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isotopes. 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.
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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 iodineisotopes 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.
