- Case Study
- Open Access
Measurement of neutron energy spectrum at the radial channel No. 4 of the Dalat reactor
- Pham Ngoc Son^{1}Email author and
- Vuong Huu Tan^{2}
Received: 7 September 2015
Accepted: 15 June 2016
Published: 24 June 2016
Abstract
Introduction
Several compositions of neutron filters have been installed at the channel No. 4 of the Dalat research reactor to produce quasi-monoenergetic neutron beams. However, this neutron facility has been proposed to enhance the quality of the experimental instruments, and to characterize the neutron spectrum parameters for new filtered neutron beams of 2 keV, 24 keV, 59 keV and 133 keV.
Case description
In order to meet the demand of neutron spectrum information for calculation and design of filtered neutron facilities at the Dalat nuclear research reactor (DNRR), the experimental determinations of neutron flux and energy spectrum, up to 8 MeV, has been performed at the inner entrance of the horizontal channel No. 4 from the core of DNRR. The Westcott neutron fluxes as well as the α-parameter that represents the deviation of epithermal neutron distribution from the 1/E law were measured by applying the cadmium ratio and the multi-foils activation methods. The fast neutron spectrum was measured based on the iterative adjustment procedure with threshold reactions.
Discussion and evaluation
A set of pure metal thin foils with the diameter of 1.27 cm and thickness of 0.125 mm were used as threshold detectors to measure the integrated fluxes, and a calculation procedure on iterative adjustment was implemented to derive the differential neutron energy spectrum from the integrated values.
Conclusions
The neutron fluxes and spectrum parameters were characterized with the measured values of 4.80 × 10^{9}, 1.98 × 10^{7}, 5.06 × 10^{8} cm^{−2} s^{−1} and 0.0448 for the thermal, epithermal, fast neutron fluxes and the α-shape factor, respectively. The present result has been significantly applied to the input data for the Monte Carlo simulations in the developments of filtered mono-energetic neutron beam facility at the institute.
Keywords
- Neutron spectrum
- Neutron flux
- Iterative adjusted spectrum
Introduction and background
The Dalat research reactor was originally a TRIGA MARK II reactor with a nominal power of 250 kW completed construction and reached the critical state in 1963. The reactor then has been upgraded to the nominal power of 500 kW since 1984. There are three radial and one tangential neutron beam ports at DRR, each of which penetrates the concrete shield structure and the reactor water to provide external beams of neutron originated from the reactor core. The horizontal channel No. 4 is one of the radial channels of the Dalat nuclear research reactor. Several compositions of neutron filters have been installed in the channel to produce quasi-monoenergetic neutron beams of 0.0253, 54 and 148 keV, with neutron fluxes of 1.7 × 10^{6}, 6.7 × 10^{5} and 3.9 × 10^{6} cm^{−2} s^{−1}, respectively. The filtered neutron beams have been applied for measurement of neutron capture cross section, and for development of a prompt gamma neutron activation analysis system (PGNAA) in recent years. However, this neutron facility has been proposed to be renovated in order to enhance the quality of the experimental instruments, and to characterize the neutron beams parameters for calibrations of neutron detectors and dosimeters. This work is also required for expanding the channel for new filtered neutron beams of 2, 24, 59 and 133 keV. In this progress, it is requested to measure precisely the neutron energy spectrum, at the inner beam port position of the radial channel No. 4, for optimal simulation and design of the neutron filter configurations and the radiation shielding structure. This work presents the experimental procedures and measured results as a case study of differential neutron energy spectrum determination at the radial channel No. 4 of the Dalat research reactor.
Conventional Westcott flux
The Eq. (3) is a 1st order linear equation of intercept nv_{0} and slope nv_{0}r(T/T_{0})^{1/2}. If two different flux monitors are irradiated under the same condition, a common intercept and slope can be determined from the resulting reaction rates.
Determination of α-factor in the E^{−(1+α)} epithermal neutron spectrum
Spectrum modification by interactive adjustments
Case study
The above-mentioned methods have been applied to measure the partial neutron energy spectra corresponding to the energy ranges of thermal, epithermal and fast neutrons. The experiments were performed at inner entrance position of the horizontal channel ‘No. 4’ of the Dalat research reactor. The partial spectra were matched to each other to obtain a full energy spectrum.
Thermal and epithermal neutron energy spectrum
Conventional Westcott fluxes
Nuclear data and parameters of Au and Co monitors
Monitor | σ_{0} (barns) | g | \(I_{0}^{\prime }\) (barns) | s _{0} | G _{ th } | G _{ epi } |
---|---|---|---|---|---|---|
Au | 98.70 | 1.005 | 1563.56 | 17.325 | 0.999 | 0.992 |
Co | 37.18 | 1.000 | 74.0 | 1.782 | 0.999 | 0.997 |
Experimental results of epithermal index and Westcott fluxes
nv _{0} (cm^{−2} s^{−1}) (%) | nv _{0} r(T/T _{0})^{1/2} (cm^{−2} s^{−1}) (%) | r(T/T _{0})^{1/2} (%) |
---|---|---|
4.80 × 10^{9} ± 3.5 | 1.98 × 10^{7} ± 3.5 | 0.00413 ± 3.5 |
Determination of the α-parameter
Nuclear data of resonance monitors used for the α-parameter measurement
Monitor | reaction | M | θ (%) | σ_{0} (barn) | I_{0} (barn) | \(\left\langle {{\text{E}}_{\text{r}} } \right\rangle\) (De Corte et al. 1981) (eV) | T_{1/2} | E_{γ} (keV) | γ (%) |
---|---|---|---|---|---|---|---|---|---|
Au | ^{197}Au(n, γ)^{198}Au | 196.97 | 100 | 98.7 | 1563.56 | 5.47 | 2.697 d | 411.8 | 95.53 |
In | ^{115}In(n, γ)^{116m}In | 114.82 | 95.7 | 164.3 | 2600 | 1.45 | 54.2 m | 416.9 | 30.0 |
Mn | ^{55}Mn(n, γ)^{56}Mn | 54.98 | 100 | 13.4 | 11.76 | 337.1 | 2.582 h | 847 | 99.99 |
Measured values of α-coefficient, Q(α), a and b
α | b | a | Q(α)_{ Au } | Q(α)_{ Mn } | Q(α)_{ In } |
---|---|---|---|---|---|
0.045 ± 0.001 | 2.211 ± 0.055 | −1.483 ± 0.037 | 14.54 ± 0.37 | 1.227 ± 0.031 | 16.48 ± 0.42 |
Measurement of the fast neutron energy spectrum
The experimental results of integral fluxes and reaction rates
Reaction | E_{eff} (MeV) | Integral flux (cm^{−2} s^{−1}) | σ_{eff} (barn) | Reaction rate/atom |
---|---|---|---|---|
^{238}U(n, f)^{140}La | 1.55 | 6.56E+09 | 0.35 | 2.09E−15 |
^{115}In(n, n′)^{115m}In | 1.65 | 5.98E+09 | 0.65 | 3.29E−16 |
^{58}Ni(n, p)^{58}Co | 3.45 | 5.06E+08 | 0.6 | 3.04E−16 |
^{47}Ti(n, p)^{47}Sc | 3.5 | 4.36E+08 | 0.13 | 5.66E−17 |
^{54}Fe(n, p)^{54}Mn | 3.75 | 9.57E+07 | 0.4 | 3.83E−17 |
^{56}Fe(n, p)^{56}Mn | 7.7 | 6.88E+07 | 0.13 | 8.95E−18 |
^{27}Al(n, a)^{24}Na | 8.15 | 1.43E+07 | 0.12 | 1.72E−18 |
^{48}Ti(n, p)^{48}Sc | 8.5 | 1.16E+07 | 0.065 | 7.57E−19 |
Conclusions
The differential neutron energy spectrum, at the inner entrance position of the radial channel No. 4 from the core of the Dalat nuclear research reactor, including the conventional Westcott fluxes, α-coefficient and fast neutron spectrum have been measured by the multi-foil activation method. The measured neutron energy spectrum show that, the thermal and epithermal neutron density fluxes are 4.80 × 10^{9} ± 0.072 and 1.98 × 10^{7} ± 0.031 cm^{−2} s^{−1}, respectively. The experimental value of α-coefficient is 0.0448 ± 0.001. The energy neutron spectrum up to 10^{7} eV has been obtained. The present results are proposed to be used as input information for optimal simulations and design of neutron facilities and radiation shielding, which are under developing at the radial beam port No. 4 of the Dalat research reactor. We are expected to obtain collimated neutron beams, after transferring through a combination of filter materials, with a pure thermal flux higher than 10^{6} cm^{−2} s^{−1}, or quasi-mono-energetic neutron flux of about 10^{5} cm^{−2} s^{−1} in keV energy region.
Declarations
Authors’ contributions
PNS carried out the research work and manuscript preparation; and VHT carried out the experimental data analysis and review the manuscript. Both authors read and approved the final manuscript.
Acknowledgements
This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under Grant No. “103.04-2012.59”.
Competing interests
Both authors declare that they have no competing interests.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Authors’ Affiliations
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