Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
1999-06-14
2002-04-30
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
C250S363010, C378S063000
Reexamination Certificate
active
06380541
ABSTRACT:
TECHNICAL DOMAIN
This invention relates to a device for localizing radiation sources.
It is particularly applicable to locating radiation sources that may be contained in a room, for example such as a high activity cell, or which may accidentally be present in a room.
STATE OF PRIOR ART
A device for localizing radiation sources has previously been described in the following document which should be referred to:
(1) French patent application No. 8500088, Jan. 4 1985 (see also EP-A-0 188 973 and U.S. Pat. No. 4,797,701).
The device described in the application mentioned above localizes radiation sources by using a pinhole chamber in which a film sensitive to radiation and a film sensitive to visible light are placed in the area in which sources of radiation are likely to be located, together with a shutter that opens to take a photograph in visible light and which is transparent to radiation from sources.
The radiation sources can be localized in their environment after these films have been developed and superposed (but not in real time).
An improvement to the device described in document (1) is known by the following document which should be referred to:
(2) French patent application No. 8913281, Oct. 11, 1989 (see also EP-A-0425333 and U.S. Pat. No. 5,204,533).
A particular embodiment of the device described in this document (2) is shown diagrammatically in FIG.
1
.
This device is designed to determine the location of radiation sources
2
in real time, and particulary gamma radiation sources (for example X or beta radiation).
It comprises a pinhole chamber
4
formed in a body
6
that shields chamber
4
from gamma radiation.
The shielding thus absorbs radiation from sources
2
and parasite radiation from other sources that may be outside the field.
The body
6
may be made of an appropriate material such as a tungsten based alloy known under the name “Denal”.
Means
8
symbolize a rotatable support of body
6
and therefore of the device.
The body
6
comprises a collimator
10
facing the chamber
4
.
The wall of the collimator
10
consists of two coaxial cones with the same vertex angle, opposite each other through their common summits in which a hole is drilled to form the pinhole
12
.
This collimator
10
may comprise a part
14
opaque to visible light originating from the examined area but permeable to gamma radiation, around the pinhole
12
, to deal with the case in which the activity of the gamma radiation sources that are to be localized (pinhole with double diaphragm) is insufficient.
Furthermore, the collimator
10
may be interchangeable, so that a single or double diaphragm collimator can be chosen with a vertex angle appropriate to the presumed activity of the gamma sources
2
to be located.
Furthermore, changing the collimator
10
can increase or reduce the object field covered by the device, depending on the taper and focal length chosen for this collimator.
The device also comprises a mechanical shutter
16
designed to prevent visible light from the area in which the sources
2
are located, from penetrating into chamber
4
, while allowing gamma radiation to pass.
This shutter
16
is a camera type iris, or for example a retractable metal plate perpendicular to the axis
18
of the chamber
4
(the axis of two cones forming the optical axis of the device) and located close to the pinhole
12
on the side of chamber
4
.
Movements of the plate forming the shutter
16
are remote controlled by electromechanical means
20
themselves controlled by the remote control box
22
.
This remote control box may be located at a long distance from the device if necessary.
The device also comprises a luminescent screen
24
in chamber
4
facing the pinhole
12
, which is in contact with a circular shoulder inside body
6
, at the same level as the bottom of the conical surface of the collimator
10
.
There is a camera
26
behind screen
24
connected to real time means
28
for the acquisition, processing and displaying electrical signals output by the camera, and storage means
30
.
When the shutter
16
is closed, the image of the gamma radiation sources is obtained at the end of a specific time (a few seconds, for example 10 s).
This image is stored in a first memory area of means
28
.
By controlling the aperture of shutter
16
, an image (in visible light) of the observed area containing the sources
2
is then obtained almost instantaneously.
This second image is also stored in the second memory area in means
28
distinct from the first memory area.
After processing of the images and particularly coloring of “spots” due to the activity of sources
2
in order to clearly identify these sources and distinguish their “gamma luminosity” from the luminosity (in visible light) of objects present in the observed area but which do not emit any gamma radiation, the first and second images are displayed superposed on the screen of means
28
, so that gamma radiation sources can be identified.
Note also that the luminescent screen
24
is transparent in the visible range and is capable of converting the gamma radiation from sources
2
reaching it through the pinhole
12
into visible radiation through camera
26
that is designed to output an image of the scene that this camera observes through the pinhole
12
(when the shutter
16
is open) in the form of electrical signals.
The entry window into the camera
26
is placed in contact with screen
24
, the screen being thus placed between the pinhole
12
and the camera
26
.
The choice of the screen material depends on the activity of sources to be located.
If the activity is very low, an NaI screen can be used; if it is not too strong, a bismuth germanate (BGO) screen can be used, and if the activity is strong, a scintillating plastic screen can be used, for example sufficient to detect X or beta radiation.
One possible choice, which is in no way restrictive, is to use a camera
26
of the type marketed by the LHESA company which has a sensitivity of 10
−7
lux and which comprises an image reducer with optical fibers
26
a,
on which the plane input face is in contact with the screen
24
, this reducer being followed by an image intensifier
26
b
that is itself followed by a charge transfer matrix (CCD) marked in
FIG. 1
as reference
26
c.
Coupling by optical fiber image reducer
26
d
links matrix
26
c
to intensifier
26
b.
An improvement to the device described in document (2) is also known in the following document, which should be referred to:
(3) French patent application No. 9403279, Mar. 21 1994 (see also EP-A-0674188 and U.S. Pat. No. 5,557,107).
This device known through document (3) comprises a collimator in front of the pinhole chamber, comprising two half-collimators free to move in rotation around a common rotation axis.
This particular collimator performs the following three functions:
easy interchangeability with the collimator,
the possibility of changing from the visible observation range to the gamma observation range (shutter), and
variation of the focal length of the collimator.
In the device shown in
FIG. 1
, the quality of the image in visible light depends mainly on the size of the diaphragm used for formation of this image.
This size must not be too large to prevent geometric blur, and it must not be too small to prevent blur due to diffraction.
As we have already seen, an attempt is made to optimize the image quality in visible light by using a pinhole consisting of a double diaphragm, namely a small diaphragm adapted to the formation of this visible image, and a larger diaphragm adapted to the formation of an image of radiation sources (for example gamma).
However, even after optimizing the aperture in the diaphragm, the quality of images in visible light obtained with a device of the type shown in
FIG. 1
is not satisfactory.
The same is true for the device described in document (1).
DESCRIPTION OF THE INVENTION
The purpose of this invention is to overcome the disadvantage mentioned above by suggesting a device for localizing radiation sources capable of identifying t
Gal Olivier
Gaucher Séverine
Laine Frederic
Anderson Kill & Olick
Commissariat a l'Energie Atomique
Ham Seungsook
Lee Shun
Lieberstein Eugene
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