The activity of thin alpha-particle sources with negligible self-absorption can be absolutely determined using 2 pi counting geometry systems, correcting for backscattering from the source backing. This procedure requires to perform an extrapolation to zero energy in the experimental counting rate, due to the existence of events produced by recoiling daughters and electronic noise in the low-energy region. In addition, the Monte Carlo simulation has proven that the energy distribution of the backscattered alpha particles is not flat, showing a "peak" at the low-energy region which is due to multiple scattering in the backing. In this work, we demonstrate that a significant part of the backscattered particles included in this "peak" are not contained in the extrapolated counting rate, which implies an underestimation of the source activity if the total backscattering coefficient is considered. We applied MC simulation with the well-known code SRIM to evaluate this underestimation depending on the energy of alpha emitters and on the backing. Our results show that the underestimation in the activity can be even close to 1 % in the case of backings with high atomic numbers, which can be considered as significative in metrological measurements for the standardization of alpha-particle sources. In addition, a new procedure is proposed here to correct for this effect, which includes only the simulation of alpha particles in the source backing, without attending to the source substrate. This new procedure is finally applied to some sources from the literature, where the backscattering coefficients were obtained experimentally, providing satisfactory results.

Some Miras -- long-period variables in late evolutionary stages -- have meandering pulsation periods and light curve asymmetries, the causes of which are still unclear. We aim to understand better the origin of these phenomena by investigating a sample of solar-neighbourhood Miras. We characterised this group of stars and related their variability characteristics to other stellar parameters. We analysed observations from several databases to obtain light curves with maximum time span and temporal coverage for a sample of 548 Miras. We determined their pulsation period evolution over a time span of many decades, searched for changes in the periods, and determined the amplitude of the period change. We also analysed the Fourier spectra with respect to possible secondary frequency maxima. The sample was divided into two groups with respect to the presence of light curve bumps. IR colours and indicators of the third dredge-up were collected to study the sample stars' mass-loss and deep mixing properties. Our analysis revealed one new star, T~Lyn, with a continuously changing period. The group of Miras with meandering period changes is exclusively made up of M-type stars. The Fourier spectra of the meandering period Miras have no prominent additional peaks, suggesting that additional pulsation modes are not the cause of the meandering periods. We confirm that bumps are more common among S and C Miras and show, for the first time, that Miras with bumps have lower mass-loss rates than those with regular, symmetric light curves. Also Miras with meandering period changes have relatively little mass loss. We conclude that Miras with strongly changing periods or asymmetries in their light curves have relatively low dust mass-loss rates. Meandering period changes and light curve asymmetries could be connected to He-shell flashes and third dredge-up episodes.

In this work, we introduce a new software application developed to reproduce α-particle spectra measured with silicon detectors. It takes into consideration the main physical processes involved in the interaction of alpha particles with the source and the detector. This application is considerably more user-friendly than multipurpose codes, being also the runtimes to obtain a spectrum much lower. It makes use of the TRIM simulation code for tracking alpha particles in the source and the detector entrance window. Concerning to the response function of a silicon detector, the contribution of electronic excitation and ionization produced by the alpha particles is also obtained by simulation, while the electron-hole pair statistics and the broadening produced by the amplifier system (electronic chain) are included as convolutions of theoretical functions. The code α-SpecTrim is written in Python 3 language using Flask framework, so it can be run in every PC or laptop. It is free and can be provided if requested to the authors.

The proton irradiation in a PET cyclotron produces radioactive by-products with high levels of activity in the target components, which are strongly dependent on the specific parameters used in the cyclotron facility. Because the target assembly parts must be replaced periodically, external exposure to operators must be assessed. In this work, high-resolution gamma-ray spectrometry was used to determine the activity levels for the specific radionuclides induced in the target components of a medical 9.6 MeV MINItrace cyclotron. The focus was on three target components, which are periodically replaced: Havar foil, Titanium foil and the Helicoflex seal located on the path of the proton beam just in front of the silver vessel containing the enriched water. Eight radionuclides were identified in the Havar foil: Mn-54, Co-56, Co-57, Co-58, Co-60, Tc-95, Cd-109 and Re-183. In the titanium foil, the nuclides Sc-46, V-48, Cr-51, Co-56, Co-57, and Se-75 were identified, while only Cr-51, Co-58, and Co-60 were detected in the Helicoflex seal. The total effective dose rates to which staff are exposed at the moment of replacing the target were calculated. The waste management for these target components was also considered, using the half-lives of the detected radionuclides in order to determine the time necessary for the activity levels in the target components to be below the exemption levels recommended by the IAEA.

As known, the detector response function in the detection of alpha particles is characterized by the following distributions: electronic excitation and ionization, electron–hole pair statistics, and electronic noise contribution. The distribution due to the ionization–excitation process is of particular relevance, because it is not Gaussian and contributes essentially to the asymmetry of the alpha lines. For this work, we adapted the well-known code SRIM, to obtain and analyze the ionization/excitation distributions for alpha-particles in silicon, in a wide range of energies from 0.5 to 10 MeV. These curves were later well-fitted to a function corresponding to the convolution of a Gaussian with exponentials truncated in the low-energy zone of the distribution. A detailed study about the dependence of all the fitting parameters on energy was performed. The parametrization carried out in this work can also be an useful tool to generate the corresponding ionization–excitation curves required in the task of reproducing real alpha-particle spectra.

Gamma-ray emission probabilities for 243Am were published in 1996. Three new gamma transitions were then found: 46.84, 98.36 and 102.02 keV. In the last evaluation by the Decay Data Evaluation Project, the emission probabilities of 46.84 and 102.02 keV transitions were not included. Alpha-gamma coincidence measurements have been now used to check and revise the values for these two transitions and their emission probabilities. The emissions of the 31.13, 43.53, 74.66, 86.71 and 141.89 keV transitions were also studied.

In this work, we present and describe the program ALPHACAL, specifically developed for the calibration of alpha-particle sources. It is therefore more user-friendly and less time-consuming than multipurpose codes developed for a wide range of applications. The program is based on the recently developed code AlfaMC, which simulates specifically the transport of alpha particles. Both cylindrical and point sources mounted on the surface of polished backings can be simulated, as is the convention in experimental measurements of alpha-particle sources. In addition to the efficiency calculation and determination of the backscattering coefficient, some additional tools are available to the user, like the visualization of energy spectrum, use of energy cut-off or low-energy tail corrections. ALPHACAL has been implemented in C++ language using QT library, so it is available for Windows, MacOs and Linux platforms. It is free and can be provided under request to the authors.

In the pyrolysis process carried out to obtain charcoal from plants, a concentration of the radionuclides found in trace amounts in the raw material is produced. This fact would influence its possible uses. Radioactive characterization of a wide set of charcoal samples from different provenances was analysed. Activity concentrations of the radionuclides from the 238U and 232Th series, and also for 40K, 134Cs and 137Cs nuclides were obtained by gamma-ray and alpha-particle spectrometry. A discussion of these results is included comparing them with coal. A possible contamination of charcoal samples by fossil matter, such as coal, was studied via 14C analysis carried out by accelerator mass spectrometry.

Gamma-ray emission probabilities for (243)AM were published in 1996. Three new gamma transitions were then found: 46.84, 98.36 and 102.02 keV. In the last evaluation by the Decay Data Evaluation Project, the emission probabilities of 46.84 and 102.02 keV transitions were not included. Alpha-gamma coincidence measurements have been now used to check and revise the values for these two transitions and their emission probabilities. The emissions of the 31.13, 43.53, 74.66, 86.71 and 141.89 keV transitions were also studied.

Gamma-ray spectrometry was used for the identification and quantification of the activation products induced during the production of [18F]FDG in a cyclotron with a beam of 9.6 MeV protons, a silver target and Havar entrance window. Samples of the irradiated water collected before and after the 18F separation, and of the final product [18F]FDG were measured in the particular conditions of a beam current of 45 μA and an irradiation time of 25–30 min The radionuclides 52Mn, 55Co, 56Co, 57Co, 58Co, 95Tc, 96Tc, and 109Cd were identified in the irradiated water samples, but not detected in the final [18]FDG product. The requirements for the transport of the recovered enriched water are also discussed.

The nuclides 210Pb and 241Am are used in geochronological studies. In this work, we examine the influence of the sediment chemical composition on the self-attenuation corrections needed for the accurate determination of specific activities for 210Pb and 241Am used for sediment dating. A theoretical exercise was carried out evaluating the relative bias obtained by four different analytical laboratories in the quantification of the 210Pb and 241Am activity concentration by gamma-ray spectrometry. The laboratories considered the same density for the sediment sample, but each one used a different chemical composition in the Monte Carlo calculations, and six different HPGe detectors (including n and p-types). An estimate of the impact that would have the relative biases found in the estimation of the 210Pb sediment ages, applying the Constant Rate of Supply (CRS) dating model, is also given. In addition, the performance scores that the laboratories would have obtained in a hypothetical IAEA proficiency test are also presented.

Activity concentrations of dissolved (222)Rn and (226)Ra were measured in several underground aquifers, which are candidates for repositories or for the study of analogue natural escapes of CO2. The concentration of both radionuclides in water was determined using liquid scintillation counting. The values obtained for the (222)Rn concentrations varied from 0 to 150 Bq l(-1), while the levels of (226)Ra were in general very low. This indicates that (222)Rn is coming from the decay of the undissolved (226)Ra existing in the rocks and deep layers of the aquifers, being later transported by diffusion in water.

The well-known code Stopping and Range of Ions in Matter (SRIM) and the more recent code AlfaMC were used in this work to evaluate the backscattering corrections required in the measurement of alpha particle sources. The differences found in the energy and angular distribution of backscattered particles for point sources mounted on backings of aluminum, silver, and platinum, were analyzed taking into account the models of multiple scattering included in each code. The lateral dispersion of alpha particles and the backscattering coefficients obtained with SRIM were in all the cases some greater than those derived with AlfaMC.

Abstract Measurements of α-particle sources require corrections to the counting rate due to scattering and self-absorption in the source and the backing material. In this study, we describe a simple procedure to estimate these corrections using the new Monte Carlo code AlfaMC to consider the effects of scattering and self-absorption conjointly, and so to determine the activity of α emitters. The procedure proposed was applied to 235UO2 sources deposited on highly polished platinum backings. In general, the dependence of the efficiency with source thickness was in good agreement with a simple model considering a linear and a hyperbolic behavior for thin and thick sources, respectively, although significant deviations from this model were found for very thin sources. For these very thin sources, the Monte Carlo simulation revealed to be as a required method in the primary calibration of α-particle sources. The efficiency results obtained by simulation with AlfaMC were in agreement with available efficiency data.

Although coal and charcoal have similar physical and chemical characteristics, there are several crystallographic procedures used to distinguish and characterize them. But if the matrix is crushed, there is no standard procedure to distinguish coal from charcoal. In this work, a procedure to characterize coal and charcoal samples based on the radioactive content is proposed. The first assay is by gamma-ray spectrometry, which allows a part of the radioactive content to be determined rapidly and non-destructively. Then, alpha-particle spectrometry is applied to assay the content of those radionuclides which are difficult to determine precisely by gamma-ray spectrometry. This second technique requires prior chemical purification of the carbon sample in order to separate the corresponding radionuclides of interest.

The activity of alpha-particle sources with negligible thickness can be absolutely determined using 2π counting geometry detectors, requiring corrections for backscattering from the source backing. The experimental determination of these corrections is subject to large uncertainties, because the contribution of the backscattered alpha particles to the total counting is generally very low. An interesting alternative is then to use Monte Carlo methods which simulate the transport of alpha-particles into the source. The programme AlfaMC, a new Monte Carlo code developed to simulate specifically the transport of alpha particles, was here applied to the study of the backscattering in alpha-particle sources. Energy and angular distributions for the backscattered alpha particles were deeply analysed based on a multiple scattering process, as a result of a large number of weak collisions with atomic electrons. Some calculated values for the backscattering coefficient were compared with experimental values, showing a good agreement.

Improvements to the conventional methods for alpha-particle spectrometry measurement and analysis have recently been implemented in our laboratory. They include the application of corrections for energy drift in long-duration measurements, the development and application of an efficient deconvolution method for complex alpha spectra using the new computer code ALFITeX, an alpha–gamma coincidence system using a dual-parameter multichannel analyzer, and the digitization of this coincidence system.

The dependence of efficiency of a gas-flow proportional counter with respect to the source thickness and α-particle energy was evaluated using the code SRIM. Results for the mass-efficiency curves were evaluated for 209Po and 241Am in a substrate of NaNO3. The results revealed good agreement with a linear and a hyperbolic dependence for low and high thickness sources, respectively. However, some deviations were found for very thin thicknesses, which can be explained by taking into account scattering effects. A function is proposed for predicting the dependence of efficiency with α-particle energy in the range from 4 to 8 MeV.

The influence of different source compositions and α-particle energies on the detection efficiency of a gas-flow proportional counter was examined using experimental measurements and Monte Carlo simulations. Efficiency variation with alpha-particle energy was very marked, being less significant with the substrate composition. These results show that the determination of gross alpha activity in an unknown sample must be carried out very carefully in order to give a correct estimation of its activity.

The analysis of solid environmental samples by α-particle spectrometry generally involves processes requiring an initial treatment to destroy the complexes in the matrix, and dissolve the radionuclides of interest. This study compared the activities obtained for several natural radionuclides (238U, 234U, 230Th, 226Ra, and 210Po) in previously well-characterized materials, using two procedures: acid leaching and digestion in a microwave oven. The measured activities were in general very similar for the two procedures, with a strong statistical correlation between the two sets of values.