PPT - IAEA Nuclear Data Services

Report
TAGS Measurements by Valencia-Surrey Group
and More
Jose L. Tain
Instituto de Fisica Corpuscular (IFIC), CSIC-U. Valencia
 Results from 2009 TAGS measurements at JYFL
• S. Rice PhD Thesis (U. Surrey)
• E. Valencia PhD Thesis (U. Valencia)
 Summary of June 2014 Valencia TAGS Workshop
Consultants’ Meeting on Total Absorption Gamma-ray Spectroscopy for Decay
Heat Calculations and Other Applications
J.L. Tain
December 15-17 (2014) IAEA Vienna
Experiment: November 2009
JYFL Accelerator Laboratory
IGISOL separator +
ion guide source:
refractory elements
JYFLTRAP
Penning trap:
isotopic purification
“Rocinante” TAS
First measurement with the
new spectrometer!
• Compact 12-fold segmented
BaF2 spectrometer
• Low neutron sensitivity
• Cascade multiplicity information
Total Absorption Gamma-ray Spectroscopy
Measurements of Fission Fragments 86Br, 91Rb & 94Sr
• Reactor Decay Heat
• Reactor Anti-neutrino spectrum
• Comparison with Greenwood et al.
Isotope
T1/2 (s)
Qb (MeV)
Key
86Br
55.1(4)
7.632(4)
91Rb
58.4(4)
5.907(9)
94Sr
75.3(5)
3.508(8)
PR1(DH)
Rud90
norm.
Contam.
S. Rice, PhD Thesis
Univ. Surrey
86Br
Experiment versus
reconstructed
spectrum
Accumulated beta
intensity distribution
91Rb
Experiment versus
reconstructed
spectrum
Accumulated beta
intensity distribution
Comparison average gamma and beta energies
Total Absorption -Ray Spectroscopy of b-delayed neutron emitters
n

Isotope
bn
(n,)
b
Pn (%)
Sn (MeV) Qb (MeV)
87Br
(*)
2.43(14)
5.515(3)
6.818(3)
88Br
(*)
6.75(18)
7.053(3)
8.975(4)
94Rb
10.24(21) 6.828(10) 10.281(8)
(*) Priority 1 (DH)
E. Valencia, PhD Thesis
Univ. Valencia
Astrophysics: The r-process
Neutron
capture
processes
R-process: A short and very high
neutron flux produces very neutronrich nuclei in a short time, which then
decay to stability.
A-1Z+1 AZ+1
bn decay
b -decay
AZ
A+1Z
(n,)
classic/hotPr-process
n (%)
• The b-decay half-life determines
(n,)-(,n) equilibrum
& instantaneous
freeze-out
r-process
path From R. Surmann
the speed of the process and
shapes the abundance distribution
• The delayed neutron emission
probability modifies the abundance
distribution
• In the (classical) equilibrium flow
picture (n,) cross section plays no
role
Importance of (n,) in r-process nucleosynthesis beyond iron
hot r-process during freeze-out
b-decay/(n,)
competition
Core collapse supernova
cold r-process
b-decay-(n,)
equilibrium
Neutron star merger
• … but they need to be
considered under nonequilibrium conditions:
for cold r-process, and
during freeze-out
Arcones et al., PRC83-045809
• …and affect the final abundances
• However this cross sections are not measurable: usually they
are taken from Hauser-Feshbach statistical model calculations
• Parameters for the statistical calculations are obtained from
data close to stability
• How can we constrain HF estimations for very neuron-rich
nuclei?
There is an analogy between (n,) and bn
Beta delayed neutron emission:
Radiative neutron capture:
n
A-1Z
b
n
AZ-1
En
Sn
A-1Z
Sn


AZ
Gg G n
4p
s g ( E ) = 2 gJ
F(E)
k
Gg + G n
AZ
I bg ( Ex ) =
Gg
Gg + G n
T1/2 f (Qb - Ex ) Sb ( Ex )
• Can we actually observe the -emission from states above Sn
populated in b-decay: Gn >>G !?
• Only few -rays in a handful of isotopes have been observed in
HPGe spectroscopy: 87Br, 137I, 93Rb, 85As, …
Reconstruction of TAS b-gated spectra after deconvolution
87Br
reconstructed
spectrum
Sn
pile-up
94Sr
94Rb
b-gated
Qb
n-interactions
+ 93Sr
Reconstructed spectrum: from bintensity obtained in the deconvolution
88Br
Contaminants:
Daughter: Measurement or Geant4
simulation. Normalization: Bateman or best
fit.
bDN: Geant4 simulation using realistic
event generator + ENDF/B.VII.0 + capture
cascade generator. Normalization: Pn value
Summing-pileup: real event based MC
simulation including ADC behaviour.
Normalization: counting rate + ADC gate
length
Comparison of high resolution (ENSDF) with TAS b-intensity
87Br
94Rb
ENSDF
TAS
88Br
• In all three cases TAS reveals
considerable Pandemonium
effect
Isotope
<E>
ENSDF
<E>
TAS
87Br
3057 keV
3945 keV
88Br
2861 keV
4591 keV
94Rb
1729 keV
4060 keV
• Impact on reactor decay heat and anti-neutrino spectrum
summation calculations
Comparison of high resolution (ENSDF) with TAS
accumulated b-intensity
87Br
94Rb
88Br
TAS
ENSDF
Intensity above Sn:
(%)
87
Br
88
Br
94
Rb
Ibn: deconvolution of n-spectra (ENDF/B-VII.1)
SIbn=Pn SIb (TAS) ENSDF
0.6%
2.43(14) 3.5(3)
6.75(18) 1.6(2)
10.24(21) 0.53(15)
Can we understand the ratio
between Ib and Ibn from
Hauser-Feshbach model?
Comparison of experimental G/(G+Gn) with Hauser-Feshbach calculations
How good are the statistical
model parameters used?
For 87Kr there is neutron
reaction data (Jp=1/2-,3/2-):
NLD is ~correct
Gn is ~4 times too low
G is ~3 too low
Error band: 15% changes in pileup subtraction
Conclusions:
• Analysis of of 86,87,88Br, 91,94Rb has been completed
• Significant, large, very large Pandemonium effect
• Impact on reactor DH and ne spectrum should be calculated
• New application of TAGS technique has been demonstrated
• Impact on (n,) cross section estimation for very unstable
nuclei
• Impact on Pn theoretical calculations
Collaboration:
IFIC-Valencia: J. Agramunt, A. Algora, E. Estevez, D. Jordan, A. Perez,
B. Rubio, J.L. Tain, E. Valencia
U. Surrey: W. Gelletly, Z. Podolyak, P. Regan, S. Rice
Subatech-Nantes: M. Fallot, Z. Issoufou, A. Porta
JYFL-Jyvaskyla: J. Aysto, V. Eloma, T. Eronen, A. Jokinen, A. Kankainen
I. Moore, H. Penttila, S. Rinta-Antila, J. Riisanen,…
CIEMAT-Madrid: D. Cano-Ott, T. Martinez
BNL-Brookhaven: A. Sonzogni
IPN-StPetersburg: L. Batist
http://indico.ific.uv.es/indico/conferenceDisplay.py?confId=2149
• 27 participants
• Review status of 1) current efforts, 2) up-coming
measurements, and 3) plan for future proposals
• 20 presentations: facilities and instruments, physics
cases: nuclear structure, astrophysics, nuclear technology
• Facilities: IGISOL-JYFL, ISOLDE, ALTO-IPN, BigRIBSRIKEN, DESIR-SPIRAL2, SFRS-FAIR, SPES-LNL
• Theoretical input
• New ideas
• Proposals, LoIs, …
Available Instruments
LUCRECIA:
• NaI(Tl) single crystal
• Permanent @ ISOLDE
• ep=48% @ E=5MeV
• [email protected]=0.66MeV
• Moderate neutron
sensitivity
Jose L. Tain
Rocinante:
• BaF2 12 crystal
• Compact
• ep=40% @ E=5MeV
• [email protected]=0.66MeV
• Low neutron sensitivity
• Good timing Dt=1ns
• -Multiplicity
DTAS:
• NaI(Tl) 18 crystal
• Movable
• ep=48% @ E=5MeV
• [email protected]=0.66MeV
• Moderate neutron
sensitivity
• -Multiplicity
TAS Workshop, June 26-28, 2014, Valencia
BACKUP SLIDES
TAGS analysis Valencia method in a nutshell
1) Reduce the analysis to a
linear inverse problem
taking the b.r. as parameters:
di = å Rij ( b) × f j
3) Construct the spectrometer
response using MC
simulations: need to make
careful calibrations
j-1
rj = å b jkg jk Ä rk
j
2) Make a reasonable choice
of b.r. matrix: we use the
nuclear statistical model
plus known level-scheme
k=0
R j = b j Ä rj
4) Apply any suitable
(deconvolution) algorithm:
we use the EM method
5) Study the effect of different
b.r assumptions: systematic
errors
NIM: A430(1999)p333, A571(2007)p728, A571(2007)p719
94Rb
Assumed discrete level scheme in the final nucleus:
3(-)
7/2+
From ENSDF,
levels actually seen
in bn decay
7/2+
7/2+
88Br
(2-)
87Br
7/2+
3/2-
86Kr
87Kr
93Sr
7/2+
b-gated spectra: the issue of
beta efficiency shape
The help of BELEN bDN
measurements:
bintensity
above Sn
Effect on deconvolution:
befficiency
bspectra
How accurate is Geant4 MC prediction of neutron contamination?
Experimental verification: Neutron sensitivity of LaBr3
Tain et al. NIMA774 (2015) 17
PTB Braunschweig
Mono-energetic n-beams:
7Li(p,n)/3H(p,n) + ToF
• Geant4 with the right data bases and
supplemented with a realistic capture
cascade generator is able to reproduce
neutron response of inorganic
scintillators
• Should be verified for every scintillator!
1.5”1.5” crystal
Multiplicity information to
verify/improve the b.r.
matrix used in the analysis
94Rb
M>0
M=1
M=3
M=2
M=4
Lucrecia @ ISOLDE
Valencia-Surrey-Strasbourg-Madrid
Large NaI(Tl) monocrystal
Æ38cm ´38cm
•
•
•
•
Permanent installation at ISOLDE
Good efficiency (ep=48% @ E=5MeV )*
Good energy resolution (7% @ E=662keV)
Moderate neutron sensitivity
* With tape transport system, plastic detector and HPGe telescope
Rocinante (vTAS)
Valencia-Surrey
12-fold segmented
compact BaF2 TAS
25cm
25cm
5cm
•
•
•
•
•
•
•
Easy transport and installation (used at JYFL and ATOMKI)
Quite good efficiency (ep=40% @ E=5MeV )*
Moderate energy resolution (15% @ E=662keV)
Very good timing resolution (~1ns)
Low neutron sensitivity
Large intrinsic a-background
Multiplicity information (for improved analysis)
* With tape transport system and Si detector
DTAS
Valencia et al. (DESPEC TAS Collab.)
•
•
•
•
•
•
16/18 NaI(Tl) modules:
15x15x25cm3
Designed for FAIR, transportable
Good efficiency (ep=48% @ E=5MeV )*
Good energy resolution (8% @ E=662keV)
Poor timing resolution (~10ns)
Moderate neutron sensitivity
Multiplicity information (for improved analysis)
* DTAS18 with tape transport system, plastic detector and HPGe detector

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