Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21G—CONVERSION OF CHEMICAL ELEMENTS; RADIOACTIVE SOURCES
  • G21G4/00—Radioactive sources
  • G21G4/04—Radioactive sources other than neutron sources
  • G21G4/06—Radioactive sources other than neutron sources characterised by constructional features

Definitions

• the present invention relates to a source, preferably non-contaminating, of alpha ( ⁇ ) and X radiation, a PIXE-XRF simultaneous analysis device, using this source, and a method of manufacturing such a source.
• This invention applies in particular to the manufacture of a portable device for simultaneous analysis PIXE-XRF.
• the PIXE (“Particle Induced X-ray Emission”) method is a known technique for X-ray fluorescence analysis that uses a particle accelerator as a radiation generator. This method has disadvantages: its implementation requires expensive equipment and is not possible with immovable objects or difficult to transport. In addition, portable PIXE analysis devices are known which make it possible to remedy these drawbacks. These devices use non-contaminating sources of ⁇ radiation instead of a particle accelerator. The material contained in these sources is preferably polonium 210 ( 210 Po).
• the XRF method (for "X-Ray Fluorescence") is another known technique for X-ray fluorescence analysis.
• an excitatory source it uses either a radioactive source, containing for example 109 Cd, 55 Fe or 241 Am, or an X-ray tube.
• This technique makes it possible to correctly analyze the elements whose atomic numbers are greater than 22, provided that appropriate energy radiation is used.
• this method is complementary to the PIXE method.
• the present invention aims to overcome the above disadvantages.
• this device comprising a non-contaminating radioactive source capable of emitting not only ⁇ radiation but also X-radiation.
• the subject of the invention is such a device, comprising a radioactive source intense and non-contaminating, of sufficiently long period, at least equal to 5 years, emitting not only ⁇ radiation but also X-ray radiation of sufficient energy, at least equal to 15keV, this device allowing the identification of elements whose numbers Atomic values are greater than 10, from the same sample.
• the 244 Cm satisfies all the criteria mentioned above: it has a period of 18.1 years, an emission ⁇ at 5.7862 meV and 5.804 MeV (85% ) as well as an emission X of average energy 17, 3keV (10, 5%) coming from its descendant 240 Pu.
• another problem arises, namely the problem of manufacturing a source containing 244 Cm and, more generally, the manufacture of a source containing an actinide, capable of emitting ⁇ and X radiation.
• electrodeposition processes are already known for depositing actinides from aqueous solutions.
• these methods have the disadvantage that they do not make it possible to obtain high deposition efficiencies for the actinides.
• the present invention also aims to overcome this disadvantage.
• the present invention firstly relates to a source of alpha and X radiation, this source comprising a support consisting of a chemical element whose atomic number is less than 10 or a plurality of chemical elements each having an atomic number less than 10, which support is covered with a noble metal layer, having a thickness of less than 0.2 ⁇ m, and on which is deposited a layer of a material selected from actinides.
• the support may be flat but not necessarily.
• the support that comprises the source object of the invention advantageously has the shape of a ring.
• the material is 244 cm.
• the activity of the material is in the range of from 5 MBq to 50 MBq.
• the noble metal is preferably selected from gold, silver and platinum.
• the present invention further relates to a PIXE-XRF simultaneous analysis device, this device comprising a source according to the invention.
• the source used in this device is non-contaminating.
• the material is deposited on one side of the support, called the active face, this face being thus able to emit the alpha and X radiation
• the source further comprises a window which is permeable to these radiations alpha and X, resistant to these radiations and able to protect the active face, this window consisting exclusively of a chemical element whose atomic number is lower at 10 or a plurality of chemical elements each having an atomic number less than 10.
• the window may be made of polyimide, diamond or DLC, that is to say diamond type carbon (diamond-like carbon).
• the thickness of the window is preferably between 2 microns and 10 microns.
• this device further comprises an X-ray fluorescence detector.
• This detector is preferably placed near the source.
• the support comprises an active face, on which is deposited the layer of the material selected from actinides, this support has a hole and the detector is placed opposite this hole. and the opposite side to the active face.
• the support has the shape of a ring and the detector is placed opposite the hole of this ring.
• the present invention also relates to a method of manufacturing the object source of the invention, in which the layer of the material is formed by electrochemical deposition, from an organic electrolyte based on dimethylformamide and containing ions of the material. Preferably, the electrochemical deposition is performed in galvanostatic mode.
• the electrochemical deposition is preferably carried out at room temperature.
• Such a method therefore applies to the manufacture of a radiation source ⁇ and X, in which the material is an actinide.
• This process can also be used in nuclear research.
• a source of radiation ⁇ and X this source comprising a support, which is made of a metal or covered with a layer of this metal, and a material chosen from actinides and deposited on the supported by this electrochemical deposition process.
• Such a source is therefore particularly applicable to PIXE-XRF simultaneous analysis but can be applied to other areas of nuclear research.
• stainless steel is usable as a metal for constituting or cover the substrate but can not be used in an application of the source to PIXE-XRF because it contains nickel, chromium and iron which induce parasitic fluorescence. This is why a metal J2 ° is used for such an application.
• a solid metal support would induce an excessive parasitic fluorescence signal in the application to the PIXE-XRF analysis.
• a support coated with a thin metal layer in noble metal according to a preferred embodiment
• a support coated with a thin metal layer in noble metal according to a preferred embodiment
• [3] is sealed with two alumina membranes (Al2O 3 ) and these membranes therefore contain aluminum which is likely to induce parasitic fluorescence when measured by PIXE and XRF.
• the sources known from document [4] are not even sealed. In addition, they are prepared by high temperature condensation of metal curium vapor on silicon substrates to form compounds of CmSi 2 , Cm 2 Si 3 , CmSi and Cm 5 Si type. They therefore contain silicon which is also susceptible to induce parasitic fluorescence during PIXE and XRF measurements.
• the source that comprises the device object of the invention does not have this drawback. In a preferred embodiment, it is also non-contaminating and has a reliable and durable confinement, necessary for the analysis of samples where they are. In addition, it is easy to recycle the radioactive material contained in this source.
• the document [4] describes a multi-source device, in which sources of small dimensions (in the form of pellets) are juxtaposed.
• sources of small dimensions in the form of pellets
• the activity of curium is distributed very unequally.
• each pellet In order to obtain a sufficient average activity for a good signal-to-noise ratio, each pellet must relatively more activity than for a single source of uniform distribution.
• the source of the invention preferably has an annular shape where the activity is uniformly distributed on one of the faces of the source support, which makes it possible to reduce by a factor of 2 or 3 the dose per unit of ionizing radiation surface that is received by the source medium, compared to a source of the type of that described in document [4].
• a source according to the invention can be manufactured which has the advantage of still being non-contaminating after at least 18 months of use, and of having no contact contamination.
• the device of the invention is feasible in an integrated and portable form. It can thus be brought to sites, for example archaeological sites, whose access is difficult or impossible for heavy equipment.
• FIG. 1 is a schematic and partial sectional view an example of a radioactive source, usable in the present invention
• FIG. 2 is a diagrammatic sectional view of an installation for the electrochemical deposition of 244 Cm to form this source
• FIG. 3 is a schematic sectional view of the source, placed in an envelope
• FIG. 4 is a schematic view of an exemplary PIXE-XRF analysis device according to the invention.
• the manufacture of a device according to the invention comprises three distinct steps clearly identified: 1) manufacture of a source support of
• ring of a material made of chemical elements each having an atomic number less than 10 for example a polyimide ring marketed under the name Kapton®, covered with a noble metal, for example the gold, lead shielding, electrical contact between gold and lead on the edge of the support;
• Electrodeposition in an organic medium proved to be a particularly suitable method for the production of 244 Cm of quantitative deposits (in particular because of the low current density, the short electrodeposition time, the good adhesion of deposits and high electrodeposition efficiency for actinides).
• the selection of the constituent solvent in particular because of the low current density, the short electrodeposition time, the good adhesion of deposits and high electrodeposition efficiency for actinides.
• the electrolyte is obviously a crucial preliminary step.
• this electrolyte must not only have good chemical compatibility with aqueous solutions of nitric acid (initial medium of 244 cm) but also be composed only of elements including atomic numbers Z are less than 10. Indeed, the active surface of the source must in no case be contaminated by elements likely to subsequently induce parasitic fluorescence during PIXE / XRF measurements, even if these elements are in the form of traces.
• the process for depositing 244 Cm is therefore based on an electroplating of curium in a dimethylformamide (DMF) medium.
• DMF dimethylformamide
• the source support for electroplating the 244 Cm in the DMF comprises a solid Kapton® ring 2 (see FIG. 1) 1 mm thick, having an outer diameter of 24 mm and an internal diameter of 5 mm. This material was chosen for its high resistance to irradiation.
• this solid Kapton® ring On one of the faces of this solid Kapton® ring is deposited a thin layer of gold 4 whose thickness is less than 0.2 ⁇ m and is for example 0.1 to 0.2 ⁇ m, according to a conventional method vacuum metallization.
• This layer of gold will allow the Kapton® ring to perform the cathode function on which the curium will be deposited by electrolysis (electroprecipitation). It has been shown that such a thickness of gold on the source medium is low enough not to induce a large parasitic X-ray, which may disturb the subsequent spectrometry measurements.
• reference 4a represents the curium layer that will be deposited to obtain a source of ⁇ and X radiation according to the invention.
• noble metal platinum, silver
• the use of noble metals for electrodes is essential to avoid any risk of contamination of the deposited layer. In the case of source manufacture, this makes it possible to obtain sources of high purity and to avoid parasitic fluorescence originating from other components of the source which could mask the useful signal coming from the sample to be analyzed by PIXE-XRF analysis.
• the golden Kapton® source support Before use, the golden Kapton® source support is heated at 150 ° C. in an oven for 30 minutes in order to increase the adhesion of the gold layer to the Kapton®. After cooling to room temperature, a lead ring 6 of 0.5 mm in thickness, whose outer diameter is 25 mm and the internal diameter 5 mm, is fixed to the back of the source support. When using the source for PIXE / XRF measurements, this shielding strongly attenuates the X-ray radiation of the 244 Cm (average energy of the order of 17 keV) towards the detector.
• the electroplating operations of the 244 Cm and the conditioning of the sources are carried out in a glove box, or BAG, marketed by the company Jacomex®, class I (ISO 10648-2 standard), connected to the active network of a laboratory which is located in a controlled area.
• BAG is equipped with a 99.99% efficient inlet and outlet filter system and hypalon® gloves marketed by Piercan.
• the preparation of an annular source of 244 cm is carried out in a solid and polished Teflon® electrolysis cell.
• This cell comprises the following elements: a base, a reservoir chimney, a central screw, a threaded crown and a rotating anode.
• the base 8 (see FIG. 2) is intended to receive the annular source support (Pb / Kapton® / Au). It is equipped with a current supply provided with an electrical contact 10 (metal spring). This contact exerts a pressure against the lead layer of the source support during the immobilization of this support at the bottom of the base of the cell.
• the current supply is connected to the negative pole of a DC electric generator 12 of the type LKB 2301 Macrodrive 1.
• the stack 14 forming a reservoir for the electrolyte, has a useful volume of 10 ml. It is terminated by an open conical base with a diameter of 14mm. This conical base has on the underside a flange forming a seal, 1 mm thick, coming into contact with the gold surface of the source support.
• the chimney is also provided with a groove (not shown) in which is positioned an insert (not shown). This insert is screwed into the inner edge of the base of the cell. This prevents rotation of the chimney in the base of the cell when tightening the assembly.
• the central screw 16 is made of plastic or Teflon®. Its diameter is 5 mm. It is intended to immobilize the source support on the base of the cell.
• the flat head of this screw has a diameter of 7 mm and also ensures, by pressure, the seal in the center of the source support.
• the threaded ring 18 is made of Teflon®. It allows, by simple tightening, the sealed assembly of the various constituent elements of the cell.
• the rotating anode consists of a platinum wire 1 mm in diameter, which is folded to form a triangle 20.
• the length of the base of this triangle is slightly greater than the outer diameter of the radioactive deposit.
• the anode is fixed in the mandrel 21 of an electric motor 22 which is located above the cell.
• the electrical connection of the rotating anode, which is connected to the positive pole of the above-mentioned direct current electric generator, is provided by a mercury contact (not shown).
• the gold surface available for curium deposition is limited to (1, 0 + 0, 1) cm 2 .
• the electrolysis cell is immobilized independently of the stirring motor on a plate 23 of adjustable height, type "Support Boy". This makes it easy to set the inter-electrode distance to the optimum value of (5.0 ⁇ 0.7) mm.
• the electroplating parameters relate to the preparation of the electrolyte and the preparation of the 244 Cm deposit.
• Electroplating is at room temperature. This avoids heating the elements, particularly radioactive elements such as Curium, to temperatures where it could occur.
• Optimized experimental conditions of electroplating are summarized in Table II. They make it possible to achieve deposition yields of 244 cm greater than 95%, for a total activity of 244 cm, which is less than or equal to 30 MBq, for a nitric acid concentration of the electrolyte, which is between 1.5 ⁇ 10 -3 and 2.5 ⁇ 10 -3 mol / l, and for [H 2 O] less than 5%.
• the 244 Cm source extracted from the electrolysis cell is placed in a cylindrical metal containment envelope, which is made of zirconium.
• This envelope comprises two parts, namely an outer ring 24 (see Figure 3) and a central ring 26 which are secured to one another through an annular Kapton® window 28.
• Kapton® and epoxy resin were chosen for their excellent mechanical strength, their resistance to irradiation and the absence of elements that can cause parasitic fluorescence.
• the small thickness of the Kapton® window makes this window not very absorbent with respect to the ⁇ radiation while ensuring its function as a confinement barrier for the radioactive material.
• a two-component epoxy resin layer R is cast on the lead shield 6 so as to confine the source of 244 cm.
• the source 29 thus contained is mounted in an envelope 30 PVC (polyvinyl chloride) whose front face comprises an annular mechanical protection grid 32 Nylon® son, facing the annular window 28.
• This gate 32 is thus facing the active face of the source.
• the rear face of the envelope 30 is closed by a lid 34 also made of PVC, which is screwed to the envelope 30 by means of screws 35.
• the 244- cm source thus wrapped is then ready to be integrated into the X-ray detector of a portable spectrometric measuring chain.
• an embodiment of a source of 244 cm is given.
• the nominal activity (28 MBq of 244 cm) of this source corresponds to the activity required to perform PIXE / XRF analysis with a 15 minute acquisition time.
• the inter-electrode distance is adjusted using the "support-boy" type plate and an outer ruler, with an accuracy of 0.5 mm.
• a first distance measurement is performed, after putting the anode in contact with the flat head of the central screw.
• the anode is raised by a distance x taking into account the height ⁇ of the screw head, so as to obtain an inter-electrode distance x + ⁇ equal to (5.0 ⁇ 0.7) mm.
• the electrodeposition of 244 Cm comprises six steps.
• Step 1 The electrolyte, namely the DMF (volume of the order of 3 ml) containing the 244 cm 2, is introduced into the electroplating cell.
• Step 2 The agitation motor of the anode is put into operation and then the speed of rotation is adjusted to (200 + 2) revolutions per minute. - Step 3. Using a stabilized external power supply, connected to the electrolysis circuit, imposes a continuous current of 4.5 inA whose value is accurately measured by an ammeter connected in series in the electrical circuit. .
• the electrodeposition is thus done in galvanostatic mode (that is to say at constant current) and not in potentio-static mode (that is to say at constant potential difference). Electrolytic deposition carried out under a constant potential difference does not make it possible to obtain a homogeneous deposition of the actinide material layer due to current variations, which are capable of inducing variations in the rate of electrodeposition.
• the potential difference between the electrodes (rotating anode and source support) is measured during the electrolysis using a voltmeter having a high input impedance, of the order of 1 G ⁇ . Any anomaly during the electroplating operation is thus immediately detected by the observation of a sharp increase in the voltage across the electrodes.
• Step 4 After an electrolysis time of (15 + 1) minutes, the electrical circuit is cut off and the cell electrolyte is immediately emptied by withdrawal using a Polyethylene Pasteur pipette. This electrolyte is then packaged in a glass vial for later analysis. - Step 5. Introduce into the cell about 3 ml of isopropanol (Propanol-2) to rinse the source support before the cell is drained. This operation is repeated a second time.
• the residual isopropanol of the last rinse on the active surface of the source the cell is dismantled.
• the source of 244 Cm is extracted with care.
• the dismantling operations of the cell are carried out in the reverse order of the assembly operations previously described.
• the electrodeposition efficiency (R C m) of 244 Cm can be calculated by the analysis of diluted fractions of the electrolyte before and after electrodeposition of 244 Cm.
• the analytical method used is liquid scintillation (SL) counting in glass flasks containing 10 ml of Ultimagold® scintillating liquid (marketed by Packard).
• the measuring apparatus used is of the type that is marketed by WALLAC under the reference Guardian 1414.
• the activity to be dispensed in the vials to be analyzed must be less than 1 kBq in order to overcome the problems associated with the non-linearity of this device for higher activities. Under these conditions, the detection efficiency ⁇ can reach 99.8%. A counting time of 600 s is sufficient to obtain a good counting statistic.
• Di dilution factor of the electrolyte Pi: sampling of the dilution of
• Ci counting per second of the sample Pi (comparable to the activity).
• Table IV which follows presents the results of the liquid scintillation analysis of the various fractions making it possible to calculate the electrodeposition efficiency of 244 Cm by means of formula (1), for the source of 28 MBq.
• A A 1 XR 0n , (2) with:
• a 1 initial activity of 244 Cm contained in the electrolyte that is to say (28.5 ⁇ 0.6) MBq.
• Re m yield of electrodeposition of 244 Cm that is to say (0.97 + 0.02).
• This device constitutes a measurement chain which comprises a detector 38 (see FIG. 4) of X-ray of SDD type or silicon drift detector, for example of the kind that is marketed by the KETEK GmBH company.
• This detector has an area of 10mm 2 and a resolution of 1.42 eV, at an energy of 5.9 keV. It is associated with a multi-channel analyzer
• the PVC casing 30, containing source 29 of 244 Cm, is attached to the detector 38 through an adapter ring (not shown).
• a device 50 for scanning with helium gas is fed by a bottle 52 of this gas.
• This device is intended to scan the area between the grid 32 (and therefore the source 29) and the object 42 to be studied, by means of helium, at a flow rate of 15 liters per hour.
• the spectra obtained by the multi-channel analyzer 40 are processed by a portable computer 54 and displayed on the screen 56 of which this computer is equipped.
• Quantitative measurements are also possible, provided that the studied object is homogeneous or has a known stratigraphy.
• the processing of the results can then take place after separation of the respective contributions PIXE and XRF, thanks to calculation algorithms which are integrated with commercially available software, for example GUPIX of
• the background noise spectrum of the device PIXE-XRF analysis is obtained using a sample of polyethylene, a material that is composed solely of carbon and hydrogen and whose chemical formula is [CH 2 -CH 2 J n .
• the observed lines are mainly due to the elastic scattering of 244- cm X-rays on polyethylene.
• the characteristic gold rays (Kapton® plating material of the source support) are negligible.
• the usable energy window for PIXE / XRF analysis is between 0 and 10 keV.
• the calibration certificate associated with this reference shows that the material is composed mainly of the following oxides: SiO 2 62.78%, Al 2 ⁇ 3 13.67%, Fe 2 O 3 5.14%, K 2 O 2, 77%, MgO 2.72%, CaO 2.62%, Na 2 O 0.90%, TiO 2 0.63%.
• a qualitative treatment of the spectrometric data, acquired during 15 minutes, makes it possible to identify almost all the alkaline or metallic cations, present in the form of various oxides, up to concentrations close to 1% for some of them (sodium and titanium).
• the invention applies in particular to the field of archeology.
• the invention also applies to the field of geology.
• the "beige" face of this block is characteristic of a sound rock (fresh break during sampling) and the greyish face is characteristic of the rock exposed to the internal atmospheric conditions of the cave.
• Basalt powder of underwater origin was also measured.
• the sample is a volcanic (basaltic) rock originating from the ocean floor of the Pacific Ocean. This rock was ground and then dry pelletized, without binder, so as to obtain a homogeneous sample. A preliminary (destructive) chemical analysis showed that this rock had the following composition: SiO 2 49.83%, Al 2 O 3 14.5%, Fe 2 O 3 11.32%, MgO 8.68%, CaO 11 17%, Na 2 O 2.47%, TiO 2 1.44%.
• the spectrometric data obtained made it possible to identify metals such as zinc, copper, iron, titanium, aluminum and magnesium. Sulfur and phosphorus have also been detected. Elements of the alkaline series (calcium and potassium) are also visible on the spectrum obtained.
• the analysis method by PIXE / XRF reveals in this case all its analytical power, allowing the detection of elements whose atomic numbers range from 12 to 30.
• the invention also applies to the field of sedimentology.
• the PIXE / XRF method once again demonstrates its relevance in a field such as chemical analysis in sedimentology.
• the invention also applies to the field of metallurgy.
• a fountain of I9 th century consists of three parts: a threaded cylindrical base in its upper part, a cover screwed on that basis and a glass ink containing an ink residue and from to lodge inside the metal base. Traces of wear of the plating layer reveals in place a yellowish material. The purpose of the analysis is to determine the nature of the plating layer as well as that of the underlying material.
• the spectrum obtained shows the presence of nickel, copper, zinc and calcium. It can be concluded that the yellowish alloy is brass (alloy of copper and zinc) and is covered with a nickel plating (greyish metal). The presence of calcium can be attributed to external contamination.
• the fate of the source 244 Cm resulting from the process according to the invention is easily manageable because the radioactive material can be easily recovered and purified for possible reuse.
• the deposit of 244 cm is re-dissolved by acid lixiviation using a few hundred ⁇ l of HNO 3 with a concentration greater than 0.1 mol / l.
• this operation must be carried out in an installation identical to the one mentioned above (containment).
• This separation Cm / Pu can be carried out according to the conventional methods of "extensive reprocessing", well known to chemists in the nuclear sector. Among these, we can mention the best known as solvent extraction and extraction chromatography.

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