Measurement of thin oil layers by PIXE-α

Transcription

1 Measurement of thin oil layers by PIXE-α P. Brisset, D. Chambellan and J. de Sanoit CEA-LIST Département des technologies du Capteur et du Signal Gif-sur-Yvette Cedex, France International conference on Recent dvelopments and applications of nuclear technologies september 28, Bialowieza, Poland 1 Principle of the PIXE -αmethod détecteur X source alpha X α α 2 PIXE analysis of the silver coating of a Roman coin (III century BC) 3 1

2 Si Al Si Ar K K Ca Vernice Falsa Energia (kev) Ceramica Attica Energia (kev) Fe Fe Characterisation of the blue pigments of Madonna del Roseto (Luca della Robbia, XV+ century Florence, Italy) 4 Analysis of the black pigment Conteggi Body >>> false Conteggi Basis >>> authentified 5 General advantages of the method Non destructive analysis Analysis of light elements ( Z < 26 ) Surface analysis (some mm) samples analysis with dimensionnal or administrative constraints Field equipment 6 2

3 PIXE -αadaptation to thin layer thickness measurement principle Source Detector Excitation by α Emission of X-ray Oil Studied material Metallic plate CEA EU patent 7 Radioactive source specifications Pure α emission ( >>>> 21 Po ) High activity (37MBq) Annular geometry Source : sealed but thin Resistance to radiolysis 8 21 Po desintegration scheme T = 138,4 jours 21 Po 83,1 a1 a2 = 5.3 MeV (99,99%) γ (.1%) 26 Pb 9 3

4 21 Po radiological and chemical safety -Chemical safety : -very low level of the toxicity limit mg/m 3 -Polonium compounds are very volatile - Radiological safety (annual incorporation limit) - Workers: Bq - Public : Bq From Journal Officiel des Communautés Européennes (JOCE, 198) 1 Chemical reaction for source preparation Spontaneous electrochemical replacement (Haïssinsky, 1937) Po e Po ( Ag Ag + + e ) x2 Po Ag 2 Ag + + Po 11 Electrodeposition cells Annular truncated concave source Annular source 12 4

5 Sources socket MYLAR / Silver (,2 mm) Annular truncated concave source Annular source Confinement barrier Layer of aromatic epoxy resin (e <,5 µm) KAPTON window (e < 2 µm) NYLON grid (mechanical protection) Po Source preparation deposition kinetics Po deposition yield (%) Po deposition yield vs contact time 4 ml of aqueous HCl or HCl/N 2 H 4, 2 HCL containing.8 MBq of carrier free polonium silver electrode area = 1.77 cm 2 Stirring 2 rpm [HCl] = 2 M [HCl] = 2 M; [N 2 H 4, 2 HCl] = 1 M,,5 1, 1,5 2, time (hours) Po Source ready to use 15 5

6 21 Po source experimental arrangement Common EU patent CEA + IN FN Technology transfer from CEA to INFN 16 Experimental device Detail of the PIXE -αhead Area of measurement NaI(Tl) detector 17 Experimental program Objectives : Influence of the thickness of demoulding oils on the aesthetic quality of concrete facings Studies on the influence of oils deposition method on film thickness Materials: 2 types of concrete 2 types of oils Oil deposition methods Spraying with conic nozzle at 2 cm from surface spread after spraying with a rubber scraper 18 6

7 Studied materials Concrete composition Constituents Silex 5/15 Aggregate 4/8 Sand /4 Cement CEM I 52,5 Filler Water E/L* Quantities (kg/m 3 ) Oils characteristics Properties Vegetable-based oil (V) Mineral-based oil (M) Nature Color Flash point ( C) Density (g/cm 3 ) Viscosity at 2 C (mpa.s) Liquid Straw-coloured > 9 C Liquid yellow > 8 C Contact angle ( ) Measured spectra Metallic Mylar surface (steel) Metallic surface Infinite (steel) Mylar 2 Calibration with mylar disks Mylar Discs Disc # 1 Disc # 2 Disc # 3 Mass (mg) Thickness (µm) The calculation of each equivalent thickness is done according to the following equation: density of the mylar Equivalent thickness = Thickness of the disc density of the studied oil 21 7

8 Calibration curves Impulsion (c/s) Transmission (%) Equivalent thickness (µm) Mineral Vegetable Steel Steel + Disc # Steel + Disc # Steel + Disc # Steel + infinite Mylar an approximate equation of these curves is of the form : y = a + bx 3 + c.lnx By fitting on the results we obtain the equations coefficients, thus : For the mineral oil: For the vegetable oil: -6 3 y = x ln x -6 3 y = x ln x 22 Calibration curves Transmission (%) Gauging of mineral-based oils Thickness of the oil film (µm) Gauging of vegetable-based oils Thickness of the oil film (µm) 23 Measurement uncertainties σ = - x R x t e x x with R : counting rate with no oil t : measurement time x : thickness of the measured oil x : characteristic constant of the oil absorption x (µm) σ x (µm) σ x / x (%) Standard deviation on the thickness measure 24 8

9 Comparison between gauging and weighting results Oil Thickness (µm) Sprayed film Scraped film after spraying Mineral oil Between 3 to 5 1. Vegetable oil Between 2 to Conclusion -PIXE method really adapted for this kind of measurement -Range of measurement : 1 to 1 µm -Film thicknesses are between 1 to 2 µm after scraping sprayed film -A film of 1 to 2 µm is enough to obtain a high quality facing allowing minimization of oil quantities -the studied vegetable oil allows obtaining a facing with a better aesthetical quality than the mineral oil -Many other applications are possible and some have been tested (teflon for ex.) - Evolution to Curium 244 source (half life,.) 26 Thank you for your attention 27 9