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Neutron spectroscopy by time of flight method and determination of neutron beam

Neutron spectroscopy by time of flight method and determination of neutron beam. Prepared by : Sameh Hassan , Yomna Abd El-Moaty Supervisors: L Pikelner, V.Shvetsov FLNP, Dubna. Motivation.

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Neutron spectroscopy by time of flight method and determination of neutron beam

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  1. Neutron spectroscopy by time of flight method and determination of neutron beam Prepared by: Sameh Hassan , Yomna Abd El-Moaty Supervisors: L Pikelner, V.Shvetsov FLNP, Dubna Summer Student Practice, 2009, JINR Dubna

  2. Motivation - Studying the processes of the interaction of slow neutrons with nuclei ( 1- 105 ev) -Radioactive capture with gamma emission is the most common type of reaction at certain energies for slow neutrons. This (n,) reaction often results in product nuclei which are radioactive. For example: So it is a method of studying dependence of neutron cross-section on its energy.

  3. Targets and methods For example to study total neutron cross-sections of tungsten (W) The time-of-flight (TOF) method is used to measure the transmission of the sample

  4. The neutron Time of Flight (TOF) spectrum Fig.1 ) The neutron TOF spectrum for sample-in and open beam along with background level of W sample

  5. Spectrum processing The total neutron cross-section is determined by measuring the transmission of neutrons through the samples. Thus the neutron total cross-section is related to the neutron transmission rate T(E) as follows: N is the atomic density per cm2in the sample. N and N0are the foreground counts for the sample in (sample beam) and out (open beam), BGS and BGO are the background counts for sample in and out respectively. The atomic density N in the sample can be calculated from the formula

  6. By inserting the values of N and transmissions from the fig.1 we measured the total cross-sections of the entire samples depending on neutron energies. • The measured cross-sections are compared with the evaluated ones from ENDF/B-VI and some other published data

  7. Detection system Our detection system for Ɣ rays emitted during neutron capture is liquid scintillation detector consists of six photo multiplier tubes surrounding the sample

  8. Scintillation detector

  9. L ∆L Sample Source Flight path L, m Detector Collimator Transmission measurements dt ∆E= 2.77. 10 -2∆t(μs) E3/2 L(μs) ∆E= 2∆t∆E = 2∆L E t E L

  10. nσ0Г/Δ

  11. Breit-Wigner formula for cross section capture Capture cross section :total resonance width :width of neutron resonance :energy at the center of the resonance

  12. Application of neutron cross section 1) Finding the neutron flux at certain energy 2) Determine resonance parameter ГƔ,Гn

  13. Experiment • Sample :Ta181 n = 1.5*1021 nuclei /cm2 • Time of irradiation:360 min • curve

  14. Results

  15. Measured flux

  16. Conclusion • This method is good in measuring flux as we get almost the same fraction in our three resonances • The relation between the energy and flux is inversely proportional • Resonances are corresponding to the energy states in our sample

  17. thanks

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