Pohang Experiment Pohang Neutron Facility (First Presentation of Prof. Cho ’ s Class) 09.09.2003

1. Pohang Experiment Pohang Neutron Facility (First Presentation of Prof. Cho’s Class) 09.09.2003 --------Hossain Ahmed--------

2. Introduction Purpose of Experiment Nuclear data are needed to support a number of areas of scientific fields like: 1.To design a nuclear reactor and for the evaluation of the neutron flux density and energy spectrum around a reactor. 2. Nuclear-oriented Study & Research, e.g. basic study of nuclei interaction with matter, nuclear structure, level density etc. 3. Nuclear Astrophysics --- Nuclear Energy Production in Stars --- Nucleosynthesis in Massive Stars --- Nucleosynthesis of Heavy Isotopes etc.

3. Introduction ………continued Purpose of entire samples In, Cu, Ti, W, Hf, Zr etc. • In the energy region 0.01 to 100eV: • a) some samples like Cu, Ti and Zr has no resonance but • b) In, W and Hf has resonance’s • So we use these two type of samples : • To check the method that we used to measure the total cross section is good or not with the evaluated data or other measured data • To know about 1/v or t/d spectrum which has an important role in the characterization of pulse neutron sources for TOF • To measure the time-of-flight path lengths by using the resonance energies of W

4. Introduction ………continued Theoretical Concept • In order to measure the total cross-sections the transmission method is used. i.e. • incident neutron flux: • -ejectile or transmitted neutron flux: 0  Sample Source 0  HV transmitted beam incident beam x L Transmission Method reflected beam

5. Introduction ………continued Transmittance T= / 0 where  = 0exp [-Nx] Where, N is the atomic density of the sample,  is the total cross-section and x is the thickness of the sample. From the above equations we get: The total cross-section: N = NA/M N = atom density (atom/cm3)  = density (g/cm3) NA= Avogadro’s number (6.022 * 1023 atoms/mole) M = gram atomic weight flux is cancel out!! • yi

6. TOF Channel to Energy conversion tn t0 t1 vi Neutron Detector L Where, l = flight of Neutron=10.84  0.01m Wc= channel width of TDC = 2s/channel,  = delay time=2.85s

7. Energy Resolution Energy Resolution dt composed of the uncertainties a) the flight path 0.01m, b) moderator thickness 0.03m, c) pulse width of the linac 1.5s and d) channel width of TDC 2 s . Energy Resolution in PNF Energy(eV) 10-1 100 101 102 Time t(s) 2478.37 783.73 247.83 78.37 0.61 0.86 2.09 6.52

8. Pohang Neutron Facility [PNF] 100-MeV electron Linac Energy: 65~70 MeV Beam Current:30mA (1.5s width) Repetition Rate: 10 Hz

9. A water-cooled Ta(Tantalum) target with water moderator Ta161(,n)Ta160 10 Ta Plates - 3 (40 mmx 2mm t) - 2 (40 mmx 3mm t) - 1 (40 mmx 4mm t) - 4 (40 mmx 6mm t) with 2 mm t Ti cover • The number of collision : n = 1/ ln E0/E/ • = 1+ (A-1)2/2A ln (A-1)/(A+1) or • = 2/A+2/3 for A>10 Water level is fixed to 3cm above the target surface

10. Time-of-flight Path Install Automatic Sample Changer

11. Data Acquisition System

12. n- separation

13. Samples + TOF spectrum Time(hours) Sample/no sample Sample Size Atomic Mass,u Abundance natural 30.02/30.02 Natural Ti 100*100*0.5mm3 47.867 Natural W 100*100*0.2mm3 183.85 natural 25.2/25.2 Ti time-of-flight spectrum W time-of-flight spectrum

14. Samples + TOF spectrum Time(hours) Sample/no sample Sample Size Atomic Mass,u Abundance natural 30.02/30.02 Natural Ti 100*100*0.5mm3 47.867 Natural W 100*100*0.2mm3 183.85 natural 25.2/25.2 Ti time-of-flight spectrum W time-of-flight spectrum

15. Data Processing Background Estimation Ti time-of-flight spectrum W time-of-flight spectrum

16. Data Processing ………continued Measurement of time-of-flight path length Neutron TOF spectra for W sample

17. Data Processing ………continued Measurement of time-of-flight path length Isotope Resonance Energy[eV] Channel Number 4.15 W182 194  2 143  3 W183 7.6 92  2 18.8 W186 27.03 77  3 W183 46.26 59  3 W183 and

18. Data Processing ………continued Measurement of time-of-flight path length A fit of the flight path length to a resonance

19. Data Processing ………continued PNF Flux Estimated PNF neutron flux

20. Measurement of Total Cross Sections  = 1/Nx sqrt(1/1+ 1/ 2) Calculation of N N =  * x * An / A [a.m.u] Samples  [gm/cm3 ] x [cm] An A[a.m.u] N / cm2 Natural Ti 4.5 0.05 6.023*1023 47.867 2.83*1021 19.3 6.023*1023 Natural W 0.02 183.85 1.26*1021

21. Result Total Cross Section of Ti

22. Result Total Cross Section of W

23. Discussion • The total cross-sections were measured for Ti and W. • The measured total cross-sections were compared with the evaluated ones from ENDF/B-VI and some other published data. • We have a good agreement between measured and evaluated data. • In some energy regions the statistics should be more.