(c) doc b(c) doc b5. Uses of Radioactive-isotopes emitting alpha, beta or gamma ionising radiation

Doc Brown's Chemistry

KS4 science GCSE/IGCSE/AS Physics Revision Notes

How do we use radioisotopes for? How can we use alpha particle radiation, beta particle radiation and gamma radiation rays? How do we relate the use of ionising radiation with its physical properties e.g. it penetration into material or the half-life of the radioactive source.

Gamma and beta emitting radioisotopes are extensively used in medical diagnostic and treatment procedures,

Radioisotopes are used in a variety of ways in industry to improve productivity and, in some cases, to gain information that cannot be obtained in any other way. Radioisotopes are used in radiography, gauging applications and mineral analysis. With short-lived radioisotopes are used to trace flow and fluid mixing systems. Gamma ray sterilisation procedures are used in preparing medical supplies packaged food preservation.

The technicalities of the 'half-life' of a radioisotope is dealt with in detail in section 6.

But to fully understand this page you specifically need to know

(i) Relative penetrating power of the ionising radiations: gamma > beta > alpha

(ii) The half-life of a radioisotope is the time taken for the radioactivity to halve



5. The Uses of Radioactive Isotopes emitting alpha, beta or gamma radiation

The uses of radioactive isotopes depends on their penetrating power and the value of their half-life (see later).

5a (c) doc b Uses of alpha particle sources

  • (c) doc bBecause alpha particles are easily stopped, an alpha source is used in some smoke detectors.
    • A sealed weak alpha source of americium-241, with a half-life 458 years, it effectively produces a constant signal in a detector - formed of two electrodes with a potential difference across them.
    • It does this by sending a stream of alpha particles to a sensor across an air gap which causes ionisation, electrical current flow and hence a constant electrical signal.
    • The nuclear decay equation is: 24195Am  ===> 23793Np  +  42He   (+ (c) doc b)
    • Any smoke present will block and absorb some of the alpha particles and change the sensor signal by changing the amount of ionisation, and this change in signal triggers the alarm.
    • Beta and gamma radiation would be of no use because the smoke particles would not stop them, no change in signal, no alarm triggered!
    • Note:
      • Although gamma radiation is also emitted, the smoke particles have no effect on it.
      • This type of smoke detector can be used in the house because it is a very weak source using a tiny amount of the americium radioisotope.
      • An average smoke detector for domestic use contains about 0.29 micrograms of Am-241 (in the form of americium dioxide), and its activity is around 37000 Bq (37000 disintegrations/second). It sounds a lot, but don't worry about it, non of the alpha particles can get out of the detector chamber and there are thousands of particles hitting or going through your body every second with no ill-effect!
  • (c) doc bAlpha sources are too readily absorbed to show up with a Geiger counter or other detector and so are not suitable for 'tracer' applications.
    • However, an alpha particle emitting isotope of radium (radium-223, half-life 11.4 days) can be directly injected in tiny quantities into tumourous tissue to directly irradiate and kill cancer cells.
      • 22388Ra ===> 21986Rn + 42He
    • Its an excellent medical use of an alpha emitter.
    • Since they are not very penetrating, there is less chance of damaging healthy cells surrounding the tumour.
    • This is an example of internal radionuclide therapy.
  • more on the properties of alpha particles and nuclear equations for alpha decay

5b (c) doc b (c) doc bUses of beta radiation sources

  • (c) doc b Most Beta particles are stopped by a few mm or cm of solid materials.
    • The thicker the layer the more beta radiation is absorbed.
    • A beta source is placed on one side of a sheet of material.
    • A detector (e.g. a Geiger counter) is put on the other side and can monitor how much radiation gets through.
    • The signal size depends on thickness of the sheet and it gets smaller as the sheet gets thicker.
    • Therefore the signal can be used to monitor the sheet thickness.
    • However, the radioisotope must give a stable and constant emission to give create a stable constant signal from the detector.
    • Therefore the half-life must be quite long so that any change in the signal does not result from rapid decay but only from change in the thickness of material.
  • (c) doc b This idea is used to control production lines of paper, plastic or steel sheeting.
    • After the sheet material passes through 'flattening' rollers, it passes between a beta source and detector.
    • The detector signal is checked against that for a preset thickness.
    • The signal controls the position of the rollers producing the sheet of material.
    • If the signal is too big, the sheet is too thin, and the rollers are moved apart to thicken the sheet.
    • If the signal is too small, the sheet is too thick, and the rollers are moved closer together.
  • Some radioisotopes can be injected into the human body or taken in a tablet and then what happens to the this 'tracer' isotope as it is moved around the person's body can be monitored from outside with a suitable detection system.
    • It is important that a low dose of the radioisotope is used AND has a relatively short half-life of a few hours or a few days to minimise the risk of cell damage from the emitted beta or gamma radiation.
      • A short half-life means the radioactivity in the body will rapidly disappear to almost zero.
    • A computer can analyse the detector signals from either beta of gamma radiation to build up on a screen a picture of e.g. blood circulation in the body can be followed.
    • Another example is the use of iodine-131 to check the functioning of the thyroid gland. If the thyroid gland is functioning normally its expected uptake of iodine can be 'raced' using this radioisotope - an example of a diagnostic scan.
      • Lack of a concentrated signal from the thyroid gland would indicate it is malfunctioning.
      • 13153I  ==> 13154Xe   + 0-1e  (+ (c) doc b)
      • I've read that iodine-123 is now used, which gives a more pure and safer gamma emitting radioisotope.
    • ?
  • more on the properties of beta particles and nuclear equations for beta decay

Advanced Chemistry Page Index and Links

5c (c) doc b Uses of gamma radiation sources

  • (c) doc b Gamma radiation is highly penetrating and so gamma sources are used where the radiation must be detected after passing through an appreciable thickness of material.
    • This is used in various tracer situations and usually the half-life should be relatively short to avoid any health hazards.
  • (c) doc b A gamma emitting tracer can be added to the flow of water in a pipe and the outside of the pipes monitored with a Geiger counter.
    • Any leaks would be detected by an increase in radiation reading. The flow of water in underground streams can be followed in a similar way.
  • (c) doc b Radiotherapy (radiation therapy)
    • It seems ironic that the very radiation which causes cancer, can also be used to treat it.
    • A beam of gamma radiation is directed onto the tumor site to kill the cancer cells, but it must be of an appropriate dose to minimise damage to healthy cells.
    • High does of radiation will kill living cells and the idea is to focus a beam of radiation onto the cancer cells.
    • Unfortunately the radiation passes through the 'good' tissue too and kills or damages 'good' cells and this damage can cause sickness, but, if the cancer cells are all killed, surely its worth it.
    • Modern techniques use multiple rotating gamma sources that are focused on to the tumor.
    • This means the surrounding 'good cells' are less frequently hit and minimises potential harmful side-effects on the rest of the body (e.g. sickness or other mutations).
    • Radiotherapy also avoids the need for intrusive surgery which has its own risk factors.
    • The gamma emitters used have relatively long half-lives to give the instrument a good working life.
  • (c) doc bGamma radiation can be used in a non-destructive way to test the structure of a material.
    • In a sense it is an alternative to X-ray photography for more dense materials e.g.
    • It is used test the structure and quality of pipe welds.
      • A gamma source is placed inside the pipe and photographic paper wrapped around the weld.
      • If there is any gap or flaw in the weld, more gamma radiation gets through and shows up as increased exposure on the 'gamma-ray picture'.
      • Its better to find out the fault now, rather than later when it fractures, and has to be 'dug up' or retrieved from the bottom of the sea!
  • (c) doc b Because gamma radiation is so deadly and penetrating it can be used to sterilise surgical equipment or packaged food. A strong gamma emitter is required with a long half-life which can last for many years with out replacement.
    • The radiation is deadly for bacteria even in the most microscopic pockets of apparently smooth and shiny stainless steel of surgical instruments.
      • A high does of gamma radiation will kill any microbe-bacteria cells.
      • It has the advantage over old fashioned 'boiling in water' of not requiring heating and even plastic instruments can be sterilised at room temperature.
    • It is very convenient for 'convenience' food!
      • Again, a high does of gamma radiation will kill bacteria and prevent the food decaying.
      • The food is quite safe to eat and NOT radioactive.
      • After cooking and sealing in a plastic packet, you don't need to reopen to complete the sterilization to give it a long shelf-life!
  • The gamma emitting radioisotope sodium-24, can be used in tracer studies of animal blood circulation, an important diagnostic tool in clinical medicine.
    • It undergoes beta decay with a half-life of 15 hours, a safe time for medical use.
      • 2411Na  ==> 2412Mg + 0-1e  (+ (c) doc b)
      • The emitted beta or gamma radiation can be detected outside of the body.
  • (c) doc b (c) doc bTechnetium-99 is a gamma emitter (half-life 6 hours) and is used in medicine as a tracer.
    • In medical applications, in a suitable chemical form, the radioisotope is injected into the body and its 'movement' can be followed.
    • Time is allowed for the radioactive tracer to spread and its progress tracked with a detector outside the body.
    • The patient can be placed next to a 'detection screen' that shows where the radioactive tracer is.
    • The effective function of organs like the liver and digestion system can be checked.
    • The half-life must be relatively short so it does not linger in the body increasing the harmful effects of cell damage.
    • Technetium atoms can be incorporated into many organic chemicals called radiopharmaceuticals which can be used to monitor biochemical aspects of the bodies chemistry e.g. the functioning and performance of a particular organ.
  • (c) doc bSimilarly, a patient can breathe in air with a gaseous gamma emitter in it, and the effectiveness and structure of the lungs can be checked.
    • The detector system can be focussed on rib cage and lung area of the body once the gaseous radioactive compound has been breathed in.
    • The gas must be a molecule containing a suitable radioactive atom.
  • (c) doc bIodine-131, another gamma emitter (half-life = 8 days), can be used to check on the functioning of a thyroid gland. The body needs iodine to make the hormone thyroxine and so the take up of iodine can be monitored by measuring the gamma radiation from the thyroid gland. Gamma radiation, being the most penetrating, it passes out through the body and so readily be detected outside the body by some suitable detector e.g. with a special camera or fluorescent screen.
    • The half-life should be long enough to allow good detection BUT NOT too long to be dangerous to the body over a period of time!
    • One method of treating thyroid cancer is to inject Iodine-13 into the body in a soluble salt form e.g. potassium iodide, so that it deliberately concentrates in the thyroid gland and the gamma radiation kills the thyroid cancer cells.
    • This is another example of 'medical physics' and important diagnostic technique in clinical medicine.
      • (c) doc bBeta sources can be used, though not as penetrating as gamma and have an increased risk of cell damage.. 
      • (c) doc bAlpha sources are too readily absorbed to show up via a detector and so are not suitable for these 'tracer' applications.
      • However, an alpha particle emitting isotope of radium can be directly injected in tiny quantities into tumourous tissue to directly irradiate and kill cancer cells (see uses of alpha radiation).
  • more on the properties of gamma radiation and nuclear origin of gamma radiation


1. Atomic structure, fundamental particles and radioactivity

2. What is radioactivity? Why does it happen? What radiations are emitted?

3. Detection of radioactivity, measurement, dose units, ionising radiation sources, background radiation

4. The properties and dangers of alpha, beta & gamma radioactive emission

 5. The uses of radioactive Isotopes emitting alpha, beta or gamma radiation

6. Half–life of radioisotopes, how long does material remain radioactive? Uses of decay data & half–life values

7. Nucleus changes in radioactive decay? how to write nuclear equations? Production of Radioisotopes

 8. Nuclear fusion reactions and the formation of 'heavy elements'

 9. Nuclear Fission Reactions, nuclear power energy resources

Advanced Chemistry Page Index and Links

(c) doc b(c) doc bRADIOACTIVITY multiple choice QUIZZES and WORKSHEETS

Easier-Foundation Radioactivity Quiz

or Harder-Higher Radioactivity Quiz

 (c) doc b five word-fills on radioactivity * Q2 * Q3 * Q4 * Q5and ANSWERS!

crossword puzzle on radioactivity and ANSWERS!