Patent Publication Number: US-2023142667-A1

Title: Personal radiation dosimeter and density meter system and methods of use

Description:
FIELD OF THE INVENTION 
     A handheld portable densitometer utilizing a personal radiation detection dosimeter for the analysis of unknown volumes for unexpected density profiles. 
     BACKGROUND OF THE INVENTION 
     Detection of visually hidden items and radioactive materials presents a challenge that is especially important to law enforcement, boarder control and first responders. For example, in the United States, Customs and Border Protection (CBP), an agency of the Department of Homeland Security (DHS), is responsible for targeting, selecting, and examining cargo deemed high risk for terrorist-related activity, smuggling of contraband, and trade law violation. As well as large stationary devices, such as x-ray imaging systems capable of automatically scanning entire vehicles, and area radiation monitors, smaller portable devices for individual use are included in the enforcement agent&#39;s arsenal. These include radiation dosimeters and density meters. 
     There are several available radiation dosimeters where a first class is referred to as a “passive” dosimeter that is sensitive to ionizing radiation and which records a value of cumulative radiation dose. Passive dosimetry devices, such as for example thermoluminescent dosimeters (“TLD”) are widely used to monitor exposure to radiation. These devices, although useful, are limited in that they do not provide real time feedback to the user, where a reading is provided weeks or months after an actual exposure to ionizing radiation. A second class of dosimeter is referred to as an “active” dosimeter, which may continuously measure radiation and provides a communication reporting the dose value to the user. 
     As referred to herein, active personal dosimeters are denoted Personal Radiation Dosimeters (PRDs). PRDs can also denote Spectroscopic Personal Radiation Dosimeters (SPRD). PRDs that are not SPRDs can detect in real time a dose value but are blind with respect to the kind of radiation. SPRDs not only detect radiation in real time but can also provide spectroscopic information. For example, where a non-spectroscopic PRD may be able to detect gamma-radiation strength, an SPRD can provide information about radiation strength as well as gamma-ray spectroscopic information. The gamma-ray spectroscopic information from an SPRD may be used to provide identification of radionuclides. SPRDs may also be equipped with other detectors, such as neutron detectors. PRDs are known in the art, for example as described in U.S. Pat. Nos. 5,572,027; 6,388,250; 10,782,420; and 10,365, 378, which are incorporated by reference herein in their entirety. 
       FIGS.  1 A and  1 B  illustrate a prior art PRD.  FIG.  1 A  shows a front view of a PRD  100  indicating a view screen  102  and control buttons  104 .  FIG.  1 B  shows a back view of the PRD  100  indicating the location of a detector  106 , and the location of a batteries  108 . Both non-spectroscopic PRDs and SPRDs can have a similar form factor but have different components in their interior (not shown in  FIGS.  1 A,  1 B ). For example, an SPRD can have multiple detectors, additional circuitry, more computer processing power, and different algorithms required for spectroscopic analysis. This can also translate to a larger size and weight for SPRDs, as well as a different user interface to activate additional/different features. Some other features (not shown of PRDs can include clips or straps for attachment to a belt or directly to a user (e.g., an arm) and the PRD can come equipped with a carry holster. The user can passively wear the device, for example, as the user inspects cargo, or the user can more actively hold the device towards an area of interest, either directly, or even with an extension arm or flexible tether. The devices can also be wirelessly (e.g., WiFi, BlueTooth, ZigBee) and GPS enabled for central tracking and monitoring. 
     As used herein, “density meters” or “densitometers” refer to portable devices for scanning a volume and detecting hidden or obscured objects in the volume. Density meters use low intensity gamma sources combined with a radiation detection system.  FIG.  2    shows a diagrammatic view of a prior art density meter  200 . The density meter  200  includes a gamma source  202  and detector  204 . The device is positioned against a surface  206  to allow gamma rays  208  to penetrate through barrier  210 , and the level of backscattered radiation  212  detected by detector  204  is measured. The measured backscattered radiation  212  is proportional to the density of the volume  214  behind the surface  206 . This value is compared to expected density ranges for the volume  214  to give an indication of possible material  216  hidden in the volume  214 , such as in a cavity. This technology is used extensively in border patrol type activities and checkpoint inspections. For example, this technology is used by border patrol to examine containers and vehicles for smuggled goods at security checkpoints. Vehicle doors panels, seat cushions, tires, packaged items and goods (coffee bags, stuffed toys, cereal boxes, etc.) can be checked for contraband, money, guns, and drugs. 
     The gamma radiation selected for use in densitometers is highly scattered by light elements (e.g., H, O, C, and N). This makes the detection of these elements possible by the backscattered radiation, where the same radiation is absorbed by heavier elements (e.g., Fe). Typically, radiation is selected for penetration through several millimeters of steel. The advent of a high backscatter from behind a steel surface can be indicative of materials, such as drugs, money, or other contraband. 
     While there are the above identified portable solution for monitoring radiation and concealed items, these often require two separated devices. Considering many other items strapped or worn by the user, such as armor, a side arm, chemical analyzers, communication devices etc., there is a need in the art for solutions that consolidate, modularize and reduce the footprint and weight of these items, both for reasons of convenience, comfort, and cost. In addition to being functional, the devices should be rugged and easy to use in difficult to reach areas. 
     SUMMARY 
     In accordance with a first aspect, a personal radiation and density meter (PRDM) system includes a housing, a radiation detection subsystem and a radiation emitting sub-system. The housing includes an interior portion configured as an interior space, and a slot. The radiation detection sub-system includes a personal radiation dosimeter (PRD) positioned in the slot. The radiation emitting sub-system includes a shield assembly, a source, an actuator, a trigger, and an aperture. The shield assembly is in the interior portion and surrounds a radiation source. The actuator is also in the interior portion and is coupled to the shield assembly, where the actuator is configured under user-initiated control to move the shield assembly from a shielding configuration to an exposure configuration. The trigger is mounted to the housing and coupled to the actuator for one-hand control of the actuator. The aperture is defined through a wall of the shield assembly and configured to direct radiation out of the shield assembly when the shield assembly is in the exposure configuration. 
     In accordance with a second aspect, a method for probing a density is provided, the method including holding the PRDM system and positioning the aperture opposite to a first area of a surface bounding a volume to be probed; engaging the trigger to move the shield assembly from the shielding configuration to the exposure configuration; acquiring first measurements with the PRD from backscattered radiation from the radiation source, said first measurements indicative of a first density in the volume; moving the system to a second area of the surface and acquiring second measurements with the PRD from backscattered radiation from the radiation source, said second measurements indicative of a second density in the volume; and disengaging the trigger and allowing the shield assembly to return to the shielding configuration. 
     According to a third aspect, a personal emission device for converting a dosimeter to a density meter includes; a housing, a radiation source, a shield assembly, an actuator, a trigger, an aperture, and a slot. The housing includes an interior portion defining an interior space. The radiation source is in the interior portion, where the shield assembly is in the interior portion and surrounds the source. The actuator is also in the interior portion and is coupled to the shield assembly, the actuator is configured under user control to move the shield assembly from a shielding configuration to an exposure configuration. The trigger is mounted to the housing and coupled to the actuator for one-hand control of the actuator. The aperture is defined through a wall of the shield assembly and is configured to direct radiation out of the shield assembly when the shield assembly is in the exposure configuration. The slot is configured for removable placement of a PRD. 
     The PRDM systems described combined PRD with a source in a housing, where the PRD provides detection of scattered radiation derived from the source. This is economical both with respect to space and monetary resources, since a single PRD can be coupled with the source without need of a separate density meter. Furthermore, the system is designed for ease of positioning of the PRD in the slot, so that conversion from a dosimeter to a density meter is efficient. The PRDM systems are also designed for ruggedness and ease of use, such as single handed/ambidextrous use. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and advantages of the present embodiments will be more fully understood from the following detailed description of illustrative embodiments taken in conjunction with the accompanying drawings 
         FIG.  1 A  is a front view of a PRD. 
         FIG.  1 B  is a back view of the PRD shown in  FIG.  1 A . 
         FIG.  2    is a diagrammatic view illustrating a typical usage of a density meter. 
         FIG.  3    is a block diagram illustrating various components of a personal radiation and density meter (PRDM) system, according to some implementations. 
         FIGS.  4 A- 4 D  and illustrate some externally visible features of a PRDM system, according to some implementations.  FIG.  4 A  shows an isometric view,  FIG.  4 B  shows a front view, and  FIG.  4 C  shows a back view.  FIG.  4 D  shows three views (panels I, II and III) of a switch. 
         FIG.  5 A  shows a blown-up 3D view of the PRDM system depicted in  FIGS.  4 A- 4 D .  FIG.  5 B  shows an 3D view of a boot for the PRDM, according to some implementations. 
         FIGS.  6 A- 6 B , show details of the interior portions of the PRDM system, according to some implementations.  FIG.  6 A  shows a front view of the PRDM system, where a housing cover  602  is shown removed to reveal the interior elements.  FIG.  6 B  show an isometric view of interior components. 
         FIGS.  7 A- 7 E  show views of the shield assembly, according to some implementations.  FIG.  7 A  shows a shielding configuration in isometric view and  FIG.  7 B  shows an exposure configuration in isometric view.  FIG.  7 C  shows an isometric view of a wall of the shield assembly and relative positioning of a PRD.  FIG.  7 D  shows a 3D view of the wall oriented to view the back of the wall.  FIG.  7 E  shows a bottom view of a container for holding a source. 
         FIGS.  8 A- 8 D  show additional views of the shield assembly.  FIG.  8 A  shows a front view of the shield assembly in the shielding configuration.  FIG.  8 B  shows a back view of the shield assembly in the shielding configuration.  FIG.  8 C  shows a front view of the shield assembly in the exposure configuration.  FIG.  8 D  shows a back view of the shield assembly in the exposure configuration. 
         FIG.  9 A- 9 H  show additional details of interior components of the PRDM system, according to some implementations.  FIG.  9 A  shows a front view.  FIG.  9 B  shows an isometric view.  FIG.  9 C  is a detailed right-side view.  FIG.  9 D  is another detailed right-side view.  FIG.  9 E  is a detailed top view.  FIG.  9 F  is detailed right-side view.  FIG.  9 G  is another detailed right-side view.  FIG.  9 H  is a detailed left-side view. 
         FIG.  10    is a flow diagram showing steps for using a PRDM system, according to some implementations. 
         FIGS.  11 A and  11 B  show cartesian coordinates for a PRDM system shielding, according to some implementations.  FIG.  11 A  is a front view while  FIG.  11 B  is a right-side view. 
         FIGS.  12 A- 12 E  are radial plots showing dose rates from a PRDM system, according to some implementations.  FIG.  12 A  shows emission dose rate around the y-axis with the shutter closed.  FIG.  12 B  shows emission dose rate around the x-axis with the shutter open.  FIG.  12 C  shows emission dose rate around the x-axis with the shutter closed.  FIG.  12 D . shows emission dose rate around the z-axis with the shutter open.  FIG.  12 E  shows emission dose rate around the z-axis with the shutter closed. 
     
    
    
     The figures referred to above are not drawn necessarily to scale, should be understood to provide a representation of particular embodiments, and are merely conceptual in nature and illustrative of the principals involved. Some features of the radiation detector depicted in the drawings have been enlarged or distorted relative to others to facilitate explanation and understanding. The same reference numbers are used in the drawings for similar or identical components and features shown in various alternative embodiments. Radiation detectors, sources and density meters as disclosed herein would have configurations and components determined, in part, by the intended application and environment in which they are used. 
     Where cartesian coordinates (X, Y, Z) are indicated, the arrows show the positive directions, “O” indicates an arrow pointing outwards and perpendicular to the page, “X” indicates an arrow pointing inward and perpendicular to the page. These provide guidance for orientation and relationships of various components and do not denote a magnitude. Also, as used herein, a front view is viewing in the −Y direction, the back view is viewing in the +Y direction, a right-side view is viewing in the −X direction, a left-side view is viewing in the X direction, a top view is viewing in the −Z direction, and a bottom view is viewing in the +Z direction. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In the description of the invention herein, it is understood that a word appearing in the singular encompasses its plural counterpart, and a word appearing in the plural encompasses its singular counterpart, unless implicitly or explicitly understood or stated otherwise. Furthermore, it is understood that for any given component or embodiment described herein, any of the possible candidates or alternatives listed for that component may generally be used individually or in combination with one another, unless implicitly or explicitly understood or stated otherwise. Moreover, it is to be appreciated that the figures, as shown herein, are not necessarily drawn to scale, wherein some of the elements may be drawn merely for clarity of the invention. Also, reference numerals may be repeated among the various figures to show corresponding or analogous elements. Additionally, it will be understood that any list of such candidates or alternatives is merely illustrative, not limiting, unless implicitly or explicitly understood or stated otherwise. In addition, unless otherwise indicated, numbers expressing quantities of ingredients, constituents, reaction conditions and so forth used in the specification and claims are to be understood as being modified by the term “about.” 
     Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the subject matter presented herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the subject matter presented herein are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical values, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. 
       FIG.  3    is a block diagram showing an implementation of a personal radiation and density meter (PRDM) system  300 . The PRDM system  300  includes a housing  302 , a radiation emitting sub-system  304 , and a radiation detection sub-system  306 . 
     The housing  302  can be designed for compactness, ruggedness, and ergonomic use. For example, the housing is dimensioned to be handheld, such as to be used single handedly and ambidextrously by a typical adult user (female or male). Materials for construction can be selected to be durable, light weight, and rigid. Without limitations, materials selected for the housing can include engineering plastics and light or thin metals. For example, the materials used for housing  302  are chosen so that the various components do not move, except as indicated herein, relative to each other. For example, relative movement of the source  322  in the exposure configuration  326  to the PRD  100  in slot  310 , is less than 1 mm under handling conditions. Other features of the housing  302 , such as hooks, grips, fasteners, straps and combinations thereof, can be included for convenience, safety and ergonomic needs. 
     The housing  302  integrates the various components into the PRDM system  300 . The radiation emitting sub-system  304  includes an interior portion  312  in the housing  302  and a trigger  318  mounted to the housing  302 . The interior portion  312  is configured as an interior space in the housing  302  and includes a shield assembly  314  and an actuator  316 . The shield assembly  314  surrounds or encloses a radiation source  322 . The trigger  318  is coupled to the actuator  316 . The shield assembly  314  includes a wall  328  which includes an aperture  320  therethrough. The radiation detection sub-system includes a slot  310  in the housing. The slot  310  is configured for placement or positioning of the PRD  100  therein. 
     The shield assembly  314  includes a shielding configuration  324  wherein the radiation source  322  is completely or maximally enclosed. The purpose of the shielding configuration  324  is to limit or eliminate radiation escaping from the radiation source  322  to the environment. In the shielding configuration  324 , the PRDM system  300  cannot be used for density measurement since no or insufficient radiation is emitted from the radiation source  322  for any measurable backscatter to be produced. The shield assembly  314  also includes an exposure configuration  326 . In the exposure configuration  326 , the radiation source  322  can emit radiation out of the shield assembly  314  through the aperture  320 , which is defined in a wall  328  of the shield assembly  314 . In the exposure configuration, the PRDM system  300  can be used for density measurements. 
     The radiation source  322  can include a gamma emitting element. For example, the radiation source can be selected to include Ba-133, Be-7, Na-22, Na-24, Mn-54, Co-57, Co-60, Ga-66, Tc-99m, Pd-103, Ag-112, Sn-113, Te-132, 1-125, 1-131, Xe-133, Cs-134, Cs-134, Cs-137, Ba-133, La-140, Ce-144, Eu-152, Yb-169, Ir-192, Au-198, Bi-207, Rn-222, Ra-226, Th-228, Am-241, Cf-252, Fm-252, or Lu-176. In some implementations, the radiation source  322  is a source determined by the US Nuclear Regulatory Commission to be exempt from requirements for a license, as listed at www.nrc.gov/reading-rm/doc-collections/cfr/part030/part030-0071.html, accessed Sep. 27, 2021, and incorporated by reference herein in its entirety. In some implementations, the gamma source includes Ba-133. 
     The shield assembly  314  can include elements with high Z number which will absorb radiation. For example, in some implementations, the elements tungsten, lead, iron, and alloys thereof can be included in the shield assembly  314 . In some implementations, the shielding material includes at least about 50% (e.g., at least about 60%, 70%, 80%, 90% or 99%) tungsten and a thickness of at least about 1 mm (e.g., at least about 2 mm, 3 mm, 4 mm or 5 mm). In some implementations, the tungsten thickness is between about 1 mm and about 100 mm (e.g., between about 5 mm and about 60 mm). In some implementations, a workable tungsten alloy having about 80% tungsten is used in the shielding assembly with a thickness between about 1 and about 100 mm (e.g., between about 5 mm and about 60 mm) is used. It is understood that the shielding requirements depend on the type and amount of radiation source  322 . For example, in implementations using a 370 kBq, 10 μCi Ba-133 gamma source, the radiation at 45 cm is at least about 85% attenuated by a titanium wall of thickness of at least about 10 mm. In some implementations, shielding reduces radiation emitted from the source in any direction at least by about 50% (e.g., at least about 60%, 70%, 80%, 90% or 99%). 
     The shield assembly  314  can include a shutter to cover the aperture  320  when the shield assembly  314  is in the shielding configuration  324 . For example, the shutter can include a wall, leaf, screen or other barrier that moves (e.g., linearly, curvilinearly) in front of, or into the aperture  320 , thereby sealing/covering the aperture  320 . The shutter can also move to a position not sealing/covering the aperture  320  when the shield assembly  314  is in the exposure configuration  326 . In some implementations, the shield assembly  314  can move the aperture away from the radiation source  322 , where a solid part of wall  328  or another portion of the shield assembly  314  is positioned in front of the radiation source  322 . 
     The actuator  316  is any device that can toggle the components of the shield assembly  314  from the shielding configuration  324  to the exposure configuration  326 , and from the exposure configuration  326  back to the shielding configuration  324 . Without limitation, and by way of example, the actuator  316  can include gears, cogs, springs, rails, slots, pins, pulleys, levers, chains, belts, wheels, and combinations thereof. The actuator  316  is controlled by the trigger  318 , which can be engaged by one-hand of a user to toggle between the shielding configuration  324  and the exposure configuration  326 . The actuator  316  can translate a first movement vector of the trigger  318  to a second movement vector required to change the shielding configuration. For example, in one implementation, the trigger  318  can be a button, wherein when the button is pressed it moves in a first direction and a first distance, the actuator  316  translating this first movement and first distance, to a second movement and second distance. Without limitation, the trigger  318  can include a button, a lever, a switch, a pull cord, or a knob. 
     Three views of an embodiment of the PRDM system  300  are shown by  FIGS.  4 A- 4 C  and illustrate some externally visible features.  FIG.  4 A  shows an isometric view,  FIG.  4 B  shows a front view, and  FIG.  4 C  shows a back view. The PRD  100  is shown in the slot  310  of the housing  302  ( FIGS.  4 A,  4 B ). The trigger  318  is shown mounted to a left side of the housing  302  ( FIGS.  4 B,  4 C ). 
     The position of the aperture  320  is shown ( FIG.  4 C ). In this embodiment, the aperture  320  is covered by a radiation transparent window  402 , such as a mylar window ( FIG.  4 C ). In some other embodiments, other radiation transparent materials can be used, including thin metal foils (e.g., Titanium and Aluminum) or thin plastic films. Although optional, the radiation transparent window  402  protects the interior portion  312  of the PRDM system  300  from contamination from environmental contaminants such as water, dirt, and dust. As used herein “radiation transparent” refers to material that allow radiation emitted from the radiation source  322  to pass therethrough. For example, at least 50% (e.g. at least 60%, 70%, 80%, 90%, 99%) of the radiation is not scattered, reflected or absorbed by the radiation transparent window. On a front side  414 , a viewing window  404  can be included in the housing  302  ( FIGS.  4 A,  4 B ). The viewing window  404  provides a view to the interior portion  312  of the housing  302 . 
       FIG.  4 C  shows the positioning of a detector  412  of the PRD  100 . The detector  412  is positioned on a back-side  416  of the housing  302 . The detector  412  is positioned to detect backscattered radiation traveling in a general direction towards the back  416  of the housing  302  and the detector  412 . As used herein “detector” can refer to multiple detectors. For example, in embodiments when the PRD is an SPRD, several detectors can be used to detect different energy and types of radiation. The detector  412  can be any radiation detector such as PIN detectors and scintillation counters. In some implementations, the detector is a silicon photomultiplier (SiPM) detector. 
       FIGS.  4 A- 4 C  also show a safety latch  406  mounted to the right side of the housing  302 . The safety latch  406  is configured to bloc movement of the shield assembly  314  from the shielding configuration  324  and avoids unintentionally engaging the exposure configuration  326 . 
     In some implementations, the back-side  416  includes a low friction surface  417 , shown in  FIG.  4 C  as partially covering the back-side  416 . It is understood that part or the entire back-side  416  can include the low friction surface  417 . The low friction surface  417  is selected to allow the surface of the back-side  416  to easily slide across a surface of an object being inspected while also not damaging the surface (e.g., non-scratching). The material allows for a user to slide the PRDM system  300  against a surface at a constant rate, without sticking/stopping. For example, a low friction surface  417  can include woven and non-woven fabrics with an adhesive that is applied to the back-side  416  so that the fabric forms an outer surface covering at least a portion of the back-side  416 . Some non-limiting low friction surfaces  417  include felt and the loop side of hook and loop materials. In some implementations, the materials used for low friction surface  417  are low wetting materials so that they do not absorb and retain water and dirt. Generally, rubber is not used as a low friction surface since such materials can make it hard to slide the PRDM system  300  against a surface at a constant rate. In some implementations, the back-side  416  also protrudes out (in the +Y) direction along a lip  419 , with a uniform distance of protrusion. In some implementations this protrusion of back-side  416  is between about 1 mm and about 5 mm. 
     The slot  310  includes a front-facing opening  408 , which provides access to an operator interface  410 ,  410 ′ of the PRD  100  ( FIG.  4 A,  4 B ). In this embodiment, the operator interface includes a view screen  410  and control buttons  410 ′. Access to the PRD  100  is also available through a bottom wall  418  of the housing  302 , which includes a bottom opening  420 , which is shown covered by a door  422 . In some implementations, the bottom opening  420  includes a latching mechanism for securing the PRD  100  in the slot  310 . In the shown embodiment, the latching mechanism is configured as a latch or a bar  424  that mates with door hooks  426 . In some implementations, the front-facing opening  408  includes a transparent cover, such as a flexible transparent cover that allows access to the operator interface  410 ,  410 ′. 
     In some implementation, the trigger  318  partially enters the interior portion  312  ( FIG.  3   ) through a trigger opening  430  as illustrated by  FIG.  4 D .  FIG.  4 D  shows detailed views of the trigger  318 : the left panel (I) shows the trigger in a resting position (e.g., not engaged by a user), center panel (II) shows the trigger in an activated position (e.g., engaged by a user), and the right panel (III) shows the trigger in a blown-up configuration. The trigger opening  430  is defined in a trigger mount  432 , which is used to couple the trigger  318  to the housing  302  ( FIG.  4 B ). The trigger mount  432  also defines an interior sub-portion  434 , which comprises a part of the interior portion  312 . The trigger opening  430  can include a flexible interface which contacts sides  436  of the trigger  318 . For example, the flexible interface can be a gasket placed at the trigger opening  430 . The flexible interface maintains a seal to the interior portion  312  and provides a wiping action against the sides  436  of the trigger  318  when the trigger  318  moves into the interior portion  312  (i.e., the interior sub-portion  434 ). This helps mitigate against unwanted materials such as water, dust, dirt, and grease entering the interior portion  312 . 
       FIG.  5 A  shows a blown-up 3D view of the embodiments depicted in  FIGS.  4 A- 4 C  to illustrate the placement of the PRD  100  into the slot  310  of the housing  302  through the bottom opening  420 . The latch  424  pivotally couples to the door  422  by female/male features  528 / 530 . The latch  424  rotates into position engaging the door hooks  426  to secure the door  422  to the bottom wall  418 , covering the bottom opening  420 . This provides a secure coupling of the PRD  100  into the housing  302 , which assures the detector  412  ( FIG.  4 C ) of the PRD  100  is always positioned in about the same place relative to the radiation source  322  ( FIG.  4 C ). This also allows easy removal of the PRD  100  from the housing  302  as may be required, for example, for maintenance (e.g., battery replacement, cleaning, charging, shipping, replacement or upgrading to a new or different PRD), or for use as a standalone PRD. Similarly, the housing  302  can be separately isolated this way from the PRD  100  as needed (e.g., as a radiation source). 
     In some implementations, the PRDM system  300  ( FIG.  4 A ) includes a boot  500  as shown in  FIG.  5 B . The boot  500  can be made using shock absorbing materials. Without limitation, and by way of example, these shock absorbing materials can include silicone, rubber, leather, plastics (e.g., polyurethane, polycarbonate), thin metals (e.g., titanium, aluminum), fabrics, and combinations of these. The construction of the boot  500  is configured to allow stretching and a snug fit against the housing  302  ( FIG.  5 A ). The boot  500  can also include features such as additional material or bumpers at corners, which may be rounded. In some implementations, top portion  502  of the boot  500  incudes additional material since the PRDM system  300  tends to be top heavy and in a fall top portion  502  is most likely to first contact the floor. For example, in some implementations, the top portion  502  has thicker walls than at other positions of the boot  500 . In addition to shock, the boot  500  can provide anti-scratch and additional environment protection to the PRDM system. 
     The boot  500  includes cutouts such as placement cutout  504  for removable placement of the housing  302  ( FIG.  5 A ) into the boot  500 . Once the PRD  100  is placed in the boot  500 , the cutouts allow access to various components. A PRD cutout  506  is aligned to front-facing opening  408  ( FIG.  4 A ). A trigger cutout  508  provides user access to the trigger  318 , and on the opposite side a safety latch cutout  510  provides user access to the safety latch  406  ( FIGS.  4 A- 4 C ). A front cutout  512  is provided for viewing the front side  414  ( FIG.  4 A ). The back-side of the boot  500  is open, including the back cutout  514 , so that the radiation source  322  and the detector  412  ( FIG.  4 C ) do not have additional material to penetrate through. In some implementations, the lip  419  ( FIG.  4 C ) aligns with the back cutout  514 , and the back-side protrudes out of the housing  302  so that the back-side  416  of the housing  302  is approximately co-planar with the back surface of the boot. This allows the low friction surface  417  to be contacted with a surface of a volume to be probed and allows the radiation source  322  and the detector  412  to be positioned as close as possible to the surface of the volume to be probed. 
     Details of externally visible elements of an embodiment of the PRDM system  300  have been described above. The forgoing  FIGS.  6 A- 9 H , will described details of the interior portions of the PRDM system  300 . 
       FIG.  6 A  shows a front view of the PRDM system  300 , where a housing cover  602  is shown removed to reveal the interior elements. Placement of the housing cover  602  against the front of walls  604  provides an interior space. The interior portion  312  is highlighted by a dotted line. The position of the interior sub-portion  434  is also indicated, as is the PRD  100  in the slot  310 . In some implementations, access to the interior portion is restricted, for example by fasteners placed through holes  606  and  608 , which couple the walls  604  to the housing top cover. Other fastening means can be used such as snap fittings, clamps, straps, adhesives and compression fittings. In some implementations, a gasket commensurate with the front of walls  604  is included. The gasket helps seal the interior portion  312  from the outside environment. 
       FIG.  6 B  is an isometric view of components in the interior portion  312 . The shield assembly  314  and the actuator  316  are mounted to a base  610 . The base can be made using any rigid material. In some implementations, the base includes aluminum, titanium, steel, a thermoset, or a thermoplastic. In some implementations, the base is an aluminum alloy. The base is fastened to the housing by any useful means. 
       FIGS.  7 A and  7 B  show isometric views of the shield assembly  314 . Relative positioning of the PRD  100  in the slot  310  are also shown. The slot  310  and the PRD  100  are not shown to scale relative to the shield assembly  314  in these figures, nor are they rendered in 3D: rather, the slot  310  and the PRD  100  are depicted to show the approximate relative positioning with respect to the shield assembly  314 .  FIG.  7 A  shows the shielding configuration  324 , and  FIG.  7 B  shows the exposure configuration  326 . 
     The shield assembly  314  includes a container  702  mounted on rail  704 . The radiation source  322  (not seen) is positioned in the container  702 . The container  702  moves along the rail  704  to toggle between the shielding configuration  324 , and the exposure configuration  326 . As illustrated by  FIGS.  7 A and  7 B , two rails are used in this embodiment. The aperture  320 , included in wall  328 , is shown in  FIG.  7 A . The rail  704  and the wall  328  are fastened to the base  610 . For example, using fasteners such as  706 . 
     As illustrated in  FIG.  7 A , in the shielding configuration  324 , the container  702  is distal to the slot  310 . Conversely, as illustrated in  FIG.  7 B , in the exposure configuration  326 , the container  702  is proximate to the slot  310 . This design helps to minimizes escaping radiation from the source  322  which can raise the background noise created from direct irradiation from the radiation source  322  to the detector  412  in the PRD  100  (i.e., direct irradiation of PRD  100  is less in the shielding configuration as compared to the exposure configuration). 
       FIG.  7 C  shows an isometric view of the wall  328  and relative positioning of the PRD  100  in the slot  310 . As in  FIGS.  7 A and  7 B , the PRD  100  and the slot  310  are not shown to scale or in 3D and are included to illustrate the general orientation and relative position to the wall  328 . The wall  328  includes a large protrusion  710  and a small protrusion  712 , both of which provide shielding, in addition to the container  702 , for the radiation source  322 . The protrusion  710  is larger or thicker than the protrusion  712 . This design provides a higher shielding towards the bottom, where the PRD  100  is positioned when it is in the slot  310 , and helps to further minimize signal noise created from irradiation from the radiation source  322  to the detector  412  in the PRD  100 . The aperture  320  is shown and has a boundary  722  on a front surface  714  of the wall  328 . 
       FIG.  7 D  shows a 3D view of the wall  328  oriented to view the back of the wall  328 . The aperture  320  is cone shaped through the wall  328 . That is, a boundary  718 , which is on a back surface  720  of the wall  328 , is larger than the boundary  722 . The aperture  320  is a collimator and serves to collimate radiation emitted from the radiation source  322 . 
       FIG.  7 E  is a bottom view of the container  702  and rails  704 . In some implementations, the container  702  is assembled from at least a front part  703  and a back part  705 . These are nested together such that they are join at a stepped interface, shown in the dashed circle  707 . This nesting reduces radiation leaking out of the container, as compared to a coupling that is not stepped. 
       FIGS.  8 A- 8 D  show additional views of the shield assembly  314 .  FIG.  8 A  shows a top view of the shield assembly  314  in the shielding configuration  324 .  FIG.  8 B  shows a back view of the shield assembly  314  in the shielding configuration  324 .  FIG.  8 C  shows a top view of the shield assembly  314  in the exposure configuration  326 .  FIG.  8 D  shows a back view of the shield assembly  314  in the exposure configuration  326 . The radiation source  322  is positioned in the container  702  which moves along the rail  704  to toggle between configurations. 
     The wall  328  is shown in  FIGS.  8 B and  8 D  as transparent with boundaries as dashed lines so that the features of the container  702  can be viewed through wall  328 . A solid portion  802  of wall  328  is indicated. The radiation source  322  is shown in the container  702 . An opening  804  in the container  702  is positioned above the radiation source  322 . In the shielding configuration  324 , the solid portion  802  of the wall  328  covers the opening  804 . In the exposure configuration  326  the opening  804  is at least partially aligned with the aperture  320 . The position of the radiation source  322  and the opening  804  is shown in dashed outline in  FIGS.  8 A and  8 C . 
       FIGS.  9 A and  9 B  show additional features of the interior portion  312 .  FIG.  9 A  is a top view and  FIG.  9 B  is an isometric view in the shielding configuration  324  ( FIG.  8 A ). An indicator  902 , a tensioner  904 , a tensioner  904 ′, a switch activator  906 , the safety latch  406 , the shield assembly  314 , and components of the actuator  316  are shown. The position of the PRD  100  when it is in slot  310  ( FIG.  6 A ) is also indicated, as well as a switch  908  in the PRD  100 . 
     The shield assembly  314  is coupled to the PRD  100  by the switch  908  which is positioned in the PRD  100 . In some implementations, the switch  908  is mounted to an outer surface of the PRD  100 . The switch activator  906  is connected to the shield assembly at a shield rack  910 . The shield rack is attached to the container  702 , for example by fasteners  911 . The switch activator  906  is far from the switch  908  when the shield assembly  314  is in the shielding configuration  324 , as shown in  FIGS.  9 A and  9 B . When the shielding configuration  314  is in the exposure configuration ( FIG.  8 B ) the switch activator  906  is brought closer to the PRD  100 , which activates the switch  908 . 
     In the embodiment shown by  FIG.  9 A , the switch activator  906  is a magnet mechanically coupled to the container  702  and the switch  908  is a reed switch. The magnet is brought into proximity to the reed switch in the exposure configuration  326 , thereby activating the reed switch. Other switches are contemplated requiring some minor modification. For example, a Near Field Communication device can be used where the switch activator  906  is configured as a read only tag and the switch  908  includes reading circuitry to recognize the read only tag. In another embodiment, the switch  906  can be configured as a mechanical switch, for example mounted to the PRD  100 . The switch activator  906  can be configured as an arm or the like to physically activate the mechanical switch. 
     The switch  908  is connected to a computer  912  including at least a CPU, a volatile memory, and a nonvolatile memory for executing algorithms written to the nonvolatile memory. The CPU also includes connections to various components of the PRD  100  such as the operator interfaces  410  and  410 ′ and the detector  412  ( FIG.  4 A- 4 C ). The computer  912  is also connected to a power source, such as batteries in the PRD  100 . Other components, such as transmitters and receivers for wireless communication can be included in the PRD  100  which are connected to the computer  912 . 
     The computer  912 , by executing various commands of the algorithms, can collect data from the detector  412  of the PRD  100 , display data on the operator interface  410 , and can accept inputs from the operator interface  410 ′ ( FIGS.  4 A- 4 C ). In addition, the computer  912  includes at least a dose monitoring algorithm and a density monitoring algorithm. The switch  908  engages the dose monitoring algorithm of the PRD  100  when the shield assembly  314  is in the shielding configuration  324  and engages the density detection algorithm of the PRD  100  when the shield assembly  314  is in the exposure configuration  326 . 
     The shield assembly  314  is coupled to an alert. The alert is configured to alert the user when the shield assembly  314  is in the exposure configuration  326 . In the embodiment shown by  FIGS.  9 A and  9 B , the alert is a visible indicium provided by the indicator  902 . The container  702  is coupled to the shield rack  910 . The shield rack  910  includes the indicator  902  on an outer surface  4 . The outer surface  4  is approximately opposite the opening  804  ( FIG.  8 B ). As previously described, the housing  302  includes the viewing window  404  ( FIG.  4 A,  4 B ). The position of the viewing window  404  is shown in  FIGS.  9 A and  9 B , where the housing supporting the window is not shown so that the interior portion  312  can be seen. The viewing window  404  is positioned facing the outer surface  4 . The indicator  902  moves to a position framed by the viewing window  404  and provides a view of the indicator  902  to the user when the shield assembly  314  is in the exposure configuration  326 . In some implementations, the shield rack  910  includes a second indicator on the outer surface  4 , where the second indicator moves to a position framed by the viewing window  404  and provides a view of the second indicator to the user when the shield assembly  314  is in the shielding configuration  324 . Thus, the visible indicium comprises the indicator  902  moving into, and out of, a position framed by the viewing window  404 . 
     In some implementations, the alert can be an audible indicator. For example, the alarm can be a speaker of the PRD  100  which is coupled to the computer  912  and is activated by the switch  908 . In some other implementations, the alert can be a light indicator, such as an LED light of the PRD  100  coupled to the computer  912  and the switch  908 . In yet other implementations, the alert can be a bell which is coupled to the housing  302  or the PRD  100  and is struck by a striker attached to the shield rack  910 . 
     In some implementations, the interior portion  312  is coupled to the safety latch  406 . As shown in  FIGS.  9 A and  9 B , in the shielding configuration  324 , a stop  930  contacts a pin  932  and does not allow movement of the container  702  from the shielding configuration  324  to the exposure configuration  326 . The pin  932  is coupled to the container  702  by a ledge  934  which is part of the shield rack  910 .  FIG.  9 C  is a detailed side view of the safety latch  406  in an engaged position, and  FIG.  9 D  is a detailed side view showing the safety latch  406  when it is not engaged.  FIG.  9 E  is a top detailed view showing another embodiment of the ledge  934 . 
     In some implementations, the shield assembly  314  is coupled to the tensioner  904  and the tensioner  904 ′ ( FIGS.  9 A, 9 B ), which provide tension holding the shield assembly in the shielding configuration. The tensioner  904 ′ is a first spring which keeps the actuator  316  in the shielding configuration  324  and will be described in more detail below. As shown in detailed right view  FIG.  9 F , the tensioner  904  is a second spring that is attached at a first end to the rail  704  by a pin  918 , and the second spring is attached at a second end to the container  702  through a pin  920  which protruded out of the rail  704  through slot  922 . The second spring keeps, returns or pulls the container  702  to shielding configuration  324  as shown, when the trigger  318  is not engaged by the user. In some implementations, additional tensioners can be added, for example, to balance the forces acting on container  702 . For example, part of the tensioner  904 ″ is seen at the top left of  FIG.  9 A  which provides a balancing force to the tensioner  904 . In some implementations, one or more tensioners  904  and  904 ′ can be an elastic material or gas filled piston. In some other implementations, only one tensioner, such as tensioner  904  or  904 ′, is used. 
     As shown in  FIG.  9 A , the actuator  316  includes several sub-components: a first lever  940 , a second lever  942 , an arm  944 , a first rack  946 , a second rack  948 , a large gear  950 , and a small gear  952  (under and obscured by the larger gear, shown in  FIG.  9 H ). 
       FIG.  9 G  shows a 3D detailed view from the right-side of part of the actuator  316 . The first lever  940  is pivotally connected at a first end of the first lever  940 ′ to the base  610 , which is connected to the housing  302  ( FIG.  5 A ). A second end of the first lever  940 ″ is pivotally connected to a fulcrum  956 . The second lever  942  is pivotally connected at a first end of the second lever  942 ′ to the fulcrum  956 . A second end of the second lever  942 ″ is pivotally connected to a first end of the arm  944 ′. 
       FIG.  9 H  shows a left-side detailed view of part of the actuator  316 . The first rack  946  is connected to a second end of the arm  944 ″. The small gear  952  is connected to the first rack  946 . The small gear  952  is connected to the large gear  950  by an axel  958 . The large gear  950  is connected to the second rack  948 . The second rack  948  is connected to the shield rack  910 , which is connected to the container  702 . 
     The actuator  316  is activated by depressing the fulcrum  956  as shown by trigger vector  960 , moving the arm  944  in the direction of an arm vector  962  ( FIG.  9 A ). By virtue of the coupling through the first rack  946 , the small gear  952 , the axel  958 , the large gear  950 , and the second rack  948 ; the shield rack  910  moves in the direction of a container vector  964 . Due to the different gear sizes, small gear  952  and the large gear  950 , the magnitude of the container vector  964  (a second direction and magnitude) is larger than the magnitude of trigger vector  960  (a first direction and magnitude) and the arm vector  962 . The difference in magnitude can be adjusted by changing the gear  952  to the gear  950  size ratio, as well as lengths of the first lever  940  and the second lever  942 . The trigger  318  ( FIG.  4 B ) is positioned to provide the trigger vector  960  when depressed by a user. 
     The tensioner  904 ′ is a spring which is compressed when arm  944  moves in the direction of the arm vector  962 . The spring provides a force to counter this movement. Accordingly, the tension  904 ′ keeps or returns the shield assembly  314  to shielding configuration. 
     The PRDM system  300  described herein can be conveniently used for probing a volume, such as the volume  214  to discover a hidden object, such as object  216  ( FIG.  2   ).  FIG.  10    is a flow diagram showing the steps  1000  for using the PRDM system  300 . In a first step  1002 , the PRDM system  300  is held by a user, optionally with one hand. The user holds the PRDM system so that the aperture  320  is positioned opposite a first area of a volume to be probed. Once the PRDM system  300  is against the first area, the trigger  318  is engaged in a second step  1004 . The trigger  318  is engaged by depressing it as previously described. This action moves the shield assembly  314  from the shielding configuration  324 , to the exposure configuration  326 . As previously described, the trigger  318  activation also activates the density monitoring algorithm of PRD  100 . In optional embodiments where the PRDM system  300  does not have the switch  908 , the density monitoring algorithm can be activated, such as by the user engaging the operator interface  410 ,  410 ′. With the PRDM system  300  in the exposure configuration  326 , the radiation source  322  emits radiation through the surface of the volume being inspected, and backscattered radiation provides a first measurement  1006  indicative of a first density in the volume. Once the first measurement data is collected, the user moves the PRDM system  300  to a second area of the surface, in step  1008 . A second measurement is collected in step  1010 . The procedure is completed by step  1012  which includes disengaging or releasing the trigger  318 . 
     In some implementations, a continuous steady movement is used between the first area and second area where measurements of backscattered radiation are collected between the first and the second area. Generally, this can be done at a speed between about five feet per second to about one inch per second. The user may use a slower speed of movement to probe an area in more detail, such as about 1 foot or less per second, and the user may use a faster speed such as more than 1 foot per second for a more cursory review. An area can be examined multiple times as well. 
     In implementations of the PRDM system  300  having the safety switch  406 , the safety switch  406  is disengaged prior to engaging the trigger ( FIG.  9 D ). The safety switch  406  is then engaged to secure the PRDM system  300  in the shielding configuration  324 . 
     In some implementations, the PRDM system  300  is used as a personal dosimeter. For example, the PRDM system  300 , when not in the exposure configuration  326 , can monitor radiation. In addition, the PRDM system  300  can include an algorithm to detect radiation that is not due to backscatter from the radiation source  322  and can be configured to provide an alarm if this radiation is above a selected threshold. 
     In some implementations, the PRDM system  300  can included in a kit. The kit can include material for use of the PRDM system  300 . For example, the kit can include a carry case for holding the PRDM system and other items of the kit. The kit can include a strap or lanyard to attach to the PRDM system  300 . The kit can include instructions, such as in a booklet or on a wall of the carry case. The kit can also include a holster. In some implementations, the holster includes shielding material (e.g., tungsten or lead). The kit can also include calibration materials. 
     EXEMPLIFICATIONS 
     I. A PRDM system was constructed as described herein. Three tests were conducted to detect visually hidden items. 
     Example 1: Contraband Simulant Behind a Metal Barrier 
     Two metal barriers were used to “hide” a contraband simulant. 
     In a first test, a thick (3-4 mm) steel sheet barrier was positioned in front of a 5 lb. bag of flour. The bag of flour was position 1-2 cm from the steel barrier. The PRDM system was then used to scan from the opposite side from the bag of flour. In a second test, the 5 lb. bag of flour was placed in a steel cabinet, about 1-2 cm from the cabinet door. The cabinet door had a thickness of about 1 mm. Table 1 lists the results for both tests. The results are listed in a unitless value which corresponds to the density of low atomic number elements (e.g., C, N, O, H). 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Contraband Simulation Test 
               
            
           
           
               
               
               
            
               
                   
                 Test 1: Thick Steel 
                 Test 2: Thin steel 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Area with No 
                   
                 Area with No 
                   
               
               
                 Repeat # 
                 material behind 
                 Simulant 
                 material behind 
                 Simulant 
               
               
                   
               
               
                 1 
                 25-30 
                 34-38 
                 21-25 
                 31-35 
               
               
                 2 
                 25-30 
                 34-38 
                 21-25 
                 31-35 
               
               
                   
               
            
           
         
       
     
     The PRDM system showed an increase in density when it was positioned in front of where the simulant revealing its presence. 
     Example 2 Detection of Water Level 
     A stainless-steel mug (coffee mug) was partially filled with water. The PRDM system was used to scan the upper and lower surface areas of the mug. A difference in relative density was registered as listed in Table 2. The results are in the unitless density values as above. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Scan over stainless steel mug, partially full of water. 
               
            
           
           
               
               
            
               
                   
                 Mug 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Water filled 
                   
               
               
                   
                 Repeat # 
                 Empty top half 
                 bottom half 
                 Alarm 
               
               
                   
                   
               
               
                   
                 1 
                 25-30 
                 45-50 
                 yes 
               
               
                   
                 2 
                 25-30 
                 45-50 
                 yes 
               
               
                   
                   
               
            
           
         
       
     
     The PRDM system easily identified the presence of water. An alarm was also set (&gt;30 relative density). This threshold can be arbitrarily set as an additional way of detecting a density change and alert the user to a hidden item/material. 
     Example 3: Stud Finder 
     The PRDM system was used against a drywall supported by wooden studs to detect the location of the studs. The results, as listed in Table 3, show that the studs could be easily identified by the increase in relative density. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Scanning over drywall to find studs. 
               
            
           
           
               
               
               
            
               
                   
                 Wall 
                   
               
            
           
           
               
               
               
            
               
                 Repeat # 
                 No stud 
                 Stud 
               
               
                   
               
               
                 1 
                 21-25 
                 30-32 
               
               
                 2 
                 21-25 
                 30-32 
               
               
                   
               
            
           
         
       
     
     II. Effect of Shielding. 
     A PRDM system as described herein was constructed.  FIGS.  11 A and  11 B  show the relative position of a Ba-133 source  322  where the shutter is closed (the shielding assembly is in the shielding configuration). The source is inside 80% tungsten shielding material. Orientation in the figures is indicated by the labeled cartesian directions (X, Y, Z) where in  FIG.  11 A  +Y is out of the page and in  FIG.  11 B  +X is out of the page. The thickness of shielding from the source to the outer surface of the tungsten is listed in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Tungsten Thickness 
               
            
           
           
               
               
               
            
               
                   
                 Direction 
                 Thickness (mm) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 +Z 
                 48.4 
               
               
                   
                 −Z 
                 16.8 
               
               
                   
                 +X 
                 12.7 
               
               
                   
                 −X 
                 12.3 
               
               
                   
                 +Y 
                 9.5 
               
               
                   
                 −Y 
                 9.7 
               
               
                   
                   
               
            
           
         
       
     
       FIGS.  12 A- 12 E  are radial plots showing dose rates, measure at the indicated angle. The axis of rotation perpendicular to the page and the origin is approximately at the center of the source. The orientation of the PRDM system  300  is shown, where the position of the aperture  320  is indicated. The arrow indicates that the PRDM system  300  is positioned at the origin, and a detector, recording the radiation, rotates around the PRDM system  300 . The radial distances indicate dose rates in R2 (μR/h), and the angle of detection is indicated in degrees (0-360°).  FIG.  12 A  shows rotation around the y-axis with the emission dose rate at 45 cm distance to PRDM system  300  with the shutter closed.  FIG.  12 B  shows rotation around the x-axis with the emission dose rate at 45 cm distance to the PRDM system  300  with shutter open.  FIG.  12 C  shows rotation around the x-axis with the emission dose rate at 45 cm distance to the PRDM system  300  with shutter closed.  FIG.  12 D  shows rotation around the z-axis with the emission dose rate at 45 cm distance to the PRDM system  300  with shutter open.  FIG.  12 E  shows rotation around the z-axis with the emission dose rate at 45 cm distance to the PRDM system  300  with shutter closed. Inter alia, these figures show that even with the shutter open, the dose rate is low, about 10 μR/h. 
     Those having skill in the art, with the knowledge gained from the present disclosure, will recognize that various changes can be made to the disclosed apparatuses and methods in attaining these and other advantages, without departing from the scope of the present disclosure. As such, it should be understood that the features described herein are susceptible to modification, alteration, changes, or substitution. For example, it is expressly intended that all combinations of those elements and/or steps which perform substantially the same function, in substantially the same way, to achieve the same results are within the scope of the embodiments described herein. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. The specific embodiments illustrated and described herein are for illustrative purposes only, and not limiting of that which is set forth in the appended claims. Other embodiments will be evident to those of skill in the art. It should be understood that the foregoing description is provided for clarity only and is merely exemplary. The spirit and scope of the present disclosure is not limited to the above examples, but is encompassed by the following claims. All publications and patent applications cited above are incorporated by reference in their entirety for all purposes to the same extent as if each individual publication or patent application were specifically and individually indicated to be so incorporated by reference.