Alpha Spectra Research Articles

New Approach to Alpha Spectrum Analysis:Iterative Monte Carlo Simulations and Fitting

A novel alpha spectrum analysis program which combines the Monte Carlo simulations with spectrum fitting is introduced. The shapes used in the fitting are obtained from the simulations. The program is developed especially to analyze complex alpha particle energy spectra – such as those obtained from non-processed aerosol filters, swipe samples or isolated particles emitting alpha radiation. In addition to activities of the nuclides present in the sample, the program can provide source characterization. In particular, the program can be used to characterize samples of nuclear material, i.e. those containing fissionable isotopes such as U or Pu. In the present paper we illustrate the use of the program to identify and quantify alpha-particle emitting isotopes in a depleted U projectile found in Kosovo and to estimate the depth distribution of alpha-particle emitting aerosols in a glassfibre filter.

Advanced alpha spectrum analysis based on the fitting and covariance analysis of dependent variables

Abstract The correct handling of statistical uncertainties is crucial especially when unfolding alpha spectra that contain a low number of counts or overlapping peaks from different nuclides. For this purpose, we have developed a new spectrum analysis software package called ADAM, which performs a full covariance calculus for alpha-particle emitting radionuclides. By analyzing a large number of simulated and measured spectra, the program was proved to give unbiased peak areas and statistically correct uncertainty limits. This applies regardless of the peak areas and the number of unknown parameters during the fitting. In addition, ADAM performs reliable deconvolution for multiplets, which opens the way for the determination of isotope ratios, such as 239 Pu/ 240 Pu.

Precise and accurate determination of theB8decay spectrum

Accurate measurements of the B-8 neutrino spectrum are important for the interpretation of solar neutrino data. Experimentally, the B-8 neutrino spectrum can be obtained from the measurement of the beta-delayed alpha spectrum. We report on an alpha-alpha coincidence measurement performed at the IGISOL facility in Jyvaskyla, Finland. Our measurement allows extensive cross-checks to be performed and gives a more intense neutrino spectrum at high energies compared to the present standard. The deviation reaches 4% at the end point of the spectrum. Below 11 MeV, the deviation is less than 1%.

A new approach to the analysis of alpha spectra based on neural network techniques

The analysis of alpha spectra requires good radiochemical procedures in order to obtain well differentiated alpha peaks in the spectrum, and the easiest way to analyze them is by directly summing the counts obtained in the Regions of Interest (ROIs). However, the low-energy tails of the alpha peaks frequently make this simple approach unworkable because some peaks partially overlap. Many fitting procedures have been proposed to solve this problem, most of them based on semi-empirical mathematical functions that emulate the shape of a theoretical alpha peak. The main drawback of these methods is that the great number of fitting parameters used means that their physical meaning is obscure or completely lacking. We propose another approach—the application of an artificial neural network. Instead of fitting the experimental data to a mathematical function, the fit is carried out by an artificial neural network (ANN) that has previously been trained to model the shape of an alpha peak using as training patterns several polonium spectra obtained from actual samples analyzed in our laboratory. In this sense, the ANN is able to learn the shape of an actual alpha peak. We have designed such an ANN as a feed-forward multi-layer perceptron with supervised training based on a back-propagation algorithm. The fitting procedure is based on the experimental observables that are characteristic of alpha peaks—the number of counts of the maximum and several peak widths at different heights. Polonium isotope spectra were selected because the alpha peaks corresponding to 208Po, 209Po, and 210Po are monoenergetic and well separated. The uncertainties introduced by this fitting procedure were less than the counting uncertainties. This new approach was applied to the problem of resolving overlapping peaks. Firstly, a theoretical study was carried out by artificially overlapping alpha peaks from actual samples in order to test the ability of the ANN to resolve each peak. Then, the ANN procedure was checked by determining the activity levels of different spectra obtained from certified samples for which one knows a priori the radioactive content, and its results were compared with those of other methods.

Surface’s weights of electrodeposited thorium samples determined by alpha spectrometry

The aim of this work was the preparation of samples with thorium on the steel discs by electrodeposition for determination of natural thorium by alpha spectrometry and for following analysis by secondary ion mass spectrometry. The samples with 232Th isotope were prepared by electrodeposition from solution Th(NO3)4·12H2O on steel discs in electrodeposition cell with use of solutions of Na2SO4, NaHSO4, KOH and ammonia oxalate by electric current of 0.75 A. Weights of electrodeposited thorium samples were calculated on the basis of intensities of peak of 232Th isotope in the alpha spectra. The layer thickness was calculated for following analysis of surface layers of thorium using secondary ion mass spectrometry.

Characterization of bismuth tri-iodide single crystals for wide band-gap semiconductor radiation detectors

Bismuth tri-iodide is a wide band-gap semiconductor material that may be able to operate as a radiation detector without any cooling mechanism. This material has a higher effective atomic number than germanium and CdZnTe, and thus should have a higher gamma-ray detection efficiency, particularly for moderate and high energy gamma-rays. Unfortunately, not much is known about bismuth tri-iodide, and the general properties of the material need to be investigated. Bismuth tri-iodide does not suffer from some of the material issues, such as a solid state phase transition and dissociation in air, that mercuric iodide (another high-Z, wide band-gap semiconductor) does. Thus, bismuth tri-iodide is both easier to grow and handle than mercuric iodide. A modified vertical Bridgman growth technique is being used to grow large, single bismuth tri-iodide crystals. Zone refining is being performed to purify the starting material and increase the resistivity of the crystals. The single crystals being grown are typically several hundred mm 3 . The larger crystals grown are approximately 2 cm 3 . Initial detectors are being fabricated using both gold and palladium electrodes and palladium wire. The electron mobility measured using an alpha source was determined to be 260±50 cm 2 /Vs. An alpha spectrum was recorded with one of the devices; however the detector appears to suffer from polarization.

Enhanced connectivity between visual cortex and other regions of the brain in autism: a REM sleep EEG coherence study

Functional interregional neural coupling was measured as EEG coherence during REM sleep, a state of endogenous cortical activation, in 9 adult autistic individuals (21.1±4.0 years) and 13 typically developed controls (21.5±4.3 years) monitored for two consecutive nights in a sleep laboratory. Spectral analysis was performed on 60 s of artefact-free EEG samples distributed equally throughout the first four REM sleep periods of the second night. EEG coherence was calculated for six frequency bands (delta, theta, alpha, sigma, beta, and total spectrum) using a 22-electrode montage. The magnitude of coherence function was computed for intra- and interhemispheric pairs of recording sites. Results were compared by Multivariate Analysis of Variance (MANOVA). Each time the autistic group showed a greater EEG coherence than the controls; it involved intrahemispheric communication among the left visual cortex (O1) and other regions either close to or distant from the occipital cortex. In contrast, lower coherence values involved frontal electrodes in the right hemisphere. No significant differences between groups were found for interhemispheric EEG coherence. These results show that the analysis of EEG coherence during REM sleep can disclose patterns of cortical connectivity that can be reduced or increased in adults with autism compared to typically developed individuals, depending of the cortical areas studied. Superior coherence involving visual perceptual areas in autism is consistent with an enhanced role of perception in autistic brain organization.

Comments on “Surface plasmon resonance of metal nanoparticles sandwiched between dielectric layers: theoretical modeling”

The Maxwell-Garnett's and Toudert's methods detailed in Appl. Opt.48, 778 (2009)APOPAI0003-693510.1364/AO.48.000778, based on the Maxwell-Garnett and Yamaguchi effective medium models, respectively, have been used for calculating the absorbance alpha of a (BaF(2)/Ag)(5)/BaF(2) nanocomposite thin film identical to the one presented in Fig. 1 of Appl. Opt.48, 778 (2009)APOPAI0003-693510.1364/AO.48.000778]. We propose that the discrepancies observed in this reference between the alpha spectra calculated by the two methods are due to a non rigorous use of both effective medium models by the author and show that adequate calculations lead to superposed spectra.

Characterization of radioactive particles using non-destructive alpha spectrometry

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.

Asymmetry in resonant breakup peaks in 6Li+ 209Bi reaction

The exclusive cross section for the breakup of 6Li by 209Bi has been measured at E l a b = 40 and 36 MeV. Sequential breakup, via the resonant state ( 3 + ) of 6Li in the continuum, dominates the total breakup cross section. The two sequential breakup peaks corresponding to the above resonant state, in both alpha and deuteron spectra, were found to be asymmetric. Continuum discretized coupled-channel (CDCC) calculations show the influence of both the Coulomb as well as the nuclear field on breakup.

Deconvolution of liquid scintillation alpha spectra of mixtures of uranium and radium isotopes

A method for the determination of uranium and radium isotopes in water samples is proposed. Liquid scintillation techniques were used for collecting alpha spectra, which were then analyzed by fitting the alpha peaks with overlapping Gaussians. The analysis can quantify the observed isotopes with accuracy depending on the activity of each isotope. In order to simulate the peaks with Gaussian normal distribution functions, the centroid of each peak as well as the full width at half maximum (FWHM) are required, as they depend on the quenching of the sample. For this purpose, samples with known activities of 226Ra and its decay products and also of the uranium isotopes 238U and 234U, at various quenching levels, were used to establish the correlation of the peaks' shift with the quench effect. In addition, the correlation of the FWHM with the centroid of a peak was determined, using the same procedure. Following the above analysis technique, an average of 97+/-2% of detection efficiency and a lower limit of detection of 8.2 mBq kg(-1) for alpha isotopes were achieved.

Experimental and simulation methods to evaluate the alpha self-absorption factors for radioactive aerosol fiber filters

Air sampling for particulate radioactive material involves collecting airborne particles on a filter in order to measure the radioactivity in the environment or in working areas. The amount of alpha radioactivity collected on the sampling filter is frequently determined by global alpha-particles measurements. Several factors can affect the alpha energy while passing through the filter to reach the detector. The most affecting factor on the alpha spectrum degradation is the absorption of alpha particle energies in the filter fibers. The fibers' density can range from 1 to 9 mg cm −2. The counting losses can accordingly be important, and the global activity in the filter can be underestimated. The complexity of the experiments and the diversity of the filter types, filtration conditions as well as detector types used for survey incite us to formulate a numerical model to simulate the correction factors of the degraded activity. Comparisons between experimental and simulated correction factors for a commonly used filter are presented. The good agreement found between experimental and calculated values validates the method in the studied conditions.

Self-absorption effects on alpha-induced atmospheric nitrogen fluorescence yield

Nitrogen fluorescence induced by radiation can be used to detect the presence of radioactive contamination in the environment. Contamination quantification from the fluorescence signal requires: the source’s effective alpha spectrum; the specific radiation quantum fluorescence efficiency; optical attenuation length in air of the fluorescence signal; the absolute throughput and quantum efficiency of the optical instrumentation; calibration of the instrumentation; and radiation transport modeling of the “effective” array exposure rate given the alpha particle spectrum. Field testing conducted on optical instrumentation measured the nitrogen fluorescence yield generated by 241Am alpha emissions. Laboratory studies of 241Am via alpha spectrometry determined whether the presence of solids on source surfaces produced sufficient self-absorption to decrease fluorescence. Results from the laboratory studies provided correction to the effective alpha-source activity values in a model of the earlier optical-sensor field measurements, and determined the air fluorescence efficiency of alpha particles generated by the 241Am sources used in the field experiments.

APPLICATION OF THE MONTE CARLO METHOD TO STUDY THE ALPHA PARTICLE ENERGY SPECTRA FOR RADIOACTIVE AEROSOL SAMPLED BY AN AIR FILTER

An alpha spectrometer including a semi-conductor detector is commonly used for measurements of the emergent alpha particles from an air filter, on which was sampled a radioactive aerosol. The alpha spectrometry and the detection efficiency are necessary input information for real radioactivity measurements. The MCNPX code based on the Monte Carlo method has been applied to simulate the detection process in order to obtain spectrum peaks and determine the detection efficiency for modeled geometry. First simulations with MCNPX have been carried out in order to validate the alpha particle energy spectrometry of an electrodeposited solid source and an initial simulated filter model. Furthermore, to improve our first filter model, the real spatial distribution of radioactive aerosols across the filter thickness, found experimentally, is taken into account in a multi-layer filter model. Such an alpha particle distribution allows achieving an adequate simulation of the filter. Comparison between measured and simulated alpha spectra highlights the good agreement in spectral parameters and in detection efficiency even under different aerosol spatial distributions inside the volume of the filter.

Synthesis of functional monolayer surfaces for rapid radiometric determination of plutonium

Glass or silicon substrates functionalized with a monolayer of carbamoylmethylphosphonate (CMP) ligands effectively bind tetravalent actinides from optimized mineral acid solutions to enable rapid, high quality radiometric assay by alpha spectrometry. The observed alpha spectra compare favorably with the highest quality electroplated samples. The CMP-functionalized surfaces have been used to develop simplified analytical methods to determine plutonium from complex mixtures.

SU‐EE‐A1‐01: Development of a System to Measure Neutron Microdosimetry Spectra in a Mixed Proton‐Neutron Field

Purpose: To develop a miniature tissue‐equivalent proportional counter (TEPC), timing‐coincidence veto, and pulse‐height analysis system for the purpose of measuring neutron Microdosimetry spectra in a proton beam. Method and Materials: TEPC's were constructed with active volume geometry consisting of a 2.5mm right circular cylinder and employing a 10μm diameter stainless steel wire as the detector anode centered on the axis of an A150 tissue‐equivalent plastic cylinder with 2mm thick wall. Stainless steel field tubes define the active volume which is filled with propane based tissue‐equivalent gas to 168torr simulating a tissue density volume with 2μm diameter. Two fully depleted transmission‐type silicon detectors with diameter of 31.6mm will be operated in timing coincidence with the proportional counter as a charged particle veto system. Detector pulses are digitized in a 60MS/s sampling ADC and the data acquisition software is written in the LabVIEW graphical programming language which acquires and writes pulse waveforms to disk where pulse heights and timing information are extracted for further analysis. Results: A TEPC was tested in a mixed field produced in a proton treatment room with the proton beam incident on a closed tungsten MLC. The timing and energy resolutions for the TEPCs can be estimated from alpha spectra taken with a FWT LET‐1/2 detector attached to the data acquisition system. Timing and lineal energy resolution for the TEPCs are estimated to be 200ns and >15keV/μm, respectively. Conclusion: Preliminary testing shows that the TEPC and silicon detector timing‐coincidence veto system is a viable method for extracting neutron Microdosimetry spectra from the mixed fields present in a proton therapy treatment room. This work was supported by the US Army Medical Research and Materiel Command under Contract Agreement No. DAMD17‐W81XWH‐07‐2‐0121. Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the US Army.

Characterisation of nasal swab samples by alpha spectrometry

A positive nasal swab taken at a radiation emergency, when properly collected and analysed, is a good indication of a potential inhalation intake. It may be expected to be a useful method for early dose assessment in cases of accidental inhalation of an alpha emitter. To improve the first estimation of intake activity, the quality of a nasal swab measurement was experimentally investigated. Alpha spectrometry was used to examine the experimental nasal swab samples involved with a plutonium solution or particles. Also, a numerical simulation analysis on the alpha spectrum using advanced alpha-spectrometric simulation was made to characterise the experimental results. It was observed that the alpha energy spectrum had a quite different shape among samples, and it was characterised by the type of contaminant. This could be the second advantage of using alpha spectrometry in addition to nuclide identification. The absorption of alpha radiation within the experimental nasal swab sample was different between the types of contaminants. For a quantitative discussion, the absorption for a swab sample must be determined for each type of contaminant. This new finding could be very useful for first responders. A nasal swab sample measured using an alpha spectrometer will give more useful information during the first response of an emergency.

Local Scale Exponents of Blood Pressure and Heart Rate Variability by Detrended Fluctuation Analysis: Effects of Posture, Exercise, and Aging

Heart rate self-affinity is often assessed by detrended fluctuations analysis, obtaining two coefficients only: a short-term (alpha(1)) exponent and a long-term (alpha(2)) exponent. Our aim is to show the limits of this approach and alternatively propose the estimation of the whole spectrum of local exponents alpha(n) for heart rate and blood pressure. To illustrate the advantages of this approach, we assess the effects of autonomic activations and age on alpha(n). We measured ECG and arterial pressure in 60 volunteers for 10 min, considering three conditions at increasing sympathetic activation: supine rest, sitting, and sitting during exercise. We computed alpha(n) of R-R intervals and systolic, mean, and diastolic blood pressures, as the slope of the detrended fluctuations function in a log-log plot. Volunteers were divided into age groups and compared. Results indicate that: 1) alpha(1) cannot be defined because short-term coefficients decrease with n, while alpha(2) cannot be defined only for blood pressure during supine rest; 2) heart rate and blood pressure scaling structures differ during supine rest but not during exercise; and 3) age effects appear mainly in supine rest, explaining discrepant results in literature. In conclusion, we recommend estimating the whole alpha(n) spectrum before possibly providing the "two-exponent" description only.

Study on radon dispersion modes from the U-mine disposal sites at Žirovski Vrh (Slovenia)

Long-term averages of outdoor radon levels give no information on time and spatial behaviour of dispersed radon that exhales from U-mine disposal sites. A comprehensive network of automatic stations for continuous measurements of short-lived radon decay products was installed in the early nineties at the Žirovski Vrh uranium mine. The instruments were positioned at key locations, on-site and off-site uranium mining area, and recorded EEC levels, alpha spectra, and local temperatures, all at least on hourly basis. Analyses of simultaneous records of EEC time series from several locations and analyses of corresponding alpha spectra gave more detailed information on characteristic patterns of radon behaviour and its dispersion from the sites under study. The identified modes of radon dispersion, depending on the presence and type of temperature inversion and the related major findings on the radon impact to the environment are shortly presented.

The nonpsychoactive cannabis constituent cannabidiol is a wake-inducing agent.

Cannabidiol (CBD) is a constituent of Cannabis sativa that induces nonpsychotropic effects, and some of its biological actions in sleep have been described by the authors' group. Here, the authors report that when administered 10 or 20 microg/1 microl during the lights-on period directly into either lateral hypothalamus (LH) or dorsal raphe nuclei (DRN), which are wake-inducing brain areas, CBD enhanced wakefulness and decreased slow wave sleep and REM sleep. Furthermore, CBD increased alpha and theta power spectra but diminished delta power spectra. Additionally, CBD increased c-Fos expression in LH or DRN. These findings suggest that this cannabinoid is a wake-inducing compound that presumably activates neurons in LH and DRN.