chadwickcenbg

Americium Cross Sections & Progress on ENDF/B-VII: 

Americium Cross Sections & Progress on ENDF/B-VII Mark Chadwick Group Leader, X-1 Collaborators: Kawano, Talou, MacFarlane, Young, Little, Vieira, Ullmann, Haight, MacInnes, etc. Overview: Nuclear data evaluations and reaction calculations Nuclear fission theory Measurement program New ENDF/B-VII database

Slide3: 

241Am(n,2n) and Neutron Capture on 241Am 240Am/241Am Is analogous to 238Pu/239Pu)obs - 238Pu/239Pu)in but with no ingoing correction - Sensitive to high-energy neutrons T240 = 6.7 MeV T238 = 5.7 MeV U N C L A S S I F I E D U N C L A S S I F I E D

Slide4: 

U N C L A S S I F I E D U N C L A S S I F I E D Experimental Overview A set of measurements to understand 240Am/241Am ratio 1. Measurement of (n,2n) cross section, especially near threshold - these measurements are in progress at TUNL (Duke Univ.) (supported by NA-22 & NNSA Stewardship Academic Alliance - not LDRD) 2. 240Am(n,fission) experiment is planned - target to be made at Berkeley & flown to LSDS/LANSCE (NA-22 & NNSA Stewardship Academic Alliance program / not LDRD) Measurements that bear on understanding 242Cm/241Am ratio 1. 241Am(n,g) on DANCE (LDRD supported) 2. 242mAm(n,g) on DANCE (LDRD supported) - a LLNL lead measurement 3. 241Am(n,g) to 242mAm or 242gAm isomer ratio measurement - planned activation measurement – target to be made at LANL, irradiated at Karlsruhe, Cm-Am radchem & counting at LANL (supported by NA-22) Measurements on 243Am to understand 244Cm/243Am ratio 1. 243Am(n,g) on DANCE (LDRD supported)

Slide5: 

U N C L A S S I F I E D U N C L A S S I F I E D Experiments: Surrogate Measurements 240Am fission. 241Am capture? DANCE can measure directly below a few hundred keV We have integral critical assembly data (new 1 MeV) Could a surrogate measurement be done in the 0,5- 1 MeV range? Bordeaux has done such measurements. LANL had a surrogate program in the 1970s (Wilhelmy, Gavron, Britt etc) LLNL has an ongoing effort with Berkely & Yale (Bernstein et al.)

Overall Cross Section Evaluation Perspective: 

Overall Cross Section Evaluation Perspective New and Upgraded Evaluations of Nuclear Data We await new experimental data of: LANSCE/DANCE 241Am(n,g) FZK meta/ground-state production ratio for capture reaction TUNL 241Am(n,2n) Future 242mAm(n,g) measurements at DANCE if available More theoretical work (& exp?) for prediction of 240Am+n reactions We have issued new evaluations of 241Am, 242gAm, 242mAm, 243Am These new valuations were included in ENDF/B-VII complete ENDF-formatted evaluations (cross sections, spectra, angular distributions), for both production-depletion and transport Significant improvements in predictions of several important physical properties for nuclear systems. Open Issues for Future

Slide7: 

Los Alamos Nuclear Modeling Physics Codes GNASH code is our LANL capability for modeling nuclear reactions on medium and heavy nuclei - Used worldwide in nuclear physics and nuclear data community - Includes Hauser-Feshbach, Preequilibrium, Direct, and Fission nuclear reaction mechanisms - Our “workhorse” for creating ENDF cross section data files - Evaluated data use GNASH calculations & experimental data - McGNASH is our modern version of GNASH NJOY is our code for processing ENDF files for use by application transport codes. International standard. MCNP is used for radiation transport simulations of critical assemblies, for our integral data testing & validation. International standard code.

Study on Nuclear Reaction Mechanisms for Americium: 

Study on Nuclear Reaction Mechanisms for Americium New GNASH calculation resulted in a higher cross sections around 14 MeV than the previous evaluation in 2005. Evaluated 241Am(n,2n) Cross Section Direct reactions ECIS code (from CEA) Compound reactions GNASH/McGNASH Hauser-Feshbach model code Theory on Level density Width fluctuation Fission decay (Fission Barriers) Pre-equilibrium reactions Quantum FKK theory Classical exciton model Semi-classical Monte Carlo model

History of Upgrades to 241Am (n,2n). Work in progress!: 

History of Upgrades to 241Am (n,2n). Work in progress! Evaluated 241Am(n,2n) Cross Section 1991. Old ENDF/B-VI. - Too low at 14 MeV; Threshold low 2004. Initial fix of 14 MeV region - Used in calcs by Gorman, Kao - 14 MeV low by 6%; threshold low 2005, ENDF/B-VII beta 1 - Threshold region “accurate” - 14 MeV still low by 6% - Used in attribution studies & at LLNL 2006. ENDF/B-VII beta 2 14MeV region increased by ~ 6% (Gancarz LANL data found) Threshold region “accurate”

Uncertainty Quantification for QMU: Combining Experimental and Theoretical Information: 

Uncertainty Quantification for QMU: Combining Experimental and Theoretical Information (n,2n) Cross Section, and Error Band GNASH + KALMAN Calculation Model input parameters in the GNASH calculations are optimized by using a Bayesian statistical technique. The calculated (n,2n) cross sections are consistent with the LLNL & LANL experimental data. The KALMAN calculation gives an error band for the final evaluation, based on experimental uncertainties and theory uncertainties KALMAN calculation predicts that the uncertainties in the (n,2n) cross sections are about 25% near 9 MeV, and 2% near 14 MeV. We are continuing our UQ studies here to assess role of error correlations, which will impact our final n2n uncertainty

241Am Neutron Capture Cross Section: 

241Am neutron capture cross sections were significantly improved by including updated experimental information. Capture cross section measurement as a ratio to gold, by Wisshak et al. 241Am Neutron Capture Cross Section Our higher value of isomeric ratio for 241Am(n,g) were also supported by the actinide burn-up calculations for fast reactor cores.

Slide12: 

U N C L A S S I F I E D U N C L A S S I F I E D 242mAm / 242gAm Isomer Ratio Experiment Isomer ratio is not well known calculations predict sg / stot to fall off at ~1 MeV (T. Kawano et al.) An activation experiments is planned using the quasi-monoenergetic neutron source at Karlsruhe 1. 7Li(p,n) source – 109 n/cm-s tunable from 25 g 500+ keV (monitor via Au activation) irradiate several 10 mg 241Am targets 2. convert 241Am g 242Am at ~10-10 atom ratio/day gs decays to 242Cm w/ 16 hour half-life 3. radiochemically extract Cm from Am (a significant challenge!) & a count 242Cm 4. let Cm grow in from 242mAm decay for 6 months (~10-3 fraction) and repeat step 3 D.C. Hoffman et al., UCB/LBNL funded SAA proposal

Slide13: 

241Am(n,g) capture: Validation tests suggest Calculated predictions should be higher near 1 MeV Fundamental measurements and calcs Jezebel expt calc,using MCNP Integral (single-effect) validation test Hardness of neutron spectrum LANSCE experiments using new DANCE detector will measure this cross section precisely 241Am(n,g) (barns) Energy (MeV) Jezebel DANCE Integral 241Am(n,g)

Slide14: 

U N C L A S S I F I E D U N C L A S S I F I E D 2005 DANCE data on 241Am and 243Am JENDL-3.3 100 mg / 5 days 14 ms + 2 ms segmented + continuous mode data 60 mg / 5 days Preliminary analysis Preliminary analysis

Slide15: 

U N C L A S S I F I E D U N C L A S S I F I E D Development of Fission Tagging Detector for DANCE Destruction of 242mAm (and 242gAm) by (n,f) effects the 242Cm/241Am ratio (n,g) and (n,f) processes compete for fissioning actinides Both emit g-rays and are only partially resolved in DANCE data A 4p fission-tagging detector that surrounds the target was developed to resolve this problem This leads to improved (n,g) data as well as capture-to-fission (a = sg/sf) measurements Also <Eg> and <Mg> distributions can be obtained for fission events LLNL (& Mac Fowler) leading effort

Slide16: 

U N C L A S S I F I E D U N C L A S S I F I E D PPAC Detector for Capture and sg/sf Measurements A double Parallel Plate Avalanche Counter (PPAC) was fabricated & tested (operated at 6 torr of isobutane @ 200 V) & Target ½ “ 1 5/8” Tested with 252Cf and 235U data collected in 2005 - detector worked well - analysis in progress There was a problem in preparing the 242mAm target at LLNL last year; they have regrouping and are planning to make the target this year Other planned PPAC runs include 239,241Pu, 233U, & several threshold-fissioning actinides

Slide17: 

Planned 242mAm PPAC Run – LLNL Lead Experiment 242mAm capture cross section is essential unmeasured in the 0.1 – 100 keV region LLNL has 98% enriched (double mass separated) 242mAm sample (2 mg=20 mCi) LLNL radiochemists (Stoyer, Moody & Wilk) will prepare electroplated DANCE targets to run with the PPAC in 2006 U N C L A S S I F I E D U N C L A S S I F I E D

242m Am data: 

242m Am data

243Am data: 

243Am data

Fission Theory: Moller et al.: 

Fission Theory: Moller et al.

Fission Modes and Associated Nuclear Shapes: 

Fission Modes and Associated Nuclear Shapes

Theory is needed to predict n+240Am fission (unmeasured). Insights into 243Am (n+242Am) and 241Am (n+240Am) properties: 

Theory is needed to predict n+240Am fission (unmeasured). Insights into 243Am (n+242Am) and 241Am (n+240Am) properties No measured data for 241Am system, but there are data for 243Am system. Goal: use theory to provide us with insights into the relative difference in 241 and 243, so as to infer 241 from measured 243 data. First Barrier (MeV) Second Barrier (MeV) 241Am 6.59 4.76 243Am 6.73 5.24 Exp data here No exp data

New Results for Actinide Barrier Parameters: 

New Results for Actinide Barrier Parameters Axial asymmetry may reduce the calculated heights here. (Fragments are axially asymmetric in shape). Exp. data are not direct, but inferred. 241Am CN data from LANL transfer surrogate experiments (Wilhelmy, Britt, Gavron, et al.)

240Am: Eric Lynn theory predictions: 

240Am: Eric Lynn theory predictions

Slide25: 

Future: Include in second barrier peak region to account for shapes of emerging fragments. We have included axial asymmetry in the ground-state to first peak region. Is important both in gs and first barrier peak. Axial Asymmetry in Fission Calculations

Slide26: 

U N C L A S S I F I E D U N C L A S S I F I E D 240Am(n,fission) Experiment Just like 242mAm, 240Am is expected to have a large fission cross section - this is an important destruction channel that strongly effects the 240Am/241Am ratio - a measurement is needed We are planning a measurement using the recently commissioned lead slowing-down spectrometer at LANSCE LSDS is capable of measuring fission cross section with ~10 ng samples 240Am target to be produced at 88” at LBNL via 242Pu(p,3n) or 237Np(a,n) ~10 ng / day production rate Radiochemically extract Am from target (a challenge!); electroplate onto Be; ship to Los Alamos Measure fission rate (~103 f/day @ 10 keV) in LSDS over several days (t1/2 = 2.1 d) normalize to 239Pu or 235U fission D.C. Hoffman et al., UCB/LBNL funded SAA project LSDS in the Blue Room / WNR

Slide27: 

Future Work Needed Refine fission modeling, including full axial asymmetry capability Utilize predicted 241Am and 243Am compound nucleus fission barriers in GNASH calculations, to predict n+240Am fission Finalize new n+240Am evaluation Incorporate DANCE n+ 241,242m,243Am capture & fission data Further validation against 241Am(n,g) critical assembly Use DANCE 242mAm(n,g) with GNASH theory to predict 242gAm(n,g) Update evaluations based on additional measurements (TUNL n2n, Karlsruhe m/g capture ratio, LANL/LBNL 240Am fission meas.), and other feedback on performance in integral experiments Finalize uncertainty information (including covariances)

Slide28: 

U N C L A S S I F I E D U N C L A S S I F I E D Large Collaborative Effort on Am Measurements Los Alamos C-INC: D.J. Vieira E. Bond T.A. Bredeweg M. Jandel R.S. Rundberg J.B. Wilhelmy LANSCE-NS: J.L. Ullmann R.C. Haight R. Reifarth J.M. O’Donnell Others: J. FitzPatrick (C-AAC) A. Slemmons (C-AAC) J.M. Wouters (IM-8) Livermore CMS: K.J. Moody M. Stoyer P.A. Wilk PAT: J.A. Becker R.A. Macri R. Clement (at LANL) C.Y. Wu Contract: M.M. Fowler Universities UC Berkeley/LBNL: D.C. Hoffman H. Nitsche R. Sudowe + students Duke: W. Turnow A. Tonchev + students Karlsruhe: F. Kaeppeler + students

Slide29: 

ENDF/B-VII Database for Nuclear Technology The ENDF/B Cross Section Database Serves Many Applications: Reactor design, advanced fuel cycles, waste transmutation Nonproliferation (eg detection of SNM) & National Security Nuclear medicine (simulations of external beam radiation therapy) Physics facility design, eg Spallation Neutron Source New ENDF/B-VII Database will be released in July 2006: Collaboration of over 60 people from US National Labs and universities New features: - New “standards” cross sections - Major improvements in actinide cross sections (fast & thermal) - Excellent performance in integral validation testing - Photonuclear data & improved delayed neutron and delayed gamma data (nonproliferation applications) - Fission product data much improved - Light nucleus evaluations for astrophysics

Modeling fission products: 

Modeling fission products 72 (out of 219) evaluations with EMPIRE (x-sec, photo-production, ang. distr., exclusive spectra, recoils) EMPIRE input = 95% of evaluation (RIPL-2 parameters adjusted to available experimental data) Nuclear Reaction Models: CC or DWBA (reaction x-sec, Tl's, scatt. to discrete levels) MSD(TUL)+MSC(NVWY) (inelastic to continuum) Exciton model (PE charge exchange reactions, photon emission) Iwamoto-Harada (PE cluster emission) HRTW (width fluctuations) Hauser-Feshbach (multiple CN decay)

Slide31: 

Latest modifications in going from Beta-1 to Beta-2 Upgraded s-alpha-betas (MacFarlane) 16O(n,alpha) reduced, based on new measurements 208Pb reevaluated… resulting in improved reflection Standards cross sections used in all databases FP further improved Am isotope upgrades included New decay data file Final issues to be resolved before final release: - 233U thermal nubar will be reduced to standards value - Adress any surprises coming from data testing

Data Testing with ICSBEP Benchmarks:Thermal HEU Solutions: 

Data Testing with ICSBEP Benchmarks: Thermal HEU Solutions Smaller assemblies Blue curve =beta1. We expect beta2 to be raised and have a flatter trend

Data Testing with ICSBEP Benchmarks:Thermal U-O2 Rods.: 

Data Testing with ICSBEP Benchmarks: Thermal U-O2 Rods. Closed circles = beta2 Closed squares =beta1 Open squares = 6.8 Russian expts French expts Japanese expts US expts

Data Testing with ICSBEP Benchmarks:Fast Metallic Systems.: 

Data Testing with ICSBEP Benchmarks: Fast Metallic Systems.

Data Testing with ICSBEP Benchmarks:Beryllium Reflectors on Fast Systems.: 

Data Testing with ICSBEP Benchmarks: Beryllium Reflectors on Fast Systems. Closed circles = beta2 Open squares = 6.8 Lines= eye guides. Reflector thickness bias is much reduced,

MCNP v TRIPOLI comparisons(MacFarlane/Kahler and Sublet): 

MCNP v TRIPOLI comparisons (MacFarlane/Kahler and Sublet) This LCT6 difference is not real, And will be repeated by Sublet