Half-life radon daughter

Radon-222 [14859-67-7] Rn, is a naturally occuriing, iaert, radioactive gas formed from the decay of radium-226 [13982-63-3] Ra. Because Ra is a ubiquitous, water-soluble component of the earth s cmst, its daughter product, Rn, is found everywhere. A major health concern is radon s radioactive decay products. Radon has a half-life of 4 days, decayiag to polonium-218 [15422-74-9] Po, with the emission of an a particle. It is Po, an a-emitter having a half-life of 3 min, and polonium-214 [15735-67-8] Po, an a-emitter having a half-life of 1.6 x lO " s, that are of most concern. Polonium-218 decays to lead-214 [15067-28A] a p-emitter haviag = 27 min, which decays to bismuth-214 [14733-03-0], a p-emitter haviag... 

Figure 4a shows the results for CN levels at 70 cm 3 and below. As pointed out earlier (Holub, 1984), there are no attached radon daughters because the attachment rate is negligible compared to 218Po half life. There is no observable growth and the clusters are very close to the oxide of 218Po. All sets agree reasonably well. Error bars are from repeated measurements. 

Radon-222 also undergoes radioactive decay and has a radioactive half-life of 3.8 days. Radon-220 and -219 have half-lives measured in seconds and are not nearly as abundant as Radon-222. Thus the discussion of radon health effects here centers on Radon-222. Radon-222 decays into radon daughters or progeny, which are radioactive elements. Two of these (polonium-218 and polonium-214) emit alpha particles (high-energy, high-mass particles, each consisting of two protons and... 

Radon is an inert noble gas and in the natural enviromnent its most important isotopes are Ra and °Rn. Rn (half-hfe 3.8 days) is an immediate daughter nuclide of Ra, but °Rn (half-life 55 s) is a product of " Ra decay [24]. From... 

Secular Equilibrium—If a parent element has a very much longer half-life than the daughters (so there is not appreciable change in its amount in the time interval required for later products to attain equilibrium) then, after equilibrium is reached, equal numbers of atoms of all members of the series disintegrate in unit time. This condition is never exactly attained, but is essentially established in such a case as Ra and its transformation series to stable ° Pb. The half-life of Ra is about 1,600 years of Rn, approximately 3.82 days, and of each of the subsequent members, a few minutes. After about a month, essentially the equilibrium amount of radon is present then (and for a long time) all members of the series disintegrate the same number of atoms per unit time. At this time, the activity of the daughter is equal to the activity of the parent. 

The long-lived isotope of radium, Ra, decays hy alpha particle emission to its daughter radon, Rn, with a half-life of 1622 years. The energy of the alpha particle is 4.79 MeV. Suppose 1.00 g of Ra, freed of all its radioactive progeny, were placed in a calorimeter that contained 10.0 g of water, initially at 25°C. Neglecting the heat capacity of the calorimeter and heat loss to the surroundings, calculate the temperature the water would reach after 1.00 hour. Take the specific heat of water to be 4.18 J g. ... 

Radon (Rn-222) is an odorless and colorless natural radioactive gas. It is produced during the radioactive decay of radium-226, itself a decay product of uranium-238 found in many types of crustal materials, that is, rocks and soils. Rn-222 has a short half-life (3.8 days) and decays into a series of solid particulate products, known as radon progeny or radon daughters, all of which have even shorter half-lives ( 30 min or less). Other isotopes of radon also occur naturally, but due to differences in half-life and dosimetry their health significance is minimal compared to that from exposure to Rn-222. 

Radon is eliminated mainly in exhaled air ( 90% in the first hour and the remainder within 6 or 7h), whereas radon daughters are eliminated mainly by excretion in feces and urine. The biological half-life of radon is reported to be 3.823 days. 

Table 1. Elements in the uranium-238 decay chain and their half-lives. Note the very long half-life of (approximately equal to the age of the earth) which provides the continuing source of all other chain members. The half-lives of the radon daughters (highlighted in Figure 1) are all less than 30 minutes and so may reach varying degrees of equilibrium with radon in air depending on the factors which act on them.

As can be seen in Figure 1, radon itself and its polonium daughter products are alpha emitting nuclides, while the isotopes of lead and bismuth produced are beta/ gamma emitters. The short half-lives of the daughter products prior to Pb (Table 2) result in the rapid production of a mixture of airborne radioactive materials which may attain equilibrium concentrations within a relatively short time. The half-life of °Pb is 22 years and at this point in the decay chain any activity inhaled is largely removed from airways in which it is deposited before any appreciable decay occurs. 

Such systems are called radioisotope generators. Rn is sometimes used for the radiotherapeutic treatment of cancer. This product is isolated by separating it as a gas from the parent substance Ra which is normally in the form of solid or a solution of RaBr2. Rn grows into the radium sample with a half-life of 3.8 d. After a 2-week period, following a separation of radon from radiiun, approximately 90% of the maximum amount of radon has grown back in the radium sample. Consequently, it is useful to separate Rn each 2 weeks from the radium samples since further time provides very little additional radioactivity. The Rn is an a emitter the ther utic value comes from the irradiation of the tissue by the y-rays of the decay daughters Pb and Bi which reach radioactive uilibrium extremely rapidly with the Rn. 

Food Chain Bioaccumulation. Information on bioaccumulation of radon and radon daughters in the food chain is not available. Therefore, the potential for bioconcentration in plants, aquatic organisms or animals, or for biomagnification in the food chain is unknown. However, due to the short half-life of radon, it would not tend to bioaccumulate. Studies of the bioaccumulation of radon in the food chain are not necessary at this time. 

It appears that it is the radioactive products—that is, the daughters of radon— that actually cause cancer. Radon-222 is an alpha emitter with a half-life of 3.82 days. Its decay, as shown in Equation (19.21), produces polonium-218, which itself is an alpha emitter with a half-life of 3.11 min. 

Radium ( Ra) has a half-life of 1600 yr and is the decay product of Radium is often found in waters draining U-bearing rocks and in the U processing wastes. Radium exists in the environment typically as a divalent cation, Ra " which behaves similarly to Ba or Ca and may form aqueous complexes with sulfate ions or carbonate ions. The fate and behavior of Ra in soil and sediment directly affects the dose of public exposure to radioactivity for the Ra decay daughter product, radon, is responsible for 55% of this type of radioactivity (NCRP, 1987). Compared with U, Ra has a higher mobility in soils and higher accessibility to the food chain. The activity ratio (AR) of in the soil is about 0.1, but Ra greatly... 

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