Direct Alpha Spectrometry Research Articles

Direct alpha spectrometry as a screening method for assaying thick, highly-radioactive materials

Single-crystal (sc) chemical vapor deposition (CVD) prepared diamond semiconductor detectors have been used as alpha spectrometers to analyze untreated, thick-matrix materials with high beta radiation emission rates. Tests using a scCVD diamond detector to assay alpha emissions from high burn-up irradiated nuclear fuel show the ability to produce reasonable thick-matrix alpha spectra when the beta radiation field exceeds the alpha radiation field by up to six orders of magnitude. Simple semi-quantitative analyses of thick matrix spectra have been used to confirm the presence of higher-energy alpha-emitting actinides (plutonium and curium) when in the presence of lower-energy alpha emitting actinides (uranium).

Direct alpha spectrometry for analysing leached ThO2 pellets

The next generation application of nuclear energy has shown an interest towards ThO2 or mixed oxides fuels. However, more knowledge is needed, for example, on the microstructural and matrix dissolution behaviour of ThO2. The objective of this study was to examine surface properties of thick ThO2 pellets by non-destructive alpha analysis method accompanied with Monte Carlo simulations before and after a leaching experiment. This study has been conducted to investigate the contents, and surface layer thickness of crystalline 232ThO2 pellet leached in aqueous solution with excess of 229Th tracer in the beginning of the experiment. The simulation results have suggested a maximum 0.1 μm concentrated layer of 229Th on the pellet surface. The presence of this layer suppresses further dissolution of the pellet.

Performance of an air sampler and a gamma-ray detector in a small unmanned aerial vehicle

The performance of an air sampler and a small gamma-ray spectrometer was tested in an unmanned aerial vehicle (UAV) able to carry payload with mass up to 0.5 kg. Operation of the sampler was investigated with the aid of radon progeny normally present in outdoor air. Detection limits for several transuranium nuclides in air are of the order of 0.3 Bq m−3 assuming 0.5 h sampling time and 1 h counting time in direct alpha spectrometry. Unshielded 137Cs and 60Co point sources at the ground level were used to test the CsI spectrometer. Detection limits are approximately 1 GBq or larger depending on the flying altitude.

Direct high-resolution alpha spectrometry from nuclear fuel particles in an outdoor air sample

The potential use of direct high-resolution alpha spectrometry to identify the presence of transactinium elements in air samples is illustrated in the case when alpha-particle-emitting radionuclides are incorporated in nuclear fuel particles. Alpha particle energy spectra are generated through Monte Carlo simulations assuming a nuclide composition similar to RBMK (Chernobyl) nuclear fuel. The major alpha-particle-emitting radionuclides, in terms of activity, are 242Cm, 239Pu and 240Pu. The characteristics of the alpha peaks are determined by fuel particle properties as well as the type of the air filter. It is shown that direct alpha spectrometry can be readily applied to membrane filter samples containing nuclear fuel particles when rapid nuclide identification is of relevance. However, the development of a novel spectrum analysis code is a prerequisite for unfolding complex alpha spectra.

Direct alpha spectrometry for characterising hot particle properties

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.

MINIMUM DETECTABLE ACTIVITY CONCENTRATION IN DIRECT ALPHA SPECTROMETRY FROM OUTDOOR AIR SAMPLES: CONTINUOUS MONITORING VERSUS SEPARATE SAMPLING AND COUNTING

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 U, U, Pu, and Pu 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.

Simulation of alpha particle spectra from aerosol samples

A Monte Carlo code is developed for simulating energy spectra of alpha particles from aerosol samples. Geometrical detection efficiency and energy loss of the alpha particles in the source itself and in the material between the source and detector are simulated. Different characteristics of the aerosol particles and medium material are taken into account in the computation. An excellent agreement with earlier results and measurements is found. The code can be applied for example in designing optimal aerosol sampling methods in direct alpha spectrometry.

Plutonium isotopes, 241Am and 137Cs activity concentrations in marine sediments of Gökova Bay, Aegean Turkish Coast

Samples of marine surface sediments of different grain sizes collected in Gokova, a small bay on the Aegean Turkish Coast, have been examined to measure alpha- and gamma-radioactivity. The purpose of this research is to define a baseline study of man-made radionuclides on sediments along Gokova Bay, using a combination of direct gamma-spectrometry, radiochemical separation and alpha spectrometry. The analysis of these samples revealed measurable quantities of some artificial radionuclides namely: 239+240Pu (from 0.13±0.017 to 0.85±0.15 Bq.kg–1). 137Cs, 241Am and 238Pu were identified at a very low level. Concentration ratios of 238Pu to 239+240Pu obtained seem to confirm that this artificial radioactivity is due mainly to Chernobyl accident.

Intakes of thorium while using thoriated tungsten electrodes for TIG welding.

Thoriated electrodes are used in TIG welding. TIG welders, along with persons who grind thoriated electrodes and persons located near relevant welding and grinding sites, might be at risk of thorium intake. The isotopes of radiological relevance are 232Th, 230Th, and 228Th. The studies described in the literature do not provide a consistent picture of the actual hazards, and changes in European and German radiological protection laws have now made it necessary to determine the risks. To accomplish this, a field test was conducted under real working conditions in 26 different welding shops. The airborne activity generated through welding, and through grinding of electrodes, was measured using personal air samplers. Stationary samplers were also used. The filters' samples were evaluated by means of direct alpha spectrometry with proportional counting and by means of gamma spectrometry following neutron activation. The results clearly showed that considerable intake can occur during both alternating-current welding and electrode grinding, if no suction systems are used. The range of 232Th intakes to welders were estimated from 0.1 Bq y(-1) to 144 Bq y(-1) during welding and from 0.02 Bq y(-1) to 30.2 Bq y(-1) during grinding. In 6 of the 26 cases the recent annual limit on intake derived from the most recent ICRP publications was exceeded--in the worst case it was exceeded by a factor of 10--if it is assumed that the persons studied were not exposed workers (not routinely monitored for radiation exposure). When the significantly more restrictive German limits are applied, the amounts by which the limits were exceeded were even greater. Because many qualified welders have very long careers, the risks can thus be considerable. The paper also discusses parameters that influence exposure, and it presents a catalogue of recommended measures for dosage reduction.

Determination of natural radionuclides in drinking water; a tentative protocol

Routine analysis of drinking water is in general limited to artificial radionuclides although some naturally occurring radionuclides have radiotoxicities well comparable to those of the worst artificial ones. This unsatisfactory situation is mainly due to problems with traditional radiochemical preparation methods. They are very time consuming and the chemistry involved is too high a hurdle for many laboratories. A simplified protocol for the determination of natural radionuclides in drinking water has been setup and tested. It makes full use of the gamma-spectrometry's analyzing power and of state-of-the-art liquid scintillation alpha-spectrometry combined with extractive scintillators. It also includes the use of metal-adsorbing thin layers for direct alpha-spectrometry. The protocol does not offer record-low detection limits, but allows for a rapid check that no individual natural radionuclide present in the water will contribute more than 50 μSv to the annual dose.

Experiences with large-area frisch grid chambers in low-level alpha spectrometry

The properties of parallel-palte gridded ionization chambers with areas of 300 cm 2, developed by us for alpha spectrometry of samples with low specific alpha activity are reported. Several practical hints for optimum operating conditions are presented. The chambers can be operated routinely at atmospheric pressure for several days, without the need for purification of the gas filling (P10). The minimum detectable activity at 5 MeV is 0.01 pCi, based on 4.65 standard deviations of background and 1000 min counting time. At the GSF Research Center ionization chambers of this type are used for the analysis of natural alpha emitters, as well as of transuranium nuclides in environmental samples by: (a) direct alpha spectrometry without any previous treatment of the sample, (b) semi-direct spectrometry after removal of organic matter by low-temperature ashing and (c) spectrometry after chemical separation. Some typical examples of application are given. Furthermore the range of application of the chambers in comparison to semiconductor detectors in the field of low-level alpha spectrometry is discussed.

Alpha scanning of solid surfaces and the measurement of plutonium migration in irradiated ceramic fuels

A technique for measuring plutonium distribution in irradiated ceramic reactor fuels is based on direct alpha spectrometry of suitably prepared metallographic fuel specimens. The technique consists of three parts: (a) an alpha autoradiograph is taken, showing detailed distribution of alpha emitting materials within the specimen, (b) an alpha energy spectrum is taken with an alpha counter measuring the solid surface activity through a pinhole collimator; this allows differentiation between plutonium and other alpha emitters at each point in the specimen, and, (c) a wet chemical analysis of the whole specimen is carried out to establish the gross integral amount of the species. Alpha spectrometry of “infinitely” thick sources is discussed. An expression for the energy spectrum of a plane homogeneous source is derived in terms of the stopping cross-section of the source material. Experimental values of stopping cross-section for (U, Pu)O 2 are determined.

Carnotite as a source of uranium

Routine analysis of drinking water is in general limited to artificial radionuclides although some naturally occurring radionuclides have radiotoxicities well comparable to those of the worst artificial ones. This unsatisfactory situation is mainly due to problems with traditional radiochemical preparation methods. They are very time consuming and the chemistry involved is too high a hurdle for many laboratories. A simplified protocol for the determination of natural radionuclides in drinking water has been setup and tested. It makes full use of the gamma-spectrometry's analyzing power and of state-of-the-art liquid scintillation alpha-spectrometry combined with extractive scintillators. It also includes the use of metal-adsorbing thin layers for direct alpha-spectrometry. The protocol does not offer record-low detection limits, but allows for a rapid check that no individual natural radionuclide present in the water will contribute more than 50 μSv to the annual dose.