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Precision Measurements of the (n,2n ) Reaction Cross Sections on Actinides. Goal: Improve partial cross section data of actinide nuclei for the Stockpile Stewardship Program Emphasis : The 239 Pu(n,2n ) cross section - PowerPoint PPT Presentation
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Precision Measurements of the (n,2n) Reaction Cross Sections on Actinides
TUNL and Duke Univ.
Goal: Improve partial cross section data of actinide nuclei for
the Stockpile Stewardship Program
Emphasis : The 239Pu(n,2n) cross section
Technique: High-resolution -ray spectroscopy measurements:
in beam with pulsed and monoenergetic neutron beam
off-line with DC neutron beam
Modeling: Hauser-Feshbach theory (GNASH, EMPIRE)
TUNL and In-beam Measurements
TUNL and Duke Univ.
DENIS Shielded Neutron Source Area
D(d,n) neutron source
n = 3x104 n /(cm2 sec)
Tunable from 4 – 18 MeV
Pulsed at 2.5 MHz
Neutron production
Id =2A
7.8 atmbeam
pick-off
Deuterium gas cell
TUNL and In-beam Measurements
TUNL and Duke Univ.
DENIS Shielded Neutron Source Area
Neutron Collimator and Beam Profile
TUNL and Duke Univ.
Shielded Neutron Source Area
Scanning conditions
step: 0.3 cm in and direction
nd
75 cm
Neutron profile scan
d=215 cm d=427 cm
NNSA Setup at TUNL
TUNL and Duke Univ.
4 Clovers + BGO
2 Planars + BGO
10 keV < E < 10 MeV
200 < lab < 1600
array = 1.4%@E = 1.33 MeV
Excellent tool for precision neutron induced cross section measurements in the fast energy region (4 En 18 MeV)
- coincidence measurements
Angular distribution measurements
Lifetimes (by Doppler method)
Capabilities
n-beam
Neutron Induced Cross Section on 235U
TUNL and Duke Univ.
En = 10 MeV, Beam time = 87 h
234U
First Results from 238U(n,n)238U at TUNL
TUNL and Duke Univ.
Egamma Transition TUNL OakRidge1) LANL2)
(keV) (mb) (mb) (mb)
635.2 1- --> 2+ 83 (4) 76(7) 67(2)
687.0 3- --> 2+ 86 (4) 80(7) 106(2)
885.5 (1-) --> 2+ 63 (4) 56(7) 79(2)
905.5 2- --> 2+ 34 (3) 33(5) 40(2)
957.3 3+ --> 4+ 50 (3) 45(5) 65(2)
1060.3 2+ 0+ 95 (4)
A. Hutcheson et al. NIMB (2007) in press.
Partial Cross Sections at En = 6 MeV
93(11) 116(3)
1) D.K. Olsen, et al., ORNL report TM-6832 1979.
2) N. Fotiades et al., PRC 69 (2004) 024601.
Motivation for the 241Am(n,2n) Reaction Cross Section Measurements
TUNL and Duke Univ.
Improved 241Am(n,2n) cross sections are needed for:
Nuclear forensics ΔA(240Am/241Am) Analogous to P (238Pu/239Pu) Sensitive to high-energy neutrons Advance Fuel Cycle / new fast reactors Important in transmutation studies
Goal: 5-10% measurement from threshold (6.7 MeV) to 14.5 MeV
241Am(n,2n)240Am Measurements
TUNL and Duke Univ.
(n,2n) data for 241Am around
14 MeV
Energy dependence near 14 MeV
No data below ~13 MeV
Different evaluation
241Am(n,2n)240Am Measurements
TUNL and Duke Univ.
(n,2n) data for 241Am around
14 MeV
Energy dependence near 14 MeV
No data below ~13 MeV
Different evaluations
The recent data shows very high
(n,2n) CS at En 11MeV
Phys. Rev. C 73, 067601 (2006)
Need to extend the 241Am(n,2n)240Am cross section to lower energies
Activation Measurements at TUNL
TUNL and Duke Univ.
Irradiation setup
n = 1x108 n /(cm2 sec)
~ 1mg 241Am targets
3 monitor foils (Al, Ni, Au)
n-flux monitoring: 3 neutron detectors (00, 100)
Activation parameters
DENIS Neutron TOF area
Preparation room
Activation Measurements at TUNL
TUNL and Duke Univ.
Highly enriched 241Am
HPGe detectors
Genie 2000 spec. system
High Res. Gamma Spec.
Low-background counting system
DENIS Neutron TOF area
TUNL and Activation Measurements
TUNL and Duke Univ.
Irradiation setupLow-background counting system
DENIS Neutron TOF area
241Am(n,2n)240Am Measurements
TUNL and Duke Univ.
Activation technique: count 240Am activity after irradiation of 241Am
trick: attenuate the low-energy -rays (59.5 keV) coming from 241Am target using 3 mm Pb
Irradiated target with mono-energetic neutrons produced by D(d,n) reaction TUNL
En= 7.6 - 14.5 MeV / n ~ 107–108 n/cm2-s
~1 mg/cm2 241Am target / 1 cm dia. sandwich targets on Pt backing
Measure neutron fluence using a set of witness foils mounted before & after target
197Au(n,2n)196Au (t1/2 = 6.2 d), T= 8.1 MeV
27Al(n,)24Na (t1/2 = 15 hr), T= 3.2 MeV
58Ni(n,p)58Co (t1/2 = 71 d), T= 0 MeV
58Ni(n,2n)57Ni (t1/2 = 36 hr), T= 12.4 MeV
240Am
240Pu 0+; 0.0 keV2+; 42.94+; 141.8
3+; 1030.6, T1/2 = 1.32 ns
99.6(11)%
987.8 keV
888.8
25.1(4)%
73.2(10)%
High-Resolution Gamma Ray Spectra
TUNL and Duke Univ.
4
44
4
Plastic ring Foil 8 Foil 9 Plastic ring
0.5 mil Pt 0.5 mil Pt
519 g/cm2
241Am513 g/cm2
241Am
Fabrication of 241Am target (LANL and LLNL)
3 stippled targets (Evelyn Bond/LANL)
6 electroplated targets after additional
chemical purification (Mark Stoyer/LLNL)
~ 2% statistical uncertainties
Improved -spectra from the electroplated targets
Need for nuclear radiochemists
First Results on 241Am(n,2n)240Am Reaction Cross Section
TUNL and Duke Univ.
First Results on 241Am(n,2n)240Am Reaction Cross Section
TUNL and Duke Univ.
First Results on 241Am(n,2n)240Am Reaction Cross Section
TUNL and Duke Univ.A. Tonchev et al. PRC in preparation.
Summary
TUNL and Duke Univ.
Complete cross section measurements of the 241Am(n,2n)240Am reaction.
Preliminary data from TUNL support the recent statistical prediction from LANL (2005 Kawano) Intense, pulsed, monoenergetic TUNL neutron source provides
powerful capabilities for Science-Based Stockpile Stewardship and Nuclear Science.
More than 160 new parities measured in nuclei: 40Ar, 88Sr, 92Zr, 96Mo,112,124Sn, 138Ba, 140Ce, 172,174,176Yb, 164,162Dy, 207Pb.
Strong TUNL-LANL-LLNL Collaboration Effort
Participants*
TUNL and Duke Univ.
Los Alamos
E. BondJ. FitzPatrickR.S. RundbergA. SlemmonsD.J. VieiraJ.B. Wilhelmy
Livermore
J.A. BeckerD. Dashdorj*
J. KenneallyR.A. MacriD. ShaughnessyM.A StoyerCh.Y. Wu
TUNLke: Duke: A.S. Crowell B. Fallin C.R. Howell A. Hutchison A.P. Tonchev W. Tornow
Univ. of N. Carolina: H.J. Karwowski C.T. Angell N. Carolina State: J.H. Kelley D. Dashdorj*
NC A&T: R. S. Pedroni
*(n,2n) measurements supported by the NNSA Stewardship Science Academic Alliance and by DOE/NNSA LANL & LLNL
Participants
TUNL and Duke Univ.
Extra Viewgraphs
TUNL and Duke Univ.
240Am Gamma-ray Signature
TUNL and Duke Univ.
- 889 keV line is partially contaminated by a weak 241Am line, but the 988 keV line is clean
- Measured 2000-3000 events after a 1-2 day irradiation and 1day count time
- Measured 11 energies in March, Nov., Dec. 2006 runs
Total amount of used beam time: 120 days
Collaborators from 2 National Labs and 3 Universities
www.tunl.duke.edu/groups/nnsa
Completed Experiments
TUNL and Duke Univ.
Time Reaction Energies [MeV]
May 2003 238U(n,2n )237U 6, 10
Aug 2004 238U(n,2n )237U 8, 10, 14
Feb 2005 90Zr(n,n' )90Zr 6
Feb 2005 89Yb(n,n' )89Yb 6
Feb 2005 112Sn(n,n' )112Sn 6.5, 7.5, 8.0
Feb 2005 124Sn(n,n' )124Sn 6.5, 7.5, 8.0
May 2005 235U(n,n' )235U 5
Jun 2005 235U(n,2n' )234U 12
Jun 2005 natHf(n,xn' ) 12
Jun 2005 16O(n,n' )16O 7
Jun 2005 12C(n,n' )12C 7
Dec 2005 235U(n,2n' )234U 12
Time Reaction Energies [MeV]
Jan 2006 235U(n,2n' )234U 10, 8
Jan 2006 181Ta(n,2n' )180Ta 14.5
Feb 2006 140Ce(n,2n' )139Ce 14.5
Mar 2006 94Zr(n,n' ) 5.0
Mar 2006 241Am(n,2n) 8-14
Jun 2006 natCu, natPb(n,n‘ ) 8,12
Oct 2006 235,238U(n, 2n ) 10
Nov 2006 241Am(n,2n) 8-16
Dec 2006 241Am(n,2n) 8-16
Dec 2006 235U(n, 2ng) 12
Jan 2007 235U(n,2ng) 8
Feb 2007 235U(n,2ng) 10
Time Reaction En [MeV] Time Reaction En [MeV]
Neutron Monitors
TUNL and Duke Univ.
Tact = 12.5 h
n-flux fluctuationn-monitors / BCI
NRF Spectra on 138Ba
Primary transitions to the 2+ states
138Ba
En = 8.5 MeV
0+
2+
E2
2+
8434 keV
8074
1-
1-
TUNL and Duke Univ.
143622182639
E = 8.50.08 MeV
Branching ratio (1- 2+) 3% !
2+
Decay Scheme of Am Isotopes
TUNL and Duke Univ.
Absolute Flux Measurements at HIS
TUNL and Duke Univ.
Compton Scattered Setup Compton Scattered Spectra
NNSA Synergistic Activities at TUNL
TUNL and Duke Univ.
NNSA (n,xn) activity: low-energy introduction to nuclear experimental techniques for the Research Experience for
Undergraduates (REU) program at TUNL
Average 8-10 REU students every summer For the past three years one or two has been involved in the TUNL NNSA project Diversification of the NNSA setup for basic research:
nuclear structure nuclear astrophysics neutrino and dark matter
Synergistic activities at TUNL
Beam Correlated Measurements
TUNL and Duke Univ.
Start Stop
n-beam
TUNL pulsed n-beam
~2ns ON / 400ns Off
0
200
400
6000
600
1200
1800
800 900 1000 1100 1200 1300
200
400
600
200 400 600 800
200 400 600 800
200 400 600 800
Fe *U Fe
Fe
Fe
*
*
*
U
*
* ***
*
**
*UU FeFe
Fe
TOF
Energy (keV)
Co
un
ts
TOF
TOF
G-BG
G
U
Laser Compton Backscattering
UNDULATOR
E2
E1
TUNL and Duke Univ.
Laser Compton Backscattering
CAARI 2004
UNDULATOR
E2
E1
P
TUNL and Duke Univ.
Laser Compton Backscattering
CAARI 2004
UNDULATOR
E2
E1
P
TUNL and Duke Univ.
Laser Compton Backscattering
CAARI 2004
UNDULATOR
E1
P
E2
γ
TUNL and Duke Univ.
Laser Compton Backscattering
CAARI 2004
UNDULATOR
E2
E1
P
TUNL and Duke Univ.
TUNL and Duke Univ.