5. Uses of Radioactive-isotopes emitting alpha, beta or gamma ionising radiation
Doc Brown's Chemistry KS4 science GCSE Physics Revision Notes
IDEAS: These revision notes on how to use ionising radiation in a variety of industrial, medical and environmental situations should help with GCSE/IGCSE physics courses and A/AS level physics courses. How do we use radioisotopes for? How can we use alpha particle radiation, beta particle radiation and gamma radiation rays? How do we relate the use of ionising radiation with its physical properties e.g. it penetration into material or the half-life of the radioactive source. Gamma and beta emitting radioisotopes are extensively used in medical diagnostic and treatment procedures. Radioisotopes are used in a variety of ways in industry to improve productivity and, in some cases, to gain information that cannot be obtained in any other way. Radioisotopes are used in radiography, gauging applications and mineral analysis. Short-lived radioisotopes are used to trace flow and fluid mixing systems. Gamma ray sterilisation procedures are used in preparing medical supplies packaged food preservation. How does PET scanning work? The world of medical physics uses various diagnostic techniques to investigate blood flow and metabolic functions.
But to fully understand this page you specifically need to know
(i) Relative penetrating power of the ionising radiations: gamma > beta- > alpha
(ii) The half-life of a radioisotope is the time taken for half of the radioactive atoms of a specific isotope to decay
and (iii) an understanding of nuclear equations is assumed, refer to section 7.
An introduction to the use of radioisotopes and nuclear radiation in medicine
The medical uses of nuclear radiations and radioisotopes are expanding all the time as technology improves and hopefully become cheaper so more patients can be diagnosed and treated. However, as with the 'humble' X-ray, there are serious health and safety issues that must be addressed. You have to weigh the possible positive outcomes versus the possible dangers!
Ionisation caused by radiation can kill cells completely or damage it so it can't divide, whichever happens, the effect is damage to tissue. Although harmful in itself, if the radiation damages and alters the genetic material in the cell (DNA) it can cause mutations. Some mutations can cause the cell to divide and multiply out of control producing cancer tumours. Hence the need in any ionising radiation treatment to limit the patient's exposure to it.
Like it or not, any extra exposure to nuclear radiation or X-rays increases the risk of tissue damage and cancer. In any radiation treatment or diagnostic procedure the patient should be given the lowest possible effective dose and experience the shortest possible exposure time. Lead shielding can be used to protect areas of the body not being treated and wherever possible to radiation focussed onto the part of the body under examination or treatment.
What goes for patients must also apply to medical personnel carrying out the treatment or examinations using potentially harmful nuclear radiation procedures. Examples of protective measures include ...
Nuclear radiation sources can be used internally and externally to treat cancer tumours.
Decisions: Generally speaking internal treatments have no side-effects other than maybe discomfort from the implant procedure, but external treatments like radiotherapy can have both short-term and long-term effects which may be immediate or show up months or years later.
Developing new treatments
Some examples of radioactive isotopes used in medicine
Note: (i) (t½ = half-life) and (ii) some of these examples are discussed in more detail in the next sections 5a-5d.
Technetium-99m (t½ = 6 hours): 99Tc, a beta emitter used in to image the skeleton and heart muscle in particular, but also for brain, thyroid, lungs (perfusion and ventilation), liver, spleen, kidney (structure and filtration rate), gall bladder, bone marrow, salivary and lachrymal glands, heart blood pool, infection and numerous specialised medical studies.
Cobalt-60 (10.5 mins/5.29 years): 60Co, beta/gamma emitter once used for external beam radiotherapy.
Iodine-123 (t½ = 13 hours): 12353I Increasingly used for diagnosis of thyroid function, it is a gamma emitter without the beta radiation of I-131.
Iodine-125 (t½ = 60 days): 125I, a gamma emitter used to diagnostically evaluate the filtration rate of kidneys and to diagnose deep vein thrombosis in the leg. It is also widely used in radioimmuno- assays to show the presence of hormones in tiny quantities.
Iodine-131 (t½ = 8 days): 131I a beta and gamma emitter, is widely used in treating thyroid cancer and in imaging the thyroid gland also in diagnosis of abnormal liver function, renal (kidney) blood flow and urinary tract obstruction.
Iridium-192 (t½ = 74 days): 192Ir, a gamma emitter can be supplied in wire form for use as an internal radiotherapy source for cancer treatment and after use it can removed.
Potassium-42 (t½ = 12 hours): 42K, a beta minus and gamma emitter used for the determination of exchangeable potassium in coronary blood flow.
Sodium-24 (t½ = 15 hours): 24Na, is a beta- and gamma emitter is used to study of electrolytes in the body.
Xenon-133 (t½ = 5 days): 13354Xe, a beta- and gamma emitting gas used for pulmonary (lung) ventilation studies.
Krypton-81m (t½ = 13 seconds) 36, from Rubidium-81 (t½ = 4.6 hours), 81Kr gas provides images of pulmonary ventilation in the lung, e.g. in asthmatic patients, and provides early diagnosis of lung diseases and function.
Footnote: Although the above examples are all medical there are lots of industrial uses of using nuclear radiation from radioactive isotopes and many are described in sections 5a to 5d below.
The uses of radioactive isotopes usually depend on their penetrating power and the value of their half-life
Both specific industrial and medical applications of nuclear radiation sources are described.
An introduction to the use of radioisotopes and radiation in medicine (medical physics)
Alpha emitting radioisotopes are usually too dangerous and not sufficiently penetrating to be of use in medicine. However despite the dangers, beta minus (electron emission), beta plus (positron emission) and gamma emitting radioisotopes are widely used in diagnostic medicine and treatments for dangerous medical conditions such as cancer.
5d Uses of positron radiation sources (beta plus decay nuclides) - PET scan use
Introduction to PET scans: Positron emission tomography (PET) scans are used in medicine to produce highly detailed three-dimensional images of the inside of the human body. PET images can clearly show the part of the body being investigated, including any abnormal areas, and can highlight how well certain functions of the body are working. PET scans are often combined with computerised tomography (CT) scans to produce even more detailed 3D images, known as a PET-CT scan. PET scans may also occasionally be combined with a magnetic resonance imaging (MRI) scan, known as a PET-MRI scan.
Why are PET scans are used? An important advantage of a PET scan over other diagnostic techniques is that it can show how well certain parts of your body are working, rather that showing what a particular part of the body looks like. PET scans are particularly helpful for investigating confirmed cases of cancer, to determine how far the cancer has spread and how well it's responding to treatment i.e. keep track of the behaviour of a tumour. Sometimes PET scans of blood vessel function are used to help plan operations, such as a coronary artery bypass graft of the heart or brain surgery for epilepsy. They can also help diagnose some conditions that affect the normal workings of the brain, such as dementia.
How do PET scans work? PET scanners work by detecting the gamma radiation given off by a substance called a radiotracer as it collects in different parts of your body. In most PET scans a radiotracer called fluorodeoxyglucose (FDG) is used, which is similar to the naturally occurring sugar, so your body treats it in a similar way in its energy releasing metabolic chemistry. By analysing the areas where the radiotracer does and doesn't build up (varying concentration), it's possible to work out how well certain body functions are working and identify any abnormalities. For example, a concentration of FDG in the body's tissues can help identify cancerous cells because cancer cells use glucose at a much faster rate than normal cells because of an increase in rate of cell division.
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