Radioactivity It is the property of an element that causes it to emit radiation Discovered by Becquerel (1896) Radiation comes from the nucleus of the atom There are three types of radiation : alpha particles (α), beta particles (β) and gamma rays (γ) γ Alpha particles (α) : - these are positively charged particles and are, in fact, the nucleus of a helium atom, ie., 2 protons, 2 neutrons and a charge of +2. - they have low penetrating power and can be stopped by a piece of paper or thin aluminium foil
- they would not penetrate the outer layer of the skin and are harmless to the body - ingestion of substances emitting α particles could cause local damage - it results from the decay of heavy elements, for eg., uranium Beta particles (β) β : - these are negatively charged high speed electrons - they are produced in the nucleus by breakdown of a neutron into p + and e - - have slight penetrating properties - they would pass through paper but would be stopped by heavy clothing - ingestion of substances emitting β particles would damage cells and organs
Gamma rays (γ) : - they have no charge, are not particles and have no mass - they are a form of electromagnetic radiation - they originate from unstable atoms releasing energy to gain stability - they are very penetrating and will pass through the - they are very penetrating and will pass through the body causing cellular damage
Detection and Measurement of Radiation Detecting and measuring radiation is very important in medical work, especially in regard to protection of personnel A Geiger counter or a Scintillation counter is used to measure the amount of radiation
Protection Against Radiation Materials such as lead protect the body against radiation Increasing the distance between the source of radiation and the body helps decrease the effect of the radiation Limit the length of time of exposure Personnel in regular contact with radiation should use film badges to monitor the amount of radiation they are exposed to
Effect of Radiation on Body Cells It affects molecules within a cell. It causes ionisation within cells and alters the chemical processes going on within the cell. Ionisation alters the DNA which may cause some cells to die leading to genetic mutation that may affect future generations. Rapidly dividing cells are very susceptible to radiation therefore pregnant women and growing children should avoid unnecessary irradiation. At the same time, radiation is an effective treatment for some cancers as cancer cells are also rapidly dividing cells. Excessive exposure to radiation can produce cataracts, sterility and leukemia.
Exposure to large amounts of radiation can cause radiation sickness Symptoms are nausea, vomiting, diarrhea, general body weakness, a drop in red and white blood cell counts, loss of hair and skin damage Extremely high doses may lead to death.
Radioisotopes in Medicine For a radioisotope (radioactive isotope of an element) to be used it must meet the following criteria : - the radioactive compound must be contained in a compound that tends to accumulate in the area of the body under examination - it must emit γ radiation so as to pass through the body and be picked up by the detector - should have a short half life and be easily eliminated from the body (What is half life?) Examples : -technetium 99m is used for scans of the brain, thyroid, liver and bone marrow for the detection of tumors and cancerous tissue
- iodine 131 and iodine 123 are used in the diagnosis of thyroid conditions - cobalt 60 and cobalt 52 are used to treat many types of tumors. 60 Co is a good source of β- particles and γ-rays - Boron Neutron Capture Therapy (BNCT) : the stable 10 B isotope is carried into tumor cells by drugs, antibiotics or natural product derivatives and concentrate in tumor cells. 10 B is then irradiated with low-energy neutrons, which have little effect on cells and tissues but cause the B to emit α-particles which destroy the nearby cancer cells.
X-Rays X-rays are penetrating radiation similar to γ-rays but of lower energy. The amount of radiation and extent of penetration can be set on the x-ray machine. So, soft radiation can be used to treat skin conditions and more penetrating rays can be used for cancer. They do not pass through bones and teeth easily and can therefore be used to detect abnormalities.
Radioopaque compounds absorb x-rays allowing body parts to become visible, for eg., barium sulphate to detect abnormalities in the stomach and esophagus. Ultrasonography Uses high frequency sound waves instead of x- Uses high frequency sound waves instead of x- rays. The ultrasound waves are sent into the body and the reflected waves are picked up and displayed on an oscilloscope.