Radioactivity is the process under which the nucleus can

change spontaneously from one element to another

particles

particlesRays

Check out interesting videos on radioactive elements on TED Talks

Henri BecquerelMarie CuriePierre Curie

UraniumPoloniumRadium

Radioactivity occurs when an unstable nucleus decays. There are three ways that it can do so. It may give out radiation in the form of:-an alpha particle a beta particle a gamma ray

Sources of Radioactivity

• Most of the radioactivity you are normally exposed to is from natural sources.

• In fact, you've grown up on a planet which has, in places, quite a high level of background radiation, and life on Earth has evolved to cope with this. Your cells have self-repairing mechanisms which allow them to survive relatively unscathed.

cosmic rays are are gamma rays coming in from space.

Dangers of Radioactivity

•The main danger from radioactivity is the damage it does to the cells in your body.

•Most of this damage is due to ionisation when the radiation passes, although if levels of radiation are high there can be

damage due to heating effects as your body absorbs the energy from the radiation, rather like heating food in a

microwave oven. This is particularly true of gamma rays.

•Radon is a naturally occurring radioactive gas which originates from the decay of uranium in rocks and soils. It is colourless, odourless and

tasteless and can only be measured using special equipment. When radon surfaces in the open air, it is quickly diluted to harmless

concentrations, but when it enters an enclosed space, such as a house or other building, it can sometimes accumulate to unacceptably high

concentrations.

Alpha Particles (a)Alpha particles are slow, have a short range in air, and can be stopped by a

sheet of paper.You might therefore assume that alpha particles are the least dangerous of

the three types of radiation.• Wrong! Whilst they cannot penetrate your skin, you could easily

eat or drink something contaminated with an a source. This would put a source of a particles inside your body, wreaking havoc by

ionising atoms in nearby cells. If this happens to part of the DNA in one of your cells, then that cell's instructions about how to live and grow have been scrambled. The cell is then likely to do something very different to what it's supposed to do, for example, it may turn cancerous and start multpilying uncontrollably.

• Thus alpha particles, whilst they have a low penetrating power, can be the most dangerous because they ionise so strongly.

would put a source of a particles inside your body, wreaking havoc by ionising atoms in nearby cells. If this happens to part of the DNA in one of your cells, then that cell's instructions about how to live and grow have been scrambled. The cell is then likely to do something very different to what it's supposed to do, for example, it may turn cancerous and start multpilying uncontrollably.

Beta Particles (b)

beta-particles have a longer range than alpha particles but ionise much less strongly, with the result that they do around 1/20th of the damage done by the same

dose of alpha particles. However, they do have more penetrating power, which means that they can get

through your skin and affect cells inside you.

Gamma Rays

Gamma rays hardly ionise atoms at all, so they do not cause damage directly in this way. However, gamma rays are very difficult to stop, you require lead or concrete shielding to keep you safe from them. When they are absorbed by an atom, that atom gains quite a bit of energy, and may then emit other particles. If that atom is in one of your cells, this is not good!

Detection of Radiation

• Radioactivity is invisible, has no smell, makes no sound - in fact it cannot be detected by any of our senses. However, because radioactivity affects the atoms that it passes, we can easily monitor it using a variety of methods.

Geiger-Müller tube

• Most people have heard of a "Geiger Counter" for measuring radioactivity. This is actually a Geiger-Müller tube with some form of counter attached, which usually tells us the number of particles detected per minute ("counts per minute").

• GM tubes work using the ionising effect of radioactivity. This means that they are best at detecting alpha particles, because -particles ionise strongly.

• Different models of GM tubes are available for detecting , and radiation.

Uses of Radioactivity

• Smoke Detectors • Smoke alarms contain a weak source

made of Americium-241.Alpha particles are emitted from here, which ionise the air, so that the air conducts electricity and a small current flows. If smoke enters the alarm, the current reduces, and the alarm sounds. Am-241 has a half-life of 460 years.  

 

Sterilising

• Even after it has been packaged, gamma rays can be used to kill bacteria, mould and insects in food.

• This process prolongs the shelf-life of the food, but sometimes changes the taste.

• Gamma rays are also used to sterilise hospital equipment, especially plastic syringes that would be damaged if heated.

Radioactive Dating

• Animals and plants have a known proportion of Carbon-14 (a radioisotope of Carbon) in their tissues.

• When they die they stop taking Carbon in, then the amount of Carbon-14 goes down at a known rate (Carbon-14 has a half-life of 5700 years).

• The age of the ancient organic materials can be found by measuring the amount of Carbon-

14 that is left.

Cancer Treatment • Because Gamma rays can kill living cells,

they are used to kill cancer cells without having to resort to difficult surgery. This is called "Radiotherapy", and works because cancer cells can't repair themselves when damaged by gamma rays, as healthy cells can.

• It's vital to get the dose correct - too much and you'll damage too many healthy cells, too little and you won't stop the cancer from spreading in time. Some cancers are easier to treat with radiotherapy than others - it's not too difficult to aim gamma rays at a breast tumour, but for lung cancer it's much harder to avoid damaging healthy cells. Also, lungs are more easily damaged by gamma rays, therefore other treatments may be used.

Exam questions

Higher level

• 2014 Q4 (c)• 2013 Q.10(c)• 2012 Q4 (b)• 2011 Q 11(a)• 2010 Q.10 (c)• 2010 Q11 (b)• 2009 Q4 (b)• 2008 Q4 (c)• 2007 Q11 (a)• 2006 Q 4 (c)• 2005 Q5 (a)

• 2004 Q11 (a)

Ordinary Level

• 2014 Q4 (h)• 2013 Q5(c)• 2011 Q11(a)• 2009 Q10 (a) (b)• 2007 Q5 (c)• 2006 Q5 (b)