DEVELOPMENT OF BETA SPECTROMETRY USING CRYOGENIC DETECTORS M. Loidl, C. Le-Bret, M. Rodrigues, X. Mougeot CEA Saclay – LIST / LNE, Laboratoire National Henri Becquerel, France MetroFission WP 5: Nuclear Decay Data

METALLIC MAGNETIC CALORIMETERS: ONE TYPE OF CRYOGENIC DETECTORS ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 2 Thermal detectors:  T = E /C Paramagnetic thermometer  T  M SQUID magnetometer  M  V Thermal link  d = C /G Very low temperature (10 – 20 mK) : C  T (metals at very low T)  T = E /C  d = C /G  E  k B T 2 C thermodynamic fluctuation noise

| PAGE 3 ICRM 2013 | Antwerp, Belgium | June 2013 Pour personnaliser le pied de page et la date : « Insertion / En-tête et pied de page » Personnaliser la zone de de pied de page Cliquer sur appliquer partout METALLIC MAGNETIC CALORIMETERS FOR BETA SPECTROMETRY Source embedded inside the detector absorber 4  sr solid angle no back-scattering at the detector surface energy loss of beta particles in the source: energy should be detected anyway Determination of the absorber dimensions by Monte Carlo simulation detection efficiency close to 100 % Very low T low thermodynamic fluctuation noise high energy resolution low energy threshold

MEASUREMENT OF AN ALLOWED BETA SPECTRUM OF LOW MAXIMUM ENERGY: Ni-63

Ni- 63: THEORETICAL SPECTRUM ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 5 Allowed transition: Theoretical spectrum can be calculated with high degree of confidence validate measurement method by comparison experiment - theory Exchange effect (creation of beta electron into a bound orbital; simultaneous emission of a bound electron) has been included in the code BetaShape developed at LNHB

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 6 Ni- 63: SPECTRUM MEASURED USING DRIED SOURCES Sources made by drying a drop of NiCl 2 solution Experimental spectra differ from one another and from theory Agreement with theory better when including exchange effect No clear influence of - carrier concentration (MD8) - absorber material (MD11) Part of energy in NiCl 2 metastable states detection of  energy incomplete?

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 7 Ni- 63: ELECTROPLATED SOURCES (1) Requirements: metallic Ni deposit activity / surface ~ 100 Bq / mm 2 minimize quantity of inactive Ni electrolyte containing a small Ni concentration Nickel chloride concentration [mol/L] 0.01 Hypophosphite ion concentration [mol/L] 0.25 Acetic acid concentration [mol/L] 0.5 Mass activity [kBq/g] 67.5 Anode material Pt Cathode material Au Temperature [°C] 70 Current density [mA/mm 2 ] Deposition time [min] 2 Activity per unit surface [Bq/mm 2 ] 274

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 8 Ni- 63: ELECTROPLATED SOURCES (2) Energy threshold: 200 eV Energy resolution: 51 eV 59.5 keV Excellent agreement experiment - theory when taking account of exchange effect Confirmation of the calculation of the exchange effect in the code BetaShape (developed at LNHB) 241 Am 59.5 keV  line

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 9 Ni- 63: ELECTROPLATED SOURCES (3) Au absorber Ag absorber Theory w. exchange effect Ag K  escape peak 241 Am 59.5 keV  line Energy (keV) Counts / 100 eV Au / Ag absorbers: no influence of the absorber material

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 10 MEASUREMENT OF A FORBIDDEN BETA SPECTRUM OF LOW MAXIMUM ENERGY: Pu-241

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 11 Pu- 241: SPECTRUM MEASURED WITH A DRIED SOURCE (1) Good agreement between experiment and theory starting from ~ 7 keV Discrepancy at low energies First forbidden, non-unique transition; no shape factor used for theoretical spectrum discrepancy at low energies due to insufficiency of theory or to our detector / source?

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 12 Case of 241 Pu: very small error if calculated as an allowed transition: “  approximation” well fulfilled: 2  =  Z/2R > E 0 Discrepancy at low energies greatly reduced if the exchange effect is taken into account Remaining discrepancy most likely due to the use of a dried source Pu- 241: SPECTRUM MEASURED WITH A DRIED SOURCE (2) >

STUDY OF ABSORBERS FOR HIGHER ENERGY (1) Higher energy beta spectra: Correction for energy loss by escape of Bremsstrahlung photons from the detector must be considered. Example: 36 Cl Pure beta emitter; second forbidden non-unique transition E max = 709 keV Au absorber thickness for stopping 709 keV electrons: 260 µm Monte Carlo simulation: 36 Cl source  = 300 µm enclosed inside a Au cylinder  = 1 mm, thickness 2 x 260 µm

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 14 STUDY OF ABSORBERS FOR HIGHER ENERGY (2) Input: theoretical spectrum of 36 Cl Output: simulated detected spectrum Calculation of a correction function

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 15 CONCLUSION AND PERSPECTIVES Metallic magnetic calorimeters are in an excellent position for the precise measurement of the shapes of low energy beta spectra Great influence of the type of beta source: drop deposited sources: discrepant spectra electroplated sources: reproducible spectra, good agreement experiment – theory promising alternative: source implantation into absorber Higher energy beta spectra: correction for energy loss by escape of photons from the detector must be considered -

ICRM 2013 | Antwerp, Belgium | June 2013 | PAGE 16 METALLIC MAGNETIC CALORIMETERS FOR BETA SPECTROMETRY (2) Linearity check using (external) 55 Fe, 109 Cd and 241 Am sources Experimental data pointsLinear fit Tabulated line energy [keV] Experimental line positions [channels] Residuals < fit uncertainty (≤ 0.1 %); No tendency fit uncertainty