Radium-226, measurement decay

The subsoil is the principal source of radon in this house. Both the activity concentration of radium-226 in subsoil and of radon in soil gas are above levels for building ground that might result in significant indoor radon concentrations. The radon decay-product concentration in the dwelling before remedial measures were taken was substantially higher than the reference value of 120 mWL. 

Marie (NLP 1903, NLC 1911 ) and Pierre (NLP 1903 ) Curie took up further study of Becquerel s discovery. In their studies, they made use of instrumental apparatus, designed by Pierre Curie and his brother, to measure the uranium emanations based on the fact that these emanations turn air into a conductor of electricity. In 1898, they tested an ore named pitchblende from which the element uranium was extracted and found that the electric current produced by the pitchblende in their measuring instrument was much stronger than that produced by pure uranium. They then undertook the herculean task of isolating demonstrable amounts of two new radioactive elements, polonium and radium, from the pitchblende. In their publications, they first introduced the term radio-activity to describe the phenomenon originally discovered by Becquerel. After P. Curie s early death, M. Curie did recognize that radioactive decay (radioactivity) is an atomic property. Further understanding of radioactivity awaited the contributions of E. Rutherford. 

We must now more fully consider the radium emanation — a substance with more astounding properties than even the radium compounds themselves. By distilling off the emanation from some radium bromide, and measuring the quantities of heat given off by the emanation and the radium salt respectively, Professors Rutherford and Barnes proved that nearly three-fourths of the total amount of heat given out by a radium salt comes from the minute quantity of emanation that it contains. The amount of energy liberated as heat during fre decay of the emanation is enormous one cubic centimetre liberates about four... 

Radon s main use is as a short-lived source of radioactivity for medical purposes. It is collected from the decay of radium as a gas and sealed in small glass capsules that are then inserted at the site of the cancer. It is also used to trace leaks in gas and liquid pipelines and to measure their rate of flow. The rate at which radon gas escapes from the Earth is one measurement that helps scientists predict earthquakes. 

In the environment, thorium and its compounds do not degrade or mineralize like many organic compounds, but instead speciate into different chemical compounds and form radioactive decay products. Analytical methods for the quantification of radioactive decay products, such as radium, radon, polonium and lead are available. However, the decay products of thorium are rarely analyzed in environmental samples. Since radon-220 (thoron, a decay product of thorium-232) is a gas, determination of thoron decay products in some environmental samples may be simpler, and their concentrations may be used as an indirect measure of the parent compound in the environment if a secular equilibrium is reached between thorium-232 and all its decay products. There are few analytical methods that will allow quantification of the speciation products formed as a result of environmental interactions of thorium (e.g., formation of complex). A knowledge of the environmental transformation processes of thorium and the compounds formed as a result is important in the understanding of their transport in environmental media. For example, in aquatic media, formation of soluble complexes will increase thorium mobility, whereas formation of insoluble species will enhance its incorporation into the sediment and limit its mobility. 

The E-pH diagram for 10 M Ra is presented in Figure 6.6. This concentration is used because such a solution of the most long-lived radium isotope Ra-226 (half-life 1620 years) would be decaying at the rate of about 3 billion atoms per minute per liter. Such a radioactivity could be worked with given special apparatus and precautions, but more concentrated solutions would require more demanding measures. The discovery of the element Ra was in 1898 by Marie Sklodowska Curie, Pierre Curie, and M. G. Bemont who isolated its salts from large quantities of pitchblende. 

Dorn as a product of the radioactive decay of radium. Ramsay made enough of it to measure its properties in 1908. 

Another procedure is based on the measurement of the radioactive isotope radon-222 (half-life 3.8 days), the decay product of natural radium-226. At the bottom of lakes and oceans, radon diffuses from the sediment to the overlying water where it is transported upward by turbulence. Broecker (1965) was among the first to use the vertical profile of 222Rn in the deep sea to determine vertical turbulent diffusivity in the ocean. 

The Bq is a minute measure of radioactivity and any sizeable amount of radioactive material will contain very many atoms and thus emit considerable amounts (TBq or GBq) of radiation. Another popular unit of decay is the curie, a non-Sl unit (historically calculated from the disintegrations of radium) which is equivalent to 37 x 10 Bq. Importantly, radioactivity decays exponentially, where a population of atoms in a sample will have a characteristic half-life (fi/2). The half-life is the key parameter when considering radioactivity and associated safety of radioisotopes, where fi/2 represents the time taken for the radioactivity to fall to a half the recorded level, as illustrated in Figure 10.4. Half-lives and associated properties of common radioactive isotopes are given in Table 10.2. 

Taking into consideration the method of °Sr analysis, the activity equilibrium state between °Sr and its decay product °Y is very important. This state is attained 12 days after the separation of radiostrontium [62]. The reliability of the received results of °Sr determination depends on the minimum detectable activity (MDA) [5]. The MDA should be calculated for each analysis sample. Generally, the separation of °Sr with the use of fuming HNO3, and subsequent co-precipitation of radium, lead, and barium as chromates, is used for the analysis of flora, soil, ash filters, and water samples. The fusion products (e.g., Cs) are removed by co-precipitation of the hydroxides, then transformed into yttrium oxalate, and the activity of °Y measured in a low-level proportional counter. The yield is controlled by measuring the activity of Sr (gamma emitter) added to each sample before analysis as an internal tracer [1, 46]. The accuracy of the analytical results obtained should be verified in a validation process with the use of certified reference materials (CRMs). 

Radioactivity is measured in decays per second, the SI unit of which is the Becquerel (Bq) which is defined as one decay per second. The Curie (Ci), which originally corresponded to the number of decays per second in 1 g of radium, is still used and is now related to the Becquerel by the definition ... 

The curie (Ci) is a commonly used unit for measuring nuclear radioactivity I curie of radiation is equal to 3.7 X 10 ° decay events per second (the number of decay events from 1 g of radium in 1 s). 

Whether in the environment or in the human body, uranium will undergo radioactive decay to form a series of radioactive nuclides that end in a stable isotope of lead (see Chapter 3). Examples of these include radioactive isotopes of the elements thorium, radium, radon, polonium, and lead. Analytical methods with the required sensitivity and accuracy are also available for quantification of these elements in the environment where large sample are normally available (EPA 1980,1984), but not necessarily for the levels from the decay of uranium in the body. More sensitive analytical methods are needed for accurately measuring very low levels of these radionuclides. 

Radon ( Rn) measurements made by the ARCAS provide a simple, reliable, real-time indicator of the relative maritime or continental nature of the air over coastal or oceanic areas (8). With a half-life of 3.8 days, Rn originates from the decay of Ra, a member of the decay chain. At least 98% of Rn originates from land masses (9). The radon flux at the surface depends on the radium content of the soils and rocks, the permeability of the source materials, atmospheric pressure, soil moisture, and vegetative cover (10). Relatively abrupt changes in the radon concentration over the ocean usually indicate changes in air masses and the passage of frontal systems. 

An important characteristic of radioactive decay is that the momentum of the emitted particle must be balanced by the momentum of the product nucleus. In suitable cases it should be possible to detect the recoil nucleus. Thorium-228, which decays to radium-224 having an energy of 97 keV, has been used to study the oxidation of a number of metals. Its advantages are its low volatility (as thorium oxide) and its relatively low rate of diffusion in lighter metals. The maximum range of recoils in solids is of the order of 300-500 A and for thinner oxide layers, its distance from the surface can be measured. One difSculty with quantitative work is that the radium undergoes a sequence of further decay, which complicates calculation of recoil ranges, and calibration may be necessary. 

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... 

Evidence for the second viewpoint comes from measurements of longer-lived radionucleides within the radium decay sequence, specifically bismuth-210 and lead-210. The major routes for nuclei conversion within the radium decay scheme are shown in Fig. 7-27. The direct decay product of radium-226, an alpha-emitter, is radon-222, which escapes the Earth surface. Only the continents are a source the contribution from the oceans is negligible. Since the half-life time of radon-222 is only 3.8 days, its distribution in the troposphere is rather uneven. Over the continents the mixing ratio declines with increasing altitude (see Fig. 1-9). Over the oceans, the vertical gradient is reversed, as the oceans act as a sink and the zonal circulation keeps supplying material from the middle and upper troposphere. The immediate... 

In 1911 Ernest Rutherford asked a student, George de Hevesy, to separate a lead impurity from a decay product of uranium, radium-D. De Hevesy did not succeed in this task (we now know that radium-D is the radioactive isotope °Pb), but this failure gave rise to the idea of using radioactive isotopes as tracers of chemical processes. With Friedrich Paneth in Vieima in 1913, de Hevesy used °Pb to measure the solubifity of lead salts—the first appfication of an isotopic tracer technique. De Hevesy went... 

The curie (Ci) is a commoniy used unit for measuring nuciear radioactivity 1 curie of radiation is equai to 3.7 X 10 decay events per second (the number of decay events from 1 g radium ini s). A1.7-mL sampie of water containing tritium was injected into a 150-ib person. The totai activity of radiation injected was 86.5 mCi. After some time to aiiow the tritium activity to equaiiy distribute throughout the body, a sampie of biood piasma containing 2.0 mL water at an activity of 3.6 piCi was removed. From these data, caicuiate the mass percent of water in this 150-ib person. 

Radon is a radioactive gas produced when radium in soil and rock decays. It is a known carcinogen. The data above show radon levels measured in a community in Australia. Select a method for graphing these data. Explain the reasons for your choice, and graph the data. 

As stated in Section 5.2.1, soil is the primary source of radon. As such, radon is not released to soil but is the result of radioactive decay of radium-226 within the soil. The radon concentration in the soil is a function of the radium concentration, the soil moisture content, the soil particle size, and the rate of exchange of air with the atmosphere (Hopke 1987). Hopke (1987) states that normal soil-gas radon measurements are in the range of 270 to 675 pCi radon-222/L of air (10,000 to 25,000 Bq/m However, levels exceeding 10,000 pCi radon-222/L of air (370,000 Bq/m ) have been documented. 

---