Half-life and radioactivity

The alkali metals form a homogeneous group of extremely reactive elements which illustrate well the similarities and trends to be expected from the periodic classification, as discussed in Chapter 2. Their physical and chemical properties are readily interpreted in terms of their simple electronic configuration, ns, and for this reason they have been extensively studied by the full range of experimental and theoretical techniques. Compounds of sodium and potassium have been known from ancient times and both elements are essential for animal life. They are also major items of trade, commerce and chemical industry. Lithium was first recognized as a separate element at the beginning of the nineteenth eentury but did not assume major industrial importance until about 40 y ago. Rubidium and caesium are of considerable academic interest but so far have few industrial applications. Francium, the elusive element 87, has only fleeting existence in nature due to its very short radioactive half-life, and this delayed its discovery until 1939. 

The SI unit of activity is the becquerel (Bq) 1 Bq = 1 transformation/second. Since activity is proportional to the number of atoms of the radioactive material, the quantity of any radioactive material is usually expressed in curies, regardless of its purity or concentration. The transformation of radioactive nuclei is a random process, and the rate of transformation is directly proportional to the number of radioactive atoms present. For any pure radioactive substance, the rate of decay is usually described by its radiological half-life, T r i.e., the time it takes for a specified source material to decay to half its initial activity. The activity of a radionuclide at time t may be calculated by A = A° e ° rad where A is the activity in dps, A ° is the activity at time zero, t is the time at which measured, and T" is the radiological half-life of the radionuclide. It is apparent that activity exponentially decays with time. The time when the activity of a sample of radioactivity becomes one-half its original value is the radioactive half-life and is expressed in any suitable unit of time. 

Rutherford was awarded a scholarship to be a research student at the University of Cambridge and began research under J.J. Thomson. He soon abandoned research on his radio wave detector to work on the power of X-rays to confer electric charge on gases but soon turned to researching the problem of the rays emitted by thonum. Rutherford found three kinds of radiation, which he named alpha, beta, and gamma. In collaboration with Frederick Soddy, he was able to isolate a substance, thorium X, and identify the phenomenon of radioactive half-life and formulated an explanation of radioactivity. Rutherford was awarded the 1908 Nobel Prize for chemistry for his work in radioactivity. 

Figure 1 Schematic illustration of the production and fate of Th in seawater. Radioactive decay of dissolved produces Th that initially exists as a dissolved species. Dissolved Th may either undergo radioactive decay to Ra, or it may be adsorbed to particles. Radioactive decay is represented by a decay constant, A (A = ln(2)/radioactive half-life)), and uptake by particles (scavenging) is represented by a first-order rate constant, k. Th is initially sorbed by small slowly settling particles (supersript s ), which form the vast majority of partiele mass in the ocean. Th sorbed to small particles may undergo radioactive decay to Ra it may desorb (return to solution, represented by the first-order rate eonstant -i) or it may sink from the water colunm, where the loss of particulate Th is represented by the first-order rate constant 2-Similar processes influence " Th, which is produced by radioactive decay of and which...

Discovery of Radioactivity Nuclear Notation Radioactive Decay Detecting Radioactivity Half Life and Radioisotope Dating ChemLab The Radioactive Decay of Pennium ... 

The amounts of a radionuclide in organs, or the burden, were calculated based on a constant exposure rate, maintained for a period sufficiently long so that an equilibrium would be established between the intake of the material and the effective elimination rate. The effective elimination rate, or effective half-life, is a combination of the radioactive half-life and the biological half-life based on the rate at which the material would be eliminated from the body. The relationship is given by the following equation ... 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

A D—T fusion reactor is expected to have a tritium inventory of a few kilograms. Tritium is a relatively short-Hved (12.36 year half-life) and benign (beta emitter) radioactive material, and represents a radiological ha2ard many orders of magnitude less than does the fuel inventory in a fission reactor. Clearly, however, fusion reactors must be designed to preclude the accidental release of tritium or any other volatile radioactive material. There is no need to have fissile materials present in a fusion reactor, and relatively simple inspection techniques should suffice to prevent any clandestine breeding of fissile materials, eg, for potential weapons diversion. 

Radioactive waste is characterized by volume and activity, defined as the number of disintegrations per second, known as becquerels. Each radionucHde has a unique half-life,, and corresponding decay constant, A = 0.693/tj 2 For a component radionucHde consisting of JS1 atoms, the activity, M, is defined as... 

Radioactive isotopes are characterized by a number of parameters in addition to those attributable to chemistry. These are radioactive half-life, mode of decay, and type and quantity of radioactive emissions. The half-life, defined as the time required for one-half of a given quantity of radioactivity to decay, can range from milliseconds to biUions of years. Except for the most extreme conditions under very unusual circumstances, half-life is independent of temperature, pressure, and chemical environment. 

The diversity of radionucHde half-life and chemical nature of commonly used radiopharmaceuticals demands a variety of formulation matrices, packaging containers, and storage conditions. The containers, ingredients, and processes used in these products must meet the stringent requirements for parenteral pharmaceuticals, as well as provide safe conditions for storage, handling, and disposal of the radioactive material. 

Radioactivity decays exponentially according to the half-life and time. All effluents can undergo dry deposition by sorption onto the ground surface. 

Decau.se its longer half-life and lower energy make it more convenient to handle, is replacing "" P as the radioactive tracer of choice in. sequencing by the Sanger method. "" S-ct-labeled deoxynucleotide analogs provide die. source for incorporating radioactivity into DNA. 

Radon-222, a decay product of the naturally occuring radioactive element uranium-238, emanates from soil and masonry materials and is released from coal-fired power plants. Even though Rn-222 is an inert gas, its decay products are chemically active. Rn-222 has a a half-life of 3.825 days and undergoes four succesive alpha and/or beta decays to Po-218 (RaA), Pb-214 (RaB), Bi-214 (RaC), and Po-214 (RaC ). These four decay products have short half-lifes and thus decay to 22.3 year Pb-210 (RaD). The radioactive decays products of Rn-222 have a tendency to attach to ambient aerosol particles. The size of the resulting radioactive particle depends on the available aerosol. The attachment of these radionuclides to small, respirable particles is an important mechanism for the retention of activity in air and the transport to people. 

The decay of Rn-222 and Rn-220 in the atmosphere produces low vapor pressure progeny that coagulate with other nuclei or condense on existing aerosols. These progeny include 3.0-min (radioactive half-life) Po-218, 26.8-min Pb-214, and 10.6-h Pb-212. A... 

A quantitative and fairly easy method to obtain particle reworking rates in deep sea sediments became possible after the elegant work of Nozaki et al., [68] based on 210Pb distribution in them. The radioactive half-life of 210Pb is too short (22.6 yrs) to produce measurable depth profiles in deep sea sediments based on sedimentation alone since its activity would be limited to the top 1 mm layer. In such a case its depth profile predominantly records the effects of particle reworking and its distribution can be approximated as ... 

But many people talk emotionally of radioactivity because radioactive materials are so poisonous , and one of the clinching arguments given to explain why radioactivity is undesirable is that radioactive materials have long half-lives . What is a half-life And why is this facet of their behaviour important And, for that matter, is it true that radioactive materials are poisonous ... 

The only difference between a chemical and a radioactive half-life is that the former reflects the rate of a chemical reaction and the latter reflects the rate of radioactive (i.e. nuclear) decay. Some values of radioactive half-lives are given in the Table 8.2 to demonstrate the huge range of values t j2 can take. The difference between chemical and radioactive toxicity is mentioned in the Aside box on p. 382. A chemical half-life is the time required for half the material to have been consumed chemically, and a radioactive half-life is the time required for half of a radioactive substance to disappear by nuclear disintegration. 

If one knows the half-life and amount remaining radioactive, you can then use equation (2) to calculate the rate constant, k, and then use equation (1) to solve for the time. This is the basis of carbon-14 dating. Scientists use carbon-14 dating to determine the age of objects that were once alive. 

E = 137keV). The accompanying emission of 7-radiation can be used for scintigraphic imaging but also makes patient isolation necessary. The different half-lifes and /3 -energies allow individual therapeutic demands such as the pharmacokinetics of the tracer molecule, the linear energy transfer of the nuclides or the biodistribution and clearance of the radiolabeled drug to be met. The principles of the application of radioactive materials for therapy are summarized in an excellent review. ... 

Radon-222 also undergoes radioactive decay and has a radioactive half-life of 3.8 days. Radon-220 and -219 have half-lives measured in seconds and are not nearly as abundant as Radon-222. Thus the discussion of radon health effects here centers on Radon-222. Radon-222 decays into radon daughters or progeny, which are radioactive elements. Two of these (polonium-218 and polonium-214) emit alpha particles (high-energy, high-mass particles, each consisting of two protons and... 

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