Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Patent
1992-06-19
1994-07-05
Fields, Carolyn E.
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
250369, 250393, 250394, G01S 1708
Patent
active
053269748
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and device for determining a distance on the basis of measuring the time of travel of gamma radiation.
In the metal industry there are problems of range-finding related to the surface level in ore reduction furnaces; these problems are complicated by the corroding and hot flue gases present in the range-finding space. The object of the present invention is to eliminate these problems.
Among the range-finding methods currently used in industry, the method according to the present invention is in principle similar to pulsed time-of-flight laser range-finding, in which the time of travel of light is used for range-finding. Owing to the limitations associated with the use of the laser, it cannot be used in all range-finding applications. The most significant of the limitations is perhaps the requirement of visual contact with the target to be measured by the laser beam. For this reason, for example, smoke, gases, dust, etc., prevent range-finding or hamper it. Another difficulty in the use of the laser appears in the measuring of targets having a high temperature, which increases noise in the measuring receiver and thereby increases imprecision in the measurement. On the other hand, imprecision increases because the propagation speed of light changes when the temperature of the medium changes. However, in industry there are numerous range-finding targets of the type mentioned above, and therefore it is necessary to develop other possible range-finding methods.
SUMMARY OF THE INVENTION
It has now been discovered that gamma radiation can be exploited in range-finding. Gamma quanta travel in air at the vacuum speed of light, regardless of the pressure, humidity or temperature of the air. Furthermore, owing to their high energy they will penetrate media (about 10 g/cm.sup.2), and so visual contact with the target is not needed. The method and device according to the invention are thus suitable for the determination of the surface level in the metal industry, for example in converters in the steel industry and in flash smelting furnaces in the copper industry. Furthermore, the invention also has uses in other metal industry processes, in which light arc furnaces are used in which the melting and reduction of the batch cannot be monitored using present-day surface level meters. The surface to be measured may be metal, mineral, or metal covered by slag. The method and device according to the invention can also be used for determining the thickness of a layer of slag or ceramics on top of metal. It is a further advantage of the method and device according to the invention that they save energy by improving process control. The source used may be a positron-emitting radio isotope, for example an Na-22 isotope.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a generic block schematic diagram of a range-finding device constructed according to the teachings of the present invention;
FIG. 2 is a functional diagram of the device of FIG. 1;
FIG. 3 is an example of a distance spectrum obtained by the device of FIG. 1;
FIG. 4 is another example of a distance spectrum obtained by the device of FIG. 1;
FIG. 5 is an example of a width of a distance spectrum which may be used to measure thickness of a layer or a target; and
FIG. 6 is a generic block schematic diagram of another embodiment of the range finding device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the method according to the invention, collimated gamma radiation is emitted to the target 16 to be measured, and the scattered gamma radiation returning from the target 16 is detected using a detector 14 or 10, as shown in FIGS. 1 and 6, respectively. The invention is based on .beta..sup.+ annihilation. When the source of radiation used is, for example, an Na-22 radio isotope, a 1.28 MeV gamma quantum and a positron are produced as a result of radioactive decay. The life of the positron produced is short, after which it is annihilated with an electron. In the annihilation the masses of the
REFERENCES:
patent: 3099744 (1963-07-01), Spooner
patent: 3567938 (1971-03-01), Piekenbrock
patent: 3718817 (1973-02-01), Afanasjev et al.
patent: 4559597 (1985-12-01), Mullani
Karras Matti
Kostamovaara Juha
Fields Carolyn E.
Rautaruukki Oy, A Corp. of Finland
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