Monoenergetic Heavy Ions Research Articles

Space radiation research with heavy ions at HIMAC

The HIMAC (Heavy Ion Medical Accelerator in Chiba) was originally designed principally for carbon ion therapy, but heavy ion research projects in medicine, physics, chemistry and biology have been conducted under a collaborative research framework since 1994. One major application is space radiation research. The radiation in space of greatest interest for human space exploration consists of energetic protons and heavy ions which can affect the health of space crew and lead to the failure of electronic devices. Ground-based experiments at heavy ion accelerators are crucial for ensuring mission crew safety and for understanding the biological effects of long-term exposure to space radiation. HIMAC provides a range of linear energy transfer (LET) beams from protons to Xe ions at energies up to 800 MeV/u, representing the most biologically-significant components of the space radiation field. At HIMAC a variety of radiation detectors and instruments are characterized and calibrated for dosimetry using specific mono-energetic heavy ion beams, the performance of shielding materials for mitigating space radiation dose is evaluated, radiation hardness of electronic devices is tested to ensure their safe operation in space, and the radiobiological studies are conducted to understand biological effects in humans during long-term space activities. HIMAC is an indispensable simulator of space radiation for the new decade of space exploration.

Quasi mono-energetic heavy ion acceleration from layered targets

In the present work, we demonstrate acceleration of quasi monoenergetic heavy ions during the interaction of a high-intensity short-pulse laser with multi-layer targets. The targets, consisting of layers of high-Z (gold) and low-Z (carbon) species a few nm thick, have been used to tailor the energy spectra of the high-Z ion species. Au-ion bunches of energy around 500 keV with an energy spread of less than 20% are observed. Particle-in-cell simulations provide explanation for a number of features of the experimental observations. Several behaviors, in addition to the expected sheath-field acceleration, were found to be involved. It is found that the Au layer is pistoned outward by the underlying Si substrate whilst simultaneously being tamped at its leading edge by the carbon overlay. The simulations show best agreement with the experiments when the carbon layer is first rarefied by the laser prepulse. In these cases, the simulations reproduce the double-humped spectra found in the experiment. Ion-electrostatic instabilities rapidly lead to the formation of a single trapping-like structure in phase space of relatively long wavelength. This long-lived structure dominates the ion acceleration and produces a double-peaked energy spectrum. It is suggested that the instability responsible may be of the Pierce-type.

Mono-energetic heavy ion acceleration from laser plasma based composite nano-accelerator

High intensity ultrashort pulse driven ion acceleration is an important area of research due to its richness in underlying physics and potential technological applications. A strong impediment towards employing such sources, in practice, lies in the inherent challenge of producing mono-energetic ions with fine energy control. We demonstrate consistent, highly reproducible, charge-independent mono-energetic acceleration of heavy gold ions to sub-MeV energies with a reasonably high flux of 9 × 1010 ions per shot from the gold-carbon nano-composite target irradiated at moderate laser intensities of 1018–1019 W/cm2. The experimental results establish that the thermal pressure of the expanding hot plasma, instead of the “hot” electrons, is responsible for the acceleration of the mono-energetic heavy Au ions. Our results pave the way for a simple and new way of producing mono-energetic heavy ions. This may find potential applications in advanced particle accelerators, isochoric heating of matter, surface science, swift heavy ion sources, and basic plasma physics.

Generation of quasi-monoenergetic heavy ion beams via staged shock wave acceleration driven by intense laser pulses in near-critical plasmas

Laser-driven ion acceleration potentially offers a compact, cost-effective alternative to conventional accelerators for scientific, technological, and health-care applications. A novel scheme for heavy ion acceleration in near-critical plasmas via staged shock waves driven by intense laser pulses is proposed, where, in front of the heavy ion target, a light ion layer is used for launching a high-speed electrostatic shock wave. This shock is enhanced at the interface before it is transmitted into the heavy ion plasmas. Monoenergetic heavy ion beam with much higher energy can be generated by the transmitted shock, comparing to the shock wave acceleration in pure heavy ion target. Two-dimensional particle-in-cell simulations show that quasi-monoenergetic ion beams with peak energy 168 MeV and considerable particle number are obtained by laser pulses at intensity of in such staged shock wave acceleration scheme. Similarly a high-quality ion beam with a well-defined peak with energy 250 MeV and spread can also be obtained in this scheme.

Drag of ballistic electrons by an ionic beam: Giant oscillations of the drag current

Foundations of the theory of Coulomb drag of ballistic electrons of a quantum nanowire by a flux of monoenergetic heavy ions moving with the same velocity V have been elaborated. The ratio of the drag current to the initial current of the ionic beam has been determined. It has been shown that the drag current is a nonmonotonic function of the velocity V. This function has a sharp maximum at the velocity V = vnF/2, where n is the number of the upper active (i.e., participating in the charge transfer) electron miniband (channel) and vnF is the corresponding Fermi velocity. Thus, it turns out that the phenomenon of giant oscillations of the Coulomb drag current can be used for studying the electron spectra of ballistic nanostructures.

Generation of high-energy mono-energetic heavy ion beams by radiation pressure acceleration of ultra-intense laser pulses

Generation of high-energy mono-energetic heavy ion beams by radiation pressure acceleration (RPA) of intense laser pulses is investigated. Different from previously studied RPA of protons or light ions, the dynamic ionization of high-Z atoms can stabilize the heavy ion acceleration. A self-organized, stable RPA scheme specifically for heavy ion beams is proposed, where the laser peak intensity is required to match with the large ionization energy gap when the successive ionization state passes the noble gas configurations [such as removing an electron from the helium-like charge state (Z−2)+ to (Z−1)+]. Two-dimensional particle-in-cell simulations show that a mono-energetic Al13+ beam with peak energy 1.0 GeV and energy spread of only 5% can be obtained at intensity of 7×1020 W/cm2 through the proposed scheme. A heavier, mono-energetic, ion beam (Fe26+) can attain a peak energy of 17 GeV by increasing the intensity to 1022 W/cm2.

Physical Modelling of Proton and Heavy Ion Radiation using Geant4

Protons and heavy ion particles are considered to be ideal particles for use in external beam radiotherapy due to superior properties of the dose distribution that results when these particles are incident externally and due to their relative biological effectiveness. While significant research has been performed into the properties and physical dose characteristics of heavy ions, the nuclear reactions (direct and fragmentation) undergone by He 4 , C 12 and Ne 20 n u c l e i u s e d i n r a d i o t h e r a py i n m a t e r i a l s o t h e r t h a n w a t e r i s s till l a r g e l y unexplored. In the current project, input code was developed for the Monte Carlo toolkit Geant 4 version 9.3 to simulate the transport of several mono-energetic heavy ions through water. The relative dose contributions from secondary particles and nuclear fragments originating from the primary particles were investigated for each ion in both water and dense bone (ICRU) media. The results indicated that the relative contribution to the total physical dose from nuclear fragments increased with both increasing particle mass and with increasing medium density. In the case of 150 MeV protons, secondary particles were shown to contribute less than 0.5% of the peak dose and as high as 25% when using 10570 MeV neon ions in bone. When water was substituted for a bone medium, the contributions from fragments increased by more than 6% for C 12 and Ne 20 .

Acceleration of heavy ions by perpendicular collisionless shocks: Impact of the shock front nonstationarity

[1] Both hybrid/full particle simulations and recent experimental results have clearly evidenced that the front of a supercritical quasi-perpendicular shock can be nonstationary. One responsible mechanism proposed for this nonstationarity is the self-reformation of the front itself being due to the accumulation of reflected ions. Important consequences of this nonstationarity are that not only the amplitude but also the spatial scales of fields components at the shock front (ramp and foot) are strongly varying within each cycle of the self-reformation. On the other hand, several studies have been made on the acceleration and heating of heavy ions but most have been restricted to a stationary shock profile only. Herein, one-dimensional test particle simulations based on shock profiles fields produced in PIC simulation are performed in order to investigate the impact of the shock front nonstationarity on heavy ion acceleration (He, O, Fe). Reflection and acceleration mechanisms of heavy ions (with different initial thermal velocities and different charge-mass ratios) interacting with a nonstationary shock front (self-reformation) are analyzed in detail. Present preliminary results show that: (1) the heavy ions suffer both shock drift acceleration (SDA) and shock surfing acceleration (SSA) mechanisms; (2) the fraction of reflected heavy ions increases with initial thermal velocity, charge-mass ratio and decreasing shock front width at both stationary shocks (situation equivalent to fixed shock cases) and nonstationary shocks (situation equivalent to continuously time-evolving shock cases); (3) the shock front nonstationarity (time-evolving shock case) facilitates the reflection of heavy ions; (4) a striking feature is the formation of an injected monoenergetic heavy ions population which persists in the shock front spectrum for different initial thermal velocities and ions species. The impact of the shock front nonstationarity on the heavy ions spectra within the shock front region and the downstream region are detailed separately. Present results are compared with previous experimental analysis and theoretical models of solar energetic particles (SEP) events. The variations of Fe/O spectra in high energy part have been retrieved, and the nonstationary effects of shock front strongly amplify these variations.

Ion acceleration with mixed solid targets interacting with circularly polarized lasers

The interaction of a circularly polarized laser pulse with a mixed solid target containing two species of ions is studied by particle in cell simulations and analytical model. After the interaction tends to be stable, it is demonstrated that the acceleration is more efficient for the heavier ions than that in plasmas containing a single kind of heavy ion and the acceleration efficiency is higher when its proportion is lower. To obtain monoenergetic heavy-ion beams, a sandwich target with a thin mixed ion layer between two light ion layers and a microstructured target are proposed. The influences of parameters of the laser pulse and target on ion acceleration are discussed in detail. It is found that, when the target is thick enough, a cold target is more appropriate for heavy-ion acceleration than a warm target, and the velocity of the reflected heavy ions is proportional to the laser amplitude.

Generating Monoenergetic Heavy-Ion Bunches with Laser-Induced Electrostatic Shocks

A method for efficient laser acceleration of heavy ions by electrostatic shock is investigated using particle-in-cell (PIC) simulation and analytical modeling. When a small number of heavy ions are mixed with light ions, the heavy ions can be accelerated to the same velocity as the light ions so that they gain much higher energy because of their large mass. Accordingly, a sandwich target design with a thin compound ion layer between two light-ion layers and a micro-structured target design are proposed for obtaining monoenergetic heavy-ion beams.

Experimental determination of particle range and dose distribution in thick targets through fragmentation reactions of stable heavy ions

In radiation therapy with highly energetic heavy ions, the conformal irradiation of a tumour can be achieved by using their advantageous features such as the good dose localization and the high relative biological effectiveness around their mean range. For effective utilization of such properties, it is necessary to evaluate the range of incident ions and the deposited dose distribution in a patient's body. Several methods have been proposed to derive such physical quantities; one of them uses positron emitters generated through projectile fragmentation reactions of incident ions with target nuclei. We have proposed the application of the maximum likelihood estimation (MLE) method to a detected annihilation gamma-ray distribution for determination of the range of incident ions in a target and we have demonstrated the effectiveness of the method with computer simulations. In this paper, a water, a polyethylene and a polymethyl methacrylate target were each irradiated with stable 12C, 14N, 16O and 20Ne beams. Except for a few combinations of incident beams and targets, the MLE method could determine the range of incident ions R MLE with a difference between R MLE and the experimental range of less than 2.0 mm under the circumstance that the measurement of annihilation gamma rays was started just after the irradiation of 61.4 s and lasted for 500 s. In the process of evaluating the range of incident ions with the MLE method, we must calculate many physical quantities such as the fluence and the energy of both primary ions and fragments as a function of depth in a target. Consequently, by using them we can obtain the dose distribution. Thus, when the mean range of incident ions is determined with the MLE method, the annihilation gamma-ray distribution and the deposited dose distribution can be derived simultaneously. The derived dose distributions in water for the mono-energetic heavy-ion beams of four species were compared with those measured with an ionization chamber. The good agreement between the derived and the measured distributions implies that the deposited dose distribution in a target can be estimated from the detected annihilation gamma-ray distribution with a positron camera.

The intercomparison of cosmic rays with heavy ion beams at NIRS (ICCHIBAN) project

The ICCHIBAN-2 experiment, the first dedicated to the ground-based intercomparison of passive space dosemeters, was carried out between 23 May and 28 May 2002 at the National Institute of Radiological Sciences in Chiba, Japan. The primary objective of the ICCHIBAN-2 experiment was to intercompare the response of passive dosemeters used in space crew dosimetry to monoenergetic heavy ions of charge and energy spanning a significant portion of the galactic cosmic ray (GCR) spectrum. During the ICCHIBAN-2 experiment, dosemeters from 12 different laboratories in 9 countries were irradiated under identical conditions to heavy ion beams of 150 MeV n(-1) (4)He, 400 MeV n(-1) (12)C, 490 MeV n(-1) (28)Si and 500 MeV n(-1) (56)Fe at the NIRS Heavy Ion Medical Accelerator.

Unusual heavy ion injection events observed by Freja

Abstract. Heavy ion injection events (registered in the C+/N+/O+ mass channel) into the ionosphere at 1700km height are surveyed using the Swedish-German Freja satellite data. Heavy ion injections from the inner magnetosphere are mostly found in the nightside sector with a few exceptions that occur on the dayside. We report on these exceptional cases, particularly two specific events which seem to have a different generation/transport mechanism of heavy ions from the majority of cases: 1) mono-energetic heavy ion injection near local noon with oxygen first and protons later; and 2) a multiple heavy ion dispersion event at 9 MLT. Both events are unique without any similar events in terms of dispersion pattern during the more than 2 years of the entire Freja operation, and these events are found during the main phase of major magnetic storms (peak Dst is -144nT and -105nT). The first event is probably of dayside origin but the exact mechanism to make both energy filter and mass filter is unknown. The second event can be traced back to one localized energization of dense oxygen with strong pitch-angle anisotropy within 1000km distance from the spacecraft.

Ridge filter design and optimization for the broad-beam three-dimensional irradiation system for heavy-ion radiotherapy.

The broad-beam three-dimensional irradiation system under development at National Institute of Radiological Sciences (NIRS) requires a small ridge filter to spread the initially monoenergetic heavy-ion beam to a small spread-out Bragg peak (SOBP). A large SOBP covering the target volume is then achieved by a superposition of differently weighted and displaced small SOBPs. Two approaches were studied for the definition of a suitable ridge filter and experimental verifications were performed. Both approaches show a good agreement between the calculated and measured dose and lead to a good homogeneity of the biological dose in the target. However, the ridge filter design that produces a Gaussian-shaped spectrum of the particle ranges was found to be more robust to small errors and uncertainties in the beam application. Furthermore, an optimization procedure for two fields was applied to compensate for the missing dose from the fragmentation tail for the case of a simple-geometry target. The optimized biological dose distributions show that a very good homogeneity is achievable in the target.

Some aspects of the time response of thin film breakdown counters for heavy charged particle detection

Time response of thin film breakdown counters (TFBC) for heavy charged particles was investigated in detail by the measurement of 252Cf fission fragments time of flight spectra. The time response dependences on the energy and angle of incidence were observed. The intrinsic time resolution of TFBC for monoenergetic heavy ions was estimated to be of ∼0.15 ns (fwhm). A mechanism of the observed dependences as well as the applicability of TFBC for accurate time of flight measurements are discussed.

Inactivation of Human Kidney Cells by High-Energy Monoenergetic Heavy-Ion Beams

Presented are fundamental data on the biological effects of monoenergetic beams of carbon (400 MeV/amu), neon (425 MeV/amu), and argon (570 MeV/amu). Cell survival of human kidney T-1 cells was measured under aerobic and hypoxic conditions over a range of mean LETinfinity from 10 to 600 keV/..mu..m. RBE and OER were measured under hypoxic and aerobic conditions with attention paid to dose, mean LETinfinity, and particle charge effects. (DS)