Contribution Of Alpha Particles Research Articles

Effect of boron compounds on the biological effectiveness of proton therapy.

We assessed whether adding sodium borocaptate (BSH) or 4-borono-l-phenylalanine (BPA) to cells irradiated with proton beams influenced the biological effectiveness of those beams against prostate cancer cells to investigate if the alpha particles generated through proton-boron nuclear reactions would be sufficient to enhance the biological effectiveness of the proton beams. We measured clonogenic survival in DU145 cells treated with 80.4-ppm BSH or 86.9-ppm BPA, or their respective vehicles, after irradiation with 6-MV X-rays, 1.2-keV/μm (low linear energy transfer [LET]) protons, or 9.9-keV/μm (high-LET) protons. We also measured γH2AX and 53BP1 foci in treated cells at 1 and 24h after irradiation with the same conditions. We found that BSH radiosensitized DU145 cells across all radiation types. However, no difference was found in relative radiosensitization, characterized by the sensitization enhancement ratio or the relative biological effectiveness, for vehicle- versus BSH-treated cells. No differences were found in numbers of γH2AX or 53BP1 foci or γH2AX/53BP1 colocalized foci for vehicle- versus BSH-treated cells across radiation types. BPA did not radiosensitize DU145 cells nor induced any significant differences when comparing vehicle- versus BPA-treated cells for clonogenic cell survival or γH2AX and 53BP1 foci or γH2AX/53BP1 colocalized foci. Treatment with 11 B, at concentrations of 80.4ppm from BSH or 86.9ppm from BPA, had no effect on the biological effectiveness of proton beams in DU145 prostate cancer cells. Our results agree with published theoretical calculations indicating that the contribution of alpha particles from such reactions to the total absorbed dose and biological effectiveness is negligible. We also found that BSH radiosensitized DU145 cells to X-rays, low-LET protons, and high-LET protons but that the radiosensitization was not related to DNA damage.

Experimental investigation at CATANA facility of n-10B and p-11B reactions for the enhancement of proton therapy.

The aim of the NEPTUNE (Nuclear process-driven Enhancement of Proton Therapy UNravEled) project is to investigate in detail both the physical and radiobiological phenomena that could justify an increase of the proton-induced cytogenetic effects in cells irradiated in presence of an agent containing natural boron. In this work, a double-stage silicon telescope coupled to different boron converters was irradiated at the CATANA proton therapy facility (INFN-LNS) for studying the proton boron fusion and the neutron boron capture reactions by discriminating secondary particles from primary protons. Different boron targets were developed by depositing boric acid, enriched with a higher than 99% content of 10B or 11B, on a 50 µm thick PolyMethilMetacrylate (PMMA) substrate. The 10B target allows to evaluate the contribution of lithium and alpha particles produced by the boron neutron capture reaction triggered by secondary thermal neutrons, while the 11B target is exploited for studying the effect of the p + 11B → 3α nuclear reaction directly triggered by primary protons. Experimental results clearly show the presence of alpha particles from both the reactions. The silicon telescope is capable of discriminating, by means of the so-called "scatter plots", the contribution of alpha particles originated by thermal neutrons on 10B with respect to the ones produced by protons impinging on 11B. Although a reliable quantitative study of the alpha production rate has not been achieved yet, this work demonstrates that low energy and, therefore, high-LET particles from both the reactions can be measured.

The contribution of alpha particles to the solar wind angular momentum flux in the inner heliosphere

Context. An accurate assessment of the Sun’s angular momentum (AM) loss rate is an independent constraint for models that describe the rotation evolution of Sun-like stars. Aims. In situ measurements of the solar wind taken by Parker Solar Probe (PSP), at radial distances of ~28−55 R⊙, are used to constrain the solar wind AM-loss rate. For the first time with PSP, this includes a measurement of the alpha particle contribution. Methods. The mechanical AM flux in the solar wind protons (core and beam), and alpha particles, was determined as well as the transport of AM through stresses in the interplanetary magnetic field. The solar wind AM flux was averaged over three hour increments, so that our findings more accurately represent the bulk flow. Results. During the third and fourth perihelion passes of PSP, the alpha particles contain around a fifth of the mechanical AM flux in the solar wind (the rest is carried by the protons). The proton beam is found to contain ~10−50% of the proton AM flux. The sign of the alpha particle AM flux is observed to correlate with the proton core. The slow wind has a positive AM flux (removing AM from the Sun as expected), and the fast wind has a negative AM flux. As with previous works, the differential velocity between the alpha particles and the proton core tends to be aligned with the interplanetary magnetic field. Conclusions. In future, by utilising the trends in the alpha-proton differential velocity, it may be possible to estimate the alpha particle contribution when only measurements of the proton core are available. Based on the observations from this work, the alpha particles contribute an additional 10−20% to estimates of the solar wind AM-loss rate which consider only the proton and magnetic field contributions. Additionally, the AM flux of the proton beam can be just as significant as the alpha particles, and so neither should be neglected in future studies.

Experimental studies of plasma-antenna coupling with the JET Alfvén Eigenmode Active Diagnostic

This paper presents a dedicated study of plasma-antenna (PA) coupling with the Alfvén Eigenmode Active Diagnostic (AEAD) in JET. Stable AEs and their resonant frequencies f, damping rates γ < 0, and toroidal mode numbers n are measured for various PA separations and limiter versus X-point magnetic configurations. Two stable AEs are observed to be resonantly excited at distinct low and high frequencies in limiter plasmas. The values of f and n do not vary with PA separation. However, |γ| increases with PA separation for the low-f, but not high-f, mode, yet this may be due to slightly different edge conditions. The high-f AE is detected throughout the transition from limiter to X-point configuration, though its damping rate increases; the low-f mode, on the other hand, becomes unidentifiable. The linear, resistive MHD code CASTOR is used to simulate the frequency scan of an AEAD-like external antenna. For the limiter pulses, the high-f mode is determined to be an n = 0 GAE, while the low-f mode is likely an n = 2 TAE. During the transition from limiter to X-point configuration, CASTOR indicates that n = 1 and 2 EAEs are excited in the edge gap. These results extend previous experimental studies in JET and Alcator C-Mod; validate the computational work performed by Dvornova et al (2020 Phys. Plasmas 27 012507); and provide guidance for the optimization of PA coupling in upcoming JET energetic particle experiments, for which the AEAD will aim to identify the contribution of alpha particles to AE drive during the DT campaign.

4He irradiation of zircon, ZrSiO4, using a micro-patterned, Si-based energy filter

The quantitative evaluation of alpha-particle damage in the mineral zircon, ZrSiO4, using 4He irradiation experiments is difficult because the vast majority of atomic knock-ons in the target are concentrated in a narrow depth range near the ends of the He-ion trajectories. Here we present a new concept to overcome this problem, namely, tailoring the depth profile of damage by means of a micromechanically fabricated “energy filter”. Lamellae of 1.5 μm thickness, prepared from ZrSiO4 using the focused-ion-beam technique, were subjected to irradiation with 8.8 MeV 4He ions. Five irradiations with ion fluences in the range 2.5 × 1015–1 × 1017 cm−2 have resulted in mild to severe damage, as monitored by the broadening and downshift of SiO4-stretching Raman bands. Our results may provide a means for quantifying the contribution of alpha particles to the total self-irradiation damage in zircon.

Radioactive Nuclei Induced Soft Errors at Ground Level

The role of all natural alpha emitters on the soft-error rate of integrated circuits is quantified. The impact of seven materials is given in FIT per mass unit. For instance, platinum has an isotope that is a natural alpha emitter, which may increase the Soft Error Rate up to 53 FIT/ng. Moreover, secular equilibrium of uranium is simulated by a Monte Carlo method. Only 90 parts per trillion of uranium is enough to explain the emissivity of wafers. Simulations show the trends of the alpha SER with scaling from the 250 nm technology node down to the 90 nm node. The contribution of alpha particles emitted by impurities to the SER is shown to become more important as the feature size decreases.

An updated simulation of particle fluxes and cosmogenic nuclide production in the Earth's atmosphere

Since the publication of our first paper devoted to this subject, we have extended our model, using new cosmic ray and nuclear data. Therefore, we revised particle fluxes in the atmosphere and used them in concert with experimental or evaluated cross sections to calculate the production rates of 3H, 7Be, 10Be, 14C, and 36Cl. The dependencies of these production rates on solar activity and geomagnetic field intensity were investigated in detail. Our simulations cover a whole range of these two parameters observed in the past. Comparison of the production rates calculated from two of the most frequently used primary galactic cosmic ray spectra showed weak dependence on the shape of the spectra. Alpha particles were included in the simulations for the first time, and we showed that the previously used scheme for estimation of alpha particle contribution to the total production rates is more complicated and latitude dependent. The production rates obtained agree well with most published experimental values.

Single Event Upsets Induced by 1–10 MeV Neutrons in Static-RAMs Using Mono-Energetic Neutron Sources

The neutron-induced SEU sensitivity in the 1-10 MeV energy range is investigated using monoenergetic neutron beams at 2.5, 4, 6, and 14 MeV. Below the 0.25 mum technology node, bulk technologies exhibit a relatively high sensitivity to neutrons between 4 and 6 MeV which is explained by the contribution of alpha particles coming from (n, alpha) reactions. In the terrestrial environment, the contribution to SER of neutrons in this energy range exceeds 10%.

Stabilization of the ideal m=1 internal kink by alpha particles and ICRF heated ions

The plasma potential energy delta Wtot associated with m=1 internal kink displacements is calculated for JET equilibria, taking into account the presence of alpha particles and ions heated by ion cyclotron resonance frequency (ICRF) waves. In the latter case the heated ion distribution is modelled as a simple function of ICRF parameters, which is consistent with numerical Fokker-Planck calculations. It is likely that the kink energy is an important parameter in determining the properties of sawtooth oscillations: in the ideal limit, positive values of delta Wtot indicate that kink displacements are stable. Alpha particles give rise to a stabilizing kinetic term in delta Wtot, but also exert a destabilizing influence owing to their effect on the Shafranov shift. The alpha particle contribution to delta Wtot is found to be destabilizing when the central value of the safety factor q0=0.75, but stabilizing when q0=0.9. The effect of ICRF heated minority ions can be calculated in terms of fluid and kinetic corrections to delta Wtot. Both trapped and passing ICRF heated ions play a significant stabilizing role. Complete stabilization of the ideal kink mode, due to either alpha particles or ICRF heated ions, is most easily achieved if q0 lies close to unity or if the radius of the q=1 surface is small

Diffuse alpha particles upstream of simulated quasi‐parallel supercritical collisionless shocks

One‐dimensional hybrid simulations of quasi‐parallel collisonless shocks have been performed. Alpha particles are included in the simulations self‐consistently in such a way that sufficient simulation particles are present to give reasonable statistics. It is found that a fraction of the incoming solar wind protons and alpha particles is accelerated near the shock and escapes upstream. These particles constitute a diffuse upstream particle population. The density ratio bias factor, i.e., the density ratio of diffuse alpha particles to diffuse protons normalized to the solar wind He++ to H+ density ratio varies between 0.5 and 4.0, and depends on the solar wind He++ to H+ density ratio and on the shock Mach number. The density ratio bias factor for a low Mach number shock (MA = 4.6) is f ∼ 0.5 when the alpha particles are treated as test particles and increases to ∼1 when the solar wind ratio of alpha to protons is 0.25. For a high Mach number shock of MA = 8.9 with a very small alpha particle contribution to the solar wind we obtained a density ratio bias factor of f ∼ 4.

Incorporation of ENDF-V neutron cross section data for calculating neutron-induced single event upsets

The authors report on improved methodologies of predicting upset rates of sensitive devices for neutron energies less than 20 MeV and between 20 and 50 MeV in silicon and apply these to predicting the neutron-induced single-event upset (NSEU) in the atmosphere for one of the most SEU-sensitive LSI bipolar RAMs (93L422). The improved method uses the differential cross section in both energy and angle from the most recent Evaluated Neutron Data File (ENDF-V), an extrapolation of the ENDF data to neutron energies in the 20-50-MeV range, and the detailed energy and angular dependence of the energy deposited as ionization in the sensitive volume of the device. The revised conclusions principally are: (a) elastic scattering contribution is reduced from that predicted by previous methods by an energy-dependent factor approaching an order of magnitude at 19 MeV; (b) the contribution due to inelastic scattering processes is dominant, particularly for neutron energies above 10 MeV, as opposed to dominance by the elastic scattering predicted previously; and (c) the previously neglected alpha particle contribution in (n,alpha) reactions is significant for critical charges >

Effects of alpha particles on the scattering function in CO2 laser scattering

It is shown that the alpha-particle contribution to the scattered power can be dominant in the coherent scattering of a CO2 laser in a Maxwellian plasma. For Ti = Te = 10 keV, the optimal forward-scattering angle is around 1.0°, with detection of the electron density fluctuation wavenumbers k⊥ >> k‖ (relative to the toroidal magnetic field). A strong resonance occurs at the lower hybrid frequency. Because of the strong dependence of the scattered signal on the alpha-particle temperature and the alpha distribution function, it seems feasible that CO2 laser scattering, using heterodyne techniques, could give detailed local information on fusion alphas.

The calibration of 6Li semiconductor sandwich spectrometers

The 6Li Semiconductor Sandwich Spectrometers which are commonly used for the measurement of fast-neutron spectra, especially in reactors, are subject to a variety of effects which, if not taken into account, can lead to significant calibration errors. The effects which are here discussed in detail are: 1. (1) the energy degradation in the sensitive layer of the spectrometer, 2. (2) the alpha-particle contribution to the “response function” used to deconvolve the lower-energy part of the neutron spectra, and 3. (3) the superposition of a high-energy contribution on the lower part of the measured spectrum in one mode of operation of the spectrometer. It will be shown that the failure to take account of these effects can in some circumstances lead to energy-calibration errors of ∼30 keV and errors of up to 50% in measured neutron spectra.