Bertram BlankCEN Bordeaux-Gradignan

• main physics goals• detector scans• source measurements• MC simulations

ISOLDE workshop, December 5-7, 2011

Determination of experimental values for 0+

0+: measurement of T1/2, BR, QEC vector coupling constant Gv (CVC hypothesis) Vud element of CKM quark matrix

Precision required: < 10-3

Future subjects:- experimental tests of isospin

corrections dc- test of CVC on larger range

- measurements with more exotic isotopes

Measurements for A > 54 Measurements for Tz ≤ -1

Ft = 3073.660.75 s

Ft = ft (1 + d’R) (1 + dNS - dC)

= for T=1

K 2 G2

v (1+DvR)

beam preparationwith REXtrap

Half-life of 38Ca:

B. Blank et al., EPJA 44 (2010) 363 BR = 75.45(58)%

ISOLDE 2007

T1/2 = 443.8 ± 1.9 ms

Kavanagh et al. Zioni et al. Present work Gallman et al. Wilson et al.

• basically 100% super-allowed decay• very small non-analog decays• precision of e.g. 10% for a 1% transition: 0.1%

• many decay channels open• strong non-analog transitions• high precision of g efficiency needed 0.1%

• thick dead zone on interior side• thin external dead layer• request of high-precision for• crystal size• crystal position• dead zones

• large dewar• aluminum entrance window

• X-ray radiography

• g-ray detector scans

• source measurements

• MC simulations

(GEANT4 or CYLTRAN)

develop a model of the detector

to calculate efficiency at any energy

at a fixed distance of 15 cm

rough size of crystal tilt of crystal with respect to detector housing of 1° according to GEANT4 simulations no influence on results

• AGATA scan table at CSNSM: strongly collaminated 137Cs source

HPGe

X-Y table137Cs (477MBq)

A. Korichi et al.

• AGATA scan table at CSNSM: strongly collaminated 137Cs source (662 keV)

HPGe

X-Y table

137Cs (477MBq)

• Scan at CENBG: strongly collaminated 241Am source (60 keV)

total

full-energypeak

• excellent full-energy peak spectrum• good total-energy spectrum• problem with thickness of entrance window?

total

full-energypeak

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

Source position

high-precisionX-Y-Z table

• all source measurements at exactly 15 cm from entrance window position precision of better than 0.1%

• Fixed 137Cs and movable 241Am: 6ms of shaping time

• To develop detector model:

• which code to use: GEANT4, CYLTRAN, EGGS….

• GEANT4: (J. Souin, PhD student…. he quit….)• almost all features needed• errors in decay schemes external event generator• no g-g correlations (1% effect) external event generator• not extremely well tested for low-energy g rays• different packages, which one to use?

• CYLTRAN: (BB)• very well tested J. Hardy• FORTRAN77…• only single g rays or electrons in the input

upgrade to « source-type » input via an external event generator• positron annihilation-in-flight not included

to be included; significant effect on escape peaks

• which code to use: GEANT4, CYLTRAN, EGGS….

• two ways:• correct experimental data for summing effects to get single g-ray efficiencies

• certain number of approximations• « collimated » simulations, opening cone:

much less events to simulate• peak-to-total can be included a posteriori

J. Hardy et al.

• to simulate whole decay schemes• no approximations needed as long as decay scheme is known• need of event generator including g-g angular correlations• peak-to-total needed in simulations• need of a lot of simulated events to get statistics for all g rays!!

B. Blank et al.

• presently only CYLTRAN simulations

• 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%) at largely different energies

• standard sources: 60Co, 88Y, 133Ba, 134Cs, 152Eu, 207Bi

• short-lived online source at ISOLDE: 24Na, 27Mg, 56Co, 66Ga, 75Se

• one absolute efficiency source: 60Co with activity precision of 0.7‰

57Co 51Cr 85Sr 54Mn 60Co

+133Ba, 56Co

vendor specifications

adjusted parameters

length of crystal 79.2 mm 79.25 mm radius of crystal 34.8 mm 34.54 mmlength of central hole 59.5 mm 71.2 mmradius of central hole 5 mm 7.15 mmexternal dead zone <0.5 mm 0.5 mminternal dead zone 0.5 mm 0.5 mmend dead zone 0.5 mm 1 mmdistance window - crystal 5 mm 5.73 mm

!!

• rescan front with 241Am• check entrance window thickness• measure entrance window to cristal distance• test pile-up correction for different energies and shaping times• improve sources 133Ba and 56Co• add sources 66Ga, 75Se, 134Cs, 152Eu• measure other 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-ray efficiency

detector model with 0.1-0.2% efficiency precision

• J. Souin, PhD student• A. Korichi and Hoa Ha, CSNSM• A. Herlert and K. Johnston, ISOLDE• J. Hardy, Texas A & M• Exotic Nuclei group at CENBG

Born to be wild…..

Thanks for your attention!

… or what????

full-energypeak

• nice over-all agreement• holding structure reasonably well reproduced

full-energypeak

• slight difference…• there was a problem during the scan…

total

full-energypeak

• good agreement for full-energy peak• reasonable agreement for total spectrum

full-energypeak

• does not help a lot…• effect of holding structure very important

b detector

Gedetectors

Tapetransportsystem

QEC

T1/2

0+

0+

BRg

38Ca ISOLDE beam from REXtrap

• fixed 137Cs source and pulser on other channel

137Cs:conversion electrons

57Co 51Cr 85Sr 137Cs 54Mn 60Co