Light Ion Beams Research Articles

Biologically Optimized 3-Dimensional In Vivo Predictive Assay-based Radiation Therapy Using Positron Emission Tomography-Computerized Tomography Imaging

PET-CT is probably the ultimate tool for accurate tumor imaging and 3-dimensional in vivo predictive assay of radiation sensitivity. By imaging the tumor twice during the early course of therapy, it should be possible to quantify both the tumor responsiveness to therapy and the rate of loss of functional tumor cells using the presently derived equations. This new information is ideal for use together with biologically based therapy optimization and makes it possible accurately to quantitate the dose-response relation, at least for the bulk of the tumor cells. Since the tumor responsiveness is available after about one and a half weeks of therapy, the information is also ideal for use with adaptive therapy where all forms of deviations from the original treatment plan can be accurately corrected for since they generally influence the still functional, but mainly doomed tumor cell compartment. Thus, uncertainties such as: 1) the geometric misalignment of the therapeutic beam with the tumor, 2) deviations of the delivered dose distribution from the planned delivery whether due to 3) an erroneous treatment planning algorithm or 4) treatment equipment uncertainties and 5) deviations in the anticipated responsiveness of the tumor of the patient based on historical response data, can all be taken into account. Fortunately, when a larger tumor cell compartment than expected is seen an increased dose during the remainder of the treatment should always be delivered independently on whichever combination of the above deviations was the true reason. With high-energy photon and hadron therapy it is even possible to image the integral dose delivery in vivo during or after a treatment using PET-CT imaging. The high-energy photons above about 20 MeV produce positron emitters through photonuclear reactions in tissue which are proportional to the photon fluence and thus approximately also to the absorbed dose. Light ion beams, the ultimate radiation modality with regard to physical and biological selectivity, instead produce PET emitters through direct nuclear interactions in tissue, but can also be used as radioactive beams consisting of intrinsic PET emitters such as 8B, 11C, 13N and 15O. These radioactive beams allow more accurate imaging of the Bragg peak distribution and thus indirectly the absorbed dose. The most universal feedback for adaptive radiation therapy would then be to use the measured image of mean dose delivery during the early part of the treatment while revising the treatment plan based on the initially planned dose distribution and the radiation responsiveness of the tumor as seen after the first week or two of therapy. By this so-called BIO-ART approach (Biologically Optimized 3D in vivo predictive Assay-based Radiation Therapy) radiation therapy optimization may become an almost exact science, where the patient's true individual radiation response, considering hypoxia and general radiation resistance as well as possible dose delivery and planning errors, is taken into account.

Radioisotope production at the Kazakhstan cyclotron

Cyclotrons play an important role for production of ‘carrier-free’ radioisotopes for various applications in the nuclear medicine, industry, ecology and science. Kazakhstan variable energy isochronous cyclotron, K = 50 MeV, is a 150 cm compact-pole 3 sector positive ion machine. It generates different beams of light ions: protons 6-30 MeV, deuterons 12.5-25 MeV, 3He-ions 18.5-62 MeV, alpha-particles 25-50 MeV. In the last years the cyclotron is rather intensively used for radioisotopes production to meet the needs of the Republic of Kazakhstan. The main users of radioisotope products are the Institutions of Healthcare Ministry and enterprises of oil-chemistry, metallurgy, mining, scientific institutes etc. In this submission a survey on radionuclides production including 201Tl, 67Ga, 57Co, 109Cd, 88Y, 85Sr is presented. Practically at all production stages (target preparation, extraction, purification and concentration of a product) original approaches were realized: (1) at target production by means of electrolysis the modes of reverse plating of the material for irradiation and technological layers were finalized, and at 67Ga production new extraction with better characteristics were used; that made the deeper purification from zinc, copper and iron possible. At the development of the technologies of the sealed sources production the following results were obtained: (1) 109Cd production for X-ray fluorescence analysis, and production of experimental samples for Mossbauer sources 57Co at rhodium and palladium backings. The tracers 237Pu, 88Y and 85Sr used for development of the set of methods for 239Pu, 240Pu, 90Sr and 241Am determination in the samples from Semipalatinsk Test Site were produced via nuclear reactions with alpha-particles on 235U and protons on 88Sr, 85Rb targets. Produced radiopharmaceutical preparations 201Tl chloride and 67Ga citrate are supplied to medical centers of Almaty.

Developments in high-intensity two-step target design

The two-step fission-product target concept is analyzed to design a prototype target for testing at the ISAC facility. A two-step target consists of an inner cylinder of heavy metal irradiated by an energetic light ion beam; neutrons produced emerge from the target into a coaxial secondary target (blanket) of fissionable material. With this approach, the production of fission product activities is enhanced compared to other products that can interfere in experiments, and significantly less energy is deposited in the secondary target than for direct irradiation. The design is mechanically simple and provides independent control of operating temperatures. The analysis determined appropriate target and blanket dimensions, and energy deposition profiles, temperature distributions and fission production rates. The production rates of some neutron-rich isotopes for selected elements are summarized. A conceptual design is presented, along with issues on cooling the primary target and heating of the secondary target.

Optical waveguides produced in LiF by MeV ion beam bombardment

In this letter, the development of a simple method, based on high-energy light-ion beam irradiation, to create active waveguides in alkali halide materials is reported. A 1.1 MeV He+ beam at normal incidence was used to irradiate lithium fluoride crystals, with different ion doses varying from 1×1012 up to 6×1015 cm−2, producing thin colored strips. All strips showed several guided modes, confirming the effectiveness of this technique to create the conditions to allow guided propagation. Values of 1.5 dB/cm were found for the propagation losses.

A multiaperture electron filter for volume-type H− ion source

Negative light ion beams have been used widely in many applications over the past decades. One of the most popular methods of producing H− and D− beams is the so-called volume production, in which a plasma is contained in a multicusp magnetic field. The beam is extracted using an electric field applied in the extraction gap. Accompanying the negative ions is up to 100 times greater number of electrons, which have to be removed from the beam. This is usually done by placing a transverse magnetic field in the extraction region. With this method the electrons can be quite effectively removed from the beam. The problem is that we dump a high intensity, high energy electron beam in the extraction electrode and dissipate a lot of power in the process. The negative ion beam is also deflected in this strong magnetic field which has to be corrected either by tilting the source compared to the extraction or by adding an opposite transverse magnetic field. In the latter method the beam is laterally displaced from the original axis. In the Plasma and Ion Source Technology Group at the Lawrence Berkeley National Laboratory, we are developing a multi-aperture extraction in which the electrons are removed from the beam before they are accelerated to high energy with the use of a honeycomb-structured electron filter and a weak magnetic field. This way the power dissipated by the electrons and the ion beam deflection are minimized. The initial results of these experiments will be described in this presentation.

Liquid-lithium cooling for 100-kW ISOL and fragmentation targets

Advanced exotic beam facilities that are currently being developed will use powerful driver accelerators for the production of short-lived rare isotopes. Multi-beam drivers capable of producing high power beams from very light to very heavy ions are now technically feasible. A challenge for such facilities is the development of production targets to be used for a variety of reaction mechanisms with beam powers of about 100 kW. This paper presents engineering concepts that have been developed recently for using liquid lithium coolant for two types of targets, one for use with light-ion beams on high atomic number ( Z) targets and the other for heavy-ion beams on low- Z targets.

Nuclear Physics with Light Ion Beams

Nuclear Physics with Light Ion Beams

Study of the irradiation damage in SiC by ion channeling

The importance of silicon carbide as a wide band gap semiconductor is widely accepted and well documented. Its excellent physical properties (chemical inertness, high-temperature strength, low thermal expansion, extreme hardness) make it the most promising substitute for traditional semiconductors, especially when high-temperature, high-voltage power, and high-frequency devices are concerned. In the present work, the gradual amorphization of a SiC Lely (21R) crystal when irradiated with 8 MeV 7Li ions in a random direction up to a maximum dose of approximately 1×10 16 particles/cm 2, is being studied, using the progressive change of channeling parameters for different depths. The results refer to the energy region of ∼1 MeV/nucleon, and an attempt is made in order to explain the peculiarities of the experimental spectra and the mechanism of defect production in SiC. As in previous studies, a change in color was observed after irradiation in the random mode, indicating that the problem of irradiation damage in SiC caused by light ion beams needs further investigation.

Design of a centre for biologically optimised light ion therapy in Stockholm

Radiation therapy is today in a state of very rapid development with new intensity-modulated treatment techniques continuously being developed. This has made intensity modulated electron and photon beams almost as powerful as conventional uniform beam proton therapy. To be able to cure also the most advanced hypoxic and radiation resistant tumours of complex local spread, intensity modulated light ion beams are really the ultimate tool and only slightly more expensive than proton therapy. The aim of the new centre for ion therapy and tumour diagnostics in Stockholm is to develop radiobiologically optimised three-dimensional (3D)-pencil beam scanning techniques. Beside the `classical' approaches using low ionisation density hydrogen ions (protons, but also deuterons and tritium nuclei) and high ionisation density carbon ions, two new approaches will be developed. In the first one lithium or beryllium ions, that induce the least detrimental biological effect to normal tissues for a given biological effect in a small volume of the tumour, will be key particles. In the second approach, referred patients will be given a high-dose high-precision `boost' treatment with carbon or oxygen ions during one week preceding the final treatment with conventional radiations in the referring hospital. The rationale behind these approaches is to reduce the high ionisation density dose to the normal tissue stroma inside the tumour and to ensure a microscopically uniform dose delivery. The principal idea of the centre is to closely integrate ion therapy into the clinical routine and research of a large radiotherapy department. The light ion therapy centre will therefore be combined with advanced tumour diagnostics including MR and PET-CT imaging to facilitate efficient high-precision high-dose boost treatment of remitted patients. The possibility to do 3D tumour diagnostics and 3D dose delivery verification with the same PET camera will be the ultimate step in high quality adaptive radiation therapy where alterations in the delivered dose can be performed by subsequent treatments. The increased knowledge in tumour and molecular biology will hopefully further improve the efficiency of this very unique new treatment modality that will be planned and delivered by radiobiologically optimised 3D-pencil beam scanning techniques to maximise the complication-free tumour cure and minimise normal tissue side effects. Finally, the design, cost, time scale and treatment capacity of the centre are reviewed. After a few years of running, the centre will be capable of treating 1000 patients/year with light ions and almost 3000 patients/year with the high-precision boost techniques.

Fast ignitor concept with light ions

A short-laser-pulse driven ion flux is examined as a fast ignitor candidate for inertial confinement fusion. Ion ranges in a hot precompressed fuel are studied. The ion energy and the corresponding intensity of a short laser pulse are estimated for the optimum ion range and ion energy density flux. It is shown that a lightion beam triggered by a few-hundreds-kJ laser at intensities of ≳1021 W/cm2 is relevant to the fast ignitor scenario.

Ion beam aperture-array lithography

We explore a new technique, ion beam aperture-array lithography (AAL), for fabricating low cost, large area nanostructure arrays. In this approach, a broad beam of light ions illuminates a stencil mask containing a periodic array of circular apertures. The array of transmitted beamlets is moved over the substrate, thereby printing an array with the same period but arbitrary unit cell. AAL has several advantages over ion beam proximity lithography: (1) the mask pattern density is lower, (2) the unit cell patterns are defined by software, and (3) dose and shape correction can be applied to compensate for system blur. Dose optimization methods are discussed and experimental results with 150 nm apertures presented.

Radiation damage studies of a recycling integrator VLSI chip for dosimetry and control of therapeutical beams

A VLSI chip based on a recycling integrator has been designed and built to be used as front-end readout of detectors for dosimetry and beam monitoring. The chip is suitable for measurements with both conventional radiotherapy accelerators (photon or electron beams) and with hadron accelerators (proton or light ion beams). As the chips might be located at few centimeters from the irradiation area and they are meant to be used in routine hospital practice, it is mandatory to assert their damage to both electromagnetic and neutron irradiation. We have tested a few chips on a X-ray beam and on thermal and fast neutron beams. Results of the tests are reported and an estimate of the expected lifetime of the chip for routine use is given.

Fusion at the barrier with light radioactive ion beams

The experimental results recently obtained for fusion reactions at energies close to the Coulomb barrier with light radioactive (loosely bound) beams are reviewed and critically discussed. There have been two conflicting views on the effect of the loose binding of the projectile on the fusion cross section. On the one hand one expects an enhancement of the fusion cross section due to the loose binding while, on the other hand, the easy breakup of the projectile is expected to inhibit the fusion cross section. We critically discuss these two aspects of loose binding by comparing the experimental results for a number of radioactive beams. The data for 17F (where the last neutron binding energy S n=0.601 MeV), neither show breakup effects nor enhancement when compared with the fusion of the nucleus 19F. The data for a 6He beam ( S 2n=0.975 MeV) show enhancement, very strong in one case, and the strong breakup (BU) +transfer cross section may be related to this. The fusion data obtained with the halo nucleus 11Be ( S n=0.504 MeV) do not show enhancement below the barrier, compared with 9Be, and show moderate effects above the barrier. Moreover, 9Be ( S n=1.665 MeV) shows a very strong BU +transfer cross section as in the case of 6He, but this apparently has no direct effect on fusion. The data with the neutron-rich 38S, 29,31Al radioactive beams do not differ much from data with the stable 32S, 27Al, respectively. In conclusion we observe: (i) effects of loose binding in neutron skin nuclei but not with other halo nuclei, (ii) a reduction of the fusion cross section above the barrier due to breakup effects. The various theoretical approaches developed up to now based on “simple” assumptions give opposite predictions for fusion, with some expecting enhancement of the cross section while others expect a hindrance of the cross section. However, most of these approaches do not correctly treat the transitions to the continuum which are expected to be induced easily in these weakly bound nuclei. It is necessary to develop a more complete and possibly “simple” theoretical treatment that incorporates the continuum coupling which will play an important role in subbarrier fusion.

Special radiation protection aspects of medical accelerators.

Radiation protection aspects relevant to medical accelerators are discussed. An overview is first given of general safety requirements. Next, shielding and labyrinth design are discussed in some detail for the various types of accelerators, devoting more attention to hadron machines as they are far less conventional than electron linear accelerators. Some specific aspects related to patient protection are also addressed. Finally, induced radioactivity in accelerator components and shielding walls is briefly discussed. Three classes of machines are considered: (1) medical electron linacs for 'conventional' radiation therapy, (2) low energy cyclotrons for production of radionuclides mainly for medical diagnostics and (3) medium energy cyclotrons and synchrotrons for advanced radiation therapy with protons or light ion beams (hadron therapy).

Application of ion beams to nuclear waste issues:: evaluation of nuclear ceramics

Oxide ceramics are promising matrices for nuclear waste immobilization or transmutation. The most important issue concerning these materials is the investigation of their physico-chemical properties with respect to safety criteria. This paper shows the potentiality of ion beams for the evaluation of ceramics as nuclear waste matrices. Several items are concerned. The different sources of radiation damage occurring in the reactor and during the storage term may be simulated by irradiation of the matrix with a variety of ions in a wide energy range. The doping of the material with foreign species produced by radioactive desintegration may be performed by ion implantation of stable or radioactive isotopes. The modifications induced in the matrices may be characterized by nuclear microanalysis techniques using medium-energy light ion beams. Examples relative to these various items are provided.

KeV Astrophysics with GeV Beams; Blazing a New Trail on the Summit of Nuclear Astrophysics

GeV beams of light ions and electrons are used for creating a high flux of real and virtual photons, with which some problems in Nuclear Astrophysics are studied. GeV 8B beams are used to study the Coulomb dissociation of 8B and thus the 7Be(p,gamma)8B reaction. This reaction is one of the major source of uncertainties in estimating the 8B solar neutrino flux and a critical input for calculating the 8B Solar neutrino flux. The Coulomb dissociation of 8B appears to provide a viable method for measuring the 7Be(p,gamma)8B reaction rate, with a weighted average of the RIKEN1, RIKEN2, GSI1 and MSU published results of S17(0) = 18.9 +/- 1.0 eV-b. This result however does not include a theoretical error estimated to be +/- 10 %. GeV electron beams on the other hand, are used to create a high flux of real and virtual photons at TUNL-HIGS and MIT-Bates, respectively, and we discuss two new proposals to study the 12C(alpha,gamma)16O reaction with real and virtual photons. The 12C(alpha,gamma)16O reaction is essential for understanding Type II and Type Ia supernova. It is concluded that virtual and real photons produced by GeV light ions and electron beams are useful for studying some problems in Nuclear Astrophysics.

Review of light-ion driver development for inertial fusion energy

The concept of a light ion beam driver for Inertial Fusion Energy (IFE) is based on multi-terawatt, multi-megavolt pulsed power generators, two-stage ion acceleration and charge neutralised transport. In this paper we discuss the present status for each of these components and identify the main issues for research. Only modest extrapolations from presently available technologies seem necessary for the high voltage pulse generator. The greatest challenge of this approach is the accelerator, which will consist of two stages, the injector and the post-accelerator. Large progress has been made in understanding the physical phenomena occurring in the injector gap. This progress has become possible by new sophisticated diagnostics that allowed detailed temporally and spatially resolved measurements of field and particle densities in the acceleration gap and by relativistic fully electromagnetic PIC-simulation tools, that stimulated analytic models. The conclusions drawn from these studies, namely limiting the ion current density to small enhancements to reduce the beam divergence need still to be verified experimentally. Systematic experimental research on post-acceleration at high power and voltage must aim at a complete understanding of instabilities coupling from the injector to the post-accelerator and at limiting voltages and barriers for the extraction of unwanted ions from plasmas at the injection side. Ultimately the light ion approach requires rep-rateable large area ion sources with ion masses greater than 1 and particle energies around 30 MeV. Although different cleaning protocols were able to reduce the amount of parasitic ions in the Li beam from a LiF field emission source the achievements are still insufficient. A field of common interest between light and heavy ion beam driven fusion is beam transport from the accelerator to the target. Supposedly the most favourable concept for both approaches is self-pinched transport. Experimental evidence for self-pinched transport has recently been achieved in an experiment at NRL. Further experiments are needed to determine the dynamics and magnitude of net current formation, the efficiency of transport and the effect of bunching.

Studies on nonconventional high-gain target design for ICF

This paper reports some of the studies on nonconventional ICF approaches performed at the ICF Physics and Technology Laboratory of the AEEF in Frascati, Italy. Having as reference potential difficulties associated to the conventional central spark ignition (fuel mixing) and to the usual approach to fast ignition by laser (transfer and coupling of the energy pulse, fast electrons energy tuning), we have made explorative work on possible alternatives. The performances of targets ignited near stagnation by pulses of heavy ion beams (HIB) or by macroparticle impact were previously studied. The needed driver energy, the power, and the beam quality requirements, as well as the level of synchronization the implosion and the igniting pulse have been found. More recently, to relax some requirements on the HIB beam parameters set by the previous approach, the injected entropy approach (IE) has been introduced. In this method, the conditions for spark formation are set in the final stages of the implosion, when the spark fuel size is a few times the final size at stagnation (volume a few tens of the final). Energy is injected at this time to set the spark fuel on a high adiabat. In this paper, for illustration and comparison purposes, some relevant results we previously obtained for near-stagnation ignition are first introduced and critically reviewed. The new IE method, after a short analytical introduction, is presented and illustrated by the results of extensive 2-D numerical simulations. The considered cases refer to imploding cylinders of finite length. As required by this approach, one or two opposing beams axially injected additional energy, whereas the acceleration stage of the cylindrical low-entropy implosion was assumed driven by a different driver. Heavy ion beams, soft X-rays (SXR), and laser generated light ion beams were considered as vectors for the entropy injection. Issues related to the feasibility of these generators are discussed. The study was made for various initial conditions leading to different ignition modes and burn propagation. The most recent results on the injected entropy method to the ignition of high gain targets are included.

Results from the NA50 experiment on J/Ψ suppression in PbPb collisions at the CERN SPS

The NA50 experiment has measured, at the CERN SPS, the dimuon production in PbPb collisions at 158 GeV/c per nucleon, following the program of the previous NA38 and NA51 experiments, performed with proton and light ion beams. The J/Ψ production has been studied by NA50 as a function of the centrality of the collisions. The results of the analyses performed on three data samples, collected from 1995 to 1998, show that for peripheral collisions the J/Ψ cross section can be understood in terms of ordinary nuclear absorption, consistently with the extrapolation of previous measurements extending from p-p to S-U. On the contrary, the central events show an anomalous J/Ψ suppression, and the pattern of J/Ψ yield versus centrality features two discontinuities that cannot be described by conventional models based on hadronic scenarios. These results can be considered as a strong indication of the creation of a new state of matter in central PbPb collisions at the SPS.

Focusing of heavy ion beams by a high-current plasma lens

Results are presented from studies of the focusing of wide-aperture low-energy (100–400 eV) and moderate-energy (5–25 keV) beams of heavy-metal ions by a high-current electrostatic plasma lens. It is found experimentally that, because of the significant electron losses, the efficient focusing of such beams can be achieved only if the external potentials at the plasma-lens electrodes are maintained constant. Static and dynamic characteristics of the lens are studied under these conditions. It is shown that, as the beam current and the electrode voltage increase, the maximum electrostatic field in the lens tends to a certain limiting value because of the increase in the spatial potential near the lens axis. The role of spherical and moment aberrations in the focusing of wide-aperture low-divergence ion beams is revealed. It is shown that, even when spherical aberrations are minimized, unremovable moment aberrations decrease the maximum compression ratio of a low-energy heavy-ion beam because of the charge separation of multiply charged ions in the focal region. At the same time, as the ion energy increases, the role of the moment aberrations decreases and the focusing of high-current heavy-ion beams by a plasma lens becomes more efficient than the focusing of light-ion (hydrogen) beams. This opens up the possibility of using electrostatic plasma lenses to control ion beams in high-dose ion implanters and high-current accelerators of heavy ions.