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

4. 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

5. 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

6. TOF Channel to Energy conversiontn 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 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)
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
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. 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

14. 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

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

16. Measurement of time-of-flight path length
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
W186
18.8
27.03
W183
77  3
46.26
59  3
W183
and

18. 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

19. Data Processing ………continued Estimated PNF neutron flux
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
Natural W
19.3
0.02
6.023*1023
183.85
1.26*1021

21. Total Cross Section of Ti
Result
Total Cross Section of Ti

22. Total Cross Section of W
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.