1. GOVERNMENT OF ROMANIA Structural Instruments 2007-2013 Sectoral Operational Programme „Increase of Economic Competitiveness” “Investments for Your Future” Extreme Light Infrastructure – Nuclear Physics (ELI-NP) - Phase I Project co-financed by the European Regional Development Fund Study of nuclear collective states above neutron threshold using monochromatic γ-ray beams at ELI-NP 14 th International Conference on Nuclear Reaction Mechanisms, Varenna, June 15 - 19, 2015 W. Luo 1, D.M. Filipescu 1, I. Gheorghe 1, C. Matei 1, H. Utsunomiya 2, F. Camera 3,4, V. Varlamov 5 1 Extreme Light Infrastructure - Nuclear Physics, Bucharest, Romania 2 Konan University, Kobe, Japan 3 University of Milano, Department of Physics, Italy 4 INFN section of Milano, Milano, Italy 3 5 Physics Faculty, Lomonosov Moscow State University, 119991 Moscow, Russia EUROPEAN UNION

2. Study of nuclear collective states above neutron threshold using monochromatic γ-ray beams at ELI-NP Outline 1. ELI-NP facility - current status - overview of physics program at ELI-NP - Gamma above neutron threshold 2. Purpose of present study - measurements of (g,xn) x>=1 reaction cross sections 3. Flat efficiency detection technique 4. Development of a flat efficiency neutron detector 5. Proposals for the upcoming measurements

3. ELI-NP NUCLEAR Tandem accelerators Cyclotrons γ – Irradiator Advanced Detectors Biophysics Environmental Physics Radioisotopes

4. The construction will be finished in 2016. The facility will deliver the first gamma ray beam in 2018. 2016

5. 14 th International Conference on Nuclear Reaction Mechanisms, Varenna, June 15 - 19, 2015 HPLS GBS Laboratories Experimental caves ±1 mm @ < 10 Hz anti-vibration slab ELI-NP – Laser and Gamma Beam systems Laser beam system: 2 HPLS up to 10 PW – 6 output lines 2 x 0.1 PW 2 x 1 PW 2 x 10 PW Gamma beam system High intensity High energy resolution Experiments with: -High power laser beams (HPLS) -Gamma ray beams (GBS) -Laser + gamma ray beams

6. ELI-NP  -ray beam expected parameters

7. Nuclear resonance fluorescence (NRF) studies Gamma above neutron threshold studies (ELI-GANT) Charged particle induced reactions Photo-fission studies Nuclear physics at ELI-NP

8. ELI-GANT workgroup: Conveners: – Prof. Dr. Hiroaki Utsunomiya Konan University of Kobe, Japan Memorandum of understanding between Konan and ELI-NP – Prof. Dr. Franco Camera University of Milano, Department of Physics, Italy INFN section of Milano, Milano, Italy Collaborator: – Prof. Dr. Vladimir Varlamov Physics Faculty, Lomonosov Moscow State University, Moscow, Russia Liason: – Dr. Dan Filipescu, ELI-NP

9. ELI-GANT – Physics program

11. Purpose of present study - Measurements of partial and total photoneutron cross sections for 209 Bi Most of the photoneutron cross section measurements were performed using quasi-monochromatic annihilation – QMA photons using positron in flight annihilation at two major facilities: – Saclay (France) – Lawrence Livermore National Laboratory (USA) Large discrepancies in ( ,xn) c.s. measured at the two facilities: – (γ, 1n) c.s. are generally noticeably larger at Saclay than at Livermore – (γ, 2n) c.s. are generally larger at Livermore than at Saclay. Livermore - 84Saclay - 80 Both – 42 Main problem Many bremsstrahlung data Other - 10 No systematic way to resolve the discrepancies: New and reliable measurements are required!

12. 14 th International Conference on Nuclear Reaction Mechanisms, Varenna, June 15 - 19, 2015 Livermore data 116 Sn 159 Tb Physically not reliable negative cross section values are correlated with physically forbidden values F 2 > 0.50 F2F2  ( , 1n)  ( , 2n) F 2 = ________________________ < 0.50 (!)  ( , 1n) + 2  ( , 2n) + 3  ( , 3n) +… Dramatic disagreements: F 2  1.5 – 2.0! Significant disagreements: F 2 > 0.6! F2F2 F2F2 Behavior of F 2 for many nuclei is quite different and do not satisfy the criteria proposed

13. For ( ,1n) cross sections – measurements using LCS  -ray beam and the high efficiency neutron detector developed at GACKO offer the required precision and reliability E  <S 2n  ( ,1n) Average energy E avg determined using the ring ratio method

14. Example: E  <S 3n  ( ,1n) + ( ,2n) Neutrons from (g,1n) reactions Average energy E 1 Energy range: 0 to E g -S n Neutrons from (g,2n) reactions emitted by the: - A X nucleus -Energy range: ~( 0 to E g ‒S 2n ) - A-1 X nucleus -Energy range: ~( 0 to E g ‒S 2n ) Average energy E 2 E 1  E 2  ε(E 1 )  ε(E 2 ) For ( ,2n), ( ,3n), … cross sections

15. Let us assume E  <S 4n  ( ,1n), ( ,2n), ( ,3n) induced reactions N 1, N 2, N 3 = number of (g,1n), (g,2n), (g,3n) induced reactions E 1, E 2, E 3 = average energy of (g,1n), (g,2n), (g,3n) neutrons N s, N d, N t = number of single, double and triple neutron events Adjust experimental conditions to have maximum one reaction per  -ray beam pulse N s, N d, N t - we measure directly N 1, N 2, N 3 - we must determine to obtain the cross sections E 1, E 2, E 3 - ? Can not be determined using the ring ratio method. PROBLEM! A neutron multiplicity sorting technique with a flat efficiency neutron detector is required!

16. Considering a flat efficiency neutron detector and E  <S 4n we have: Single neutron events: Double neutron events: Triple neutron events: N s, N d, N t - we measure directly ε - known by direct measurement and by simulation N 1, N 2, N 3 - we determine to obtain the ( ,1n), ( ,2n), ( ,3n) cross sections

17. Neutron multiplicity sorting with a 4π neutron detector Search for a flat efficiency 4π neutron detector: - number of rings - distance between beam axis and center of each ring - number of detectors per ring - size of moderator

18. Neutron multiplicity sorting with a 4π neutron detector Flat-efficiency 4π neutron detector -> ε(E n ) no longer depends on E n Configuration 3 He countersDistance Inner ring45.5 cm Middle ring913 cm Outer ring1816 cm Total31 Moderator size: 46 cm Search for a flat efficiency 4π neutron detector: - number of rings - distance between beam axis and center of each ring - number of detectors per ring - size of moderator

19. Neutron multiplicity sorting with a 4π neutron detector Detection efficiency: ( ,n) neutrons: ε = 40% ( ,2n) neutrons: Both neutrons detected: ε 2 = 16% Only one neutron detected: ε(1- ε) = 24% ( ,3n) neutrons: 3 neutrons detected: ε 3 = 6.4% 2 neutron detected: ε 2 (1- ε) = 9.6% Only one neutron detected: ε(1- ε) 2 = 14.4%

20. Neutron multiplicity sorting with a 4π neutron detector Sensitivity to displacements of counters from the inner ring. Sensitivity to moderator size.

21. Preparatory experiment - Photoneutron measurements of Sm and Nd isotopes at NewSUBARU Participated to the measurements - Electron energies between 573 and 850 MeV -Q-switch Nd : YVO 4 laser INAZUMA -5.87 – 13 MeV  -ray beams -High efficiency 4π neutron detector -LaBr3 detector for energy monitor -80% NaI-Tl detector flux monitor -enriched samples of 144 Sm, 147 Sm, 148 Sm, 149 Sm, 150 Sm, 152 Sm, and 154 Sm in oxide form (Sm 2 O 3 )

22. Preparatory experiment - Photoneutron measurements of Sm and Nd isotopes at NewSUBARU I. Gheorghe analyzed the Sm data following the instructions and guidance of prof. Utsunomiya Energy calibration of LaBr 3 detector Pile-up and Single spectra of a 13.03 MeV LCS  -ray beam recorded with the NaI-Tl detector Final cs. - results of the Taylor expansion method

23. Preparatory experiment - Photoneutron measurements of Sm and Nd isotopes at NewSUBARU Microscopic calculations performed by S. Goriely D. M. Filipescu et al., Phys. Rev. C 90, 064616 (2014)

24. 209 Bi(g,xn) cross sections measurements to be performed in Japan July 2015 (g,1n) measurements: 7.5 to 14.35 MeV  -ray beams Nd:YVO 4 laser INAZUMA – 1 st harmonic Electron energies - 600 to 900 MeV High efficiency 4π neutron detector (g,2n), (g,3n) measurements: 14.5 to 28 MeV  -ray beams Nd:YVO 4 laser INAZUMA – 2 nd harmonic Electron energies - 640 to 900 MeV Flat efficiency 4π neutron detector LaBr 3 detector for energy monitor 100% NaI-Tl detector flux monitor Monoisotopic thick 209 Bi target Efficiency calibration of the flat-efficiency detector at NIMJ (National Institute of Metrology of Japan) in Tsukuba.

25. 14 th International Conference on Nuclear Reaction Mechanisms, Varenna, June 15 - 19, 2015 Proposals for future measurements using The ELI-NP monoenergetic  –quanta source with energies up to ~ 19 MeV. The new measurements for isotopes for which we found out the most prominent disagreements between experimental and evaluated reaction cross sections are of great interest on the first stage. 1-st priority: 159 Tb (B2n = 14.9 MeV), 181 Ta (B2n = 14.2 MeV), 208 Pb (B2n = 14.1 MeV). 2-nd priority: 94 Zr (B2n = 14.9 MeV), 186,188,189,190,192 Os (B2n = 14.9,14.3,13.9,13.7,13.3 MeV). 3-d priority (measurements would be possible for narrow 115 In (B2n = 16.3 MeV), energy range (~ 2 - 3 MeV)) 116 Sn (B2n = 17.1 MeV). 4-th priority new data will be evaluated further. Because the correspondent final nuclei ( 157,158 Tb, 179 Ta, 206,207 Pb, 92,93 Zr, 184 Os, 113 In, 114,115 Sn) are not suitable candidates for activation measurements.

26. ELI-NP Team, March 5, 2013 Thank you! 26