M4 – Explain how excessive exposure to radiation can cause harm.

The amount of radiation given to patients in diagnosis is dependent on how close vital organs and tissues are to the malignant tumour, there are two terms commonly used by scientists when dealing with radiation doses, absorbed dose, the amount of energy received by a mass of tissue, which is measured in kilograms (Kg), It has the unit J/Kg and is called the gray (Gy). Effective dose, if the ionising radiation types are compared using the same amounts of energy, alpha particles cause much biological damage, 20 times more damage than X-rays. In medicine radiation affects different tissues and organs in different ways and so each tissue or organ has a number which is used as a quality factor, the absorbed dose is multiplied by this number to give the figure for effective dose, also measured in J/kg b called Sievert (Sv).

Major effects of ionising radiation on the body

Injury to living tissue results from the transfer of energy to atoms and molecules in the cellular structure. Ionizing radiation causes atoms and molecules to become ionized or excited. These excitations and ionizations can:

• Produce free radicals.
• Break chemical bonds.
• Produce new chemical bonds and cross-linkage between macromolecules.
• Damage molecules that regulate vital cell processes (e.g. DNA, RNA, proteins).

High doses delivered to the whole body of healthy adults within short periods of time can produce effects such as blood component changes, fatigue, diarrhea, nausea and death. These effects will develop within hours, days or weeks, depending on the size of the dose. The larger the dose, the sooner a given effect will occur.

• Delayed effects: effects such as cataract formation and cancer induction that may appear months or years after a radiation exposure, such as :

Cataracts

 Cataracts are induced when a dose exceeding approximately 200-300 rem is  delivered to the lens of the eye.  Radiation-induced cataracts may take many months to years to appear.

Cancer

• Studies of people exposed to high doses of radiation have shown that there is a risk of cancer induction associated with high doses.
• The specific types of cancers associated with radiation exposure include leukaemia, multiple myeloma, breast cancer, lung cancer, and skin cancer.
• Radiation-induced cancers may take 10 - 15 years or more to appear.
• There maybe a risk of cancer at low doses as well.

The need for legislative requirements and dose limits

Substitution

The isotope selection process is another effective method to reduce potential radiation exposures. The areas to be considered are: the radioactive half-life, the energy and type of emissions, the quantity of isotope, and the chemical form of the isotope. The half-life of the isotope selected can affect waste management. Generally, shorter lived isotopes are preferred over longer lived.

The energy and type of emissions from the perspective isotopes must be considered. Selection of low energy beta or gamma emitters is preferred because radiation hazards are proportionally related to the energy. Beta emitters are preferred over gamma emitters because betas require less shielding. The radiation hazard is also proportionally related to the quantity (radioactivity) of the isotope to be used. The use of small activities is preferred. The chemical form selected for the experiment can also affect the radiation hazards associated with the work. It is preferred to avoid the use of compounds that are or produce volatile or gaseous compounds.