We’re venturing tentatively into the border region between chemistry & physics today, with a look at some of the different types of nuclear radiation. These types vary in their composition, characteristics, and uses, but here’s an attempt to sum up the most common in one succinct graphic.
One thing that the different types of radiation featured here have in common is their ability to ionise. Ionising radiation is radiation that has enough energy to remove electrons from atoms and molecules, and cause them to form ions (charged particles); in some cases, it can also lead to the breaking of chemical bonds. This ionisation can cause damage to living cells, and is the main danger that radiation can pose. Very high levels of radiation can have very serious health effects, and death can occur in hours if a person is exposed to a large enough amount.
Alpha particles have the highest ionisation ability of the three types of radiation we’ll examine here. Each alpha particle is essentially a helium atom which has had its electrons stripped away: they’re composed of two protons, and two neutrons. This gives them a rather large mass, and helps explain their high ionisation ability, as they move more slowly and can collide with more atoms. Additionally, the two protons in each particle give them a strong positive charge.
Whilst the bulk of alpha particles might lend them a high ionisation ability, it also limits their ability to penetrate materials. Even just a thin piece of paper will stop alpha particles in their tracks, and human skin is also thick enough to bar their passage. As such, alpha radiation is very easy to shield against externally; the only case in which is can cause problems for human health is when it is ingested.
This is a point that has been fairly recently illustrated, through the death of Alexander Litvinenko in the UK back in 2006. Litvinenko was a former Russian Secret Service agent who had fled Russia for the UK in 2000 to escape charges relating to his implicating of the Russian government in several assassinations and terrorist acts. In November of 2006, he became rapidly ill, and was hospitalised. Initially, the cause of his illness was unclear; however, it was eventually established that he had met with two ex-KGB agents on the day he fell ill.
Tests revealed a high level of polonium-210, an isotope that decays releasing alpha radiation, in his body. From there, a radioactive breadcrumb trail could be followed to trace the poison’s origin. The residual radiation left behind by the Russian agents’ transport of the radioactive element could be picked up in the planes they had travelled in, the hotels they had stayed in, and even at the table at which they’d met with Litvinenko. Some objects, such as the bath tub in one of the hotel rooms, were so contaminated they had to be disposed of as radioactive waste.
Andrei Lugovoy, a Russian politician and also a former KGB agent, was heavily implicated in Litvinenko’s death by the radiation trail. However, Russia has refused UK requests for his extradition, as their constitution does not allow for the extradition of its citizens to foreign countries, so it seems unlikely that he will ever face charges.
As we’ve mentioned, alpha radiation is benign unless ingested, and there’s probably some being emitted inside your home. Many smoke detectors use americium-241, an alpha particle emitter, to detect smoke. The particles cannot escape the plastic casing of the smoke detector, but inside they ionise the air particles present, and in doing so produce a detectable current. If smoke is present, alpha particles hit these instead, reducing the ionisation of air particles, and causing a drop in current. This can be detected by the detector, and causes the alarm to sound.
In a select number of heart pacemakers, alpha emitters are also used. They have the advantage of being able to run for many years longer than more conventionally powered pacemakers. However, they obviously pose more of a risk, as they also use polonium to produce the alpha radiation. Similar powering devices have also been used to power some space probes, including the Mars Curiosity rover.
Beta particles are composed of single, high energy electrons. Their smaller size explains their higher penetration ability compared to alpha particles, and it takes a thin sheet of aluminium to bring them to a halt. Their ionisation ability is, however, lower compared to that of alpha particles.
One of the most common uses of beta particles is in the field of medicine. They can be used as ‘tracers’; these are chemical compounds which have had one or more atoms replaced by radioactive isotopes of the same element. They can be used to track the spread of substances in the body, and are a very useful medical diagnostic tool. This concept also has industrial applications, and can be used to image underground pipes in order to detect leaks or blockages.
Because beta radiation can penetrate human skin, another of its applications is in the treatment of cancers. It’s also the reason that people in the area surrounded the Fukushima reactor in Japan were supplied with iodine tablets immediately after the meltdown that occurred there during the disastrous tsunami of 2011. Radioactive iodine produced during radiation leaks can be taken up by the thyroid gland, which can cause subsequent health issues. If normal iodine, in the form of potassium iodide pills, is given shortly prior to exposure to radioactive iodine, it can prevent radioactive iodine’s uptake – the thyroid is essentially already full.
Another industrial application of beta particles is in the materials industry. It can be used in the production of paper, aluminium, and plastics to help control their thickness. The amount of beta radiation that is able to pass through the material gives a gauge as to its thickness, and allows adjustments to be made during production.
Gamma radiation differs from alpha and beta radiation in that it is in the form of electromagnetic waves. Because of this, it’s also the most penetrating of the three types featured here, and a few centimetres of lead are required in order to halt its progress. However, as they have no mass, they are less ionising than alpha or beta particles.
Caesium-137 is one gamma-emitting isotope which has been used in radiation therapy for cancer, and has also been involved in several radiation exposure incidents over the years. Probably the most well-known was all the way back in 1987, when a caesium source from a radiation therapy system was scavenged from an abandoned hospital in Goiânia in Brazil. The glowing source was handled by a number of people after its theft; four people died, and a staggering 249 people were also had significant levels of radioactive materials detected on them.
Cobalt-60 is another gamma-emitting isotope which is used to sterilise medical equipment and foodstuffs. Irradiated food does not become radioactive itself, but it helps reduce the levels of pathogens in food, and mostly eliminate the risk of food-borne illnesses. It can also be used to help slow ripening of fruits and vegetables, and remove insects.
Finally, gamma radiation can also be used in astronomy. Several telescopes are equipped to observe astronomical gamma rays, and observing them can help us learn more about the universe. These gamma rays can come from a number of sources, such as pulsars, stars which also emit radio waves.
Other Types of Radiation
Another type of radiation that isn’t featured here is X-ray radiation. As this post has been examining nuclear radiation, X-rays have been omitted, although they’re very similar to gamma rays. The difference between them was formerly defined in terms of energy, but now, electromagnetic radiation of nuclear origin is referred to as gamma radiation, whereas X-rays are defined as being emitted by electrons. These aren’t definitions that are always stuck to in all fields, however.
Neutron radiation is the other type of radiation we haven’t mentioned. This is the release of neutrons from atoms, and is a consequence of nuclear fusion or nuclear fission. Nuclear power is something we’ll take a look at in a future post, so we’ll examine neutron radiation more closely then!
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References & Further Reading
- Understanding radiation – United States Environmental Protection Agency
- How radioactive poison became the assassin’s weapon of choice – W Storr
- Does potassium iodide protect people from radiation leaks? – L Greenemeier, Scientific American
10 replies on “A Guide to the Different Types of Radiation”
“This aren’t definitions that are always stuck to in all fields, however.”
“These aren’t definitions that are always stuck to in all fields, however.”
Feel free to delete this comment.
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One other comment, typically beta emitters are not used as imaging agents in medicine, but rather treatment agents. The beta particles typically do not escape the patient to allow for imaging. For this reason, gamma emitters are more often used for imaging, and beta emitters for treatment. However, beta decay is often accompanied by gamma decay, and those gammas can often be imaged.
Happy to be corrected, but I’ve read in several places of cases where they are used diagnostically? I suspect gamma emitters are more commonly used, but as an example, I’ve read of phosphorus-32, a beta emitter, being used in the detection of malignant tumours.
Good point. P-32 is one of the most commonly used tracers in a laboratory setting and for identification of tumors. As far as I know (as a veterinary radiation oncologist and radiochemist), its not used clinically in patients, but is probably used on some biopsy specimens. I think its a matter of semantics and not correction. Thank you for these articles!
No love for neutron radiation?
Nope, none whatsoever.
Nah, just kidding, as mentioned in the post I’ll probably look at neutron radiation in a little more detail in a future post on nuclear power!
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Very nice, concise guide! It is probably beyond the scope of the guide to explain about the positron-emitters such as sodium-22. One tiny typesetting quibble: You seem to have used the German “ss” (ß) for the Greek letter beta (β; Unicode letter may not show on all browsers).
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