Abstract:
A system and methods relating to the detection of unattached radioactive particles. Seismic events are correlated with an increased release of radon and related decay chain products. An apparatus is described for determining the increase in the unattached particles as an indicator for seismic activity. The apparatus may be used with fracking rigs or petrochemical wells to provide controls responsive to predicted seismic events.

Description:
CROSS REFERENCES TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application 61/702139, filed Sep. 17, 2012, incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to radiation decay products. Specifically, embodiments relate to radon decay products and seismic even detection. 
     BACKGROUND 
     Radon decay has previously been studied and the typical decay pathway is known. Radon itself a decay product from uranium and thorium. There are some hundreds of publications devoted to earthquake research and a significant fraction of these include the measurement of radon ( 222 Rn) (Friedman, 2010, Klusman et al., 1981, Mogro-Campero, 1980). Studies include seismic velocity changes, tilting of the earth&#39;s surface, strain accumulation, soil gas helium, mercury, radon emanation rate and radon increase in ground water. Changes in soil gas radon and groundwater are measured indicators. As yet there are no measurements of thoron ( 220 Rn) emanation rate as a predictor of stress accumulation in soil. 
     SUMMARY 
     Long term (4 month) measurements of the particle size distribution in outdoor air were made at two locations using the long lived radon decay product  210 Pb as the tracer for short lived radon decay products,  218 Po (3.05 min),  214 Pb (26.8 min) and  214 Bi (19.7 min). The sites were, outdoors at a New Jersey home and at Fernald, Ohio, the former uranium processing facility, on top of their large (150 TBq, but contained)  226 Ra source in storage silos. The particle size distribution measurements showed the unattached fraction of radon decay products ( 218 Po) to be &lt;2% in typical outdoor air but 16% over the large source of  226 Ra. Radon decays to  218 Po and its buildup over a “freshly” emanating  226 Ra source of radon permits the unattached  218 Po (2-4 nm) to rapidly trace changing local radon concentrations. The concentration ratio (silo/outdoor) of unattached decay products (16/2) was not in line with the radon concentration ratios (96 Bq m −3 /27 Bq m −3 ) because radon gas has longer time to disperse and dilute. 
     It is proposed that real time, rather than our long term proof of principle measurements of unattached radon decay products ( 218 Po/ 214 Pb) made in the present research, may be used to identify rapidly changing radon concentration. Radon is shown to exhibit increased exhalation from soil prior to earthquakes mainly due to microfracture cracks and increased soil porosity. 
     Additional features, advantages, and embodiments of the present disclosure may be set forth from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the present disclosure and the following detailed description are exemplary and intended to provide further explanation without further limiting the scope of the present disclosure claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, aspects, features, and advantages of the disclosure will become more apparent and better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1A-B  illustrate aerosol particle diameter distribution measured at a New Jersey home 19 Feb. to 21 May 2005 using a integrating miniature particle size (“IMP”) sampler. 
         FIGS. 2A-B  illustrate aerosol particle diameter distribution measured on top of the 150 TBq  226 Ra storage silos at Fernald, Ohio, 17 Jul. to 21 Nov. 2002, using the IMP sampler. 
         FIG. 3  is a graphical depiction of the unattached  218 Po buildup over time. 
         FIG. 4  is a graphical depiction of the calculated steady state unattached  218 Po over the attached  218 Po ratio as a function of the aerosol concentration. 
         FIG. 5  is a bar graph illustrating the radioactivity of  222 Rn and  210 Pb in the general outdoor environment and above the silo. 
         FIG. 6  illustrates a collection vessel. 
         FIG. 7  illustrates a computer system for use with certain implementations. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure. 
     Earthquakes or other seismic events may be preceded by microfracturing and other increases in soil porosity along with releases of subterranean materials, particularly gases or liquids. Detection of radioactive elements released from below the earth&#39;s surface can be utilized to determine microfacturing or other stresses that may be indicative of an earthquake. The ratio of a detectable decay element that serves as an immediate tracer of the time variation of an local radioactive element “upstream” in the decay chain may be utilized. The ratio may be monitored to determine when it exceeds a certain threshold associated with seismic activity, i.e. a threshold considered significant and above a “noise” or background level. Further, the ratio may be monitored to determine a rate of change in the ratio to provide an indication of the direction of change, for example is a release of radon increasing or decreasing. Further, in certain implementations the concentration of a particular element in the decay chain is used rather than a ratio. In a further implementation, the concentration of one species of a particular element, such as those unattached to aerosols, is used. It is believed that the concentration of the unattached (very small size 1-5 nm) decay product  218 Po is the key to a pressure pulse, i.e., initiation prior to a seismic event. There is a background concentration of unattached due to normal soil diffusion of radon and unattached 218Po formation. A baseline can be established for a location using ongoing measurements. For example, the baseline can be the average of daily measurements for each month. A concentration of unattached  218 Po significantly above this baseline indicates an underground pressure pulse. In one embodiment, this would be at least a specific increase over a specific time duration. For example, say a factor of 2 increase in  218 Po over 4 hours duration. 
     In one embodiment, methods and systems rely on the fact that the radon decay product,  218 Po, formed as a positively charged atom from radon decay. A fraction of  218 Po atoms are neutralized and all  218 Po rapidly form molecular clusters of about 0.5 to 5 nm diameter with water vapor or other constituent molecules. These nanometer size decay products are called the unattached fraction of radon decay products. Some unattached  218 Po decays to  214 Pb which remains unattached (nanometer diameter) with the ratio of unattached  218 Po/ 214 Pb about 10/1. Within about 30 seconds a cluster attaches to the local aerosol particles usually 200-400 nm diameter and are attached decay products. Therefore, the unattached decay products are immediate tracers of the time variation of the local radon concentration wherever they are measured. 
     Increased radon emanation from soil can be directly related to microfracturing due to stress and increase in soil porosity (Ramola et al., 2008). Real time monitoring of the unattached fraction of  218 Po or  214 Pb above ground or in a below ground vault, provides a criterion for earthquake prediction. A sharp increase in the concentration of unattached  218 Po or  214 Pb or in the ratio of unattached to attached is an indication of a release of radioactive decay chain materials from the soil, which is predictive of seismic activity. 
     The entire decay product chain  218 Po,  214 Pb,  21 4Bi can be utilized with systems and methods of various embodiments, as their effective half-life is relatively short (about 30 minutes). Because most are attached to larger particles (200-400 nm) their capture gets complicated by the fact that the total activity must be measured with a filter that captures everything. Thus, for embodiments using decay products that attach to larger particles, a backup filter is used and measured. 
     The unattached  218 Po only exists for about 30 seconds before attaching to the local aerosol particles. Because of its small diameter, a single screen filter captures about 60%. Thus,  218 Po is preferred because it is tracking  222 Rn (radon) rapidly and selectively. 
     There is a slight complication in measuring total decay products. The Thorium decay series ( 222 radon is in the uranium decay series) has another radon isotope,  220 Rn (thoron). This is usually at a much lower concentration than  222 Rn (radon). The thoron decay product  212 Pb has a 10 hour half-life and contributes to the total activity. However, for certain embodiments, the presence of this decay product can be ignored because it would be in the background baseline. Further, the 22 year half-life  210 Pb radon decay product can similarly be ignored. 
     Systems and methods of invention may apply to seismic events, including induced seismic events from human activity such as hydraulic fracturing. In one embodiment, the detection of increased radon or radon decay chain elements can be utilized in a mining, drilling, or other subterranean extraction processes. In particular, the systems and methods described herein may be utilized with hydraulic fracturing. Specifically, the well head or upstream from the well head in the well sensors may be utilized to detect the changes in concentrations of radioactive elements. Further, the flowback from the fracturing may be monitored to determine the concentrations of radioactive elements. 
     Other implementations of the present invention may be related to environmental monitoring. The absolute level of elements (or a ratio of elements) within a decay chain may be monitored or the rate of change of an element (or a ratio of elements) within the decay chain. 
     In one implementation, a system is provided for monitoring the unattached fraction, such as either by concentration or by ratio to the attached fraction. In one implementation the system includes a real-time monitoring apparatus and may include a long term monitoring apparatus. The real-time monitoring apparatus provides information on the concentration of the unattached fraction or the ratio of the unattached to the attached fraction. In one implementation, the long term monitoring apparatus provides information regarding one or more of the aerosol level of the environment, and the attached fraction concentration. 
     In one implementation, the real-time monitoring device comprises a collection vessel  200 . One implementation is illustrated in  FIG. 6 . The collection vessel  200  is particle size selective such that larger particles, particularly the attached fraction, are filtered from the small particles, particularly the unattached fraction. The collection vessel  200  includes an inlet  210  that provides an area for particles to enter the vessel  200 . In one embodiment, the inlet  210  is a plurality of holes in a surface of the vessel  200 , such as an inlet plate  211  serving as a top portion of the vessel  200 . One or more filters  220  may be provided to selectively capture particles of a predetermined size. An impactor plate  221  may be included above the scinllation screen  231 . Inlets  210  about the periphery and an impactor plate  221  with a central opening (e.g., approximately ¼ the diameter of the vessel  200 ) function to filter the larger particles which cannot “turn” quickly enough to avoid hitting the impactor plate  221 . The smaller, lighter particles such as unattached  218 Po will be able to transition from the outer periphery at the inlet to the inner portion to pass though the impactor plate. In one implementation, a scintillation screen  231  is included. The scintillation screen  231  is positioned downstream (with respect to the air flow) from the impactor  221  and may be upstream from the filter  220 . The scintillation screen  231  fluoresces when struck by an alpha particle. Very small particles, about 0.5 to 5 nanometers, have a large diffusion coefficient and because they are moving rapidly and they interact with the screen efficiently(only unattached get collected). Larger particles just pass through the screen without interacting. Because only a small percentage of unattached radioactive elements would be other than  218 Po, the scintillation screen  231  can be correlated to unattached  218 Po. In one implementation, the scintillation screen is about 60 to about 400 mesh, i.e., openings per inch. 
     In one implementation, the light pulse generated when an alpha particle from  218 Po hits the screen  231  is channeled via a fiber optic channel to a phototube. In one implementation, the collection vessel includes an outlet  215  to allow the filtered air to pass. An counting/imaging mechanism  240 , such as a phototube, is utilized to capture the fluorescence. The imaging mechanism  240 , in one implementation, includes a phototube and a scaler and software to record counts for remote access etc. The phototube is optically coupled via connector  241 , for example fiber optic cable, to the scintillation screen  231 . Phototubes are the standard to detect the light signal from the/any scintillation phosphor. The phototube turns one light pulse into a voltage pulse and the voltage operates the counting system to measure one count on a scaler. Then digital electronics in the counting/imaging mechanism  240  can integrate the counts for selected time intervals, store them for downloading, be accessed remotely and other marvelous things like, sending the data, graphing on phones or computers remotely. 
     In on implementation, the counting mechanism  240 , is a digital signal sensor, positioned in communication with the phototube. The screen  231  collecting the unattached fraction can, in one implementation, be made of a scintillation material. When unattached  218 Po is deposited on the screen it emits an alpha particle that hits/interacts with the scintillation phosphor and emits a light pulse. As noted above, a fiber optic  241  (one or more) may be connected to a counting mechanism  240 , such as a standard scintillation detector (small phototube), to record each light pulse i.e., a count in a scaler. 
     For example, the imaging mechanism may operate as a counter, recording a “count” each time the scintillation screen fluoresces. It should be appreciated that the scintillation screen may fluoresce in more than one location at the same time and that the system can accommodate that and count each emission as a single count. Each count from the scintillation screen is directly related to the airborne concentration of  218 Po through a calibration factor. The calibration factor can be determined, in one embodiment, from the background level of unattached  218 Po, such as determined in the manner described herein. 
     In one implementation, a solid state sensor may be used for real time monitoring. The solid state sensor gives alpha particle energy as well as the activity in a radioactive source. However. the solid state sensor is positioned to view the screen directly over or under. 
     It is believed that there are significant pressures in the earth near an upcoming seismic event of any kind, including but not limited to fracking The earth has to start moving in some way before internal pressures are great enough to cause actual slippage. This movement may be caused by natural geologic sources or man-made stress sources such as fracking, construction, or significant terraforming of an area such as damning of a waterway. These stresses squeeze radon over and above the normal ground soil diffusion release. 
     In one implementation, the monitoring system is in communication with a control system of associated with a fracking rig. When the monitoring system detects that the likelihood of a seismic event is above a predetermined threshold, the control system can shut down or regulated. The control of the fracking rig or the extraction process may be for preservation, i.e. because a seismic event is predicted the rig is put in a position to minimize damage if a seismic event does occur. For example, once extraction has begun, if a seismic event is predicted, the well head may be capped or additional flare pipes engaged to deal with the impact of a possible seismic event on the well. The control of the fracking rig or extraction process may also be preventative, i.e. the fracking process may be modified to try to reduce the stress on the rock to less the likelihood or severity of a seismic event. For example, as fracking typically utilizes a pressurized liquid, the pressure may be reduced. Further, the size of the proppant used to hold the fracture open may be altered, such as reduced, in response to a predicted seismic event. 
     EXAMPLE 
     Long term particle size distribution measurements were made in two locations: (1) typical New Jersey outdoor air and (2) over a large but contained  226 Ra source at Fernald, Ohio the former uranium processing facility. The measurements show that the unattached fraction of radon decay products can be used as short term tracers of the local radon concentration with unattached fraction over the  226 Ra source a factor of about 8 larger. 
     An integrating miniature particle size sampler (IMP) was developed to determine the long term average particle size distribution for the purpose of calculating accurate exposure assessment for lung and bronchial dose from exposure to radon decay products. 
     Screen arrays are used extensively to collect aerosol particles for aerosol size assessment (Cheng et al.,1992). The equations for penetration efficiency has been determined in many experiments. The IMP (diameter 3.5 cm, height 3.5 cm) has 6 filtration stages, one inlet impactor stage with size cutoff of about 2.5 μm, is followed by 4 fine mesh stainless steel screens and an exit Millipore backup filter to capture all residual particles. Each sampler operates with a low flow Gast pump (4-6 lpm). The IMP sampler can operate for up to 5 months depending upon the airborne aerosol mass. Radon gas exists in all atmospheres producing its alpha particle emitting decay products. The short lived decay products of radon decay to long lived  120 Pb (22 y) and  210 Po (138 d). The  210 Pb on the filtration stages arises either from deposited short lived decay products or  210 Pb sampled from the atmosphere. The  210 Po decay product of  210 Pb is an alpha emitter and all filtration stages are measured directly in the low background (5 counts per day) alpha scintillation counters (Harley et al. 2012) after disassembly from the sampling head. This technique is useful for long term sampling but real time monitoring at short intervals for the unattached  218 Po is best for rapid predictive purposes. 
     The particle size distribution in the IMP is calculated from the measured alpha activity on the  6  filtration stages using a deconvolution program developed by Patti Pentero of the University of Helsinki The  210 Pb/ 210 Po are exquisitely sensitive tracers for atmospheric particles. The integrated aerosol particle size distribution (from 1 to 10,000 nm) and concentration were determined. In the long term  210  Pb/ 210 Po IMP system the measured radioactivity on the 6 filtration stages is subject to computer software (deconvolution program) to obtain the particle size spectrum. 
     In contrast to the setup for the background determinations, in one embodiment the collection vessel  200  relies upon the mesh size of the scintillation screen  231  to “select” for the unattached particles, i.e particles about 0.5 to about 5 nm in size. 
     The average value of the  218 Po attachment rate to aerosol particles was measured as 0.025 sec −1  (El-Hussein 1996). The half-life of an unattached cluster can be estimated as,
 
λ Att =0.025 sec −1 =ln(2)/ T   1/2   ;T   1/2 =27 sec
 
This provides evidence that unattached  218 Po is a short time variation tracer for any radon concentration.
 
     However, the steady state concentration of unattached  218 Po,  214 Pb is mainly dependent on the local aerosol concentration and so can change due to normal aerosol fluctuations (El-Hussein 1996). It can be shown that the steady state fraction of unattached  218 Po,  214 Pb is
 
 f   218 =λ 218 /[β+λ 218 ]
 
and of  214 Pb is
 
 f   214 =λ 214 /[β+λ 214 ]
 
Where, f 218 =ratio of  218 Po (unattached)/ 222 Rn
         N=aerosol particle concentration/cm 3      β=Attachment coefficient for any species, charged or uncharged=[(10 −5 ) (N)]   10 −5  is the attachment rate in cm −3  sec −1      λ 218,214  etc.=decay constant for  218 Po,  214 Pb=0.00379 sec −1 , 0.000418 sec −1  
 
For an aerosol particle concentration of 10 4  particles cm −3  
 
 f   218 =0.00379/[0.1+0.00379]=0.036 or about 4%
       

     If the aerosol concentration were to increase to 2×10 4  particles cm −3  the steady state unattached fraction of  218 Po would be 0.019 or about 2%, a factor of 2 change in unattached concentration. 
     RESULTS 
     The measurements presented are from two sources: 1) outdoor particle size distribution measurements at a New Jersey home and 2) outdoor particle size distribution measurements on top of the 150 TBq  226 Ra storage silos at Fernald, Ohio a former uranium processing facility. 
     The outdoor measurements at the New Jersey home were made from February to May 2005, and the Silo measurements at Fernald were made from July to November 2002. The data in FIGS. 1A-B show that a typical outdoor size distribution has an unattached fraction of the total  210 Pb activity of somewhat less than 2% with median diameter of 2 nm, and median aerosol particle diameter of 400 nm. The average outdoor radon concentration at this site, measured over 6 years, was 11±1 Bq m −3 . The  210 Pb, measured over this 4 month sampling interval was 460 μBq m −3 . 
     The data in  FIGS. 2A-B , show that over a large but contained  226 Ra source (150 Tbq) the unattached fraction of the  210 Pb activity was about 16% with median diameter of 4 nm and median aerosol diameter of 150 nm. The size distribution in the attached peak was much broader over the silo and probably indicates a bi or trimodal distribution in this region because of industrial activity. The radon concentration measured on top of the silos and over the same interval as the particle size sampling was 96±1 Bq m −3 . The  210 Pb measured over this 4 month sampling interval was 760 μBq m −3 . 
     The data suggest that the unattached fraction of the total  210 Pb activity over the silos is due to the measurement of “freshly” exhaled radon with little chance of  210 Pb buildup. Typical outdoor air has a longer time cycle to permit somewhat greater buildup of  210 Pb. This is seen from the  210 Pb ratios (760/460) relative to the radon ratios (96/11). 
     The ratio of unattached over the silo to the unattached outdoor New Jersey (16/2 to 3=8 to 5) is about what is expected from the ratio of the radon concentrations (96/11=8). This implies that the aerosol particle loading of the two locations is probably about the same. 
     In the observed data, there was no pressure squeeze over the  226 Ra silos, just a high release of radon continuously from a large radon source. This is proof of principle that radon release could be tracked by the very short lived  218 Po. Further, it should be appreciated that there are two different measurement situations. The large radon source at the tested silos were emanating radon at a more or less constant rate from a very large  226 Ra source and radon could be tracked by the  218 Po. In contrast, a seismic event requires detecting large transient pulses that could be coming from a large source due to squeezing of a large mass of the earth&#39;s surface. 
     One implementation may utilize a computer system, such as shown in  FIG. 6 , e.g., a computer-accessible medium  620  (e.g., as described herein, a storage device such as a hard disk, floppy disk, memory stick, CD-ROM, RAM, ROM, etc., or a collection thereof) can be provided (e.g., in communication with the processing arrangement  610 ). The computer-accessible medium  620  may be a non-transitory computer-accessible medium. The computer-accessible medium  620  can contain executable instructions  630  thereon. In addition or alternatively, a storage arrangement  640  can be provided separately from the computer-accessible medium  620 , which can provide the instructions to the processing arrangement  610  so as to configure the processing arrangement to execute certain exemplary procedures, processes and methods, as described herein, for example. 
     System  600  may also include a display or output device, an input device such as a keyboard, mouse, touch screen or other input device, and may be connected to additional systems via a logical network. Many of the embodiments described herein may be practiced in a networked environment using logical connections to one or more remote computers having processors. Logical connections may include a local area network (LAN) and a wide area network (WAN) that are presented here by way of example and not limitation. Such networking environments are commonplace in office-wide or enterprise-wide computer networks, intranets and the Internet and may use a wide variety of different communication protocols. Those skilled in the art can appreciate that such network computing environments can typically encompass many types of computer system configurations, including personal computers, hand-held devices, multi-processor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, mainframe computers, and the like. Embodiments of the invention may also be practiced in distributed computing environments where tasks are performed by local and remote processing devices that are linked (either by hardwired links, wireless links, or by a combination of hardwired or wireless links) through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices. 
     Various embodiments are described in the general context of method steps, which may be implemented in one embodiment by a program product including computer-executable instructions, such as program code, executed by computers in networked environments. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps. 
     Software and web implementations of the present invention could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various database searching steps, correlation steps, comparison steps and decision steps. It should also be noted that the words “component” and “module,” as used herein and in the claims, are intended to encompass implementations using one or more lines of software code, and/or hardware implementations, and/or equipment for receiving manual inputs. 
     With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for the sake of clarity. 
     The foregoing description of illustrative embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.