Nuclear Physics Institute, Academy of Sciences of Czech Republic Department of Nuclear Reactors, Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague Cross-section Measurements of (n,xn) Threshold Reactions O. Svoboda, A. Krása, M. Majerle, J. Vrzalová, V. Wagner Ondřej Svoboda EFNUDAT scientific workshop on Slow and Resonance Neutrons 23 25 September 2009 Budapest
Outline Motivation for σ Requirements for σ TSL Uppsala facility Cyclotron in Řež facility Evaluation process Preliminary results Conclusion
Motivation for σ E+T Energy plus Transmutation N yield S C C t ( λ t0 ) p abs irr real irr = ( λ t ) ( λ Iγ ε P ( E) Coi Carea tlive m foil 1 e 1 e 1 e λ t real t irr )
cross-sections Energy plus Transmutation Cross-section [b] 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Au(n,2n) 196 Au ENDF 0 10 20 30 40 50 Cross-section [b] 2.0 1.5 1.0 0.5 0.0 ENDF Au(n,4n) 194 Au 0 10 20 30 40 50 Cross-section [b] 2.0 1.5 1.0 0.5 0.0 209 Bi(n,xn) (n,4n)206bi (n,5n)205bi 0 50 100 150 Cross-section [b] 10 1 0.1 0.01 (n,6n)204bi (n,7n)203bi (n,8n)202bi (n,9n)201bi (n,10n)200bi (n,11n)199bi (n,12n)198bi 209 Bi(n,xn) 0 50 100 150
Requirements for σ Requirements for using activation method of measurement: - high energy neutron source with good intensity - (quasi)monoenergetic neutrons with well known spectrum - pure monoisotopic samples - good spectroscopic equipment: γ and X-rays detectors - knowledge about the corrections on beam fluctuation, self-absorption, non-point like emitters neutron spectrum neutron spectrum simulated cross-section Arbitrary units simulated cross-section 0 10 20 30 40 50 Energy [MeV] 0 10 20 30 40 50 Energy [MeV]
TSL Uppsala site Site Blue hall Irradiations User-oriented facility Protons 25-180 MeV Neutron spectra from 7 Li(p,n) 7 Be reaction well known for proton energies 25, 50, and 97 MeV
TSL Uppsala Blue hall Site Blue hall Irradiations 1E8 10 8 Experimental setup in the Blue hall Neutron flux density [1/(cm2.s)] 1E6 10 6 1E4 10 4 1E2 10 2 spallation source at JINR quasi-monoenergetic source at TSL 1E0 1E-7 10-7 1E-5 10-5 1E-3 10-3 1E-1 10 1E+1 10 1 1E+ 10 3 Neutron Energy [MeV] Neutron spectra comparison
TSL Uppsala - irradiations Site Blue hall Irradiations Proton beam energy [MeV] 25 50 97 7 Li-target thickness [mm] 2 4 8.5 Proton beam current [µa] 5 5 2 Average energy of peak neutrons [MeV] 22 47 94 Fraction of neutrons in the peak [%] 50 39 41 Peak neutron flux density [10 5 cm -2 s -1 ] 6 13 14.5 8 hours irradiation at each energy June 2008, supported from the EFNUDAT program
Cyclotron Řež Protons 18 37 MeV on 7 Li target Neutron spectra known for 20, 25, 30, and 35 MeV Y. Uwamino et al., NIM A389 (1997) 463 Beam-line Graphite stopper Facility Diodes High neutron intensities: 10 8 cm -2 s -1 Well equipped spectroscopic laboratory (NSD-NPI) Samples Li-target Experiments on 20, 25, 32.5, and 37 MeV p beams ~ 15 hours of irradiation
Silicon diods for neutrons monitoring Facility Diodes BPW 34F, CMRP and Si-1 silicon diods tested at Řež Originally proposed as dosimeters (CERN), but can be also used as high-energy neutron monitors Irradiation with fast neutrons causes shift of the current-voltage curve (measurement at constant current few ma for a period of hundreds of ms) Neutron intensity range 2.10 12 4.10 14 cm -2 at BPW 34F, respectively 1.10 8 2.10 12 cm -2 at CMRP
Measured materials Materials Process Corrections Background Reaction E thresh [MeV] Half-life Au (n,2n) 196 Au 8.1 6.183 d Au (n,3n) 195 Au 14.8 186.1 d Au (n,4n) 194 Au 23.2 38.02 h Au (n,5n) 193 Au 30.2 17.65 h Au (n,6n) 192 Au 38.9 4.94 h Au (n,7n) 191 Au 45.7 3.18 h Au (n,8n) 190 Au 54.5 43 min Au (n,9n) 189 Au 61.8 29 min Au (n,10n) 188 Au 70.9 9 min iodine (KIO 4 ) In Řež also measured: Mg, Ni, Fe, Zn
Evaluation process Materials Process Corrections Background Irradiation HPGe Spectra evaluation N Yield 1,01 1,00 0,99 0,98 ( ) 0,6 0,5 0,4 0,3 0,2 0,1 24.7 MeV p-beam, 2 mm Li-target 49.5 MeV p-beam, 4 mm Li-target 97.6 MeV p-beam, 8 mm Li-target 0,97 2x2 cm emmiter 0,96 Ep Et 0,95 0,94 0 2 4 6 8 10 12 14 16 Corrections Cross-section 0 0 20 40 60 80 100 Production in peak Talys1.0
Spectroscopic corrections Materials Process Corrections Background Correction factor [-] Self-absorption factor [-] Non-point-like emitters 1.01 1.00 0.99 0.98 0.97 2x2 cm emmiter 0.96 Ep ε p Et ε t 0.95 0.94 0 2 4 6 8 10 12 14 16 Source - detector distance [cm] Self-absorption 2.5 Tabular value Used gamma-lines 2 1.5 1 0.5 0 500 1000 1500 Energy [kev] Efectivity [-] 0.16 0.12 0.08 0.04 0 Detector efficiency ep ε p -p2 na p2 ep ε p -p3 na p3 et ε t na -p2p2 et ε t -p3 na p3 0 1000 2000 3000 Energy [kev] Real γ-γ cascade coincidences Beam instability correction
Production by background neutrons Materials Process Corrections Background σ comparisons between and TALYS mostly good agreement We believe the simulated σ shape is OK, only the absolute value can be shifted data Au(n,2n) 196 Au TALYS Following the neutron spectrum knowledge, we calculated ratio between production in neutron peak and total production With this ratio we multiplied the yields to subtract background production
Experimental results Au, Al, Ta Au, Al, Ta Bi Cross-section [b] 3.0 2.0 1.0 0.0 Preliminary results from Uppsala and Řež Our data from Uppsala Our data from Řež Au(n,2n) 196 Au 0 25 50 75 100 3.0 2.0 1.0 0.0 Our data from Uppsala Our data from Řež 181 Ta(n,2n) 180 Ta 0 25 50 75 100 Cross-section [b] 0.20 0.15 0.10 0.05 Our data from Uppsala Our data from Řež 27 Al(n,α) 24 Na 0.25 0.20 0.15 0.10 0.05 Our data from Řež Our data from Uppsala 27 Al(n,p) 27 Mg 0.00 0.00 0 25 50 75 100 0 25 50 75 100
Experimental results Bi Au, Al, Ta Bi Cross-section [b] 0.4 0.3 0.2 0.1 0.0 Our data from Uppsala Preliminary results from Uppsala 209 Bi(n,7n) 203 Bi 0 50 100 150 0.4 0.3 0.2 0.1 0.0 Our data from Uppsala 209 Bi(n,8n) 202 Bi 0 50 100 150 0.3 209 Bi(n,9n) 201 Bi 0.12 Cross-section [b] 0.2 0.1 Our data from Uppsala 0.08 0.04 Our data from Uppsala 209 Bi(n,10n) 200 Bi 0.0 0 50 100 150 0.00 0 50 100 150 Netron energy [MeV]
Conclusion Summary and prospects Thanks Our cross-section cover wide range of neutron energies (17-94 MeV) New cross-sections measured in neutron energy region, where no data available so far (40-94 MeV) Measured even cross-sections of reactions that have not been measured yet at all (e.g. I) Preliminary results show that we are close to known cross-section values This method of σ can be used also for other materials Plans for future finalize Řež experiments analysis next experiments at Uppsala uncertainty analysis publish final results complete comparison with TALYS
Acknowledgements Summary and prospects Thanks We would like to thank to Dr. Bém and his colleagues for the possibility to joint their irradiations on cyclotron in Řež! This work was supported from the EFNUDAT and from the grant CTU0808214. Thank you for your attention..