Choose an application
- Aerospace
- Chromatography
- Clinical Analysers
- Confocal Microscopy
- Electron Microscopy
- Film Scanners
- Glass Inspection
- High Energy Physics (HEP)
- Level Gauges
- LIDAR
- Liquid Scintillation Counting (LSC)
- Luminometers
- Mass Spectrometers
- Medical Imaging
- Oil Well Logging / MWD
- Particle Counting
- Particle Sizing
- Pollution Monitoring
- Radiation Monitoring
- Radiometry
- Scintillation Spectroscopy
- Sorting
- Spectrometry - fluorescence
- Spectrometry - other
- Steel Thickness Gauging
- Telecine
- X-ray Diffractometer
Aerospace
Photomultipliers can be used for civil / military aerospace applications including moving maps and aircraft monitoring systems.
astronomy
Many types of astronomical observations can only be done from above the earth's atmosphere. Special rugged photomultipliers are used in the instruments which are launched aboard spacecraft. ET Enterprises' products have been used for many NASA and ESA missions. Some of the most noteworthy are the Hubble Space Telescope, the Compton Gamma Ray Observatory, the SOHO solar observatory, the Hipparcos star mapping satellite, and the Ulysses solar polar mission.
Chromatography
Photomultipliers are used in instruments which analyse chemical mixtures by separating the constituents in a column.
Clinical Analysers
An example is an instrument that measures glucose levels in the blood in the diagnosis of diabetes. Another instrument tests blood for diseases such as HIV.
Confocal Microscopy
The principle of confocal imaging is that light is only registered from the part of the specimen which is in focus. Out of focus regions of the sample appear black, thus eliminating all unwanted glare. A laser beam scans the sample and a photomultiplier fitted with a unique optical enhancer receives the reflected light.
Electron Microscopy
An electron microscope can be used to examine objects such as viruses which are too small to be seen with a conventional microscope. This is because the wavelength of an accelerated electron is shorter than that of visible light and can therefore resolve smaller features.
Film Scanners
In the print industry photographs often need computer enhancing or manipulation before they are ready to go in the publication. A transparency is scanned with a bright light and filters separate the colours into cyan, yellow, and magenta channels which are recorded by photomultipliers. The three signals are then digitised and stored in a computer's memory.
Glass Inspection
Glass for windows is produced in a giant crucible and flows out in a river of glass which is up to a mile long before the glass cools enough to be cut into large sheets. To test the quality of the glass the sheet is scanned with a light spot prior to cutting, a linear array of photomultipliers picks up the light and detects any bubbles or flaws in the glass allowing each sheet to be graded.
High Energy Physics (HEP)
Large numbers of photomultipliers are used in high energy physics (HEP) experiments. Electron Tubes has a long history of supplying them. There are three main areas of research:
Particle accelerators, where particles are accelerated to nearly the speed of light, acquiring energies which have not been reached since the birth of the universe. The particles are made to collide at the focus of vast calorimeters which detect the new particles created in the collision. The data is used to test the fundamental theories of the strong and weak forces and the quark structure of matter.
Neutrino, dark matter and weakly interacting particle detectors which are located in vast underground chambers to screen them from the cosmic ray background. Astrophysicists use the results to test theories of both these particles and the mechanisms powering stars, supernovas, and active galaxies.
Air shower telescopes, where arrays of photomultipliers view the night sky in remote parts of the world where there is an absence of light pollution. Showers of particles produced by cosmic rays striking the upper atmosphere allow the study of physics at energies much higher than those that can be created in any man made accelerator.
Level Gauges
To measure how full storage silos and tanks are a radioactive source emitting gamma rays is positioned on one side of the vessel and is monitored by a long scintillator (a material which emits light when struck by gamma rays) viewed by a photomultiplier. The amount of radiation absorbed by the material in the tank is proportional to how full the tank is. A computer counts the gamma rays and can open valves to refill the tank when the level drops below a predetermined point.
LIDAR
LIDAR or laser radar originally developed for range finding is now a key tool for atmospheric research including the study of pollution and the damage to the ozone layer. In principle an intense laser beam is fired into the atmosphere where changes in density and composition cause some light to be reflected. A photomultiplier detects the reflections and the time of their occurrence allows the distance to the perturbation to be calculated. The photomultipliers are often gated so that they are not affected by the initial laser blast.
Liquid Scintillation Counting (LSC)
Liquid scintillation counting is widely used for the study of biological functions, tumours, viruses, and new drugs. More famously it is used for radioactive dating of archaeological finds. It does this by counting the alpha or beta particles emitted by radioactive isotopes such as Tritium (3H) or Carbon 14 (14C). In biological applications these are made to attach to the molecule under study, the number of counts is proportional to the potency of a drug for example. Alpha and beta particles are best detected when the sample is dissolved in a liquid scintillator which emits a weak pulse of light for each decay. Usually two photomultipliers view the sample vial in coincidence, recording a count only when both see the light.
Luminometers
Luminescence techniques are extensively used in clinical medical testing, and their application in the food and pharmaceutical industries is growing. Examples include HIV testing and inspecting products such as meat and cheese for the presence of antibiotics, drugs, insecticides or bacteria. The same chemical that makes fireflies glow is used to react with the ATP molecule, which distributes energy in living cells, to produce light.
Mass Spectrometers
Analysis of gas molecules or vaporised samples by ionising the molecules and then using an electric and magnetic field to separate them according to their mass. The ions are measured by targeting them onto a dynode which produces a shower of electrons onto a phosphor screen viewed by a photomultiplier.
Medical Imaging
The gamma camera allows images to be taken of the flow of a radioactive isotope in a patient's blood stream, in this way the function of the patient's internal organs can be monitored leading to a diagnosis. The gamma camera consists of dozens of photomultipliers connected in a honeycomb array to a large Thallium doped sodium iodide scintillator.
Oil Well Logging / MWD
In the search for new oil deposits and mapping their extent a number of measurements are made down test bore holes and even while drilling a hole. Radiation from a radioactive source is scattered by the rock and detected by a photomultiplier and scintillator combination. Special photomultipliers are used which can withstand temperatures of up to 200°C encountered several thousand meters underground. Metal Ceramic photomultipliers are the most rugged types and can survive the violent shocks and vibrations experienced while drilling.
Particle Counting
Many pharmaceutical and electronics industrial processes have to be carried out in dust free conditions, a particle counter is essential to monitor the amount of airborne particles. Light is scattered by the particles in a sample and detected by a photomultiplier, the amount of light scattered is proportional to the dust concentration.
Particle Sizing
The size of particles in powders, sprays, and emulsions is important if they are to be manufactured with the required properties. Scattered laser light is detected by a photomultiplier and analysed for correlations by a special computer. The particle size distribution can be calculated from the results.
Pollution Monitoring
Nitrogen oxides are air polluting gasses emitted by car exhausts which can cause acid rain and other damage to the environment. In a NOx analyser a sample of exhaust gas is mixed with ozone, resulting in a chemiluminescent reaction. The light produced is measured by a photomultiplier and the concentration of the NOx gasses is determined.
Radiation Monitoring
Many people work in the nuclear power industry, the nuclear pharmaceutical industry and in hospital radiography departments, where they are exposed to radiation on a daily basis. Portable radiation meters incorporating a photomultiplier and scintillator measure the radioactive dose received by these workers or detect radioactive contamination on their gloves or clothes protecting them from exceeding a safe level. The same equipment can be used to protect the environment by monitoring levels of fallout from nuclear accidents or leaks.
Radiometry
Many manufacturing processes from paper and plastic sheets to metal foil and steel plates employ radioactive sources and photomultiplier / scintillator detectors for production control.
Scintillation Spectroscopy
When radioactive isotopes are present in nuclear waste or in the products of accelerators they can be identified by the energy of the gamma rays they emit. The amount of light produced by a scintillator when a gamma ray strikes and hence the output of a photomultiplier attached to it is proportional to the energy of the gamma ray. An analyser separates the output peaks and using a library of signatures, identifies the isotopes.
Sorting
Transmitted or reflected light measured by photomultipliers is the basis of many sorting and inspection techniques used in manufacturing from potato or diamond sorting, by size, to inspecting drink cans for pinholes.
Spectrometry - fluorescence
This technique is widely used for chemical analysis especially in molecular biology. A particular wavelength of light from a Xenon lamp is selected by a diffraction grating monochromator and illuminates a molecular sample causing electrons to be excited into a higher energy state. These subsequently emit light at longer wavelengths dependent on the molecular structure which is detected by a photomultiplier. The wavelengths of emission identify the chemicals present. Another photomultiplier monitors the lamp intensity at each wavelength.
Spectrometry - other
In addition to the above technique other spectrophotometers utilise absorption, transmission, reflection, atomic absorption, and emission in a flame or electric discharge to perform chemical analysis.
Steel Thickness Gauging
In steel mills the hot metal is rolled out into sheet steel by powerful rolls. The steel thickness is controlled by measuring the absorption of x-rays from an x-ray generator, via a scintillator / photomultiplier assembly on the other side of the sheet. The measuring system adjusts the pressure on the rolls to control the thickness.
Telecine
With the advent of digital video and high definition TV, old copies of films on celluloid need to be converted into digital format. Because the original film often has defects such as scratches, optical and computer image enhancement are usually employed. A white light source illuminates the film and the image is split into red, green, and blue channels by filters. Three photomultipliers designed for high light levels measure the light intensity in each channel and their outputs are digitised and passed to a computer.
X-ray Diffractometer
X-ray crystallography is the study of solid or molecular structures by the diffraction of an intense collimated beam of x-rays. The angular pattern of x-rays produced is recorded by a radiation detector, often a photomultiplier and scintillator assembly. The double-helix structure of the DNA molecule was discovered in this way.
