Neutron spectrometry with lanthanum bromide scintillation detectors

Neutron spectrometry with lanthanum
bromide scintillation detectors
A. Oberstedt
The 2nd ERINDA Progress Meeting and Scientific Workshop
Jyväskylä, Finland
January 8-11, 2013
Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 1 Outline
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Andreas Oberstedt Background!
Experimental setup!
Photon – fission fragment coincidences!
-  252Cf(SF)!
-  235U(nth,f)!
Neutron measurements with LaBr3:Ce detectors!
-  geometric profile!
-  cross section!
-  neutron spectra!
Summary !
Conclusions!
Outlook!
2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 Background
Prompt fission γ-ray measurements!
•  252Cf(SF) at IRMM in Geel!
•  235U(nth,f) at KFKI in Budapest!
Instrumentation!
•  Fission fragment spectrometer VERDI!
•  Poly-crystalline chemical vapor deposited diamond detectors
(fission trigger)!
•  LaBr3:Ce (and LaCl3:Ce) scintillation detectors (photon
measurements)!
Applied technique!
•  Coincidence technique!
•  Time-of-flight measurement!
Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 3 Experimental setup
LaBr3 Fission fragment spectrometer VERDI 252Cf sample (Af ≈ 5500 /s) εgeom = 46,18% Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 4 Coincidence measurements
Photon – fission fragment coincidences with 2 in. x 2 in. LaBr3:Ce detector 252Cf(SF) Prompt fission γ-­‐rays n, n’"
γ-­‐decay aYer inelas6c neutron scaZering Previously: focus on prompt fission γ-­‐rays Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 Intrinsic and external background 5 Coincidence measurements
Photon – fission fragment coincidences with 2 in. x 2 in. LaBr3:Ce detector 252Cf(SF) Now: focus on events from inelas6c neutron scaZering, leading to discrete γ-­‐lines -­‐-­‐> projec6on on energy-­‐axis … Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 6 Coincidence measurements
… exhibits an energy spectrum … 252Cf(SF) … iden6fied as γ-­‐decays of 79,81Br* (from the detector) and 56Fe*, aYer inelas6c neutron scaZering! Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 7 “Neutron measurements”
Time-­‐of-­‐flight distribu6ons for a γ-­‐energy depend on 1.  Geometry (size and distance from neutron source to scaZering material) 2.  Involved (n,n’) cross-­‐sec6ons 3.  Detec6on efficiency Conclusion: if two are known, the third can be determined! Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 8 “Neutron measurements”
Three examples for possible applica6ons: 1.  determina6on of geometrical profiles 2.  determina6on of cross sec6ons 3.  determina6on of neutron spectra (and flux) Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 9 Experiment on
252Cf(SF)
First example: geometry Eγ = 847 keV; 56Fe(n,n’1) Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 10 Experiment on
252Cf(SF)
Eγ = 847 keV; 56Fe(n,n’1) -­‐> background assessment (more details later) Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 11 Experiment on
252Cf(SF)
“Neutron” 6me-­‐of-­‐flight spectrum (background subtracted) Eγ = 847 keV; 56Fe(n,n’1) -­‐> explana6on? Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 Experiment on
252Cf(SF)
Eγ = 847 keV; 56Fe(n,n’1) -­‐> known cross-­‐sec6on & known neutron spectrum ν = 3.77; T = 1.42 MeV
Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 Experiment on
252Cf(SF)
Time-­‐of-­‐flight spectrum (neutron region) •  Iron at 10 cm: the shortest distance from neutron source •  … in steps of 5 cm … up to 40 cm Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 Experiment on
252Cf(SF)
Time-­‐of-­‐flight spectrum (neutron region) -­‐> complete descrip6on of 6me-­‐of-­‐flight spectrum! Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 Experiment on
252Cf(SF)
-­‐> iron profile Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 Experiment on
252Cf(SF)
-­‐> iron profile: VERDI spectrometer! ( = “rough” 1-­‐dimensional “neutron tomography”) Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 Experiment on
252Cf(SF)
Second example: cross sec6ons measurements -­‐> examine 6me-­‐of-­‐flight distribu6on for interval E = (244, 297) keV Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 18 Experiment on
252Cf(SF)
Region of interest: ΔEγ = 244 -­‐ 297 keV Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 19 Experiment on
252Cf(SF)
Background assessment Region of interest: ΔEγ = 244 -­‐ 297 keV Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 20 Experiment on
252Cf(SF)
Raw ToF spectrum Error bars: sta6s6cal Background subtracted Error bars: sta6s6cal + uncertain6es from fits of background Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 21 Experiment on
252Cf(SF)
Closer inspec6on of γ-­‐spectrum reveals: Two peaks: 262 keV 276 keV Andreas Oberstedt Reac6on: 79Br(n,n’3)
81Br(n,n’1)
Rela6ve intensity: 28.9 % 71.1 % 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 22 Experiment on
252Cf(SF)
Closer inspec6on of γ-­‐spectrum reveals: 81Br(n,n’1) (40%) Analysis procedure: 1.  interval (279, 297) keV -­‐> tof spectrum 81Br -­‐> cross sec6on 81Br Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 23 Experiment on
252Cf(SF)
Closer inspec6on of γ-­‐spectrum reveals: Analysis procedure: 1.  interval (279, 297) keV -­‐> tof spectrum 81Br -­‐> cross sec6on 81Br 2.  interval (244, 297) keV -­‐> tof-­‐spectrum all Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 24 Experiment on
252Cf(SF)
Time-­‐of-­‐flight distribu6ons (neutron region) Analysis procedure: 1.  interval (279, 297) keV -­‐> tof spectrum 81Br -­‐> cross sec6on 81Br 2.  interval (244, 297) keV -­‐> tof-­‐spectrum all 3.  tof-­‐spectrum all – tof-­‐spectrum 81Br -­‐> tof spectrum 79Br -­‐> cross sec6on 79Br Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 25 Experiment on
252Cf(SF)
From 6me-­‐of-­‐flight spectrum to cross sec6on: R = N ⋅σ ⋅ I
Reac6on rate: with N = number of atoms (known) I = neutron current (known) σ = reac6on cross sec6on Detec6on rate: Rdet = ε γ ⋅ R (measured) with ε γ = 0.45, efficiency averaged over detector volume (simulated) from ε γ = 0.74 for 276 keV (measured) Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 26 Experiment on
252Cf(SF)
Measured excita6on func6on (rebinned) … together with evaluated data libraries JENDL-­‐4.0, ENDF/B-­‐VII.0 and JEFF-­‐3.1.1 Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 27 Experiment on
252Cf(SF)
Measured excita6on func6on (rebinned) … together with evaluated data libraries JENDL-­‐4.0, ENDF/B-­‐VII.0 and JEFF-­‐3.1.1 Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 28 Experiment on
252Cf(SF)
Comparison with results in evaluated data libraries: -­‐> difficult to judge, which library describes best obtained experimental data However, JENDL-­‐4.0 reproduces experimentally observed rela6ve intensi6es. experiment JEFF-­‐3.1.1
JENDL-­‐4.0 Rela6ve intensity: 81Br(n,n’1)
71.1 % 62.3 69.3 79Br(n,n’3)
28.9 % 37.7 30.7 Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 29 Experiment on
252Cf(SF)
Third example: neutron spectra measurements Determina6on of neutron detec6on efficiency: ε n = Rdet / Rhit
Andreas Oberstedt with
and
Rdet
= detec6on rate from 6me-­‐of-­‐flight spectrum (measured) R hit = hit rate from ac6vity (known), geometry (known) and neutron spectrum (known: Mannhart evalua6on) 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 30 Experiment on
252Cf(SF)
Rate of both detected neutrons and neutrons hiung detector (logarithmic scale) Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 31 Experiment on
252Cf(SF)
Result: Experimental neutron efficiency + fit + error band -­‐> to be applied to data from another experiment! Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 32 Experiment on
235U(n
th,f)
Experiment at 10 MW research reactor of KFKI Budapest – same setup as before! γ-­‐detectors: 1 x LaBr3 (2”x 2”), 2 x LaCl3 (1,5”x 1,5”), 1 x LaCl3 (3”x 3”) sample holder cold neutron beam Andreas Oberstedt fission fragment spectrometer VERDI 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 33 Experiment on
235U(n
th,f)
E ≈ 276 keV"
-> neutron spectrum"
However, several problems were encountered with LaBr3:Ce detector: •  PH dependence of TAC signal (corrected for) •  not properly working dynode output (PH) •  loss of events Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 34 Experiment on
235U(n
th,f)
Here: experimental threshold at Eγ ≈ 266 keV •  only ≈ 74 % of en6re area covered •  corrected for •  otherwise: analysis as before -­‐-­‐> neutron spectrum extracted Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 35 Experiment on
235U(n
th,f)
“fission neutron spectrum” Boltzmann distribu6on fiZed to data (cf. literature: T = 1.29 MeV). However, due to problems with low energy background assessment and poor sta6s6cs: only illustra6on! Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 36 Summary
Demonstra6on of neutron measurements with a LaBr3:Ce scin6lla6on detector, based on γ-­‐ray 6me-­‐of-­‐flight distribu6ons Three applica6ons: Input Output 1.  Cross sec6on + neutron spectrum 2.  Neutron spectrum + geometry 3.  Geometry + cross sec6on -­‐> Geometry -­‐> Cross sec6on -­‐> Neutron spectrum Part of this work has recently been accepted for publication: A. Oberstedt et al., NIM A!
Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 37 Conclusions
1. Cross sec6on + neutron spectrum -­‐> “tomography” + informa6on about spa6al density distribu6on for a par6cular isotope (here: 56Fe) + gave understanding of 6me-­‐of-­‐flight distribu6ons -­‐ only one-­‐dimensional (radial) informa6on -­‐ “difficult” neutron spectrum (con6nuous) Possible improvements: Ÿ more detectors at different angles with simultaneous informa6on Ÿ mono-­‐energe6c neutron spectrum Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 38 Outlook
Currently not planned to be pursued! Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 39 Conclusions
2. Neutron spectrum + geometry -­‐> cross sec6ons + informa6on about excita6on func6ons for neutron induced reac6ons (here: inelas6c neutron scaZering off 79,81Br) + determina6on of neutron detec6on efficiency + possible to apply other materials to detector -­‐ challenging to assess background -­‐ probable distor6on of neutron spectrum (VERDI) Possible improvements: Ÿ measurements in environment with much less scaZering Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 40 Outlook
Low mass 252Cf source with integrated ioniza6on chamber Coincidence measurements performed at IRMM during spring 2012 •  problems with high frequency noise affec6ng data acquisi6on •  TOF spectra corrupt •  will be repeated! !
Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 41 Conclusions
3. Geometry + cross sec6on -­‐> neutron spectrum + cross sec6on relates to efficiency + low threshold depending on choice of γ-­‐energy (here: 280 keV) in comparison with standard neutron detectors (ca. 500 – 1000 keV) -­‐ low efficiency (ca. 2 – 3%) due to detector volume Possible improvements: Ÿ larger detector volume Ÿ other choice of excita6on or reac6on to enhance sensi6ve energy range and efficiency Ÿ addi6on of material with higher cross sec6on Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 42 Outlook
Extension to be filled with different materials, e.g. B4C employing the reac6on 10B + n → [11B*] → 4He + 7Li + 478 keV γ-­‐rays (94%) th
Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 43 Outlook
Extension to be filled with different materials, e.g. B4C employing the reac6on 10B + n → [11B*] → 4He + 7Li + 478 keV γ-­‐rays (94%) th
Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 44 Outlook
Limit for (n,n’) … …, but not for neutron capture: here E = 478 keV! Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 45 The collaborators
R. Billnert, A. Oberstedt, S. Oberstedt
with support by
T. Belgya, T. Bryś, C. Chaves, Th. Gamboni, W. Geerts, A. Göök, Z. Kis,
T. Martinez-Perez, L. Szentmiklosi, K. Takács, M. Vidali
This work was supported by
the ERINDA programme (agreement number 269499) and
the EFNUDAT programme (agreement number 31027)
of the European Commission
Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 46 Thank you! Andreas Oberstedt 2nd ERINDA Progress Mee6ng, Jyväskylä (Finland), January 8-­‐11, 2013 47