Presentation on theme: "Isotopes. APPLICATIONS of nuclear processes Military Power Radiation Many important economic and social benefits are derived from the use of isotopes."— Presentation transcript:
APPLICATIONS of nuclear processes Military Power Radiation Many important economic and social benefits are derived from the use of isotopes and radiation: – to observe and measure physical, chemical, and biological processes
Stable isotopes …do not undergo radioactive decay. Most of the isotopes found in nature are in this category and appear in the element as a mixture. Separation – mainly - according to isotopic mass, that have been used are electromagnetic, as in the large-scale mass spectrograph; and thermal- mechanical, as in the distillation or gaseous diffusion processes. [see other lecture]
Main advantages of stable isotopes Adv. are the absence of radiation effects in the specimens under study, the availability of an isotope of a chemical for which a radioactive species would not be suitable, and freedom from necessity for speed in making measurements, because the isotope does not decay in time.
Disadv of stable isotope Their disadvantage is the difficulty of detection.
Radioactive isotopes, or radioisotopes They are available with a great variety of – – half-lives, – types of radiation, and – energy. They come from three main sources, – charged particle reactions in an accelerator, – neutron bombardment in a reactor, and – separated fission products.
Tracer tech. The tracer method consists of – the introduction of a small amount of an isotope & – the observation of its progress as time goes on.
e.g., The best way to apply fertilizer containing phosphorus to a plant may be found – by including minute amounts of the radioisotope phosphorus-32 [half-life 14.28 days], emitting 1.7 MeV beta particles. Measurements of the radiation at various times and locations in the plant by a detector or photographic film provides accurate information on the rate of phosphorus intake and deposition.
e.g., Circulation of blood in the human body can be traced by the injection of a harmless solution of radioactive sodium, Na-24 [14.96-h half-life] For purposes of medical diagnosis, it is desirable to administer enough radioactive material to provide the needed data, – but not so much that the patient is harmed.
Flow rate – thr. Radioisotopes The flow rate of many materials can be found by watching the passage of admixed radioisotopes. The concept is the same for flows as diverse as blood in the body, oil in a pipeline, or pollution discharged into a river. A small amount of radioactive material is injected at a point, it is carried along by the stream, and its passage at a distance d away at time t is noted. In the simplest situation, the average fluid speed is d/t.
It is clear that the half-life of the tracer must be long enough for detectable amounts to be present at the point of observation; but not so long that the fluid remains contaminated by radioactive material.
Radiopharmaceutical Radionuclides prepared for medical diagnosis and therapy are called radiopharmaceuticals. They include a great variety of chemical species and isotopes with half lives - ranging from minutes to weeks, depending on the application. They are generally beta- or gamma-ray emitters. Prominent examples are – technetium-99m (6.01 h), – iodine-131 (8.04 d), and – phosphorus-32 (14.28 d).
A radionuclide generator is a long-lived isotope that decays into a short-lived nuclide used for diagnosis. The advantage over the use of the short-lived isotope directly is that speed or reliability of shipment is not a factor. As needed, the daughter isotope is extracted from the parent isotope.
The earliest example of such a generator was radium- 226 (1599 y), decaying into radon-222 (3.82 d). The most widely used generator is molybdenum-99 (65.9 h) decaying to technetium-99m (6.01 h). The Tc-99m is said to be “milked” from the Mo-99 “cow.” Tc-99m is the most widely used radioisotope in nuclear medicine because of its favorable radiations and half- life. The parent isotope Mo-99 comes from Canada and other countries.
Several iodine isotopes are used. One produced by a cyclotron is I-123 (13.2 h). The accompanying isotopes I-124 (4.18 d) and I-126 (13.0 d) are undesirable impurities because of their excessively energetic gamma rays. Two fission products are I-125 (59.4 d) and I- 131 (8.04 d).
Specialists in radiopharmaceuticals are called radiopharmacists, who are concerned with – the purity, – suitability, – toxicity, and – radiative characteristics of the radioactive drugs they prepare.