Nuclear Physics at OCL: From CACTUS to OSCAR

Transcription

1 Nuclear Physics at OCL: From CACTUS to OSCAR Sunniva Siem University of Oslo ENSAF mee)ng Sevilla oktober 2016

2 Outline of this talk Ø Our experimental setup in Oslo Ø The Oslo method - > Level densi)es and gamma- strength func)ons Ø Ac)nide program Ø Low energy enhancement Ø Inverse kinema)cs experiments at ISOLDE, CERN Ø New detector array OSCAR

3 What we can measure in Oslo: Level densities gamma strength functions Which are: Fundamental nuclear properties -> information on pairing, shell structure, temperature, collective effects inputs in cross section calculations, needed for reactor simulations and nucleosynthesis of elements in stars. Can help improve models of level densities and gamma strength functions -> needed for exotic nuclei which can t be measured Ø Not all cross sections can be measured directly Ø Simulations not better than the input data

4 Experimental OCL Beam: p, d, 3He, α with energies up to MeV CACTUS: 28 5 x 5 NaI(Tl), ε Eγ=1.33 MeV to be replaced by OSCAR! SiRi: 64 Si ΔE-E particle telescopes, Δθ 2o PPAC fission detector called NIFF

5 Ac#nide targets PPAC fission fragment detector Ø ejec)le ff γ coincidences Ø fission veto collabora)on Oslo - Debrecen ac)nide targets available: Ø 232Th Ø 233U 235U 238U Ø 237Np Ø 239Pu 240Pu 242Pu 244Pu collabora)on Oslo - Livermore

6 NaI(Tl) Par)cle iden)fica)on, Typical E- E bananas: γ α Si ΔE-E telescope 3 He 45 o Target stable nucleus Par)cle gamma coincidences

7 S n 232 Th(d,p)

8 From the primary gamma spectra: extraction of level densities and γ strength functions P( E, E ) ρ( E ) T ( E ) i γ f γ Assuming dominance of dipole radiation (E1 and M1)

9 Nuclear data for reactor physics: strength functions in the actinide region 232 Th(d,p) 233 Th ) -3 Radiative strength function (MeV -6-7 Present experiment (γ,abs) resonance data f(e1) from (n,γ) f(m1) from (n,γ) 232Th, Gurevich et al NP A273, 1976, p326 Scissors mode? -8 M. Gu_ormsen et al PRL 9, (2012) γ-ray energy E (MeV) γ Thanks to Livermore for providing the target!

10 232 Th(d,p) S n Region A Region B Test of Brink- Axel: Two sta)s)cal independent data sets ) -3 RSF (MeV E = MeV E = MeV E = MeV γ-ray energy E (MeV) γ

11 Low energy enhancement of the strength function A.Voinov et al. Phys.Rev.LeA. 93, (2004) 11

12 The new 56 Fe data taken with LaBr3 detectors ) -3 γ-ray strength function (MeV Fe( He,αγ), Voinov et al. Fe(p,p γ), NaI:Tl Fe(p,p γ), LaBr :Ce 3 Co(γ,n), Alvarez et al γ-ray energy E (MeV) γ CACTUS: 6 LaBr 3 (Ce), 3.5 x 8 22 NaI(Tl), 5 x 5 Experimentally shown to be dominantly dipole radia)on (A.C. Larsen et al., PRL 111, (2013)

13 Some theore)cal efforts: E1 nature? E. Litvinova and N. Belov, PRC 88, (R) (2013). QRPA calcula)ons. M1 nature? R. Schwengner, S. Frauendorf, and A. C. Larsen, PRL 111, (2013). Shell model calc.

14 How does the enhancement affect neutron capture cross sections? Strength function f E Mo 97Mo 97Mo 96Mo 96Mo 95Mo 94Mo 93Mo Hybrid E [MeV] Assuming the strength functions of Mo isotopes all have the same energy trend With /without enhancement A.C. Larsen and S. Goriely, Phys. Rev. C 82, (20)

15 In Oslo: stable nuclei NaI(Tl) Exotic beams, using inverse kinematics γ α Si ΔE-E telescope γ α 3 He 45 o Target stable nucleus p or 3 He target Experiment in November at Hie-Isolde to measure the gamma strength function in nutron rich Ni isotopes with two independent methods: Oslo method and Ratio Method Well established for normal kinematics, performed a proof of principle experiment in inverse kinematics at ithemba last year -> it works!

16 INVESTIGATING THE LOW ENERGY ENHANCEMENT IN THE GAMMA STRENGTH FUNCTION OF 87Kr IN INVERSE KINEMATICS Doppler corrected energy clover : Excitation energy Excita)on energy Excitation energy [kev] Preliminary 2 1 V. W. Ingeberg master thesis Clover energy [kev] gamma energy

17 AFRODITE 8 Clover detectors, segmented in four 50x70 mm HPGe chrystals covering 11% og 4pi 2 LaBr3 detectors, 3.5x8 segmented Si charged par)cle detectors: 300um (500um) + 1mm back detector

18 ) -3 γ-ray strength function (MeV 6 LaBr (Ce), Polyethylene 3 CLOVER, Polyethylene LaBr (Ce), Polystyrene 3 CLOVER, Polystyrene 86 Kr(γ,γ'), R. Schwengner, et. al. 86 Kr(γ,n), R. Raut, et. al. 7 Preliminary Kr γ-ray energy E (MeV) γ V. W. Ingeberg master thesis

19 Synergies with Large scale facilities We are bringing 6 LaBr3 detectors from Oslo for the experiment at HIE-ISOLDE Beamtime: 7-14 November Spokesperson: S.Siem + M.Wiedeking. Data will be analyzed by both Oslo and ithemba. In June we tested both digital and analog electronics for reading the signals into the miniball data acquisition system. Also tested the mechanical holding structure for the LaBr3 detectors. Gry, Frank and Tuva at ISOLDE, CERN

20 NEW INFRASTRUKTUR OSCAR: Replacing the current NaI(Tl) CACTUS detectors with LaBr3 detectors Oslo Scin)llator Array Ø 23 MNOK (ca 2.56 M Euro) Ø 30 Large volume (3,5 x 8) LaBr3 detectors Ø Better energy resolution Ø Better timing Ø Possibilities for new types of experiments Ø We welcome new collaborations Ø First experiment with full array in 2017

21 Example of difference in energy resolution: counts Target: natural Si Gate on 8904-keV peak in Ex (FWHM 0 kev) Blue: all 22 NaI Red: all 6 LaBr kev kev kev kev pxallnai Entries Mean RMS Underflow 0 Overflow 20 Integral La (from LaBr3 itself) kev kev kev Eγ [kev]

22 V.Ingeberg and F.Zeiser 22

23 New detector frame for OSCAR 23

24 24

25 h_ps://www- nds.iaea.org/crp- photonuclear/ 25

26 Current EU project under EURATOM: Univ. of Oslo, OCL is a partner in: CHANDA solving CHAllenges in Nuclear DAta Objectives: - To provide the nuclear data required for the safe and sustainable operation, and development, of existing and new reactors and nuclear fuel cycle facilities, - To prepare solutions for the challenges risen by the nuclear data measurements needed by nuclear systems, like the data for highly radioactive, short lived or rare materials, - To prepare tools that solve the challenges of quantifying and certifying the accuracy of the results of simulations based on available nuclear data and models (uncertainties), - To identify and promote synergies with other nuclear data applications.

27 Advantages and challenges with a small scale facility: Ø Oslo Cyclotron Laboratory offers excellent hands-on training for masters and PhD students. Giving them the confidence and skills needed to be useful at experiments at larger facilities like RIKEN, ISOLDE, CERN and GANIL. Ø Several master and PhD student from other Universities get data from OCL and some spend a semester in Oslo (this semester 1 master + 1 PhD student from Turkey and 1 PhD student from South Africa) Ø We can get beamtime within weeks/months when needed for our PhD and master students. Compared to waiting 3 years from submitting a proposal for HIE-ISOLDE. Ø Can have a semi permanent experimental setup with alot of time for testing/debugging. Students can take part in developing/building new equipment like the PPAC. Ø Harder to get Transnational Access funding for smaller facilities? Ø Increasing preasure from the University to find external funding for running costs.

28 6 th Workshop on Level Density and Gamma Strength Oslo, May 8 12 May 2017 Welcome to Oslo!

29 Collaborators F.L.B. Garrote, F. Giacoppo, A.Görgen, M.Guttormsen, T.W. Hagen, V.W.Ingeberg, M.Klintfjord, A.C.Larsen, H.T.Nyhus, J.Rekstad, T.Renstrøm, S.J.Rose, E. Sahin, S.Siem, T.Tornyi, G.M.Tveten, F.Zeiser, University of Oslo, Norway N.Blasi,A.Bracco, F.Camera, S.Leoni,B.Million, Milano, Italy L.Bernstein, D.Bleuel, Lawrence Livermore NL, USA M.Wiedeking, P.Jones, itemba labs South Africa A.Voinov, Ohio University, USA S.Goriely, Brussel, Belgium J.Wilson, M.Lebois, IPN Orsay, France F. Gunsing, CEA Saclay, France M. Krticka, Charles University, Prague R. Firestone, Berkeley na)onal Lab A.Spyrou, G.Perdikakis, S.Liddick, A.Brown, NSCL/MSU, USA R. Schwegner, HZDR Dresden, Germany H. Utsunomiya, Konan University, Japan

30 Thank you;- )

31 Future outlook and challenges: Ø What is the electromagnetic character of the low energy enhancement? Ø Impact of this enhancement, scissors mode and pygmy resonances on large network calculations of formation of elements in stars. Ø Is the enhancement also present in neutron rich nuclei? Ø Test of Oslo method in inverse kinematics: Experiment at ithemba Labs with stable 86 Kr beam, analysis ongoing Ø Experiment in November to study neutron rich nuclei Ni at HIE-ISOLDE, CERN Ø Beta-Oslo method experiments MSU

32 Energy resolution LaBr3 vs NaI 8keV 11keV 42 kev 118 kev