Neutron-induced reactions on U and Th a new approach via AMS in collaboration with: KIT (Karlsruhe): F. Käppeler, I. Dillmann

Transcription

1 Neutron-induced reactions on U and Th a new approach via AMS in collaboration with: KIT (Karlsruhe): F. Käppeler, I. Dillmann IRMM / Geel: A. Plompen, A. Krasa IKI Budapest: T. Belgya, L. Szentmiklosi TSL Uppsala: A. Prokofiev et al. VERA (Vienna): P. Steier, S. Winkler, C. Lederer A. Wallner The Australian National University (ANU) AMS ANU (Canberra): L.K. Fifield, S. Tims, M. Srncik neutrons ETH Zurich: M. Christl, J. Lachner ANSTO: M. Hotchkis Univ. Heidelberg: J. Lippold IAEA: R. Capote, V. Semkova

2 European collaborations AMS at VERA / ANU / ETH / ANSTO neutron activations at IRMM / KIT / BRR / PTB

3 Motivation: 238 U(n, )/ 232 Th(n, ): E n > thermal ratio of capture to fission of the fissile isotopes existing data via TOF and detections of prompt -rays; multiple scattering corrections due to large sample size in previous exp.? (e.g. 2 gram) HPRL (NEA) listed = highest priority AMS: mg samples large discrepancies above thermal E n k eff in reactor technology: even 5-10% discrepancy in cross section too much very few exp. data above thermal energies AMS: atom counting activation + AMS is an independent method; no influence from fission channel! discrepancy of evaluations! new method does not rely on previous drawbacks simple direct method!

4 238 U(n, ) 239 U EXFOR database MeV

5 232 Th(n, ) 233 Th MeV MeV

6 (n,3n) for 238 U and 232 Th

7 Activation (I) AMS-Measurement (II) fusion / fission / ADS / nuclear astrophysics (I) Recent neutron irradiations: KIT Karlsruhe: 3.7 MV Van de Graaff: 7 Li(p,n) 7 Be: 25 kev Maxwell- Boltzmann, 120 kev, 180 kev, 500 kev,...) IRMM Geel: 7 MV Van de Graaff: (T(p,n) 3 He: E n = MeV) II) atom counting of the reaction IRMM Geel: 7 MV Van de Graaff: (D(d,n) 3 He: E n = 2 5 MeV) products using the most sensitive IRMM Geel: 7 MV Van de Graaff: (T(d,n) 4 He: E n = MeV) technique: AMS TU Dresden/Rossendorf: 300 kv (T(d,n) 4 He: E n = MeV) Atominstitut Vienna: research reactor, thermal neutrons IKI Budapest: research reactor, thermal neutrons; cold neutrons TSL Uppsala: cyclotron, 7 Li(p,n): 45 MeV neutrons

8 AMS at different labs ANU/Canberra Vienna ANSTOSydney ETH Zurich

9 ANU s AMS facility

10 How to derive cross sections? Z E n N Z N E n 1 tot tot e. g. E n U U 1 tot for 238 U ( n, ) 239 U AMS monitor reaction (Au)

11 238 U(n, ) 239 U -> 239 Np -> 239 Pu (24 kyr) IKI FZK 235 U(n, ) 236 U (23 Myr) - simultaneously

12 236 U & 239 U: Production & Decay 236 U: t 1/2 = 23.4 Myr 239 U: t 1/2 = 23.5 min 239 Np: t 1/2 = 2.35 days 239 Pu: t 1/2 = 24.1 kyr

13 Analytical Strategy Au for fluence Sample 233 U and 242 Pu spike Chemical separation of U / Pu AMS 239 Pu / 242 Pu 233 U / 236 U / 238 U 238 U(n, ) 239 U 235 U(n, ) 236 U

14 typical AMS-spectrum for Pu measurements 242 Pu 5+ clear separation / no interference Pu 5+ Pu Pu Nd 3+ & 236 U-sensitivity: 236 U/ 238 U ~ Pu 5+ overall 10 AMS-beamtime sessions for 235 U(n, ): +- 3 % overall 6 AMS-beamtime sessions for 238 U(n, ): +- 3 %

15 238 U(n, ) 239 U -> 239 Np -> 239 Pu (24 kyr) IKI FZK IRMM 232 Th(n, ) 233 Th -> 233 Pa -> 233 U (159 kyr)- simultaneously

16 233 Th & 239 U: Production & Decay: (n, ) low MeV 233 Th: t 1/2 = 22.3 min 233 Pa: t 1/2 = 27 days 233 U: t 1/2 = 159 kyr 239 U: t 1/2 = 23.5 min 239 Np: t 1/2 = 2.35 days 239 Pu: t 1/2 = 24.1 kyr

17 Fast neutron induced reactions: Th / U IRMM IRMM U/Th simultaneously the same geometry the same fluence (n,3n), (n,4n), (n,2n), (n,a) in the same irradiation

18 232 Th & 238 U: Production & Decay: (n,x) fast n 231 Th: t 1/2 = 25.5 h 231 Pa: t 1/2 = 32.8 kyr 229 Th: t 1/2 = 7.88 kyr 236 U: t 1/2 = 23.4 Myr 237 U: t 1/2 = 6.75 days 237 Np: t 1/2 = 2.14 Myr

19 new data 238 U(n, ) 239 U EXFOR database kev exp. data > 1980

20 Status kev data 235 U(n, ) 236 U 235 U(n, ) 236 U 238 U(n, ) 239 U 238 U(n, ) 239 U this work recommended this work recommended IKI-2: ± 3 barn* barn IKI-2: reference for AMS (2.72 barn JENDL) thermal IKI-1: 99.5 ± 3 barn* barn IKI-1: reference for AMS 2.68 barn KIT-1: 646 ± 38 mbarn ENDF: 679 mbarn 25 kev (ENDF = JEFF) this work (AMS ratio): U-8 / U-5 = 0.60 ± 0.05 ENDF: U-8 / U-5 = 0.59 KIT-2: 161 ± 7 mbarn 163 mbarn (ENDF,JEFF) 426 kev 171 mbarn (JENDL) relative to 233 U-spike AMS vs ENDF: U-5 ( 25 kev) = 0.95 ± 0.06 AMS vs ENDF: U-8 ( 25 kev) = 0.96 ± 0.06 AMS vs ENDF: U-5 (426 kev) = 0.99 ± 0.04 AMS vs ENDF: U-8 (426 kev) = 0.99 ± 0.04 KIT-1: 386 ± 25 mbarn KIT-2: 108 ± 4 mbarn 401 mbarn (ENDF,JEFF) 109 mbarn (ENDF, JENDL) 119 mbarn (JEFF) this work (AMS ratio): U-8 / U-5 = 0.67 ± 0.04 ENDF: U-8 / U-5 = 0.67

21 25 kev Maxwell-Boltzmann: JANDEL : U-5 = 0.70 ± 0.06 ENDF/B-VII.1 U-5 = this work (AMS): U-5 = ± AMS vs JANDEL: U-5 ( 25 kev) = 0.92 ± 0.10

22 Status 232 Th(n, ) 233 Th & 238 U(n, ) 239 U for 0.5 / 1.0 / 2.1 / 5.0 MeV ANU finished - for both reactions and all energies AMS ratio measurements: uncertainties 5% 15% still pending: careful check of neutron energy distribution for final fluence / cross section values o) low energy component in the distribution o) T(p,n) reaction for neutron production (0.5, 1.0 & 2.1 MeV) o) D(d,n) reaction for neutron production (2.1 & 5.0 MeV) AMS at the ANU

23 238 U(n, ) 239 U

24 232 Th(n, ) 233 Th

25 First results U(n,3n) 236 U MeV: AMS finished - ± 2% MeV: AMS finished - ± 2%! Preliminary data: ca. 3-4x previous values? MeV: = (2.69 ± 0.05) barn MeV: = (3.05 ± 0.05) barn? Fluence! number of neutrons/sample

26 First results Th(n,2n) 231 Th MeV: AMS finished - 3x AMS (Vienna, Zurich, Sydney) MeV: AMS finished - 3x AMS (Vienna, Zurich, Sydney) MeV: AMS finished - 3x AMS (Vienna, Zurich, Sydney) MeV: AMS finished - 3x AMS (Vienna, Zurich, Sydney) (pending: normalisation)

27 First results Th(n,4n+a) 229 Th

28 AMS & neutron fluence this work (AMS ratio): U-8 / U-5 = 0.60 ± 0.05 ENDF: U-8 / U-5 = 0.59 this work (AMS ratio): U-8 / U-5 = 0.67 ± 0.04 ENDF: U-8 / U-5 = 0.67 systematic study of Maxwellian-averaged xs from precise AMS measurements

29 addendum: Fe AMS data new data: MeV long-lived reaction products: 56 Fe(n,2n) 55 Fe 54 Fe(n,2n) 53 Fe [ 53 Mn] 54 Fe(n, ) 55 Fe 54 Fe(n,np+d) 53 Fe 53 Mn 58 Ni(n,a) 55 Fe 55 Fe - AMS: ± 2%

30 53 Fe / 53 Mn 53 Mn: t 1/2 = 3.7 My

31 Conclusion - actinides AMS represents an independent method for studying nuclear reactions leading to long-lived radionuclides direct method: atom counting as isotope ratio; i.e. no sophisticated data reduction or corrections required not a universal method AMS is used for some 25 radionuclides if it can be applied usually very (the most) sensitive method can serve as an important tool to provide some anchor points can it help to solve the Au-standard issue? new neutron-producing facilities (FRANZ, Frankfurt, Germany), SARAF (Israel) offer a much higher kev-neutron flux

32

33 Comparison AMS other meas. / ENDF AMS data (not U) relative to Au- Ratynski-Käppeler for 25 kev all activations with the same geometry at KIT as used in Ratynski & Käppeler

34 30 kev MACS for 197 Au(n, ) (Maxwellian-averaged cross sections) ENDF/B-VII ± 8 mb 5.3 %