4. Alpha, Beta & Gamma Radiation

Properties and Dangers of atomic/nuclear/ionising radiation

Doc Brown's Chemistry Doc Brown's GCSE Physics Revision Notes

IGCSE/GCSE Physics & Chemistry revision notes on Radioisotopes - this page describes the properties of alpha particle radiation, beta particle radiation and gamma radiation in terms of their charge, mass, penetration of materials, behaviour in an electric field, their relative ionising capacity and the dangers of ionising radiation from both external radioactive sources and internally ingested radionuclide. These revision notes on the properties of alpha, beta and gamma ionising radiation and their dangers should help with GCSE/IGCSE physics courses and A/AS level physics courses

4a. The Properties of the three types of Radioactive Emission and symbols

and 4b. The Dangers of Radioactive Emissions - beware of ionising radiations from radio-isotopes!

(c) doc bNote there is a separate page for ... uses of radioactive Isotopes emitting alpha, beta or gamma radiation

AND 4c. is an extra advanced physics section which most students do NOT need, just did it for my own interest)



4a. The Properties of the three types of Radioactive Emission and symbols

IONISING RADIATIONS emitted when unstable atomic nuclei undergo radioactive decay

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Experiment to show there are at least three types of emissions from radioactive substances.

Left to right - alpha particles, gamma rays and beta particles

The radioactive emissions become separated in a strong electromagnetic field because alpha particles (+2) and beta particles (-1) have different charges, so go in opposite directions in electric or magnetic fields. Gamma photons (rays of electromagnetic radiation) have no charge (0) and go straight on to the detector (photographic plate, electronic screen, ionisation effect - electronic signal). The beta particles are deflected more because they have a much smaller mass than alpha particles (for more details see table below). Beta particles are so easily deflected that in a magnetic field they might spiral around!


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Two simple diagrams (above & below) to show the penetration of alpha particle radiation, beta particle radiation and gamma radiation (for more details see table below).



The three radiations highlighted are the one you most likely need to know, but maybe the other two as well?

Type of radiation emitted & symbol

Nature of the radiation

formation, structure, relative mass, electric charge

Other nuclear Symbols

Penetrating power (and speed), and what will block it (more dense material, more radiation is absorbed BUT smaller mass or charge of particle, more penetrating)

Ionising power - the ability to remove electrons from atoms to form positive ions, the process is called ionisation

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Alpha particle radiation

a helium nucleus of 2 protons and 2 neutrons, mass = 4, charge = +2, is expelled at high speed from the nucleus

Low penetration, slowest speed (but still ~10% speed of light!), biggest mass and charge, stopped by a few cm of air or thin sheet of paper

Very high ionising power, the biggest mass and charge of the three radiation's, the biggest 'punch' in ripping off electrons from molecules, other ions are formed

e beta minus particle radiation

high kinetic energy electrons, mass = 1/1850, charge = -1, expelled when a neutron changes to a proton in the nucleus

beta minus, beta

Moderate penetration (~90% speed of light),  'middle' values of charge and mass, most stopped by a few mm of metals like aluminium, will travel quite a few metre in air

Moderate ionising power, with a smaller mass and charge than the alpha particle, but still quite good at knocking off electrons from molecules - moderate ionisation

e+ beta plus particle emission

high KE positive electron called a positron, mass = 1/1850, charge = +1, expelled when a proton changes to a neutron in the nucleus.

beta plus, beta +

Theoretically as above, BUT, the positron is the antiparticle of the electron. it is identical to an electron but opposite in charge. Destroyed when it meets an electron (see on right) producing two high energy gamma ray photons, so it doesn't get very far. Theoretically as above, BUT when electron meets positron, kapow !

e+ + e   ==> 2 high KE

actually called annihilation !

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Gamma radiation

very high frequency electromagnetic radiation, mass = 0, charge = 0, gamma emission often accompanies alpha and beta decay

Very highly penetrating (100% speed of light !), smallest mass and charge and greatest speed, most stopped by a thick layer of steel or a very thick layer of concrete, but even a few cm of dense lead doesn't stop all of it! gamma rays can pass through many m of air.

The lowest ionising power of the three, gamma radiation carries no electric charge and has virtually no mass, so not much of a 'punch' when colliding with an atom to remove an electron, weak ionisation

n neutron radiation neutron, mass = 1, charge = 0, fundamental particle of the nucleus Highly penetrating (more than alpha & beta & sometimes gamma). However, neutrons are most readily absorbed by light nuclei so hydrogen-rich materials like water, poly(ethene) plastic and concrete are used for neutron radiation shielding. The nuclei formed often emit gamma radiation so an extra thick protective layer of lead is needed around a neutron rich environment ! Can't ionise directly, but they are absorbed by the nuclei of atoms they pass through. This can make the atom unstable - radioactive, hence other nuclear radiations may then be produced, producing an 'indirect ionisation' effect. So neutron radiation is as dangerous as any of the others.

IMPORTANT NOTE: The emission of an alpha particle or beta particle leads to a change in the composition of a nucleus in terms of protons or neutrons. The emission of a gamma photon does NOT change the composition of the nucleus, it only lowers the energy associated with the nucleus.

Nuclear radiation:

Why is it also called 'ionising radiation'?

What causes ionisation and what is ionisation?

When a neutral atom or molecule loses or gain electrons, a charged particles called an ion is formed.

When alpha particles or beta particles or gamma photons hit atoms they knock off negative electrons causing ionisation, that is, in this case, the formation of positive ions.

These atomic or molecular ions are very reactive and can bring about chemical changes.

The relative ionising power is further explained below.

The more ionising the radiation, the less penetrating it is, because the stronger the ionising interaction with matter, the quicker it loses its energy, and its penetration power.

Extra note on the relative masses, velocities (speeds) and kinetic energies of alpha, beta and gamma radiations

Their relative masses (m), velocities (v) and kinetic energies (KE) have a considerable bearing on the properties described above. Note the formula for kinetic energy: KE = 1/2mv2

(c) doc bAlpha particle radiation:

Alpha particles have a velocity of ~1/10th to 1/20th of the speed of light (a very high velocity helium nucleus).

Alpha particles have the greatest kinetic energy, because, although they have the slowest speed of the three radiations, they have by far the greatest mass, and this makes all the difference.

Compared to beta particles, alpha particles have a speed of, at the least, 18 times (9/10 ÷ 1/20) less than beta radiation.

BUT, the mass of an alpha particle is 7400 times greater  (4 ÷ 1/1850) than that of a beta particle.

Although alpha particles have the largest kinetic energy, they have the least penetrating power because of the larger mass, and, especially, the double positive charge (+2). These fast moving positive electric fields will strongly interact with the negative electrons of the atoms the alpha radiation is passing through so it gets slowed down as it loses its kinetic energy.

As argued above, although the alpha particles have the slowest velocity, their greater mass and higher charge enable an alpha particle to 'knock off' electrons from atoms the most easily, i.e. the greatest ionising power.

The doubly positively charged alpha particle will attract and abstract two electrons from atoms/molecules hit forming new ions.

(c) doc bBeta particle radiation:

Beta particles (a very high velocity electron) can be emitted with up to 9/10ths of the speed of light.

As argued above, although beta particles have speeds of up to 18 times greater than alpha particles, with a mass of 7400 times less than alpha particles, the kinetic energies of beta particles are much less than those of alpha particles.

With a smaller mass than alpha particles, and a smaller charge (-1) there is less interaction with any medium the beta radiation is passing through, so it is more penetrating than alpha radiation and has a lower ionising power.

One singly charged negative electron will repel another, so when a beta particle hits the outer electrons of an atom or molecule, it will knock out an electron with a combination of a momentum-repulsion collision effect to form new ions.

(c) doc bGamma radiation:

Gamma radiation consists of photons, which of course travel at the speed of light, like all electromagnetic radiation.

BUT, photons have ~zero mass, so although they can have a tiny impact effect when striking material, their kinetic energy transfer is much less than for alpha and beta particle collisions when they interact with matter.

Despite having the greatest velocity ('speed of light'), with no electric charge and effectively ~zero mass, there isn't a lot to cause interaction with any material the gamma radiation is passing through, so, it penetrates into matter the furthest but causes the least ionisation.

An electrically neutral gamma photon still has sufficient 'kinetic energy' on collision to knock off an outer electron from an atom or molecule forming ions.

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

uses of alpha, beta and gamma radiation & nuclear equations for alpha and beta decay


(c) doc b4b. The Dangers of Radioactive Emissions - beware of ionising radiations from radio-isotopes!

The penetration trends and the effects of Ionisation from radioisotopes

  • 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.
  • For thing is for sure, the greater the radiation dose your body receives, the greater the chance of DNA damage and cancer cells developing.
  • But although low radiation doses don'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 (ions).
    • Positive ions are formed on electron loss and negative ions are formed by electron gain.
    • The positive ions maybe unstable and very reactive and cause other chemical changes in the cell molecules.
    • 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,
      • and for electric charge the order is +2 > -1 > 0,
      • 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 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.
    • Uranium miners and 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.
    • 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 gloves and tongs if possible and at arms length.
      • Increasing the distance between you and the radioactive source reduces exposure and alpha particles are absorbed by a few cm of air.
    • 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.
      • 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?
  • -

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4c. APPENDIX: One day I asked myself the following questions

(ignore if you are not interested, rather than be exposed to the danger of a chemist doing physics calculations especially when I follow it up with some relativistic calculations using an equation from Einstein's theory of relativity!)

What is the velocity-speed of alpha particle radiation? What is the relative kinetic energy of alpha radiation (alpha particles)?

What is the  velocity-speed of beta particle radiation? What is the relative kinetic energy of beta radiation (beta particles)?

What is the velocity of gamma radiation? What is the kinetic energy of gamma radiation (gamma photons)?

How do these values of  velocity and kinetic energies relate to the relative penetration properties and ionising power of alpha, beta and gamma radiations?

Why can these radiation cause genetic damage by breaking chemical bonds in DNA molecules?

These questions have been partly (and sufficiently) answered for GCSE chemistry/physics and A level chemistry in section 4a on the properties of alpha, beta and gamma radiation.

So, the calculations I've done below are (as far as I know) NOT required for pre-university examinations, but I hope you might find them, and my resulting comments, interesting. The calculations are a bit simplistic in some ways but the results serve my purpose.

The energy of emitted particles from radioactive decay are usually quoted in megaelectronvolts (MeV)

An electronvolt is a unit of energy equal to the work done on an electron in accelerating it through a potential difference of one volt. A megaelectronvolt is 106 electron volts, which is also equal to 1.60 x 10-13 joules

So 1 MeV = 1.60 x 10-13 J and 1 MeV = 10-16 kJ

On average the MeV energy sequence is alpha particles > beta particles > gamma photons

BUT there is wide variation and much overlap between the energy ranges of these three radioactive emissions.

Alpha typically 3 to 9 MeV, beta typically 0.1 to 10 MeV, gamma typically 0.03 to 5 MeV

Now as a chemist I am used to thinking in terms of molar quantities, so I'm going to multiply some MeV energy values by the Avogadro Constant (6.02 x 1023 specified entity per mole) to give the energy of the particles per mole.

so using MeV x 10-16 x Avogadro Constant = kJ per mole of particles

0.03 x 10-16 x 6.02 x 1023 = 1.8 x 106 kJ per mole of 'particle'

10 x 10-16 x 6.02 x 1023 = 6.02 x 108 kJ per mole of 'particle'

Typical chemical covalent bond energies lie in the range 100-500 kJmol-1

You can readily deduce that an individual alpha particle, beta particle or gamma photon, has an enormous potential to break a lot of covalent bonds in organic molecules e.g. DNA cell damage due to radioactivity near a cell.

Theoretically, therefore, there is enough energy in particle/photon to break between 3.6 x 103 and 6 x 106 chemical bonds, though the energy is also dissipated in ionisation collisions and exchange of kinetic energy releasing heat.

Having looked at the MeV values from a data book I decided to do some other calculations of kinetic energies.

But these calculations gave quite different results, but all the calculations support the statement above about breaking chemical bonds which can damage life and also material structures e.g. the steel and concrete of a nuclear reactor.

Calculation of particle kinetic energies

  particle mass    
kinetic energy  = ------------------------ x v2

KE = 1/2mv2      (kinetic energy in J, mass in kg, velocity in m/s)

(you will come across this equation in GCSE physics and A level physics)

The speed of light = c =  3.00 x 108 m/s, this is needed because the velocity of alpha and beta particles is often quoted as a fraction or percentage of the speed of light in a vacuum.

(c) doc bThe velocity of alpha particles and the calculation of the kinetic energy of alpha particles

The mass of an alpha particle = 6.64 x 10-27 kg, typical speed alpha particle is 1/10th of the speed of light (0.1 c).

  6.64 x 10-27      
kinetic energy  = -------------------- x (0.1 x 3.00 x 108)2 = 3.00 x 10-10 J

of alpha particle


This gives the highest kinetic energy of the three radiations from the radioactive decay of an unstable nucleus.

(c) doc bThe velocity of beta particles and the calculation of the kinetic energy of beta particles

The mass of a beta particle (electron) = 9.11 x 10-31 kg, typical beta particle speed is 90% of the speed of light (0.9 c).

This calculation ignores relativistic effects (relativity theory) whereby the mass of a particle dramatically increases, the nearer its velocity is to that of light. (Note that the mass of a beta particle with a speed of 0.9 c is 2.09 x 10-30 kg).

  9.11 x 10-31      
kinetic energy  = --------------------- x (0.1 x 3.00 x 108)2 = 3.32 x 10-14 J

of beta particle


Despite the high speed of beta particles, their kinetic energy is far less than that of typical alpha particle.

(c) doc bThe velocity of gamma photons and the calculation of the kinetic energy of gamma photons

Photons (of electromagnetic radiation) are considered to have zero mass (you can calculate what is called a 'rest mass', but NOT here).

Instead I've adopted a different approach using Planck's equation to calculate the energy an individual gamma photo carries.

Planck's equation is E = hν

E = energy of gamma photon in J, h = Planck's Constant = 6.63 x 10-34 J,

v (f) = frequency of electromagnetic radiation in Hz (s-1)

Gamma photons from a radioactive decay process have frequencies of >=1019 Hz

So the minimum sort of energy of a gamma photon would be

E = hν

E = 6.63 x 10-34 x 1019

Energy of gamma photon = 6.63 x 10-15 J

If we simplistically equate this with the kinetic energy that might be imparted when gamma rays strike a material, then this does work out to be a bit less than the kinetic energy of beta particles. However, gamma rays can have frequencies of up to 1022 Hz from some nuclear changes, giving them kinetic energies greater than beta particles.

General comments based on the above calculations of kinetic energy.

The calculations partly explain why the order of biological molecular damage from radiations is alpha > beta > gamma,

if the radiation directly impacts on living tissue releasing the kinetic energy (KE of alpha > beta > gamma).

But, the effects of ionisation are also very important in causing 'molecular damage' too, which coincidently is the same order.

The energy on impact may be dissipated as heat from particle-molecule collision, ion formation or used in the endothermic (energy absorbing) process of breaking chemical bonds, the latter being how DNA molecules are damaged.

To put this in perspective, a chemist (like me) thinks in terms of bond enthalpies (bond energies), so how does the kinetic energy of an alpha particle measure up to breaking a chemical bond?

We can do a simple 'molar' calculation by multiplying the KE of an alpha particle by the Avogadro constant (6.02 x 1023 defined particles/mole).

3.00 x 10-10 x 6.02 x 1023 = 1.81 x 1014 J = 1.81 x 1011 kJ per mole of alpha particles

Now typical chemical covalent bond energies lie in the range 100-500 kJmol-1

This means the impact energy of a single alpha particle, theoretically has the energy to break between

3.6 x 108 and 1.8 x 109 chemical bonds, kapow!

Now much of the energy is absorbed as heat from 'mechanical impact' and also in ion formation BUT many bonds in organic molecules would be broken, hence the damage to DNA by radioactive emissions.

Please note that this humble simplistic calculation, indirectly, shows the vast difference in nuclear energy changes, compared to chemical energy changes!


uses of alpha, beta and gamma radiation & nuclear equations for alpha and beta decay


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

(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!

ALPHABETICAL SITE INDEX for chemistry     

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