Nuclear disintegration rates

Table 4. Numerical values of the coefficients for the calculation of the nuclear disintegration rate Nio3o(Pc) and the attenuation length A(Pc) according to Equations (18) and (19), respectively (Dunai 2001b).

The only difference between a chemical and a radioactive half-life is that the former reflects the rate of a chemical reaction and the latter reflects the rate of radioactive (i.e. nuclear) decay. Some values of radioactive half-lives are given in the Table 8.2 to demonstrate the huge range of values t j2 can take. The difference between chemical and radioactive toxicity is mentioned in the Aside box on p. 382. A chemical half-life is the time required for half the material to have been consumed chemically, and a radioactive half-life is the time required for half of a radioactive substance to disappear by nuclear disintegration. 

The variation in 7Be with altitude and time at 46 °N was very similar to the variations in the activities of the bomb-produced radionuclides, except in the case of short lived fission products whose seasonal variations were obscured largely by debris from recent nuclear tests. Figure 3 shows the 137Cs disintegration rate plotted as function of time for several altitudes. As for 7Be, 137Cs reached a maximum at 40,000 feet and below on June 5, 1967 and then decreased. The activities of 137Cs and the other bomb-produced radionuclides increased sharply again from 20,000 to 40,000 feet after October 23. 

An empirical parameter that describes the temperature dependence of the rate constant, active site (1) The region of an enzyme molecule where the substrate reacts. (2) The effective catalytic site on the surface of a heterogeneous catalyst, activity (1) In thermodynamics, a, the effective concentration or pressure of a substance J. (2) In radioactivity, the number of nuclear disintegrations that occur per second. 

The rate of change of concentration of some species A (e.g., d A /dt ) is a measure of the rate of chemical reaction. Most of the equations in chemical kinetics are differential equations meaning they involve at least one derivative. In addition, nuclear disintegrations (such as 14C—> 14N+< - ) use the same rate equations as do many unimolecular decompositions (suchas CU —> 2NO2). 

As the disintegration rate of the fission products with ti/2 > 1 s is about five times the rate of fission, the activity of the fuel several seconds after shutting off the reactor is xl7 10 Bq (a 5 10 Ci) per MW of thermal energy produced. The p activity per MW and the heat production of the fission products are plotted in Fig. 11.19 as a function of the time after shutting off the reactor. The heat production requires cooling of the fuel elements, because melting of the fuel and volatilization of fission products may occur under unfavourable conditions. produced by the nuclear reactions U(n, y) U(n, and U(n, 2n) U causes a relatively high initial activity of uranium. As decays with a half-life of 6.75 d ... 

There is one important practical difference between chemical kinetics and nuclear kinetics. In chemical kinetics the concentration of a reactant or product is monitored over time, and the rate of a reaction is then found from the rate of change of that concentration. In nuclear kinetics the rate of occurrence of decay events, —dN/dt, is measured directly with a Geiger counter or other radiation detector. This decay rate—the average disintegration rate in numbers of nuclei per unit time—is called the activity A. 

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... 

In order to measure the absorption of nuclear radiation, the experiments must be performed in such a manner as to eliminate as many of the interfering factors as possible. Usually a well-collimated beam is used. This is illustrated in Figure 6.1 for a point radioactive source. The relation between the disintegration rate A and die count rate R is given by (4.45) ... 

The determination of absolute disintegration rates is of great importance in all areas of nuclear chemistry, tracer work, age calculation, etc. Numerous methods have been employed, many using techniques described above, as track counting, liquid scintillation measurements, 47t proportional counters, etc. If the nuclei decay through 0-y emission, the absolute rate may be obtained by two detectors placed close to each side of a thin sample, one detector jS-sensitive and the other y-sensitive. 

Radioanalytical chemistry is devoted to analyzing samples for their radionuclide content. For this purpose, the strategies of identifying and purifying the radioelements of interest by chemical methods, and of identifying and measuring the disintegration rate ( activity ) of radionuclides by nuclear methods, are combined. Radioanalytical chemistry can be considered to be a specialty in the subdiscipline of nuclear and radiochemistry. 

Nuclear Reaction Isotope Abundance L Ei or He] Nuclear Reaction Cross Section Recoil Energy, Tritium Atom Recoil Energy, Emitted Particle Tritium atoms produced/sec Irradiation at 10 n/cm /sec Disintegration rate of H produced in one second... 

The rate at which a sample decays is called its activity, and it is often expressed as number of disintegrations per unit time. The becquerel (Bq) is the SI unit for expressing activity. A becquerel is defined as one nuclear disintegration per second. An older. 

SECTIONS 21.4 AND 21.5 The SI unit for the activity of a radioactive source is the becquerel (Bq), defined as one nuclear disintegration per second. A related unit, the curie (Ci), corresponds to 3.7 X 10 disintegrations per second. Nuclear decay is a first-order process. The decay rate (activity) is therefore proportional to the number of radioactive nuclei. The half-life of a radionuclide, which is a constant, 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 count the emissions from radioactive samples. The ease of detection of radioisotopes also permits their use as radiolracers to follow elements through reactions. 

The rate at which a sample decays is called its activity, and it is often expressed as number of disintegrations per unit time. The becquerel (Bq) is the SI unit for expressing activity. A becquerel is defined as one nuclear disintegration per second. An older, but still widely used, unit of activity is the curie (Ci), defined as 3.7 X 10 disintegrations per second, which is the rate of decay of 1 g of radium. Thus, a 4.0-mCi sample of cobalt-60 undergoes... 

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