1. Cross-sections of Neutron Threshold Reactions Studied by Activation Method 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 NEMEA-6, Krakow, 25.-28.10.2010 J. Vrzalová, O. Svoboda, A. Krása, M. Majerle, A. Kugler, A. Laredo, M. Suchopár, V. Wagner

2. 2 Outline - Motivation - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Motivation Cross-section measurements Neutron sources in NPI and TSL Background subtraction Experiments on Cyclotron in Řež TSL Uppsala experiments Comparison Conclusion

3. 3 Motivation measurement of spatial distribution of neutrons is important part of studies by means of set-ups based on spallation neutron source the activation detectors are very useful tool for neutron field determination in this case for neutron detection are used threshold reactions on Au, Al, Bi, In, Ta, Co, Y almost no experimental cross-section data for most of observed threshold reactions are available for higher neutron energies (E>30MeV)→it is necessary to perform new cross-section measurements - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion

4. 4 Detection of neutrons -Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion AlAuBiCoIn Ta Reaction E thresh [MeV] Half-life 197 Au (n,2n) 196 Au8.16.183 d 197 Au (n,3n) 195 Au14.8 186.1 d 197 Au (n,4n) 194 Au23.238.02 h 209 Bi (n,3n) 207 Bi14.4231.56 y 209 Bi (n,4n) 206 Bi22.556.243 d 115 In (n,2n) 114 In9.121.2 min

5. 5 Evaluation - DEIMOS - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion

6. 6 Spectroscopic corrections - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Detector efficiency Self-absorption Real γ-γ cascade coincidences decay during cooling decay during irradiation unstable irradiation non-point like emitters detector dead time

7. 7 Evaluation - total yield - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Peak areaSelf-absorption correction Beam correction Dead time correction Decay during cooling and measurement γ line intensity Detector efficiency Correction for coincidences Square-emitter correction Weight normalization Decay during irradiation

8. 8 Cross-section measurements - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Requirements for  -measurements by activation method:  high energy neutron source with good intensity  monoenergetic (quasi-monoenergetic) neutrons or well known spectrum  pure monoisotopic samples  good spectroscopic equipment –  and X-rays detectors Then we can calculate N yield and finally : Evaluation process: Irradiation→HPGe→Deimos→Yield →Corrections →Cross-section Number of neutrons in peak foil sizerelative mass Avogadro´s number

9. 9 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, Uppsala - Conclusion Neutron sources Neutron source on cyclotron U-120M Blue Hall, Uppsala Quasi-monoenergetic neutron source Beam Beam-line Li-target Graphite stopper Samples NPI ASCR Řež: Energy range 10 – 37 MeV, neutron intensity ~ 10 8 n.cm -2.s -1 TSL Uppsala: Energy range 20 – 180 MeV, neutron intensity ~ 10 5 n.cm -2. s -1

10. 10 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, Uppsala - Conclusion Neutron spectra from p/Li source in NPI uncertainty in spectrum determination - 10% proton beams of energies 20, 25, 32.5, 37 MeV were used

11. 11 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Background subraction background contribution was determined by folding of the neutron source spectrum and calculated cross-sections (TALYS 1.0) we calculated ratio between production in neutron peak and total production and with this ration we multiplied the yields to subtract background production

12. 12 TALYS 1.0 – nuclear models - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion ld1 - Fermi model ld2 – backshifted Fermi model ld3 - superfluid model ld4 - Goriely table ld5 - Hilairey table models with different nuclear level density change the shape of cross- section dependency on neutron energy

13. 13 TALYS 1.0 – nuclear models - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Difference between cross-sections models with different nuclear level density and default Fermi model, reaction 209 Bi(n,3n) 207 Bi it is necessary to analyze influence of this faktor on determination of radioactive nuclei number in the future

14. 14 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Uncertainty analysis  HPGe detector calibration uncertainty: less than 3%  Gauss-fit of the gamma peaks: > 1% (usually less than 10%)  spectroscopic corrections uncertainty: less than 1%  neutron spectra determination: 10%  neutron beam intensity determination: 5% at NPI, 10% at TSL  uncertainty of background subtraction - will be analyzed in the future

15. 15 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Experiments in NPI  four measurements in years 2008-2009  proton beam energies 20, 25 MeV (August 2008), 32.5 (April 2009) and 37 MeV (Mai 2009)  irradiation time about 20 h.,irradiated foils: Ni, Zn, Bi, Cu, In, Al, Au, Ta, Fe and I  the sample distances from the lithium target – 11 to 16 cm

16. 16 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Experiments in TSL  proton beam energies 25, 50, 100 MeV (June 2008); 62, 70, 80, and 93 MeV (February 2010)  irradiation time about 8 h.,irradiated foils: Au, Bi, In, Al, Ta, Co, Y and I

17. 17 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion NPI and TSL results Comparison of cross-section reaction (n,2n) 197 Au with EXFOR and TALYS

18. 18 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion NPI and TSL results Comparison of cross-section reaction (n,4n) 194 Au with EXFOR and TALYS

19. 19 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion NPI and TSL results Comparison of cross-section reaction (n,6n) 192 Au with EXFOR and TALYS

20. 20 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion NPI and TSL results Comparison of cross-section reaction (n,4n) 206 Bi with EXFOR and TALYS

21. 21 - Motivation Detection of neutrons Evaluation Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Conclusion  eleven cross-section measurements were performed in years 2008-2010  energy region from 17 MeV to 94 MeV was covered  good agreement between our data and other experimental data and code TALYS was observed in many cases  previous measurements in NPI and TSL are now completely processed and were published at scientific workshop EFNUDAT – Slow and Resonance neutrons in 2009 in Budapest and at International Conference on Nuclear Data for Science and Technology in April 2010 in South Korea  only preliminary cross-section data from the last measurement are presented  by the means of this new measurement we covered energy range 59-89 MeV, where no data were available so far Thanks for attention