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Nuclear structure information fromcross section measurements
A. Negret, C. Borcea, A. Olacel
Horia Hulubei National Institute for Physics and Nuclear Engineering, Bucharest-Magurele, ROMANIA
ENSDF Workshop, IAEA, April 2015
A.J.M. Plompen
European Comission, Joint Research Center, Institute for Reference Materials and Measurements, Geel, BELGIUM
A. Negret – Nuclear structure information from cross section measurements
Summary
1. Neutron inelastic cross section measurements using GAINS at EC-JRC-IRMM
2. What can we learn?
3. Examples
4. Conclusions
ENSDF Workshop, IAEA, April 2015
Cross section measurements with GAINS
1. Neutron inelastic cross section measurements using GAINS at EC-JRC-IRMM
2. What can we learn?
3. Examples
4. Conclusions
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
GELINA (Geel Linear Accelerator):
the white neutron source
• Neutron source: GELINA (white flux 100 keV – 20 MeV), operated by EC-JRC-IRMM, Geel, Belgium
• TOF technique (200 m flight path):Amplitude gamma energyTime neutron energy
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
GAINS:
• Array of 12 HPGe detectors (e=100%) used for highly precise neutron inelastic cross section measurements.
Gamma Array for Inelastic Neutron Scattering
• Digitizer-based acquisition (Acqiris DC440, 420 MS/s, 12 bits)
• Beam monitoring: 235U Fission chamber
• TOF technique (200 m flight path):Amplitude gamma energyTime neutron energy
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
GAINS:
Basic Idea of data analysis
Amplitude gamma energy
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
Time neutron energy
GAINS:
The gamma spectroscopy used to determine X(n,n’g)X cross sections
12 x HPGE yield FC yield
HPGe Efficiency: Monte-Carlo simulation
FC Efficiency
Gamma Production cross sections
ENSDF: level scheme
Total inelastic cross sectionLevel cross sections
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
Experim. result: g production cross sections
(= excitation functions)
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
28Si(n,n’g)28Si
Experim. result: level cross sections,total inelastic cross section
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
28Si(n,n’g)28Si
What can we learn
1. Neutron inelastic cross section measurements using GAINS at EC-JRC-IRMM
2. What can we learn
3. Examples
4. Conclusions
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
What can we learn: assignment of gs to levels
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
28Si(n,n’g)28Si
What can we learn: branching ratios
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
28Si(n,n’g)28Si
If two gammas decay from the same level:
- Their gamma production cross section has the same shape
- The ratios of gamma production cross sections for each point is the branching ratio.
So we actually can determine the branching ratio for each neutron energy (about 2000 values).
Examples
1. Neutron inelastic cross section measurements using GAINS at EC-JRC-IRMM
2. What can we learn
3. Examples
4. Conclusions
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
The 3-, 3076.2 keV level in 56Fe
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
We did 56Fe(n,n’g)56Fe and were able to build level cross sections for all low lying levels…
Except this one:
The 3-, 3076.2 keV level in 56Fe
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
Eg=991 keV
Branching ratios in 206Pb
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
gs coming from the same level have similar shapes (and of course the same threshold). The proportionality factor is the branching ratio.In 206Pb(n,n’g)206Pb, for several levels, we saw more then one decaying g.
EL=1684.0 keV
EL=2196.7 keV
Branching ratios in 206Pb
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
In 206Pb(n,n’g)206Pb, for several levels, we saw more then one decaying g:
37.5(7)100
100
100
100
100
78.9(12)
58.4(19)24.6(18)
81.6(14)
100.3(25)
36.9(39)
The 2041-keV transition in 206Pb
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
• Possible source of neutron-induced background for neutrinoless double beta decay experiments [Qbb(76Ge)=2039.06 keV]
0
5
10
15
0 2 4 6 8 10 12 14 16(m
b)
E n (MeV)
2025303540
2 2.02 2.04 2.06 2.08 2.1
Coun
ts /
keV
E (MeV)
206 Pb(n,n’ )206 Pb; E = 2041 keV
Inte
grat
ion
Back
grou
nd
Back
grou
nd
Eth ≈ 3 MeV
Conclusions
1. Neutron inelastic cross section measurements using GAINS at EC-JRC-IRMM
2. What can we learn
3. Examples
4. Conclusions
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
Conclusions
A. Negret – Nuclear structure information from cross section measurements
ENSDF Workshop, IAEA, April 2015
• Neutron inelastic cross section data produced at GELINA could contain nuclear structure information valuable for ENSDF:
- level and gamma transition sequence
- branching ratio
• Other pieces of information like Eg values are actually ignored due to the fact that the primary purpose of this experimental effort is directed towards production of precise reaction.
