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Photoneutrons from a beryllium reflector: a potential source of problems with Zr-Au flux monitors in k 0 standardization based neutron activation analysis.

Koster-Ammerlaan MJ, Bode P, Winkelman AJ - J Radioanal Nucl Chem (2011)

Bottom Line: The Monte Carlo calculations indicate a distortion of the 1/E (1+α) relationship at the higher energy edge of the epithermal neutron spectrum.This distortion is attributed to the formation and thermalisation of both photoneutrons and (n, 2n) produced fast neutrons in the beryllium, and has a direct impact on the resonance activation of (95)Zr, other than represented by the 1/E (1+α) function.The obtained relationship between neutron flux and neutron energy was also used for estimating the f-value and compared with the value obtained by the Delft Cr-Mo-Au flux monitor.

View Article: PubMed Central - PubMed

Affiliation: Reactor Institute Delft, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands.

ABSTRACT

The assumption that the shape of the epithermal neutron spectrum can be described, in any research reactor, by the 1/E (1+α) function is a fundamental starting point of the k 0 standardization. This assumption may be questioned from a reactor physics viewpoint. The type of moderator, the existence of neutron reflectors, the additional production of (γ, n) neutrons and resonance capture by construction materials may be different for each reactor, with consequences for the shape of the neutron spectrum. This dependency may explain that various practitioners reported contradicting experiences with the use of Zr-Au flux monitors for the determination of the α-parameter. An objective view on the influence of the design of the reactor and irradiation facility on the shape of the neutron spectrum can be obtained by modeling. This has been applied in the Reactor Institute Delft for reactor configurations in which the irradiation facilities face the fuel elements with the presence of beryllium reflector elements. The Monte Carlo calculations indicate a distortion of the 1/E (1+α) relationship at the higher energy edge of the epithermal neutron spectrum. This distortion is attributed to the formation and thermalisation of both photoneutrons and (n, 2n) produced fast neutrons in the beryllium, and has a direct impact on the resonance activation of (95)Zr, other than represented by the 1/E (1+α) function. The obtained relationship between neutron flux and neutron energy was also used for estimating the f-value and compared with the value obtained by the Delft Cr-Mo-Au flux monitor.

No MeSH data available.


Related in: MedlinePlus

Modeled neutron spectra of the pneumatic tube, the reflector and in-core irradiation facilities. The energy of the neutrons is plotted as a function of lethargy
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Fig2: Modeled neutron spectra of the pneumatic tube, the reflector and in-core irradiation facilities. The energy of the neutrons is plotted as a function of lethargy

Mentions: The neutron flux and the neutron spectrum parameters f and α determined by modeling and measurement were in very good agreement, as already presented in the 5th k0-users workshop [11] (Belo Horizonte, Brazil, 13–17 September 2009). The output of the modeling is shown in Fig. 2. The energy of the neutrons is plotted as a function of lethargy. In the lethargy presentation the 1/E-relationship changes into a horizontal line and the deviations described by α can be schematically represented as shown in Fig. 3.Fig. 2


Photoneutrons from a beryllium reflector: a potential source of problems with Zr-Au flux monitors in k 0 standardization based neutron activation analysis.

Koster-Ammerlaan MJ, Bode P, Winkelman AJ - J Radioanal Nucl Chem (2011)

Modeled neutron spectra of the pneumatic tube, the reflector and in-core irradiation facilities. The energy of the neutrons is plotted as a function of lethargy
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4514619&req=5

Fig2: Modeled neutron spectra of the pneumatic tube, the reflector and in-core irradiation facilities. The energy of the neutrons is plotted as a function of lethargy
Mentions: The neutron flux and the neutron spectrum parameters f and α determined by modeling and measurement were in very good agreement, as already presented in the 5th k0-users workshop [11] (Belo Horizonte, Brazil, 13–17 September 2009). The output of the modeling is shown in Fig. 2. The energy of the neutrons is plotted as a function of lethargy. In the lethargy presentation the 1/E-relationship changes into a horizontal line and the deviations described by α can be schematically represented as shown in Fig. 3.Fig. 2

Bottom Line: The Monte Carlo calculations indicate a distortion of the 1/E (1+α) relationship at the higher energy edge of the epithermal neutron spectrum.This distortion is attributed to the formation and thermalisation of both photoneutrons and (n, 2n) produced fast neutrons in the beryllium, and has a direct impact on the resonance activation of (95)Zr, other than represented by the 1/E (1+α) function.The obtained relationship between neutron flux and neutron energy was also used for estimating the f-value and compared with the value obtained by the Delft Cr-Mo-Au flux monitor.

View Article: PubMed Central - PubMed

Affiliation: Reactor Institute Delft, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands.

ABSTRACT

The assumption that the shape of the epithermal neutron spectrum can be described, in any research reactor, by the 1/E (1+α) function is a fundamental starting point of the k 0 standardization. This assumption may be questioned from a reactor physics viewpoint. The type of moderator, the existence of neutron reflectors, the additional production of (γ, n) neutrons and resonance capture by construction materials may be different for each reactor, with consequences for the shape of the neutron spectrum. This dependency may explain that various practitioners reported contradicting experiences with the use of Zr-Au flux monitors for the determination of the α-parameter. An objective view on the influence of the design of the reactor and irradiation facility on the shape of the neutron spectrum can be obtained by modeling. This has been applied in the Reactor Institute Delft for reactor configurations in which the irradiation facilities face the fuel elements with the presence of beryllium reflector elements. The Monte Carlo calculations indicate a distortion of the 1/E (1+α) relationship at the higher energy edge of the epithermal neutron spectrum. This distortion is attributed to the formation and thermalisation of both photoneutrons and (n, 2n) produced fast neutrons in the beryllium, and has a direct impact on the resonance activation of (95)Zr, other than represented by the 1/E (1+α) function. The obtained relationship between neutron flux and neutron energy was also used for estimating the f-value and compared with the value obtained by the Delft Cr-Mo-Au flux monitor.

No MeSH data available.


Related in: MedlinePlus