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
Uses of alpha particle sources
sources are too readily absorbed to show up with a Geiger counter or
other detector and so are not suitable for 'tracer' applications.
Because 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
- 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
- The nuclear decay equation is:
24195Am ===> 23793Np +
- 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!
- 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
- 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!
more on the properties of alpha particles and
nuclear equations for alpha decay
- 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
- 22388Ra ===> 21986Rn
- 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
Uses of beta radiation sources
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.
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
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.
more on the properties of beta particles and
nuclear equations for beta decay
- 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 (+
- I've read that iodine-123 is now used, which gives a more
pure and safer gamma emitting radioisotope.
Uses of gamma radiation sources
Radiotherapy (radiation therapy)
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.
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.
radiation can be used in a non-destructive way to test the structure of a
- 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.
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.
- 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!
The gamma emitting
can be used in tracer studies of animal blood circulation, an important
diagnostic tool in clinical medicine.
- 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
- 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'
- Again, a high does of gamma radiation will kill
bacteria and prevent the food decaying.
- The food is quite safe to eat and NOT
- 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!
Technetium-99 is a gamma emitter (half-life 6 hours) and
is used in medicine as a tracer.
- It undergoes beta decay with a half-life of 15 hours, a
safe time for medical use.
- 2411Na ==> 2412Mg
- The emitted beta or gamma radiation can be detected
outside of the body.
Similarly, a patient can breathe in air with a gaseous gamma emitter in it, and the effectiveness and structure of the lungs can be checked.
- 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
- 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.
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 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
more on the properties of gamma radiation and
nuclear origin of gamma radiation
- 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.
sources can be used, though not as penetrating as gamma and have an
increased risk of cell damage..
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).
RADIOACTIVITY and NUCLEAR PHYSICS INDEX
Atomic structure, fundamental particles and radioactivity
is radioactivity? Why does it happen? What radiations are emitted?
3. Detection of radioactivity, measurement,
dose units, ionising radiation sources, background radiation
properties and dangers of alpha, beta & gamma radioactive emission
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
changes in radioactive decay? how to write nuclear
equations? Production of Radioisotopes
Nuclear fusion reactions and the formation of 'heavy elements'
9. Nuclear Fission Reactions, nuclear power energy resources
multiple choice QUIZZES and WORKSHEETS
word-fills on radioactivity
puzzle on radioactivity