Device for the real time location of radiation sources

A device locating radiation sources includes a pinhole camera, a collimator means for closing off or obturating the camera, a luminescent or phosphor screen, and a camera optically coupled to the screen. The collimator comprises two half-collimators rotatable about a common rotation axis (AA').

TECHNICAL FIELD AND PRIOR ART 
The present invention relates to a collimator-shutter assembly, 
particularly for a gamma camera. 
The invention more particularly applies to a device like that described in 
European patent application EP-A-425 333 filed in the name of the 
applicant (U.S. Pat. No. 5,204,533) and entitled "Device for the real time 
location of radiation sources". The device described in the above 
application is illustrated in FIG. 1. 
This device is intended for the locating of radiation sources 2, particular 
gamma radiation sources, which may be located in a room. It has a pinhole 
camera 4 formed in a body 6 constituting a shield for the said camera 4 
with respect to the gamma radiation. This body 6 can be made from a 
suitable tungsten-based alloy, such as the alloy known under the name 
Denal. It can comprise a detachable, peripheral portion 8 in which is 
inserted the remainder 10 of the body, which makes it possible to choose a 
peripheral shield 8 of varying thickness as a function of the level of 
activity of the surrounding sources 2. Means 12 symbolize an orientable 
support of the body 6 and therefore the device. 
The remainder 10 of the body 6 comprises a collimator 14 facing the camera 
4. The wall of the collimator 14 is constituted by two cones having the 
same aperture angle and opposed by their common apex, which is perforated 
in order to form the pinhole 16. 
Level and around the pinhole 16, said collimator 14 can comprise a portion 
18 opaque to the visible light coming from the examined area, but which is 
permeable to the gamma radiation, in order to take account of any 
inadequacy on the part of the activity of the gamma radiation sources 2 
which it is wished to locate (double diaphragm pinhole). 
Moreover, the collimator 14 can be interchangeable, which makes it possible 
to choose a single or double diaphragm collimator, having an aperture 
adapted to the assumed activity of the gamma sources 2 which it is wished 
to locate. 
The device also has a mechanical obturator or shutter 20 for preventing the 
visible light from the area to penetrate the chamber 4, whilst permitting 
the passage of the gamma radiation. This shutter 20 is a photographic 
camera-type iris or, for example a metal plate perpendicular to the axis 
22 of the body 6, located in the vicinity of the pinhole 16, on the side 
of the camera 4 and which is retractable. The movements of the plate 
forming the shutter 20 are remotely controlled by electromechanical means 
24, which are themselves controlled by a remote control case 26, which can 
be located at a considerable distance from the device, if this proves 
necessary. 
In the camera 4 and facing the pinhole 16, the device also has a 
luminescent or phosphor screen 28, which rests against an internal, 
circular shoulder of the body 6, level with the base of the conical wall 
of the collimator 14. 
Behind the screen 28 is located a camera 30 connected to means 40 for the 
real time acquisition, processing and display of electrical signals and to 
the storage means 42. 
When the shutter 20 is closed, at the end of a certain time (a few seconds, 
e.g. 10 s) the image of the gamma radiation sources is obtained. This 
image is stored in a first area of the memory of the means 40. 
Then, by controlling the opening of the shutter 20, in quasi-instantaneous 
manner an image is obtained (in visible light) of the area observed and in 
which are located the sources 2. This second image is also stored in a 
second memory area of the means 40, which is separate from the first 
memory area. 
The device shown in FIG. 1 can also comprise retractable means 44 for 
attenuating the gamma rays before they reach the screen 28. The means 44 
are e.g. constituted by a tungsten screen or shield, whose thickness can 
be approximately 1 to 3 mm and which is perpendicular to the axis 22 of 
the device and is positioned in the vicinity of the pinhole 16 on the side 
of the cone of the collimator 14. The tungsten screen and the plate 20 can 
be mobile in an appropriate recess made in the body 6, or located at the 
inlet of the collimator. 
Electromechanical means 46 are provided in the body 6 in order to control 
the retraction and putting into place of the screen 44. These means 46 are 
themselves controlled from the case 26 provided for this purpose. 
The screen 44 makes it possible to evaluate the energy of the gamma photons 
by transmission, the intensity of the spot, relative to a gamma radiation 
source, on the image of the sources, being weaker when the tungsten screen 
44 closes off the collimator 14 than when it is retracted and this applies 
the lower the energy of the radiation. 
Although this device is satisfactory in certain respects, it still causes 
certain problems. Thus, the obturation system makes it possible to ensure 
the interchangeability of the collimator 14 (which permits the choice of a 
collimator having an aperture adapted to the assumed activity of the gamma 
sources 2 which it is wished to locate), as well as an all or nothing 
obturation in order to permit the passage from the visible to the gamma 
range. However, it does not make it possible to ensure a variation of the 
focal length of the collimator. 
DESCRIPTION OF THE INVENTION 
The invention proposes solving this problem. It aims at providing a device 
for locating sources with a collimator making it possible to ensure the 
three following functions: 
an easy interchangeability of the collimator, 
the possibility of passing from the visible observation range to the gamma 
observation range (obturation), 
the variation of the focal length of the collimator. 
Moreover, as a result of the conditions under which the observations are 
made, the obturation and focal length variation functions must be ensured 
in remote manner during observation. 
The invention therefore relates to a device for the real time location of 
radiation sources, liable to be located in an area, said device comprising 
a pinhole camera, whose wall forms a shield with respect to the radiation 
of the sources, a collimator, means for obturating the pinhole camera, a 
phosphor screen, transparent in the luminous range and able to convert the 
radiation of the sources into a light radiation, the obturating means 
being on the one hand transparent to the radiation of the sources and on 
the other are able to prevent the light from the area reaching the screen, 
a camera which is optically coupled to the screen and able to supply, in 
the form of electrical signals, an image of the sources, as a result of 
the light radiation which it receives from the screen, and an image of the 
area, as a result of the light which it receives from said area through 
the screen when the obturating means are open, the sensitivity of the 
camera being adequate for it to obtain an acceptable image of the sources, 
for a given efficiency of the screen with respect to the detection of the 
radiation, the images being superimposable and visible due to the means 
for the processing and display of the electrical signals, characterized in 
that the collimator comprises two half-collimators rotatable about a 
common rotation axis, each half-collimator comprising: 
a large and a small aperture, said apertures being centred on the common 
rotation axis, the small aperture being located in a planar surface (P, 
P') perpendicular to said axis, 
a circular arc spotfacing of angle .alpha. centred on the common rotation 
axis and issuing into the surface containing the small aperture, 
a pin which can be incorporated into the circular arc spotfacing of the 
other half collimator, 
and in that the obturating means are in the form of a lamella located 
between the two planar surfaces and extending from one pin to the other, 
each pin passing through a hole in the lamella, the latter having an 
adequate width to be able to entirely obturate the two small apertures. 
Such a system ensures two functions, because: 
during the rotating of one of the two half-collimators about the common 
rotation axis, the shutter is firstly rotated about the pin or peg fixed 
to the other half collimator in order to be brought into the cutting off 
or obturating position in front of the two small apertures, 
when the pin of the rotating half-collimator abuts against one end of the 
circular arc spotfacing of the fixed half-collimator, the latter is made 
to move with the initially rotated half-collimator. 
It is therefore easily possible to combine this movement, which is a common 
rotary movement, with a translatory movement. 
Thus, one of the half-collimators can have a cylindrical outer surface, 
whose axis of symmetry coincides with the common rotation axis of the two 
half-collimators and which is threaded on its outer portion, said threaded 
portion engaging in a thread made in the wall of the pinhole camera. In 
this way, when the second half collimator is rotated, its movement is 
transformed into a translatory movement. 
The rotation of the first half-collimator can e.g. be ensured by the fact 
that said first half-collimator is integral with a cylindrical, notched, 
outer ring. 
Thus, the two functions of obturating and varying the focal length can be 
remotely ensured during inspection. 
In addition, a single control can ensure these two functions, because one 
of the functions (obturation) is ensured first and the other second. 
The objective or lens can be rotated by a motor located outside the pinhole 
camera and means are provided for transmitting the movement of the motor 
to the lens. 
The detection means can incorporate a phosphor screen, a camera optically 
coupled to the screen and means for processing and displaying signals from 
the camera. 
The camera can be placed inside or outside the pinhole camera. In the 
latter case it is coupled to the phosphor screen by an optical fibre 
bundle. 
Finally, the assembly can be inserted in a mechanical protection envelope.

DETAILED DESCRIPTION OF EMBODIMENTS 
FIG. 2 is a sectional view of a source locating device according to the 
invention. It is possible to see an outer body 52 or envelope for 
providing a mechanical and radiological protection for the complete 
camera. 
This mechanical protection contains a second envelope or protective wall 54 
which serves, when the camera is inserted in an environment where gamma 
rays are emitted, to protect electronic or optoelectronic components which 
might be sensitive to said rays. The envelope or wall 54 defines a pinhole 
camera 55 and has a front opening 56 for receiving the lens 58 (FIG. 2). 
This collimator, which is also shown in greater detail in FIGS. 3 and 4, 
comprises two portions 60, 62, each of which has a large 64, 66 and a 
small 68, 70 aperture. The two portions are rotatable about a common axis 
AA'. Hereinafter the portion 60 will be called the front half-collimator 
and the portion 62 the rear half-collimator. 
The large and small apertures of each half-collimator are inscribed on a 
cone of revolution, whose axis of symmetry coincides with the common 
rotation axis of the two half-collimators. The apex angle of the cone can 
e.g. be between 25.degree. and 90.degree. and the lower the radiation 
energy emitted by the sources to be located the larger said angle. 
Thus, two sets of half-collimators are obtained, one having an apex angle 
of 38.degree. and the other an apex angle of 52.degree.. 
The small and large apertures of each half-collimator are consequently 
centred on the common rotation axis AA' and each aperture is contained in 
a planar surface perpendicular to the axis AA'. For the small aperture, 
said planar surface is designated by P and P' in FIG. 4 for the 
half-collimators. 
In each half-collimator and issuing into the plane P,P' corresponding 
thereto is provided a circular arc spotfacing 72, 74 of angle .alpha., 
centred on the common rotation axis AA' of the two half-collimators. 
Preferably the angle .alpha. is 90.degree.. 
The spotfacings 72, 74 are clearly visible in FIGS. 5a to 5c, which 
constitute a section along CC in FIG. 2, as well as FIG. 4. In addition, 
each of the half-collimators of the lens comprises a pin or peg 76, 78 for 
incorporating into the circular arc spotfacing of the other 
half-collimator. These pins also traverse two holes located at the end of 
a lamella 80, positioned between the two planar surfaces P, P' and which 
fulfils the function of a shutter, when it passes between the two small 
apertures 70, 68. 
FIG. 5a will be used for explaining the operation of the collimator and in 
it the two pins 76, 78 are in abutment in the circular arc spotfacings 72, 
74. 
When a rotation about the common rotation axis AA', symbolized by the arrow 
82 in FIG. 5a, is imparted to the front half-collimator 60, the circular 
arc spotfacing 74 and the pin 76, both of which form part of the front 
half-collimator 60, are also rotated about the same axis AA'. Thus, the 
upper end of the lamella 80 also rotates, but around the pin 78, which 
remains fixed because it is integral with the rear half-collimator 62. The 
hole of the lamella 80, traversed by the pin 76, has an oblong shape, so 
that the rotation of the lamella 80 can be correctly ensured. At 
midtravel, the lamella 80 is consequently in the vertical position, as 
illustrated in FIG. 5b and closes off the small apertures 68 and 70. 
If the camera is a gamma camera, the visible rays emitted by the external 
radiation sources are stopped by said lamella 80, in their propagation in 
the direction of detection elements located within the body 54. However, 
the gamma rays could traverse the lamella 80 and then, with the aid of 
means to be described hereinafter, an image could be formed of the 
distribution of the sources emitting said gamma rays in the direction of 
the camera. 
If rotation is continued in the same direction (arrow 84 in FIG. 5b), the 
circular arc spotfacing 74 and the pin 76 continue their respective 
travel. At the end of travel, the position of the lamella illustrated in 
FIG. 5c is arrived at, i.e. the small apertures 68 and 70 are freed. 
Therefore, once again an observation in the visible range is possible. 
It must be stressed that during the rotation of the front half-collimator 
60, as illustrated in FIGS. 5a to 5c, the rear half-collimator 62 is never 
rotated. The front half-collimator is also guided in its rotation by a 
ballbearing 77, whose inner race 81 and outer race 83 respectively bear on 
the outer surface of the front half-collimator 60 and the inner surface of 
a ring 75, which extends the rear half-collimator 62 towards the front in 
such a way as to surround the front half-collimator 60. 
It is only when the rotary movement of the front half-collimator 60 
continues as from the position of FIG. 5c (broken line arrow 86) that said 
rear half-collimator 62 is also rotated, as a result of the abutment 
position of the pin 76 at the end of the circular arc spotfacing 72. The 
lamella 80 then remains in the same position with respect to the two 
half-collimators 60, 62 and the three elements 60, 72, 62 undergo the same 
rotary movement. 
If, however, the movement of the front half-collimator is reversed from the 
position of FIG. 5c (arrow 88), the lamella 80 and the front 
half-collimator 60 are returned to the position of FIG. 5b, the rear 
half-collimator 62 still remaining stationary. 
Thus, this system successively fulfils two functions: 
firstly the obturation and then non-obturation of the small apertures 70 
and 68 whilst not modifying the position of the rear half-collimator 62 
and with no variation of the focal length, 
secondly the rotation of the two half-collimators, the lamella 80 being in 
a position in which it does not close off the apertures 70 and 68, so that 
the observer sees in the visible range. It is possible to provide a 
mechanism or means for combining the rotary movement of the rear 
half-collimator with a translatory movement. Thus, if said half-collimator 
62 has a cylindrical outer surface 90 (cf. FIGS. 3 and 4) and if said 
outer surface is threaded, said half-collimator 62 can be engaged in a 
thread 92 formed in the body of the protective envelope 54. Thus, the 
rotation of the rear half-collimator 62 automatically brings about its 
displacement, e.g. towards the rear of the camera, and makes it pass from 
the front position I, illustrated in FIG. 3, to the rear position II 
therein. Thus, the thread 90 must be provided over an adequate length for 
the displacement of the collimator to be ensured between the two extreme 
positions. It can extend over the entire outer surface of the front 
portion 75 of the rear half collimator. 
Segments 85, 87 respectively fixed to the front half-collimator 60 and the 
rear half-collimator 62 make it possible, in combination with the 
ballbearing races 81, 83, to drive the front half-collimator following the 
rear half-collimator, in particular in a displacement towards the rear of 
the apparatus (direction I.fwdarw.II in FIG. 3). 
In the apparatus constructed by the applicant, the variation between the 
two extreme positions is 50 mm. 
A ring-shaped part 94 integral with the front half-collimator 60 and 
outside the latter makes it possible to rotate said half-collimator 60. As 
illustrated in FIGS. 3 and 4, the ring has a notched inner surface 96 on 
which is engaged a pinion 98, which transmits, via a shaft 100, the rotary 
movement of a motor 102 (FIG. 2). In order to ensure the centring and a 
better guidance of the ring, the latter can bear on other pinions integral 
with the envelope 54, particularly in the exit position (e.g. reference 
104 in FIG. 3). 
The speed and rotation direction of the motor 100 can be controlled from 
the outside of the case 52 by a not shown device. For a maximum focal 
length of 50 mm, a motor driving the assembly at a speed of 1 mm/s permits 
the traversing of the entire travel in 50 seconds. 
Thus, a single control system makes it possible to control two functions of 
the lens, on the one hand the passage from the visible observation range 
to the gamma observation range (obturation) and on the other hand the 
variation of the focal length of the lens. 
During any focal length manipulation towards the front or rear, the lamella 
80 does not obturate the aperture 70 and 68 and the user can observe what 
occurs in the field of the camera invisible light. At any time, e.g. when 
the focal length is appropriately adjusted, he can interrupt the variation 
of the focal length and pass to gamma observation. For this purpose it is 
merely necessary to reverse the rotation direction of the front 
half-collimator 60 and make it undergo a rotation of angle .alpha./2, 
which returns the lamella 80 to the position of obturating the apertures 
70 and 68. 
This system also makes it possible to ensure a perfect correspondence 
between the fields observed in the visible and gamma ranges. Thus, during 
the passage from the position where the apertures 60 and 78 are obturated 
by the lamella 80 (FIG. 5b) to the non-obturation position (FIGS. 5a or 
5c), the front half-collimator 60 does not rotate the rear half-collimator 
62 and consequently there is no change to the focal length. 
Thus, as from a position of non-obturation (observation in the visible 
range), only the rotation direction of the motor makes it possible to 
choose between the two obturation and focal length variation functions. 
Different means permitting the observation of the radiation from the 
sources 2 must be provided. These means can be those described in U.S. 
Pat. No. 5,204,533, granted on Apr. 20, 1993 and whose content is 
incorporated by reference into the present description and which are dealt 
with hereinbefore in conjunction with FIG. 1: 
a phosphor screen 28, located behind the above-described lens and referred 
to in conjunction with FIGS. 2 and 3, 
a camera 30 optically coupled to the screen 28 and referred to in 
conjunction with FIG. 2, 
means 40 for the real time acquisition, processing and display of the 
electrical signals supplied by the camera, 
storage means 42. 
Thus, the screen 28 can on the one hand be transparent in the visible range 
and on the other can convert the gamma radiation of the sources 2 into a 
radiation detectable by the camera 30. 
The material chosen for the screen will preferably be a dense material 
having a good light output ratio. The screen is preferably thin (a few mm 
thick) so that there is a good spatial resolution. 
Preferably, the camera 30 is very sensitive in order to permit the use of a 
thin screen, made from a scintillating material transparent in the visible 
range and having a good gamma radiation detection sensitivity. It is also 
preferable for the camera 30 to have a good resistance to gamma conditions 
and a good reliability. 
For example, the entrance window of the camera 30 is engaged against the 
screen 28, which is consequently positioned between the lens and the 
camera 30. 
Thus, the camera can be located outside and remote from the body 54. A 
bundle of optical fibres able to conduct the visible radiation emitted by 
the screen and the visible light from the observed area, then connects the 
screen 28 to the camera 30, whilst traversing the body 54. One end of the 
fibre bundle normally leads to the screen and covers the surface of the 
latter. The other end of the bundle normally leads to the camera entrance 
window and covers the same. 
The mechanism for varying the focal length of the camera has been explained 
hereinbefore. 
During use, when the shutter 80 is closed, at the end of a certain time (a 
few seconds, e.g. 10 s) the image of the gamma radiation sources is 
obtained and is stored in a first memory area of the means 40. Then, by 
controlling the opening of the shutter 80, in quasi-instantaneous manner 
an image (invisible light) is obtained of the observed area in which the 
sources 2 are located. This second image is also stored in a second memory 
area of the means 40 and which is separate from the first memory area. 
After processing the images (within particular a possibility of colouring 
"spots"), the correct positioning of the sources takes place by 
superimposing the gamma radiation image on the image in the visible range 
due to the activity of the sources 2 in order to appropriately position 
the sources and distinguish their "gamma brightness" from the brightness 
(in visible light) of objects present in the observed area, but which emit 
no gamma radiation, the first and second images being displayed in 
superimposed manner on the screen of the means 40, which permits the 
positioning of the gamma radiation sources. 
In order to carry out activity measurements of the sources 2, the camera is 
used in combination with a laser telemeter in accordance with the method 
described in U.S. Pat. No. 5,204,333. 
It is pointed out that the apparatus described hereinbefore not only makes 
it possible to fulfil the two functions of varying the focal length and 
passing from the visible observation field to the gamma observation field, 
but also permits a rapid disassembly of the lens, because it is merely 
necessary to unscrew it and replace it e.g. by a lens having a different 
aperture.