Alpha Particle Flux Research Articles

Radiation stability test on multiphase glass ceramic and crystalline ceramic waste forms

A radiation stability study was performed on glass ceramic and crystalline ceramic waste forms. These materials are candidate host materials for immobilizing alkali/alkaline earth (Cs/Sr-CS)+lanthanide (LN)+transition metal (TM) fission product waste streams from nuclear fuel reprocessing. In this study, glass ceramics were fabricated using a borosilicate glass as a matrix in which to incorporate CS/LN/TM combined waste streams. The major phases in these multiphase materials are powellite, oxyaptite, pollucite, celsian, and durable residual glass phases. Al2O3 and TiO2 were combined with these waste components to produce multiphase crystalline ceramics containing hollandite-type phases, perovskites, pyrochlores and other minor metal titanate phases.For the radiation stability test, selected glass ceramic and crystalline ceramic samples were exposed to different irradiation environments including low fluxes of high-energy (∼1–5MeV) protons and alpha particles generated by an ion accelerator, high fluxes of low-energy (hundreds of keV) krypton particles generated by an ion implanter, and in-situ electron irradiations in a transmission electron microscope. These irradiation experiments were performed to simulate self-radiation effects in a waste form. Ion irradiation-induced microstructural modifications were examined using X-ray diffraction and transmission electron microscopy. Our preliminary results reveal different radiation tolerance in different crystalline phases under various radiation damage environments. However, their stability may be rate dependent which may limit the waste loading that can be achieved.

Effect of active processes on alpha particle density in the solar wind

The properties of alpha particle fluxes, the density of which increase under the action of flares and development of coronal mass ejections (CMEs) and solar wind structural inhomogeneities, have been studied. The maximal alpha particle density in plasma fine structure volumes reaches 12 cm−3. The amount of α particles is sometimes higher than that of protons. This is explained by the effect of the mechanism by which individual solar wind zones are nonuniformly enriched in helium nuclei when strong flares develop.

New methods of highly efficient controlled generation of radiation by liquid crystal nanostructures in a wide spectral range

We report the recent results of research focused on a new kind of soft matter – the liquid-crystal nanocomposites with controllable mechanical and nonlinear optical properties. These are promising media for implementation of ultra-compact photonic devices and efficient sources of coherent radiation in a wide spectral range. We overview the technology of preparation of nematic-liquid-crystal media saturated with disclination defects. The defects were formed in different ways: by embedding nanoparticles and molecular objects, by exposure to alpha-particle flux. The defect locations were controlled by applying an electric field. We also present and discuss the recently discovered features of nematic-liquid-crystal media: a thermal orientation effect leading to the fifth-order optical nonlinearity, enormous second-order susceptibility revealed by measurements, and structural changes upon exposure to laser radiation. We report on efficient generation of harmonics, sum and difference optical frequencies in nematic-liquid-crystal media. In addition, transformation of laser radiation spectra to spectral supercontinua, and filamentation of laser beams were also observed in nematic-liquid-crystal media. We conclude that most nonlinear optical effects result from changes of the orientational order in the examined nematic liquid crystals. These changes lead to the symmetry breaking and disclination appearances.

Modeling Laterally-Contacted nipi-Diode Radioisotope Batteries

A framework for modeling the power generation of laterally-contacted n-type/intrinsic/p-type/intrinsic (nipi) diodes coupled with an alpha-particle radioisotope source is developed. The framework consists of two main parts, the alpha-particle energy deposition profile (ADEP) and a lumped parameter equivalent circuit model describing the nipi device operation. Experimental measurements are used to verify the ADEP modeling approach which determines the spatially varying energy deposited within the device. Using these results, nipi-diode radioisotope batteries are simulated and the effect of the number of junctions, the thickness of the junction, and the alpha-particle flux on output voltage and power are investigated. The modeling results indicate that a 1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> bi-layer device (consisting of one source and two adjacent nipi-diodes) with a source activity of 300 mCi can reach a power output of 2 mW, excluding radiation damage effects.

Radiolytic oxidation of UO2 pellets doped with alpha-emitters (238/239Pu)

To assess the impact of alpha radiolysis of water on the oxidative dissolution of UO2 under anoxic conditions, two series of plutonium-doped samples (specific alpha activity 385 and 18 ) were fabricated, characterized and leached in water of varying complexity (pure water, carbonated water, dissolved hydrogen). Given the very high reactivity of these samples in the presence of air and in order to minimize any prior surface oxidation, a strict experimental protocol was developed based on high-temperature annealing in Ar + 4% H2 with preleaching cycles. Failure to follow this protocol prevents absolute quantification of oxidation of the UO2 surface by water radiolysis in solutions. Preoxidation of the pellet surface can lead to uranium release in solution that is dependent on the alpha particle flux, revealing initial oxidation by radiolysis in air including potential traces of water. This makes difficult the accurate quantification of the radiolytic oxidation in water solutions. Controlling the initial surface condition of the samples finally allowed us to demonstrate that radiolytic oxidation in water-saturated media is governed by several threshold effects for which the main parameters are the sample alpha activity and the hydrogen concentration.

Accommodation of prompt alpha-particle loss in a compact stellarator power plant

Alpha loss is an important issue in stellarators, where the inherent non-axisymmetry of the magnetic geometry causes an appreciable magnetic field ripple along the flux surfaces inside the plasma. This results in a non-negligible fraction of alpha-particles being promptly lost from the plasma and hitting the plasma facing components (PFC) at energies close to their born value of 3.5MeV. The PFC armor must not only accommodate the heat load from the alpha-particle flux but it must also accommodate the He implantation resulting from the high-energy alpha fluxes while providing the required lifetime. An effort is underway as part of the ARIES-CS study to characterize the alpha-particle loss for a compact stellarator and to explore engineering solutions to accommodate the impact of these alphas on the PFC’s. This paper summarizes the initial results from this effort.

Development of a Simple and Tough Alpha-Particle Detector Used at High Temperature

Several ceramic detectors were made by use of the insulation layer formed on two types of substrate, i.e. aluminum and silicon. Each detector was irradiated with alpha-rays from an Am-241 source and the electric charge induced in the detector was measured in the temperature range from room temperature up to 450 K. The alpha-ray detection signals were well observed with an oscilloscope at the properly high bias-voltage only for very short time from several seconds to several tens of seconds before the start of the sweeping insulation breakdown. Though this type of the simple detector made of a thin ceramic layer can be hardly used for the energy analysis, it might be effectively applicable to the measurement of the flux of alpha-particles at high temperature.

Implications of the space radiation environment for human exploration in deep space

Human exploration of the solar system beyond Earth's orbit will entail many risks for the crew on these deep space missions. One of the most significant health risks is exposure to the harsh space radiation environment beyond the protection provided by the Earth's intrinsic magnetic field. Crew on exploration missions will be exposed to a complex mixture of very energetic particles. Chronic exposures to the ever-present background galactic cosmic ray (GCR) spectrum consisting of all naturally occurring chemical elements are combined with sporadic, possibly acute exposures to large fluxes of solar energetic particles, mainly protons and alpha particles. The background GCR environment is mainly a matter of concern for stochastic effects, such as the induction of cancer with subsequent mortality in many cases, and late deterministic effects, such as cataracts and possible damage to the central nervous system. Unfortunately, the actual risks of cancer induction and mortality owing to the very important high-energy heavy ion component of the GCR spectrum are essentially unknown. The sporadic occurrence of extremely large solar energetic particle events (SPE), usually associated with intense solar activity, is also a major concern for the possible manifestation of acute effects from the accompanying high doses of such radiations, especially acute radiation syndrome effects such as nausea, emesis, haemorrhaging or, possibly, even death. In this presentation, an overview of the space radiation environment, estimates of the associated body organ doses and equivalent doses and the potential biological effects on crew in deep space are presented. Possible methods of mitigating these radiations, thereby reducing the associated risks to crew are also described.

Effect of alpha irradiation on UO2 surface reactivity in aqueous media

Abstract The option of direct disposal of spent nuclear fuel in a deep geological formation raises the need to investigate the long-term behavior of the UO2 matrix in aqueous media subjected to α-β-γ radiation. The β-γ emitters account for most of the activity of spent fuel at the moment it is removed from the reactor, but diminish within a millennial time frame by over three orders of magnitude to less than the long-term activity. The latter persists over much longer time periods and must therefore be taken into account over a geological disposal time scale. Leaching experiments with solution renewal were carried out on UO2 pellets doped with alpha emitters (238Pu and 239Pu) to quantify the impact of alpha irradiation on UO2 matrix alteration. Three batches of doped UO2 pellets with different alpha flux levels (3.30×104, 3.30×105, and 3.2×106 α cm-2 s-1) were studied. The results obtained in aerated and deaerated media immediately after sample annealing or interim storage in air provide a better understanding of the UO2 matrix alteration mechanisms under alpha irradiation. Interim storage in air of UO2 pellets doped with alpha emitters results in variations of the UO2 surface reactivity, which depends on the alpha particle flux at the interface and on the interim storage duration. The variation in the surface reactivity and the greater uranium release following interim storage cannot be attributed to the effect of alpha radiolysis in aerated media since the uranium release tends toward the same value after several leaching cycles for the doped UO2 pellet batches and spent fuel. Oxygen diffusion enhanced by alpha irradiation of the extreme surface layer and/or radiolysis of the air could account for the oxidation of the surface UO2 to UO2+x. However, leaching experiments performed in deaerated media after annealing the samples and preleaching the surface suggest that alpha radiolysis does indeed affect the dissolution, which varies with the flux at the UO2/water interface.

The role of drift and convection–diffusion mechanisms in small energy global cosmic ray modulation: Application to the hysteresis phenomenon of proton and alpha particle satellite data

The hysteresis effect for small energies of galactic cosmic rays is due to two effects. The first is the same as for neutron monitor energies – the delay of the interplanetary processes responsible for cosmic ray modulation with respect to the initiating solar processes, according to the effective velocity of solar wind and shock waves propagation. Then, the observed cosmic ray intensity is connected to the solar activity variations during many months before the time of cosmic ray measurement. The second is caused by the time delay of small energy cosmic ray diffusion from the boundary of modulation region to the Earth’s orbit. The model describing the connection between solar activity variation and cosmic ray convection–diffusion global modulation for neutron monitor energies is here developed by taking into account also the time-lag of the small energy particle diffusion in the Heliosphere. We use theoretical results on drifts and analytically approximate the dependences of drifts from tilt angle, and take into account the dependence from the sign of primary particles, and from the sign of polar magnetic field ( A > 0 or A < 0). The obtained results are applied on proton and alpha-particle satellite data. We analyze satellite 5-min data of proton fluxes with energies >1 MeV, >2 MeV, >5 MeV, >10 MeV, >30 MeV, >50 MeV, >60 MeV, >100 MeV, and in intervals 10–30 MeV, 30–60 MeV, and 60–100 MeV during January 1986–December 1999. We exclude periods with great cosmic ray increases caused by particle acceleration in solar flare events. Then, we determine monthly averaged fluxes, as well as 5-month and 11-month smoothed data. We analyze also satellite 5-min data on alpha-particle fluxes in the energy intervals 60-160 MeV, 160–260 MeV and 330–500 MeV during January 1986–May 2000. We correct observation data for drifts and then compare with what is expected according to the convection–diffusion mechanism. We assume different dimensions of the modulation region (by the time propagation X 0 of solar wind from the Sun to the boundary of modulation region), for X 0 values from 1 to 60 average months, by one-month steps. For each value of X 0 we determine the correlation coefficient between variations of expected and observed cosmic ray intensities (the estimation of cosmic ray intensities values is given in Section 3 by Eq. (9), and the determination of correlation and regression coefficients in Section 3 by Eq. (8)). The dimension of modulation region is determined by the value of X 0 max , for which the correlation coefficient reaches the maximum value. Then the effective radial diffusion coefficient and residual modulation in small energy region can be estimated.

First wall issues related with energetic particle deposition in a tokamak fusion power reactor

Energetic particle deposition to the wall due to toroidal magnetic field (TF) ripple was assessed for a 2 GW fusion power reactor. When the present allowance for the loss is applied, the alpha particle flux to the wall can be as high as 2×10 18 m −2 s −1 in the reactor, eroding tungsten by ∼20 μm per year. The peak particle fluence over a 2-year operation cycle can reach 10 26 m −2, probably being larger than a critical fluence for blister formation. The result suggests that, for the steady-state tokamak fusion reactor, we should introduce a new design methodology of determining an acceptable level of TF ripple on the basis of particle fluence to the wall, instead of the present one based on a tolerable heat flux.

Effects of α and γ Radiolysis of Water on Alteration of the Spent UO2 Nuclear Fuel Matrix

ABSTRACTAn experimental approach was developed to quantify the influence of α and γ radiolysis of water on the dissolution kinetics of the spent UO2 fuel matrix. Two types of experiments were carried out: leaching experiments in deaerated media with UO2 fuel pellets doped with alpha emitters (238Pu), and leaching experiments with UO2 fuel pellets (standard or doped with alpha emitters) submitted to γ irradiation. Leaching experiments on UO2 pellets doped with alpha-emitters in deionized water and in deaerated media showed a correlation between the alpha particle flux at the reaction interface and uranium release in solution. The higher the alpha particle flux at the reaction interface, the higher the uranium release rate (mean rates over 30 days at S/V = 3 m−1: 15-year batch, r = 2.5 mg·m−2d−1; 1500-year batch, r = 0.2 mg·m−2d−1; 40 000-year batch, r = 0.04 mg·m−2d−1). These results, obtained at low flux levels that are realistic on a disposal time scale, supplement existing data describing the effect of doping on UO2 alteration at higher flux levels. Leaching experiments with the 1500-year batch under gamma irradiation allowed us to quantify the impact of a gamma irradiation field on the UO2 release. At 650 Gy·h−1 the effects of alpha irradiation appear to be fully masked since the uranium release is 450 times higher than in the presence of the alpha irradiation field alone. The Chemsimul code was also used to model water radiolysis and uranium release into solution.

Visualization of particle flux in the human body on the surface of Mars.

For a given galactic cosmic ray (GCR) environment, information on the particle flux of protons, alpha particles, and heavy ions, that varies with respect to the topographical altitude on the Martian surface, are needed for planning exploration missions to Mars. The Mars Global Surveyor (MGS) mission with its Mars Orbiter Laser Altimeter (MOLA) instrument has been providing precise topographical surface map of the Mars. With this topographical data, the particle flux at the Martian surface level through the CO2 atmospheric shielding for solar minimum and solar maximum conditions are calculated. These particle flux calculations are then transported first through an anticipated shielding of a conceptual shelter with several water equivalent shield values (up to 50 g/cm2 of water in steps of 5 g/cm2) considered to represent a surface habitat, and then into the human body. Model calculations are accomplished utilizing the HZETRN, QMSFRG, and SUM-MARS codes. Particle flux calculations for 12 different locations in the human body were considered from skin depth to the internal organs including the blood-forming organs (BFO). Visualization of particle flux in the human body at different altitudes on the Martian surface behind a known shielding is anticipated to provide guidance for assessing radiation environment risk on the Martian surface for future human missions.

Distributions of alpha particles escaping to the wall during sawtooth oscillations in the Tokamak Fusion Test Reactor

It has been observed experimentally in deuterium–tritium shots of the Tokamak Fusion Test Reactor (TFTR) [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)] that crashes of sawtooth oscillations may result in very inhomogeneous flux of alpha particles to the wall. To explain this phenomenon, both theoretical analysis and numerical simulation have been carried out. It is concluded that the “crash-induced prompt loss,” i.e., the orbital loss of marginally trapped particles arising because of the crash-induced orbit transformation of circulating particles, is responsible for the flux near the bottom of the vessel, whereas the crash-induced stochastic diffusion of moderately trapped particles explains the large signal near the equatorial plane of the torus. The calculated poloidal distributions of the integral alpha flux are in reasonable agreement with experimental data. The energy spectrum of the escaping particles has also been calculated, which can be used for diagnostics of the crash type.

Development and operation of a thin foil Faraday collector as a lost ion diagnostic for high yield d-t tokamak fusion plasmas

We are continuing our development of a radiation-hard, charged-particle detector consisting of a series of thin parallel conducting foils as a lost ion diagnostic for high yield d-t tokamak fusion plasmas. Advantages of this detector concept include economy, ability to operate in relatively intense neutron/gamma ray radiation backgrounds and at moderately high temperatures, and a modest degree of energy resolution. A detector consisting of four parallel foils of Ni, each of thickness 2.5 μm, was operated in the Joint European Torus during the recent DTE-1 experiment. During the highest yield pulses of this campaign, (16 MW), the flux of energetic alpha particles at the detector was measured to be less than about 2 nA/cm2. This upper limit is significantly greater than the expected flux assuming classical losses and given the geometry of the detector. During most of the nearly 2500 pulses of the DTE-1 experiment for which the detector response has been inspected, a relatively intense (up to 200 nA/cm2) flux of low energy positively charged particles was observed which appears related to the D-α photon flux at the plasma edge. Similar detector designs have been recently evaluated using monoenergetic helium ion beams from the tandem accelerator at Sandia National Laboratories. One such detector, consisting of six foils of 6 μm thick Al demonstrated an energy resolution of about 7% for 7 MeV alpha particles. Possible improvements to this detector concept include the fabrication of an “integrated circuit” like design consisting of alternately deposited layers of insulator and conductor. Future applications of the detector concept include first wall lost ion diagnostics for the ignition device to test engineering concepts and NSTX.

Modelling the field soft error rate of DRAMs by varying the critical cell charge

The Field Soft Error Rate (FSER) has been determined by the variation of the critical charge and the measurement of the charge collection volume determined by alpha-particle irradiation. The modelled FSER versus critical charge dependence agrees well to the one of the Field Soft Error measurements. The results futher show, that the impact of the on-chip Alpha-Particle flux can be neglected.

Characterization of large-area reference sources for the calibration of alpha-contamination monitors

A simple method has been developed whereby the activity of a large-area reference source for the calibration of alpha-contamination monitors can be determined from the measured alpha-particle flux. A correction factor k is determined from the pulse height spectrum of the source in a large-area proportional counter to take into account backscattering and self-absorption in the source. This correction factor is used to calculate the activity with an uncertainty not exceeding 10%.

Observation of space radiation environment with EXOS-D

Space radiation environmental data, mainly in the radiation belt, were obtained during the quiet condition of the magnetosphere from March 1989 to December 1991. The measured electron and proton energy spectra for the EXOS-D satellite were harder than predicted spectra from the NASA radiation belt models. The spatial distribution of alpha particle flux was obtained. Alpha particles in the radiation belt were very limited, but they are important for dose calculations. The new data will be very useful for estimating the dose for spacecraft and astronauts in the inner radiation belt. The observation period included some big geomagnetic storms, and the data are helpful for making clear the detailed behavior of charged particles in the radiation belt.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Etched track detectors in solar neutrino experiments

Within the framework of LOREX experiment the mineral Lorandite (TlAsS2) of the old (5 × 106 years) arsenic mine Allchar (Kavadarci, Macedonia) will be used to estimate average solar neutrino flux from the amounts of 205Pb isotope (T12=1.5 × 107 years) induced by 205Tl (ve, e-205Pb reaction. In order to evaluate the amount of the 205Pb isotope induced by 204Pb (n, γ) 205Pb reaction the thermal neutron flux inside and above the mine was measured by our high sensitive etched track neutron dosemeters (CR-39/BE, CR-39/BN-1). The thermal neutron flux was found to be (2.7 ± 0.4) × 10-3 cm-2 s-1. In addition to cosmic muon interactions and spontaneous fissions the neutrons can be produced through various (α, n) reactions due to the high alpha particle flux from the decay chains of uranium and thorium. Therefore radon concentration in the mine was measured by our diffusion chamber type dosemeter utilizing CR-39 detector and was found to be 1.5 × 104 Bq m-3. The possibilities to extend the application of etched track detectors to another solar neutrino experiments are discussed.

Solar wind from a corona with a large helium abundance

Observations of quasi‐steady high‐speed solar wind streams show that the proton mass flux density at 1 AU is remarkably constant, varying by less than 10% over long time periods. These observations are problematic, for simple theoretical models predict that the proton mass flux density is a sensitive function of the coronal base temperature, which is not expected to be unvarying to the degree required by the observations. In this paper we investigate the possibility that the presence of alpha particles in the coronal base region can reduce the sensitivity of the proton mass flux to the base temperature. The equations of mass and momentum conservation are solved for electrons, protons, and alpha particles using a variety of assumed temperature profiles for each species. A wide range of base conditions are considered. We find that for an alpha particle to proton density ratio at the base as small as 10%, alpha particles can reduce the sensitivity of the proton mass flux density to variations in the base temperature. We also study the effects of enhanced collisional coupling and of Alfvén waves on the flux of protons and alpha particles. As an aid to future observational determination of the alpha particle density in the corona, we present calculations of the intensities of the resonantly scattered lines He II λ304 and H I λ1216 for selected models.