Patent Application: US-50382309-A

Abstract:
the disclosed invention proposes a reconfigurable radiation shield that , compared to art static shields , improves the protected volume / weight ratio . the reconfigurable shield is applicable in the medical field , in the aerospace industry , in mobile radiological laboratories and decontamination vehicles , as well as in other fields where intensity - fluctuating radiation and variable direction radiation represent a hazard .

Description:
in a non - limitative version of realization , the radiation shield proposed herein consists of a set of articulated plates , slats or slabs , for example articulated with hinges , or with elastic articulations , such that the relative positions of the plates can be modified . the adaptive shield also includes radiation sensors , the necessary radiation measuring circuitry , a control system that controls the positions of the plates , and actuators to change the positions of the plates . in a non - limitative example of realization , the plates can have plane - parallel ( thin parallelepiped , slat -, slab -) shape , and the assembly of plates encloses and protects an inside space of desired shape , for example , parallelepiped or cylindrical shape . the main operating principle of the adaptive shield is described below . by modifying the tilt of the plane of an absorption plate with respect to the direction of incident radiation , the apparent width of the plate , as seen by the radiation , that is , the distance traveled by the primary radiation through the plate , is modified . namely , if the actual width of the plate is d , then by inclining the plate with an angle θ , the distance traveled by the radiation through the plate becomes δ ( θ )= d /| cos θ |. at large inclination angles , the equivalent increase of the absorption depth may increase by a factor of 10 with respect to the actual width of the plate . consequently , the attenuation of the primary radiation is correspondingly increased . in this description , we do not analyze the problem of secondary radiation , which can be dealt with using appropriate materials known to the art for a two - section shield . the absorption produced by the plate is governed by the absorption law where k is the absorption coefficient , which is dependent of nature of the radiation , of the spectral composition of the radiation and of the nature of the absorption material of the plate . above , φ 0 is the incident radiation flux , and φ ( θ ) is the radiation flux passing beyond the shield , at an inclination angle θ of the plate with respect to the incident radiation . for example , for an inclination of 60 ° of the plate with respect to the direction of the incoming radiation , δ ( θ )= 2d , therefore the attenuation increases by a factor of with respect to the case of the plate normal to the radiation direction . for large inclinations , for example of 80 °, one obtains δ ( θ )= d /| cos θ |≈ 5 , 75 · d . correspondingly , a reduction of radiation by a factor of e 4 . 75d is obtained , compared to the case of normal incidence of the radiation . the absorption plates may be realized of materials with uniform composition and absorption , or from composite materials , or of layers of different absorption materials , or of several plates with different absorption properties , in such a way as to efficiently absorb both the primary and the secondary radiation . the adaptive shield invention does not claim any specific material for shielding . any known radiation - absorbent material can be a candidate for the design of the plates composing the shield . the purpose of the invention describing the basic shield with movable plates is to improve the efficiency of shields in an adaptive manner , not to devise new materials for shields . subsequently , in connection to fig1 , 2 and 3 , we present a non - limitative example of realization for the adaptive radiation shield and we describe the operation and adaptation principle . fig1 illustrates a non - limiting example of shield composed of radiation absorption plane - parallel plates ( 1 ), slates or slabs , connected through joints ( 2 ). the joints ( 2 ) can be any type of hinge , mechanical joint , or elastic articulation that allows the relative change of position of the plates , slabs or slates ( 1 ). the assembly of the plates is forming the adaptive shield ( 3 ). the sketch in fig1 represents a non - limiting version of the adaptive shield that initially delimits a space of square transversal section . as a consequence of the increase of an incident radiation ( 4 ), the shield modifies its shape in order to reduce the effect of the radiation in the delimited protected space . the plates attenuate the incident radiation ( 4 ) in order to reduce the level of the internal radiation ( 5 ) to an acceptable level , thus protecting the inside space ( 6 ) delimited by the shield . fig2 illustrates the distance ( 7 ) traveled by the radiation through the plates , distance that represents the effective , apparent ( not geometrical ) thickness of the shield . that thickness is modified by the inclination of the plate with respect to the incident radiation , by a factor of 1 /| cos θ |. in this way , the radiation that penetrates in the protected space is reduced . the assembly of plates ( 1 ) of the adaptive shield ( 3 ) can take the form of a spatial zigzag , with variable angles between the articulated plates , as illustrated in fig3 . the articulations can be made with hinges or with elastic materials , or with any other known means . various configurations of the shield and shield plates can be used . as a matter of example , fig4 shows a shield formed of equilateral plates that compose a hexagonal tile . this tiling configuration allows the deformation of the shield in three directions , allowing for more adaptability , which is very convenient when the direction of the radiation changes . fig5 illustrates how a regular polygonal section of the shielding allows for a large interval of values for the angle between the plates , when transforming the convex polygonal section into a non - convex one . in fig6 it is shown that a shielding folding based on a pattern of non - isosceles triangles ( in cross - section ) allows an improved attenuation by increasing the apparent thickness of the shield . such patterns of non - isosceles triangles can be formed using slabs of the same width , but with a non - identical folding angle . also in fig6 , upper panels , right , it is illustrated how slabs articulated by sliding hinges can deform to increase the apparent thickness . fig7 and 8 show various geometries of protected spaces and various types of shields with different deformation patterns ; such cases can suit a large range of applications . the position of the assembly of plates ( 1 ) that form the radiation shield ( 3 ) is automatically controlled by a measuring system that monitors the incident radiation at the exterior of the shield . the system may also measure the radiation entering in the interior of the shield . in conformity with these measured values , a control system and the related actuating ( driving ) devices adjust the position of the plates of the shield with the aim of reducing under an acceptable limit the radiation that enters the protected region . the control system includes for this purpose radiation sensors ( 8 ) placed externally with respect to the protected region , and possibly sensors ( 9 ) placed in the protected region ( 6 ). the sensors also determine the direction from which the dominant radiation flux comes , such that the protection is produced preferentially toward that direction . the control system comprises , as sketched in fig9 , apart from the external ( 8 ) and internal ( 9 ) directional radiation sensors , a measuring system ( circuits annexed to the sensors ), and a digital control system ( 10 ), moreover a system ( 11 ) of actuating / driving the elements of the shield . the actuation system ( 11 ) may be mechanical , pneumatic / hydraulic , magnetic , electrodynamic , or of different nature . the automatic control system of the shield computes the optimal inclination angle for each of the plates , taking into account the radiation levels inside and outside the plate , as well as the geometrical constraints of the plate assembly . apart from determining the optimal geometrical configuration of the plate system , the control system commands accordingly the plates &# 39 ; actuation system . the actuation system may be based on hydraulic or pneumatic pistons , or on electric motors and gears , or on systems known from the automatic curtain manufacturing , or on electromagnetic actuating systems . the need for sensors to the inside of the protected space , possibly of sensors carried by the personnel , is due to the fact that the radiation in the protected space may vary from point to point , moreover secondary effects may be produced , such as the secondary radiation produced from the shield or from objects inside the protected space . in a non - restrictive construction variant , the sensor is replaced by an assembly of sensors , as sketched in fig1 , mounted on a mobile support ( 12 ) such that , by the movement of the support , the sensor can scan and monitor a wide solid angle for the incoming radiation . in yet another non - restrictive construction variant , instead of a single sensor , several sensors are used in a sensor array , mounted on a mobile support ( 12 ), the sensors comprising a plate ( 13 ) of pre - determined thickness realized from the same material or materials as the shield , a protecting shield ( 14 ) that prevents radiation from undesired lateral directions to penetrate to the actual sensor ( 15 ), the actual ( electronic ) sensor ( 15 ) being included in a sensor chamber ( 16 ) which , in a realization version , can consist of a phantom to model the absorption properties of the human body or of the equipment to be protected . the different thicknesses of the sensor shields ( 13 ) correspond , from the point of view of radiation dampening , to the dampening produced by specified shapes of the reconfigurable shield . the sensors may also be included in phantoms — such as to determine the radiation effect on the human body , rather than the radiation &# 39 ; s physical effect . the use of phantoms is motivated by the need to determine overall — primary plus secondary — radiation effects . the energetic spectral information , total — primary plus secondary — internal radiation flux , and the direction information , are all fed to the controller in order to determine the best shape the adaptive shield must take . the adaptation of the reconfigurable shield is performed according to a radiation dose minimization criterion with restrictions . the restrictions are related to the maximal dose in any of the monitored points in the space delimited by the shield . as a matter of example , in case the shield protects a single person , the dose in various regions of the body of the person must all be submitted to a radiation dose less than a specified value , while the sum of doses received by the whole body must be minimized . assuming the radiation is monitored inside the delimited space by sensors connected to the head , upper abdomen , lower abdomen and legs , the optimization problem with restrictions is expressed as : reconfigure shield such that to minimize the total dose σ k d k w k subject to the conditions d k & lt ; d k — max , where d k are the measured doses per unit surface in the body region k , d k — max are the corresponding maximal doses allowed , and w k are weights related to the total surface of the corresponding region of the body . this method of adaptation differs to those previously proposed . baudro invented a radiation shield composed of interconnected slants , which can be easily deployed , the deployed shield having a support that is also collapsible and easily deployable . the deployed shield has essentially a predetermined planar shape and , according to the drawings in the quoted patent is positioned normal to the radiation propagation direction . this position of the plates is not favorable for radiation attenuation , as explained above . toepel invented a radiation shield composed of hinged plates . in toepel &# 39 ; s invention , the position of the panel , as represented by the angle between the panel plane and the direction of the incident radiation plays no role . in contrast , our invention essentially relies on the control of that angle . short presented a radiation shield with variable attenuation that is essentially able to partly or completely interact with the radiation moreover that can change its structural properties at a microscopic scale in order to change its radiation attenuation . short teaches a shield that is able to produce only intermediate levels of attenuation , between the attenuation provided when the slabs are perpendicular to the radiation propagation direction and zero attenuation . therefore , short &# 39 ; s shield and shield adaptation method can not increase the attenuation over the level obtained when the slabs are perpendicular to the radiation direction . the significant distinction of the shield described in this invention compared to the state of the art is that it teaches a method to significantly improve the attenuation above the level achieved when the slabs are perpendicular to the radiation direction . the increase in attenuation , according to the present invention , is , however , obtained in general by a decrease of the volume of the protected space . in this example , the actuation system consists of hydraulic / pneumatic pumps ( 25 ), driven by motors ( 24 ), and connected through flexible tubes ( 26 ) to a set of pistons ( 18 ) such that each piston can be individually controlled by the control system ( 10 ). the digital control system ( 10 ) may be , in a non - limitative example , a microcontroller . the microcontroller is connected through power circuitry to the set of motors that drive the pumps . each piston ( 18 ) is connected to an external frame ( 19 ) and to a joint ( 2 ) of the shield . the joints are alternately disposed , as to allow for the deformation of the shield structure . this example uses twice the number of pistons , pumps and motors required by the example in fig1 . fig1 a illustrates the sketch of a shield with hydraulic or pneumatic actuators , each used to move two successive plates . the actuators are externally placed with respect to the shield . as each piston corresponds to two adjacent plates ( 1 ) of the shield , there is no need for an external frame to the shield . fig1 b shows the sketch of a shield with hydraulic or pneumatic actuators , each used to move two successive plates . the actuators are internally placed with respect to the shield , in contrast to fig3 . the details are provided as examples , for the easy understanding of the main ideas in the description . the actual realization needs not follow any of these examples . the joints of the shield assembly may be driven , in a non - limitative example , by gears driven by electric motors . the electric motors ( 24 ) actuating the elements of the shield are fixed directly to one of the plates in each couple of successive plates connected by hinges ( one motor on every second plate ). the digital control system ( e . g . microcontroller ) controls the motors ( 24 ) through an appropriate high current driver . fig1 shows a detailed view of a sensor assembly ( 9 ), including an opamp ( operational amplifier ) ( 22 ), the elementary sensor ( 23 ) and the signal conditioning ( 24 ). fig1 a shows the motor ( 24 ) driving the first wheel ( 27 ) of the gear . the second wheel ( 28 ) of the gear is connected to the axis ( 29 ) of the hinge . such a gear mechanism can be used to rotate two successive plates . ( fig1 a shows only one section of the hinge .) skilled mechanical and electrical engineers can design , using current cad tools , various joint elements , pneumatic , hydraulic , and electro - mechanical actuators , as well as driving and control circuitry . these elements are known to the art and are not patentable parts of the proposed system , although they are needed for the actual realization of some variants of the proposed system . some of these elements can be purchased as commercially available parts . in another non - restrictive construction variant , the shield is made of an elastic material , such as rubber with an elevated content of radiation absorption material , elastic material that may be deformed and adapted in terms of shape according to the requirements of optimal protection . in contrast to example 1 , this variant does not need hinges , but needs means to fold the elastic material and to guide the folds according to a specified shape of the shield . means to fold can be laces pulled by wheels / pulleys driven by electric motors . the anti - radiation shield also behaves adaptively in the case of two or several directional radiation sources . in that case , the angle formed by the successive plates , or the shape of the elastic shield — if the shield is made out of elastic material — is controlled depending on the directions and intensities of the two sources of radiation , aiming to maximize total absorption of the radiation coming from the two sources . i further disclose elements suitable for one or several realizations . in another non - limiting realization , at least some of the radiation sensors inside the protected space are worn by the protected personnel . in this case , the control information for the shield comes directly from the personnel and the shield orients such that it offers the best protection in those work areas . indeed , it is known that for shields of irregular shapes , the level of ensured protection is not the same in all points of the protected space . therefore , especially in the case in which people modify their position in time , optimal adaptation is achieved depending on the positions of the protected people . information flow from the people - borne sensors to the control system may be realized either through radio , infrared , or other communication method . in another non - restrictive construction , the control system uses either only external sensors , case in which the system has to compute the level of radiation in the protected space , or uses only internal sensors , case in which the adaptation may be realized only depending on the information about the level of radiation in the protected space . in another non - limiting design , the radiation shield is formed out of a primary , non - adaptive shield supplemented by a system of directional — adaptive shields — which ensure protection only in a specified direction . the adaptive shield can be temporarily moved toward the direction from where high intensity radiation comes from . thus , the assembly comprising a primary , non - adaptive , omni - directional , and a supplementary adaptive shield includes mobile elements that allow for the displacement of shielding elements with respect to the direction from where temporary strong radiation occurs , the said displacement being performed such as to maximize the absorption of the radiation . in another non - limiting design , the measuring system of internal / external radiation is supplemented with an alarm system triggered at the increase in radiation levels . in another non - restrictive construction , in which the internal sensors are not carried by the personnel , the radiation shield may feature a system of position sensors for automatic detection of the position of the protected persons , such that the computation of the position of the plates or slates composing the shield the related computation of the shape of the shield is aimed to optimal radiation dampening in the work area of those persons . the radiation shield is adaptive as it allows for the variation of the protected volume in order to ensure the radiation in the protected area below a maximum permitted value . thus , in the case of an increase in incident flux , the shield can restrain the protected volume in order to ascertain the interior radiation flux under the specified “ safe ” value . in the event of a drop in external radiation flux , the shield can distend to allow for a larger protected volume . if the protected structure is cylindrical , in a non - limitative design , the shielding system may use a single internal / external sensor — or a pair of sensors — one internal and the other external — able to move on a helicoidal path , such as to cover the entire protected surface . in the case of radiation obliquely incident to the shield , the dampening effect of the shield may be reduced compared to the dampening for radiation of normal incidence . therefore , for an obliquely incident radiation , the optimal shape of the shield is different than the optimal shape for normally incident radiation . in order to determine which one is the angle of incidence of the most intense radiation , the sensors ( 16 ) will be able to do a precession - type rotation ( 17 ). the optimal shield shape will be computed taking into account the radiation &# 39 ; s angle of incidence . on the same principle , radiation protection clothes can be conceived . “ radiation shield ”- clothes can be manufactured out of fabrics that contain radiation - absorbing materials and have shapes that can be modified through controlled folding / contraction in the more - in - need of protection areas , or through controlled distension in the less - in - need of protection areas . the less - in - need of protection areas are characterized by a smaller radiation input . as described , the clothes obtain a larger apparent thickness in the high radiation input areas . the extension / contraction may be realized , in a non - limitative design , by pulling straps / wires in the fabric . the straps / wires are operated by a control system in a similar way existing clothes are manipulated to form pleats and folds , or current ripplefold system or accordia - fold system draperies are used . in yet another version of realization of the shield , the plates or the elastic or textile material used to absorb the radiation may be realized of or covered in magnetic material , such as to confer them magnetic properties . the shield is coupled to a magnetic field generator , such that it is magnetized . by changing the position of the plates , the intensity of the magnetic field is increased in the vicinity of the plates and the charged particles constituting a component of the radiation will be at least partially deflected by the magnetic field . it is well known that strong solar activity can cause major disruptions in the electric distribution energy . the application of adaptive shielding for critical buildings such as power plants might be useful in preventing similar disruptions in the future . in a non - limitative design , the building &# 39 ; s walls ( 3 ) may be mobile and formed out of articulated plates ( 1 ). the adaptive shield &# 39 ; s control system must also take into account the sun &# 39 ; s relative movement to earth &# 39 ; s surface . thus , the shield will have to continually adapt in order to provide the best attenuation in the sun &# 39 ; s direction . in all realizations , the radiation shield may be controlled according to an algorithm that minimizes the effect of primary or of total radiation on the people inside the protected space , taking into account the specific absorption coefficients of the human body and biological effects of radiation . in the description of the invention up to this point , only the primary radiation case has been dealt with . here , we add the solution for the case when the secondary radiation is also important , because of the high - energy primary radiation that produces secondary radiation in the shield . in the case of potentially powerful secondary radiation , the shield is composed of at least two layers , one used to absorb the energetic particles / radiation , and the second used to absorb the less energetic particles / radiation generated as secondary - radiation , the first said layer being realized from a material including heavy atoms , while the second including lighter atoms . the shield can also be realized of a composite or mixed material to ensure appropriate absorption of both high and low energy particles . radiation - absorbing materials are known to the art and do not constitute the object of this invention . fig1 summarizes the principle of the invention and provide further examples of adaptation . fig1 illustrates a shield with rectangular initial shape that improves the protection of the personnel ( 30 ) either by global rotation of the shield without change in shape , or by both global rotation and change of shape , moreover compares the method of adaptation of the initially rectangular shield with the method of adaptation of the shield shown in fig1 . the skilled reader will recognize the unity of the solution in all the variants . indeed : i ) all variants are based on a single major idea , namely that change of orientation of a ( macro -, micro -, or nano -) shield may strongly modify the radiation absorption . the idea is applied to macroscopic plates , to macroscopic elastic absorbing materials , and to textiles and absorbent draperies . moreover , it is applied to devise “ active ” principles for non - homogeneous anisotropic materials that can be changed to adapt to the incoming radiation , ensuring best shielding . ii ) all the proposed embodiments , either macro - or micro - embodiments of the above idea serve the same practical purpose : reconfigurable radiation shields . the radiation shield has several advantages . among others , it ensures a significantly increased protection , at the same mass of the shield and the same materials composing the shield , compared with static , rigid , non - adaptive shields . moreover , the shield operates automatically and implicitly can offer an alarm to the personnel occupying the protected space . to protect the personnel , the shield allows the temporary reduction of the protected space , when the levels of incoming radiation impose this situation . compared to a static shield of the same mass , the disclosed reconfigurable shield improves the ratio ( protected volume )/( weight ). the adaptive radiation shield can be industrially used in applications like space transport , in the medical domain , as well as in other terrestrial domains where intensity fluctuating radiation and variable direction radiation can be a hazard . the adaptive shield is technologically feasible with today means and with commercially available parts and materials . the precise design can be produced using existing cad tools . in case of the adaptive shield variant based on ferro - fluids , it can be developed based on the current knowledge in the field , as reflected in the literature . although only a few embodiments have been described in detail above , those skilled in the art can recognize that many variations from the described embodiments are possible without departing from the spirit of the invention . the skilled worker will recognize that the radiation shielding system presented is suitable with minor adaptations to various purposes , including the protection of personnel and patients in medical facilities , the protection of power equipment against unpredictably variable cosmic radiation , and in space applications . 1 . science in nasa &# 39 ; s vision for space exploration , committee on the scientific context for space exploration , space studies board , division on engineering and physical sciences , national research council of the national academies , 2006 , www . nap . edu 2 . space radiation hazards , ad hoc committee on the solar system radiation environment and nasa &# 39 ; s vision for space exploration : a workshop , space studies board , division on engineering and physical sciences , national research council of the national academies , 2006 , www . nap . edu 3 . evaluation of the influence of aircraft shielding on the aircrew exposure through an aircraft mathematical model . ferrari , m . pelliccioni , r . villari , radiation protection dosimetry 108 : 91 - 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