Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/04—Measuring microscopes

Definitions

• the present invention relates to a device for counting and measuring the true length of elements or traces included in a sample studied under a microscope, and in particular the application which is made of it in the technique known as "fission traces" which makes it possible to date certain minerals such as Apatite and which are also used in chronothermometry.
• Uranium 2308 The spontaneous fission of Uranium 238, by releasing two highly energetic nucleus fragments, causes in minerals a disorganization of the target atoms resulting in the presence within the mineral of a rectilinear "trace" of a maximum length of 20 microns and a diameter of ten nanometers. On a polished section of the mineral observed under a microscope, these traces are perfectly visible and countable after revelation by chemical attack.
• the determination of the age of these samples involves measuring the density Ps of the fossil traces of the sample, but also by measuring the density Pi of the induced traces resulting from the fission of uranium 235 caused by irradiation. neutron of the sample. This operation determines the uranium content of the mineral. Indeed, the density of fossil traces Ps is not only a function of the age of the mineral but also of this uranium content.
• a first object of the invention is to have a microscope whose vertical displacement of the stage (therefore the variation of the focusing plane) is perfectly determined and known with great precision, of the order of a hundredth of a micron.
• This object is achieved by the use of piezoelectric ceramic, for example, to finely move the plate.
• a second object of the invention is to provide a device allowing safe counting for which it is certain that all the elements to be taken into account have been counted once and only once.
• This goal is achieved by creating a synthetic image of a current point, a synthetic image that is superimposed on a screen on a video image from the microscoDe.
• This image represents the slice of the studied sample located in the focusing plane of the microscope for a given adjustment and a known Z position of the stage.
• the device according to the invention for counting and / or measuring the real length of elements included in a sample comprises:
• - a video monitor to visualize the image formed by the camera, - means connected to the video monitor to locate a point of this real image of coordinates X and Y with respect to two axes of its plane, to form the synthetic image of this point on the screen, measure and record the X, Y coordinates of said points and means for calculating a length from the recording of the X, Y, Z coordinates, and record this length.
• the means for fine displacement of the plate are piezoelectric micro-positioners and an electrical supply for supplying said micro-positioners.
• the device according to the invention can obviously be used for counting or measuring the lengths of all kinds of elements visible under the microscope. It is an application to which it is particularly suitable, namely counting and measuring the length of traces of fossil or induced fission in a sample containing uranium such as Apatite, in particular for paleothermometric and dating studies. geological terrain.
• the following description of a particular embodiment of the device according to the invention, illustrated by attached FIG. 1, will allow a better understanding of the object of the invention and its interest.
• the microscope 3 in FIG. 1 is optically adjusted to sample 2 of Apatite, the surface of which has been polished and slightly etched with acid to reveal the traces of fission.
• the rough displacements of the stage 1 of the microscope are ensured by the proper means of displacement of the stage, namely a system of conventional screws and rack manually operated and which is used to approach the focusing.
• the fine displacement of plate 1, in the example of embodiment described here is provided by at least one piezoelectric ceramic 10.
• a piezoelectric ceramic is a component whose thickness varies under the action of an electric field. When the electric field increases, the ceramic swells, but this swelling is not linear due to hysteresis. This is why a displacement sensor is integrated into the ceramic.
• Such ceramics which are found on the market working in closed loop, by comparison of the measured value and a set value, the integrated sensor making it possible to correct the effects of hysteresis by slaving of the THT (Very High Voltage) to the set value.
• THT Very High Voltage
• the piezoelectric ceramic, supplied by an electrical supply 13 is fixed on the one hand by its lower part to a flat base plate 12, itself secured to the stage 1 of the microscope, and on the other hand by its part greater than a mechanical part 11 having a flat part situated above the plate 12 and on which the sample 2 or the preparation to be studied is mounted.
• the rotation of the button 16 of the power supply 13 of the piezoelectric ceramic (s) has the effect of varying the electric field applied to them, which causes them to swell, therefore - a variation in their thickness along the vertical, and consequently the movement of the mechanical part 11 with respect to the plate 1. It is by manually acting on this button 16 that the fine movements necessary for measuring the lengths are carried out.
• a voltmeter 14, connected to the power supply, enables the applied voltage to be read directly. There is an unequivocal relationship, depending on the characteristics of piezoelectric ceramics, between the voltage applied to them and the displacement Z which the sample is subjected to.
• the voltmeter 14 is connected to a microcomputer 9 having means for transforming the voltage indication sent by the voltmeter into indication of movement Z.
• a video camera 4 making it possible to obtain a geometrically non-distorted image, for example a High Resolution tube camera for better resolving the ends of the traces, is fixed on. the microscope. This camera is arranged and optically adjusted so as to be able to provide an image of the observation plane in which the slice of the sample to be studied is located.
• the camera 4 is connected, via a mixing box 5, to a video monitor 6, with screen on which the image of the section of the sample to be analyzed is viewed.
• the light illuminating the crystal is diffracted by the fission trace, creating two symmetrical snaps with respect to the direction of incidence.
• the angle of these two layers depends on the diameter of the trace and can therefore be different from one trace to another depending on the conditions of development, for example.
• the angle of inclination of the fission trace therefore means that, depending on the focus plane of the microscope, the image of a fission trace will appear according to an egret formed by the intersection of the dihedron formed by the diffraction layers and the observation plane.
• the diffraction layers correspond to the 1st zero minimum of diffraction, the egret will be dark on a light background.
• the angle of the wings of the egret will be all the more open as the trace will be slightly inclined relative to the optical axis and as its diameter will be small.
• a synthetic image in which a current point is created thanks to the use of what is now commonly called in the computer field a "mouse" 15, making it possible to validate a point of coordinates X, Y in a marker plane and to provide a measure of the variations in coordinates X, Y when the point in this plane is changed by moving the mouse.
• the mouse is connected to the microcomputer 9 with screen 8 making it possible to visualize certain results and data.
• the current point is entered on the monitor 6 via the mixer 5. After validation, its X and Y coordinates are stored in 7.
• mouse there are many commercial sets comprising these three elements: mouse, microcomputer and screen for which, if used alone, the marker plane linked to the mouse coincides with the surface of the screen, the image summary of validated points appearing on said screen.
• the microcomputer 9 is connected via a memory 7 to the video monitor 6, which is itself connected to the screen 6, so that the marker plane of the mouse coincides with the screen 6.
• the mixer 5 one can observe on screen 6 the superimposition of the video image provided by the camera 4 and of the synthetic image of the current point moved by the mouse, after the information transmitted by the camera and the information transmitted by the mouse via the microphone and the memory have been mixed by the mixer 5.
• the procedure is as follows: first of all, using the microscope screw, focus on the surface of the sample.
• the microcomputer is equipped with a means such that memorizing the coordinates of these two points validated one after the other causes the creation of a line connecting these two points materializing the trace, or at least its projection in the plane horizontal. This allows the manipulator to avoid forgetting or doublets in his counts and measurements and even to interrupt his operation for some time. This is done step by step.
• the microcomputer is equipped with means making it possible to calculate, from the sets of coordinates Xi, Yi, Zi of the points Pi and X'i, Y'i, Z'i of the points Pi 'the lengths of the segments limited by these points , therefore the actual length of the traces present in the studied sample, each trace being defined by two sets of successive coordinates and the refractive index of the studied crystal.
• the microcomputer can also be equipped with means making it possible to supply the histogram of these lengths, or to supply the number of traces processed, or even to supply the density of these traces.
• the results can be printed and / or viewed on the screen 8 of the microcomputer 9, or printed if a printer is connected to the microcomputer.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Microscoopes, Condenser (AREA)
• Details Of Measuring And Other Instruments (AREA)

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Publications (1)

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Citations (4)

• 1989
  • 1989-03-23 FR FR8903845A patent/FR2644885B1/fr not_active Expired - Fee Related
• 1990
  • 1990-03-22 WO PCT/FR1990/000191 patent/WO1990011486A1/fr active Application Filing
  • 1990-03-22 DE DE19904090411 patent/DE4090411T/de not_active Withdrawn
  • 1990-03-22 JP JP2505155A patent/JPH04503857A/ja active Pending

Patent Citations (4)

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