Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/167—Measuring radioactive content of objects, e.g. contamination
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T7/00—Details of radiation-measuring instruments

Definitions

• the field of this invention is the measurement of ionizing radiation emitted by a source, and here we are concerned with correcting the measurement by overcoming the influence of background noise.
• the term “detector” has a broad meaning and can be translated in reality by a set of several detection sets. Attempts have already been made to avoid the effect of the background noise produced by this surrounding radioactivity. It is therefore common for the main detector, responsible for measuring the radiation from the source, to be supplemented by an auxiliary detector specifically responsible for measuring background noise. When it detects background noise of a level deemed to be excessive, the measurement of the radiation from the source is not undertaken and we can wait for more favorable circumstances for the which, however, is not convenient.
• the auxiliary detector completely envelops the main detector and the source when it is present: it then measures the ambient radiation originating from all directions in a uniform manner, but it does not prevent part of the ambient radiation to cross it and reach the main detector, which further falsifies the measurement.
• This radiation can be transmitted directly or after having been diffused and affected by the Compton effect, that is to say supplied at a different energy, which makes it difficult to evaluate according to the part of the radiation that the auxiliary detector has stopped.
• auxiliary detector is also sensitive to radiation originating from the source, transmitted directly or after passing through the main detector, it can be understood that these correction calculations are difficult to apply and require a complicated electronic operating system (anti-Compton devices) .
• the object of the invention is therefore to correct the influence of background noise, in the particular case of ionizing radiation measurements where it is very difficult to distinguish the influence of the various origins of the radiation, by means of a set detection and a process each improved.
• the invention consists in correcting the measurements of the main detector, responsible for evaluating the radiation from the source, estimating the background noise it records and subtracting it from these measurements; it relates to a unit for measuring ionizing radiation, comprising a main detector responsible for measuring radiation emitted by a determined source and an auxiliary detector responsible for measuring ambient radiation, characterized in that it comprises means for correlating the measurements made by the two detectors and the correction of the measurements made by the primary detector as a function of the results of the correlation; as well as a method for measuring ionizing radiation, comprising a main measurement of a main radiation emitted by a determined source and an auxiliary measurement of ambient radiation, as well as corrections of the main measurement as a function of the auxiliary measurement, characterized in that the main measurement begins before bringing the source and is compared with the auxiliary measurement to obtain a correlation, and in that, when the source has been brought, the main measurement is corrected according to the correlation and simultaneous auxiliary measurement.
• Figure 1 is a schematic view of the detection assembly
• Figures 2 and 3 are graphs of raw and corrected measurements.
• the whole of the invention which in a particular form can constitute an assembly called a portal for detection in specialized language, is in this case intended primarily to measure the activity of radioactive objects of various natures which pass in front of it. It comprises at least one main detector or measurement detector 1 responsible for measuring the activity of an irradiating source, and at least one auxiliary detector or guard detector 2 responsible for measuring the ambient radiation responsible for the background noise.
• Detectors 1 and 2 can be placed side by side at a greater or lesser distance from each other, or possibly, what is shown here, on either side of a location 3 occupied the source S.
• the source S is any object, of undetermined size and often of low activity in practice, such as the loading of a truck, a concrete block, a barrel of waste, etc.
• Detectors 1 and 2 which are only shown here, conventionally include a number of radiation detectors which receive ionizing radiation and convert it into electrical signals.
• the measurement detector 1 is of course sensitive to radiation from location 3, while the guard detector 2 can be made sensitive to radiation from all directions except location 3, from which it is separated by a shielding 4. These conditions are general enough for a large number of arrangements of detectors 1 and 2 to be possible.
• the application of the invention is not limited to gamma radiation, but is also possible for other types of radiation: alpha, beta, and X, in particular configurations of the main detector and the auxiliary detector.
• the work required of the detection unit generally includes relatively short measurement periods separated by much longer periods of inactivity and which can reach several hours. However, these periods of inactivity are used to make measurements of ambient radioactivity.
• the measured values alo-r-s by the two detectors 1 and 2 are recorded separately and compared.
• the inventors made the important observation that the measurements were correlated with one another and could therefore be deduced from each other by a regression operation.
• the counters 5 and 6 to which the detectors 1 and 2 are respectively connected and which serve to simultaneously record their measurements are read by a computer 7 which calculates the coefficients of the correlation curve, which in practice is sufficiently approximated by a straight line.
• the guard detector 2 continues to measure the ambient radiation.
• the computer 7 deduces therefrom the effect of this radiation on the measurement detector 1, that is to say the intensity of the background noise which it must restore and subtracts it from the total provided by the counter 5 to obtain the value of the radiation from source S. The results currently obtained have demonstrated the validity of the process.
• FIG. 2 shows, in addition to the corap-tage rates g and m for acquisition periods T of 10 min, measurements m X ⁇ , m x and m x3 carried out in a measurement period P3 with three successive sources.
• Line L is the detection limit, below which it is estimated that radiation can no longer be measured properly: “reduced” noise is still below this limit and the results appear suitable even for the third source, whose activity is barely above this limit.
• the invention does not only facilitate the detection of radiation, but also its measurement; it can therefore be applied to devices other than detection gates.

Landscapes

• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Physics & Mathematics (AREA)
• High Energy & Nuclear Physics (AREA)
• Molecular Biology (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Measurement Of Radiation (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=8847043

Family Applications (1)

Country Status (4)

Families Citing this family (4)

Family Cites Families (10)

• 2000
  • 2000-02-16 FR FR0001900A patent/FR2805048B1/fr not_active Expired - Fee Related
• 2001
  • 2001-02-15 EP EP01907808A patent/EP1256018A1/de not_active Withdrawn
  • 2001-02-15 US US10/182,782 patent/US20030004406A1/en not_active Abandoned
  • 2001-02-15 WO PCT/FR2001/000448 patent/WO2001061378A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events