Radioactive decay, constant

From the radioactive decay constants and measurement of the amount of argon in a rock sample, the length of time since formation of the rock can be estimated. Essentially, the dating method requires fusion of a rock sample under high vacuum to release the argon gas that has collected through radioactive decay of potassium. The amount of argon is determined mass spectrometrically,... 

The 210Pb inventory in the sediments was calculated in a similar way to the 239,240pu method described previously, but 1 cm increments were used in determining the integrated deposition. The deposition rate of the 210Pb for each core was determined as the product of the integrated deposition and the radioactive decay constant, (A. =. 0311 yr-1). Since the unsupported 210Pb (t ... 

Although the radioactive decay constants are independent of temperature and pressure, the retention of the radiogenic daughter in a mineral depends strongly on temperature because at high temperatures diffusivity is high, resulting in... 

Lee, . . M. and Steinle-Neumann, G. (2008) Ab-initio study of the effects of pressure and chemistry on the electron-capture radioactive decay constants of 7Be, 22Na, and 40K. Earth and Planetary Science Letters, 267, 626-628. 

Thus the half-life is inversely proportional to the radioactive decay constant. Table 2.5 lists the most frequently used 0-emitting isotopes together with their half-lives and particle energies. 

Qlu, Qia Flux of unattached, attached 218Po to surface (Bq m-2 s 1) vu, va Velocity of deposition of unattached, attached 218Po (m s 1) Aj, X2, A3 Radioactive decay constants of 218Po, 214Pb, 214Bi (s 1)... 

XDa and XDu will depend on the air movement in the room, the area and nature of the surfaces, and the strength of any electrostatic fields. For XDa, the size distribution of the nuclei in the air, and the presence or absence of thermal gradients near surfaces may also be important. Despite the variables, some experimental and observational data are available which allow XDa andXDu to be compared in order of magnitude with the radioactive decay constants and with the rate constant for ventilation. 

The decay of a radionuclide is a statistical process in the sense that it is not possible to predict exactly when a particular nucleus will disintegrate. One may, however, ascribe a probability that a nucleus will decay in unit time. This probability is known as the radioactive decay constant (transformation constant), X, of the radionuclide. The number of atoms of a radioactive substance disintegrating per unit time, 6N/dt, which is referred to as the activity of the substance, is proportional to the total number, N, of radioactive atoms present at time t, the constant of proportionality being X. 

The factor of proportionality A is called the radioactive decay constant, it is characteristic of the kind of atom. By integration we find... 

Any radionuclide, whatever the type of radiation emitted, is characterized by its half-life T (Table 17.1), which is the time taken for half of corresponding atom population in the sample to decompose (from initial time, t = 0). Calling A the radioactive decay constant, the law of radioactivity decay allows calculation of the number of atoms N present after time t for a population containing Nq atoms initially. The integrated form of this law is written as equation 17.4 ... 

In this equation D (m2.s 1) represents the radon diffusivity, X the radioactive decay constant (s 1), C (Bq.m3) the radon concentration in the pore space, R (Bq.kg1) the radium concentration in the material, p (kg.m3) the bulk density of the dry material, E (dimensionless) the radon emanation power coefficient for the pore spaces, s (dimensionless) the total porosity and 0 (dimensionless) the moisture. The solution of the diffusion equation for an homogeneous medium represents the flux release from the waste material to the surface, Jt (Bq.m 2.s ). For a system without cover we obtain (Rogers, 1984) ... 

For a given neutron density n and speed u, the product o4> is the first-order rate constant and is the fraction of the reacting nuclei consumed by the reaction per unit time. It plays the same role in rate equations as the radioactive decay constant X. 

Radioactive decay constant Absorption cross section, b Direct yield from U fission, y atoms per atom fissioned... 

Thus to estimate the lifetime of 85Kr does not even require knowledge of its atmospheric abundance Q, but only of the radioactive decay constant. Consequently, it does not matter whether 85Kr is uniformly mixed throughout the entire atmosphere or not to estimate its lifetime. In a case where the removal process is first-order, then even for a poorly mixed species a simple and accurate estimate for its lifetime can be obtained provided that its removal rate constant can be accurately estimated. 

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