Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
  • G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
  • G01N21/718—Laser microanalysis, i.e. with formation of sample plasma

Definitions

• the present invention relates to a method and a device for remote measurement of uranium or plutonium in radioactive materials, such as e.g. in waste glasses.
• the laser beam hits the sample, a tiny amount of it is ablated, which is why one speaks of a quasi-non-destructive method.
• the laser creates a plasma of the sample from which light is emitted.
• the emission spectrum of the plasma is imaged in a spectrograph and then evaluated using an analysis unit. The spectral lines found then allow corresponding statements to be made about the presence of uranium or plutonium in the sample.
• a delay unit which signals the start of the analysis process, i.e. in particular the mathematical integration of the measured emission spectra over time is delayed with regard to the time at which the laser pulse is emitted. This makes it possible to set an optimal signal / noise ratio of certain spectral lines to one another by varying this delay time. Furthermore, it can be ensured that analysis is only carried out when the material removed from the sample is completely atomized.
• the focusing unit focusing the laser beam can be arranged directly on the laser, so that a laser beam leaving the focusing unit of the laser can strike the sample directly through the free space. Furthermore, it is possible to arrange the imaging unit, which images the light emitted by the laser-generated plasma in the spectrograph, directly on the spectrograph itself. Here, too, the emitted light reaches the spectrograph directly through the free space. Due to the relatively large distances that the laser light and the light emitted by the sample plasma have to travel in free space, corresponding scattering and loss of intensity of the light beams can occur.
• the laser beam is preferably brought closer to the sample and, on the other hand, the light emitted by the sample is guided earlier in spatial terms, so that the total distances to be covered by the light beams in free space are reduced.
• a measuring head that can be placed on the sample is provided.
• the laser beam is fed to the measuring head and the light emitted by the sample is passed on from the measuring head to the spectrograph with the aid of light guides.
• the measuring head has a plurality of tubular connections in which the lens systems of the focusing unit or the imaging unit are arranged. The optical axes of the lens systems are aligned so that their extensions run essentially through the area in which the laser-generated plasma of the sample is located during the measurement.
• At least one feed line can be provided on the underside of the measuring head, through which a rinsing fluid is supplied to a chamber formed in the measuring head, in which the sample is located, for the purpose of shielding the plasma from the ambient air.
• This flushing fluid can be an inert gas, preferably argon, or dust-free air.
• a light guide coupling unit is provided which is firmly connected to the housing of the laser and enables the end of the light guide facing the laser to be rotated on the one hand about its two transverse axes and on the other hand in the direction of these transverse axes and its longitudinal axis to move linearly.
• Figure 1 is a side view of an embodiment of the device according to the invention.
• FIG. 2 is a bottom view of the device according to the invention according to Figure 1;
• FIG. 3 shows a table with data of the fiber optics used for the transport of the Nd: YAG laser beam and of the focusing optics;
• Figure 4 is a table with data used to image the plasma
• FIG. 5 shows the optics for coupling the light emitted by the laser-generated plasma into the four-armed light guide
• FIG. 6 shows a table with data on the spectral window and the detector resolution in different wavelength ranges
• FIG. 7 shows the front view of an optical fiber coupling unit of the Newport MF 91-CL type
• FIG. 8 shows a side view of the optical fiber coupling unit according to the invention according to FIG. 7;
• Figure 9 is a bottom view of the invention
• FIG. 10 shows a beam profile of the Nd: YAG laser beam behind the light guide
• Figure 1 1 shows the transmission of the light guide as a function of the injected pulse energy
• FIG. 12 the relative transmission of the four-armed light guide
• FIG. 14 shows a chromium / iron calibration measurement with three different ones
• Figure 1 5 shows the emission spectra of the glass samples VG 98/12, GP 98/1 2 and GP 98/1 2 + U02 at 590 nm;
• Figure 1 6 shows a measurement of the uranium distribution in the glass sample GP 98/1 2 + U02;
• Figure 1 7 shows the time dependence of the signal / noise ratio of the uranium atom line 591, 539 nm, measured with and without a light guide at a
• Figure 1 8 shows the time dependence of the signal-to-noise ratio with three different integration times, namely l O ⁇ s, 20 ⁇ s and 30 ⁇ s, measured with the measuring head;
• FIG. 19 shows a comparison of the results of the measurements according to the invention with and without a light guide.
• the device 30 according to the invention shown in FIG. 1 has an Nd: YAG laser (Spectron SL 401), a spectrograph 4 with a detector unit 23, an analysis unit 6 and a delay unit 7 arranged between the latter and the laser 1.
• a computer not shown, is connected to the detector unit 23.
• the analysis unit 6 is the multi-channel analyzer system OMAIII from EG&G.
• the delay unit 7 is connected to the laser 1 and the analysis unit 6 via corresponding signal lines 24.
• laser 1 is operated with its fundamental wavelength of 1064 nm and a pulse length of 5 ns.
• the pulse energy is preferably 20 mJ.
• the measuring head 14, which has a square outline according to FIG. 2, can be placed on the sample 3.
• a total of five tubular connecting pieces 1, 6.1, 7 are arranged on it, of which only three can be seen in the side section of FIG.
• the focusing unit 2 consisting of the light guide 10 and the lenses 8 and 9, is arranged in the stub 16 of the measuring head 14 which is vertically upward, the light guide 10 naturally only running over a comparatively short length within the stub 16.
• the remaining four laterally projecting nozzles 1 7 accommodate the four imaging units 5, each consisting of the light guide 1 3 and the lenses 1 1 and 12 or 1 1 'and 12'. Because of the four imaging units 5 provided here, one also speaks of a four-armed light guide 13.
• the two nozzles 17, which are not visible in FIG. 1, lie one behind the other in the viewing direction of FIG. 1 and symmetrically to the drawing plane of FIG. 1. This ensures that the largest possible part of the light emitted in all spatial directions is imaged in the spectrograph 4.
• the light guides 10 and 13 are held in the socket 16 and 17 by guide pieces 25 and 26, respectively. Glass fibers or glass fiber cables are preferably used as light guides.
• the technical data of the focusing and fiber optics of the focusing unit 2 can be found in the table in FIG. 3.
• the technical data of the focusing and fiber optics of the four imaging units 5 are contained in the table according to FIG. 4.
• the measuring head 14 has four feed lines 22 on its underside, through which a flushing fluid flow can be fed into the chamber 15 of the measuring head 14 according to the arrows A.
• the flushing fluid flow should flow along the surface of the sample 3 and have such a vertical extent that the laser-generated plasma 18 is flowed around as completely as possible.
• the use of the noble gas has proven to be particularly favorable Argon proved to be a flushing fluid.
• An argon flow of approximately 40 l / h is preferably selected.
• Figure 5 shows the structure of the optics used for coupling into the four-armed light guide 1 3.
• the working distance E of the 2-lens systems 11, 12 of the imaging units 5 can be seen, in which the light-emitting plasma 18 must lie.
• the imaging units 5 used also make it possible to image and analyze radiation from layers of the plasma 18 near the surface.
• the table according to FIG. 6 shows the pixel width and the simultaneously observable spectral window in different spectral ranges of the multi-channel analyzer system used.
• FIGS. 7, 8 and 9 show the optical fiber coupling unit 19. It serves for the optimal coupling of the laser beam coming from the laser 1 into the light guide 10. It has a laser beam introduction opening 21 and a light guide connection 20.
• the entire optical fiber coupling unit 19 is mechanically detachably attached to the housing of the laser 1, so that a misalignment of the optical fiber to the laser beam and thus a possible destruction of the optical fiber end surfaces during misalignment is avoided.
• the fiber ends are flushed with dust-free air.
• a quartz lens with a focal length of 55.8 mm at a laser wavelength of 1064 nm is used to couple the laser beam into the optical fiber.
• the optical fiber with a core diameter of 600 ⁇ m is positioned about 14 mm behind the focal point of the lens.
• the fiber is granted a total of five degrees of freedom.
• the light guide 10 connected to the light guide connection 20 can be pivoted at its end facing the laser 1 about its two transverse axes y, z and can be linearly displaced in the direction of these two transverse axes and its longitudinal axis x.
• an attenuation filter is placed between the laser 1 and the fiber of the light guide 10 during the adjustment, so that only about 0.01 mJ / pulse is coupled into the optical fiber at a pulse energy of about 10 mJ.
• FIG. 10 shows the result of an examination of the beam profile of the light emerging from the fiber of the light guide 10, which was determined by means of a photodiode cell. It is the beam profile of the laser beam behind the optical fiber with optimized coupling. A symmetrical profile can be seen. After careful adjustment of the optical fiber, pulse energies of up to 30 mJ were easily coupled into the fiber. These pulse energies are still approximately one order of magnitude below the specified destruction threshold of the light guide 10.
• a focus radius of approx. 320 ⁇ m was realized on sample 3.
• a maximum signal / noise ratio with a laser energy of 20 mJ and a focus radius was determined on sample 3 of 90 ⁇ m, which corresponds to an irradiance of approximately 6.3 x 1010 W / cm2.
• the radiation density at the same pulse energy of laser 1 was only about 5 x 109 W / cm 2 because of the larger focus diameter. This led to an approximately one order of magnitude lower sample removal.
• FIG. 12 shows the relative transmission of the four-armed light guide 13 for the plasma radiation in the wavelength range between 200 and 600 ⁇ m.
• the transmission measurement was carried out using a mercury vapor lamp.
• the transmission curve shows the relative course with all optical components during measurements in air.
• the intensity ratio of measurements with and without light guide is plotted against the wavelength.
• Figure 1 3 shows the absolute transmission of the light guide 13 specified by the manufacturer.
• the maximum absolute transmission is approximately 64%.
• FIG. 14 shows a calibration measurement of chromium against iron with three different matrices (steel: NBS sample, glass: sample from Hoesch, aluminum: samples from Pechiney and Alusuisse).
• Atomic emission lines at 425.435 nm (Cr (l)) and 302.639 nm (Fe (l)) were used.
• the intensity ratio is plotted against the concentration ratio.
• a time delay of 6 ⁇ s after the laser pulse (pulse energy 20 mJ) was measured.
• the integration time was 40 ⁇ s. 50 spectra were added.
• the slope of the compensating straight line is one in double logarithmic representation. All measurement data lie on the straight line within 5%. This shows that a matrix-independent measurement is possible.
• FIG. 15 shows spectra of the glass samples VG 98/12, GP 98/1 2 and GP 98/12 + 0.98% UO2. With a delay of 6 ⁇ s and an integration time of 20 ⁇ s, 50 spectra were integrated. The sample removal was about 0.15 ng / shot at an irradiance of 5 x 109 W / cm2. In addition to the uranium atom line at 591, 539 nm, two emission lines of the matrix component titanium (Ti (l) 591, 855 nm, Ti (l) 592.212 nm) and an atom line of the protective gas argon (591, 208 nm) can be seen.
• the measurement shown in FIG. 16 for the homogeneity of the uranium distribution in the sample GP 98/1 2 + U02 was carried out under the same measuring conditions. Each measuring point represents the average of five measurements. A relatively homogeneous uranium distribution is shown, based on the diameter of the focal spot of 320 ⁇ m. The standard deviation of the individual measurements is between 6 and 12%, that of the mean value is 6%.
• Figure 1 7 shows the signal / noise ratio of the uranium atom line 591, 539 nm as a function of time. A maximum ratio with a time shift of 6 ⁇ s can be seen both when measuring with a light guide and when measuring without a light guide. The intensity of the analysis lines is higher with shorter delay times
• the sample removal for measurements with a light guide is smaller than for measurements without a light guide.
• the measured intensity of the analysis lines is about 66% greater than that of the measurements without a light guide if the removal of the sample is comparable by reducing the laser intensity in the measurements without a light guide.
• FIG. 18 shows the time dependency of the signal / noise ratio at different integration times (10 ⁇ s, 20 ⁇ s and 30 ⁇ s). With an integration time of 20 ⁇ s and a delay of 6 ⁇ s you get an optimal ratio.
• the table according to FIG. 19 compares the measurements according to the invention without light guide 10.13 on the one hand and with light guide 10.13 on the other.
• the comparison of the results shows that the absolute detection limits for uranium are smaller for measurements with light guides than for measurements without light guides.
• the detection limit could be reduced by a factor of 2-3 if the detector 23 were cooled, although it would be necessary to purge the detector 23 with a dry gas.
• higher pulse energies lead to greater ablation and, with a suitable choice of the delay in the detection, to lower relative detection limits.
• the device according to the invention enables fast and structurally simple analysis of highly radioactive samples 3.
• the device required for analyzing the emitted light is portable, the measuring head 14 and the light guides 10, 13 being stationary units during the measurement, while the laser 1 , the spectrograph 4 and the detector 23 can be installed with a connected computer in a mobile unit.
• the advantage of the measuring head 14 is, in particular, that it can be positioned as desired, and it is also possible to use flexible and flexible light guides 10, 13 of very great length. Furthermore, the measurements take place under an argon flow at atmospheric pressure, so that the use of closed sample chambers with complex mechanics for changing samples is not necessary.
• the measuring head 14 can be positioned on the sample 3 by means of a manipulator or a robot arm, so that the experiment can be carried out remotely and without direct contact with radioactive material.

Landscapes

• Health & Medical Sciences (AREA)
• Physics & Mathematics (AREA)
• Life Sciences & Earth Sciences (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=7770810

Family Applications (1)

Country Status (5)

Families Citing this family (9)

Family Cites Families (23)

• 1995
  • 1995-08-30 DE DE19531988A patent/DE19531988A1/de not_active Ceased
• 1996
  • 1996-08-22 US US09/029,730 patent/US6259757B1/en not_active Expired - Fee Related
  • 1996-08-22 EP EP96929306A patent/EP0847525A1/de not_active Withdrawn
  • 1996-08-22 WO PCT/EP1996/003702 patent/WO1997008539A1/de not_active Application Discontinuation
  • 1996-08-22 JP JP09509827A patent/JP3081648B2/ja not_active Expired - Fee Related

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events