Nuclear Physics Institute Academy of Sciences of Czech

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-sections of Neutron Threshold Reactions Studied by Activation Method NEMEA-6, Krakow, 25. -28. 10. 2010 J. Vrzalová, O. Svoboda, A. Krása, M. Majerle, A. Kugler, A. Laredo, M. Suchopár, V. Wagner

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

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

Detection of neutrons -Motivation • Detection of neutrons • Evaluation • Corrections - Cross - section measurements - Neutron sources - Background subtraction Reaction E thresh Half-life [Me. V] 197 Au (n, 2 n) 196 Au 8. 1 6. 183 d 197 Au (n, 3 n) 195 Au 14. 8 186. 1 d 197 Au (n, 4 n) 194 Au 23. 2 38. 02 h 209 Bi (n, 3 n) 207 Bi 14. 42 31. 56 y 209 Bi (n, 4 n) 206 Bi 22. 55 6. 243 d 9. 12 1. 2 min 115 In (n, 2 n) 114 In - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion Al Au Bi Co In Ta 4

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

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

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

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

Neutron sources - Motivation • Detection of neutrons • Evaluation • Corrections Beam-line Beam - Cross - section measurements Graphite stopper Samples - Neutron sources - Background subtraction Li-target - NPI Řež - TSL Uppsala - Comparison NPI, Uppsala - Conclusion Blue Hall, Uppsala Quasi-monoenergetic neutron source Neutron source on cyclotron U-120 M NPI ASCR Řež: Energy range 10 – 37 Me. V, neutron intensity ~ 108 n. cm-2. s-1 TSL Uppsala: Energy range 20 – 180 Me. V, neutron intensity ~ 105 n. cm-2. s-1 9

- Motivation • Detection of neutrons • Evaluation • Corrections Neutron spectra from p/Li source in NPI - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, Uppsala uncertainty in spectrum determination - 10% proton beams of energies 20, 25, 32. 5, 37 Me. V were used - Conclusion 10

Background subraction - Motivation • Detection of neutrons • Evaluation • Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion 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 11

TALYS 1. 0 – nuclear models - Motivation • Detection of neutrons • Evaluation • Corrections ld 1 - Fermi model ld 2 – backshifted Fermi model ld 3 - superfluid model ld 4 - Goriely table ld 5 - Hilairey table - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL models with different nuclear level density change the shape of crosssection dependency on neutron energy - Conclusion 12

TALYS 1. 0 – nuclear models - Motivation • Detection of neutrons • Evaluation • Corrections Difference between cross-sections models with different nuclear level density and default Fermi model, reaction 209 Bi(n, 3 n)207 Bi it is necessary to analyze influence of this faktor on determination of radioactive nuclei number in the future - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion 13

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

Experiments in NPI - Motivation • Detection of neutrons • Evaluation • Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL § four measurements in years 2008 -2009 § proton beam energies 20, 25 Me. V (August 2008), 32. 5 (April 2009) and 37 Me. V (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 - Conclusion 15

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

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

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

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

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

Conclusion - Motivation • Detection of neutrons • Evaluation • Corrections - Cross - section measurements - Neutron sources - Background subtraction - NPI Řež - TSL Uppsala - Comparison NPI, TSL - Conclusion § eleven cross-section measurements were performed in years 2008 -2010 § energy region from 17 Me. V to 94 Me. V 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 Me. V, where no data were available so far Thanks for attention 21