Neutron-induced reaction cross sections measured at. Triangle Universities Nuclear Laboratory. John Kelley

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1 Neutron-induced reaction cross sections measured at Triangle Universities Nuclear Laboratory John Kelley North Carolina State University and Triangle Universities Nuclear Laboratory Supported in part by the NNSA under the Stewardship Science Academic Alliances Program DOE grant #DE-PS52-05NA25930, and by DOE DE-FG02-97ER41033 (Duke) and DE-FG02-97ER41042 (NC-State).

2 Anton Tonchev Group Leader

3 Neutron Production DENIS Shielded Neutron Source Area Neutron production D(d,n) neutron source φ n = 3x10 4 n /(cm 2 sec) Tunable from 4 18 MeV Pulsed at 2.5 MHz

4 Neutron Collimator and Beam Profile Shielded Neutron Source Area Neutron profile scan d=215 cm d=427 cm d n 75 cm Scanning conditions step: 0.3 cm in and direction

5 NNSA Setup at TUNL 4 Clovers + BGO 2 Planars + BGO 10 kev < E γ < 10 MeV n-beam 20 0 < θ lab < ε array = 1.4%@E γ = 1.33 MeV Capabilities γ-γ coincidence measurements Angular distribution measurements Lifetimes (by Doppler method) Excellent tool for precision neutron induced cross section measurements in the fast energy region (4 E n 18 MeV)

6 Beam Correlated Measurements TUNL pulsed n-beam Start Stop n-beam ~2ns ON / 400ns Off Counts Fe U * Fe U Fe U * * * * * * * Fe * * U * G G-BG TOF TOF Fe TOF * Fe U * Fe Energy (kev)

7 Selected Experiments Time Reaction Energies n [MeV] [MeV] May U(n,2n ) 237 U 6, 10 Aug U(n,2n ) 237 U 8, 10, 14 Feb Zr(n,n' ) 90 Zr 6 Feb Yb(n,n' ) 89 Yb 6 Feb Sn(n,n' ) 112 Sn 6.5, 7.5, 8.0 Feb Sn(n,n' ) 124 Sn 6.5, 7.5, 8.0 May U(n,n' ) 235 U 5 Jun U(n,2n' ) 234 U 12 Jun 2005 nat Hf(n,xn' ) 12 Jun O(n,n' ) 16 O 7 Jun C(n,n' ) 12 C 7 Dec U(n,2n' ) 234 U 12 Time Reaction Energies n [MeV] [MeV] Jan U(n,2n' ) 234 U 10, 8 Jan Ta(n,2n' ) 180 Ta 14.5 Feb Ce(n,2n' ) 139 Ce 14.5 Mar Zr(n,n' ) 5.0 Mar Am(n,2n) 8-14 Jun 2006 nat Cu, nat Pb(n,n ) 8,12 Oct ,238 U(n, 2n ) 10 Nov Am(n,2n) 8-16 Dec Am(n,2n) 8-16 Dec U(n, 2ng) 12 Jan U(n,2ng) 8 Feb U(n,2ng) 10 Collaborators from 2 National Labs and 3 Universities

8 Participants

9 94 Zr(n,n γγ): Mixed symmetry States In early 2006 we collaborated with Steve Yates et al., from the University of Kentucky to carry out a study of mixed symmetry states in 94 Zr. In this experiment we utilized the high efficiency of our clover array, by measuring 94 Zr(n,n γ γ) two γ-ray coincidence data.

10 neutron-induced backgrounds for deep underground experiments Open questions that can be addressed in 2β2 decay studies : Are n Majorana particles? (self anti-particles) Is lepton number conserved? (Standard Model) Σ 2039 kev

11 neutron-induced backgrounds for deep underground experiments We are measuring partial cross sections for neutron-induced γ-ray transitions on Cu, Ge,, and Pb.

12 Precision Measurements of the (n,2nγ) Reaction Cross Sections on Actinides Goal: Improve partial cross section data of actinide nuclei for the Stockpile Stewardship Program Emphasis : The 239 Pu(n,2nγ) cross section Technique: High-resolution γ-ray spectroscopy measurements: in beam with pulsed and monoenergetic neutron beam off-line with DC neutron beam Modeling: Hauser-Feshbach theory (GNASH, EMPIRE)

13 Collaborators* 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 Livermore J.A. Becker D. Dashdorj * J. Kenneally R.A. Macri D. Shaughnessy M.A Stoyer Ch.Y. Wu Los Alamos E. Bond J. FitzPatrick R.S. Rundberg A. Slemmons D.J. Vieira J.B. Wilhelmy 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

14 Participants

15 First Results from 238 U(n,n γ) 238 Uat TUNL Partial Cross Sections at E n = 6 MeV Egamma Transition TUNL OakRidge 1) LANL 2) (kev) (mb) (mb) (mb) > (4) 76(7) 67(2) > (4) 80(7) 106(2) (1-) --> (4) 56(7) 79(2) > (3) 33(5) 40(2) > (3) 45(5) 65(2) (4) 93(11) 116(3) 1) D.K. Olsen, et al., ORNL report TM ) N. Fotiades et al., PRC 69 (2004) A. Hutcheson et al. NIMB (2007) in press.

16 Neutron Induced Cross Section on 235 U E n = 10 MeV, Beam time = 87 h 234 U

17 241 Am(n,2n) Reaction Cross Section Measurements Improved 241 Am(n,2n) cross sections are needed for: Nuclear forensics A( 240 Am/ 241 Am) Analogous to P ( 238 Pu/ 239 Pu) 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

18 241 Am(n,2n) 240 Am Measurements (n,2n) data for 241 Am around 14 MeV Energy dependence near 14 MeV No data below ~13 MeV Different evaluation

19 241 Am(n,2n) 240 Am Measurements (n,2n) data for 241 Am 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 E n 11MeV Phys. Rev. C 73, (2006) Need to extend the 241 Am(n,2n) 240 Am cross section to lower energies

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21 241 Am(n,2n) 240 Am Measurements Activation technique: γ count 240 Am activity after irradiation of 241 Am trick: attenuate the low-energy γ-rays (59.5 kev) coming from 241 Am target using 3 mm Pb Irradiated target with mono-energetic neutrons produced by D(d,n) reaction TUNL E n = MeV / φ n ~ n/cm 2 -s ~1 mg/cm Am target / 1 cm dia. sandwich targets on Pt backing Measure neutron fluence using a set of witness foils mounted before & after target 197 Au(n,2n) 196 Au (t 1/2 = 6.2 d), T= 8.1 MeV 27 Al(n,α) 24 Na (t 1/2 = 15 hr), T= 3.2 MeV 58 Ni(n,p) 58 Co (t 1/2 = 71 d), T= 0 MeV 58 Ni(n,2n) 57 Ni (t 1/2 = 36 hr), T= 12.4 MeV kev (4)% 73.2(10)% 240 Am 99.6(11)% 4 + ; ; Pu 0 + ; 0.0 kev 3 + ; , T 1/2 = 1.32 ns

22 Activation Measurements at TUNL DENIS Neutron TOF area Preparation room Activation parameters φ n = 1x10 8 n /(cm 2 sec) ~ 1mg 241 Am targets 3 monitor foils (Al, Ni, Au) n-flux monitoring: 3 neutron detectors (0 0, ± 10 0 ) Irradiation setup

23 Activation Measurements at TUNL Irradiate highly enriched 241 Am targets Low-background counting system 60% HPGe detectors Genie 2000 spec. system

24 High-Resolution Gamma Ray Spectra Plastic ring Foil 8 Foil 9 Plastic ring µg/cm Am 0.5 mil Pt 0.5 mil Pt 519 µg/cm Am Fabrication of 241 Am target (LANL and LLNL) 3 stippled targets (Evelyn Bond/LANL) 6 electroplated targets after additional chemical purification (Mark Stoyer/LLNL) ~ 2% statistical uncertainties Improved γ-spectra from the electroplated targets Need for nuclear radiochemists

25 First Results on 241 Am(n,2n) 240 Am Reaction Cross Section

26 First Results on 241 Am(n,2n) 240 Am Reaction Cross Section

27 First Results on 241 Am(n,2n) 240 Am Reaction Cross Section A. Tonchev et al. PRC in preparation.

28 Summary Intense, pulsed and quasi-monoenergetic neutron beams at TUNL provide capabilities for Nuclear Physics Research. Application motivated basic research 1. Ongoing analysis of 235,238 U(n,2nγ) (A. Hutcheson poster) 2. Cross section measurements of the 241 Am(n,2n) 240 Am reaction. Curiosity driven research 1. n-induced backgrounds in deep underground experiments 2. Nuclear Structure: 94Zr(n,n 2γ) Strong TUNL-LANL-LLNL Collaboration Effort

29 Extra Viewgraphs

30 Decay Scheme of Am Isotopes

31 240 Am Gamma-ray Signature kev line is partially contaminated by a weak 241 Am line, but the 988 kev line is clean - Measured γ events after a 1-2 day irradiation and 1day count time - Measured 11 energies in March, Nov., Dec runs

32 Neutron Monitors n-monitors / BCI n-flux fluctuation T act = 12.5 h

33 NNSA Synergistic Activities at TUNL NNSA (n,xnγ) 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

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