3He Ion Beam Research Articles

The effect of nanocrystalline microstructure on deuterium transport in displacement damaged tungsten

The influence of grain boundaries (GBs) on the deuterium (D) transport and the creation of defects in nanocrystalline tungsten (W) films deposited on a W substrate was studied. Samples with three different grain sizes were produced for this purpose: a sample with a film having nanometer-size grains, a sample with hundred nanometer-grained film and a sample with micrometer-grained film. Samples were irradiated by 20 MeV W ions at 300 K to create displacement damage and exposed to 300 eV D ions at 450 K to populate the created and any pre-existing defects. The D transport and retention was assessed by measuring D depth profiles after certain exposure times by nuclear reaction analysis (NRA) using a 3He ion beam. From the final D concentration in the damaged area we could determine the concentration of defects that trap hydrogen, showing that the sample with the smallest grain size had the highest D concentration and it decreases with the increase of the grain size. Therefore, in nanocrystalline tungsten irradiated at 300 K, GBs do not improve radiation resistance, which would lead to fewer defects. For the first time, we show experimentally, that D transport is faster inside the nanometer-grained sample as compared to the micrometer-grained sample, meaning that D atoms have enhanced bulk diffusion along GBs. Accidentally, the film thickness was so thin that the W irradiation reached the interface between the W film and substrate, where NRA showed enhanced retention of oxygen. At that depth, two times higher D concentration was observed compared to D concentration in the damaged area in the middle of the film indicating on defect stabilization due to the presence of oxygen.

Polarimetry for 3He Ion Beams from Laser–Plasma Interactions

We present a compact polarimeter for 3He ions with special emphasis on the analysis of short-pulsed beams accelerated during laser–plasma interactions. We discuss the specific boundary conditions for the polarimeter, such as the properties of laser-driven ion beams, the selection of the polarization-sensitive reaction in the polarimeter, the representation of the analyzing-power contour map, the choice of the detector material used for particle identification, as well as the production procedure of the required deuterated foil-targets. The assembled polarimeter has been tested using a tandem accelerator delivering unpolarized 3He ion beams, demonstrating good performance in the few-MeV range. The statistical accuracy and the deduced figure-of-merit of the polarimetry are discussed, including the count-rate requirement and the lower limit of accuracy for beam-polarization measurements at a laser-based ion source.

Physical characterization of 3He ion beams for radiotherapy and comparison with 4He

There is increasing interest in using helium ions for radiotherapy, complementary to protons and carbon ions. A large number of patients were treated with 4He ions in the US heavy ion therapy project and novel 4He ion treatment programs are under preparation, for instance in Germany and Japan. 3He ions have been proposed as an alternative to 4He ions because the acceleration of 3He is technically less difficult than 4He. In particular, beam contaminations have been pointed out as a potential safety issue for 4He ion beams. This motivated a series of experiments with 3He ion beams at Gesellschaft für Schwerionenforschung (GSI), Darmstadt. Measured 3He Bragg curves and fragmentation data in water are presented in this work. Those experimental data are compared with FLUKA Monte Carlo simulations. The physical characteristics of 3He ion beams are compared to those of 4He, for which a large set of data became available in recent years from the preparation work at the Heidelberger Ionenstrahl-Therapiezentrum (HIT). The dose distributions (spread out Bragg peaks, lateral profiles) that can be achieved with 3He ions are found to be competitive to 4He dose distributions. The effect of beam contaminations on 4He depth dose distribution is also addressed. It is concluded that 3He ions can be a viable alternative to 4He, especially for future compact therapy accelerator designs and upgrades of existing ion therapy facilities.

Modifications of WNOx films by keV D and H ions

We have investigated modification of WNOx films (thickness of 20–80 nm) by D and H ions with the energy of ~1 keV, where D and H ions are retained within the film and compared with the results by medium-energy and high-energy (~1 MeV/u) ion irradiation. WNOx films are prepared on C-plane-cut-sapphire (C-Al2O3) substrate. The composition x is determined to be ~0.4 and the film thickness by Rutherford backscattering spectroscopy (RBS) of He+ ions. X-ray diffraction with Cu- Kα radiation (XRD) is employed to study structural modification. We find monotonic decrease of the XRD intensity with D and H ion fluence, and lattice expansion and compaction for low and high D fluence, respectively. D and H retention is measured by nuclear reaction analysis (NRA) using 15N and 3He ion beams, and elastic recoil detection (ERD). It is discussed whether effects of energy deposition by ions can be separated from inclusion effects of D and H.

Laser-induced acceleration of Helium ions from unpolarized gas jets

In order to develop a laser-driven spin-polarized 3He-ion beam source available for nuclear-physics experiments as well as for the investigation of polarized nuclear fusion, several challenges have to be overcome. Apart from the provision of a properly polarized 3He gas-jet target, one of the biggest milestones is the demonstration of the general feasibility of laser-induced ion acceleration out of gas-jet targets. Of particular importance is the knowledge about the main ion-emission angles as well as the achievable ion-energy spectra (dependent on the optimal set of laser and target parameters). We report on the results of such a feasibility study performed at PHELIX, GSI Darmstadt. Both 3He- and 4He-gas jets (ngas ∼ 1019 cm−3) were illuminated with high-intensity laser pulses, . The main ion-emission angles could be identified (±90° with respect to the laser-propagation direction) and the ion-energy spectra for all ion species could be extracted: for the optimal laser and target parameters, the high-energy cut-offs for He ions were 4.65 MeV (with a normalized energy uncertainty of ) and 3.27 MeV (), respectively.

Influence of grain size on deuterium transport and retention in self-damaged tungsten

The influence of grain size on deuterium transport and retention in tungsten was studied. For this purpose an experiment was carried out on three polycrystalline tungsten samples with different grain sizes and a single crystal sample with surface orientation <100>. In order to increase deuterium retention and hence the sensitivity for detection, samples were first damaged by high energy W ions. After damaging, the samples were exposed to a flux of deuterium atoms at 600 K for 70 h. During the exposure the depth profile of the retained deuterium was measured by Nuclear Reaction Analysis using a 3He ion beam. After the exposure the samples were also analysed by Thermal Desorption Spectroscopy. A clear difference in the time dependence of deuterium uptake was noticed between different samples. The experimental results were modeled using a rate-equation model. The influence of different grain size was modeled by changing the effective height of the potential barrier for deuterium atoms to enter into the bulk. We managed to successfully describe the transport of deuterium into the bulk of tungsten by reducing the potential barrier for samples with smaller grain sizes while the barrier for the sample with larger grain size was close to the value for the damaged single crystal sample.

Cross sections of fusion and transfer reactions in interactions between 3He and Pt and 197Au nuclei in the subbarrier energy region

The reactions of complete and incomplete fusion, along with nucleon transfer reactions in the range of 3He energies from 10 to 24.5 MeV, are investigated by irradiating gold and platinum targets with an accelerated 3He ion beam on the U-120M cyclotron at the Institute of Nuclear Physics, Czech Academy of Sciences, Řež. Activation is used to determine the yield of nuclides resulting from nuclear reactions. The γ-activity induced in the targets is measured using a with high-resolution HPGe detector. Despite the low binding energy of 3He and the reactions with positive Q values, the measured cross sections of fusion reactions exhibit no specific features, compared to reactions conducted using beams of other light stable particles. Transfer neutron reactions in the subbarrier energy region have relatively high cross sections. These cross sections continue to grow as the energy of 3He rises. When a neutron is captured by a nucleus of 3He, the cross sections of these reactions reach their maximum values in the Coulomb barrier region.

Study of correlation of deuterium content in a-C:D dust induced by laser irradiation from the co-deposited surface with the grain size and velocity

In the study described here, the laser ablation method was applied to clean thick (40–60 μm) a-C:D co-deposits on the ALT-II limiter blade from the TEXTOR tokamak, and at the same time to characterize the ejected particles formed during ablation and measure the amount of fuel carried by them. Ablation was accomplished by ∼ 3.5 ns, 0.5 J Nd:YAG laser pulses in either vacuum or an O2 atmosphere at different pressures. Fast camera tracking of the process provided an estimate of the population and velocity of up to 100 m s−1 for larger dust particles. In the same experiment, the dust particles were caught using ultra-light Si aerogel collectors placed in front of the ablation target. SEM analysis of aerogel surfaces verified the speed estimate, providing the trapped particles’ size distribution and particle yield during ablation. The D/C atomic concentration ratio was measured with the 3HE ion beam nuclear reaction analysis method in deposited layers before ablation and with a micro-ion beam in individual particles on aerogel collectors. This indicated that most of the D was thermally released during ablation, leaving no more than 5% of its original amount in the particles. The effect of ablation conditions on the acceleration of ejected particles, their population, composition and D content is the main subject of this paper.

Cross sections of 43Sc, 44Sc, 46Sc isotopes formed in the 45Sc + 3He reaction

Reactions 45Sc(3He, αn)43Sc, 45Sc(3He, α)44Sc and 45Sc(3He, 2p)46Sc in the 3He energy range of 5 to 24 MeV are investigated in experiments performed with a 3He ion beam during the irradiation of U-120M cyclotron scandium targets. Activation is used to determine the yield of nascent Sc isotopes. The γ activity induced in targets is measured using a high-resolution HPGe detector. The character of the excitation function changes during the formation of these ions and differs from the excitation functions for deuterons, despite the low bond energy of 3He and the positive values of the Q reactions leading to the formation of 44Sc and 46Sc isotopes. The cross sections of 44Sc formation reach their maximum value at the Coulomb barrier of the reaction, due to the stable 4He nucleus that accompanies the formation of 44Sc. The contribution from different reaction mechanisms to the cross sections of 43Sc, 44Sc, and 46Sc isotope formation are considered.

Fuel retention study in fusion reactor walls by micro-NRA deuterium mapping

Nuclear Reaction Analysis (NRA) with a 3He ion beam is a powerful analytical technique for analysis of light elements in thin films. The main motivation for 3He focused beam applications is lateral mapping of deuterium using the nuclear reaction D(3He,p)4He in surfaces exposed to a tokamak plasma, where a lateral resolution in the μm-range provides unique information for fuel retention studies.At the microprobe at the Jožef Stefan Institute typical helium ion currents of 300pA and beam dimensions of 4×4μm2 can be obtained. This work is focused on micro-NRA studies of plasma-facing materials using a set-up consisting of a silicon partially depleted charge particle detector for NRA spectroscopy applied in parallel with a permanently installed X-ray detector, an RBS detector and a beam chopper for ion dose monitoring. A method for absolute deuterium quantification is described. In addition, plasma-deposited amorphous deuterated carbon thin films (a-C:D) with known D content were used as a reference.The method was used to study deuterium fuel retention in carbon fibre composite materials exposed to a deuterium plasma in the Tore Supra and TEXTOR tokamaks. The high lateral resolution of micro-NRA allowed us to make a detailed study of the influence of topography on the fuel retention process. We demonstrated that the surface topography plays a dominant role in the retention of deuterium. The deep surfaces inside the castellation gaps showed approximately two orders of magnitude lower deuterium concentrations than in areas close to the exposed surface.

Measurement of hydrogenic retention and release in molybdenum with the DIONISOS experiment

Molybdenum targets are exposed in the DIONISOS experiment to a deuterium (D) plasma ( Γ D ∼ 10 21 m −2 s −1) at target biases of 30–350 V and target temperatures of 300–700 K while simultaneously diagnosing the D in the surface with a 3.5 MeV 3He ion beam. The 3He diagnostic beam creates displacements in the Mo lattice which can then trap D, allowing retention far beyond the plasma ion implantation range. The conversion of displacements to trap sites averaged over the ion range is non-linear with a scaling (dpa) α, 0.25 ⩽ α ⩽ 0.5. The beam-induced traps are distributed from the surface to the end of range as opposed to the damage (dpa) profile that is concentrated at the end of range. Measurement of the near-surface D time-dependence has allowed inference of an effective surface recombination rate, which is lower than predicted by theory and at the low end of those found in literature.

Bending tests on T91 samples implanted with 0.25 at.% helium: Experiments and mechanical analysis

In order to investigate helium effects on the fracture properties of martensitic mod 9Cr–1Mo (T91) steel, miniature Charpy specimens were implanted at 250 °C in the notch region to 0.25 at.% helium using a degraded 34 MeV 3He ion beam and subsequently submitted to static bending tests at room temperature. For the six implanted specimens, a ‘pop-in’ phenomenon, which is an arrested unstable crack extension, was systematically recorded during testing. In the implanted zones of the samples, the fracture mode was fully brittle with both intergranular and cleavage fracture, whereas for unimplanted samples tested at −170 °C, the fracture mode was found to be 100% cleavage. Finite element simulations of the tests performed on unimplanted and implanted specimens were also carried out to determine stress and strain fields at the onset of crack propagation. Based on these computations, the fracture toughness of implanted T91 was tentatively evaluated using the Beremin model of the local approach to brittle fracture.

Design of an Ion Source for 3He Fusion in a Low Pressure IEC Device

Recent developments in helicon ion sources and Inertial Electrostatic Confinement (IEC) device performance at UW-Madison have enabled low pressure (< 50 μtorr, 6.7 mPa) operating conditions that should allow the 3He-3He fusion reaction to be observed in an IEC device. An ion source capable of delivering a ~ 10 mA 3He ion beam into an IEC device with minimal neutral gas flow has been designed and tested. Furthermore, a new IEC device that has never been operated with deuterium has been constructed to avoid D-3He protons from obstructing the 3He-3He reaction product spectrum, and to minimize Penning ionization of deuterium by excited helium, which in the past is suspected to have limited the ionized density of He. These developments make it possible to study beam-background 3He-3He fusion reactions with > 300 mA recirculating ion currents.

Improved Photoconductivity of ZnO by Ion Beam Bombardment

ABSTRACTIn this study, single crystal ZnO films are grown by pulsed laser deposition and ion beam processing is used alter the resistivity of the films. A 3He ion beam was chosen with a specific energy to transmutate oxygen into nitrogen. Analytical ion beam techniques were used to monitor the transmutation process, and changes in film characteristics were monitored by making resistance, photoconductivity and luminescence measurements before and after ion beam processing. The amount of nitrogen produced by this method was estimated to be ∼ 1014 cm−3, and was too low to be observable as a p-type dopant due to compensation by the naturally n-type material. However, the ion beam processed films improved dramatically in resistivity, defect luminescence was reduced and photoconductivity increases consistent with the improvements with resistivity were observed. These improvements were attributed to ion beam annealing of the crystal resulting in a reduction of point defects. In some films, blistering of the surface occurred and was attributed to the formation of gas bubbles which causes delamination of the film from the substrate.

Cellular parameters and RBE-LET dependences for modelling heavy-ion radiotherapy

Sets of four parameters (m, E0, sigma0 and kappa) of the cellular track structure model of Katz have been fitted to recently published data concerning human melanoma (AA) and mammalian (V79) cells exposed to a variety of lighter ions and to mixed ion-Co60 and ion-ion irradiation. Using these parameters, model predictions of V79 survival were verified against experimental data. RBE-LET dependences were calculated and compared with experimental data obtained for V79 cells after exposure to 3He, 12C and 20Ne ion beams. The presented track-segment approach used in track structure calculations, while satisfactory for heavier ions, may be of limited value for predicting the RBE-LET dependence of proton and helium radiotherapy beams in regions close to the distal range of these particles. We discuss the predictive capability of this model and propose standards in reporting cellular radiobiology data for application in modelling heavy ion beam radiotherapy.

Production of Neptunium and Plutonium Tracers in Nuclear Reactions of 236U with 21-to-60-MeV 3He Ions1

Production of 236Pu, 237Pu, and 235Np by the reactions 236U(3He,tβ-)236Pu, 236U(3He,2n)237Pu, and 236U(3He,p3n)235Np with 43- and 60-MeV 3He ion beams on the K-130 cyclotron of the University of Jyvuaskylua was studied. The cross sections for the reactions were determined. The curves of yields with thick targets were derived from the cross sections. The results are discussed and compared with previous data on the other reactions yielding the same final products.

イメージングプレートを用いた荷電粒子放射化オートラジオグラフィによる金属中軽元素分布像の観察

A new method for the observation of the macroscopic distribution images of light elements in metals by the charged particle activation-au-toradiography was developed by the use of the highly sensitive imaging plate (IP) instead of the conventional X-ray film.Surfaces of metallic samples (max. size: about 120 mm×120 mm×5 mm) were irradiated by the 3He ion beam of cyclotron, and then were kept in contact with the IP's for appropriate exposure times. Light elements such as B, C and O were activated in higher yields compared with other coexistent elements and the macroscopic two dimensional distribution images of radionuclides produced from those elements (e.g.: 11C from B or C and 18F from O) were obtained by the above-mentioned IP-autoradiography.The method developed was applied to observe the distribution images of C and O in steels and B and 0 in Al alloys. The results obtained were consistent with the results by chemical analysis. The method was considered to be useful especially for the evaluation of macroscopic defects in metallic materials such as segregations, inclusions or surface contaminations.

Measurement of a knock-on process induced by an ion beam

Understanding of collision processes, which are induced by irradiation of neutrons and ions, is important for predicting the material performance in operational fission and proposed fusion reactors. Specially, an energetic primary knock-on atom (PKA) plays a crucial role in the production of collision cascade damage. The target of single phase TiD 1.61 was irradiated by ion beams of 4He and 3He with energies of 50, 100, 150 and 200 keV. In the experiments with a 3He ion beam, the deuterium density in the target was monitored by the detection of a nuclear reaction of D( 3He, p)α. A high energy primary knock-on process has been successfully observed by monitoring the nuclear reaction of D(d, p)t. Experimental results were compared with the results calculated by the Monte Carlo code TRIM. It was confirmed that the Monte Carlo code can successfully predict the production of energetic primary knock-on atoms under irradiation of the ion beam.

Micro-radiosurgery: a new concept for radiotherapy based upon low energy, ion-induced nuclear reactions

Traditionally, proton radiotherapy has required the use of high energy proton beams (50–200 MeV) which can penetrate into a patient's body to the site of a tumor that is to be destroyed through irradiation. However, substantial damage is still done to healthy tissue along the path of the incident proton beam, as much as 30% of that done at the tumor site. We propose a new concept for the production and delivery of energetic protons for use in medical radiotherapy, based upon the fact that low energy, ion-induced nuclear reactions can produce radiation products suitable for use in radiotherapy applications. By employing specially fabricated “conduit needles” to deliver beams of energetic ions to selected target materials plugging the end of the needle, ion beam-induced nuclear reactions can be generated at the needle tip, emitting reaction-specific radiation products directly at the tumor site. In this paper, we show that the 13.6 MeV protons produced by the d( 3He, p) 4He nuclear reaction can deliver a lethal dose (7 krad) of radiation to a 4.4 mm diameter sphere of tissue in only 30 s using a 1 μA, 800 keV 3He ion beam. If also proven clinically feasible, the use of low energy, ion-induced nuclear reactions would allow the utilization of relatively inexpensive, compact, low energy ion accelerators for proton radiotherapy and minimize unintended radiation damage to healthy tissue by providing much greater precision in controlling the irradiated volume.

Characterization of external 3He ion beams used for ex-vacuo nuclear reaction analysis of deuterium

In-air D(3He, p)4He nuclear reaction analysis (NRA) using external 3He ion beams is now routinely used to characterize deuterium in both fusion and fission reactor materials. The depth resolution, lateral resolution, and detection sensitivity attainable in these ex-vacuo analyses is influenced by the energy spread, the spatial divergence, and the nuclear reaction background produced by extraction of the 3He ion beam through a suitable exit window foil and subsequent transmission of the beam through one or more millimeters of air to the target. In the present paper, the energy and spatial distributions of ex-vacuo MeV 3He ion beams are measured for transmission distances in air of 0 to 15 mm. Exit windows made from both commercially produced foils (3.81 μm thick Au/Al) and foils prepared in the laboratory (1.14 μm thick Au/Al) by e-beam evaporation onto NaCl have been examined. The measured distributions are compared to TRIM simulations, and the resolution of in-air D(3He, p)4He NRA is assessed. Finally, interfering background nuclear reaction yields in air are measured as a function of ex-vacuo 3He beam energy, and the resulting deuterium detection sensitivity is discussed.