Curie, defined

ACTIVITY (Radioactivity). The activity of a quantity of radioactive nuclide is defined by the 1CRU as AN/At, where N is the number of nuclear transformations that occur in this quantity in time At. The symbol A preceding the letters N and t denotes that these letters represent quantities that can be deduced only from multiple measurements that involve averaging procedures. The special unit of activity is the curie, defined as exactly 3.7 x 10l° transformations per second. See Radioactivity. 

Radioactivity is measured by observing the high-energy particles produced directly or indirectly as a result of the disintegration process. A convenient unit of radioactivity is the curie, defined by... 

Radioactive decay of nuclei is a first-order reaction decay rate (activity A) is therefore dependent on the concentration (content) of the radionuclide and is the product of this concentration (more precisely, the number of atoms of radionuclide N) and the decay constant X (in s" ) A =-(dN/dt) = X.N. The basic unit of activity, according to the System International (SI system) is the Bq (becquerel). One Bq (in s ) is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. Previously, the frequently used unit was the Ci (curie) defined as 3.7 x 10 decays per second. For conversion, the following relationship can be used 1 Ci = 3.7 x lO Bq. Number of radionuclide atoms transformed in time t is f T=NQ.e", where Nq is the initial number of atoms of the radionuclide at the time t=0. During conversion, the number of radioactive atoms of the radioactive nuclide is continuously decreasing. Combining both equations we get the relation expressing the dependence of activity on time A = -(dN/dt) The... 

The activity is a measure of the quantity of radioactive material. For these radioactive materials it is customary to describe the activity as the number of disintegrations (transformations) per unit time. The unit of activity is the curie (Ci), which was originally related to the activity of one gram of radium, but is now defined as that quantity of radioactive material in which there are ... 

The radioligand should also have a high specific activity so that very small quantities of bound ligand can be accurately measured. The specific activity, simply defined as the amount of radioactivity, expressed in becquerels (Bq) or curies (Ci) per mole of ligand, is dependent on the half-life of the isotope used and on the number of radioactive atoms incorporated into the ligand molecule. A radioisotope with a short half-life decays rapidly so that many disintegrations occur in unit time,... 

Lind (1961) defines radiation chemistry as the science of the chemical effects brought about by the absorption of ionizing radiation in matter. It can be said that in 1895, along with X-rays, Roentgen also discovered the chemical action of ionizing radiation. He drew attention to the similarity of the chemical effects induced by visible light and X-rays on the silver salt of the photographic plate. This was quickly followed by the discovery of radioactivity of uranium by Becquerel in 1896. In 1898, the Curies discovered two more radioactive elements—polonium and radium. 

About 1910, M. Curie suggested that ions were responsible for the chemical effects of radioactive radiations. Soon thereafter, mainly due to the pioneering work of Lind on gases, the notation M/N was introduced for a quantitative measure of the radiation effect, where N is the number of ion pairs formed and M is the number of molecules transformed—either created or destroyed. This notation, referred to as the ion pair yield, was most conveniently employed in gases where N is a measurable quantity. However, for some time the same usage was extended to condensed systems assuming that ionization did not depend on the phase. This, however, is not necessarily correct. The notation G was introduced by Burton (1947) and others to denote the number of species produced or destroyed per 100 eV absorption of ionizing radiation. In this sense, it is defined... 

The System Internationale (SI) unit for radioactivity is becquerel (Bq), which is defined as one disintegration per second. The SI units and the conversion factors between curie and SI units are listed in Table 15.2. 

The curie unit (Ci) is based on the activity of 1 g of pure radium-226, which undergoes 3.7 X 1010 transformations per second. It is therefore defined as the quantity of a radioactive isotope which gives 3.7 X 1010 disintegrations per second. The SI unit of activity is the becquerel (Bq), which is equal to one nuclear transformation per second. Hence ... 

One unit for A is dpm (number of disintegrations per minute). Another unit is the curie (Ci), which is defined as 3.7 x 10 ° disintegrations per second. 

Lind [2] has defined radiation chemistry as the science of the chemical effects brought about by the absorption of ionizing radiation in matter. It should be distinguished from radiation damage which refers to structural transformation induced by irradiation, particularly in the solid state. The distinction is not always maintained, perhaps unconsciously, and sometimes both effects may be present simultaneously. Following a suggestion of M. Curie around 1910, that ions were responsible for the chemical effects of radioactive radiations, the symbol MjN was introduced to quantify the radiation chemical effect, where M is the number of molecules transformed (created or destroyed) and N is the number of ion pairs formed. Later, Burton [3] and others advocated the notation G for the number of species produced or destroyed per 100 eV (= 1.602 x 10 J) absorption of ionizing radiation. It was purposely defined as a purely experimental quantity independent of implied mechanism or assumed theory. 

At temperatures much higher than D, the susceptibility becomes much more isotropic and the average may approximate well to the Curie law, or more generally to the relationship of equation (57) with 6 small. However, anisotropy usually remains, and the susceptibilities in individual directions are of the form of equation (57) but 0 is of the order of, and linearly related to, D. For the 4A2g ground term, in axial symmetry where E is zero, we have the parallel direction defined as Z and obtain 6>y = —4D/5k and 8 = 2D 15k. 

An older unit of radioactivity that still finds some use is the curie (Ci). It is defined as... 

The units of radioactivity are normally disintegrations per second. An activity of 3.7 X 1010 disintegrations per sec has been termed a curie . However, this is a very high activity and millicurie or microcurie are more frequently used. Specific activity is defined as the number of disintegrations per second per gram of material. 

Analytical pyrolysis is defined as the characterization of a material or a chemical process by the instrumental analysis of its pyrolysis products (Ericsson and Lattimer, 1989). The most important analytical pyrolysis methods widely applied to environmental samples are Curie-point (flash) pyrolysis combined with electron impact (El) ionization gas chromatography/mass spectrometry (Cp Py-GC/MS) and pyrolysis-field ionization mass spectrometry (Py-FIMS). In contrast to the fragmenting El ionization, soft ionization methods, such as field ionization (FI) and field desorption (FD) each in combination with MS, result in the formation of molecule ions either without, or with only very low, fragmentation (Lehmann and Schulten, 1976 Schulten, 1987 Schulten and Leinweber, 1996 Schulten et al., 1998). The molecule ions are potentially similar to the original sample, which makes these methods particularly suitable to the investigation of complex environmental samples of unknown composition. 

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