The spatial distribution of neutrons was measured at the muon science laboratory of KEK by the activation detector method
using an imaging plate for the radioactivity measurement. It was confirmed that this method is highly sensitive to detect
the average neutron dose of 10 µSv/h. The distribution of thermal and epithermal neutrons was also measured in the experimental
room. The cadmium ratio inside the experimental room is one except for the neutron leakage point. The spatial distribution
of neutrons inside the concrete shield of KENS was measured by the same method. Aluminum and gold foils were used for the
measurement of fast and thermal neutrons, respectively. Two dimensional change of the reaction rate of the 27Al(n,α)24Na reaction shows a good agreement with the results calculated by the Monte Carlo simulation using MARS14 code. Thermal and
epithermal neutron flux ratio on the beam axis was measured by the cadmium ratio method. The flux ratios were about 30 and
almost constant for every slot except for the surface of the shield, because the cadmium ratio is 2. This method was very
useful to measure the activity of many pieces of detector simultaneously without any efficiency and decay correction. Wide
dynamic range and high sensitivity are also the merit of this method.
A pilot plant operation at the Savannah River Site will remove 90Sr, 137Cs, and transuranics from a high-level liquid waste stream prior to encapsulation in a Saltstone Facility. Monitors are required to determine the concentrations of all radionuclides, including transuranics, in real-time on this processed waste stream. A neutron counter used to measure the concentration of each actinide isotope present in the stream is described. The neutron counter assembly consists of nested annular layers of shielding, reflectors, detectors, and moderators. On-line, live-time system control and calibration is provided by a time-tagged neutron source embedded in the moderator assembly.
The Budapest Research Reactor’s Prompt Gamma Activation Analysis (PGAA) and Neutron-Induced Prompt gamma Spectroscopy (NIPS)
facilities were significantly upgraded during the last few years. The higher neutron flux, achieved by the partial replacement
and realignment of the neutron guides, made feasible the automation and specialization of the two experimental stations. A
new neutron flux monitor, computer-controlled beam shutters and a low-level counting chamber have been put into operation
to assist with in-beam activation experiments. An automatic sample changer has been installed at the PGAA station, while the
NIPS station was redesigned and upgraded with a Compton suppressor to use for the non-destructive analysis of bulky samples.
In the near future the latter setup will be completed with a neutron tomograph and a moving table, to turn it into a Neutron
Radiography/Tomography-driven PGAA equipment.
The determination of Ir and Pt in rhodium neutron monitors was investigated via192Ir and199Au after neutron activation, via191Pt and194Au–196Au after proton activation. Ir was determined by instrumental NAA. A chemical separation of gold, with a yield measurement method by a radioactive tracer, was developed for platinum determination after neutron or proton irradiation.
A fast-neutron analysis (FNA) system is being developed at the Swedish Defence Research Agency. The experimental set up, consisting
of a SODERN Genie 16 (D-T) 14 MeV neutron generator, a HPGe-detector, a neutron monitor detector and related electronics,
is described in some detail. Results from preliminary measurements on bulk samples containing mainly carbon and nitrogen are
presented. Finally future objectives are discussed.
A 14-MeV FNAA system for oxygen analysis has been developed in which both data collection and processing are controlled by a PC-type computer equipped with an ORTEC ACETM-MCS multichannel scaler card. A single loop pneumatic transfer system automatically moves samples to the irradiation position and returns them to a counting position between two NaI(Tl) detectors operated through a summing amplifier. Software for data processing has been developed. Dead times of the BF3 neutron monitor and gamma-ray counting system have been separately determined. Results are presented for a variety of standard samples.
A benchmark study was carried out to verify whether MCNP is useful in the design stage of a PGNAA facility for large samples
up to 1 m length and 0.15 m diameter, using a 2.54 cm diameter thermal neutron beam. For this facility neutron self-shielding
and gamma-attenuation correction methods have to be developed. The relative spatial neutron-density distributions within three
samples with different macroscopic scattering and absorption cross sections were studied in a comparison between an MCNP simulation
and an irradiation experiment using copper wires as neutron monitors. The neutron density in the sample was within statistical
agreement between experiment and simulation. Typically the relative spatial neutron-density distributions agreed to within
1%. Therefore, MCNP can be used in design studies for the development of a large sample PGNAA facility as specified.
The application, the advantage and limits of neutron monitoring techniques, such as Hf-monitors, fissile material accumulation and concentration monitors are being discussed. The active neutron counting technique applied to emptied pulsed extraction columns containing Hf-sieve plates allows conclusive answers as to the position of the plates in the columns. Pu-accumulations on Hf-sieve plates in pulsed extraction columns can be estimated within a factor of two, whereby the detection limit is about equal to or less than 1 g Pu/plate. Fissile material concentration changes of 1.1 g/l can be detected in the case of235U in solution and of 0.4 Pu/l if a239Pu/240Pu ratio of 4 to 1 is assumed.
A technique for using internal standards in the determination of Si in rocks using fast neutron activation is presented. Different
weights of barium acetate were irradiated for 30 seconds then cooled for 10 seconds before counting for one minute. A peak
area, at 0.662 MeV due to137mBa, versus weight of barium calibration curve (I) was made. Similarly, barium acetate, which served as the neutron flux monitor,
was mixed with known weights of standard rocks, BCR-1 and G-2. Then a peak area (at 1.78 MeV due to28Al) versus weight of silicon (present in the standard rocks) calibration curve (II) was constructed which was corrected for
flux variations. Flux corrections were made possible using curve (I). Utilizing curve (I) and curve (II) the percentage Si
in granite samples obtained from Llano, Texas, was determined. This technique avoids any external neutron monitor or sample
rotation system. The applicability of this approach may be limited to samples in which the internal flux monitor can be dispersed.