Measurements of DN Yields and Time Spectra from p(1 GeV) + nat Pb & p(1 GeV) Bi

Transcription

1 Measurements of DN Yields and Time Spectra from p(1 GeV) + nat Pb & p(1 GeV) Bi D. Ridikas 1, A. Barzakh 3, V. Blideanu 1, J.C. David 1, D. Doré 1, D. Fedorov 3, X. Ledoux 2, F. Moroz 3, V. Panteleev 3, A. Plukis 4, R. Plukiene 4, A. Prévost 1, O. Shcherbakov 3, A. Vorobyev 3 1 CEA Saclay, DSM/DAPNIA, Gif-sur-Yvette, France 2 CEA/DIF, DAM/DPTA, Bruyères-le-Châtel, France 3 Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, Russia 4 Institute of Physics, Savanoriu pr. 231, Vilnius, Lithuania Collaboration: PNPI, Russia IoP, Lithuania PSI, Switzerland Financial support: CEA FR Ministry of Foreign Affairs GEDEPEON

2 Introduction high-energy high-power accelerators use of liquid metal targets (Hg, Pb, Pb-Bi, ) long flowing metal loop activated metal close to electronics, in hot cells, heat exchanger, pumps, short transit time moving beta, photon and delayed neutron (DN) radioactivity Goal: Characterization of DNs from high-energy spallation-fission reactions

3 Examples (A) J-PARC/JAEA - thanks to H. Nakashima Delayed neutrons Prompt neutrons short Hg transit time delayed neutron (DN) activity

4 MegaPie/PSI - thanks to F. Groeschel Examples (B) Beam on the target from 14 August to 23 December! E p I p W V PbBi Main pump 570 MeV 1.2 ma (1.8) 0.7MW (1.0) ~ 82 liters ~4.00 l/s MegaPie target PbBi Fission chambers DN/PN =? ~5.3 m T transit ~20 s DN and PN estimates using MCNPX+CINDER 90 Φ n (DN)~ 10 6 n/(s cm 2 ) Φ n (PN)~ 10 6 n/(s cm 2 ) Important: DN yields are very sensitive to the choice of physics models! 1MW protons D. Ridikas et al., Proc. of PHYSOR2006, Vancouver, Canada

5 Model-dependence of DN yields INCL4 +ABLA model CEM2k model Group T 1/2, s a i, n/p times 10 6 T 1/2, s a i, n/p times Total/average Difference by 2 orders of magnitude! D. Ridikas et al., Proc. of Fission2005, CEA Cadarache, France

6 Model-dependence of Y in (A,Z) yields Br-35 p(1 GeV) + Pb Rb sigma(mb) GSI data INCL ISABEL BERTINI CEM2k sigma(mb) GSI data INCL ISABEL BERTINI CEM2k A INCL4-ABLA gives reasonable predictions other models overestimate significantly the neutron-rich side A 1. Fission yields on the very neutron-rich side are difficult to reach 2. No available data on DN yields from high energy fission-spallation

7 DN measurements from p (1GeV)+Pb at PNPI Gatchina (Russia) PNPI synchrocyclotron SC Location of the experiment 1 GeV protons ~20 na Pb target 3 He counter

8 Experimental strategy He-3 counter calibration: 252 Cf neutron source + Monte Carlo Proton beam monitoring: 27 Al foils and gamma spectroscopy from 22 Na, 24 Na and 7 Be Measurement strategy: a) No target at all long irradiations b) Concrete block long irradiation c) Iron thick target long irradiations d) Lead target of variable thickness; short (350 μs), intermediate (20 s) and long (300 s) irradiations

9 Proton beam monitoring Beam size/profile: by photo-films at exit and entrance positions Beam intensity: by 27 Al foils and gamma spectroscopy from 22 Na, 24 Na and 7 Be Photo-films 1GeV protons Al foils 27 Al(p,x) 7 Be monitor reaction cross section 7.5 ± 0.3 mb was taken as a reference ratios of 24 Na & 22 Na with respect to 7 Be were equal to 1.73 ± 0.15 & 1.99 ± 0.07 uncertainty in proton beam monitoring from 8 % to 12 %

10 Accumulated raw data

11 5 10 DN decay curve: Pb 55 cm p + nat Pb (55 cm) 4 10 DN( t) = ai exp( λit)(1 exp( λitirrad )) + C i N counts Li 10 1 background 88 Br 87 Br Group D. Ridikas et al., EPJ A (2007); in print Half-life, s Decay (s) Precursor 87 Br 88 Br 17 N 9 Li P n (β-n), % Understandable from x-sections p(1gev)+pb 9 Li ~ 1000 μb p(1gev)+pb 17 N ~ 600 μb p(1gev) +Pb 87 Br ~30 μb

12 DN decay curves: p + nat Pb Reproduced with 4 major contributions : 9 Li, 17 N, 88 Br, and 87 Br

13 DN decay curves: p Bi The same 4 major contributions : 9 Li, 17 N, 88 Br, and 87 Br

14 Experimental precursor yields (atoms/proton) 17 N 87 Br DN( t) = ai exp( λit)(1 exp( λitirrad )) + C P i i n Y DN( t = 0) = a i = ai /( ε He 3I pδtchncycles i i + C ) 88 Br 17 N Saturation is observed for targets thicker than 20 cm 87 Br 88 Br Similar shapes and absolute values both for Pb and Bi D. Ridikas et al., EPJ A (2007); in print

15 Precursor yields: data versus PHITS simulations 17 N 87 Br 88 Br INC (JAM) + EVAP(GEM) JAM: Jet AA Microscopic Transport Model GEM: Generalized Evaporation Model H. Iwase, K. Niita, T. Nakamura, Journal of Nuclear Science & Technology 39 (2002) Predictions within a factor of 2!

16 Extraction of x-sections : 17 N & 87,88 Br p(1gev)+a-->17n 100,00 10,00 Dostrovsky'65 Batist'77 This work Using thin targets sigma (mb) 1,00 0,10 0, ,0E+01 Br-35 A 1,0E+00 sigma (mb) 1,0E-01 Good agreement with old data and/or systematics! 1,0E-02 MCNPX (INCL4+ABLA) PHITS(NMTC-JAM+GEM) GSI data This work 1,0E A

17 Conclusions and outlook importance of DNs in liquid metal targets for radioprotection issues importance of the measurements to test model calculations DN yields and time spectra measured for the 1 st time for p(1gev) on thick nat Pb and Bi targets Estimates of errors on DN decay curves : below 20 % Major contributors are: 87 Br, 88 Br and 17 N extraction of x-sections PHITS code recommended for such studies Consequences and in-situ experiment

18 Absolute DN production yields: consequences Assumption: p(1gev) + Pb (55 cm thick; 10 cm ) at 1mA (1 MW) Delayed neutrons Prompt neutrons ~ n/s Important data for: SNS based on liquid metal targets ToF facilities (DNs background neutrons) ~20 s after

19 CEA/DSM/DAPNIA s contribution for MegaPie DN MEGAPIE (Preliminary) Delayed neutrons ~2-3m 3 He I = 250 μa I = 1.2 ma U5 WD 10 3 Time (x 200 ms) Np Am Prompt neutrons U5 WD Moniteurs U5 WD 1MW protons MegaPie target PbBi Fission chambers 1 m 1,3 cm

20 MegaPie: geometrical model down down top up up Spallation region Cross section S, cm 2

21 MegaPie measurements PNPI data Use of parameters extracted from PNPI/Gatchina experiments n n a 1 exp( λτ i a) Estimates: a( x) = ai ( x) = ai exp i= 1 i= 1 1 exp( λit ) τ a ~0.5 s irradiation i d x T ~20 s relaxation τ d ~10 s heat exchanger ( λτ ( ))

22 DN decay curves: Fe and brick p(1gev) + nat Fe 9 Li 17 N p + brick 9 Li, 17 N, p(1gev) + brick p + nat Fe 9 Li, 17 N,

23 He-3 counter calibration Cf neutron source at y = 170cm and different x modeling with MCNPX: agreement within 5-6 % 3D modeling with Monte Carlo Efficiency, events/s x 10-5 Neutron flux, n/s x Pb Target length, cm 01 MeV 05 MeV 1 MeV y x z 2. Use of Monte Carlo with exact experimental conditions variable target thickness variable DN energy estimated uncertainty below 10 %

24 Photo of the experimental setup He-3 neutron counter 3 He (8 atm.) + Ar(2 atm.)

25 Example (A) SNS, J-PARC, EURISOL liquid Hg MegaPie, ADS liquid PbBi SNS/ORNL - thanks to F. Gallmeier

26 Physics: ratios of relative yields relative to 87 Br Target thickness, cm 5 a 2 ( 88 Br)/a 1 ( 87 Br) 1.7 a 3 ( 17 N)/a 1 ( 87 Br) 354 Experiment stable decreasing Produced by different reaction mechanisms Target thickness, cm a 2 ( 88 Br)/a 1 ( 87 Br) a 3 ( 17 N)/a 1 ( 87 Br) a 4 ( 9 Li)/a 1 ( 87 Br) Confirmed by PHITS predictions

27 DN yield as a function of incident neutron energy (n,pf) p(1gev) U in 2007 p Pa8 U6 4nU5 (n,4nf) Th5 (n,3nf) (n,αf) U7 3n α (n,2nf) n + U9 U8 n U8 2n (n,f) (n,nf) MeV Séminaire Saclay 53 Thanks to P. Romain et al. CEA/DIF/DPTA What is beyond 20 MeV?

28 Why only 4 exponentials are sufficient? Production of Br isotopes 1,0E-01 1,0E-02 yield/fission 1,0E-03 1,0E-04 1,0E-05 p(1gev)+pb p(1gev)+u 1,0E-06 n(14mev)+u n(fiss)+u 1,0E Mass A U fission Pb fission; low energy high energy