# US 5,326,974 A · Range-finding method and device

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- Number: US 5,326,974 A
- Document ID: US5326974A
- Status: Granted
- Kind: A
- Application number: 07/863,300
- Filed: 1992-06-19
- Granted: 1994-07-05
- Earliest claimed: 1989-12-20
- Assignees: Rautaruukki Oy, A Corp. of Finland
- Inventors: Matti Karras; Juha Kostamovaara
- Web page: https://patentgrep.com/patent/US5326974A

## CPC

- G01S 17/02: Systems using the reflection of electromagnetic waves other than radio waves (G01S17/66 takes precedence)
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES

## Abstract

The invention relates to a method for determining the distance of a target in difficult industrial conditions, method in which (i) one of the gamma quanta produced from a radioactive source in annihilation and traveling in opposite directions is aimed at the target and the other one at a detector, which detects it, and time measuring starts; (ii) the quantum Compton-scattered from the target is detected by the same or a separate detector, and time measuring stops; (iii) the distance of the target is calculated from the time difference between (i) and (ii). The invention also relates to a device for carrying out the method, the device comprising a radioactive source, a scintillation crystal counter/counters, a time-amplitude converter (TAC) and a pulse height analyzer (PHA).

## Claims

### Claim 1

A method for determining distance of a target comprising: (i) one of the gamma quanta, traveling in opposite directions, created from a radioactive source in .beta..sup.+ annihilation, travels to the target and the other one to a detector, which detects it, and time measuring starts; (ii) a quantum Compton-scattered from the target is detected by the same or a separate detector, and time measuring stops; (iii) the distance of the target is calculated from the time difference between (i) and (ii).

### Claim 2 (depends on 1)

A method according to claim 1 wherein the target is steel.

### Claim 3 (depends on 1)

A method according to claim 1 wherein the radioactive source is a positron emitter.

### Claim 4 (depends on 1)

A method according to claim 1 wherein a layer of medium is disposed between the target and the source.

### Claim 5 (depends on 1)

A method according to claim 1 wherein a layer of medium is disposed on the target.

### Claim 6 (depends on 5)

A method according to claim 5 wherein the layer of medium on the target is slag.

### Claim 7 (depends on 5)

A method according to claim 5 wherein the layer of medium on the target has a thickness measured on the basis of a width of a distance spectrum.

### Claim 8 (depends on 1)

A method according to claim 1 wherein the radioactive source is a Na-22 radioisotope.

### Claim 9

A device for determining distance of a target comprising:
(a) a radioactive source in which two gamma quanta, traveling in opposite directions, are produced;
(b) a first scintillation crystal detector, which detects the first gamma quantum and is located on the opposite side of the radioactive source in relation to the target;
(c) a second scintillation crystal detector, which detects the second gamma quantum, traveling to the target and being Compton scattered from it, which detector may be the same as the detector detecting the first gamma quantum or another, separate detector;
(d) a time-amplitude converter, to which pulses from the first and the second scintillation crystal detectors are taken and which converts the time difference between the observed first and second gamma quanta into an output pulse amplitude; and
(e) a pulse height analyzer, in which the measuring result is stored and printed out.

### Claim 10 (depends on 9)

A device according to claim 9 wherein the radioactive source is a positron emitter.

### Claim 11 (depends on 9)

A device according to claim 9 wherein the radioactive source is a Na-22 isotope.

### Claim 12 (depends on 9)

A device according to claim 9 wherein the radioactive source is a .beta..sup.+ emitter.