A method was proposed for measuring macroscopic absorption and scattering cross-sections for thermal neutrons. It is based on a Pu-Be neutron source and He-3 neutron detectors assembly. Beams of neutrons were obtained from the source imbedded in a water tank. Incident neutron beams were above and below Cd cut-off energy. Standard solid and liquid samples characterized with different absorption and scattering cross-sections were prepared. The He-3 detectors oriented inside the sample and at 180 degree , 90 degree and 0degree with respect to the incident neutron beams were used to register neutrons after interaction with samples. A semi-imperial model describing the detector responses as a function of effective macroscopic cross sections was proposed and successfully fitted the results.
Dear A. Elabd,
It is an interesting question.
I have also been using a similar type of neutron source (Am/Be neutron source) for measuring reaction cross section. However, for detecting the activity I use HPGe detector. By the way, as you said your incident neutron energy range is +-0.5eV (Cd Cutoff) you may consider 1/v detector.
Dear Rumman Zaman ,
What you are measuring are reaction cross sections. I assume you measure capture cross section ( for thermal neutrons ) and resonance integral ( for epithermal neutrons). The capture cross sections among others types of cross sections are lambed by the so-called macroscopic absorption cross section. Is not it?
Yes you are right. But we also unfolded the fast neutron spectrum of this neutron source . (0.5-11MeV) @ A Elabd
Ok.
You measure fast neutron cross section . I think you will need much time to irradiate you sample (in case of the activity of the source is small). Additionally, activation foils with different threshold energies are required .
I have a paper but for measuring average flux of fission neutrons ( for reactor) . I did not get spectrum from data .
1- A. El Abd. Measurement of the fission neutron spectrum average cross sections for the 95Mo (n, p) 95Nb, 92Mo (n,a) 89Zr, 90Zr (n, 2n) 89Zr and 60Ni (n, p)60Co reactions.Applied Radiations and Isotopes, Vol. 68 (10), pp. 2007-2012, 2010.
What is the code do you use to get the spectrum of the Am-Be source from your results?
Well,
I need long irradiation for those reactions whose cross sections are very small.(mb) But for the reactions having high cross section(b) we dont need to irradiate for a long time. And yes definitely activation foils like Nickel, Zinc, Molybdenum, Ti, Au, In etc of different threshold energy are required to monitor the neutron flux.. However we used SULSA to unfold the fast neutron spectrum. Though SULSA demands manual input unlike TALYS/ STAPRE.
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