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

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.

Purpose of entire samples In, Cu, Ti, W, Hf, Zr etc. 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

Theoretical Concept Introduction ………continued 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 incident beam transmitted beam x L Transmission Method reflected beam

N = NA/M N = atom density (atom/cm3) Introduction ………continued Transmittance T= / 0 where  = 0 exp [-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

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

Energy Resolution in PNF 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

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

A water-cooled Ta(Tantalum) target with water moderator 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

Time-of-flight Path Install Automatic Sample Changer

Data Acquisition System

n- separation

W time-of-flight spectrum Ti time-of-flight spectrum 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 W time-of-flight spectrum Ti time-of-flight spectrum

W time-of-flight spectrum Ti time-of-flight spectrum 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 W time-of-flight spectrum Ti time-of-flight spectrum

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

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

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 W186 18.8 27.03 W183 77  3 46.26 59  3 W183 and

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

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

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 Natural W 19.3 0.02 6.023*1023 183.85 1.26*1021

Total Cross Section of Ti Result Total Cross Section of Ti

Total Cross Section of W Result Total Cross Section of W

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.