1. TUNL_Retreat_2011 A new opportunity to study the IVGQR in nuclei Studies in the 70s and 80s produced data on the energy, width and strength of this global feature of nuclei with large uncertainties. Advances in nuclear structure computational techniques make a new high accuracy investigation both interesting and timely. Some of the most robust and unambiguous results came from studies using Compton scattering where the IVGQR was observed via its interference with the GDR. The 100% polarized beams at HI  S along with a new technique and a world class detector system will allow for an order of magnitude improvement in the determination of the properties of the IVGQR of nuclei.

2. TUNL_Retreat_2011 Pb  IVGQR Studies 208 perpendicular to polarization plane parallel to polarization plane Unpolarized

3. TUNL_Retreat_2011 Our Measurement Technique The [Dal92] experiment only had beam polarization ~25% and only measured at a backward angle. Will see that simultaneous forward and backward measurements lead to unambiguous IVGQR parameters. Our recent experiment (PhD for Seth Henshaw) exploits the 100% polarization of the  S beam.

4. TUNL_Retreat_2011 Scattering Theory Assumptions: (GDR Dominates) Modified Thomson Amp included in C E1 E2 strength due to IVGQR

5. TUNL_Retreat_2011 Scattering Theory Assumptions: (GDR Dominates) Modified Thomson Amp included in E2 strength due to IVGQR

6. TUNL_Retreat_2011 Polarization Ratio

7. TUNL_Retreat_2011 HINDA Setup 209 Bi Scattering Target 2” Diameter x 1/8” thick 9*10 21 nuclei/cm 2 12mm collimated  S beam 3 x 10 7  ’s/sec  E/E=2.5 %  =  MeV 6 Detectors 3  @  60(55) (Left, Right,Down) 3@  =120(125) (Left, Right, Down)  msr

8. TUNL_Retreat_2011 Analysis Fit 12 C NRF spectra with G EANT 4 simulation to determine Response Function for monoenergetic  s Fit Data with Lineshape + Background Subtract Background Sum Resulting Data

9. TUNL_Retreat_2011 Results

10. TUNL_Retreat_2011 Results SR=0.6 +/- 0.04 IVQ-EWSRs E=23+/- 0.13 MeV  =3.9 +/- 0.7 MeV

11. TUNL_Retreat_2011 Results

12. TUNL_Retreat_2011 Results

13. TUNL_Retreat_2011 Results

14. TUNL_Retreat_2011 Results

15. TUNL_Retreat_2011 Proposal Perform similar measurements on 8 targets between A=60 and A=240 at HI  S. Use the full 8-detector HINDA array. Data as good or better than obtained for 209 Bi can be obtained in 40 - 100 hours per target (depending on Z). A ~500 hour program will produce accurate results (x10) for the energy, width and strength of the IVGQR in nuclei as a function of A. This will allow testing of model predictions of quantities such as the A- dependence of the energy, the splitting and/or fragmentation of the IVGQR, and the search for missing strength. Both collective models and no-core shell models can be applied and refined, and extended to exotic nuclei.

16. TUNL_Retreat_2011 A New Method for Identifying Special Nuclear Materials Based Upon Polarized ( ,n) Asymmetries A TUNL/HI S Project funded by the NSF/DNDO through their Academic Research Initiative program H. R. Weller—PI M. Ahmed and Y. Wu -- Co PIs Collaborators: N. Brown, S.S. Henshaw, H. J. Karwowski, J. M. Mueller, S. Stave, B. A. Perdue, J. R. Tompkins—TUNL B. Davis and D. Markoff—NCCU G. Feldman—GWU L. Myers—UIUC M. S. Johnson--LLNL A New Method for Identifying Special Nuclear Materials Based Upon Polarized ( ,n) Asymmetries A TUNL/HI S Project funded by the NSF/DNDO through their Academic Research Initiative program H. R. Weller—PI M. Ahmed and Y. Wu -- Co PIs Collaborators: N. Brown, S.S. Henshaw, H. J. Karwowski, J. M. Mueller, S. Stave, B. A. Perdue, J. R. Tompkins—TUNL B. Davis and D. Markoff—NCCU G. Feldman—GWU L. Myers—UIUC M. S. Johnson--LLNL

17. TUNL_Retreat_2011 Introduction Premise: Linearly polarized  rays having energies between threshold and 20 MeV can be a useful tool for the interrogation of materials Induce the emission of several MeV neutrons which can then be detected as a function of energy and emission angle relative to the plane of polarization In fissionable nuclei, energetic neutrons are produced even at energies effectively below ( ,n) threshold –

18. TUNL_Retreat_2011 Formalism where a 2 =A 2 /A 0,P 2 is the second Legendre polynomial Using Satchler ‘s expressions for linearly polarized  rays (Proc. Phys. Soc., 68A:1041, 1955), when both detectors are at 90 degrees: I par /I perp depends only on a 2 For unpolarized  -ray beams, the angular distribution of the outgoing neutrons assuming pure electric dipole absorption can be written as:

19. TUNL_Retreat_2011 Overview of a 2 From Baker and McNeill, Can. J. Phys., 39:1158, 1961 a 2 varies from -0.1 to -0.7 for Z between 23 (Vanadium) and 92 (Uranium) Leads to a range of I par /I perp from 1.0 to 8.0 I par /I perp has not been measured before this project began. These are the targets that were used in our intial measurements.

20. TUNL_Retreat_2011 Sensitivity when using 2-detectors I par /I perp -a 2 Linearly polarized beam increases sensitivity over unpolarized measurement

21. TUNL_Retreat_2011 Experiment Setup—Four detectors left, right, up and down at 90 o. BC-501A Liquid scintillators Target at  =45 ˚,  =45 ˚ to make the out-going path material length similar for all  =90 ˚ detectors  -ray beam direction into the screen Using 1” collimator Approximate flux: 1x10 7  /s 1 meter flightpath I par I perp

22. TUNL_Retreat_2011 238 U target: 15.5 MeV Linear pol. Peaking seen in- plane only

23. TUNL_Retreat_2011 Average from 5 MeV to max E n 238 U target: Linear pol. 238 U target: 15.5 MeV Linear pol. I par /I perp Peaking at 2.5 near max E n 1 at lower energies Uncertainties are from statistics and a detector efficiency correction

24. TUNL_Retreat_2011 Flight path is one meter. Up, down, left and right detectors at 55, 90 and 125 degrees.

25. TUNL_Retreat_2011 Preliminary results from the Feb. 22-28, 2010 run for 238 U

26. TUNL_Retreat_2011 New data were obtained on Pb, 235 U, and 238 U; results at 15.5 MeV are shown here and compared to results on other targets at 90 o.

27. TUNL_Retreat_2011 Neutron production below ( ,n) threshold Running at a  -ray energy of ~6.0 MeV and looking at neutrons above 2 MeV only produces counts for fissionable nuclei, except for d, Li and 9 Be. These can be identified by their unique spectra. This provides a very promising tool for interrogation and is receiving further study.

28. TUNL_Retreat_2011 238 U target: 6.2 MeV Circular pol. Same neutron yields both in- and out- of-plane, as expected

29. TUNL_Retreat_2011 238 U target: 6.2 MeV Linear Pol. Neutron yield enhancement is observed in both in- plane detectors

30. TUNL_Retreat_2011 Understanding the Ratio for 238 U First take the measured angular distribution of fission fragments as a function of E  for 238 U from Rabotnov [Yad. Fiz. 11, 508 (1970)] Using the formalism for linearly polarized  rays from Ratzek [Z. Phys. A 308, 63 (1982)] the angular distribution of fission fragments can be written as: where  is the CM polar angle and  is the CM azimuthal angle of the emitted fragment measured with respect to the plane of polarization; P  is the linear polarization of the  -ray beam

31. TUNL_Retreat_2011 Angular Distribution of Fragments E  (MeV)abcd 5.650.0340.9660.0401.380 5.950.0780.9220.0391.079 6.400.1270.8730.0341.032 a, b, and c terms from Rabotnov d term can be calculated using formalism given in Ratzek with the simplification that the low lying transition states can be represented by dipole plus the K=0 quadrupole terms [Huizenga and Vandenbosch, Nuclear Fission (1973)] Dominated by dipole transition but with a small quadrupole contribution

32. TUNL_Retreat_2011 Neutron energy distribution Then assume the neutrons are emitted isotropically in the center-of-mass frame of each fragment and have an energy distribution based upon an evaporation model from Fraser [Phys. Rev. 88, 536 (1952)] Neutron energy distribution

33. TUNL_Retreat_2011 Fission fragment mass distribution Distribution of fragment masses taken from neutron induced fission data for 235 U All the neutrons emitted from the fragments are boosted back into the lab frame Ratios are then formed at 90 degrees using simulated detectors both in and out of the plane of polarization 235 U fission fragment masses and relative yields from NNDC

34. TUNL_Retreat_2011 Simulation Results for 238 U Data and Simulation at 90 degrees Both trends as a function of incident  -ray energy and outgoing neutron energy are recreated by the simulation Simulation tends to under-predict at low and over- predict at higher  - ray energies Rabotnov data taken using a brem. beam

35. TUNL_Retreat_2011 Conclusion I par /I perp has been measured for 238 U with E  =5.7 to 6.5 MeV The results show ratios which deviate significantly from 1.0 and change as a function of  -ray energy The results agree well with a new simulation based upon previously measured unpolarized angular distributions of fission fragments along with the assumption of dipole plus quadrupole excitations Higher statistics data have already been taken on 238 U as well as 235 U, 239 Pu, and 232 Th The analysis and interpretation are underway with results expected within the next year

36. TUNL_Retreat_2011 Summary We have begun to create a catalogue (graphical and tabular) of polarization asymmetries both for incident  -ray energies from 11 to 15.5 MeV and in the threshold region where photofission neutrons can be isolated. Targets to date include Ta, Cd, Sn, Pb, Bi, Fe, Cr, Cu, Be, 238 U, 235 U, 239 Pu, 232 Th. Next: 233 U, 237 Np, 241 Am, B, N, Ni, Al, W, V, As, Rb, Sr, Ag, Ba, La, Ce, Hg.

37. TUNL_Retreat_2011