Neutron Spectrometry
Jiří Cvachovec


Motivation
}Neutron spectral flux density – “neutron spectrum” – “what energies are present and what is their
proportion”
}Applications:
}verification of functionality of nuclear reactors
}estimation of pressure vessel damage
}radiation protection
}radiotherapy
}estimation of biological effects
}nuclear weapons (mainly in the past)
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Scintillation Detector



Block Scheme
block_di.EMF


Neutron-Gamma Separation
dspektr.PNG


The Unfolding Problem
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}j(En) neutron energetic spectrum (this is what we want to measure)
}z(Ep, En) detector response function (obtained by Monte Carlo simulation)
}Z(Ep) measured proton spectrum (detector output)

Maximum Likelihood Estimation
}Discrete form:
}Assumption: neutron and proton spectra are random vectors with mutually independent,
Poisson-distributed components
}Likelihood function for f:
where
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}
}Algorithm:

Mathematica Code



Detector Response Function
}Obtained by Monte Carlo simulation
}The interaction of the neutron with the detector is modeled.
}What must be taken into account:
}detector geometry (cylinder)
}chemical composition (C, H, O, B, ...)
}different kinds of interactions (elastic and inelastic scattering, capture)
}library data (describe stochastic properties of interactions)
}user settings (energetic step, desired output format, etc.)

Sample Response Matrix
matice_1.png


Verification of Results
Neutron line 13.9 MeV (stilbene F=1cm, H=1cm, coaxial impact)
Measured and calculated response En=5 MeV, perpendicular impact
Neutron spectrum from spontaneous fission of a 252Cf source
Neutron spectrum from a 239Pu-Be source

Further Work
}In frame of TA ČR no. TA01011383
}replace analog part with digital equipment
}develop software for controlling and processing
}improve current methods
}incorporate new detectors
}My main responsibility: software part
}neutron-gamma discrimination
}lead software development (evaluation procedures and response functions)
}increase level of automation
}improve propagation of uncertainties

Publications
}Determination of AKR-2 beam and verification at iron and water arrangements
Košťál, Michal - Cvachovec, František - Cvachovec, Jiří - Ošmera, Bohumil - Hansen, Wolfgang.
Annals of Nuclear Energy, Volume 38, Issue 1, 8 s. ISSN 0306-4549. 2011.
}Maximum Likelihood Estimation of a Neutron Spectrum and Associated Uncertainties
Cvachovec, Jiří - Cvachovec, František. Advances in Military Technology, Brno : Univerzita obrany,
Vol. 3, No. 2, 14 s. ISSN 1802-2308. 2008.
}Neutron Response Function for BC-523A Scintillation Detector in the Energy Range 0.5 to 20 MeV
Cvachovec, Jiří - Cvachovec, František - Pošta, Severin - Ošmera, Bohumil. Journal of ASTM
International, Vol. 5, No. 5, 4 s. ISSN 1546-962X. 2008.
}Výpočet funkce odezvy pro detektory s dopovanými scintilátory (II)
Cvachovec, Jiří - Cvachovec, František - Pošta, Severin - Ošmera, Bohumil. ÚJV Řež, 2004.
12107-R,D.
}Multiparameter multichannel analyser system for characterisation of mixed neutron-gamma field in
the experimental reactor LR-0
Bureš, Zbyněk - Cvachovec, Jiří - Cvachovec, František - Čeleda, Pavel - Ošmera, Bohumil. In
Reactor Dosimetry in the 21st Century: Proceedings of the 11th International Symposium on Reactor
Dosimetry Brussels, Belgium 18 - 23 August 2002. Brussels : World Scientific Publishing Company,
2003. od s. 194-201, 8 s. ISBN 9812384480.
}Anisotropy of light output in response function of stilbene detectors
Cvachovec, F. - Cvachovec, J. - Tajovský, P. Nuclear Instruments & Methods in Physics Research A,
Elsevier Science Publishers, 476, 1-2, od s. 200-202. ISSN 0168-9002. 2002.

Q & A
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