Radioactivity decay rates

It has been hoped [20,21] that a method could be developed which would directly detect the radioatoms that are present in nature by an efficient ultra-sensitive mass spectrometer technique which would not itself depend upon the fact that the atoms being investigated are radioactive. The advantage of an efficient mass spectrometer system for long-lived radioisotopes can be seen from the equation for calculating the number of atoms present in a sample from its measured radioactive decay rate ... 

Disintegrations per minute (dpm) The unit measurement of radioactive decay rates. 

Radioactive decay rates are statistical averages of large numbers of decaying atoms. Because of the relatively short half-life of carbon-14, only trace amounts would be left after 50,000 years—too little to be statistically accurate. 

The constancy of the half-life for a first-order reaction is illustrated in Figure 12.7. Each successive half-life is an equal period of time in which the reactant concentration decreases by a factor of 2. We ll see in Chapter 22 that half-lives are widely used in describing radioactive decay rates. 

Subatomic Particles radioactive decay rate electronic random number generators. 

Step 13. Count the sample for beta particles with proportional counter for 6,000 s and record results in Data Table 10.1 Measure the background count rate for 6,000 s immediately before or after the sample measurement. To check radioactive decay rate, repeat counting under identical conditions every second or third day for at least two weeks. 

Solve problems involving radioactive decay rates. 

Radioactive decay rates are measured in half-lives. A half-life is the time required for one-half of a radioisotope s nuclei to decay into its products. For example, the half-life of the radioisotope strontium-90 is 29 years. If you had 10.0 g of strontium-90 today, 29 years from now you would have 5.0 g left. Table 25-4 shows how this decay continues through four half-lives of strontium-90. Figure 25-13 presents the data from the table in terms of the percent of strontium-90 remaining after each half-life. 

The radioactive decay rates for °Pb and Ra in white lead paint taken from Emmaus in 1968 were 8.5 and 0.8 disintegrations per minute per gram of lead (dpm/g), respectively, (a) How many half lives of °Pb had elapsed between 1660 and 1968 (b) If Vermeer had painted Emmaus, what would have been the decay rate of °Pb in 1660 Comment on the reasonableness of this rate value. 

Usually the radioactive decay rate Aj is measured, rather than the number of atoms Ny. Recalling A = AN/At = XN, (15.3) and (15.8a) yield... 

Standard radioactive Material (SRM) solutions are radioactive materials with accurately known radionuclide content and radioactive decay rate or rate of particle or y-ray emission. They are used primarily to calibrate radiation detection instruments and to prepare QC samples that test analytical accuracy. The supplier prepares radionuclide standard solutions in flame-sealed glass ampoules. Other standard radionuclides are in the form of point sources (usually on thin backing) or as solids in configurations that represent actual samples. 

RADIOACTIVE DECAY RATES AND DETECTION OF RADIOACTIVITY (SECTIONS 21.4 AND 21.5) The SI unit forthe activity of a radioactive source is the becquerel (Bq), defined as one nuclear disintegration per second. A related imit, the curie (Ci), corresponds to 3.7 X lO disintegrations per second. Nuclear decay is a first-order process. The decay rate (activity) is therefore directly proportional to the number of radioactive nuclei. The half-life of a radionuclide, which is a constant independent of temperatiu e, is the time needed for one-half of the nuclei to decay. Some radioisotopes can be used to date objects C, for example, is used to date organic objects. Geiger counters and scintillation counters coimt the emissions from radioactive samples. The ease of detection of radioisotopes also permits their use as radiotracers to foUow elements through reactions. 

The radioactive decay rate constant we will probably have to calculate the decay rate to be able to calculate all other quantities. 

The Voyager space vehicle launched in 1977 contained a gold-plated copper disk electroplated with a patch of pure uranium-238 isotope. If this disk were recovered by some advanced alien civilization, the disk s age could be determined from the radioactive decay rate of the isotope. 

The half-life is the time it takes for one-half of the parent nuclides in a radioactive sample to decay to the daughter nuclides. One can relate the half-life of objects to find their radioactive decay rates. 

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