Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: M. Koster-Ammerlaan x
  • All content x
Clear All Modify Search

Abstract  

The laboratory for INAA in Delft processes several thousands of samples per year for multielement determinations in a variety of matrices. Samples are measured on different spectrometers (using well-type and coaxial detectors), by different persons and using many different analytical protocols. All these results should be consistent with each other with respect to the degree of accuracy, i.e., the combination of trueness and precision. A rigorous internal quality control program has been implemented with automatic on-line evaluation. Annually an additional evaluation of the internal quality control results is carried out using statistical techniques. The Naji-plot approach has proven to be an important graphical tool since it provides direct insight in both trueness and precision. It is demonstrated that the degree of accuracy of the results obtained under the large variety of operational parameters is under constant improvement.

Restricted access

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 95Zr, 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.

Open access

Abstract  

The Compton continuum in large sample neutron activation analysis has a measurable contribution from scattering of gamma-rays in the sample itself besides from scattering in the detector. The continuum, therefore, contains information on the sample’s composition, which may be made available by chemometrics. This hypothesis was tested on four types of animal fodder with similar amounts of mineral supplements. First results indicate indisputable discrimination of the sample types if using peakless parts of the gamma-ray spectra of the natural radioactivity of the materials as well as of those obtained after neutron activation of 1 kg samples. It indicates that the valuable information on differences in, e.g., organic constituents may be obtained by analyzing the Compton continuum.

Restricted access

Abstract  

A benchmark experiment was performed for Neutron Activation Analysis (NAA) of a large inhomogeneous sample. The reference sample was developed in-house and consisted of SiO2 matrix and an Al–Zn alloy “inhomogeneity” body. Monte Carlo simulations were employed to derive appropriate correction factors for neutron self-shielding during irradiation as well as self-attenuation of gamma rays and sample geometry during counting. The large sample neutron activation analysis (LSNAA) results were compared against reference values and the trueness of the technique was evaluated. An agreement within ±10% was observed between LSNAA and reference elemental mass values, for all matrix and inhomogeneity elements except Samarium, provided that the inhomogeneity body was fully simulated. However, in cases that the inhomogeneity was treated as not known, the results showed a reasonable agreement for most matrix elements, while large discrepancies were observed for the inhomogeneity elements. This study provided a quantification of the uncertainties associated with inhomogeneity in large sample analysis and contributed to the identification of the needs for future development of LSNAA facilities for analysis of inhomogeneous samples.

Restricted access

Abstract  

Large Sample Neutron Activation Analysis (LSNAA) was applied to perform non-destructive elemental analysis of a ceramic vase. Appropriate neutron self-shielding and gamma ray detection efficiency calibration factors were derived using Monte Carlo code MCNP5. The results of LSNAA were compared against Instrumental Neutron Activation Analysis (INAA) results and a satisfactory agreement between the two methods was observed. The ratio of derived concentrations between the two methods was within 0.7 and 1.3. Estimation of the activity level decay with time showed that the vase could be released from regulatory control at about 3 months post-irradiation. This study provided an analytical procedure for bulk sample analysis of precious and archaeological objects that need to be preserved intact and cannot be damaged for sampling purposes.

Restricted access