Curie: radiation unit

Radiation Units. Units in use for activity of a radionuclide, ie, the curie, the roentgen (exposure to x and gamma rays), the rad (absorbed dose), and the rem (dose equivalent), should eventually be replaced by the becquerel (Bq), coulomb per kilogram (C/kg), gray (Gy), and the sievert (Sv), respectively. 

The defining event of a radioactive nuclide is the transformation of its nucleus into the nucleus of another species, that is, radioactive decay. The number of nuclear transformations occurring per unit of time is called activity . Sometimes radioactivity is used instead of activity . The traditional unit of activity has been the Curie (Ci), which is equal to 3.7 X 10 ° nuclear transformations per second. The conversion of radiation units to the international system (Sysfme International d Unit or SI) has now taken place in the United States. The more fundamental unit of activity, the Becquerel (Bq), equal to 1 nuclear transformation per second, has replaced the Curie. Both units of activity are modified by prefixes such as kilo-, milli-, and micro- to achieve standard multiples of the fundamental unit. A listing of the most commonly used prefixes is given in Table 1. 

These coefficients must be multiplied by the density of air and tissue, respectively. Figure 15.7.2-1 depicts a radiation fallout field. Let C be the curie activity/m. The radiation into a unit area receptor at z = 1 m above the ground. The area is emitting C r dr d0 gammas/s. These are attenuated in the air as exp(-p, R) and geometrically as l/(4 7t R). The radiation received by the receptor is given by equation 15.7.2-1 which becomes 15.7.2-2 by a change of... 

Curie (unit) Radiation corresponding to the radioactive decay of3.700 X 1010 atoms/s, 518 Curie, Irene, 517 Curie, Marie, 248,517 Curie, Pierre, 517 Current flow, 496... 

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. 

CURIE (Ci). The unit of activity in the field, of radiation dosimetry. One curie equals 3.7, < 1010 disintegrations per second. (The activity of 1 gram of 226Ra is slightly less than 1 curie.)... 

The curie is a huge unit of radioactivity and is approximately equal to the activity of one gram of radium. The inventories of radioactivity in a nuclear reactor upon shutdown are typically 109 Ci, whereas radiation sources used in tracer experiments have activities of p.Ci and the environmental levels of radioactivity are nCi or pCi. 

The most often used unit to quantify the activity of any radioactive material is the curie (Ci). For most level detection applications, source strengths of 100 millicuries (mCi) or less are satisfactory. A 1 Ci source will produce a dose of 1 roentgen (r) at a receiver placed 1 m (3 ft) away from the source for 1 h. Radiation is attenuated when it penetrates liquids or solids, and the rate of attenuation is a function of the density of the material. The higher the density, the more attenuation the shielding material will provide. Figure 3.122 shows how various thicknesses of different materials will attenuate (reduction factor—NB) the intensity of radiation and result in different degrees of attenuation. 

Natural radionuclides contaminate air, food, and water. The annual per capita intake of natural radionuclides has been estimated to range from 2 Becquerels (Bq) for 232Th to about 130 Bq for 4 K (Sinclair 1988). The Bq is the International System of Units (SI) unit of radioactivity 1 Bq = 1 radioactive disintegration per second. The previously used unit of radioactivity is the Curie (Ci) 1 Ci = 3.7 x 1010 disintegrations per second, and 1 Bq = 27 x 10-12 Ci. The quantity of radiation or energy absorbed is expressed in Sievert (Sv), which is the SI unit of dose equivalent. The absorbed dose (in Gy) is multiplied by a quality factor for the particular type of radiation. Rem is the previously used unit for dose equivalent 100 rem = 1 Sv. 

The Bq is a minute measure of radioactivity and any sizeable amount of radioactive material will contain very many atoms and thus emit considerable amounts (TBq or GBq) of radiation. Another popular unit of decay is the curie, a non-Sl unit (historically calculated from the disintegrations of radium) which is equivalent to 37 x 10 Bq. Importantly, radioactivity decays exponentially, where a population of atoms in a sample will have a characteristic half-life (fi/2). The half-life is the key parameter when considering radioactivity and associated safety of radioisotopes, where fi/2 represents the time taken for the radioactivity to fall to a half the recorded level, as illustrated in Figure 10.4. Half-lives and associated properties of common radioactive isotopes are given in Table 10.2. 

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... 

The curie (Ci) is a commonly used unit for measuring nuclear radioactivity I curie of radiation is equal to 3.7 X 10 ° decay events per second (the number of decay events from 1 g of radium in 1 s). 

Amounts of radioactivity are designated in terms of rads, roentgens, curies, disintegrations per unit time (minute), or counts per unit time (minute). The relationships between these various unit designations are summarized in Table 3-3. The first two units are rarely used except for measuring human exposure to ionizing radiation. It is worthy of emphasis... 

The curie, abbreviated Ci, is a standard unit of radioactive decay. It was originally defined as the rate at which 1 g of radium decays. Because of the relatively long half-life of Ra, the isotope served as a convenient standard. The curie is now defined as the quantity of any radioactive substance in which the decay rate is 3.700 X 10 disintegrations per second (2.22 X 10 DPM). Because the efficiency of most radiation detection devices is less than 100%, a given number of curies almost always yields a lower than theoretical count rate. Hence, there is the distinction between DPM and CPM. For example, a sample containing 1 /rCi of radioactive material has a decay rate of 2.22 x lO DPM. If only 30% of the disintegrations are detected, the observed count rate is 6.66 X 10 CPM. 

Unless otherwise stated, exposure levels are presented per kg of body weight. In Appendix D, standard and SI units of radiation activity (curies, becquerels) and absorbed dose (rads, grays) are compared in Table D-5 and are discussed in Sections D.2.2 Half-Life and Activity and D.3.1.2 Absorbed Dose and Absorbed Dose-Rate. 

In this section we will examine briefly the effects of radiation on biological systems. Bnt first let us define quantitative measures of radiation. The fundamental unit of radioactivity is the curie (Ci) 1 Ci corresponds to exactly 3.70 X 10 ° nuclear disintegrations per second. This decay rate is equivalent to that of 1 g of radium. A millicurie (mCi) is one-thousandth of a curie. Thus, 10 mCi of a carbon-14 sample is the quantity that undergoes... 

Radioactivity is a spontaneous nuclear transformation that results in the formation of a different element and, usually, the release of excess energy as particulate and/or electromagnetic radiation. For example, tritium transforms into He-3 and emits a beta particle. The activity of a sample is the rate of radioactive transformation and is usually symbolized by the letter A. In other words, the number of nuclear transformations occurring in a given time. There are two systems of units commonly used for radiological measurements the International System (SI) and the Traditional units. In SI units, activity is measured in bequerels (Bq) where 1 Bq = 1 transformation per second. In the traditional units, activity is measured in curies (Ci) where 1 Ci = 3.7 x 1010 transformation per second = 3.7 x 1010 Bq. The specific activity is defined as the activity of the... 

Know the common units In which radiation Intensity Is represented the curie, roentgen, rad, and rem. 

The amoimt of radiation emitted by a source or received by an individual is reported in a variety of ways, using units that describe different aspects of radiation. The curie and the roentgen describe the intensity of the emitted radiation, whereas the rad and the rent describe the biological effects of radiation. 

We have seen that the fundamental unit for the amount of a radioactive isotope is the becquerel or the curie, which are measures of the number of disintegrations per second. For the assessment of the biological effects of high-energy radiation, such as that emitted by radioactive substances, we obviously need another kind of unit. There are several in common use. 

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