Units of radioactivity

The SI unit of radioactivity is the becquerel (Bq) and is equal to one nuclear disintegration per second. The unit is named after Henri Becquerel, who discovered the phenomenon of radioactivity in 1896. A non-SI unit also in use is the curie (Ci), where 1 Ci = 3.7 x 10 Bq the curie is named after Marie Curie, who discovered the elements radium and polonium. 

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. 

The number of disintegrations emitted by a radioactive sample depends on the purity of the sample (number of radioactive atoms present) and the decay constant, A. Therefore, radioactive decay is also expressed in terms of specific activity, the disintegration rate per unit mass of radioactive atoms. Typical units for specific activity are mCi/mmole and /r,Ci//rmole. 

Although radioactivity is defined in terms of nuclear disintegrations per unit of time, rarely does one measure this absolute number in the laboratory. Instruments that detect and count emitted particles respond to only a small fraction of the particles. Data from a radiation counter are in counts per minute (cpm), which can be converted to actual disintegrations per minute if 

Units Name Multiplication Factor (relative to curie) Activity (dps) 

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Curie (Ci) A unit of radioactivity, related to the emission from 1 g of radium, it is equal to 3.7 x 10 disintegrations per gram per second. This unit has been replaced by the Becquerel (Bq) 1... 

The carbon skeleton of helminthosporal can be accounted for from three isoprene units (XVI), but they cannot be formed by cyclization of a farnesol precursor, as the three units are not joined head to tail. There is the possibility that the aldehyde carbons were joined in the early stages of biosynthesis to form helminthosporane (XVII, XX) as an intermediate, followed by later oxidation to yield the dialdehydes. As a test of this hypothesis the actively growing fungus was fed mevalonic acid labeled with carbon-14 in the 2-position (mevalonic acid being a precursor of isoprene units) (2). Thus, three units of radioactivity should be incorporated, one being the... 

Curie (Ci)—A unit of radioactivity. One curie equals that quantity of radioactive material in which there are 3.7xl010 nuclear transformations per second. The activity of 1 gram of radium is approximately 1 Ci. 

Radiopharmaceuticals are prescribed according to units of radioactivity. A pharmacist practicing nuclear pharmacy may need to convert radio activity units from curies to SI unit, becquerel and its multiples, and vice versa. The following examples illustrate the interconversion of radioactive units. 

Radiopharmaceuticals are prescribed in units of radioactivity, and the actual dispensing of the patient dose involves calculating how much radiopharmaceu-... 

The intrinsic variable expressed as units of radioactivity (in becquerels or, more traditionally, curies) per mole of a substance. One Bq corresponds to 1 disintegration per second (dps) and one Ci to 3.70 x 10 ° Bq. This parameter is especially useful in quantifying the amount of substance in biological samples. For example, if SAs is the standard specific radioactivity (say, x dps/y mol) of a standard, and if SAg is the experimental specific activity (say, x dps/(y + z) mol), then the content z in a sample can be determined from the expression (SAs/ SAe) = (y + z)/y or z = y ([SAj/SAg] - 1). This intrinsic variable can also be expressed as the gram-atom excess of a stable isotope per mole of a substance. The numerator is typically determined using a ratio mass spectrometer, and the denominator can be estimated by chemical and/or spectroscopic techniques. 

The conventional unit of radioactivity, the curie (Ci), is equivalait to 3.7 X 10 radioactive events per second. The SI unit used for denoting the amount of radioactive material contained in a given sample of matter is the becquerel (Bq) one becquerel is that quantity of a radioactive nuclide in which there is one radioactive event per second (1 Bq = 2.7 x 10 Ci). Since radionuclides decay exponentially with time, each element at its own rate, the time required for a given quantity of a radionuclide to lose one-half of its radioactivity is call its physical half-Ufe. 

The natural unit of radioactivity is disintegrations/time, such as disintegration per second (dps) or disintegrations per minute (dpm), and so on. The SI (International System) unit of radioactivity is the Becquerel (Bq) where... 

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

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 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. 

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, Ci, defined by... 

Radionuclides occur in the environment in such minute physical quantities that they are commonly referred to as being present at sub- or ultra-trace quantities. As an illustration of this Livens and Rimmer (1988) presented values relating the masses and specific activities of several artificial radionuclides and their typical concentrations in surface soils of the UK (see Table 7-1). This indicates the very small mass usually associated with one Becquerel of radioactivity, although as the half life of a radionuclide increases so does the mass per unit of radioactivity. The molarity concept is... 

An important parameter used to quantify dry deposition processes is the velocity of deposition (Kg) (Chamberlain, 1953). Vg is defined as the downward flux of aerosol or gas to a vegetation or soil surface, normalised to the ambient atmospheric gas or aerosol concentration above that surface. In the case of radionuclide deposition processes flux and concentration are, respectively, measured in units of radioactivity per unit area and volume, hence... 

Appendix 5. Units of Radioactivity and Prefixes for Multiple Units in the International System... 

A unit of radioactivity which represents 3.7 x 1010 disintegrations per second. It represents the number of disintegrations emitted from 1 g radium. 

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 basic unit of radioactive particle emission is the curie, Ci. Originally, the curie was defined as the number of disintegrations per second emitted from a gram of impure radium (3.7 X 10lo/s or 2.2 X 1012/min). This unit and its subdivisions the millicurie, mCi (2.2 X 109 dpm), the microcurie, /xCi (2.2 X 106 dpm), are the fundamental units to define radioactive particle emission rates. Radioac-... 

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