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High-precision efficiency calibration of a HP Germanium detector

High-precision efficiency calibration of a HP Germanium detector. Bertram Blank CEN Bordeaux-Gradignan. main physics goals detector scans source measurements MC simulations. ISOLDE workshop, December 5-7, 2011. Ft = ft (1 + d ’ R ) (1 + d NS - d C )

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High-precision efficiency calibration of a HP Germanium detector

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  1. High-precision efficiency calibration of a HP Germanium detector Bertram Blank CEN Bordeaux-Gradignan • main physics goals • detector scans • source measurements • MC simulations ISOLDE workshop, December 5-7, 2011

  2. Ft = ft (1 + d’R) (1 + dNS- dC) = for T=1 K 2 G2v (1+DvR) Super-allowed Fermi transitions: Introduction Determination of experimental values for 0+  0+:  measurement of T1/2, BR, QEC vector coupling constant Gv(CVC hypothesis) Vudelement of CKM quark matrix Precision required: < 10-3 Ft = 3073.660.75 s • Future subjects: • - experimental tests of isospin corrections dc • - test of CVC on largerrange • - measurementswith more exoticisotopes • Measurements for A > 54 • Measurements for Tz ≤ -1

  3. Super-allowed Fermi transitions: Ca-38 ISOLDE 2007 Half-life of 38Ca: beampreparation withREXtrap T1/2 = 443.8 ± 1.9 ms B. Blank et al., EPJA 44 (2010) 363 Kavanagh et al. Zioni et al. Presentwork Gallman et al. Wilson et al. BR = 75.45(58)%

  4. Super-allowed Fermi transitions for Tz = 0 • basically 100% super-allowed decay • very small non-analog decays • precision of e.g. 10% for a 1% transition:  0.1%

  5. Super-allowed Fermi transitions for Tz = -1 • many decay channels open • strong non-analog transitions • high precision of g efficiency needed  0.1%

  6. 70% n-type Germanium detector • thickdead zone on interiorside • thinexternaldead layer • request of high-precision for • crystal size • crystal position • dead zones • large dewar • aluminum entrance window

  7. Calibration Procedure • X-ray radiography • g-ray detector scans • source measurements • MC simulations • (GEANT4 or CYLTRAN) •  develop a model of the detector • to calculateefficiencyatanyenergy • at a fixed distance of 15 cm

  8. X-ray photography of detector • rough size of crystal • tilt of crystalwith respect to detector housing of 1° • according to GEANT4 simulations no influence on results

  9. Gamma-ray scan of detector • AGATA scan table at CSNSM: strongly collaminated 137Cs source HPGe 137Cs (477MBq) X-Y table A. Korichi et al.

  10. Gamma-ray scan of detector • AGATA scan table at CSNSM: strongly collaminated 137Cs source (662 keV) HPGe 137Cs (477MBq) X-Y table

  11. Gamma-ray scan of detector • Scan at CENBG: strongly collaminated 241Am source (60 keV)

  12. Longitudinal scan: 662 keV total full-energy peak • excellent full-energy peak spectrum • good total-energy spectrum • problem with thickness of entrance window?

  13. Front scan: 662 keV total full-energy peak • tilt…. • full-energy peak: excellent • total spectrum: raisonable • precision of the stepping motors: 10-2

  14. 70% HP Germanium on precision test bench Source position high-precision X-Y-Z table • all source measurements at exactly 15 cm from entrance window •   position precision of better than 0.1%

  15. Pile-up correction • Fixed 137Cs and movable 241Am: 6ms of shaping time

  16. Comparison: experiment - simulations • To develop detector model: • which code to use: GEANT4, CYLTRAN, EGGS…. • GEANT4: (J. Souin, PhDstudent…. hequit….) • almost all featuresneeded • errors in decayschemes externaleventgenerator • no g-gcorrelations (1% effect)  externaleventgenerator • not extremelywelltested for low-energyg rays • different packages, which one to use? • CYLTRAN: (BB) • verywelltested J. Hardy • FORTRAN77… • only single g rays or electrons in the input •  upgrade to « source-type » input via an externaleventgenerator • positron annihilation-in-flight not included •  to beincluded; significanteffect on escape peaks • which code to use: GEANT4, CYLTRAN, EGGS….

  17. Comparison: experiment - simulations • twoways: • correct experimental data for summingeffects to get single g-rayefficiencies • certain number of approximations • « collimated » simulations, openingcone: •  muchlessevents to simulate • peak-to-total canbeincluded a posteriori •  J. Hardy et al. • to simulatewholedecayschemes • no approximations needed as long as decayschemeisknown • need of eventgeneratorincludingg-gangularcorrelations • peak-to-total needed in simulations • need of a lot of simulatedevents to getstatistics for all g rays!! • B. Blank et al. • presentlyonly CYLTRAN simulations

  18. Calibration sources • peak-to-total sources: •  one single g ray with 100% branching ratio • 57Co, 51Cr, 85Sr, 137Cs, 58Co, 54Mn, 60Co, 22Na • relative efficiency sources: •  a few well-known branches (BR error <1%) atlargelydifferentenergies • standard sources: • 60Co, 88Y, 133Ba, 134Cs, 152Eu, 207Bi • short-lived online source at ISOLDE: • 24Na, 27Mg, 56Co, 66Ga, 75Se • one absoluteefficiency source: • 60Co withactivityprecision of 0.7‰

  19. Total - to - peak 57Co 51Cr 85Sr 54Mn 60Co

  20. Comparison of source measurements and simulations

  21. Comparison of source measurements and simulations +133Ba, 56Co

  22. Detector model ! !

  23. To do list..... • rescan front with241Am • check entrance windowthickness • measure entrance window to cristal distance • test pile-up correction for differentenergies and shaping times • improve sources 133Ba and 56Co • addsources 66Ga, 75Se, 134Cs, 152Eu • measureother sources: • peak-to-total: 139Ce, 7Be, 65Zn, 28Al, 37S • efficiency: 46Sc, 59Fe, 108mAg, 120Sb, 180mHf, 66Ga • add annihilation in flight to CYLTRAN • compare with GEANT4 simulations • analyse for single g-rayefficiency  detector model with 0.1-0.2% efficiencyprecision

  24. Acknowledgement • J. Souin, PhDstudent • A. Korichiand Hoa Ha, CSNSM • A. Herlert and K. Johnston, ISOLDE • J. Hardy, Texas A & M • ExoticNuclei group at CENBG Born to bewild….. … or what???? Thanks for your attention!

  25. Longitudinal scan: 60 keV full-energy peak • nice over-all agreement • holding structure reasonably well reproduced

  26. Front scan: 60 keV full-energy peak • slight difference… • there was a problem during the scan…

  27. Perpendicular scan: 662 keV total full-energy peak • good agreement for full-energypeak • reasonableagreement for total spectrum

  28. Perpendicular scan: 60 keV full-energy peak • does not help a lot… • effect of holding structure very important

  29. 0+ T1/2 QEC BR g 0+ Super-allowed Fermi transitions: experimental device b detector Tape transport system Ge detectors 38Ca ISOLDE beam from REXtrap

  30. DAQ: deadtime correction • fixed 137Cs source and pulser on other channel

  31. 137Cs: conversion electrons Total - to - peak 57Co 51Cr 85Sr 137Cs 54Mn 60Co

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