Epithermal Neutron Spectrum Shape Research Articles

Determination of effective resonance energies for the185Re(n,)186Re and187Re(n,)188Re reactions by cadmium ratio method

The effective resonance energy ($\bar{E}_{r})$ values for the $^{185}$Re(n,$\gamma )^{186}$Re and $^{187}$Re(n,$\gamma )^{188}$Re reactions were measured by using the cadmium ratio method. $^{197}$Au and $^{98}$Mo isotopes were selected as dual monitors to determine the epithermal neutron spectrum shape factor in the irradiation sites of a 37 GBq $^{241}$Am-Be neutron source. The analytical grade rhenium(VII) oxide samples were diluted with Al$_{2}$O$_{3}$ powder to reduce neutron self-shielding effects, and they were put into 1-mm thick small cylindrical polytetrafluoroethylene (PTFE) boxes. Samples were irradiated in a $^{241}$Am-Be neutron source. The activation produced in the irradiated samples was measured in close-counting geometry on the end cap of a Ge detector in order to obtain better counting statistics. The correction factors for gamma-ray self-absorption ($F_{s})$, thermal neutron self-shielding ($G_{th})$, and epithermal neutron self-shielding ($G_{epi})$ effects were determined with suitable approaches. Consequently, the experimental $\bar{E}_{r}$-values were measured to be 3.49 ± 0.54 eV for $^{185}$Re and 41.77 ± 6.79 eV for $^{187}$Re target nuclide, respectively. Furthermore, the $\bar{E}_{r}$-values were theoretically computed through up-to-date resonance data obtained from the ENDF/B VII library using two different approaches. Since there is no experimental data available in the literature for the $\bar{E}_{r}$-values of these isotopes, the results were compared with the theoretical values in the literature.

Thermal neutron capture cross-section and resonance integral measurements of 139La(n, $ \gamma$ γ )140La and 140Ce(n, $ \gamma$ γ )141Ce using a Am-Be neutron source

Thermal neutron capture cross-sections and resonance integrals of 139La(n,\( \gamma\))140La and 140Ce (n,\( \gamma\))141Ce are measured with respect to reference reactions 197Au(n,\( \gamma\))198Au and 55Mn(n,\( \gamma\))56Mn using the neutron activation technique. Measurements are carried out using neutrons from an Am-Be source located inside a concrete bunker. Two different methods are used for determining self-shielding factors of activation foils as well as for finding the epithermal neutron spectrum shape factor. For 139 La with reference to 197 Au and 55 Mn the measured thermal cross sections are \( 9.24 \pm 0.25\) b and \( 9.28 \pm 0.37\) b, respectively, while the measured resonance integrals are \( 12.18 \pm 0.67\) b and \( 11.81 \pm 0.94\) b, respectively. For 140 Ce with reference to 197 Au and 55 Mn the measured thermal cross sections are \( 0.44 \pm 0.01\) b and \( 0.44 \pm 0.02\) b, respectively, while the measured resonance integrals are \( 0.55 \pm 0.03\) b and \( 0.54 \pm 0.04\) b, respectively. The present measurements are compared with earlier measurements and evaluations. Presently estimated values confirm the established 139La(n,\( \gamma\))140La cross-sections. The presently measured thermal capture cross-section 140Ce(n,\( \gamma\))141Ce , though lower than the evaluated data, is having higher accuracy compared to previous measurements with large uncertainties. The resonance integral measured is higher (like most previous measurements) than most evaluations requiring a revision of the evaluated data.

Thermal neutron capture cross section and resonance integral of the 139La(n,γ)140La reaction

The thermal neutron capture cross section (σ0) and resonance integral cross section (I0) of the 139La(n,γ)140La reaction have been measured relative to that of the 197Au(n,γ)198Au reaction by means of the activation method. High-purity natural lanthanum and gold foils were exposed to pulsed neutrons at the Pohang neutron facility. One set of foils was irradiated directly and a second set of foils was shielded with a cadmium cover of 0.5mm thickness. The induced activities in the activated foils were measured by a γ-ray spectrometer based on a calibrated high purity germanium (HPGe) detector. In order to improve the accuracy of the experimental results the epithermal neutron spectrum shape factor (α) was determined, and the corrections for the thermal neutron self-shielding (Gth), the resonance neutron self-shielding (Gepi), the γ-ray attenuation (Fg) and the γ-ray coincidence summing effects were made. The thermal neutron cross-section for the 139La(n,γ)140La reaction has been determined to be 9.16±0.36 barn, relative to the reference value of 98.65±0.09 barn for the 197Au(n,γ)198Au reaction. By assuming the cadmium cut-off energy of 0.55eV, the resonance integral cross section for the 139La(n,γ)140La reaction is 11.64±0.69 barn, which is determined relative to the reference value of 1550±28 barn for the 197Au(n,γ)198Au reaction. The measured results are compared with literature values and discussed.

Characterization of Irradiation Sites of Apsara Reactor for $k_{0}$-Based IM-NAA and Its Validation and Application

Three irradiation positions of Apsara reactor were characterized by determining epithermal neutron spectrum shape factor <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$(\alpha)$</tex></formula> and sub-cadmium to epithermal neutron flux ratio <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(f)$</tex> </formula> for <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm k}_{0}$</tex> </formula> -based Internal Monostandard Neutron Activation Analysis (IM-NAA). The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\alpha$</tex></formula> values were determined by cadmium ratio method using six neutron flux monitors (In, Au, Co, Mo, Zn and Zr). The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f$</tex> </formula> -value was also determined by cadmium ratio method using an Au monitor. The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\alpha$</tex></formula> values of two irradiation positions are found to be positive, which indicated softened epithermal neutron spectra whereas <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\alpha$</tex> </formula> value of the third one is negative indicating hardened neutron spectrum. IAEA reference material, RM SL-1 (Lake Sediment) was analyzed by IM-NAA using experimentally determined <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$f$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\alpha$</tex></formula> values of all three irradiation positions. A total of 16 elemental concentrations were determined using Sc as the internal monostandard and the values are found to be in good agreement with respect to the certified or information values. As an application of IM-NAA, two ceramic archaeological samples along with one soil sample were analyzed using Sc as the monostandard.

Measurement of thermal neutron cross section and resonance integral for the 170Er(n, γ)171Er reaction by using a gold monitor

The thermal neutron cross section (σ0) and the resonance integral (I0) of the reaction 170Er(n,γ)171Er were measured by an activation method using a reaction 197Au(n,γ)198Au as a single comparator. The high-purity natural erbium (natEr) and gold (197Au) foils with and without Cd cover with the thickness of 0.5mm were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the activated foils were measured with a well calibrated coaxial HPGe detector. The thermal neutron cross section for the 170Er(n,γ)171Er reaction has been determined to be σ0=7.80±0.35 barn, relative to the reference value of 98.65±0.09 barn for the 197Au(n,γ)198Au reaction. By assuming the cadmium cut-off energy of 0.55eV, the resonance integral for the 170Er(n,γ)171Er reaction is I0=40.4±2.8 barn, which is determined relative to the reference value of 1550±28 barn for the 197Au(n,γ)198Au reaction. In order to improve the accuracy of the experimental results the epithermal neutron spectrum shape factor (α) was determined, and the necessary corrections for the counting loss caused by γ-ray attenuation (Fg), the thermal neutron shelf-shielding (Gth), the resonance neutron self-shielding (Gepi) effects, the γ-ray coincidence summing effect, as well as neutron flux fluctuation. The present results are compared with the reference data and discussed.

Measurement of thermal neutron cross-section and resonance integral for the 165Ho(n,γ) 166gHo reaction using electron linac-based neutron source

The thermal neutron cross-section and the resonance integral of the 165Ho(n,γ) 166gHo reaction have been measured by the activation method using a 197Au(n,γ) 198Au monitor reaction as a single comparator. The high-purity natural Ho and Au foils with and without a cadmium shield case of 0.5 mm thickness were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the activated foils were measured with a calibrated p-type high-purity Ge detector. The correction factors for the γ-ray attenuation ( F g), the thermal neutron self-shielding ( G th), the resonance neutron self-shielding ( G epi) effects, and the epithermal neutron spectrum shape factor ( α) were taken into account. The thermal neutron cross-section for the 165Ho(n,γ) 166gHo reaction has been determined to be 59.7 ± 2.5 barn, relative to the reference value of 98.65 ± 0.09 barn for the 197Au(n,γ) 198Au reaction. By assuming the cadmium cut-off energy of 0.55 eV, the resonance integral for the 165Ho(n,γ) 166gHo reaction is 671 ± 47 barn, which is determined relative to the reference value of 1550 ± 28 barn for the 197Au(n,γ) 198Au reaction. The present results are, in general, good agreement with most of the previously reported data within uncertainty limits.

Experimental evaluation of neutron performance in boron-doped low activation concrete

Reaction rate distribution in concrete with/without boron dopant up to a thickness of 60 cm was measured using Yayoi fast reactor located at University of Tokyo. The 7 reaction rates such as (197)Au(n,gamma), (59)Co(n,gamma), (115)In(n,n'), (55)Mn(n,gamma), (23)Na(n,gamma), (94)Zr(n,gamma) and (96)Zr(n,gamma) were measured at 12 different depths, and the reduction of the reaction rate as a result of boron doping was quantitatively analysed. These reaction rates were also used to determine epithermal neutron spectrum shape parameter. Monte Carlo simulations of the experimental setup were performed using the MCNP-5 code. Simulated depth profiles of reaction rates and the epithermal neutron spectrum shape parameter agreed with the experimental results with fair accuracy. This experimental results provide useful data to benchmark the accuracy of neutron transport codes in the prediction of transmission and neutron spectrum distortion in boron-doped concrete.

Thermal neutron cross-section and resonance integral of the 98Mo(n,γ) 99Mo reaction

We measured the thermal neutron cross-section and the resonance integral of the 98Mo(n,γ) 99 Mo reaction by the activation method using a 197Au(n,γ) 198 Au monitor reaction as a single comparator. The high-purity natural Mo and Au metallic foils with and without a cadmium shield case of 0.5 mm thickness were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the activated foils were measured with a calibrated p-type high-purity Ge detector. The necessary correction factors for the γ-ray attenuation ( F g), the thermal neutron self-shielding ( G th) and the resonance neutron self-shielding ( G epi) effects, and the epithermal neutron spectrum shape factor ( α) were taken into account. In addition, for the 99Mo activity measurements, the correction for true coincidence summing effects was also taken into account. The thermal neutron cross-section for the 98Mo(n,γ) 99Mo reaction has been determined to be 0.136 ± 0.007 barn, relative to the reference value of 98.65 ± 0.09 barn for the 197Au(n,γ) 198 Au reaction. The present result is, in general, in good agreement with most of the experimental data and the recently evaluated values of ENDF/B-VII.0, JENDL-3.3, and JEF-2.2 by 5.1% (1 σ). By assuming the cadmium cut-off energy of 0.55 eV, the resonance integral for the 98Mo(n,γ) 99Mo reaction is 7.02 ± 0.62 barn, which is determined relative to the reference values of 1550 ± 28 barn for the 197Au(n,γ) 198Au reaction. The present resonance integral value is in general good agreement with the previously reported data by 8.8% (1 σ).

Measurement of thermal neutron cross-section and resonance integral for the 174Yb(n,γ)175Yb reaction by the cadmium ratio method

The thermal-neutron cross-section and the resonance integral for the 174Yb(n,γ)175Yb reaction were measured by the activation method using a 55Mn monitor as single comparator. Analytical grade MnO2 and Yb2O3 powder samples with and without a cylindrical 1mm Cd shield box were irradiated in an isotropic neutron field obtained from three 241Am–Be neutron sources. The gamma-ray spectra from the activated samples were measured with a calibrated n-type high-purity Ge detector. The experimental results were corrected for the correction factors calculated for thermal and epithermal neutron self-shielding effects, epithermal neutron spectrum shape and gamma-ray self attenuation. Thus, the thermal neutron cross-section for the 174Yb(n,γ)175Yb reaction is found to be 126.5±6.6b, relative to that of the 55Mn monitor. The resonance integral value for the 174Yb(n,γ)175Yb reaction is found to be 59.6±8.5b, at cadmium cut-off energy of a 0.55eV. Using the measured cadmium ratios of 55Mn and 174Yb, the result for resonance integral of the 174Yb(n,γ)175Yb reaction has also been obtained relative to the reference value of the 55Mn monitor. The present results for the 174Yb(n,γ)175Yb reaction agree well only with the recent experimental ones obtained by Kafala et al. [1] and De Corte and Simonits [2] within uncertainty limits. However, the previously reported experimental data for the thermal neutron cross-section for this reaction are distributed between 24 and 141b, and similarly the experimental values for the resonance integral value also show a large scatter in the range of 30–69b.

Thermal neutron cross-section and resonance integral of the 186W(n, γ)187W reaction

We measured the thermal neutron cross-section and the resonance integral of the reaction 186W(n,γ)187W by the activation method using a 197Au(n,γ)198Au monitor reaction as single comparator. The high-purity natural W and Au metallic foils with and without a cadmium shield case of 0.5mm thickness were irradiated in a neutron field of the Pohang neutron facility. The induced activities in the samples were measured by high-resolution γ-ray spectrometry with a calibrated p-type high-purity Ge detector. The necessary correction factors for γ-ray attenuation (Fg), thermal neutron self-shielding (Gth), and resonance neutron self-shielding (Gepi) effects, and the epithermal neutron spectrum shape factor (α) were taken into account. The thermal neutron cross-section for the 186W(n,γ)187W reaction has been determined to be 37.2±2.1barn, relative to the reference value of 98.65±0.09barn for the 197Au(n,γ)198Au reaction. The present result is, in general, in good agreement with most of the experimental data and the recently evaluated value of ENDF/B-VII.0 by 5.7%. By assuming the cadmium cut-off energy of 0.55eV, the resonance integral obtained is 461±39barn, which is determined relative to the reference values of 1550±28barn for the 197Au(n,γ)198Au reaction. The present resonance integral value is in general good agreement with the recently measured values by 9%. The present result is lower than the evaluated ones by 10–13%.

Measurement of thermal neutron cross section and resonance integral for theEr170(n,γ)Er171reaction by using aMn55monitor

The thermal neutron cross section and the resonance integral of the reaction $^{170}\mathrm{Er}$($n,\ensuremath{\gamma}$)$^{171}\mathrm{Er}$ were measured by the Cd-ratio method using a $^{55}\mathrm{Mn}$ monitor as single comparator. Analytical grade ${\mathrm{MnO}}_{2}$ and ${\mathrm{Er}}_{2}{\mathrm{O}}_{3}$ powder samples with and without a cylindrical 1 mm Cd shield box were irradiated in an isotropic neutron field obtained from three $^{241}\mathrm{Am}$-Be neutron sources. The induced activities in the samples were measured with a 120.8% relative efficiency $p$-type HPGe detector. The correction factors for gamma-ray attenuation (${F}_{g}$), thermal neutron self-shielding (${G}_{\mathit{th}}$), and resonance neutron self-shielding (${G}_{\mathit{epi}}$) effects, and the epithermal neutron spectrum shape factor ($\ensuremath{\alpha}$) were taken into account. The thermal neutron cross section for the ($n,\ensuremath{\gamma}$) reaction in $^{170}\mathrm{Er}$ has been determined to be 8.00 \ifmmode\pm\else\textpm\fi{} 0.56 b, relative to that of the $^{55}\mathrm{Mn}$ monitor. However, some previously reported experimental results compared to the present result show a large discrepancy ranging from 8.3 to 86%. The present result is, in general, in good agreement with the recently measured values by 9%. According to the definition of Cd cut-off energy at 0.55 eV, the resonance integral obtained is 44.5 \ifmmode\pm\else\textpm\fi{} 4.0 b, which is determined relative to the reference integral value of the $^{55}\mathrm{Mn}$ monitor by using cadmium ratios. The existing experimental data for the resonance integral are distributed between 18 and 43 b. The present resonance integral value agrees only with the measurement of 43 \ifmmode\pm\else\textpm\fi{} 5 b by Gillette [Thermal Cross Section and Resonance Integral Studies, ORNL-4155, 15 (1967)] within uncertainty limits.

Measurement of thermal neutron cross section and resonance integral for (n,γ) reaction in 152Sm

Abstract This study implies that 55Mn(n,γ)55Mn monitor reaction may be a convenient alternative comparator for the activation method and thus, it was used for the determination of thermal neutron cross section (TNX) and the resonance integral (RI) of the reaction 152Sm(n,γ)153Sm. The samples of MnO2 and Sm2O3 diluted with Al2O3 powder were irradiated within and without a cylindrical 1 mm-Cd shield case in an isotropic neutron field obtained from the 241Am–Be neutron sources. The γ-ray spectra from the irradiated samples were measured by high resolution γ-ray spectrometry with a calibrated n-type Ge detector. The correction factors for γ-ray attenuation, thermal neutron and resonance neutron self-shielding effects and epithermal neutron spectrum shape factor (α) were taken into account in the determinations. The thermal neutron cross section for 152Sm(n,γ)153Sm reaction has been determined to be 204.8 ± 7.9 b at 0.025 eV. This result has been obtained relative to the reference thermal neutron cross section value of 13.3 ± 0.1 b for the 55Mn(n,γ)56Mn reaction. For the TNX, most of the experimental data and evaluated one in JEFF-3.1, ENDF/B-VI, JENDL 3.3 and BROND 2.0, in general, agree well with the present result. The RI value for 152Sm(n,γ)153Sm reaction has also been determined to be 3038 ± 214 b, relative to the reference value of 14.0 ± 0.3 b for the 55Mn(n,γ)56Mn monitor reaction, using a 1/E1+α epithermal neutron spectrum and assuming Cd cut-off energy of 0.55 eV. In surveying literature, the existing experimental and evaluated data for the RI values are distributed from 1715 to 3462 b. However, when the Cd cut-off energy is defined as 0.55 eV, the present RI value agrees with some previously reported RI values, 3020 ± 163 b by Simonits et al., 3141 ± 157 by Van Der Linden et al., and 2962 ± 54 b by Kafala et al., within the limits of error.

Thermal neutron cross-section and resonance integral for 164Dy(n,γ) 165Dy reaction

The thermal neutron cross-section ( σ 0) and the resonance integral ( I 0) of the reaction 164Dy(n,γ) 165Dy were measured by the activation method, using 55Mn(n,γ) 55Mn monitor reaction as a single comparator. The diluted MnO 2 and Dy 2O 3 powder samples within and without a cylindrical Cd shield case were irradiated in an isotropic neutron field obtained from the 241Am–Be neutron sources, moderated with paraffin wax. The γ-ray spectra from the irradiated samples were measured by high-resolution γ-ray spectrometry with a calibrated n-type Ge detector. The necessary correction factors for γ-ray attenuation, thermal neutron and resonance neutron self-shielding effects and epithermal neutron spectrum shape factor (α) were taken into account in the determinations. The thermal neutron cross-section for 164Dy(n,γ) 165Dy reaction studied has been determined to be 2672±104 b at 0.025 eV. This result has been obtained relative to the reference thermal neutron cross-section value of 13.3±0.1 b for the 55Mn(n,γ) 56Mn reaction. For the thermal neutron cross-section, most of the experimental data and evaluated one in ENDF/B-VI, in general, are in good agreement with the present result. The resonance integral has also been measured relative to the reference value of 14.0±0.3 b for the 55Mn(n,γ) 56Mn monitor reaction using a 1/ E 1+ α epithermal neutron spectrum of the 241Am–Be neutron source. By defining Cd cut-off energy 0.55 eV, the resonance integral obtained was 527±89 b. The existing experimental and evaluated data for the resonance integral are distributed from 335 to 820 b. The present resonance integral value agrees with some previously reported values, 520 b by Holden, 505 b by Simonits et al. and 575±100 b by Heft, within the limits of error.

ZAKI: a windows-based k o standardization code for in-core INAA

A new computer code ZAKI, for k o-based INAA standardization, written in Visual Basic for the WINDOWS environment is described. The parameter α measuring the deviation of the epithermal neutron spectrum shape from the ideal 1/ E shape, and the thermal-to-epithermal flux ratio f, are monitored at each irradiation position for each irradiation using the “triple bare monitor with k o” technique. Stability of the irradiation position with respect to α and f is therefore assumed only for the duration of the irradiation. This now makes it possible to use k o standardization even for in-core reactor irradiation channels without an a priori knowledge of α and f values as required by existing commercial software. ZAKI is considerably versatile and contains features which allow for use of several detectors at different counting geometries, direct inputing of peak search output from GeniePc, and automatic nuclide identification of all gamma lines using an in-built library. Sample results for two certified reference materials are presented.

Energy dependence of the epithermal neutron spectrum shape parameter α with respect to application of comparator-type NAA

The epithermal neutron spectrum shape parameter α in nuclear reactors is explained from a theoretical point of view in terms of the neutron slowing down density function. The latter is approximated by Fermi's age theory. Values for α are calculated for a simple approximation of a nuclear reactor: a disk shaped fission neutron source in an infinite graphite moderator. The model produces α-values with the correct sign and magnitude, compared to experimental values from the literature, determined in a real reactor. It is shown that α varies strongly with distance to the neutron source and less strongly with neutron energy. The inappropriateness of average α-values, obtained from the slope of quasi-straight lines produced by log-log plots of E−α versus E, for the correction of non-ideal epithermal neutron activation is discussed. Conclusions are formulated concerning the impact of an energy dependent α on comparator type NAA.