Radioactivity half-life

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 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. 

Effective Half-time - Biological half-time x Radioactive half-life... 

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 ... 

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. 

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... 

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. 

I (radioactive half-life of 8 days and a high-energy emitter), used mainly in the therapy of hyperthyroidism and thyroid cancer. 

I (radioactive half-life 13 hours) has replaced 131I for diagnostic purposes however, for in vivo imaging meta-stable technetium-99 (99mTc) is often preferred, because of its lower radiation dose, availability, and cost. 

I (radioactive half-life of 60 days and a low energy emitter), previously used in the treatment of hyperthyroidism, but now replaced by 131I because of disappointing therapeutic results (1,2). 

The short-lived decay products of 222Rn decay to 210Pb, which has a radioactive half-life of 22 a, and decays to 210Bi and 210Po as follows. 

In general, the radioactive half-life increases down the chain of fission products, but some long-lived fission products, for example 90Sr, have short-lived daughters. 

The distribution of 132I between the sampling components was different. Its radioactive half-life is short, and the activity on the sampler derived from its parent isotope 132Te (Fig. 3.1). The distribution of 132Te (Table 3.1) shows that it was almost entirely particulate. Hence the 30% of 132I found on the molecular sieve, and 5% on the charcoal pack must have derived from 132I which desorbed from the particles, either in the atmosphere or after capture on the filter. 

Tritium (3H) has a radioactive half-life of 12.3 a and decays to 3He by emitting a soft beta particle, maximum energy 18 keV. Measurements of tritium are given variously in terms of ... 

In the UK, Booker et al. (1967) used a spinning disk to make monodisperse polystyrene particles. Polystyrene was dissolved in xylene, at a concentration of 0.2%, and chromium acetyl acetonate, labelled with 51Cr, was added. The spinning disk was operated at 3 x 104 rpm to produce 40-/,polystyrene spheres. Few etal. (1970) adapted this method to produce particles of polystyrene labelled with "mTc. This isotope has only very slight beta emission, so the dose to the lung is low, and though the radioactive half-life is only 6 h, this is adequate for estimation of the ratio P/(TB + P) and for analysis of the kinetics of the mucociliary clearance. 

To calculate the dose to the lung from inhalation of insoluble particulate activity of long radioactive half-life, it is necessary to estimate the clearance from the P region. ICRP (1979) assumed a clearance half-life of 500 d. Booker et al. (1967) found half-lives in the range 150-300 d in subjects who had inhaled polystyrene particles labelled with 51Cr, but the radioactive half-life of this isotope (27 d) restricted the duration of the measurements to 100 d. In more recent... 

The isotope 203Pb is produced by bombardment of thallium with protons in a cyclotron. The radioactive half-life is 52 h and decay is by electron capture. The associated 279-keV gamma ray enables the activity in the lung and other organs of volunteer subjects to be detected by external gamma ray spectrometers (Chamberlain etal., 1975). 

In Chap. 1, we introduced the book with a quote from Albert Einstein (Schilpp 1949), which read in part that classical thermodynamics... is the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown. An important qualification to this statement is the phrase within the framework of the applicability of its basic concepts. The laws of thermodynamics are based on laboratory-scale experiments. To assume that such laws are applicable to the Universe is a big assumption. However, we have no evidence yet that contradicts this assumption on the scales of problems relevant to life. Moreover, there remain vast cosmological questions with no answers and definitely no understanding of implications even if we knew the answers. For instance, does the proton have a very long but finite radioactive half-life Does the neutrino have a very small but finite mass Is the Universe opened or closed with respect to expansion and gravitational contraction Also, the Universe may not be isolated with respect to matter/energy or it could be isolated and cyclical. 

FIGURE 7.4 Of the 16 chemistry topics examined (1-16) on the final exam, overall the POGIL students had more correct responses to the same topics than their L-I counterparts. Some topics did not appear on all the POGIL exams. Asterisks indicate topics that were asked every semester and compared to the L-I group. The topics included a solution problem (1), Lewis structures (2), chiral center identification (3), salt dissociation (4), neutralization (5), acid-base equilibrium (6), radioactive half-life (7), isomerism (8), ionic compounds (9), biological condensation/hydrolysis (10), intermolecular forces (11), functional group identification (12), salt formation (13), biomolecule identification (14), LeChatelier s principle (15), and physical/chemical property (16). 

Isotope dilution is applicable to any element for which an enriched isotope is available. Figure 1.1 of Chapter 1 indicates which elements are amenable to isotope dilution in most cases the natural element has at least two stable isotopes, but this is not necessarily the case. For example, 232Th, though radioactive (half-life of 1.4 X 1010 years), is present in the earth s crust 230Th (half-life of 7.5 X 104 years), an isotope present in nature at such low levels as to be negligible for most applications, is used as a spike for isotope dilution purposes in the author s laboratory. Another common example is the use of 233U (a synthetic isotope) as a spike for uranium analyses. The only elements not amenable to the technique are those, like cobalt and arsenic, that have only one stable isotope and all of whose radioactive isotopes have half-lives so short as to preclude their use. 

The clinical use of chelate-tagged albumin in place of 125I-albumin has the fundamental advantage of not having the protein radiolabeled until just before it is used. This permits a choice among radionuclides so that the half-life, radiations, and energies can be suited to each particular clinical procedure, and it removes the radioactive half-life as a limitation on the shelf-life of the modified protein. 

Tritium is hydrogen of mass number 3, having two neutrons and a proton in its nucleus. It is radioactive (half-life 12.4 years) in common with many isotopes having a large neutron-to-proton ratio, tritium decays with emission of an electron (called a beta ray). Such a decay can be represented by the nuclear equation (see also Chap. 27) ... 

Radioactive half-life The time during which the decay rate of a radioactive nuclide decreases by a factor of two. 

---