Radiation And Half Life Flashcards
Radiation and matter
There are two ways that we need to be aware of around radiation and matter:
• Ionisation occurs when electrons are removed from atoms or molecules to produce positive ions. All forms of radioactive decay produce radiation that can cause ionisation – hence the term ionising radiation.
• Excitation occurs when radiation transfers energy to atoms or molecules so they increase their energy level but the energy is retained in the atom. If enough energy is transferred to the electron, it will be removed from the atom and ionisation will have occurred. Gamma radiation can cause excitation
Ionising and non ionising radiation
• Non-ionizing radiation does not have enough energy to remove electrons from atoms and molecules. Non-ionising radiation is longer wavelength/lower frequency lower energy but can cause heat damage to tissues.
• Ionising radiation has sufficient energy to produce ions in matter at the molecular level so ionising radiations can cause dermatitis, burns, cell damage, cataracts, damage to DNA. While ionising radiation is short wavelength/high frequency higher energy. The change occurs in the UV part of the spectrum.
• It is the dosage that determines the amount of damage - we always use the minimum possible dose for the intended effect
Ionisation and cellular mutation
- Energy transferred by ionising radiation removes electrons from atoms to form ions.
- Ions are reactive and can cause mutations to the DNA in cells and damage to cells
- Damaged DNA can lead to cancer if not corrected by the body’s natural repair mechanisms. Damage to cells and organelles can be repaired but errors may still occur
Radiation – a cellular level
• As many cellular processes rely on molecules and if these are charged or altered they may not work the same way as before – think about the analogy with a denatured protein –it no longer functions properly so the cell undergoes lysis.
• If the radiation dose is very high many cells will undergo lysis and body functions may be severely impacted
Safety Precautions for Radiation
• The Ionising Radiations Regulations 2017 set out the minimum legal duties and the Approved Code of Practice (ACOP) gives practical advice on how to comply with those Regulations. The regulation are meant to protect employees and members of the public from:
• radiation arising from work
• radioactive substances
• any other forms of ionising radiation
• Broad measures for safety:
• Keep exposure to ionising radiations as low as reasonably practicable and not exceed specified dose limits.
• Restriction of exposure should be achieved first by means of engineering control and design features.
• Where this is not reasonably practicable employers should introduce safe systems of work
• Rely on the provision of personal protective equipment as a last resort
The three types of radiation
Alpha particle:
• Alpha particle α- is a helium nucleus, two protons and two neutrons. It has a large mass, compared to other ionising radiations, and a strong positive charge. It has a charge of +2e because it has lost two electrons.
Beta particle:
• Beta particle β- is a fast moving electron. It has a very small mass and a negative charge. It has a charge of -1e because it is an electron.
Gamma ray:
• Gamma ray γ- is a high-energy electromagnetic wave. Gamma rays are caused by changes to energy levels within the nucleus. They are part of the electromagnetic spectrum and so travel at the speed of light. They have no mass and no charge
Uses in health
• Alpha radiation is unable to penetrate skin so can’t be used for imaging and is highly ionising so can cause damage to the body if ingested or gains entry
• Beta radiation has limited utility as is can damage body tissues and does not penetrate as far as gamma although some treatments use beta decay to destroy cells
• Gamma radiation is more widely used as it is less ionising so causes less damage to the body but can be detected by gamma cameras for imaging and destroying cells during radiotherapy
Half life and count rate
• Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.
• Count-rate is the number of decays recorded each second by a detector, such as the Geiger-Muller tube.
• Radioactive decay is a random process as not all the nuclei will decay at the same time so although we can plot of graph the general trend of the graph will always be the same as we know a certain number will decay
within a certain time
Half life and health
• Any radioactive substance that is administrated into the human body such as a tracer or implanted in the body (brachytherapy) will make the person radioactive for a period of time. The body will also excrete the substance which reduced the radiation as well as natural decay.
• Iodine-131 (131I) has a half life of around 8 days and technetium-99m (99mTc) has a half life of 6 hours.
Summary of the three types
• Alpha is the most ionising type of radiation as it has highest charge of +2e. This also means it is able to do more damage to cells than the other types of radiation. However, Alpha is the least penetrating type of radiation so has less utility in health.
• Beta is a moderately ionising type of radiation due to it having a charge of +1e. This means it is able to do some slight damage to cells (less than alpha but more than gamma) However, Beta is a moderately penetrating type of radiation with limited application in health
• Gamma is the least ionising type of radiation because it is an electromagnetic wave with no charge. It can still cause damage to cells, but not as much as alpha or beta radiation. This is why it is used for cancer
radiotherapy. Gamma is the most penetrating type of radiation and is widely used in health
