Method and device for patrol inspecting and locating a radioactive substance

• US 9,829,601 B2
• Filed: 12/20/2012
• Issued: 11/28/2017
• Est. Priority Date: 12/23/2011
• Status: Expired due to Fees

• Current Assignee: Nuctech Company Limited (Tsinghua Tongfang Co., Ltd.)
• Original Assignee: Nuctech Company Limited (Tsinghua Tongfang Co., Ltd.)
• Inventors: Wang, Qiang, Zhao, Kun, Ruan, Ming
• Primary Examiner(s): Lee, Paul D
• Application Number:
  US14/367,824
• Publication Number:
  US 20150025841A1
• Time in Patent Office: 1,804 Days
• Field of Search: 702150
• CPC Class Codes: G01T 1/00 Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation G01T3/00, G01T5/00 take precedence
• CPC Class Codes: G01T 1/169 Exploration, location of contaminated surface areas
• CPC Class Codes: G01T 7/00 Details of radiation-measuring instruments
• CPC Class Codes: G01V 5/20 Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects

Abstract

A method for patrol inspecting and locating a radioactive substance, comprising: providing a background radioactive intensity value of environment; collecting radioactive intensity values from a inspecting region by a detector at a plurality of sampling points on a patrol inspection route; calculating a radioactive intensity distribution in the inspecting region on basis of the collected radioactive intensity values and the background radioactive intensity value; and determining a position of the radioactive substance on basis of the radioactive intensity distribution. Furthermore, a device for patrol inspecting and locating a radioactive substance comprises: two or more detectors configured to collect radioactive intensity values from a inspecting region around a patrol inspection route, at each of a plurality of sampling points on the patrol inspection route; and a movable carrier configured to carry the detector and to move along the patrol inspection route to pass by the sampling points. The method and device can obtain the position and the radioactive intensity distribution of the radioactive substance within the inspecting region on basis of the multiple-point observation on the patrol inspection route.

Claims

1. A method for patrol inspecting and locating a radioactive substance, comprising:

(a) providing a background radioactive intensity value of an environment;

(b) collecting, at a plurality of sampling points on a patrol inspection route, radioactive intensity values from an inspecting region by a detector carried by a movable carrier passing by the plurality of sampling points on the patrol inspection route;

(c) calculating a radioactive intensity distribution in the inspecting region on a basis of the collected radioactive intensity values and the background radioactive intensity value; and

(d) determining a position of the radioactive substance on a basis of the radioactive intensity distribution,

wherein the method further comprises a step (b2) between the step (b) and the step (c);

determining whether a barrier has had an effect on a radioactive intensity value by determining whether there is a data segment, in which the radioactive intensity values drop abruptly and then increase abruptly, in the sequence of the radioactive intensity values collected at multiple continuous sampling points, and deleting the data segment to eliminate effects of the barrier if it is present.

2. The method for patrol inspecting and locating a radioactive substance according to claim 1, wherein the method further comprises a step (b1) between the step (b) and the step (c):

determining whether the differences between the collected radioactive intensity values and the background radioactive intensity values are greater than a collecting threshold, and carrying out the step (c) if they are greater than the collecting threshold;

otherwise, if they are not greater than the collecting threshold, updating the background radioactive intensity values by a weighted average of the collected radioactive intensity values and the background radioactive intensity values and returning to the step (b) to recollect the radioactive intensity values.

3. The method for patrol inspecting and locating a radioactive substance according to claim 1, wherein the detector comprises at least two detectors facing towards the inspecting regions in different directions respectively, the detectors being separated by a shielding part from each other.

4. The method for patrol inspecting and locating a radioactive substance according to claim 1, wherein the radioactive intensity values are represented by counting rate or dose rate.

5. The method for patrol inspecting and locating a radioactive substance according to claim 1, wherein the step (c) comprises a step (c1):

dividing the inspecting region into a plurality of subregions, providing the detection efficiencies of the detector to the subregions and determining the radioactive intensity of each subregion on basis of the background radioactive intensity and the detection efficiencies.

6. The method for patrol inspecting and locating a radioactive substance according to claim 5, wherein the number of the subregions is not greater than the number of the sampling points.

7. The method for patrol inspecting and locating a radioactive substance according to claim 5, wherein the detection efficiencies are calibrated for a certain radiation energy range and/or species of the radioactive substance.

8. The method for patrol inspecting and locating a radioactive substance according to claim 5, wherein the step (c) further comprises a step (c2):

drawing a map of radioactive intensity distribution in the inspecting region on a basis of the radioactive intensity in each subregion.

9. The method for patrol inspecting and locating a radioactive substance according to claim 5, wherein the division of the subregions is carried out in one dimension, two dimensions or three dimensions.

10. The method for patrol inspecting and locating a radioactive substance according to claim 5, wherein the detector is provided on a movable carrier, the collected radioactive intensity value is

11. The method for patrol inspecting and locating a radioactive substance according to claim 10, wherein the step (c1) is performed by sparse decomposition of a vector C on a vector set D, in which the vector C=(c₁-b₁, . . . , c_N-b_N)^T, the vector set D={D_m}, D_m=(Φ

(p_m, q₁, θ

₁), . . . , Φ

(p_m, q_N, θ

_N))^T.

12. The method for patrol inspecting and locating a radioactive substance according to claim 11, wherein the step of determining the radioactive intensity of each subregion further comprises:

(c11) defining a set S of indexes and a residual vector R, and setting an initial value S₀ of the set S as an empty set, an initial value R₀ of the residual vector R as vector C, and an initial value of a_m as zero;

(c12) defining a projection of the R₀ on the vector Dm in the vector set D as P_m, defining the value of m corresponding to the maximum of Pm as n, then adding n into S₀ to update the set S and updating the residual vector R such that the updated residual vector R is a difference between the vector C and the projection of the vector C on the vector D_n;

(c13) determining whether the norm of the updated residual vector R is less than a residual threshold, and if the norm is less than the residual threshold, a_m will be calculated as the projection coefficient of the vector C on the vector D_m, in which only if m falls within the updated set S, the calculation result of a_m is nonzero, while if m falls out of the updated set S, the calculation result of a_m is zero;

otherwise, if the norm of the updated residual vector R is not less than the residual threshold, the R₀ and S₀ will be replaced by the updated residual vector R and the updated set S respectively to perform the step (c12) again to update the residual vector R and the set S repeatedly until the norm of the updated residual vector R is less than the residual threshold or a cycle number of performing the step (c12) repeatedly meets a predetermined value.

13. The method for patrol inspecting and locating a radioactive substance according to claim 12, wherein the step (d) comprises the step:

(d1) determining the subregion in which the calculation result of a_m is nonzero as an active subregion and determining the subregion in which the radioactive substance is located on a basis of the distribution of the active subregion and the calculation result of a_m.

14. The method for patrol inspecting and locating a radioactive substance according to claim 13, wherein the step (d1) comprises:

numerically solving a position of the active subregion when an error function has its minimum value, the error function being

15. A device for patrol inspecting and locating a radioactive substance and for carrying out the method according to claim 1, the device comprising:

two or more detectors, configured to collect radioactive intensity values from a inspecting region around a patrol inspection route, at each of a plurality of sampling points on the patrol inspection route; and

a movable carrier, configured to carry the detector and to move along the patrol inspection route to pass by the sampling points,

wherein the detectors face towards different directions around the sampling points respectively and are separated by a shielding part from each other.