# US 4,395,633 A · Level gauge using neutron irradiation

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- Number: US 4,395,633 A
- Document ID: US4395633A
- Status: Granted
- Kind: A
- Application number: 06/182,183
- Filed: 1980-08-28
- Granted: 1983-07-26
- Earliest claimed: 1979-09-11
- Assignees: Commonwealth Scientific and Industrial Research Organization
- Inventors: Plackottu J. Mathew
- Web page: https://patentgrep.com/patent/US4395633A

## CPC

- G01F 23/2885: {for discrete levels}
- G01F 23/288: X-rays; Gamma rays {or other forms of ionising radiation}
- G01F: MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME

## Abstract

Measurement of the level of materials in bins, hoppers, and the like is effected by a neutron monitoring technique. A sensor is located to move substantially vertically in a guide located in or near the bin or hopper. The sensor contains a fast neutron source, a detector of thermal neutrons, and a moderator-containing material in the vicinity of the detector. In a preferred form of the sensor, the neutron source and thermal neutron detector are separated by lead and cadmium screening, and the moderator-containing material is a sheath of polyethylene around the detector. With sensors of this type, material levels may be sensed whether the material contains a neutron moderator or not.

## Claims

### Claim 1

Apparatus for determining the level of a material in a container, said apparatus comprising;
(a) generally vertical guide means extending between the base and the top of the container;
(b) a sensor positioned within said guide means;
(c) means for moving said sensor along said guide means; and
(d) means for monitoring the position of the sensor within the guide means; said sensor comprising
(i) a source of fast neutrons;
(ii) a detector for thermal neutrons, and
(iii) a sheath of a moderator-containing material surrounding said detector; whereby thermal neutrons produced by irradiation of the material by said fast neutrons and thermal neutrons produced by irradiation of said moderator-containing material by neutrons reflected by the said material are detected by said detector when said sensor is positioned within said guide means at a level which is not substantially higher than the level of the material in the container.

### Claim 2 (depends on 1)

Apparatus as defined in claim 1, wherein said sheath is removably located around the detector.

### Claim 3 (depends on 2)

Apparatus as defined in claim 2, in which said moderator-containing material is polythene.

### Claim 4 (depends on 3)

Apparatus as defined in claim 3, including screening of lead and cadmium between said neutron source and said thermal neutron detector.

### Claim 5 (depends on 4)

Apparatus as defined in claim 4, in which said guide means is a conduit located within the container, a cable suspending said sensor within said conduit, a cable winch is provided for lowering and raising said sensor within said conduit, and means are provided for monitoring the movement of said cable.

### Claim 6 (depends on 1, 2, 5)

Apparatus as defined in claim 1, claim 2 or claim 5, in which said guide means is located within said container.

### Claim 7 (depends on 1, 2, 5)

Apparatus as defined in claim 1, claim 2 or claim 5, in which said guide means is located outside, but alongside, said container.

### Claim 8

A method for determining the location of the top surface of a material stored in a container, said material neither comprising nor containing a neutron moderating element, said method comprising the steps of
(a) irradiating said material with fast neutrons;
(b) monitoring the thermal neutrons generated in a neutron-moderating medium by the action of fast neutrons scattered by said material, said neutron-moderating medium being located in the vicinity of said material; and
(c) moving said neutron-moderating medium substantially vertically within the levels of the top and bottom of said container and noting the level at which there is a discontinuity in the production of said thermal neutrons.