Ion beam accelerators are machines providing kinetic energy to charged particles called ions, which bombard the target sample – the material to be irradiated and subsequently analyzed. The target can be a thin foil or a piece of mineral, rubber, textile, tissue, soil or metal. The sample can be an object such a painting, a statute, or even a bullet. Certain nuclear and atomic physics phenomena are then used to investigate the structure, composition, age or other important properties of the analyzed material.
The applications of ion beam accelerators can be divided into two broad areas: analytical methods to identify the elemental and isotopic composition and the structural state of materials; and the modification of materials.
Some ion beam analytical techniques rely on stimulating radiation to be emitted from the sample, for instance the PIXE (particle-induced X-ray emission) and NRA (nuclear reaction analysis) methods, which are sensitive to the chemical or isotopic composition of materials. Other techniques utilize the scattering and recoil of the ions from the sample to characterize the chemical and structural makeup of materials or to obtain elemental concentration depth profiles.
Analytical methods can be used to
- determine the origin of pollutants such as fine aerosols in air or sediment particles transported by water;
- characterize contaminants in food;
- image individual biological cells; and
- determine trace element distribution in tissues and the mechanisms of disease.
Ion beam methods can also be used to analyse in a non-destructive way cultural heritage items. The composition of inks, paints and glazes on ceramics and glasses can be examined to determine where works of art or archaeological artefacts come from. The method can also reveal whether an article is fake or genuine; whether it has been altered in the past; what mechanisms of corrosion and deterioration have been at work; and how affected artefacts can be preserved.
In the field of materials’ modification, ion beams find applications in
- nanotechnology, such as the creation of nanofabricated structures;
- semiconductors and electronic devices, for instance by ion implantation; and
- DNA modification, for instance mutagenic breeding of plants.
They are also useful to conduct fundamental studies of the interactions between radiation and materials. Many advanced reactor concepts would generate large fluxes of neutrons with energies much higher than current generations of reactors. These fast neutrons fluxes do far more damage to materials in the reactor, such as the cladding that surrounds nuclear fuel. Gases produced by nuclear reactions can exacerbate swelling of the cladding. Energetic ion beams can be used to accelerate the rates of damage to such materials to rates that greatly exceed those achievable in a test reactor. And, by simultaneously applying two more ion beams, hydrogen and helium gases can be produced inside the material. Therefore, all major damage processes that occur within a reactor can be simulated with ion beams, providing a rapid screening of potential candidate materials.
The most well-known applications of accelerators are in the production of radioisotopes and the creation of intense high-energy gamma sources for irradiation purposes. Compact electrostatic ion beam accelerators, such as tandems, are of growing interest in research and industry because of the increased analytical and irradiation services of the ion beams they provide. They have various applications in areas as diverse as cultural heritage, biomedicine, forensics, food and agriculture, water and air quality, advanced materials’ development, radiation
damage studies and industry. Accelerators benefit scientific research, contribute to socio-economic development and provide a bridge to the high-tech sector.
Ion beams can be used to create chains of closely coupled quantum bits (qubits), reported in Aug 2021
Quantum technology has opened a whole new world of potential advances in secure communications, information technology and high precision sensors. This technology is poised to provide solutions to some of the most pressing challenges in health care, industry and security. Ion beams find application in developing the innovative materials needed for new quantum technologies. “The IAEA is fully engaged with worldwide initiatives in quantum technology,” said Aliz Simon, a nuclear physicist at the IAEA. “Ion beam accelerator techniques offer emerging opportunities to further explore and develop research in quantum technology.”
“Taking advantage of quantum technology, we can manipulate the structure of materials at the atomic level with ion beams from accelerators, resulting in new types of materials used for quantum computing, sensing, cryptography, imaging and more,” said Simon, who leads the project. Ion beams are created when charged particles are accelerated.
Since 2017, the IAEA has united experts from around the world through a coordinated research project (CRP) to develop materials for quantum technologies. The CRP includes the development of new experimental techniques and the refinement of theoretical models, with an aim to understand radiation effects and ion interaction processes.
For example, the CRP supported researchers who discovered how to use ion beams to create chains of closely coupled quantum bits (qubits). Qubits are basic units of information that are more complex and powerful than the information-carrying “bits” used in conventional computing. While prototypes of 10- to 50-qubit computers are being used to develop quantum software, the latest discovery shows potential to form quantum systems with up to 10,000 coupled qubits over the length of 50 microns, approximately the width of a strand of human hair. “We want to play with this more, explore the effect and then integrate qubit chains with control and readout electronics for quantum sensing applications, such as to probe the activity of neurons in the brain or to detect rare dark matter interaction events,” Schenkel said. Quantum sensors with qubits formed using ions beams are being developed in labs participating in the CRP. These sensors can provide highly accurate measurements and will improve the performance of everyday devices and services, from medical diagnostics and imaging to high-precision navigation.
There are 322 ion beam accelerators in the world listed in the IAEA Accelerator Knowledge Portal, “so there is great potential to foster the utilization of ion beam accelerators for quantum technology,” she added.
The results of the study were published in the journal Applied Physics Letters in February this year. To date, CRP participants have published 55 scientific papers or book chapters related to new materials, modelling and new accelerator technology.
Universities and national laboratories, including defense laboratories, developed increasingly powerful and sophisticated accelerators for national security applications that address nuclear device characterization, detection of contraband materials, and the enrichment of nuclear materials. Examples include the induction linear accelerator (linac), originally developed for accelerator-induced fusion, used today for radiographic imaging, accelerator mass spectrometry contributions to isotope separation technology, and accelerator facilities for defense-related nuclear physics research. The early application of megavolt-energy electron linacs for photofission-based nuclear reactor fuel inspections later expanded to characterizing hazardous materials in waste drums and eventually to cargo inspection systems.
Accelerator laboratories and technologies continue to make significant contributions to the diverse needs of security and defense. These applications range from providing fundamental databases for radiation interactions with materials, nuclear forensics, isotope production, and high energy density physics to system-level technology developments of directed energy system concepts, cargo inspection and interrogation, industrial and medical radiological source replacement, and stockpile stewardship.
An important component of security and defense programs is the availability of high quality databases for materials characterization, material modification, and radiation interactions with materials. These data are necessary to reliably simulate systems for detecting chemical, biological, and nuclear threats and provide benchmarks for simulation codes needed to certify the safety and reliability of
the aging stockpile.
They also have application in one type of directed-energy weapon that uses a high-energy beam of particles to damage the structure of the target or simply overheat it until it is no longer operational. The high-power beam could originate either from a space-based or earth-based accelerator, or it could be a photon beam generated by an earth-based free-electron laser driven by an induction accelerator, or a space-based chemical laser-produced photon beam.
Since charged particle beams diverge rapidly due to mutual repulsion, neutral particle beams are more commonly proposed for directed-energy weapons. Cyclotrons, linacs, and synchrotrons can accelerate protons until their velocity approaches the speed of light. The high energy protons can capture electrons from electron emitter electrodes and become electrically neutralized. A neutral particle beam
traveling at near the speed of light and containing giga-joules of kinetic energy will nullify any realistic means of defending the target (missile).
A benefit of the Star Wars research was that it also led to several important accelerator-related developments, among them the radio-frequencyquadrupole (RFQ). Induction accelerators were also tested for propagating charged particle beams through the atmosphere for missile defense due to their capability for handling kilo-ampere beams. Induction accelerators were later used to drive free electron lasers and as flash x-ray sources for dynamic radiographic imaging. The dielectric wall accelerator promises a compact form factor and accelerating gradients on the order of 100 megavolts per meter for short pulses. This technology will enable field-deployable directed-energy technologies such as high power microwave sources, electron accelerators for producing highly directional gamma-ray beams through Compton scattering, and GeV proton accelerators for long standoff interrogation.
Accelerators play a key role in addressing many of the challenging problems related to inspecting cargo at ports-of-entry, airports, seaports, and other areas. High-energy penetrating radiation (photons and/or neutrons) from a particle accelerator are needed for effective high-throughput inspections. Accelerator systems vary in size and complexity depending on the specific application requirements. Electron accelerators are typically used to produce x-rays for radiographic scans, while active interrogation techniques, using neutrons, photons, protons, or muons, can be employed to induce detectable characteristic signals for materials discrimination.
The useful photon energy range for radiographic scans of bulk cargo is 1-15 MeV, although present federal regulations limit the energy to ≤10
MeV to protect humans (e.g., stowaways) from accidental high dose exposures and also reduce the activation of surrounding materials. Megavoltenergy photon beams are produced by electron linear accelerators (linacs) which are readily available due to their use in medical x-ray imaging and industrial non-destructive evaluation. Both normal conducting and superconducting standing-wave and traveling wave radio frequency electron linacs are available commercially.
Typical electron linacs operate at radio frequencies of 2-4 GHz (S-band), but more compact X-band systems are also being used. In recent years, the performance of compact X-band linacs has become comparable to the more common S-band machines and, thus, X-band linacs
are being used in fieldable applications including systems for screening dense cargo.
Nuclear terrorism is a serious world-wide security threat. In the early 1990s, the first seizures of nuclear material were reported and their subsequent analysis led to the new field of nuclear forensics. The early analyses were performed using methods from nuclear safeguards such as potentiometric titration (uranium content), thermal ionization mass spectrometry (isotopic composition), and optical microscopy (macroscopic parameters). Since that time, the field has rapidly evolved and particle accelerators play a prominent role.
Due to its insensitivity to molecular isobaric interferences, accelerator mass spectrometry provides ultra-trace measurements of radionuclides for nuclear forensics. Isotope ratios of 10-12 to 10-15 are measured with backgrounds as low as 10-17 in some cases. In particular, the 236U/238U ratio in uranium ores has been identified as a forensic signature which can be correlated to geological or geographical sources. Accelerator mass spectrometry is the only technique capable of analyzing 236U/238U ratios in the 10-13 to 10-10 range. In post-detonation forensics, the relative abundances of neutron activation product debris provide information related to the design and materials used in a nuclear device.
Particle accelerators enable long stand-off interrogation of nuclear materials at long distances. Passive detection is difficult since the natural radioactive emissions of nuclear materials are low; detection of interrogation-induced fission signatures can be done at long distances. An interrogation system consists of detectors and a dedicated highpower particle accelerator producing a beam of high-energy particles such as x-rays, gamma-rays, neutrons, or protons. Conventional electron linacs can be used as forward-directed high-energy (>10MeV) x-ray sources, but more advanced highcurrent, high-brightness systems are needed to accelerate other particle types. For example, a highenergy (>100 MeV) S-band RF linear accelerator can provide an interrogation beam of monoenergetic gamma-rays via inverse laser-Compton
scattering when coupled to high power laser. Highenergy proton beams can be produced with compact superconducting cyclotrons or other highgradient accelerators. Stand-off interrogation at extremely long distances (~1 km) could be achieved with gigavolt-energy protons at milliampere beam currents utilizing high gradient/high temperature superconducting technologies.
Today’s security and defense applications are driving towards the development of more compact, rugged, and low cost accelerators with requisite high efficiency, reliability, and performance. The realization of these characteristics pushes technology innovation in advanced system concepts, novel materials, advanced engineering, high-fidelity simulation tools and improved databases critical to security and defense programs. Some technologies, such as superconducting radio-frequency, x-band, and plasma wakefield accelerators intersect accelerator advancements in other fields, but they also extend to systems such as inverse free electron lasers and induction accelerators that are less actively pursued. Accelerators will also benefit from advances in high energy-recovery efficiency to minimize power consumption and reliable high-current, high-brightness particle sources. While the majority of these accelerator technologies are still in the research and development phase, they promise new and innovative solutions to the most challenging problems in security and defense.
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