Radioactive disintegrations

Autoradiography. The technique of exposing film in the presence of disintegrating radioactive particles. Used to obtain information on the distribution of radioactivity in a gel or a thin cell section. 

Tritium is the heavy isotope of hydrogen (section 5.2). Its symbol is 3H, or T. Tritium atoms are unstable and disintegrate radioactively, forming stable 3He atoms. The radioactive decay is accompanied by the emission of [1 particles, measurable in specific laboratories ... 

Thermoluminescent dating (TL). This technique is useful for dating pottery and ceramics (Wagner et al, 1983). It is based on the cumulative effect of radiation from disintegrating radioactive isotopes present in minerals of most rocks, clays and soils. The ionizing radiation may cause electrons to detach from their parent atom and become trapped in lattice defects of the material. As the material ages, defects accumulate. When a ceramic object is fired, trapped electrons are freed and, since radioactive minerals are incorporated in the object, defects start to accumulate again. 

Atoms with the same number of protons but a different number of neutrons are called isotopes. To identify an isotope we use the symbol E, where E is the element s atomic symbol, Z is the element s atomic number (which is the number of protons), and A is the element s atomic mass number (which is the sum of the number of protons and neutrons). Although isotopes of a given element have the same chemical properties, their nuclear properties are different. The most important difference between isotopes is their stability. The nuclear configuration of a stable isotope remains constant with time. Unstable isotopes, however, spontaneously disintegrate, emitting radioactive particles as they transform into a more stable form. 

An important characteristic property of a radioactive isotope is its half-life, fj/2, which is the amount of time required for half of the radioactive atoms to disintegrate. For first-order kinetics the half-life is independent of concentration and is given as... 

Since the half-life is independent of the number of radioactive atoms, it remains constant throughout the decay process. Thus, 50% of the radioactive atoms disintegrate in one half-life, 75% in two half-lives, and 87.5% in three half-lives. 

The time required for half of the initial number of a radioactive isotope s atoms to disintegrate (ti/2). 

Three common quantitative applications of radiochemical methods of analysis are considered in this section the direct analysis of radioactive isotopes by measuring their rate of disintegration, neutron activation, and the use of radioactive isotopes as tracers in isotope dilution. 

The activity in a 10.00-mL sample of radioactive wastewater containing fgSr was found to be 9.07 X 10 disintegrations/s. What is the molar concentration of 3gSr in the sample The half-life for fgSr is 28.1 years. 

Radioactive waste is characterized by volume and activity, defined as the number of disintegrations per second, known as becquerels. Each radionucHde has a unique half-life,, and corresponding decay constant, A = 0.693/tj 2 For a component radionucHde consisting of JS1 atoms, the activity, M, is defined as... 

It is possible to achieve an excellent measure of the quantity of radioactivity upon disintegration of several hundred thousand atoms, ie,... 

Atoms with the same value of Zbut different values of A are isotopes (Table 11.1). Many isotopes are stable but others are naturally or artificially radioactive, i.e. their atomic nuclei disintegrate, emitting particles or radiation. This changes the nuclear structure of the atom and often results in the production of a different element. 

The activity of a sample, source or contaminated material is the rate at which radioactive disintegrations are taking place. The initial term, named by Madam Curie for her husband was, the Curie (Table 8.3-1). The modem unit is the Becquerel named after the discoverer of... 

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... 

Radioactive materials Elements that have unstable nuclei that spontaneously disintegrate, releasing radiation in the form of subatomic particles and energy. 

Radioactivity The property of spontaneous disintegration possessed by certain unstable nucelides. 

E. Rutherford (Manchester) investigations into the disintegration of the elements and the chemistry of radioactive substances. 

The products of nuclear fission reactions are radioactive and disintegrate according to their own time scales. Often disintegration leads to other radioactive products. A few of these secondary products emit neutrons that add to the pool of neutrons produced by nuclear fission. Very importantly, neutrons from nuclear fission occur before those from radioactive decay. The neutrons from nuclear fission are termed prompt. Those from radioacth e decay arc termed delayed. A nuclear bomb must function on only prompt neutrons and in so doing requires nearly 100 percent pure (or Pu) fuel. Although reactor... 

Bromine-82 has a half-life of 36 hours. A sample containing Br-82 was found to have an activity of 1.2 X 105 disintegrations/min. How many grams of Br-82 were present in the sample Assume that there were no other radioactive nuclides in the sample. 

When Fe-55 became available, Hughes and Wilezewski4 found it possible to improve further the valuable method just described by using this radioactive isotope as an x-ray source. Four millicuries of iron, in the form of a button that initially had 15(107) disintegrations per second, was mounted as shown in Figure 5-2, the Geiger counter being movable... 

We can use Fig. 17.13 to predict the type of disintegration that a radioactive nuclide is likely to undergo. Nuclei that lie above the band of stability are neutron rich they have a high proportion of neutrons. These nuclei tend to decay in such a way that the final n/p ratio is closer to that found in the band of stability. For example, a l4C nucleus can reach a more stable state by ejecting a (3 particle, which reduces the n/p ratio as a result of the conversion of a neutron into a proton (Fig. 17.15) ... 

The principal source of radioactivity in the human body is potassium-40. About 35 000 potassium-40 nuclei disintegrated in your body while you were reading this sentence. 

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