Neutron detector and method for its preparation

Abstract

A device for detecting neutrons comprising a base, a lateral surface and a cover, thereby providing a detector housing having a central longitudinal axis, wherein the interior of the housing is divided into n (n≥2) cells wherein at least one of said cells is adapted to operate as neutron detection ion chamber by having at least one removable foil disposed parallel to said longitudinal axis, at least one removable foil positioned adjacent to, and essentially parallel with, a sector of the lateral surface, with said removable foils having neutron sensitive coating applied on at least one their faces, and an anode mounted in at least one cell bounded by said removable foils, with said housing constituting the cathode. The device is also useful for simultaneously detecting gamma irradiation and or producing radioisotopes.

Claims

1. A device for detecting neutrons, which is an in-core neturon detector, comprising a base, a lateral surface and a cover, thereby providing a detector housing having a central longitudinal axis, wherein the interior of the housing is divided into n (n≥2) cells wherein at least two of said cells are adapted to operate as neutron detection ion chamber by each having at least one removable foil disposed parallel to said longitudinal axis, at least one removable foil positioned adjacent to, and essentially parallel with, a sector of the lateral surface, with said removable foils having neutron sensitive coating applied on at least one of their faces, and an anode mounted in each one of said at least two cells adapted to operate as neutron detection ion chambers bounded by said removable foils, with said housing constituting the cathode; wherein a first neutron detection ion chamber has a first neutron sensitive coating applied on the removable foils defining the walls of the said first ion chamber, and the second neutron detection ion chamber has a second neutron sensitive coating applied on the removable foils defining the walls of the said second ion chamber, wherein said first and second neutron sensitive coatings are made of different materials; and wherein the cover is a cover assembly comprising a cover base and at least two or more tubes extending upwardly from said cover base, with each of said two or more tubes enclosing a conductor guided via the respective tube through an access hole in the cover base into a respective cell in the interior of the detector housing, said conductor being electrically insulated from the inner walls of said tube by means of an insulator occupying the annular space between the inner walls of said tube and said conductor.

2. A device for detecting neutrons according to claim 1, comprising a base, a lateral surface and a cover, thereby providing a detector housing having a central longitudinal axis, where an axially positioned rod is mounted; wherein the interior of the housing is divided into n (2<n≤10) cells, wherein each of said cells which is adapted to operate as neutron detection ion chamber is defined by: a pair of removably disposed foils extending essentially radially outward from the axially positioned rod mounted along the central longitudinal axis; and a removably disposed foil placed adjacent to, and essentially parallel with, a sector of the lateral surface.

3. A device according to claim 2, wherein the housing comprises an array of slots holding the removably disposed foils, said array of slots comprising: longitudinally-aligned central slots; longitudinally-aligned peripheral slots facing said central slots; and longitudinally-aligned lateral slots; wherein opposite edges of a removably disposed, radially extending foil are held by a pair of opposing slots, consisting of a longitudinally-aligned central slot and a longitudinally-aligned peripheral slot; and wherein opposite edges of a removably disposed foil in a position adjacent to, and parallel with, the lateral surface, are held by a pair of lateral slots.

4. A device according to claim 3, wherein the lateral surface of the housing is a lateral surface of a cylinder, with an axially positioned rod mounted inside the housing and a set of longitudinally aligned central slots provided on said axially positioned rod and a set of longitudinally aligned peripheral slots distributed around the circumference of the lateral surface, and a set of channels provided adjacent to the lateral surface.

5. A device according to claim 4, comprising n (n≥2) T-beam shaped structures distributed around the circumference of the lateral surface wherein the vertical section of each T-beam shaped structure is attached to the lateral surface and is parallel to the axially positioned rod, with the front of the two-arms section of the T-beam shaped structure facing the axially positioned rod.

6. A device according to claim 5, wherein the two-arms section has a recess extending over its length, defining a longitudinally aligned peripheral slot opposite to a longitudinally aligned central slot recessed in the axially positioned rod, with the opposite edges of a removable foil being held by said pair of opposite slots; wherein channel-like spaces are provided between the lateral surface of the housing and the back of the two-arms section of the T-beam shaped members, said channels defining pairs of opposite slots adjacent to the lateral surface, such that the opposite edges of a removable foil are held by said pair of opposite lateral slots in a position adjacent to and parallel with the lateral surface.

7. A device according to claim 1, wherein the first neutron sensitive coating is .sup.10B.sub.4C and the second neutron sensitive coating is UO.sub.2.

8. A device according to claim 1, comprising permanent partitions extending radially outward from the central longitudinal axis to join a sector of the lateral surface thereby defining cells.

9. A device according to claim 8, wherein at least one removable foil is supported onto one face of a permanent partition.

10. A device according to claim 8, wherein one or more cells defined by permanent partitions is (are) devoid of an anode and/or of removable foils.

11. A device according to claim 10, wherein one or more cells defined by permanent partitions is (are) devoid of removable foils, said cell(s) having anode mounted in their interior, said cells being suitable for detection of gamma radiation.

12. A device according to claim 10, wherein one or more cells defined by permanent partitions is (are) devoid of removable foils and anode, said cell(s) being suitable as receptacle(s) for target materials to be converted into radioisotopes by neutron activation.

13. A method for producing radioisotopes, comprising providing a device as defined in claim 12, placing targets in one or more of the cells of said device, which cells are devoid of removable foils and anode, irradiating the targets to convert into radioisotopes, while fast and slow neutron flux (and optionally gamma radiation) are constantly measured with said device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an isometric view of the device of the invention in a configuration devoid of permanent partitions, illustrating an array of slots needed to hold in place the removable foils.

(2) FIGS. 2A and 2B are an isometric view and a photo, respectively, of a device of the invention in a configuration containing permanent partitions, capable of supporting the removable foils.

(3) FIGS. 3A and 3B are photos showing the cover of the detector with electrical connections.

(4) FIGS. 4A, 4B and 4C are isomeric views of a cover assembly of the invention.

(5) FIG. 5 is a schematic diagram of the electrical connections of the detector to electrometer type preamplifier.

EXAMPLES

Example 1

Design and Manufacture of a Device of the Invention Using AM Technique

(6) 1. Using mechanical design software such as “Solid works”, define the dimensions of the detector main enclosure and its cover, File type Part(*.sldprt and *.prt). It is possible to adapt the dimensions proposed in this invention (e.g., external diameter 30 mm, active length 40 mm), or design the required length and diameter according to specific needs.

(7) 2. With the aid of the same software, define the cells of the main cylindrical enclosure and a central rod according to the embodiment presented in FIGS. 2A and 2B. Different cells may be implemented according to application requirements.

(8) 3. On the detector cover, define the holes through which the anode pins will be inserted. The position of each hole should be just above the center of a corresponding cell in the detector's main enclosure.

(9) 4. Design rails that are capable of holding a thin metal foil, as shown in FIG. 2A. Each of the permanent partitions defining cells intended to serve as neutron detection ion chambers must contain a pair of rails on at least one face thereof.

(10) 5. At the center of the detector cover define a hole through which the central rod (central screw) will pass. Also design a thin slot around the detector cover. In this groove an O-ring or soft metal (e.g. indium wire) will be inserted.

(11) 6. Convert all designed components, file type Part(*.prt) to a pre-printer file—type Parasolid (*.x_t).

(12) 7. To evaluate the design concept, convert all models files type *.sldprt to STL(*.stl) files, and manufacture demi-components (3D printing of polymer material).

(13) 8. Convert pre-printer files—(*.sldprt or *.prt) Parasolid (*.x_t) to STL(*.stl) files to evaluate manufacturing capabilities by Additive Manufacturing (AM) techniques.

(14) 9. Upload all models file STL(*.stl) (*.sldprt) to “Magic” software, and evaluate the drawing according to the relevant Additive Manufacturing (AM) machine criteria.

(15) 10. Validate the designed files for compatibility to the AM process, including supporting design.

(16) 11. Using AM techniques for aluminum alloys produce the detector main enclosure, its cells and the rails that support the metal foils. Similarly produce the components of the detector cover.

(17) 12. Release residual efforts by thermal treatment process, 300° C./2 hr in a controlled Argon environment.

(18) 13. Remove the detector main enclosure from the AM platform by EDM wire cutting process.

(19) 14. In sealing areas and joints finalize each manufactured part by common machining processes, make a bolt from the central bar of the main detector enclosure. Select a suitable nut for this screw.

(20) 15. Prepare the removable thin metal foils that will be inserted through the rails of the inner walls of cells (i.e., the permanent partitions).

(21) 16. Coat the metal foils with the appropriate neutron reacting materials. For measurements of slow neutron .sup.10B.sub.4C coating is required. Similarly, for slow and fast neutron measurements, the recommended coating material is .sup.natUO.sub.2. For fast neutron measurements, the recommended reacting material is thorium. These coating can be made by sputtering, vapor deposition or electrochemical coating methods.

(22) 17. Insert the coated foils through the rails to be supported on the permanent walls.

(23) 18. Insert thin conductors (anode wires) through the cavities in the detector cover. These wires penetrate the detector cover and serve as anodes of each ‘sub-detector’, therefore the length of such wire is a few millimeters shorter than the active length. Use Torr Seal® paste to insulate the wires from the detector cover. Keep the wires perpendicular to the detector main enclosure and let 24 h the Torr Seal® paste to dry (207).

(24) 19. On the outer side of the detector cover, solder a signal wire of a coax cable to each anode wire. On the detector side, leave the shield of the coax cable floating (un-connected). The other side of each the coax cable is connected to a BNC or similar connector according to common wiring procedures. Repeat this procedure to all neutron detection ion chambers having anode mounted in their interior.

(25) 20. Solder or lock the signal wire of a coax cable to a cable lock and insert it around the central screw (108 in FIG. 3A). Leave the shield of the coax cable floating. The other side of this coax cable is connected to a −HV power supply (typ. few hundred Volts for current measuring applications.) Connect the shield of the coax to the power supply common (GND).

(26) 21. Alternatively to 18, design and produce via 3D printing the cover assembly with protecting tubes and supporting spacers shown in FIGS. 4A-4C. With laser (e-beam) welding technique, weld the detector case with its cover.

(27) 22. Cut ceramic tubes corresponding in length to the printed protecting tube. The ceramic tubes have an outer diameter smaller than the inner diameter of the protecting tubes. The ceramic tube is pasted with Torr Seal® (for example) to the protective tube. Cut a rigid conductor wire in the length of the protective tube plus the length of anode protruding into the cell in the interior of the detector housing. The outer diameter of the rigid conductor wire is less than the inner diameter of the ceramic tube. Push the rigid wire through the ceramic tube, the exposed length inside the detector will serve as an anode while its other end at the free protecting tube end is used for further connection to coaxial cable that will feed the pre-amplifiers and HV bias.

(28) 23) The assembly of the different parts in step 22 is carried out in an argon or xenon atmosphere after replacing (flushing) the atmosphere inside the detector case with the chosen gas. The ceramic paste will seal the detector, rigid conductor wire inside the ceramic, and the ceramic inside the printed protecting tube. The paste sealing can be done near the tubes free end where radiation fields are significantly lower than near the detector case.