GB2178587A

GB2178587A - Neutron-absorbent lining for neutron-beam collimator pipes and compositions for use therein

Info

Publication number: GB2178587A
Application number: GB08616411A
Authority: GB
Inventors: Otto Pordes
Original assignee: ASTOR CHEMICAL Ltd
Current assignee: ASTOR CHEMICAL Ltd
Priority date: 1985-07-30
Filing date: 1986-07-04
Publication date: 1987-02-11
Also published as: GB8519203D0; GB8616411D0

Abstract

A neutron-absorbent lining composition is disclosed for neutron-beam collimator tubes and other neutron beam handling or generating equipment comprising a particulate neutron-absorbing compound, e.g. boron carbide, moulded and bound into a coherent, homogeneous mass using elemental sulphur as the binder.

Description

SPECIFICATION Neutron-absorbent lining for neutron-beam collimator pipes and compositions for use therein This invention relates to neutron-absorbent linings for neutron-beam collimator pipes and other apparatus used in the generation or guidance or other operation involving neutron beams, and in which it is necessary to minimize surface scattering of neutrons from that beam, and compositions for use therein.

Neutron beam collimators currently in use for carrying neutron beams from a neutron source, particularly a high energy neutron source, such as a spallation neutron source (SNS), are lined with a neutron-absorbing "black" lining, e.g. a total radiation energy absorbing lining to absorb stray neutrons which may impinge on the side walls of the collimator. Such linings comprise a neutron absorber, i.e. a compound having a high neutron capture cross-section. This is usually a boron-containing compound, but other alternatives are available, such as cadmium compounds or compounds of rare earth metals such as gadolinium, samarium, europium or dysprosium.

Most frequently, the neutron absorber is boron carbide, which has the approximate composition B4C, one such material currently being available under the Registered Trade mark TETRABOR.

For use as a neutron-absorbent lining, the neutron absorber, e.g. Tetrabor, is mixed with a synthetic resin binder, which may be, for example, a polyurethane or polyester, and depending on the nature of the binder and the relative proportions, the liner may take the form of an adherent coating on the walls of the neutron beam collimator, or it may be in the form of self-supporting, moulded blocks or sheets, which may be rigid or flexible as desired and depending on the binder.

Existing neutron-absorbing formulations, however, have the disadvantage that stray neutrons impinging on the lining tend to be scattered by the binder component, which reduces the overall neutron-absorption efficiency of the lining.

In accordance with the present invention, this problem is solved, or attempted to be solved, by using sulphur as the binder in such compositions.

Accordingly, in one aspect, the present invention provides a neutron-absorbing lining for neutron beam collimators, or other neutron beam generating, guiding or handling equipment, and neutron beam collimators or other such equipment lined therewith, said lining comprising particles of a solid neutron-absorbing compound, preferably a boron-containing compound, most preferably boron carbide, bound into a cohesive homogeneous mass with a binder, wherein the binder is sulphur.

In a second aspect, the present invention provides a composition for use as a neutronabsorbing lining in neutron beam collimators and other neutron guiding, generating or handling equipment, said composition comprising a mixture, optionally but not necessarily moulded into a compact, selfvsupporting homogeneous mass, and comprising particles of a neutron-absorbing compound and a binder therefor wherein the binder is sulphur.

Preferably the neutron-absorbing compound is a boron-containing compound, most preferably boron carbide.

In addition to its utility as a lining for neutron beam collimators, such compositions may also find utility in other situations where a neutron-absorbing composition or material is required. Such compositions may, for example, find utility in the construction of neutron shields surrounding a neutron source, although in such cases it may be necessary to include moderators to slow the neutrons down, particularly high energy, high velocity neutrons, sufficiently to permit absorption by the neutronabsorbing component.

For use as a neutron-absorbing lining for neutron beam collimators, the mixture will generally consist of from 1-99% by weight binder, i.e. sulphur, and correspondingly 99-1% neutron absorbing compound, preferably a boron compound, most preferably boron carbide. Preferred compositions will contain from 20-50% by weight binder and 80-50% neutron-absorbing compound.

The compositions of this invention can be formulated and fabricated by a variety of mixing and moulding techniques. For example, and taking advantage of the relatively low melting point of sulphur. Thus, the neutronabsorbing compound, e.g. boron carbide, particles may be blended with molten sulphur and the molten blend moulded, cast or extruded into any desired shape, or the neutron-absorbing compound and the sulphur can be dry mixed and moulded into the desired shape by moulding under heat and pressure.

To illustrate the invention, two blends were prepared by dry mixing flowers of sulphur and boron carbide particles in the proportions 30:70 and 40:60 respectively. Each blend was compacted and heated to fuse the sulphur thereby providing a homogeneous compact block of boron carbide particles bound together with sulphur. Such blocks and blends are admirably suited as a lining for neutron beam collimator pipes to eliminate or reduce surface scatter, which interferes with the object in hand, e.g. the study of particle scatter by a given target bombarded with the main neutron beam.

1. A neutron-absorbent lining composition for neutron beam collimator pipes, or other neutron-beam generating, guiding or handling

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Neutron-absorbent lining for neutron-beam collimator pipes and compositions for use therein This invention relates to neutron-absorbent linings for neutron-beam collimator pipes and other apparatus used in the generation or guidance or other operation involving neutron beams, and in which it is necessary to minimize surface scattering of neutrons from that beam, and compositions for use therein. Neutron beam collimators currently in use for carrying neutron beams from a neutron source, particularly a high energy neutron source, such as a spallation neutron source (SNS), are lined with a neutron-absorbing "black" lining, e.g. a total radiation energy absorbing lining to absorb stray neutrons which may impinge on the side walls of the collimator. Such linings comprise a neutron absorber, i.e. a compound having a high neutron capture cross-section. This is usually a boron-containing compound, but other alternatives are available, such as cadmium compounds or compounds of rare earth metals such as gadolinium, samarium, europium or dysprosium. Most frequently, the neutron absorber is boron carbide, which has the approximate composition B4C, one such material currently being available under the Registered Trade mark TETRABOR. For use as a neutron-absorbent lining, the neutron absorber, e.g. Tetrabor, is mixed with a synthetic resin binder, which may be, for example, a polyurethane or polyester, and depending on the nature of the binder and the relative proportions, the liner may take the form of an adherent coating on the walls of the neutron beam collimator, or it may be in the form of self-supporting, moulded blocks or sheets, which may be rigid or flexible as desired and depending on the binder. Existing neutron-absorbing formulations, however, have the disadvantage that stray neutrons impinging on the lining tend to be scattered by the binder component, which reduces the overall neutron-absorption efficiency of the lining. In accordance with the present invention, this problem is solved, or attempted to be solved, by using sulphur as the binder in such compositions. Accordingly, in one aspect, the present invention provides a neutron-absorbing lining for neutron beam collimators, or other neutron beam generating, guiding or handling equipment, and neutron beam collimators or other such equipment lined therewith, said lining comprising particles of a solid neutron-absorbing compound, preferably a boron-containing compound, most preferably boron carbide, bound into a cohesive homogeneous mass with a binder, wherein the binder is sulphur. In a second aspect, the present invention provides a composition for use as a neutronabsorbing lining in neutron beam collimators and other neutron guiding, generating or handling equipment, said composition comprising a mixture, optionally but not necessarily moulded into a compact, selfvsupporting homogeneous mass, and comprising particles of a neutron-absorbing compound and a binder therefor wherein the binder is sulphur. Preferably the neutron-absorbing compound is a boron-containing compound, most preferably boron carbide. In addition to its utility as a lining for neutron beam collimators, such compositions may also find utility in other situations where a neutron-absorbing composition or material is required. Such compositions may, for example, find utility in the construction of neutron shields surrounding a neutron source, although in such cases it may be necessary to include moderators to slow the neutrons down, particularly high energy, high velocity neutrons, sufficiently to permit absorption by the neutronabsorbing component. For use as a neutron-absorbing lining for neutron beam collimators, the mixture will generally consist of from 1-99% by weight binder, i.e. sulphur, and correspondingly 99-1% neutron absorbing compound, preferably a boron compound, most preferably boron carbide. Preferred compositions will contain from 20-50% by weight binder and 80-50% neutron-absorbing compound. The compositions of this invention can be formulated and fabricated by a variety of mixing and moulding techniques. For example, and taking advantage of the relatively low melting point of sulphur. Thus, the neutronabsorbing compound, e.g. boron carbide, particles may be blended with molten sulphur and the molten blend moulded, cast or extruded into any desired shape, or the neutron-absorbing compound and the sulphur can be dry mixed and moulded into the desired shape by moulding under heat and pressure. To illustrate the invention, two blends were prepared by dry mixing flowers of sulphur and boron carbide particles in the proportions 30:70 and 40:60 respectively. Each blend was compacted and heated to fuse the sulphur thereby providing a homogeneous compact block of boron carbide particles bound together with sulphur. Such blocks and blends are admirably suited as a lining for neutron beam collimator pipes to eliminate or reduce surface scatter, which interferes with the object in hand, e.g. the study of particle scatter by a given target bombarded with the main neutron beam. CLAIMS

1. A neutron-absorbent lining composition for neutron beam collimator pipes, or other neutron-beam generating, guiding or handling equipment, comprising particles of a solid neutron-absorbing compound and as a binder therefor sulphur.

2. A composition according to claim 1, wherein the neutron absorbing compound is boron carbide.

3. A composition according to claim 1 or 2, containing 80 to 50% by weight neutron absorbing compound and 20 to 50% by weight binder.

4. A neutron-beam collimator pipe, or other neutron-beam generating, guiding or handling equipment comprising a neutron-absorbent lining constructed of a composition according to any one of claims 1-3.