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An approach for in situ alpha spectrometry that allows one to measure the spectra with good energy resolution at ambient air pressure has been developed recently. Here, novel equipment is introduced for in situ measurements. Neither vacuum pumps nor radiochemical sample processing are necessary. Flat and smooth surfaces are ideal sources provided that the radionuclide contamination represents a thin layer on the surface. Other sources, such as air filters or evaporation residues, are also possible. Alpha particle collimation is used to obtain good energy resolution, but the equipment can also be used without collimation. An estimation of the detection efficiency with and without collimation is given using an extended area source containing 241Am.

Spherical particles with known properties were used to demonstrate and test a novel software package known as AASIFIT, which is able to unfold complex alpha spectra. A unique feature of the program is that it uses simulated peak shapes in the fitting process. The experimental reference particles in the testing were artificially produced U particles of diameter 1.4microm and a nuclear bomb particle with a twenty-fold greater diameter, mainly composed of U and Pu dioxides. AASIFIT was used to determine the density of the U particles. In addition, the activities of (239+240)Pu and (241)Am were determined for the nuclear bomb particle and compared to earlier determinations in the literature. The results of this investigation demonstrated that the software can be used to estimate the properties of particles emitting alpha radiation. However, the composition and geometry of the investigated particles need to be known with good accuracy for reliable estimates. Furthermore, uncertainties in the stopping power data, especially for U and Pu, may have an influence on the results obtained from the software.

Alpha particle emitting radionuclides may be released into the atmosphere as a result of a severe nuclear accident, the malevolent use of radioactive material or some other incident. Rapid detection methods are then of crucial importance for carrying out well-timed protective actions. The present paper demonstrates that a method in which an aerosol sample is collected on a filter and directly analysed by high-resolution alpha spectrometry in a vacuum chamber, but without radiochemical sample treatment, is suitable for field measurements. A detection limit of less than 0.1 Bqm(-3) for (239)Pu is achieved assuming 1-h sampling using a glass-fibre filter and 1-h data acquisition. This value is higher than in the case when sampling is performed using a porous membrane filter. A measurement system consisting of standard components is mounted in a vehicle designed for rapid field measurements.

An alpha spectrum containing peaks of radon progeny and measured from a membrane air filter in a vacuum using a high-resolution spectrometer was thoroughly analyzed. The goal was to find solutions to several pending issues in spectrum analysis that are prerequisites for an accurate spectrum unfolding. These include non-linear energy calibration, detailed peak shape (tailing) and alpha-electron coincidences. Monte Carlo simulations were used to assess the coincidence phenomena and to provide input to peak fitting. The methodology applied here for radon progeny can be used for other alpha-particle emitting radionuclides possibly present in the filter. [ABSTRACT FROM AUTHOR]

Linssi is a Structured Query Language (SQL) database for HPGe gamma-ray spectrometry. It covers the whole production chain from sample preparation to final analysis results. Static or mobile sampling and measurement and multiple sample types are supported. In addition, each sample can be split or combined any number of times. A sample may be measured multiple times and each measurement multiply analyzed as well. With Linssi, measurement setups with detectors, shields, attenuators and source geometries can be defined. Full control of calibrations, their histories and tracing of each calibration point back to its corresponding analysis and calibration measurement is supported. Linssi database and user scripts are available from . [ABSTRACT FROM AUTHOR]

Abstract: Non-destructive analysis methods, especially direct alpha spectrometry but also gamma ray spectrometry and scanning electron microscopy were applied to a nuclear bomb particle from the Thule accident. The use of high-resolution direct alpha spectrometry with the aid of Monte Carlo simulations was demonstrated here in order to determine the properties of this particle. In general, the information that can be obtained through direct alpha spectrometry depends on the information available a priori. For example, known elemental composition makes the assessment of particle dimensions possible even if scanning electron microscopy images are unavailable. Although direct alpha spectrometry may be applied for particle characterisation, further developments in spectrum analysis tools are necessary. [Copyright &y& Elsevier]

Rapid method for identifying the presence of alpha particle emitting radionuclides in outdoor air is of paramount importance should a nuclear or radiological incident occur. Minimum detectable activity concentrations of 238U, 234U, 239Pu, and 238Pu in outdoor air are calculated for two direct alpha spectrometry methods: continuous air monitoring is compared with separate sampling and subsequent alpha particle counting in a vacuum chamber. The radon progeny activity concentration typical for outdoor air and the effects for the alpha particle spectra caused by the properties of the filter and the aerosol particles are taken into account using measurements and Monte Carlo simulations. Continuous air monitoring is a faster method for identifying the presence of (trans)uranium elements when their activity concentration is considerably higher than the typical detection limit. Separate sampling and counting in a vacuum chamber is a more sensitive method when concentrations are close to the detection limit and when the duration of the sampling-counting cycle is greater than approximately 2 h. The method may serve as a tool for rapid field measurements. [ABSTRACT FROM AUTHOR]

Abstract: A Monte Carlo code, known as advanced alpha-spectrometric simulation (AASI), is developed for simulating energy spectra in alpha spectrometry. The code documented here is a comprehensive package where all the major processes affecting the spectrum are included. A unique feature of the code is its ability to take into account coincidences between the particles emitted from the source. Simulations and measurements highlight the importance of coincidences in high-resolution alpha spectrometry. To show the validity of the simulated results, comparisons with measurements and other simulation codes are presented. [Copyright &y& Elsevier]

Abstract: Measurements, Monte Carlo simulations and imaging were used to study the degradation of the alpha particle energy spectrum caused by thick samples and thickness variations. Large local inhomogeneities were detected from the samples prepared by membrane filtration. Simulations were able to correctly produce alpha particle spectra. [Copyright &y& Elsevier]

Abstract: Inelastic neutron scattering in the HPGe detector produces wide, triangular-shaped peaks in the spectrum. We develop an accurate model for the peak shape and show that the inclusion of the model in the gamma spectrum analysis makes it possible to quantify fast neutron scattering in the Ge crystal and improves the estimation of the baseline. This in turn facilitates the detection of fission products present at trace levels in environmental samples. The model, together with simulations, is used to deduce some properties of the underlying neutron energy distribution. The neutron evaporation temperature of 1.1MeV is obtained from the analysis of environmental monitoring gamma spectra. [Copyright &y& Elsevier]

Abstract: A January 1966 accident dispersed Pu and other nuclear bomb materials in the vicinity of Palomares, a village in southeastern Spain. Radioactive particles were identified in a soil sample collected in 1998 and analytical results obtained from one of the isolated particles are presented here. Isolation of the particle was performed using gamma-ray spectrometry and imaging plates. Scanning electron microscopy with X-ray microanalysis revealed the presence of U and Pu as well as Pb and Fe in the particle of ∼ 10μm diameter. Radioisotopes of U, Pu, and Am were quantified using radiometric methods, inductively coupled plasma mass spectrometry and secondary ion mass spectrometry. The elevated 235U/238U atom ratio indicates enriched U, and the Pu atom ratios are consistent with weapons-grade material. This work demonstrates that the analysis of individual particles provides information not available through bulk sample analysis. [Copyright &y& Elsevier]