Radioactive emissions

Radiometric detection technology offers high sensitivity and specificity for many appUcations in scientific research. The radioactive emission of the labeled compound is easily detected and does not suffer from interference from endogenous radioactivity in the sample. Because of this unique property, labeled compounds can be used as tracers to study the localization, movement, or transformation of molecules in complex experimental systems. 

A related mechanism of degradation involves the direct interaction of the radioactive emission with other tracer molecules in the preparation. This phenomenon is likely to occur in high specific activity compounds stored at high radiochemical concentrations in the absence of free-radical scavengers. 

The nonquantitative detection of radioactive emission often is required for special experimental conditions. Autoradiography, which is the exposure of photographic film to radioactive emissions, is a commonly used technique for locating radiotracers on thin-layer chromatographs, electrophoresis gels, tissue mounted on sHdes, whole-body animal sHces, and specialized membranes (13). After exposure to the radiolabeled emitters, dark or black spots or bands appear as the film develops. This technique is especially useful for tritium detection but is also widely used for P, P, and 1. 

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. 

Radiation Dosimetry. Radioactive materials cause damage to tissue by the deposition of energy via their radioactive emissions. Thus, when they are internally deposited, all emissions are important. When external, only those emissions that are capable of penetrating the outer layer of skin pose an exposure threat. The biological effects of radiation exposure and dose are generally credited to the formation of free radicals in tissue as a result of the ionization produced (17). 

Another difference between the wireline logs and the MWD logs is the logging speed. With a wireline, the sonde is pulled out at a speed of 500 to 2,000 ft/min (150 to 600 m/min). The time constant used to optimize the effect of the statistical variations of the radioactivity emission, varied from 2 to 6 s. Consequently, the log values are somewhat distorted and inaccurate. 

The origin of the rays was initially a mystery, because the existence of the atomic nucleus was unknown at the time. However, in 1898, Ernest Rutherford took the first step to discover their origin when he identified three different types of radioactivity by observing the effect of electric fields on radioactive emissions (Fig. 17.4). Rutherford called the three types a (alpha), (3 (beta), and y (gamma) radiation. 

Shortly after Rutherford named those two emissions, a third one was discovered. It was named gamma, the third letter in the Greek alphabet. All of these names can be bewildering, but radioactive emissions actually come in only two fundamental forms electromagnetic radiation and particles. 

Alpha and beta radiation, on the other hand, are particles that possess mass and charge. If we set the weight of a hydrogen atom as 1 and the charge on its ion as +1, then the table below gives the corresponding properties of the radioactive emissions known in the early twentieth century. 

In addition to these two common radioactive emissions, some isotopes emit neutrons when they decay. This usually happens with highly unstable isotopes. The degree of instability is measured by the isotope s half-life, which is the time it takes for... 

Isotope (Curie Symbol) Mode of Decay Half-life Major Radioactive Emissions Energies (MeV)... 

A significant source of error in nuclear orientation thermometers is due to the possible absorption of the radioactive emission in the cryostat, with a temperature increase as a consequence, low-intensity source must be used, with long counting periods to get a good statistics. 

The common type of radioactive emission that does not consist of matter is the gamma ray. 

Hara argued, To radium we owe much, for it paved the way for patient investigations which absolutely revolutionized the world s ideas as regards the working of subtle forces, hitherto postulated but by a few brave pioneers in Nature s workshop and unacceptable to the rest (551). In a move that by now should be familiar, Hara praised J. J. Thomson s and Larmor s research into radium for suggesting that radioactive emissions (which they saw as electrons)... 

Radical trapping studies, 14 277 Radicidation, 8 655 Radioactive decay, 21 287—288 particles associated with, 21 291 Radioactive decay properties of uranium isotopes, 25 393 Radioactive emission, interaction with tracer molecules, 21 276 Radioactive iodine, protection from,... 

Hehum is used for low-temperature research (—272.2°C or 34°F). It has become important as a coolant for superconducting electrical systems that, when cooled, oiler httle resistance to the electrons passing through a conductor (wire or magnet). When the electrons are stripped from the hehum atom, a positive He ion results. The positive hehum ions (nuclei) occur in both natural and man-made radioactive emissions and are referred to as alpha particles. Hehum ions (alpha particles) are used in high-energy physics to study the nature of matter. 

Np through Lr are all prepared artificially by bombardment with neutrons and/or light element ions (He-4, B-10, B-11, C-12,0-16,0-18, Ca-48, Fe-56). Some routes are presented in Table 18.1. The elements have been separated from the targets and other product species by redox reactions, ion exchange, and solvent extraction. In a typical separation, a sulfonic acid ion exchange resin is placed in a column, the tripositive ions of Am through Lr are poured into the column where they are taken up, then the column is eluted with a solution of ammonium a-hydroxybutyrate. As elution proceeds, the An+ ions come off in this order Lr-Md-Fm-Es-Cf-Bk-Cm-Am. They are detected by the distinctive energies of their radioactive emissions. 

Like the monoamine hypothesis of depression, such a simple hypothesis was appeaUng but, perhaps predictably, a Uttle too simple to be true. Further research using a technique known as positron emission tomography (PET) showed the relationship between dopamine and schizophrenia is more complex. PET detects radioactive emissions of certain isotopes these isotopes are incorporated into a molecule and injected into a patient. The machine measures the radioactivity with detectors positioned aroimd the body. PET lets researchers study the distribution of certain molecules in Uving tissue since, imUke autoradiography, the tissue is not sliced and treated chemically. The amoimt of radioactivity must be small, however, to avoid harming the human subjects. 

Figure 11. Old Physics Building at McGill University, Montreal. Here Ernest Rutherford and Frederick Soddy discovered the chemical transformations that accompany radioactive emissions. (Photo Copyright J. L. and V. R. Marshall.)...

In the case of radium, as well as any radionuclide, it is important to note that, in addition to the usual routes of exposure that must be considered (inhalation, oral, dermal, and occasionally parenteral) for toxic chemicals, there is also external and internal exposure to emissions of alpha and beta particles and gamma rays and it is these radioactive emissions which are considered to be responsible for most of the biologically deleterious effects observed in exposed persons. Further information about radionuclides is presented in Appendix B. 

It is important to note that effects observed after the ingestion of radium may be attributed not only to radium itself, but to the presence of any or all of its daughter products produced in vivo and their radioactive emissions. 

While parenteral exposure is not a route posing a significant environmental threat to human health from the isotopes of radium, data acquired in studies using this route are presented here because thousands of persons did acquire radium via this route, and most of the toxicity and metabolic studies with experimental animals have used this route. It is again important to note that effects observed after parenteral administration of radium may be attributed not only to radium itself, but to the presence of any or all of its daughter products and their radioactive emissions in vivo. 

Some important radioactive emissions and changes in the nucleus of an atom. 

The changing of radioactive elements into other elements through radioactive emissions is called either radioactive decay or radioactive disintegration. By using radioactive rays, it is possible to detect whether a substance is radioactive or not. There are several methods to detect the types of radiations and their intensities. The most commonly used device to check the intensity of radioactivity is the Geiger-Mtiller counter. 

A picture can be obtained on film or sensitive plaque with the help of radioactive emissions. This is known in medicine as roentgen film. In a roentgen film X-rays are used which are produced by electronic devices. 

Some historical instances of radioactive emissions will now be reviewed. 

The first five chapters of this book are about radioactive nuclides of potential concern to public health. In the sixth chapter, some applications to the study of boundary layer transport are discussed. In the last chapter examples are given of using radioactive aerosols to study deposition of particles in the lung and the subsequent uptake into the body. The widespread dissemination of lead aerosol from motor exhausts, its inhalation by the public, and fallout onto crops, present problems of analysis not dissimilar to those of radioactive emissions. Experiments in which volunteers inhaled motor exhaust labelled with 2°3pb provided one piece of evidence to fit into the picture. 

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