Cross-section section measurements of neutron threshold reactions in various materials

Transcription

1 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 section of neutron threshold reactions in various materials GAMMA-1, Novi Sad, J. Vrzalová, O. Svoboda, A. Kugler, M. Suchopár, V. Wagner

2 Introduction As members of international collaboration Energy and Transmutation of radioactive Waste we routinely use (n,xn) threshold reactions in various materials to measure high energy neutron flux from spallation reactions. The cross-sections of many reactions important for our activation detectors are missing. To improve situation, we studied the neutron cross-sections using different quasimonoenergetic neutron sources based on proton reaction on 7 Li target. 2

3 Outline Motivation Cross-section Neutron sources in NPI and TSL Background Experiments on Cyclotron in Řež TSL Uppsala experiments Comparison Conclusion 3

4 Motivation measurement of spatial distribution of is important part of studies of spallation based experiments Solving a Fredholm equation we can find Φ(E): E beam N = Φ ( yield E) σ ( E) de E thresh evaluated from the experiment we would like to find! the activation detectors are very useful tool for neutron field determination in this case threshold reactions on Au, Al, Bi, In, Ta, Co, Y poor knowledge, we want to measure 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 4

5 Detection of -Motivation Reaction 197 Au (n,2n) 196 Au 197 Au (n,3n) 195 Au 197 Au (n,4n) 194 Au E thresh [MeV] Half-life d d h 209 Bi (n,3n) 207 Bi y 209 Bi (n,4n) 206 Bi 115 In (n,2n) 114 In d 1.2 min Al Au Bi Co In Ta 5

6 Evaluation process Cross-section [barn] Bi(n,4n) 206 Bi EXFOR TALYS NPI Řež TSL Uppsala BACKGROUND SUBTRACTION Energy [MeV] 6

7 Spectroscopic corrections Self-absorption Detector efficiency Real γ-γ cascade coincidences 7

8 Spectroscopic corrections non-point like emitters Square-emitter correction [-] 1,00 0,98 0,96 0,94 0,92 0,90 0,88 decay during cooling decay during irradiation unstable irradiation detector dead time Distance from sample to detector [cm] 1.25x1.25 cm 2x2 cm 2.5x2.5 cm 3x3 cm iodine 3cm round 8

9 Evaluation - total yield Peak area Self-absorption correction Beam correction Dead time correction Decayduringcooling and measurement N yield γ line intensity S C ( E) B 0 t 1 e λ t ( λ t ) p abs a real irr = ( λ t ) ( λ Iγ ε P ( E) Coi C area tlive m foil 1 e 1 e Detector efficiency Correction for coincidences Square-emitter correction Weight normalization real t irr ) Decay during irradiation 9

10 Cross-section section Requirements for σ- by activation method: high energy neutron source with good intensity monoenergetic (quasi-monoenergetic) or well known spectrum pure monoisotopic samples good spectroscopic equipment γ and X-rays detectors Then we can calculate N yield and finally : Evaluation process: σ = N yield N n Number of in peak foil size S A N relative mass Irradiation HPGe Deimos Yield Corrections Cross-section A Avogadro s number 10

11 Neutron sources Beam-line Li-target Graphite stopper Samples NPI, Uppsala Neutron source on cyclotron U-120M Blue Hall, Uppsala Quasi-monoenergetic neutron source NPI ASCR Řež: Energy range MeV, neutron intensity ~ 10 8 n.cm -2.s -1 TSL Uppsala: Energy range MeV, neutron intensity ~ 10 5 n.cm -2. s -1 11

12 Neutron spectra from p/li source in NPI Number of (1/sr MeV C) 1.2E E E E E E+14 E=25 MeV E=20 MeV E=32.5 MeV E=37 MeV NPI, Uppsala 0.0E Neutron energy [MeV] uncertainty in spectrum determination - 10% proton beams of energies 20, 25, 32.5, 37 MeV were used 12

13 Neutron spectra - TSL NPI, Uppsala Neutron flux [1/MeV (peak area=1)] Neutron energy [MeV] E Neutron spectra comparison 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 Neutron flux density [1/(cm2.s)] 1E E E Neutron spectra for energies 25, 50 and 94 MeV spallation source at JINR quasi-monoenergetic source at TSL 13 1E0 1E E E E E E Neutron Energy [MeV]

14 Background 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 14

15 TALYS 1.0 nuclear models XS [barn] 2 1,8 1,6 1,4 1,2 1 0,8 Bi-207 ld1 - Fermi model ld2 backshifted Fermi model ld3 - superfluid model ld4 - Goriely table ld5 - Hilairey table 0,6 0,4 0,2 ld1 ld2 ld3 ld4 ld5 EXFOR MENDL E [MeV] models with different nuclear level density change the shape of crosssection dependency on neutron energy 15

16 TALYS 1.0 nuclear models 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 D e via tio n [-] Fermi model backshifted Fermi model superfluid model Goriely table Hilairey table Bi Energy [MeV] 16

17 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 - will be analyzed in more details 17

18 Experiments in NPI five in years 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 Y and Au samples were irradiated this year 18

19 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 19

20 NPI and TSL results Comparison of cross-section reaction (n,2n) 197 Au with EXFOR and TALYS Cross-section [barn] Au(n,2n) 196 Au EXFOR TALYS NPI Řež TSL Uppsala Energy [MeV] 20

21 NPI and TSL results Comparison of cross-section reaction (n,4n) 194 Au with EXFOR and TALYS Cross-section [barn] Au(n,4n) 194 Au Energy [MeV] EXFOR TALYS NPI Řež TSL Uppsala 21

22 NPI and TSL results Comparison of cross-section reaction (n,6n) 192 Au with EXFOR and TALYS Au(n,6n) 192 TALYS Au TSL Uppsala 0.6 Cross section [barn] Energy [MeV] 22

23 NPI and TSL results Comparison of cross-section reaction (n,4n) 206 Bi with EXFOR and TALYS Cross-section [barn] Bi(n,4n) 206 Bi EXFOR TALYS NPI Řež TSL Uppsala Energy [MeV] 23

24 Conclusion twelve cross-section were performed in years energy region from 17 MeV to 94 MeV was covered we studied various materials in the form of thin foils and observed good agreement with the data in EXFOR database and also with the calculations preformed in deterministic code TALYS. in NPI and TSL are now completely processed and were published at scientific workshop EFNUDAT Slow and Resonance in 2009 in Budapest, at International Conference on Nuclear Data for Science and Technology in April 2010 in South Korea, at scientific workshop NEMEA-6 in October 2010 in Poland and at international workshop CNR*11 in September 2011 in Prague. Some of our results are already included in EFXOR 24

25 Thank you! This work was supported by the EFNUDAT program Sources in NPI and TSL are included in program ERINDA supervisor: RNDr. Vladimír Wagner, CSc. 25