DDEP 2012 | C. Bisch – Study of beta shape spectra 1 Study of the shape of  spectra Development of a Si spectrometer for measurement of  spectra  Introduction  Beta detectors  Experimental device  Monte Carlo calculations  Conclusion and perspectives Charlène Bisch LNHB/CDF : M.-M. Bé, C. Bisch, C. Dulieu, M. A. Kellett, X. Mougeot In collaboration with IPHC, Ramses, Strasbourg (A.-M. Nourreddine)

DDEP 2012 | C. Bisch – Study of beta shape spectra 2 Introduction Users : Nuclear Power Industry (decay heat calculations), medical care sector (dose calculations), ionizing radiation metrology (liquid scintillation and ionization chamber techniques) Test and constrain calculations with perfectly controlled experiments Calculations are necessary : very short T 1/2, multiple beta decays, cascades, …  Understand the theory to make it evolve Growth of computing power  more complex models Beta spectra shapes evaluation Experiments are necessary : validation of the calculations, uncertainties of the models  Subtle understanding of the phenomena that distorting beta spectra Growth of computing power  Monte-Carlo simulations

DDEP 2012 | C. Bisch – Study of beta shape spectra Beta detectors 3 DetectorProportional Counter Scintillation Counter Magnetic spectrometer Semi- conductor (Si) Metallic magnetic calorimeter Energy resolution at 100 keV 30 keV15 keV10 eV to 1 keV ~ 8 keV (300 K) ~ 3 keV (77 K) ~ 50 eV

DDEP 2012 | C. Bisch – Study of beta shape spectra Measurements – metallic magnetic calorimeters 4 Very promising technique: Detection efficiency > 99,9 % Energy threshold of about 200 eV Energy resolution of 30 6 keV Non-linearity of 0,1 % in 6 – 80 keV But: Activity ≤ 15 Bq Measurements at 10 mK  cooling time of about 3 days Bremsstrahlung from 800 keV  deacrease of efficiency Quality of the source  distortion of the spectrum? Detectors floors Dilution cooler

DDEP 2012 | C. Bisch – Study of beta shape spectra Measurements – Silicon detector 5 Our detector specifications: PIPS: Passivated Implanted Planar Silicon Detector Window thickness (Si eq.): < 50 nm Active diameter: 23,9 mm Active thickness: 500 µm More classical technique: Good energy resolution of keV (300 K) Linear response Easy to implement But: Dead zones Bremsstrahlung Backscattering High quality of vacuum Detector thickness Si(Li) PIPS

DDEP 2012 | C. Bisch – Study of beta shape spectra Experimental aspects 6 Experimental spectra may be distorted by the detection system Experimental aspects to limit sources of distortion - Detector cooled to liquid nitrogen temperature  thermal noise - Ultra high vacuum  interactions e - /environment and dead layer due to water steam condensation - Reduction of vibrations  microphonics (additional component to electronic noise) - Distance from source to detector and centring of the source  solid angle, reproducibility, simulations - Source: ultra-thin  reduction of auto-absorption quality  minimisation of impurities homogeneous  reproducibility, simulations Any remaining factors will be quantified by Monte-Carlo simulations

DDEP 2012 | C. Bisch – Study of beta shape spectra 7 Gate valve Experimental device - General PUMP Linear feed-through GAUGE 100 cm 17 cm Detection chamber “The Cube” with the PIPS detector

DDEP 2012 | C. Bisch – Study of beta shape spectra 8 DEWARJAUGE POMPE Vanne à vide Canne de translation Experimental device - The source holder Source holderSource supportScreen Influence of X-rays

DDEP 2012 | C. Bisch – Study of beta shape spectra 9 Experimental device - The detection chamber Electrical BNC/microdot connector Detector holder in copper  detector cooled uniformly An electrical wire connects the detector to the BNC/microdot connector  to avoid thermal transfer

DDEP 2012 | C. Bisch – Study of beta shape spectra Monte Carlo simulations Utilisation of GEANT4 to optimise the source holder and the detection chamber Influence of the source-detector distance Geometry and materials least likely to scatter electrons Code validation: 10 Monte Carlo simulations VS Counts S-D distance (mm) Theory MC

DDEP 2012 | C. Bisch – Study of beta shape spectra Influence of the source-detector distance mm 20 mm 30 mm 40 mm PIPS 500 µm 24 mm 90 Y Four source – detector distances : 10 mm, 20 mm, 30 mm, 40 mm 10 6 particles emitted from 90 Y (MetroMRT project) isotropic source Thickness of active volume: 500 µm Detector thickness too small Huge influence of the solid angle

DDEP 2012 | C. Bisch – Study of beta shape spectra Influence of the thickness of active volume Y Source – detector distance: 10 mm 10 6 particles emitted from 90 Y isotropic source Four thicknesses of active volume (500 µm, 2 mm, 5 mm, 8 mm) 5 mm thickness active volume is necessary for measuring 90 Y spectra 10 mm 500 µm 2 mm 5 mm 8 mm

DDEP 2012 | C. Bisch – Study of beta shape spectra Geometry and materials of the cube mm No cube Steel cube 250 mm Steel cube 170 mm Aluminium cube 170 mm Source – detector distance: 10 mm Source – detector distance: 40 mm 250 mm

DDEP 2012 | C. Bisch – Study of beta shape spectra Sources of distortion 14 Four main sources of distortion: - Solid angle  source – detector distance - Detector thickness effect  depth of active volume - Geometry effect  geometry of active volume - Scattering and backscattering  energy, Z of the material, incidence angle Geometry effect

DDEP 2012 | C. Bisch – Study of beta shape spectra Conclusion and perspectives Development phase of experimental device is complete The experimental setup is currently being assembled We intend to do our first measurements of beta spectra early

DDEP 2012 | C. Bisch – Study of beta shape spectra 16 Thank you for your attention

DDEP 2012 | C. Bisch – Study of beta shape spectra Theory 17 Fermi (1933): Energy Probability 85 Kr Beta decay: the electron and the antineutrino share the momentum and energy of the decay  continuous kinetic energy spectra