Wednesday, 14 March 2012

♥ Application of isotopes ♥

 

Isotopes used in Medicine

Many radioisotopes are made in nuclear reactors, some in cyclotrons.  Generally neutron-rich ones and those resulting from nuclear fission need to be made in reactors, neutron-depleted ones are made in cyclotrons.  There are about 40 activation product radioisotopes and five fission product ones made in reactors.
Reactor Radioisotopes (half-life indicated)
Bismuth-213 (46 min): Used for targeted alpha therapy (TAT), especially cancers, as it has a high energy (8.4 MeV).
Chromium-51 (28 d): Used to label red blood cells and quantify gastro-intestinal protein loss.
Cobalt-60 (5.27 yr): Formerly used for external beam radiotherapy, now used more for sterilising
Dysprosium-165 (2 h): Used as an aggregated hydroxide for synovectomy treatment of arthritis.
Erbium-169 (9.4 d): Use for relieving arthritis pain in synovial joints.
Holmium-166 (26 h): Being developed for diagnosis and treatment of liver tumours.
Iodine-125 (60 d): Used in cancer brachytherapy (prostate and brain), also diagnostically to 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 (8 d)*: Widely used in treating thyroid cancer and in imaging the thyroid; also in diagnosis of abnormal liver function, renal (kidney) blood flow and urinary tract obstruction. A strong gamma emitter, but used for beta therapy.
Iridium-192 (74 d): Supplied in wire form for use as an internal radiotherapy source for cancer treatment (used then removed).  Beta emitter.
Iron-59 (46 d): Used in studies of iron metabolism in the spleen.
Lead-212 (10.6 h): Used in TAT for cancers, with decay products Bi-212, Po-212, Tl-208.
Lutetium-177 (6.7 d): Lu-177 is increasingly important as it emits just enough gamma for imaging while the beta radiation does the therapy on small (eg endocrine) tumours. Its half-life is long enough to allow sophisticated preparation for use.  It is usually produced by neutron activation of natural or enriched lutetium-176 targets.
Molybdenum-99 (66 h)*: Used as the 'parent' in a generator to produce technetium-99m.
Palladium-103 (17 d): Used to make brachytherapy permanent implant seeds for early stage prostate cancer.
Phosphorus-32 (14 d): Used in the treatment of polycythemia vera (excess red blood cells). Beta emitter.
Potassium-42 (12 h): Used for the determination of exchangeable potassium in coronary blood flow.
Rhenium-186 (3.8 d): Used for pain relief in bone cancer. Beta emitter with weak gamma for imaging.
Rhenium-188 (17 h): Used to beta irradiate coronary arteries from an angioplasty balloon.
Samarium-153 (47 h): Sm-153 is very effective in relieving the pain of secondary cancers lodged in the bone, sold as Quadramet. Also very effective for prostate and breast cancer. Beta emitter.
Selenium-75 (120 d): Used in the form of seleno-methionine to study the production of digestive enzymes.
Sodium-24 (15 h): For studies of electrolytes within the body.
Strontium-89 (50 d)*: Very effective in reducing the pain of prostate and bone cancer. Beta emitter.
Technetium-99m (6 h): 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 lacrimal glands, heart blood pool, infection and numerous specialised medical studies.  Produced from Mo-99 in a generator.
Xenon-133 (5 d)*: Used for pulmonary (lung) ventilation studies.
Ytterbium-169 (32 d): Used for cerebrospinal fluid studies in the brain.
Ytterbium-177 (1.9 h): Progenitor of Lu-177.
Yttrium-90 (64 h)*: Used for cancer brachytherapy and as silicate colloid for the relieving the pain of arthritis in larger synovial joints. Pure beta emitter and of growing significance in therapy.
Radioisotopes of caesium, gold and ruthenium are also used in brachytherapy.



THE USE OF ISOTOPES IN AGRICULTURE

Radioisotope techniques, to the naive, may represent a miracle in scientific research ­the answer to all investigational difficulties. On the other hand, to the cynic they may be considered as a fad which creates more problems than it solves. The truth seems to be somewhere between the two extremes. The real importance of these techniques are recognized by workers who are well grounded in their fields and who have been involved in the application of these techniques. They are able to recognize the important problems in their own fields, are familiar with the experimental material, and should be able to interpret results of their experiments. Nevertheless, it is only fair to recognize the many difficulties in handling, obtaining and storing radioisotopes. This paper is a brief discussion of some of the fundamentals of this research tool which has developed in recent years and some of its applications in plant research. It may give some ideas as to the possibilities of this technique in attacking some of the problems in agriculture in general and in plant research in particular. A brief review of some chemical and physical concepts familiar to all may be of some interest. All matter is composed of discrete particles, atoms, of the elements, or of larger particles, molecules, made up of combinations of these elementary atoms. Further, that "isotopes" are atoms of an element having the same chemical properties as all other atoms of the same element but differing slightly in weight. In nature a few of these isotopes are radioactive that is they are unstable and spontaneously charge into atoms of another (or the same) element with radiation of energy in the form-gamma rays, or alpha or beta particles. With the advent of controlled nuclear reactions, it has become possible to produce radioactive isotopes which do not occur in nature, by the exposure of selected elements to neutrons. Limited quantities of such "synthetic" elements had been produced earlier by the bombardment of specific target materials by other particles such as protons or alpha particles but the yields were small and the operation expensive. These atoms have some readily recognized characteristics: The radiator given off by, and the time required for disintegration of, the unstable atoms is characteristic of the particular isotope. For example, P32, the important radioisotope of phosphorus, emits only beta particles with a maximum energy of 1.69 Mev and decays at a rate such that onehalf of the initial quantity remains after 14.3 days and each ucceeding 14,3 days interval reduces the amount remaining by 50% (a "halfIife" of 14.3 days) while the isotope of, S35 gives off betas of only 1/10 the energy and has a half life of 87.1 days. C14, particularly useful in the study of biological systems, has a half life of 5568 years; emitting beta particlesof 0.155 Mev. The alpha particles, beta particles, and gamma rays emitted by the disintegrating atoms are "ionizing radiations", that is they have the common ability to produce electrons and positive ions in matter through which they pass. These pairs of oppositely charged ions are formed at the expence of energy loss from incident radiation. Instruments for the detection and measurement of ionization are extremely sensitive, the entrance of a single alpha particle into the "sensitive volume" of a modern counter can be readily detected. Since the radiation arising from the decay of radioactive atoms permits the detection of individual decaying atoms of individual decaying atoms of the element, it is possible to make quantitative measurements of extremely small quantities. For example, with good counting methods one can conveniently measure 2 X 10 - 11 brams of radioactive carbon. This extreme sensitivity of detection combined with the circumstance that the radioactive elements behave in chemical or biological systems as do their inactive counterparts, provide a technique for obtaining data hitherto an attainble and of unusual scope, the "Tracer" Technique". We can now get answers to such questions as: What proportion of a nutrient added to the soil is utilized by the crop? Is a hormone or growth regulator localized or widely translocated? And, more important perhaps, we have a means of making essentially direct observation on the fundamental or basic reactions of biological systems. 84 The "Tracer" method is not new. As early as 1913 Hevecy in Germany used a natural radioisotope of lead to study the solubility dead isotope to study the uptake and distribution of this element by plants. With the invention of the cyclotron the first man-made isotopes became available, but work was markedly limited by availability and cost. Since 1946, however, the development h as been accelerating. Through the U.S. Atomic Energy Commission usable quantities of some 20 isotopes of particular interest in plant research have become available at quite reasonable cost. These include an isotope of Carbon, C14, widely used in research on the fundamental photosynthetic process and as a label or tag in many organic compounds used as herbicides pesticides and metabolic precursors or intermediates; p32, radiophosphorus, a major plant nutrient and label for the new organophosphate insecticides; and usable isotopes of Sulphur Calcium and Iron and the important trape or micro-nutrients Cobalt Copper, Zinc, and Molybdenum. As one might expect, much of the early work, 1947 - 1952, was directed to those problems of rather "practical" nature where the results would be of general interest and would serve, too, to establish the value of the method. The U.S. Department of Agriculture during this period and in collaboration with many State Experimental Stations, carried out extensive studies on the behaviour of phosphatic fertilizers and the effect of soil type, fertilizer, management practices and crop on the uptake of phosphorus by crop plants. Evaluation of a fertilizer material or of an application method has relied on yield response - a time consuming procedure often set at naught by circumstances over which the experimenter had no control. A failure to obtain response to applied nutrient might be due to too little or too much rainfall at a critical stage of growth. Now we have a means of determining quite directly whether or not two sources of phosphorus, say, are equal in availability to a particular, crop on a selected soil or of selecting that method of application which places the fertilizer where it will do the most good since we can now differentiate between the fertilizer phosphorus and that originally present in the soil. Hence we can determine, even though circumstances may conceal or prevent yield response, what proportion of the total plant phosphorus came from that added. As an illustration of the method, suppose we add 100 black marbles identical except for color to a collection of white marbles, which are being mixed and sampled. If, we take samples of 100 marbles and each is found to include 10 black ones, then our sampling procedure is getting 10% of the added marbles. In using radioactive phosphorus we have "tagged" the fertilizer component so it may subsequently be recognized and evaluated although not in quite a black and white fashion as the illustration.Prof. Dr. Aly M. Lasheen Guru besar Plant Physiology Fakultas Pertanian Universitas Indonesia Bogor.

THE USE OF ISOTOPES IN Archaeology

Reconstructing palaeodiet
Bone recovered from archaeological sites can be analysed isotopically for information regarding diet and migration. Tooth enamel and soil surrounding or clinging to the remains may also be used in isotopic analysis. To obtain an accurate picture of palaeodiets, it is important to understand processes of diagenesis that may affect the original isotopic signal. Carbon and nitrogen isotope composition are used to reconstruct diet, and oxygen isotopes are used to determine geographic origin. Strontium and lead isotopes in teeth and bone can sometimes be used to reconstruct migration in human populations and cultural affinity
Carbon isotopes are taken up through the diet of animals during their lifetime, oxygen isotopes being taken up through the water they drink. Examining the 12C/13C isotope ratio, it is possible to determine whether animals ate predominantly C3 or C4 plants. This process ends with the organism's death, from this point on isotopes no longer accumulate in the body, but do undergo degradation. For best result the researcher would need to know the original levels, or an estimation thereof, of isotopes in the organism at the time of its death.
To obtain an accurate picture of palaeodiets, it is important to understand processes of diagenesis that may affect the original isotopic signal. It is also important for the researcher to know the variations of isotopes within individuals, between individuals, and over time.
Sourcing archaeological materials
Isotope analysis has been particularly useful in archaeology as a means of characterization. Characterization of artifacts involves determining the isotopic composition of possible source materials such as metal ore bodies and comparing these data to the isotopic composition of analyzed artifacts. A wide range of archaeological materials such as metals, glass and lead-based pigments have been sourced using isotopic characterization. Particularly in the Bronze Age Mediterranean Lead Isotope Analysis has been a useful tool for determining the sources of metals and an important indicator of trade patterns. Interpretation of Lead Isotope Data is, however, often contentious and faces numerous instrumental and methodological challenges.Problems such as the mixing and re-using of metals form different sources, limited reliable data and contamination of samples can be difficult problems in interpretation.

 Radioisotopes in Industry
 

Neutron Techniques for Analysis
Neutrons can interact with atoms in a sample causing the emission of gamma rays which, when analysed for characteristic energies and intensity, will identify the types and quantities of elements present. The two main techniques are Thermal Neutron Capture (TNC) and Neutron Inelastic Scattering (NIS). TNC occurs immediately after a low-energy neutron is absorbed by a nucleus, NIS takes place instantly when a fast neutron collides with a nucleus.

Most commercial analysers use californium-252 neutron sources together with sodium iodide detectors and are mainly sensitive to TNC reactions. Other use Am-Be-241 sources and bismuth germanate detectors, which register both TNC and NIS. NIS reactions are particularly useful for elements such as C, O, Al & Si which have a low neutron capture cross section. Such equipment is used for a variety on on-line and on-belt analysis in the cement, mineral and coal industries.

A particular application of NIS is where a probe containing a neutron source can be lowered into a bore hole where the radiation is scattered by collisions with surrounding soil. Since hydrogen (the major component of water) is by far the best scattering atom, the number of neutrons returning to a detector in the probe is a function of the density of the water in the soil.

To measure soil density and water content, a portable device with an americium-241-beryllium combination generates gamma rays and neutrons which pass through a sample of soil to a detector. (The neutrons arise from alpha particles interacting with Be-9.) A more sophisticated application of this is in borehole logging.

Gamma & X-ray Techniques in Analysis

Gamma ray transmission or scattering can be used to determine the ash content of coal on line on a conveyor belt. The gamma ray interactions are atomic number dependant, and the ash is higher in atomic number than the coal combustible matter. Also the energy spectrum of gamma rays which have been inelastically scattered from the coal can be measured (Compton Profile Analysis) to indicate the ash content.

X-rays from a radioactive element can induce fluorescent x-rays from other non-radioactive materials. The energies of the fluorescent x-rays emitted can identify the elements present in the material, and their intensity can indicate the quantity of each element present.

This technique is used to determine element concentrations in process streams of mineral concentrators. Probes containing radioisotopes and a detector are immersed directly into slurry streams. Signals from the probe are processed to give the concentration of the elements being monitored, and can give a measure of the slurry density. Elements detected this way include iron, nickel, copper, zinc, tin and lead.

X-ray Diffraction (XRD) is a further technique for on-line analysis but does not use radioisotopes.

Gamma Radiography

Gamma Radiography works in much the same way as x-rays screen luggage at airports. Instead of the bulky machine needed to produce x-rays, all that is needed to produce effective gamma rays is a small pellet of radioactive material in a sealed titanium capsule.

The capsule is placed on one side of the object being screened, and some photographic film is placed on the other side. The gamma rays, like x-rays, pass through the object and create an image on the film. Just as x-rays show a break in a bone, gamma rays show flaws in metal castings or welded joints. The technique allows critical components to be inspected for internal defects without damage.

Gamma sources are normally more portable than x-ray equipment so have a clear advantage in certain applications, such as in remote areas. Also while x-ray sources emit a broad band of radiation, gamma sources emit at most a few discrete wavelengths. Gamma sources may also be much higher energy than all but the most expensive x-ray equipment, and hence have an advantage for much radiography. Where a weld has been made in an oil or gas pipeline, special film is taped over the weld around the outside of the pipe. A machine called a "pipe crawler" carries a shielded radioactive source down the inside of the pipe to the position of the weld. There, the radioactive source is remotely exposed and a radiographic image of the weld is produced on the film. This film is later developed and examined for signs of flaws in the weld.

X-ray sets can be used when electric power is available and the object to be x-rayed can be taken to the x-ray source and radiographed. Radioisotopes have the supreme advantage in that they can be taken to the site when an examination is required - and no power is needed. However, they cannot be simply turned off, and so must be properly shielded both when in use and at other times.

Non-destructive testing is an extension of gamma radiography, used on a variety of products and materials. For instance, ytterbium-169 tests steel up to 15 mm thick and light alloys to 45 mm, while iridium-192 is used on steel 12 to 60 mm thick and light alloys to 190 mm.

Gauging

The radiation that comes from a radioisotope has its intensity reduced by matter between the radioactive source and a detector. Detectors are used to measure this reduction. This principle can be used to gauge the presence or the absence, or even to measure the quantity or density, of material between the source and the detector. The advantage in using this form of gauging or measurement is that there is no contact with the material being gauged.

Many process industries utilise fixed gauges to monitor and control the flow of materials in pipes, distillation columns, etc, usually with gamma rays.

The height of the coal in a hopper can be determined by placing high energy gamma sources at various heights along one side with focusing collimators directing beams across the load. Detectors placed opposite the sources register the breaking of the beam and hence the level of coal in the hopper. Such level gauges are among the most common industrial uses of radioisotopes.

Some machines which manufacture plastic film use radioisotope gauging with beta particles to measure the thickness of the plastic film. The film runs at high speed between a radioactive source and a detector. The detector signal strength is used to control the plastic film thickness.

In paper manufacturing, beta gauges are used to monitor the thickness of the paper at speeds of up to 400 m/s.

When the intensity of radiation from a radioisotope is being reduced by matter in the beam, some radiation is scattered back towards the radiation source. The amount of 'backscattered' radiation is related to the amount of material in the beam, and this can be used to measure characteristics of the material. This principle is used to measure different types of coating thicknesses.

Gamma Sterilisation

Gamma irradiation is widely used for sterilising medical products, for other products such as wool, and for food. Cobalt-60 is the main isotope used, since it is an energetic gamma emitter. It is produced in nuclear reactors, sometimes as a by-product of power generation.

Large-scale irradiation facilities for gamma sterilisation are used for disposable medical supplies such as syringes, gloves, clothing and instruments, many of which would be damaged by heat sterilisation. Such facilities also process bulk products such as raw wool for export from Australia, archival documents and even wood, to kill parasites. Currently ANSTO in Australia sterilises up to 25 million Queensland fruit fly pupae per week for NSW Agriculture by gamma irradiation. See also  The Peaceful Atom.

Smaller gamma irradiators are used for treating blood for transfusions and for other medical applications.

Food preservation is an increasingly important application, and has been used since the 1960s. In 1997 the irradiation of red meat was approved in USA. Some 41 countries have approved irradiation of more than 220 different foods, to extend shelf life and to reduce the risk of food-borne diseases.

Scientific Uses

Radioisotopes are used as tracers in many research areas. Most physical, chemical and biological systems treat radioactive and non-radioactive forms of an element in exactly the same way, so a system can be investigated with the assurance that the method used for investigation does not itself affect the system. An extensive range of organic chemicals can be produced with a particular atom or atoms in their structure replaced with an appropriate radioactive equivalent.

Using tracing techniques, research is conducted with various radioisotopes which occur broadly in the environment, to examine the impact of human activities. The age of water obtained from underground bores can be estimated from the level of naturally occurring radioisotopes in the water. This information can indicate if groundwater is being used faster than the rate of replenishment. Trace levels of radioactive fallout from nuclear weapons testing in the 1950s and 60s is now being used to measure soil movement and degradation. This is assuming greater importance in environmental studies of the impact of agriculture.

Tracing/Mixing Uses

Even very small quantities of radioactive material can be detected easily. This property can be used to trace the progress of some radioactive material through a complex path, or through events which greatly dilute the original material. In all these tracing investigations, the half-life of the tracer radioisotope is chosen to be just long enough to obtain the information required. No long-term residual radioactivity remains after the process.

Sewage from ocean outfalls can be traced in order to study its dispersion. Small leaks can be detected in complex systems such as power station heat exchangers. Flow rates of liquids and gasses in pipelines can be measured accurately, as can the flow rates of large rivers.

Mixing efficiency of industrial blenders can be measured and the internal flow of materials in a blast furnace examined. The extent of termite infestation in a structure can be found by feeding the insects radioactive wood substitute, then measuring the extent of the radioactivity spread by the insects. This measurement can be made without damaging any structure as the radiation is easily detected through building materials.

Wastes

Industries utilise radioactive sources for a wide range of applications. When the radioactive sources used by industry no longer emit enough penetrating radiation for them to be of use, they are treated as radioactive waste. Sources used in industry are generally short-lived and any waste generated can be disposed of in near-surface facilities.

Some industrial activities involve the handling of raw materials such as rocks, soils and minerals that contain naturally occurring radioactive materials. These materials are known by the acronym "NORM". Industrial activity can sometimes concentrate these materials and therefore enhance their natural radioactivity (hence the further acronym: TENORM - technically-enhanced NORM). This may result in:

A risk of radiation exposure to workers or the public
Unacceptable radioactive contamination of the environment
The need to comply with regulatory waste disposal requirements
The main industries that result in NORM contamination are:

Oil and gas operations
Oil and gas exploration and production generates large volumes of water containing dissolved minerals. These minerals may be deposited as scale in piping and oil field equipment or left as residues in evaporation lagoons. Occasionally the radiation dose from equipment contaminated with mineral deposits may present a hazard. More significantly contaminated equipment and the scale removed from it may be classified as radioactive waste. Oil and gas operations are the main sources of radioactive releases to waters north of Europe for instance.

Coal burning
Most coal contains uranium and thorium, as well as other radionuclides. The total radiation levels are generally about the same as in other rocks of the earth's crust. Most emerge from a power station in the light flyash. Some 99% of flyash is typically retained in a modern power station (90% in some older ones) and this is buried in an ash dam. Around 280 million tonnes of coal ash is produced globally each year.

Phosphate Fertilisers
The processing of phosphate rock to produce phosphate fertilizers (one end product of the phosphate industry) results in enhanced levels of uranium, thorium and potassium.

Process and Waste Water Treatment
Radionuclides are leached into water when it comes into contact with uranium and thorium bearing rocks and sediments. Water treatment often uses filters to remove impurities. Hence, radioactive wastes from filter sludges, ion-exchange resins, granulated activated carbon and water from filter backwash are part of NORM.

Scrap metal industry
Scrap metal from various process industries can also contain scales with enhanced levels of natural radionuclides. The exact nature and concentration of these radionuclides is dependent on the process from which the scrap originated.

Metal smelting sludges
Metal smelting slags, especially from tin smelting, may contain enhanced levels of uranium and thorium series radionuclides.

Research
Following the operation of a particle accelerator, the facility will generally be decommissioned. As radioactive materials will be present in the facility, these must be treated as radioactive wastes and handled accordingly. Following a 40 year operation of one of the new generation of particle accelerators, the volume of decommissioning waste and activity is expected to be within the same order of magnitude as for a 1 GW(e) nuclear power plant which has operated over 40 years. However, it should be noted that the concentration of radioactivity is more evenly distributed in the case of such an accelerator facility.

Radiation sources utilised within universities and research institutions also require appropriate management and disposal. Many sources are of low activity and/or short half-life. However some exceptions include high-level long-lived sources such as Radium-226 and Americium-241 used in biological and or agricultural research. These require long-term management and disposal as Intermediate-Level Wastes (ILW).

Industrial Radioisotopes

Naturally-occurring radioisotopes:  

Carbon-14: Used to measure the age of water (up to 50,000 years)

Chlorine-36: Used to measure sources of chloride and the age of water (up to 2 million years)

Lead-210: Used to date layers of sand and soil up to 80 years

Tritium (H-3): Used to measure 'young' groundwater (up to 30 years)

Artificially-produced radioisotopes:

Americium-241:
Used in backscatter gauges, smoke detectors, fill height detectors and in measuring ash content of coal.

Caesium-137:
Used for radiotracer technique for identification of sources of soil erosion and deposition, in density and fill height level switches.

Chromium 57:
Used to label sand to study coastal erosion.

Cobalt-60, Lanthanum-140, Scandium-46, Silver-110m, Gold-198:
Used together in blast furnaces to determine resident times and to quantify yields to measure the furnace performance.

Cobalt-60:
Used for gamma sterilisation, industrial radiography, density and fill height switches.

Gold-198 & Technetium-99m:
Used to study sewage and liquid waste movements, as well as tracing factory waste causing ocean pollution, and to trace sand movement in river beds and ocean floors.

Gold-198:
Used to label sand to study coastal erosion.

Hydrogen-3 (Tritiated Water): Used as a tracer to study sewage and liquid wastes

Iridium-192
Used in gamma radiography to locate flaws in metal components.

Krypton-85:
Used for industrial gauging.

Manganese-54:
Used to predict the behaviour of heavy metal components in effluents from mining waste water.

Nickel-63
Used in light sensors in cameras and plasma display, also electronic discharge prevention and in electron capture detectors for thickness gauges.

Selenium-75:
Used in gamma radiography and non-destructive testing.

Strontium-90:
Used for industrial gauging.

Thallium-204:
Used for industrial gauging.

Ytterbium-169:
Used in gamma radiography and non-destructive testing.

Zinc-65:
Used to predict the behaviour of heavy metal components in effluents from mining waste water.
 

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