Incident Alpha Research Articles

Monte Carlo dosimetry for targeted irradiation of individual cells using a microbeam facility

Microbeam facilities provide a unique opportunity to investigate the effects of ionising radiation on living biological cells with a precise control of the delivered dose. This paper describes dosimetry calculations performed at the single-cell level in the microbeam irradiation facility available at the Centre d'Etudes Nucléaires de Bordeaux-Gradignan in France, using the object-oriented Geant4 Monte Carlo simulation toolkit. The cell geometry model is based on high-resolution three-dimensional voxelised phantoms of a human keratinocyte (HaCaT) cell line. Such phantoms are built from confocal microscopy imaging and from ion beam chemical elemental analysis. Results are presented for single-cell irradiation with 3 MeV incident alpha particles.

Optical appearance of alpha-particle tracks in CR-39 SSNTDs

The optical appearance of etched alpha-particle tracks in CR-39 SSNTDs under the transmission mode of the optical microscope were studied. The mean grey levels revealed using a digital camera installed on the microscope, together with the major and minor axes were systematically determined for tracks from alpha particles with different incident energies and angles. The grey level properties for the same track could vary to large extents, which could be corrected using optimum operation conditions of the camera. Differentiation among recorded tracks was then automated using a computer program, for which the grey levels, major and minor axes values were used as inputs and from which the angle and energy of the incident alpha particles were given as the outputs. The accuracy of the determined alpha-particle energy is 0.5 MeV.

Fabrication and characterization of metallic quasi-periodic structures

A variety of intriguing interference patterns are generated as a template to create metallic quasi-periodic structures using our robust experimental setup. A combination of thermal evaporation and lift-off process, the 2D metallic quasi-periodic structures are generated, a twelve-fold symmetry structure can be clearly observed in fabricated structures with four exposures. The excitation of surface plasmon (SP) resonances, which are determined by the geometry of metallic structures, the incident angle alpha, and the refractive index n(d) of the adjacent dielectric medium, is demonstrated in the optical transmission experiments. The optical transmission of metallic quasi-periodic structures can be tuned by varying the refractive index n(d), changing the period a and altering the incident angle alpha. The experimental results agree well with the predication for SP resonances. It's the first step to investigate the interesting optical properties of metallic quasi-periodic structures.

Computer program TRACK_VISION for simulating optical appearance of etched tracks in CR-39 nuclear track detectors

A computer program called TRACK_VISION for determining the optical appearances of tracks in nuclear track materials resulted from light-ion irradiation and subsequent chemical etching was described. A previously published software, TRACK_TEST, was the starting point for the present software TRACK_VISION, which contained TRACK_TEST as its subset. The programming steps were outlined. Descriptions of the program were given, including the built-in V functions for the commonly employed nuclear track material commercially known as CR-39 (polyallyldiglycol carbonate) irradiated by alpha particles. Program summary Program title: TRACK_VISION Catalogue identifier: AEAF_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEAF_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 4084 No. of bytes in distributed program, including test data, etc.: 71 117 Distribution format: tar.gz Programming language: Fortran 90 Computer: Pentium PC Operating system: Windows 95+ RAM: 256 MB Classification: 17.5, 18 External routines: The entire code must be linked with the MSFLIB library. MSFLib is a collection of C and C++ modules which provides a general framework for processing IBM's AFP datastream. MSFLIB is specific to Visual Fortran (Digital, Compaq or Intel flavors). Nature of problem: Nuclear track detectors are commonly used for radon measurements through studying the tracks generated by the incident alpha particles. Optical microscopes are often used for this purpose but the process is relatively tedious and time consuming. Several automatic and semi-automatic systems have been developed in order to facilitate determination of track densities. In all these automatic systems, the optical appearance of the tracks is important. However, not much has been done so far to obtaining the optical appearances of etched tracks. Solution method: A computer program is prepared to study the optical characteristics of tracks in the CR-39 nuclear track detector using the ray tracing method. Based on geometrical optics, light propagation through the tracks is simulated and the brightness of all grid elements in the track wall is calculated. Additional comments: The program distribution file contains an executable which enables the program to be run on a Windows machine. The source code is also provided, but in order to build an executable the MSFLIB must be available. Running time: Running time depends mainly on the resolution (number of grid elements in the track wall) required by the user. Running time is normally less than 1 min.

Track analysis of laser-illuminated etched track detectors using an opto-digital imaging system

An opto-digital imaging system for counting and analysing tracks on a LR-115 detector is described. One batch of LR-115 track detectors was irradiated with Am-241 for a determined period and distance for linearity test and another batch was exposed to radon gas. The laser-illuminated etched track detector area was imaged, digitized and analysed by the system. The tracks that were counted on the opto-digital system with the aid of media cybernetics software as well as spark gap counter showed comparable track density results ranging between 1500 and 2750 tracks cm−2 and 65 tracks cm−2 in the two different batch detector samples with 0.5% and 1% track counts, respectively. Track sizes of the incident alpha particles from the radon gas on the LR-115 detector demonstrating different track energies are statistically and graphically represented. The opto-digital imaging system counts and measures other track parameters at an average process time of 3–5 s.

Inelastic-collision cross sections for the interactions of totally stripped H, He and C ions with liquid water

The HKS and CDW-EIS models are implemented to determine single ionization cross sections (SICS) corresponding to the impact of H +, He 2+ and C 6+ ions on liquid water, for incident energies from 0.3 to 10 MeV/u. Corrected expressions for the HKS method have been used. The same kind of initial electron wave functions and binding energies have been used with both methods, in order to compare the formalisms themselves. Double and single differential as well as total SICS of liquid water have been calculated by use of both formalisms and comparisons have been made between their theoretical predictions. Also, these results have been compared with experimental values reported previously for ionization of water vapor due to protons and alpha particles. Despite its sophistication, the CDW-EIS method does not show better results than the more simple HKS model when comparing liquid water single and double differential cross sections with experimental water vapor values. However, once the excitation cross sections are included to determine electronic stopping cross sections in liquid water, the results based on the CDW-EIS method provide the best agreement when compared with corresponding data published in ICRU reports, obtaining discrepancies of about 9%, 16% and 19% for incident protons, alpha particles and carbon ions respectively.

Calculations of Track Growth 's and Profile's Plots in Cellulose Nitrate LR-115 Detector for Alpha Particles

The aim of this research is study of tracks growth experimentally and theoretically in cellulose nitrate LR-115 detector .The detector of 12jam thickness is irradiated normally by alpha particles with incident energies from 1 to 5MeV and incident angle 90°,by using 24lAm source , The etching of the detector Pieces was implemented by using chemical etchant NaOH with concentration 10% and temperature (60±1°C) ,A computer program ,(TRACK_TEST) also used for calculating track parameters as tracks depth and plotting track-wall profiles and contours of the track opening .The results showed that a maximum energy lost is occurred when the energy of the a-particles is about 2MeV. The tracks' tip for incident alpha energies 1 and 2MeV appeared in a spherical phase which is called rounded or over etched phase ,while a sharp phase for energies 3,4 and 5MeV was investigated . It was found that the track's depth which is calculated by computer program greater than that measured experimentally and that the percentage difference between two can be about 38% for 3MeV.

Simulation of cellular irradiation with the CENBG microbeam line using GEANT4

Light-ion microbeams provide a unique opportunity to irradiate biological samples at the cellular level and to investigate radiobiological effects at low doses of high linear energy transfer ionizing radiation. Since 1998 a single-ion irradiation facility has been developed on the focused horizontal microbeam line of the CENBG 3.5 MV Van de Graaff accelerator. This setup delivers in air single protons and alpha particles of a few MeV onto cultured cells, with a spatial resolution of a few micrometers, allowing subcellular targeting. In this paper, we present results from the use of the GEANT4 toolkit to simulate cellular irradiation with the CENBG microbeam line, from the entrance to the microprobe up to the cellular medium. We show that a 3 MeV incident alpha particle may deliver a dose of 0.33 Gy to a typical cell nucleus.

Quantitative depth profiling of ultra-shallow phosphorus implants in silicon using time-of-flight secondary ion mass spectrometry and the nuclear reaction 31P(α,p 0) 34S

Concentration profiles of ultra-shallow phosphorus implants in silicon have been extracted through use of time-of-flight SIMS in combination with nuclear reaction analysis. The phosphorus implants spanned the energy range 1–30 keV with fluences from 1e13 to 1e15 cm −2. The resonance in the nuclear reaction 31P(α,p 0) 34S at incident alpha particle energy 4.96 MeV was used to measure the total retained phosphorus for an implant fluence of 1e15 cm −2, hence quantifying the associated SIMS profile. For lower fluence implants, absolute profiles were recovered from the SIMS data by scaling the profile integrals. Over the implant energy and fluence ranges we have used we find no evidence for loss of phosphorus due to self-sputtering.

Measurement of deuterium in the presence of protium by elastic recoil spectroscopy

Determining the amount of a hydrogen isotope in a material by elastic recoil spectroscopy (ERS) is a routine capability of many laboratories and the data are relatively easy to analyze when only one isotope of hydrogen is present. However, when two or more isotopes of hydrogen are present the analysis is much more complicated. This paper presents data from such samples including a relatively thick sample of erbium hydride with an approximately 2:1 ratio of protium to deuterium and a sample of silicon with ion implanted deuterium that had absorbed hydrogen on the surface. The usual technique of simulation of the data is employed to determine the hydrogen isotope concentration profiles. This is complemented by taking data from the samples at various incident alpha particle beam energies to determine the identity of individual isotopes. This enables use of the variation in stopping power and cross-section with energy to cause, for example, a buried layer of deuterium to be removed from the position in the spectrum where protium from the surface of the sample will overlap the deuterium spectrum.

Computation of etched track profiles in CR-39 and comparison with experimental results for light ions of different kinds and energies

Computation of etched track profiles needs the knowledge of the variable track etch rates along the ion trajectories. Using the depth-dependent track etch rates experimentally determined for perpendicularly incident protons, deuterons and alpha particles as well as 7 Li , 11 B , 12 C , 14 N and 16 O ions of different energies simulations of the track development were performed. Two models of track etching were applied for that purpose recently published in literature. Although the models are based on the same physical fundamentals the results are slightly different. The reasons of the discrepancies were found by analysing the algorithms in detail. Comparison of the calculated track profiles with those determined experimentally from longitudinal sections of the etch pits showed good agreement for non-overetched as well as overetched tracks. The consistency of the whole experimental data set was checked by analysing the correlation of the track etch rates with geometric track parameters for all kinds of ions and etching times covered by the experiments.

Characterization of an alpha-particle irradiator for individual cell dosimetry measurements.

A computer-controlled, alpha-particle irradiator is described that allows for the measurement of the number and location of alpha-particle hits to individual cell nuclei, and subsequent scoring of cell survival. Cells are grown on a track-etch material (LR 115) and images are obtained of the cells prior to irradiation. The cells are then irradiated from below by a planar, collimated Am-241 source. The exposure time is varied so that the average number of hits to cell nuclei ranges from 0 to 3. After cell survival has been scored, images of the etched material are obtained and spatially registered to the original cell images. The etched images and cellular images are superimposed allowing for the determination of the number and position of hits to individual cell nuclei. This paper characterizes the irradiator including the energy and fluence of the incident alpha particles. Additionally, we describe the sources of uncertainty associated with this experiment, including the cell dish repositioning and cell migration during scanning and irradiation.

Breast cancer incidence and estrogen receptor alpha in normal mammary tissue--an epidemiologic study among Japanese women in Japan and Hawaii.

We have undertaken a study to examine whether the difference in breast cancer incidence between 2 populations of similar genetic background is reflected in a similar pattern of estrogen receptor alpha expression in normal mammary gland. Study participants were 92 Japanese women from Sapporo, Japan (mean age 48.2 years) and 49 Japanese women from Honolulu, Hawaii (mean age 45.4 years), who underwent biopsy indicating normal breast tissue or benign, nonproliferative breast disease in hospitals in Sapporo, Japan and Honolulu, Hawaii. The breast tissue samples were formalin-fixed and paraffin-embedded. The estrogen receptor immunohistochemistry assays were conducted using Dako kits. Japanese women in Hawaii, who have a higher incidence of breast cancer compared with Japanese women in Sapporo, also had, as predicted, higher mean percentage of estrogen receptor alpha-positive normal mammary cells (2-tailed test, p approximately 0.09). The results of our study are compatible with the hypothesis that estrogen receptor alpha expression in normal mammary tissue increases breast cancer risk and they also indicate that the expression of these receptors is dependent, at least in part, on nongenetic factors.

A CMOS integrated pulse mode alpha-particle counter for application in radon monitoring

A custom integrated circuit for detecting alpha particles for application in the monitoring of radon has been designed and tested. The design uses the reverse-biased well to substrate capacitance of a p-n junction in a conventional CMOS process as a sense capacitor for incident alpha particles, A simple CMOS inverter is used as an analog amplifier to detect the small potential change induced by an alpha-particle strike on the sense capacitor. The design was implemented in a 1.2-/spl mu/m conventional CMOS process with a sense capacitor area of 110 /spl mu/m/sup 2/. Tests carried out under vacuum conditions using a calibrated /sup 241/Am alpha-particle source showed an output voltage swing of /spl ges/2.0 V for an alpha event. The detector is also shown to have good immunity to noise and high-quantum efficiency for alpha particles.

Recoil ranges of nuclei produced in α-induced reactions on 1107 109Ag and 115In

Integral recoil ranges of evaporation residues for the reactions 107Ag(α, 3n), 107Ag(α, α2n), 109Ag(α, 2n), 109Ag(α, 3n), 109Ag(α, 4n), 115In(α, 2n), 115In(α, 3n) and 115In(α, αn) have been measured in the energy range of 202 - 60 MeV α-particles using the conventional thick target thick catcher technique. Transfer of linear momenta to the product nuclei for the above reactions have been deduced from experimental recoil range data. Detailed comparisons of the observations with predictions of theoretical calculations based on statistical model are presented and discussed. For (α, xn) reactions, overall agreement between the theory and the experiment is found to be satisfactory specially at low projectile energy. In cases of (α, αxn) reactions, the theory failed to reproduce the experimental linear momentum transfer even at low incident alpha energy.

The interaction of fast alpha particles with pellet ablation clouds

The energy spectra of energetic confined alpha particles are being measured using the pellet charge exchange method [R. K. Fisher, J. S. Leffler, A. M. Howald, and P. B. Parks, Fusion Technol. 13, 536 (1988)]. The technique uses the dense ablation cloud surrounding an injected impurity pellet to neutralize a fraction of the incident alpha particles, allowing them to escape from the plasma where their energy spectrum can be measured using a neutral particle analyzer. The signal calculations given in the above-mentioned reference disregarded the effects of the alpha particles’ helical Larmor orbits, which causes the alphas to make multiple passes through the cloud. Other effects such as electron ionization by plasma and ablation cloud electrons and the effect of the charge state composition of the cloud, were also neglected. This report considers these issues, reformulates the signal level calculation, and uses a Monte-Carlo approach to calculate the neutralization fractions. The possible effects of energy loss and pitch angle scattering of the alphas are also considered.

Multistep scattering in the 160 MeV208Pb(α, α′) reaction

New experimental data has been obtained for the208Pb(α, α′) reaction induced by 160 MeV alpha particles, for inelastic scattering to forward angles. We use these data to investigate the applicability of the multistep scattering theory of Feshbach, Kerman, and Koonin for describing this reaction. The mechanism we study, following the work of Gadioli et al. [1], is of the incident alpha particle remaining intact throughout the scattering process, exciting nucleon particle-hole pairs through multistep process. We conclude that this mechanism, combined with compound nucleus decay at low emission energies, can account for much of the observed data. However, there are indications that other processes also contribute at energies above the compound nucleus emission regime, and we outline future theoretical analyses that are needed.

Investigation of InAs single quantum wells buried in GaAs(001) using grazing incidence X-ray diffraction

InAs single quantum wells were grown by means of a low-pressure metal-organic chemical vapour deposition technique on GaAs(001). Their nominal thickness was varied among 0.7, 2, 3 and 4 monolayers and they were buried under a thick GaAs top layer. The samples were investigated by means of the grazing incidence X-ray diffraction using the weak (200) in-plane reflection. Depth resolution was obtained setting the angle of incidence and exit alpha i and alpha f, respectively, smaller or larger than the critical angle of total external reflection alpha c. Owing to the high sensitivity near the surface the collected rod scans show pronounced thickness oscillations for alpha i> alpha c. The thickness and the In-content, which control the scattering power of the single quantum wells were evaluated via simulation using the kinematic approach to X-ray diffraction. Partial relaxation occurs whenever the single quantum wells' thickness exceeds one monolayer. It is explained by the appearance of strain-reduced and non-tetragonally deformed islands built after the two- to three-dimensional transition of the growing mode.

Variation of the critical registration angle of alpha particles in CR39: Implications for radon dosimetry

This paper describes a methodology to characterize the response of a detector to alpha particles of different incidences and energies using an experimental irradiation system and an etching model. Implications for radon dosimetry are discussed. For each incident energy there is a particular angle above which alpha particles no longer induce an observable etched track. This angle also depends on the etching and on the conditions of observation of the detector. It is necessary to known the variation of that critical angle with incident alpha particle energy for given etching and observation conditions in order to determine the theoritical detection efficiency of a radon detector. This variation was studied for a CR39 detector (Tastrack, G.B.) over the energy range of the alpha particles emitted by radon (5,5 MeV) and its two short-life daughters : Po218 (6 MeV) and Po214 (7,7 MeV).

Principle of light ions micromapping and dosimetry using a CR-39 polymeric detector: Modelized and experimental uncertainties

In this paper we propose a model for light ion track etching in CR-39. This model is rigorously applicable to the case of light ions for which the mean latent track core diameter can be considered small compared with one micron. The relations describing the opening of an etch-pit, which can be simulated on a computer screen, are given their mathematical derivation. The comparison of simulated tracks with experimental tracks has presented good qualitative agreement. It is thus possible to use the theoretical model in order to evaluate the capabilities of CR-39 SSNTD in the field of micromapping or autoradiography. This simulation showed that a single measurement of the minor and major axis of a given etched track, repeated for several etching steps, is sufficient for calculating both energy and incidence angle of the particle. The case of reverse tracks (particle generated in the detector material (n, p) conversion…) is not treated in this paper. The study of critical angle will be treated in another paper. An evaluation of the uncertainty associated with this method is necessary for interpretation of the experimental measurements. We find that both experimental and simulated data contribute to the uncertainties of the used method. In particular, the necessary use of the optical microscopy is one of the most important sources of uncertainty if we consider that CR-39 SSNTD is an ideal detector (isotropic physical and chemical properties of the bulk material). Considering the mean track diameter distributions and standard deviations for normal incident ions of calibrated energy, such an assumption is realistic at the scale of the micrometer. On the other hand, the non-linear behaviour of the geometrical parameters (diameter, minor/major axis, area,…) which were obtained as a function of energy impose the variation of uncertainty with energy. Moreover, this uncertainty also varies with a sequential etching. This can be seen on the experimental plots (energy, diameter) for normal incident alphas or protons. Finally, the average uncertainty for micromapping and autoradiography using CR-39 SSNTD depends principally on the optical measurement device and on the range/energy relation, which is experimentally determined using our method.