4b. The Dangers of Radioactive Emissions

Beware of ionising radiations from radioisotopes!

The penetration trends and the effects of Ionisation from radioisotopes

• When an object is exposed to radiation from a radioactive source it is called irradiation.

  • Technically, we are continually irradiated from background radiation, but we seem to survive ok!

  • However, to avoid a possible misconception, irradiating an object, does not mean it becomes radioactive.

    • Although this true for alpha, beta and gamma radiation, it is not true for neutrons.

    • They can be absorbed by atoms to produce radioactive isotopes from stable isotopes - its a method used to deliberately synthesise radioisotopes for medical applications and scientific research.

• Radioactive contamination
  • Radioactive contamination is the unwanted presence of radioactive isotopes in the environment.
  • Radioactive contaminants may be in the air and breathed in, swallowed or on surfaces you touch and absorbed through the skin.
  • The radioactive sources may be natural or artificial (see background radiation).
  • Whatever the source, they are potentially harmful.
  • Some radioisotopes are short lived, but others can be radioactive for hundreds and thousands of years - a long term threat to our health - see half-life and consequences.
  • Contamination can be more dangerous than external irradiation, because the radioactive substance is actually inside your body and the nuclear radiation passes directly into the surrounding cell tissues.
• Dangers from irradiation
  • An object is irradiated when it is hit by ionising nuclear radiation.
  • All radioactive emissions are extremely dangerous to living organisms.
  • All three radiations can penetrate living cells causing damage.
  • The effects of radiation on a living organism depends on the type of radiation and how much of it you are exposed.
  • Sources of ionising radiation are discussed in section 3b.
• When alpha, beta or gamma radioactive emissions hit living cells they cause ionisation (ionization) effects, and break chemical bonds e.g. in DNA causing molecular damage and destroying vital complex molecules.
• If powerful enough, ionising radiation can cause burns, kill cells directly or cause genetic damage e.g. to the DNA molecules causing mutations and cancer.
• So high intense radiation doses cause severe burn effects and can kill cells, and death can result from radiation sickness.
  • For one thing is for sure, the greater the radiation dose your body receives, the greater the chance of killing cells, or DNA damage and cancer cells developing.
  • Irradiation is a temporary effect, as long as the source of radiation is removed or you are removed from the source of radiation.
  • However, you cannot say the same for contamination. If any radioactive particles get on your clothes, skin or breathed in, they could cause irradiation over a longer time - hence lots of precautions need to be applied when handling radioactive materials.
• But although low radiation doses doesn't kill the cells, the cells can still be genetically damaged and can still replicate, these mutations can lead to the formation of cancerous cells and tumor development later.
  • It is the lower dose effects, particularly if exposed to radioactive material over a long period of time, that cause the seemingly minor damage, but may allow mutated cells to survive.
  • Mutant cells can then divide uncontrollably, that is cancer and potentially lethal tumours develop.
  • High doses of radiation kill cells, but the health hazard effects depend on ...
    • how much radiation you are exposed to,
    • the type of radiation you are exposed to,
    • the energy and penetration of the radiation,
      • best to avoid it if at all possible!
• When alpha, beta and gamma radiation collide with neutral atoms or molecules they knock off electrons and convert them into charged or ionised particles (molecular ions) and free radicals - very reactive fragments of molecules.
  • Positive ions are formed on electron loss and negative ions are formed by electron gain.
  • The positive ions and free radicals are very unstable and very reactive and cause chemical changes in the cell molecules, some of which can affect cell genetics and lead to cancer.
  • The 3 radiations have different capacities to cause cell damage.
• If the radioactive source, a 'radionuclide', gets inside the body the 'danger' order is alpha > beta > gamma.
  • The bigger the mass or charge of the particle, the bigger its ionising impact on atoms or molecule.
  • BECAUSE for the radiations the order of mass is 4 > ¹/₁₈₅₀ > 0, for > >
    • and the numerical order of electric charge is +2 > -1 > 0, for > >
    • i.e. alpha > beta > gamma for both trends in mass and charge.
    • A single alpha particles travelling at ¹/₁₀th the speed of light can devastate living cells in relatively small localised area.
    • Much of the beta and gamma (in particular) radiation will actually pass out of the body without damaging cells.
  • If the radioisotope is in the body the radiation impacts directly on cells with the consequences described above.
• However, if the radioactive source is outside the body, the order danger is reversed to gamma > beta > alpha because the danger order follows the pattern of penetrating power.
  • The smaller the mass and charge the more penetrating the radiation (reverse the order of above).
  • Gamma and beta are the most penetrating and will reach vital organs in the body and be absorbed.
  • Most gamma radiation passes through soft tissue but some is inevitably absorbed by cells.
  • Alpha radiation would not penetrate through clothing or outer skin cells (preferably dead!) and is highly unlikely to reach living cells below the skin.
  • Beta radiation is quite penetrating into the body, but not as much as gamma rays.
• Because of the dangers of this ionising or atomic radiation, all workers and medical staff who are likely to be near radioactive or ionising sources must wear lapel radiation badges containing photographic film to monitor their exposure to radiation.
  • The film is regularly developed and the darker the film the more radiation would have impacted on the person.
  • From the film exposure it is possible to estimate the dose of radiation the individual has received.
  • This is just one examples of tackling the health & safety issues when dealing with radioisotopes.
• Examples of precautions taken when handling radioactive materials or dealing with medical use of ionising radiation include ...
  • Radiographers wear lead lined aprons and anyone else involved in radiotherapy cancer treatment must take particular precautions and radiation monitored.
    • Radiographers who work in hospitals with ionising radiation (gamma or X-rays, CT scanning) have higher risk of exposure above background radiation.
    • Radiographers wear lead aprons and/or stand behind protective lead/lead glass screens in another room to work as remotely as possible to minimise their radiation dose.
    • Everything can now be done at a safe distance and the dangers from prolonged exposure to ionising radiation are virtually eliminated now.
    • when X-rays were first used for X-raying bones in the early 20th century, almost all of the first generation of radiographers died early from cancer!
    • If someone is having an X-ray or radiotherapy for cancer, apart from the area of the body under examination or treatment, the rest of the body should be protected with a lead or other radiation absorbing material, again to minimise the patient's overall radiation dose.
    • In general to minimise the annual dose of ionising radiation, medical staff can have their working conditions made safer by:
      • increasing their distance from the source - the greater the distance, the lower the intensity of irradiation (inverse square law),
      • personal shielding to absorb harmful radiation,
      • encasing the source in certain materials to absorb harmful radiation,
      • minimising the time they spend in the presence of radiation sources (this also applies to patients),
    • How might a doctor justify to a patient injecting them with a radioactive isotope in preparation for imaging using a PET scanner or gamma camera?
  • Uranium miners and (and less so) nuclear power workers are exposed to much higher levels of radiation than background radiation (discussed in 3b.)
    • Such workers need to wear face masks, protective clothing (specifically designed suite and gloves) to prevent touching or inhaling dust from radioactive materials.
    • These workers should be wearing radiation badges, and after a work shift, be thoroughly showered and checked for any radioactive contamination and regular health checks.
    • Deep in underground mines ionising radiation levels are higher because of radioactive-isotopes in the surrounding rocks.
  • The nuclear industry.
    • In nuclear fuel preparation and reprocessing, as much work is done using robotic control systems from behind steel, concrete, lead or thick lead glass panels for visual monitoring of the situation.
    • Lead is very good absorber of all types of radiation, but a thick layer in needed to stop all the gamma radiation.
    • Small samples of radioisotopes can be stored in a lead-lined box which should be brought out for the minimum of time and stored safely way in a secure room that is not used for any other purpose.
    • All radioactive materials (weakly or strongly emitting) must be handled and processed with the greatest of care.
    • There should be minimum contact time in handling radioactive materials so exposure is at a minimum.
    • There should NEVER be any contact of your skin with radioactive materials, which is why remotely-controlled robotic arms are frequently used to avoid the dangers of contact with radioactive materials.
    • Always handle containers of radioisotopes with protective clothing, gloves and tongs if possible and at arms length to prevent any particles from contaminating your clothes or skin.
      • For the most hazardous situations, protective suits and even filtered breathing apparatus might be used,
      • AND robotic arms can be used to handle the radioactive materials, operating from behind a shielded area i.e. in another room, with thick glass panels to enable you to what is going on.
      • Remote cameras are used to investigate the inside of structures (e.g. reactor cores) where it is too dangerous for people to enter.
    • Increasing the distance between you and the radioactive source reduces exposure and alpha particles are absorbed by a few cm of air.
  • Scientific research using radioactive sources
    • In research laboratories, experiments are conducted in sealed fume cupboards at the laboratory side and technicians work through sealed whole arm gloves through a thick lead glass front.
    • You can also reduce the pressure in the fume cupboard so there is no chance of pressure leakage out into the laboratory area.
    • No skin contact with any radioactive materials or bring the face anywhere near to the source.
    • Handle sample containers with tongs at arm's length.
    • All radioisotopes are kept in thick lead-lined containers, suitably labelled with the hazard warning symbol for radioactive materials. The lead lining absorbs potentially harmful radiation.
    • Industrial and research workers may need to wear a full protective suit to prevent any, even microscopic, radioactive particles to come into contact with the skin or inhaled into the lungs.
    • Thick lead/steel/concrete barriers, even lead-lined suits are needed to protect people from deadly deeply penetrating gamma radiation, though alpha and beta radiations are less penetrating.
  • At high altitude the background radiation increases so commercial airline pilots are greater risk from the dangers of cosmic rays (some even higher energy than gamma rays). I don't know if any precautions are taken?
• A few 'nuclear' historical footnotes on 'contamination'
  • Atomic weapon tests in the past
    • Between 1946 and 1992, the US and UK governments carried out hundreds of atomic weapons tests contaminating the atmosphere, land and water with radioactive isotopes formed in the nuclear explosions.
    • Somewhat unintentionally, thousands of military personnel were exposed directly to radiation or breathed in radioactive contaminants near Pacific islands or the deserts of Arizona - where civilians were also affected by windblown debris from the test explosions.
    • Subsequently many of them developed cancers and died prematurely.
    • Such tests are now banned, but lots of nuclear weapons are still stockpiled around the world.
    • Some Pacific islands are still too contaminated from radioactive fallout for people to return to them.
  • The Chernobyl nuclear reactor accident
    • In 1986 there was an explosion (not nuclear) in the power station near the Russian city of Chernobyl.
    • The city had to be evacuated within 30 hours of the explosion due to radioactive contamination.
    • Even in 2020, most of Chernobyl is still a 'ghost' town.
    • Initially, the local flora and fauna was affected, but much of the wildlife and plants are flourishing again, but it may be still many years before people can return to their home villages - if the want too!
    • The remains of the reactor are covered in a huge layers of steel and concrete, and it will be impossible to clear the site - its there forever, but shouldn't contaminate the 'world' beyond the 'casing'.
  • Decommissioning nuclear power stations
    • One of the first nuclear power stations was Calder Hall in Cumbria, north-west England, and ran for 47 years.
    • Decommissioning began in 2005, and, as with all nuclear power stations, the process will take many years because of the large and dangerous quantities of radioactive material.
    • Removal of the spent fuel rods began in 2011 and is planned to finish in 2019.
    • It will be at least 100 years before the land on the site can be re-used and the 'clean-up' will cost many millions of pounds - just for four small reactors!

• The sources of ionising radiation are discussed in section 3b.

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Appendix 1. Explaining the effect of ionizing radiations on atoms & molecules

(a) Excitation of atoms by absorbing EM radiation which then give out (emit) EM radiation

When the EM radiation has less energy than that required for ionisation, you still 'excite' an atom into a more energised state by promoting an electron from the outer shell to another, but higher level shell (which may or may not be empty).

The excited atom is unstable and will 'relax' back to its normal stable state by emitting EM radiation photons.

The diagram above illustrates the process:

1. An electron in an outer shell absorbs incoming EM radiation energy and is promoted up to the next higher empty shell (in this case, but can be a partially filled shell).

This called electron 'excitation' and the incoming photon must have the precise energy to bring about the energy level change the electron experiences.

The further the electron moves up the energy levels i.e. further from the nucleus, the more energy it has.

2. The atom is now in an 'excited' state and unstable because the electron has gained excess energy and if possible the atom would like to return its original stable state.

3. So, the promoted electron now loses energy and drops back down to the 'stable' original level stabilising the atom.

The excess energy is lost as EM radiation or heat.

NOTE danger!

The excited atoms that can be dangerous, and promote chemical reactions you might not wish to happen (e.g. in living cells) and also release their excess energy as heat.

(b) The complete ionisation of an atom

An atom is ionised if it completely loses one or more electrons.

This is a bit more energetic than 'excitation' described above.

Ionisation by EM radiation of atoms to form a positive ion

The higher energy uv, and both X-ray and gamma radiations have enough energy to cause complete ionisation.

This is going 'energetically' further than just excitation of a atom (or molecule).

==  high energy uv/X-ray/gamma ray photon  ==>  ⁺    +    e^-

The energy carried by ultraviolet light radiation, X-rays and gamma radiation is sufficient to cause ionisation of atoms by knocking off negative outer shell electrons to form a positive ion - the atom has been ionised - see diagrams and explanation below.

This represents the ionisation of a sodium atom to form a positive sodium ion and a free electron:

Na ==> Na⁺  +  eŻ  (electron configuration change of sodium from 2.8.1 ==> 2.8, as in chemistry notes!)

In this case the incoming EM radiation must have sufficient energy to promote the electron all the way up the energy levels until it is completely free of the attraction of the positive nucleus - so the atom has been ionised.

Dangers of ionising radiation

From (b) we see that excited atoms that can be dangerous and promote chemical reactions you might not wish to happen.

BUT, ions can be even more destructive on cells and break chemical bonds and cause even more genetic damage - this is usually due to the high reactivity of ionised molecules or free radicals (bits of split molecules).

This is the essence of the dangers of ionising radiation - burns and cell DNA damage leading to cell death or rogue multiplication of mutated cancer cells and the effect is greater than that from just excited atoms.

More on the dangers has already been discussed on this page

Note on the use of fluorescence tubes for lighting

Fluorescent tubes for lighting purposes, contain mercury vapour.

When you switch them on, the p.d. accelerates electrons down the tube.

The electrons hit mercury atoms and knock electrons off them - ionisation to give mercury ions and more free electrons.

The outer electrons and therefore the mercury atoms/ions are excited to higher energy levels.

When the electrons drop down to their lower more stable levels, they emit ultraviolet EM radiation.

On the inner surface of the tube is a phosphorus coating that absorbs the uv radiation and the atoms are excited to higher energy levels causing a fluorescent effect because ....

... as the excited electrons fall back down to their lower levels they emit a full range of frequencies in the visible region of the electromagnetic spectrum.

Unfortunately, mercury is a highly poisonous metal and so old tubes are a highly hazardous toxic waste and must be separated and dealt with appropriately from most other waste.

uses of alpha, beta and gamma radiation

and nuclear equations for alpha and beta decay

Atomic structure, radioactivity and nuclear physics revision notes index

Atomic structure, history, definitions, examples and explanations including isotopes

1. Atomic structure and fundamental particle knowledge needed to understand radioactivity

2. What is Radioactivity? Why does it happen? Three types of atomic-nuclear-ionising radiation

3. Detection of radioactivity, its measurement and radiation dose units, ionising radiation sources - radioactive materials, background radiation

4. Alpha, beta & gamma radiation - properties of 3 types of radioactive nuclear emission & symbols ,dangers of radioactive emissions - health and safety issues and ionising radiation

5. Uses of radioactive isotopes emitting alpha, beta (+/–) or gamma radiation in industry and medicine

6. The half-life of a radioisotope - how long does material remain radioactive? implications!, uses of decay data and half-life values - archaeological radiocarbon dating, dating ancient rocks

7. What actually happens to the nucleus in alpha and beta radioactive decay and why? nuclear equations!, the production of radioisotopes - artificial sources of radioactive-isotopes, cyclotron

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

9. Nuclear Fission Reactions, nuclear power as an energy resource

Easier Foundation Tier Radioactivity multiple choice QUIZ

Harder Higher Tier Radioactivity multiple choice QUIZ

Worksheet QUIZ Question 1 on RADIOACTIVITY - absorption of alpha, beta and gamma radiation

Worksheet QUIZ Question 2 on RADIOACTIVITY - dangers & monitoring ionising radiation levels

Worksheet QUIZ Question 3 on RADIOACTIVITY - revision of atomic structure

Worksheet QUIZ Question 4 on RADIOACTIVITY - what happens to atoms in radioactive decay?

Worksheet QUIZ Question 5 on RADIOACTIVITY - uses of radioisotope and half-life data

ANSWERS to the WORD-FILL WORKSHEET QUIZZES

Crossword puzzle on radioactivity and ANSWERS!