Curie, definition

There is no discontinuity in volume, among other variables, at the Curie point, but there is a change in temperature coefficient of V, as evidenced by a change in slope. To understand why this is called a second-order transition, we begin by recalling the definitions of some basic physical properties of matter ... 

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The basic unit of radioactivity is the curie, Ci. One curie is the amount of radioactive material that emits particles at a rate of 3.7 X 1010 disintegrations per second (dps), or 2.2 X 1012 min-1 (dpm). Amounts that large are seldom used in experimentation, so subdivisions are convenient. The milli-curie (mCi, 2.2 X 109 min-1) and microcurie (yu,Ci, 2.2 X 106 min-1) are standard units for radioactive measurements (see Table 6.2). The radioactivity unit of the meter-kilogram-seconds (MKS) system is the becquerel (Bq). A becquerel, named in honor of Antoine Becquerel, who studied uranium radiation, represents one disintegration per second. The two systems of measurement are related by the definition 1 curie = 3.70 X 1010 becquerels. Since the becquerel is such a small unit, radioactive units are sometimes reported in MBq (mega, 106) or TBq (tera, 1012). Both unit systems are in common use today, and radioisotopes received through commercial sources are labeled in curies and bequerels. 

It is important to note that in the various studies reviewed in the preparation of this document, dose levels have been presented by those authors in several ways. In order to facilitate comparisons among studies, these levels have generally been converted to an equivalent dose in microcuries (p Ci) and kilo-Becquerels (kBq). The historical definition of one curie is the disintegration rate exhibited by one gram of radium. There are 0.027 pCi per kBq. In this document, comparisons are usually made between total administered amounts of radioactivity, in pCi/kg and kBq/kg, instead of using a daily dosage level. 

The disintegration rate is an instantaneous rate measured under conditions of essential constancy of the concentration (i.e., the population) of 40K atoms. The form of the rate equation is that used in Chapter 20, with the numerical value of the rate taken from the definition of the curie. 

At a temperature below the Curie point TC1 it is plain from Eq. (3.7) that for concentrations nearer than a certain critical concentration the alloys will bo below their Curie points and will be in partly ordered phases, while for x less than this critical concentration they will be above their Curie points and will be in the disordered state. This is indicated in Fig. XVIII-7, where wo show G as a function of w for different values of x, at a temperature of 0.8 Tc. The critical concentration for this temperature is 0.277, as can be found at once from Eq. (3.7) it is noted in Fig. XVIII-7 that the curves for x = 0.1 and 0.2 definitely have their minima at w = 0, indicating complete disorder, while that for x = 0.3 is very flat at the center, and those for 0.4 and 0.5 definitely have minima for w 0, indicating a partly ordered state. Finally, in Fig. XVIII-8 we show G as a function of x, for different values of w, at this same tern-... 

In order to understand the effects of radiation on any material, let us define how one measures radiation. Radiation is measured in several units. The SI unit for radioactivity is the becquerel (Bq), which is defined as one disintegration (d) per second (s) (Bq = d/s). However, the most common unit is the curie (Ci) and its definition is based on the number of radium-226 isotopes present in 1 gram of the element that disintegrate in one second. One Ci is thus exactly equal to 3.70 x 1010 disintegrations per second... 

Radioactivity is measured in decays per second, the SI unit of which is the Becquerel (Bq) which is defined as one decay per second. The Curie (Ci), which originally corresponded to the number of decays per second in 1 g of radium, is still used and is now related to the Becquerel by the definition ... 

In 1896 there came the discovery of radioactivity by Henri Becquerel and the discovery of radium by Pierre and Marie Curie. Soon thereafter it was recognized that radioactive changes involve the spontaneous conversion of atoms of one element into those of another. It then became necessary to change the definition of element this was done by saying that one element could not be converted into another by artificial means. 

From the definition of curie, calculate Avogadro s number. Given that the molar mass of Ra-226 is 226.03 g/mol and that it decays with a half life of... 

Finally, since by definition M/H — Xmag one obtains the final sought-after temperature dependence of Xmag namely, the Curie-Weiss law ... 

To perpetuate the name of Curie, the quantity of emanation in equilibrium with one gn.m of radium was termed a curie. This is an inconveniently large amount and the milli-micro curie is frequently used as a practical unit. It is the quantity of emanation in equilibrium with one millionth of a milligram of radium. Since one-fiftieth of this can be detected with a sensitive electroscope, this method of detecting the presence of radio-elements is extraordinarily sensitive — more so even than the spectroscope. The above definition of the curie has now been superseded. In July 1950 the Joint Commission on Standards, Units and Constants of Radioactivity defined the curie as the quantity of any radioactive nuclide in which the number of disintegrations per second is 3-700 X io10. 

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