranium per gram in the kidneys – the chemical toxi-city limit.
Made for use
The iridium-192 recovered was in the form of rods, which had been removed from their protect-ive casing.
This radioactive substance is a man-made radioisotope. A radio-isotope is a radioactive version of an element that has the same number of protons in its nuclei, but a different number of neutrons.
Iridium-192 is commonly used to inspect welding seams (as in this case) and to treat certain cancers in brachytherapy, where it is inserted directly or near the tumour in the form of a seed to irradiate and kill off the cancer cells.
Ironically, exposure to iridium-192 can increase the risk of cancer.
According to the US Centers for Disease Control and Prevention (CDC), external exposure to iridium-192 can cause burns, acute radiation sickness and death.
Exposure to as low as 0.3 grays can produce mild symptoms. One gray is the absorption of one joule of energy, in the form of ionising radiation, per kilogram of matter.
Typical symptoms include nausea, vomiting and loss of appetite that begin around an hour to days after exposure. Fever and fatigue usually follow.
Although there is no treatment for acute radiation sickness, 40%-50% of those exposed to 2.5-5Gy of radiation will survive and recover.
Those exposed to more than 10Gy will also experience cramps and diarrhoea, as well as severe nausea, within a few hours of exposure. Death usually follows within two weeks.
Internal exposure from iridium-192 can occur if one swallows the seeds used in brachytherapy.
This will cause burns to the stomach and intestines, although the seed itself will be eventually excreted by the body. The long-term health effects depend on how radioactive the seed was and how long it stayed in the body.
Iridium-192 has a half life of 74 days, meaning that by 74 days, half its atoms would have become stable and no longer dangerous.
Residents and visitors to the Seri Era Apartments who suspect they might have been exposed to the radioactive materials have been advised to call the Atomic Energy Licensing Board at 03-8922 5888 or 1800-88-7999 for help.