Detection of radioactivity

Which type of radiation— alpha, beta, or gamma—is most likely to be stopped by the window of a Geiger counter  

Substances that are electronically excited by radiation can also be used to detect and measure radiation. For example, some substances excited by radiation give off light as electrons return to their lower-energy states. These substances are called phosphors. Different substances respond to different particles. Zinc sulfide, for example, responds to alpha particles. An instrument called a scintillation counter is used to detect and measure radiation, based on the tiny flashes of Hght produced when radiation strikes a suitable phosphor. The flashes of light are magnified electronically and counted to measure the amount of radiation. 

Which type of radiation—alpha, beta, or gamma—is likely to fog a film that is sensitive to X rays  

The film strip is white before exposure to radiation 

Which property of the atoms of gas inside a Geiger counter is most relevant to the operation of the device  

Solve The number of disintegrations per atom per second is given by the rate constant, k 

To obtain the total number of disintegrations per second, we calculate the number of atoms in the sample. We multiply this quantity by k, where we express k as the number of disintegrations per atom per second, to obtain the number of disintegrations per second  

We have used only two significant figures in products of these calculations because we do not know the atomic weight of Sr to more than two significant figures without looking it up in a special source. 

A sample to be used for medical imaging is labeled with F, which has a half-life of 110 min. What percentage of the original activity in the sample remains after 300 min  

Radioactivity can also be detected and measured by a Geiger counter. The operation of this device is based on the fact that radiation is able to ionize matter. The ions and electrons produced by the ionizing radiation permit conduction of an electrical current. The basic design of a Geiger counter is shown in FIGURE 21.9. A current pulse between the anode and the metal cylinder occurs whenever entering radiation produces ions. Each pulse is counted in order to estimate the amount of radiation. 

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The use of radioactive tracers was pioneered by Georg von Hevesy, a Hungarian physical chemist, who received the Nobel Prize in 1943 for his work on radioactive indicators (1). Radioisotopes have become indispensable components of most medical and life science research strategies, and in addition the technology is the basis for numerous industries focused on the production and detection of radioactive tracers. Thousands of radioactive tracers have been synthesized and are commercially available. These are used worldwide in tens of thousands of research laboratories. 

The methods for detection and quantitation of radiolabeled tracers are deterrnined by the type of emission, ie, y-, or x-rays, the tracer affords the energy of the emission and the efficiency of the system by which it is measured. Detection of radioactivity can be achieved in all cases using the Geiger counter. However, in the case of the radionucHdes that emit low energy betas such as H, large amounts of isotopes are required for detection and accurate quantitation of a signal. This is in most cases undesirable and impractical. Thus, more sensitive and reproducible methods of detection and quantitation have been developed. 

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. 

Physical methods Physical methods include photometric absorption and fluorescence and phosphorescence inhibition, which is wrongly referred to as fluorescence quenching [1], and the detection of radioactively labelled substances by means of autoradiographic techniques, scintillation procedures or other radiometric methods. These methods are nondestructive (Chapt. 2). 

The scintillators are a special type of fluorescence indicators they are employed for the fluorimetric detection of radioactively labelled substances. They are stimulated by ) -radiation to the emission of electromagnetic radiation and will be discussed in Volume 2. 

Autoradiography The detection of radioactive molecules (eg, DNA, RNA, protein) by visualization of their effects on photographic film. Bacteriophage A virus that infects a bacterium. Blunt-ended DNA Two strands of a DNA duplex having ends that are flush with each other. cDNA A single-stranded DNA molecule that is complementary to an mRNA molecule and is synthesized from it by the action of reverse transcriptase. 

Within 8 days of an intraperitoneal dose of 0.66 mL/kg tritiated mineral oil to rats, 11% of administered radioactivity was excreted in the feces, predominately in the form of mineral oil (95%) (Ebert et al. 1966). Urine during the same time frame after intraperitoneal administration contained about 8% of the administered radioactivity, but in chemical forms other than mineral oil. The detection of radioactivity in the feces after intraperitoneal administration suggests that significant biliary excretion of absorbed mineral oil can occur. 

A locally resolved detection of radioactive samples after chromatographic separation can be performed by imaging techniques which work either indirectly with Eu3+- or P-doped sensor plates and laser activated emission or directly by a micro channel array detector which works like an open Geiger-Muller counter. 

Yakubov, V.P., Antipov, V.B., Losev, DN. and Yuriev, I.A. Passive radar detection of radioactive pollution Application of the Conversion Research Results for International Cooperation SIBCONVERS 99. The Third International Symposium, Volume 2, pp 397-399, May 18-20, 1999. 

To further illustrate the diversity of hydrolytic opening reactions, we turn our attention to an isothiazole ring as found in the antipsychotic agent ziprasidone (11.129). This drug is subject to various reactions of oxidation and reduction, but also undergoes hydrolytic cleavage of the C=N bond of the isothiazole ring. Evidence for this reaction was afforded by detection of radioactive metabolite 11.130, a sulfonamide, in the urine of patients dosed... 

Planchette counting -detection of radioactive tracers [RADIOACTIVE TRACERS] (Vol 20)... 

Nuclear chemistry consists of a four-pronged endeavor made up of (a) studies of the chemical and physical properties of the heaviest elements where detection of radioactive decay is an essential part of the work, (b) studies of nuclear properties such as structure, reactions, and radioactive decay by people trained as chemists, (c) studies of macroscopic phenomena (such as geochronology or astrophysics) where nuclear processes are intimately involved, and (d) the application of measurement techniques based upon nuclear phenomena (such as nuclear medicine, activation analysis or radiotracers) to study scientific problems in a variety of fields. The principal activity or mainstream of nuclear chemistry involves those activities listed under part (b). 

Neon In advertising signs, because it glows red when electricity is passed through it In the helium-neon gas laser (Figure 11.11) In Geiger-Muller tubes, which are used for the detection of radioactivity... 

Calvin and coworkers, in their classical studies of photosynthetic processes, detected labeled triose phosphates and hexose phosphates on bi-dimensional chromatograms, using phenol-water and 1-butanol-pro-pionic acid-water as solvents.120121 In addition to the detection of radioactivity, an ammonium molybdate-nitric acid color reagent was used to detect phosphorus.16 Acidic-solvent developers were used to obviate decomposition of the esters. 

Table 3.1. Some examples of translocatable and apparently non-translocatable elements within fungal mycelia, based on detection of radioactive- or stable-isotope forms of the elements within fungal structures physically separated from the sources of such elements...

The oldest track detectors are photographic plates. They led to the detection of radioactivity by Becquerel in 1896. Photographic emulsions on plates or films indicate the position of radionuclides (autoradiography). The main advantage of autoradiography is the possibility of exact localization of radionuclides emitting a or f rays. 

Radioactive tracer A small amount of radioisotope that replaces a nonradioactive isotope of the element in a compound whose path (e.g., in the body) or whose decomposition products are to be monitored by detection of radioactivity also called a radioactive label. 

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