Given that Ra decay products had likely existed in a steady-state radioactive equilibrium with Ra isotopes in the solid shale-formation matrix for millions of years prior to drilling activities, these observations prompted us to explore the radioactive equilibrium relationships of Ra decay products in produced fluids, particularly for the longer-lived alpha-emitters, [sup.228]Th ([t.sub.1/2] = 1.91 years) and [sup.210]Po ([t.sub.1/2] = 138 days) (half-lives were extracted from the NuDat 2 Database) [National Nuclear Data Center (NNDC) 2013].
As [sup.228]Th ingrows at a rate related to its half-life, its decay product [sup.224]Ra ([t.sub.1/2] = 3.63 days), rapidly ingrows to steady-state radioactive equilibrium. Rapid ingrowth of [sup.224]Ra is followed by a series of short-lived radioactive decay products that ultimately decay to stable [sup.208]Pb (Figure 1).
Similar to the decay product scenario of Th-series Ra isotope [sup.228]Ra, establishing radioactive equilibrium of decay product radionuclides with parent [sup.226]Ra is potentially confounded by the presence of a gaseous isotope (i.e., [sup.222]Rn, [t.sub.1/2] = 3.82 days) in the decay series.
The amount ratio of radon to its decay products is defined by radioactive equilibrium factor, usually named as F factor (Mohamed 2005; Baixeras et al.
The radioactive equilibrium factor depends mostly on winding intensity and concentration of aerosol particles in the air (Clavensjo, Akerblom 1994; Ramola et al.
Radioactive equilibrium factor is used as a factor to proceed from radon volumetric activity to its decay products volumetric activity in the premises, or vice versa.
The aim of this work is to investigate the influence of tobacco smoke on changes of indoor radon and its short-lived decay products volumetric activities, evaluate the dependence of unattached fraction factor and radioactive equilibrium factor on concentration of aerosol particles in the air.
Radon volumetric activities (C), unattached fraction factor [f.sub.Po]), radioactive equilibrium factor (F) and aerosol particle concentration (N) in the air under natural living conditions were measured in all rooms of the investigated house.
Aerosol concentration in the air (Z), unattached fraction factors (f) and radioactive equilibrium
factors (F) under the different aerosol conditions indoor 2 lentele.
These values suggest that uranium and its decomposition products present in the shale are in the state of radioactive equilibrium or rather close to it.
On the background of common radioactive equilibrium in the uranium series in the studied shale, an increase in the value of [sup.234]U/[sup.238]U ratio in organic phases over unity indicates the presence of an uranium-rich matter.
Uranium-series methods are based on the concept of radioactive equilibrium
. In an "old" system (e.g., old mineral grain) the number of daughter atoms forming per unit time from parent atoms (referred to as Activity of the parent = ([A.sub.P])) will equal the number of daughters decaying to some other isotope (Activity of daughter = ([A.sub.D])) and ([A.sub.D]/[A.sub.P)] = 1.