A collimator

Abstract

A collimator 102 formed, at least in part, of dispersed media 104, said dispersed media comprising a metal medium. The metal medium may be a continuous medium in the dispersed media and any of a gaseous, liquid or further solid medium may be interspersed therewith. The dispersed metal medium may be formed by methods such as foaming, aggregating, sintering, flocculation and precipitation. The average amount of metal medium per unit volume may vary, either continuously or discretely, in the dispersed media. For example, the dispersed media may be formed from multiple foams, e.g. NiCr foams (i & ii, Fig 1a) and a NiCrMo foam (iii), formed into concentric rings and nested within one another. The collimator is suitable for collimating X-rays and / or gamma rays.

Description

TECHNICAL FIELD

[0001] This disclosure related to a collimator, suitable for collimating X-rays and / or gamma rays and formed, at least in part, of a dispersed media. BACKGROUND

[0002] The precise localisation of radioactivity is crucial in industrial environments that exploit radionuclides. For example, in the decommissioning of nuclear facilities, legacy inspection, or in medical applications.

[0003] Current solutions rely on dense, heavy materials, such as lead, and in large volumes. This makes current solutions cumbersome and maladroit. Such devices are difficult to maneuver or maintain (e.g. CT scanners). Their large dimensions inhibit their use in small areas or on small devices, such as aerial drones or robots.

[0004] Lighter materials, such as other, less heavy metals (solid aluminium for example) are not used as an alternative solution, as such materials only weakly interact with X-rays and gamma rays. These materials are unable to perform the required function of absorbing and / or collimating the radiation. BRIEF SUMMARY

[0005] According to the disclosure, there is presented a collimator, suitable for collimating X-rays and / or gamma rays formed, at least in part, of a dispersed media, wherein the dispersed media comprises a metal medium. A dispersed media is formed of multiple media (i.e. materials), each media is spread, in discrete portions, throughout the other media. The minimum media required for form a dispersed media is therefore two media. Examples of dispersed media include aerosols (gas / liquid dispersion), granulated materials (solid / gas dispersion), aerated liquids (liquid / gas dispersion), emulsions (liquid / liquid dispersion), suspensions (liquid / solid dispersion), foams (solid / gas or liquid / gas dispersions). In the aforesaid the predominant phase is listed first, e.g. For aerosols, the predominant material is the gas with a lesser amount of liquid droplets dispersed therein, as opposed to an aerated liquid which is primarily liquid with gas dispersed therein.

[0006] The dispersed metal medium may be formed in any suitable manner provided it is dispersed with another media, such methods include, but are not limited to, foaming, aggregate, sintering, flocculation, precipitation.

[0007] Suitably, the dispersed media further comprises, and interspersed with the metal medium, any of a gaseous medium, a liquid medium, a solid medium. The other media can be any that is suitable to form a dispersed media (i.e. So each media remains in discrete portions within the bulk of the dispersed media and do not mix to form a homogenous material with the media indiscernible from one another). Suitable media therefore include fluids, gases, liquids, non-miscible solids (e.g. Polymers, ceramics, or other metals).

[0008] Aptly, the metal medium is a continuous medium in the dispersed media. Here continuous medium means that a vein of metal medium runs continuously through the dispersed media. The alternative is that the metal medium is a discontinuous medium where isolated islands of the metal medium are present in the dispersed media, the islands are isolated by the other medium. The metal medium may be present as a discontinuous medium in the dispersed media if appropriate.

[0009] Optionally, the average amount of metal medium per unit volume varies in the dispersed media. There may be regions within the dispersed media where there are greater or lesser amounts of the metal medium. The dispersed media may be formed non-uniformly, that is the ratio of the metal medium compared to the other media may differ in one unit volume of the dispersed media compared to another unit volume in the same dispersed media.

[0010] Appositely, the variation of the average amount of metal medium per unit volume in the dispersed media is a discrete variation or a continuous variation. The amount of metal medium through a dispersed media may vary discontinuously with regions of relatively large amounts of metal medium immediately adjacent regions of relatively low amounts of metal medium, with a sharp transition between the two. Alternatively, the amount of metal medium by transition substantially continuously from a first amount to a second amount, without a sharp transition. There may be a gradient of metal medium from a region of a high density to a region of low density of metal medium within the dispersed media.

[0011] Suitably, X-rays and / or gamma rays neutrons are collimated by the metal medium. As such the dispersed media may be suitable to construct radiation shielding from. The other media may be selected as a low density or light weight material. The dispersion of the metal medium combined with a suitably low density or light weight material results in an effective collimator or shielding material that is light weight and maneuverable compared to prior art materials (e.g. Solid lead). BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0012] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0013] FIG. 1 illustrates a) collimator samples i, ii, and iii, and b) an example collimator.

[0014] FIG. 2 illustrates a collimator attached to a radiation detector.

[0015] FIG. 3 illustrates attenuation measurements corresponding to samples i-iii m FIG. 1A.

[0016] FIG. 4 shows three plots, A)-C) received by a collimated detector vs angle relative to a radiation source. DETAILED DESCRIPTION

[0017] Figure 1 shows a collimator 102 formed of dispersed media 104 having a metal medium component and a gaseous medium component. The metal medium is continuous throughout the dispersed media, save for a central region devoid of any metal medium (i.e. Just gaseous medium). The dispersed media is a metal / gas foam. Suitable metals include nickel, nickel alloys (iron-nickel for example), and aluminium.

[0018] The dispersed media is formed of multiple foams which are formed into concentric rings and nested within one another. The outer most of these is formed in a square cross section with a circular aperture to accept the nested rings. It will be apparent that any suitable geometry or shape may be used, and not limited to those shown, provided the different foams may be nested or arranged within one another. Example radii used for each ring are 7.5mm, 15mm, and 22.5mm, such that the attenuation coefficient changes linearly overall across the dispersed media. Other radii that produce this same effect may be used. The foam rings were arranged such that the highest density foam was arranged towards an extremity of the collimator 102 and the lowest density foam towards the interior of the collimator 102, mimicking a gradient effect.

[0019] Each portion of foam is interference fitted to another piece of foam. Although mechanical or chemical fixings (e.g. Glue or welding) could be used to secure the foams to one another if appropriate.

[0020] Each ring may be formed of the same or a different material. Each foam may be a nickel foam, or a first foam may be a nickel foam and a second foam may be an aluminum foam, in other words different, plural, dispersed media could be used to form the collimator including different metal mediums and different other mediums.

[0021] The dispersed media may also be a single material of constant bulk properties (e.g. Constant amount of metal medium per unit volume) or the dispersed media may be a single material but with varying bulk properties (e.g. Varying amounts of metal medium per unit volume).

[0022] Example metal foam properties are provided in the table below. Samples 1, 2, and 3 were used to form the collimator 102 shown in FIG. 1: Sample Attenuation Coefficient / 10 5mm 1 Density / g / cm3 Porosity / % 1 535.8 0.74 91.69% 2 430.0 0.69 92.25% 3 283.0 0.42 95.28% 4 258.3 0.36 95.96%

[0023] The samples depicted in FIG. 1A concern two 10 mm thick NiCr foams (i and ii), and one 22 mm thick NiCrMo foam (Inconel 625, iii). Sample (i) is manufactured with between 27-33 pores per linear inch, with a pore diameter of 0.6 mm (NCX2733), while sample (ii) comprises between 17-23 pores per linear inch and pore diameter of 0.9 mm (NCX1723). The density of each sample is 0.74 g / cm3, 0.69 g / cm3, and 0.36 g / cm3, respectively.

[0024] FIG. IB shows a the prototype barrel collimator formed of concentric rings, with the square panels formed from sample (i), the outer ring from sample (ii) and the inner ring from sample (iii). The thickness of the collimator face is 20 mm, and the center hole has a diameter of 20 mm. The attenuation coefficients are 530 x 10'5 mm'1, 430 x 10'5 mm'1, and 283 x 10' 5 mm'1, respectively.

[0025] As shown in FIG. 2, once formed the collimator 102 was mounted onto a detector and fitted to a gimbal. A horizontal gamma ray scan of a 252Cf source (13 MBq californium-252 (252Cf) source encased in a 0.93 m x 0.93 m x 0.9 m cuboid container of light water, with 33 mm thick steel walls) was conducted and the counts per angle are shown in FIG. 4.

[0026] The scan was conducted between -60° and +60° where the detector 204 is pointing directly at the source at ~0°. Measurements were taken at a resolution of 2°, with each interval lasting for one hour. This resulted in total runtime of 60 hours for the scan. A CeBr3 (Scionix™) detector 204 was used.

[0027] FIG. 3 shows the attenuation measurements with the spectra representing measurements with and without the foams. The 32 keV is effectively attenuated for all three samples, while a slight attenuation is observed in the 662 keV emission line. In particular the observed drop for the 32 keV line is 83.5 %, 86 %, and 88.8 %, respectively, and the count drop in 662 keV was estimated at 6.95 %, 7.66 %, and 7.23 %, respectively.

[0028] FIG. 4A) and FIG. 4B) show two example angular responses (in 10 keV bins), derived from the spectral measurements. The drop at the near centre of the scan is characteristic to barrel type collimators and an indicator of the radiation hot-spot location. Each plot depicts the data along with two simulation equivalents (Moffat and Moffat dynamic linear regression), and associated standard errors.

[0029] With reference to FIG. 4C, the results of the horizontal scan are shown as counts received in a particular angle of orientation of the collimator 102 and detector 204 relative to the 252Cf source. A minimum total counts at is observed at approximately -10° (due to potential errors in positioning the gimbal), which can be used to indicate the the location of the radiation source. This occurs due to increased scattering in the collimator material when pointing directly at the radiation source. The counts recorded reach maxima at around -50° and +40°, showing a collimation effect provided by the dispersed media 104.

[0030] The attenuation measurements were taken with one sample at a time, with each one in between the detector and a 285 kBq Cs-137 source. Repeated measurements without the samples were taken at a detector-source distance equivalent to their thickness. For the localization measurements, the hardware comprises a custom pan-tilt gimbal to enable angular radiation scans of a given environment (FIG. 2), on which a CeBn detector (crystal size: 25.4 mm diameter x 51 mm height) is mounted; and a RedPitaya™ Field Programmable Gate Array (FPGA) board, configured as a Multi-channel Analyzer. The operation of this setup is integrated with robot operating system capability.

[0031] A symmetric 120° was carried out (-60° to 60°) with 2° intervals, and a measurement time of one hour per interval. A spectrum was acquired for each angular interval, from which energy-resolved angular responses were produced.

[0032] This disclosure presents a preliminary evaluation of graded density metal foam collimator plates for use with single detector localization systems on robotic platforms. Attenuation measurements were obtained using three foams of different composition and density, while a combination of these was subsequently used to manufacture a barrel-type collimator. The angular responses obtained with this sample reveal a distinct shape that is consistent with high density equivalents, and with localization capability of gamma radiation energies of at least up to 2.5 MeV. These results suggest that low density metal foams can greatly reduce payload limitations in nuclear robotic applications and thus enable a whole new range of capability in characterization tasks.

[0033] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0034] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0035] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A collimator, suitable for collimating X-rays and / or gamma rays formed, at least in part, of a dispersed media, whereinthe dispersed media comprises a metal medium.

2. The collimator of claim 1 wherein the dispersed media further comprises, and interspersed with the metal medium, any of a gaseous medium, a liquid medium, a solid medium.

3. The collimator of claim 1 or 2 wherein the metal medium is a continuous medium m the dispersed media.

4. The collimator of any one of claims 1 to 3 wherein the average amount of metal medium per unit volume varies in the dispersed media.

5. The collimator of claim 4 wherein the variation of the average amount of metal medium per unit volume in the dispersed media is a discrete variation or a continuous variation.

6. The collimator of any one of claims 1 to 5 wherein X-rays and / or gamma rays neutrons are collimated by the metal medium.

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