What Are Gamma Rays?
Gamma rays are streams of electromagnetic waves. They are given off from elements such as radium, when they undergo a process known as radioactive decay. In 1899 the British physicist Ernest Rutherford began a study of radioactivity. He found three types of radiation which he called alpha, beta and gamma rays.
Alpha rays were stopped by a thin sheet of paper; beta rays could get through several millimeters of aluminum, and gamma rays could pierce quite thick pieces of lead. Alpha rays travel at up to 12,000 miles a second, beta rays from 80,000 to 180,000 miles a second, and gamma rays at 186,000 miles a second, the speed of light.
Gamma rays have proved very helpful in medicine and industry. These rays are also given off by radioactive isotopes obtained as by-products in production processes. They can produce radio graphs of forgings and the seams of boilers and other pressure vessels, where freedom from flaws is vital.
Gamma-rays are the most energetic form of light and are produced by the hottest regions of the universe. They are also produced by such violent events as supernova explosions or the destruction of atoms, and by less dramatic events, such as the decay of radioactive material in space. Things like supernova explosions (the way massive stars die), neutron stars and pulsars, and black holes are all sources of celestial gamma-rays.
Gamma-rays travel to us across vast distances of the universe, only to be absorbed by the Earth’s atmosphere. Different wavelengths of light penetrate the Earth’s atmosphere to different depths. Instruments aboard high-altitude balloons and satellites like the Compton Observatory provide our only view of the gamma-ray sky.
Gamma-rays have the smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum. These waves are generated by radioactive atoms and in nuclear explosions. Gamma-rays can kill living cells, a fact which medicine uses to its advantage, using gamma-rays to kill cancerous cells.
Gamma rays are high energy electromagnetic waves which are only stopped by thick lead. This means they can easily pass through medical equipment, such as syringes. As gamma rays pass through the packaging they will inactivate viruses and kill bacteria. As long as the equipment remains in a sealed plastic pack it will remain sterile.
Radioactive tracers are used to investigate a patient’s body without the need for surgery. Gamma emitters and sometimes beta emitters are used. This is because gamma rays and beta particles can pass through skin, whereas alpha particles cannot.
A small amount of radioactive material is put into the patient’s body. The radiographer puts a detector around the body to detect any gamma rays or beta particles that pass out of the patient’s body.
Nuclear radiation can damage cells. To avoid possible harm to the patient, it is important that medical tracers do not stay active in the body for long periods.
The source used is either a beta or gamma emitter. Radioisotopes with short half-lives are chosen to make sure that the tracer does not stay radioactive in the body for long periods. The radioisotope may be chemically attached to different substances, depending on the test being carried out.
The radioactive tracer is put into the body by one of the following ways:
- By an injection
- By ingestion (eating a solid with the tracer in it or drinking a liquid with the tracer in it)
The tracer is given enough time to move around the body before a radiographer positions a radiation detector outside the body. This produces a picture showing where the tracer has accumulated.
Gamma rays damage cells whether they are normal or cancerous, so gamma rays must be focused on the tumour. One way of doing this is to use a wide beam of gamma rays, but to rotate the beam around the patient, keeping the tumour at the centre. This concentrates the gamma rays on the cells that need to be killed.