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

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)


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 T1/2, 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

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Detector Proportional Counter

Scintillation Counter

Magnetic spectrometer

Semi-conductor (Si)

Metallic magnetic

calorimeter

Energy resolution at

100 keV30 keV 15 keV 10 eV to 1 keV

~ 8 keV (300 K) ~ 3 keV (77 K)

~ 50 eV


Measurements – metallic magnetic calorimeters

4

Very promising technique:

• Detection efficiency > 99,9 %

• Energy threshold of about 200 eV

• Energy resolution of 30 eV @ 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


Measurements – Silicon detector

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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 8 keV @ 100 keV (300 K) • Linear response • Easy to implement

But:• Dead zones• Bremsstrahlung• Backscattering • High quality of vacuum • Detector thickness

Si(Li)

PIPS


Experimental aspects

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• 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


Gate valve

Experimental device - General

PUMP

Linear

feed-through

GAUGE

100 cm

17 cm

Detection chamber “The Cube” with the

PIPS detector


DEWAR

JAUGEPOMPE

Vanne à vide

Canne de

translation

Experimental device - The source holder

Source holder Source support

Screen

Influence of X-rays


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


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 simulationsVS

Co

un

tsS-D distance (mm)

Theory

MC


Influence of the source-detector distance

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10 mm

20 mm

30 mm

40 mm

PIPS 500 µm

24 m

m

90 Y

• Four source – detector distances : 10 mm, 20 mm, 30 mm, 40 mm

• 106 particles emitted from 90Y (MetroMRT project) isotropic source

• Thickness of active volume: 500 µm

Detector thickness too small

Huge influence of the solid angle


Influence of the thickness of active volume

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90 Y

• Source – detector distance: 10 mm

• 106 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


Geometry and materials of the cube

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250 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


Sources of distortion

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• 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


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 2013

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Thank you for your attention


Theory

17

• Fermi (1933):

Energy P

roba

bilit

y

85Kr

• Beta decay: the electron and the antineutrino

share the momentum and energy of the decay

continuous kinetic energy spectra

Documents

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