[en] We present a new activation method based on the ¹⁹F(n,2n)¹⁸F reaction using fast neutrons produced by a p(19 MeV) + Be accelerator-driven fast neutron source providing continuous neutron spectrum up to 17 MeV with a neutron fluence rate of approximately 9 × 10¹⁰ cm⁻² s⁻¹ at a 12-µA proton beam current. We describe elimination of interferences in measurement of ¹⁸F, a pure positron emitter with T_1/2 = 1.83 h. We present results of fluorine determination for several biological and environmental reference materials with the new procedure and compare them with those achieved by other methods in terms of limits of detection, accuracy and precision, where available.

[en] Highlights: • Polyethylene neutron irradiation system with external neutron sources. • Application of neutron activation technique and gamma-spectrometry for neutron field characterisation. • MCNP simulations of neutron transport in polyethylene neutron irradiator. The paper describes neutron field characterisation of low-flux multipurpose educational irradiator developed at Czech Technical University in Prague. The irradiator is aimed for demonstration experiments including neutron activation analysis, delayed neutron counting, or studies related to neutron and/or gamma detection and spectrometric devices. It may accommodate various neutron sources including ²⁵²Cf or AmBe radionuclide sources, D-D generator, or in-reactor irradiated nuclear material serving as delayed neutron source, or gamma sources including radionuclide ones or short-lived sources produced in the adjacent reactor. The characterisation was performed based on neutron activation technique using gold foils. It included two experimental parts. The first one verified the level of response symmetry in the four irradiation channels and characterisation of the axial distribution in the irradiation channels. Within the second one, the responses to thermal and epithermal neutrons and the cadmium ratio in the central irradiation position were determined. Whereas the former was determined solely with the ²⁵²Cf source, the latter was performed for all available sources: ²⁵²Cf, AmBe, and the D-D generator. The experimental results were further compared to calculations by the MCNP Monte Carlo code.

[en] Highlights: • Activation cross section measurement. • Proton-induced reactions on Li and Ta. • p+Li neutron generator. The experimental data on cross sections are necessary to clarify existing ideas on the mechanisms of nuclear reactions and for testing of nuclear models. Proton-induced reaction on ⁷Li serves as a source of quasi-monoenergetic neutrons which are widely used in the measurement of cross sections for neutron induced reactions. Tantalum plays an important role in technology and nuclear facilities mainly for its low induced activity (screens, degraders). In order to investigate the important nuclides, we have carried out the irradiation experiments with the variable-energy cyclotron U-120M of the NPI CAS Řež. The cross section of the reaction ⁷Li(p,n)⁷Be(ground state+0.43 MeV) and the cross sections of the nuclides ^180,178mTa, ¹⁷⁸W and ¹⁷⁵Hf from reactions on natural tantalum were investigated, of which ¹⁸¹Ta(p,n)^180gTa for the first time. The stacked-foil technique was utilized. The comparison of new results with prior data and predictions of evaluations is discussed.

[en] Traditional Tibetan medicine starts to be a very popular complementary medicine in USA and Europe. These pills contain many elements essential for the human body. However, they might also contain heavy metals such as mercury, iron, arsenic, etc. This paper focuses on elemental composition of two Tibetan pills and investigation of forms of iron in them. X-ray fluorescence spectroscopy and neutron activation analysis identified the presence of several heavy metals such as mercury, iron and copper. Mőssbauer spectroscopy revealed the possible presence of α − Fe₂O₃(hematite) and α − FeOOH(goethite) in both of the investigated samples.

[en] Highlights: • We investigated a set of dosimetry reactions for measurement of the neutron fluence in the High-Flux Test Modules of DONES. • Foil stacks irradiated with a neutron source at NPI Rez providing white neutron spectrum covering reactions of interest. • All expected induced activities could be determined by gamma spectroscopy utilizing a HPGe detector. • Further work will require to adapt the set of dosimetry reactions to the very high fluences in the HFTM.. -- Abstract: The High Flux Test Module (HFTM) carries the specimens to be irradiated with the Early Neutron Source. The knowledge of the total neutron fluence on the specimen will be necessary for analysis. Neutron activation is a widely used method for neutron fluence measurement. We have tested a set of activation materials which seem to be suitable for application in the HFTM considering half-lives of the induced activities, the environmental conditions and the deployment time in the HFTM. Test foils were irradiated for 9.5 h with a cyclotron of NPI Řež in a white neutron field with energies up to 32 MeV. The induced activities were determined 61 days after the irradiation. We present the resulting saturation activities with estimated uncertainties and draw conclusions on the application of the selected activation materials in the HFTM.

[en] The LC 200N type steel was examined by Moessbauer spectroscopy, scanning electron microscopy and neutron activation analysis. The hardened and non-hardened variants were compared. The hyperfine fields of the Moessbauer spectra sextets were analyzed. While NAA was useful in the identification of the alloying elements, Moessbauer spectroscopy disclosed differences in the magnetic phase contents of the hardened and non-hardened steels and was beneficial in a detailed analysis of the nearest surroundings of the Fe atoms. (P.A)

[en] Highlights: • Neutron spectra in LR-0, VR-1 and AKR-2 reactors. • Comparison of the experimental data with calculation. • Share of reflections in VR-1 beam. • Similarity of reactor spectra with ²³⁵U PFNS. - Abstract: A well-defined neutron spectrum is an essential tool not only for calibration and testing of neutron detectors used in dosimetry and spectroscopy but also for validation and verification of evaluated cross sections. A new evaluation of thermal-neutron induced ²³⁵U PFNS was performed by the International Atomic Energy Agency (IAEA) in the CIELO (Collaborative International Evaluated Library Organisation Project) project; new measurements of Spectral Averaged Cross sections averaged in the evaluated spectrum are to be obtained. In general, a neutron spectrum in the core is not identical to the pure fission one because fission neutrons undergo many scattering reactions, but it can be shown that PFNS and reactor spectra become undistinguishable from a certain energy boundary. This limit is important for experiments, because when the studied reaction threshold is over this limit, the spectral averaged cross sections in PFNS can be derived from the measured reactions in the reactor core. The evaluation of the neutron spectrum measurements in three different thermal-reactor cores shows that this lower limit is around the energy of 5.5 – 6 MeV. Above this energy the reactor spectra becomes identical with the ²³⁵U PFNS. IAEA CIELO PFNS is within 5% of the measured PFNS from 10 to 14 MeV in a LR-0 reactor, while ENDF/B-VII evaluated PFNS underestimated measured neutron spectra.

[en] A neutron activation system (NAS) is a highly useful and reliable tool for neutron flux and energy-spectrum measurements in fusion devices. We are evaluating a fast and efficient methodology for processing of fusion NAS data. Starting with the gamma spectra of irradiated activation materials, the method ultimately produces unfolded spectrum of the incident neutrons and uncertainty estimates. Here, we test the method using data from dedicated experiments at the Joint European Torus (JET) tokamak in Culham and the Nuclear Physics Institute (NPI) in Řež. These measurements utilize few, from three to five reaction channels as input to the unfolding process. Two spectral adjustment code-packages have been adapted for this purpose: MAXED from UMG 3.3 and STAYSL-PNNL. While the former is frequently applied, the latter is a new addition to the case of fusion device NAS. We present the post-analyses of NAS data, spectral adjustments and some discussion on the experiences with these tools, required developments and our planned future studies.

[en] Highlights: • Validation of the neutron spectra in VR-1 channel. • Measurement of gamma spectra in VR-1 channel. • Comparison of the experimental data with calculation. • Discrepancies between calculational and experimental spectra. - Abstract: VR-1 is light water zero-power reactor using IRT-4 M fuel with nominal enrichment of 19.7 wt%, equipped with the radial channel being directly attached to the fuel. Enrichment at the top level of the low enriched uranium limit guarantees that the larger part of non-scattered neutrons in the spectrum is coming from ²³⁵U than in case of experimental reactors using enrichments between 2 and 5 wt% (e.g., LR-0). Thus, the measurement of the VR-1 leakage spectrum can be a valuable contribution to the validation process of predicted ²³⁵U prompt fission neutron spectrum. Presented second set of measurements is confirming the beam stability at VR-1 and compares the agreement rate in neutron spectrum shape with two benchmarks; light- and heavy water filtered neutron spectrum obtained from spheres. Additionally, gamma spectrum was measured and compared with spherical iron benchmark and VVER-1000 core simulator. Presented measurements have the character of comprehensive characterization of beamline experiments developed at reactor cores with IRT-4 M fuel. Reported good agreement between the experiment and calculation confirm the methodology of using VR-1 as a Mock-Up experiment for benchmarking of high power reactors with IRTM fuel in the neutron transport experiments.