Neutron radiography method and apparatus for the implementation thereof

Abstract

A method and apparatus for neutron radiography is provided for the examination of elongate radioactive items, primarily nuclear fuel elements, and also for the non-destructive testing of irradiated and non-irradiated objects in order to determine the internal structure and material composition thereof. The method and apparatus include placing an object under examination into a protective container. A detection system includes a rotatable limb with a mounting seat for securing neutron detectors in a diametric groove. The limb being mounted to be rotatable by a set angle about an axis parallel to the axis of the object under examination and having a semi-circular recess therein for the passage of an elongate object as the limb rotates by an angle ±α.sub.i relative to the direction of a neutron beam.

Claims

1. An apparatus for neutron radiography of an object under examination, comprising: a source of neutrons a protective container for the object under examination, a detection system having an activation detector, wherein the detection system is made in the form of a rotary limb having a seat in the form of a diametrical groove for securing the activation detector, a bed having disposed thereon a detection system being mounted such as to be rotatable by angles +α and −α about an axis parallel to the axis of the object under examination, wherein the limb has a semi-annular recess therein for the object under examination placed in the protective container, as well as for ensuring rotation of the limb at angle of +α and −α relative to the neutron source.

2. The apparatus according to claim 1, wherein a rotation center of the limb is additionally mounted in a ball-bearing integrated into the bed and the limb rests upon rollers arranged in an annular track of the limb.

3. The apparatus according to claim 1, wherein the limb is configured to automatically rotate at angles +α and −α.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an overall view of an apparatus, and

(2) FIG. 2 (a) shows a top view of the apparatus mounted on a limb, and FIG. 2 (b) shows a detector mounted in a groove.

DETAILED DESCRIPTION

(3) In Figures: 1—collimated neutron beam; 2—object under examination; 3—protective container; 4—bed; 5—mounting seat (socket); 6—locker; 7—rotatable limb; 8—groove; 9—limb rotation axis; 10—ball bearing; 11, 12—activation detectors; 13—semi-annular recess on limb; 14—mechanism for limb rotation and fixation at a pre-determined angle.

(4) An object under examination (a sample, an item) 2 is placed in a protective container 3. The container 3 is arranged on a bed 4 via a mounting seat 5 and is rigidly secured with a locker 6. The bed 4 is provided with a rotatable limb 7 in the form of a rotatable disk with an annular recess 13 an angular length of which is 180° and width is equal to a diameter of the container 3 with the object under examination 2 inside.

(5) A rotation axis 9 of the limb 7 is mounted in a ball bearing 10 integrated into the bed 4 and the limb rests upon rollers (not shown) and has an annular recess 13. Paired activation detectors 11 and 12, the height of which has to be equal to the height of the radiographically viewed object under examination 2, are mounted alternately in the groove 8. Each of the activation detectors 11 and 12 mounted downstream the object under examination 2 can be one piece or composed of several parts. For statistics purpose (to a certain extent eliminating accidents caused by low-quality photomaterials used at subsequent stages of the imaging process), the same item 2 can be examined by this method several times. A selected angle of rotation of neutron detectors with respect to the beam axis is defined with the use of a known rotation and fixation mechanism 14, for instance, a synchro pair (a synchro generator and a synchro receiver), a discrete gear drive, a hole system below the limb on a stationary support and a spring-loaded locker on the limb 7, etc. The applied method has to ensure that the activation detectors 11 and 12 will be rotated to selected incident angles of a neutron beam which are numerically equal to each other (|+α.sub.i|=|−α.sub.i|), where the neutron beam is implemented during a first session of “radiographic viewing” of an object under examination and then during the second session.

(6) After the first “radiographic viewing”, in order to capture a good (with no loses) image of the activity generated on the activation detector having a low half-life, the activity distribution obtained on the activation detector 11 is transferred to an X-ray film, without waiting for the second irradiation. After the second activation detector 12 (with the same low half-life) has been irradiated, the image capturing procedure is repeated and this image is transferred on a second X-ray film. Next, negative images on the X-ray films are, in turn, transferred in a usual way on two photocopies. Both X-ray films (or photocopies) are viewed simultaneously on the corresponding stereoscopic equipment which is configured to combine these aspects in one three-dimensional visual object. The usage of such equipment and two X-ray films makes it possible to generate a 3D-image of the item 2 under examination.

(7) By changing an orientation angle of activation detectors 11, 12 at a neutron beam (α.sub.i) and an obtained pair of X-ray images, respectively, it is possible, in two or three steps, to fully describe available patterns of defects in an object under examination, the state of shells, welds produced either during the manufacture, or in the result of modifications due to the intensive impact of reactor radiations and high temperatures.