Applications of Accelerators (outside of particle physics)

Dr. Suzie Sheehy

Research Fellow and 2010 Brunel Fellow

Royal Commission for the Exhibition of 1851

ASTeC Intense Beams Group

STFC Rutherford Appleton Laboratory

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Accelerators: Where/Why?


What can you accelerate?

You can accelerate anything that has a charge such as protons, electrons and ions. Neutrons are neutral so cannot be accelerated.

Medical Applications

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Fluorine 18 is produced using a cyclotron or linear particle accelerator to bombard a target, usually of pure or enriched oxygen-18-water (0.2% natural abundance) with high energy protons (typically ~18 MeV).

Above right slide shows normal metabolic function in the brain (right sided image).

Positron emission tomography (PET) is a nuclear medical imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Three-dimensional images of tracer concentration within the body are then constructed by computer analysis. In modern scanners, three dimensional imaging is often accomplished with the aid of a CT X-ray scan performed on the patient during the same session, in the same machine. If the biologically active molecule chosen for PET is FDG, an analogue of glucose, the concentrations of tracer imaged will indicate tissue metabolic activity by virtue of the regional glucose uptake. Use of this tracer to explore the possibility of cancer spreading to other sites is the most common type of PET scan in standard medical care (90% of current scans). However, on a minority basis, many other radiotracers are used in PET to image the tissue concentration of many other types of molecules of interest.

X-ray radiotherapy

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The whole system rotates through 360 degrees around the patient

External beam radiotherapy or teletherapy is the most common form of radiotherapy. The patient sits or lies on a couch and an external source of radiation is pointed at a particular part of the body. Kilovoltage (“superficial”) X-rays are used for treating skin cancer and superficial structures. Megavoltage (“deep”) X-rays are used to treat deep-seated tumors (e.g. bladder, bowel, prostate, lung, or brain). Commercially available medical linear accelerators produce X-rays and electrons with an energy range from 4 MeV up to around 25 MeV (megavoltage). The X-rays themselves are produced by the rapid deceleration of electrons in a target material, typically a tungsten alloy, which produces an X-ray spectrum via bremsstrahlung radiation. The shape and intensity of the beam produced by a linac may be modified or collimated by a variety of means. The main problem with X-ray radiotherapy is that it covers a large area of the body and may adversely affect healthy tissue.

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The Bragg peak is a pronounced peak on the Bragg curve which plots the energy loss of ionizing radiation during its travel through matter. For protons, α-rays, and other ion rays, the peak occurs immediately before the particles come to rest. This is called Bragg peak, for William Henry Bragg who discovered it in 1903.

The main problem with X-ray irradiation is that it will affect areas in the body that don’t need treatment.

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Medulloblastoma – affects children, malignant brain tumour which is surgically removed. Afterwards, to prevent spread, want to sterilize the spine with radiation.

Particle therapy is a form of external beam radiotherapy using beams of energetic protons, neutrons, or positive ions for cancer treatment. The most common type of particle therapy as of 2012 is proton therapy. Charged particle therapy works by aiming energetic ionizing particles at the target tumour. These particles damage the DNA of tissue cells, ultimately causing their death. Because of their reduced ability to repair damaged DNA, cancerous cells are particularly vulnerable to attack.

Neutron Spallation Sources

The Spallation Neutron Source (SNS) is an accelerator-based neutron source facility that provides the most intense pulsed neutron beams in the world for scientific research and industrial development.

Giant microscopes?

The wave particle duality theory was proposed by Louis de Broglie in 1924 in his PhD thesis. He put forward the idea that matter could have wave like properties. The de Broglie relations show that the wavelength is inversely proportional to the momentum of a particle and is also called de Broglie wavelength (l= Planck’s constant (h)/momentum (p))

The smaller the (de Broglie) wavelength – the smaller we can see.

To see things you need to bounce stuff off it, and your two options are particles or light. With no particle accelerator at all, light from stuff bounces off people and we can see them.

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We can do better than that and actually see quite tiny things with a microscope. Bottom left image is a scanning electron micrograph of a snowflake at varying magnifications. SEM just like a TV: accelerates electrons with very similar mechanism. Electrons bounce off small objects, just like light does.

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We can see smaller things still with neutrons and muons, but need a pretty serious particle accelerator to make them. We can image things on the scale of atoms and molecules; neutrons allow us to probe the structure of materials, muons act like tiny magnetic field detectors

Why neutrons?

Inside the instrument a material will be positioned for investigation. Neutrons travel into the material and are detected when they come out. The directions in which the neutrons emerge tell us about the arrangement of the atoms inside. This is called neutron diffraction. The amount of energy lost by the neutrons as they travel through the material tells us about the atomic dynamics, a technique called neutron spectroscopy.

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Neutron scattering is used to study the structure and dynamics of atoms and molecules over an enormous range of distances and times: from micrometres to one-hundred-thousandth of a micrometre, and from milliseconds to ten-million-millionths of a millisecond. While other techniques can provide information either within the same spatial range or the same temporal range as neutrons, neutron scattering provides a unique combination of structural and dynamic information.

Neutron scattering allows scientists to count scattered neutrons, measure their energies and the angles at which they scatter, and map their final positions. This information can reveal the molecular and magnetic structure and behavior of materials, such as high-temperature superconductors, polymers, metals, and biological samples. In addition to studies focused on fundamental physics, neutron scattering research has applications in structural biology and biotechnology, magnetism and superconductivity, chemical and engineering materials, nanotechnology, complex fluids, and others.

ISIS is a world-leading centre for research in the physical and life sciences at the Rutherford Appleton Laboratory near Oxford in the United Kingdom. Their suite of neutron and muon instruments allows the properties of materials to be understood at the scale of atoms. They support a national and international community of more than 2000 scientists for research into subjects ranging from clean energy and the environment, pharmaceuticals and health care, through to nanotechnology, materials engineering and IT.

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Power (P) = 800MV x 23 micro amps = 184KW

Four moderators are used to slow down fast neutrons escaping from the target to the lower speeds required for neutron scattering experiments. Two use water at room temperature, one uses liquid methane at 100 K and the fourth consists of liquid hydrogen at 20 K. The different temperatures result in different energy neutron beams. Given the mathematics of elastic collisions, as neutrons are very light compared to most nuclei, the most efficient way of removing kinetic energy from the neutron is by choosing a moderating nucleus that has near identical mass. So hydrogen for example…

Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress.

Nuclear spallation is one of the processes by which a particle accelerator may be used to produce a beam of neutrons. A mercury, tantalum, lead or other heavy metal target is used, and 20 to 30 neutrons are expelled after each impact. Although this is a far more expensive way of producing neutron beams than by a chain reaction of nuclear fission in a nuclear reactor, it has the advantage that the beam can be pulsed with relative ease. The concept of nuclear spallation was first coined by Nobelist Glenn T. Seaborg in his doctoral thesis on the inelastic scattering of neutrons in 1937.

Generally the production of neutrons at a spallation neutron source begins with a high-powered accelerator. This is more often than not a synchrotron.

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Synchrotron light sources

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High Flux: high intensity photon beam, allows rapid experiments or use of weakly scattering crystals; High Brilliance (Spectral Brightness): highly collimated photon beam generated by a small divergence and small size source (partial coherence); High Stability: submicron source stability; Polarisation: both linear and circular (with IDs) Pulsed Time Structure: pulsed length down to tens of picoseconds allows the resolution of process on the same time scale.

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Left hand slide: Left image; The collection of precise information on the molecular structure of chromosomes and their components can improve the knowledge of how the genetic code of DNA is maintained and reproduced

Right image; X-ray fluorescence imaging revealed the hidden text by revealing the iron contained in the ink used by a 10th century scribe. This x-ray image shows the lower left corner of the page.

Radiocarbon dating

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Radiocarbon dating (or simply carbon dating) is a radiometric dating technique that uses the decay of carbon-14 (14C) to estimate the age of organic materials, such as wood and leather, up to about 58,000 to 62,000 years. Carbon dating was presented to the world by Willard Libby in 1949, for which he was awarded the Nobel Prize in Chemistry. Since its introduction it has been used to date many items, including samples of the Dead Sea Scrolls, the Shroud of Turin, enough Egyptian artifacts to supply a chronology of Dynastic Egypt, and Ötzi the Iceman.

Mass Spectrometry


Mass spectrometry (MS) is an analytical technique that produces spectra (singular spectrum) of the masses of the molecules comprising a sample of material. The spectra are used to determine the elemental composition of a sample, the masses of particles and of molecules, and to elucidate the chemical structures of molecules, such as peptides and other chemical compounds. Mass spectrometry works by ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios.

Radiation and food

Food irradiation is the process of treating food with a specific dosage of ionizing radiation. This treatment slows or halts spoilage by retarding enzymic action or destroying microorganisms and it can also inactivate foodborne pathogenic organisms (reducing the risk of food borne illness). Further applications include sprout inhibition, delay of ripening, increase of juice yield, and improvement of re-hydration. Irradiation is also used to prevent the spread of invasive insect species that could be associated with fresh produce (e.g. fruit fly pests).

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By irradiating food, depending on the dose, some or all of the microorganisms, bacteria, viruses or insects present are killed. It can be used at low doses to delay food ripening and provide quarantine treatment. Medium doses are used to reduce microbes and extend shelf life of meat, poultry and seafood (refrigerated & frozen). They reduce microorganisms in spices to improve shelf life. What is the one place that you really, really don’t want to get food poisoning? In space! High dose applications sterilize meat for NASA astronauts.

Suzie’s favourites

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