Ionising radiation

Fundemental science article

Also known as

• Commonly called "radiation"
  

Physics

The structure of matter

• Matter is made of atoms, ions and electrons.
• Every atom has a central component called a nucleus. The nucleus is orbited by electrons. 
• The nucleus is made of protons and neutrons. The number of protons in an atom is equal to the number of electrons. The number of protons is known as the atomic number.
• The number of protons and neutrons together is known as the mass number.
• Each proton and neutron is comprised of subatomic particles called quarks.
• One of the fundemental interactions of the universe is known as the 'strong interaction'. It is responsible for binding together neutrons and protons in the atomic nucleus. This interaction occurs as an ongoing quark exchange between protons and neutrons. 
• As the proton number gets higher, the neutron number usually rises too.
• If there is a gain of an electron without a gain of a proton, an atom becomes a negative ion. 
• If there is a loss of an electron without the loss of a proton, an atom becomes a positive ion.
• Each element has a specific number of protons. Different atoms of the same element can have a different neutron number. These are known as isotopes of that element.
• Some elements and isotopes are very unstable systems. Generally, the higher the mass number, the more unstable the atom is.

Nuclear decay, radioactivity

• One of the fundemental interactions of the universe is known as the 'weak interaction'.
• Through this interaction, atomic nuclei can decay to a more stable state, producing a new element or a new isotope.
• Nuclear decay events result in the expulsion of alpha particles (high-energy helium-4 nuclei), beta particles (high-energy electrons), positrons (anti-electrons) or gamma rays (high-energy photons). The new isotope produced by the decay is more stable.
• Positrons interact with electrons in a process called annihilation. Both particles are destroyed but due to mass-energy conservation, symmetrical gamma rays (high-energy photons) are emitted.
• Radioisotopes undergo nuclear decay at perfectly regular intervals. This is the principle behind atomic clocks.
• The half-life of an isotope X is that amount of time that it will take for 100kg of isotope X to decay to 50kg of isotope X. The half-life remains constant for an isotope, but the emitted dose of radiation decays exponentially with time. The half-lives of some radioisotopes are billions of years.
• Alpha particles, beta particles, and gamma rays are highly energetic and ionising.  
• Ionising radiation can turn atoms into ions. This can disrupt the chemical bonds of any molecule.
• As air becomes ionised, there may be a metallic taste, a smell of ozone, or an ionised-air glow.
• Ionisation events can be detected by instruments such as the Geiger–Müller counter. These instruments display a count per second.

Activity

• Activity of a radioactivity material can be expressed as Bq (Becquerel). 1 Bq is equivalent to 1 nuclear decay per second. The greater the mass of the material, the greater the measured activity.
• The mass of radioactive material and the activity fall as the material decays.
• A material with a half-life of 100 years will have decayed to half the mass of that radioisotope after 100 years.
• Due to long half-lives and large amounts of contamination, some areas on the planet will continue to emit significant amounts of ionising radiation for thousands of years. They must remain isolated and contained to prevent future disease.

 

Doses

• When measuring ionising radiation dose, the Sievert value reflects the energy (in joules) transferred to 1kg of matter each second.
• 1 Sv = 1000 mSv.
• Approximately 1 gray per second (if gamma radiation).
• Approximately 100 rem per second.
• Approximately 100 rad per second (if gamma radiation).
• Approximately 360,000 roentgen per hour.
• Approximately 1 watt per kilogram.
• Approximately 1 joule per kilogram per second.
• The average person in the USA receives an estimated effective dose of about 3 mSv (milliSievert) per year from background (natural) radiation.
• A dose of 4-5 Sieverts or more, absorbed within a short time period, causes death in 50% of patients, within 30 days.

 

Sources of ionising radiation

Mild 

• Electronic devices
• Cosmic rays
• Natural radon gas stores

Moderate

• Radiological imaging
• Radiotherapy devices
• Brachytherapy
• Solar radiation (sunlight)

Severe

• Waste from nuclear power plants
• Use of nuclear weapons

 

Pathophysiology

• High energy ionising radiation causes damage to all exposed biological structures.
• The energy of the radiation can result in tissue damage similar to thermal or electrical burns. A sufficiently high dose will vaporise living tissue.
• The most radiation-sensitive structures within cells are the genetic materials. DNA and RNA are easily damaged or destroyed, leaving the cells incapable of functional protein synthesis.
• Successful mitosis cannot occur so destroyed cells are not replaced.
• The cell cannot repair physical damage.
• Many cells undergo apoptosis (programmed cell death).
• Tissues start to break apart.
• Any DNA damage can persist in the long-term to cause future cell dysfunction including malignant transformation.

Exposure to ionising radiation can cause:

• Acute radiation syndrome (ARS) 
• Radiation injuries
• Abortion (if pregnant)
• Birth defects (if pregnant)
• Malignancy
• Aplastic anaemia

 

Prevention of disease

• Use of a Geiger–Müller counter: Each count represents one ionisation event (i.e. one expulsion of an ionising ray or particle). These can be heard as audible clicks.
• Use of protective clothing and shielding. Lead is a useful material for absorbing ionising radiation.
• Exposure to radioactive contaminants could cause ARS, pregnancy abortions and it increases the risk of developing cancer. For this reason:
• Any fabrics, animals, crops or fluids exposed to radioactive materials must be safely identified, gathered, destroyed and contained.
• Any individuals exposed to radioactive materials must be quarantined. Contaminated corpses must be buried in coffins designed to safely contain them.
• Heavily contaminated areas must be evacuated.

 

History of radiation injuries