Neutron detector

Abstract

The present invention relates to a neutron detector that for the first time permits the construction of large detector areas of approximately 1 m.sup.2 to 2 m.sup.2, with a spatial resolution of the neutrons of under 2 mm. It is additionally possible in the case of the modular construction in a stack arrangement to attain detection sensitivities that are comparable to .sup.3He counter tubes (ca. 60%) or, with a greater number of detector elements, higher. By using thin substrate plates—such as aluminum sheets—and omission of the external pressure vessels, the neutron detectors are relatively lightweight despite their large dimensions and can be produced inexpensively. The neutron detector comprises at least one module (detector element) comprising in each case two mutually parallel substrate plates made from a first neutron-transparent material, with said plates being spanned in each case on a self-supporting frame made of a second neutron-transparent material and being coated with a neutron absorber material on a side that is remote from the self-supporting frame, wherein the side that is coated with a neutron absorber material faces the respectively other substrate plate on an inner side, and a gas-tight measurement space, which is filled with a counter gas and in which two electrode wire planes, arranged parallel to the substrate plates, having electrode wires that run parallel in the respective electrode wire planes are arranged and in which the electrode wire planes are spaced apart from one another by way of a spacer frame, is defined between the mutually facing, coated inner sides of the substrate plates. The modules can be arranged successively in a stack arrangement.

Claims

1. A neutron detector, comprising a stack arrangement of two or more detector elements, each with two mutually parallel substrate plates made from a first neutron-transparent material, which are coated on mutually facing sides with a neutron absorber material, and there being defined between the coated substrate plates facing each other a measurement space filled with a counter gas, in which two electrode wire planes, arranged parallel to the substrate plates, having electrode wires running parallel in the respective electrode wire planes are arranged, and the electrode wire planes being spaced apart from one another by means of a spacing frame, characterized in that the measurement space is gas-tight and the substrate plates being spanned between the detector elements at a side facing away from the measurement space in each case on a self-supporting frame made of a second neutron-transparent material to form a compensation volume, wherein in each case two detector elements are arranged such that the respective self-supporting frames are joined together so as to cover one another, wherein a gas passage is provided at least at one side of the joined self-supporting frames, to form a variable compensation volume.

2. The neutron detector as claimed in claim 1, wherein the first neutron-transparent material of the substrate plates and the second neutron-transparent material are in each case identical and are copper or aluminum.

3. The neutron detector as claimed in claim 1, in which the electrode wires of the two electrode wire planes are arranged at an angle of 90° with respect to the orientation of the respectively other electrode wire plane to form an electrode wire grid.

4. The neutron detector as claimed in claim 1, wherein the electrode wires in the two electrode wire planes in each case have a spacing of 1 to 3 mm.

5. The neutron detector as claimed in claim 1, wherein the spacing of the two electrode wire planes relative to one another is between 1.2 and 4 mm.

6. The neutron detector as claimed in claim 1, wherein the neutron absorber material comprises .sup.6Li, .sup.10B or gadolinium.

7. The neutron detector as claimed in claim 6, wherein the neutron absorber material is .sup.10B.sub.4C.

8. The neutron detector as claimed in claim 1, wherein the layer thickness of the neutron absorber material on the substrate plate is 500 nm to 1.5 μm.

9. The neutron detector as claimed in claim 8, wherein the layer thickness of the neutron absorber material on the substrate plate is 1 μm to 1.2 μm.

10. The neutron detector as claimed in claim 1, comprising a stack arrangement of 4 and 18 detector elements.

11. The neutron detector as claimed in claim 10, comprising a stack arrangement of 8 and 12 detector elements.

12. The neutron detector as claimed in claim 1, wherein substrate plates made from a first neutron-transparent material are spanned on both sides of a self-supporting frame, wherein the self-supporting frame, on whose two sides the plates are spanned, forms the termination of two adjoining detector elements, and wherein a gas passage is provided at least at one side of the self-supporting-frames that have been joined together, to form a variable compensation volume.

13. The use of a neutron detector as claimed in claim 1 for detecting neutrons.

Description

(1) In the figures:

(2) FIG. 1 shows a diagram of a detector element according to the invention;

(3) FIG. 2 shows a diagram in plan view of the individual constituent parts of a detector element;

(4) FIG. 3 shows a plan view of two self-supporting frames, which can be joined together so as to cover one another to form a stack arrangement of detector elements according to the invention; and

(5) FIG. 4 shows a diagram of a neutron detector having a stack arrangement of 12 detector elements, which are arranged parallel to one another.

(6) FIG. 1 shows a diagram of two layers 1, 5 of neutron absorber material .sup.10B.sub.4C, which are arranged parallel to one another, face one another and are applied onto two mutually parallel substrate plates made from a neuron-transparent material (not shown) by way of sputtering. Furthermore, two mutually parallel electrode wire planes are provided between the .sup.10B.sub.4C-layers 1, 5 that face one another, wherein the electrode wires of the two electrode wire planes are arranged at an angle of 90° with respect to the orientation of the respectively other electrode wire plane to form an electrode wire grid. A high voltage 4 (≥+−1 kV) is applied to the electrode wires. Voltage changes are captured on a delay line 2 with a high spatial resolution.

(7) When a neutron 3 is incident on one of the .sup.10B.sub.4C layers 1, 5, the counter gas is ionized as a consequence of the resulting nuclear reaction with the .sup.10B and the voltage change is detected by way of the electrode grid. Rather than .sup.10B.sub.4C, other solid neutron absorption materials such as .sup.6Li, which is preferably used in the form of .sup.6LiF, or gadolinium are able to be used for the neutron detection in the neutron detector according to the invention. .sup.10B.sub.4C layers are preferred on account of their handling characteristic and for cost reasons.

(8) FIG. 2 shows a diagram in plan view of the individual constituent parts of a detector element. The figure shows, from left to right, a self-supporting frame made from a neutron-transparent material, which is preferably square. Notches, which form a gas passage when two frames are joined together, are provided on both lateral sides. Shown next is a substrate plate coated with a neutron absorber material, which substrate plate is spanned with the side located opposite the coating on the self-supporting frame and is adhesively bonded thereto. The purpose of the spanning is that the substrate plate and coating are as even and wrinkle-free as possible. For the purposes of spanning, the self-supporting frame is slightly pushed inward on its transverse and lateral sides, the substrate plate is adhesively bonded to the frame by way of its side that is opposite the coating side, and the frame is relaxed after curing of the adhesive. A printed circuit board having electrode wire planes, which are shown as a third element, is adhesively bonded to the coated substrate plate. The same construction is repeated in the depiction from right to left and the resulting constructions are connected to one another via a spacer frame, shown here in the center, with a 90° offset. The gas space is filled with a counter gas and adhesively bonded to be gas-tight.

(9) FIG. 3 shows a plan view of two self-supporting frames, which form in each case a termination side of a detector element. Notches, which form a gas passage with an interior gas space when two frames are joined together, are provided on both lateral sides. The compensation volume in the gas space can be controlled by way of the gas passage such that a curvature of the substrate plates can be compensated by lowering or increasing the gas pressure in the compensation volume.

(10) FIG. 4 shows a diagram of a stacked arrangement of 12 detector elements, with each detector element having dedicated counter electronics. Using the stack arrangement shown, it is possible to achieve a detection sensitivity like in a .sup.3He counter tube, but with a much larger detection area than is possible with conventional neutron detectors.

(11) For the first time, the neutron detectors according to the invention permit the construction of large detector areas of approximately 1 m.sup.2 to 2 m.sup.2, with a spatial resolution of the neurons of under 2 mm. In the case of a modular construction in a stack arrangement, it is additionally possible to attain detection sensitivities that are comparable to .sup.3He counter tubes (ca. 60%) or, with a greater number of detector elements, higher. By using thin substrate plates—such as aluminum sheets—and omission of the external pressure vessels, the neutron detectors are relatively lightweight despite their large dimensions and can be produced inexpensively.