Beta particle scintillator

Organic scintillation phosphors include naphthalene, stilbene, and anthracene. The decay time of this type of phosphor is approximately 10 nanoseconds. This type of crystal is frequently used in the detection of beta particles. 

Some substances, known as fluors or scintillants, respond to the ionizing effects of alpha and beta particles by emitting flashes of light (or scintillations). While they do not respond directly to gamma rays, they do respond to the secondary ionization effects that gamma rays produce and, as a result, provide a valuable detection system for all emissions. 

FIGURE 7.11 Schematic for radiochemical detection of analytes labeled with beta-particle emitters. Radio-labeled analytes in the column effluent are mixed with scintillation cocktail to produce light, which is detected and measured by the paired photomultiplier tubes and relayed to a data acquisition system. 

Liquid scintillation counter (low-energy beta particles) 9... 

Calibration of a liquid scintillation detector for beta-particle counting is discussed in Experiment 9. 

Alpha-particle detector Beta-particle detector Gamma-ray detector proportional counters silicon (Si) diode with spectrometer proportional counters Geiger-Muller counters liquid scintillation (LS) counters thallium-activated sodium iodide (Nal(Tl) detector with spectrometer germanium (Ge) detector with spectrometer... 

Beta particle calibration sources span energies from about 100 to 3,000 keV for proportional counters, and down to a few keV for liquid scintillation counters. In this experiment, a low-background, gas-flow, end-window proportional counter with automatic sample changer for alpha- and beta-particle counting is calibrated. Beta-particles sources are counted with pulse-height discrimination to eliminate interference from alpha particles the discriminator may be turned off when no alpha particles are present. 

In this experiment, tritiated water is purified by simple distillation, and the tritium beta particles in the condensate are measured with a liquid scintillation (LS) counter. Such distillation also can collect tritiated water samples from solids. Tritium in other forms must be processed before it can be counted like tritium in water for example, tritiated hydrogen gas and tritiated organic substances can be oxidized to form water. Additional separations may be needed if the liquid or solid sample contains radioactive gases or volatile substances other than tritium that may be collected with the distilled tritiated water. Such radioactive impurities can be identified in the data output from the LS counter of an energy spectrum that differs from that of pure tritium, or of counts in energy regions where tritium counts are not found. 

Oikari, T., Kajola, H., Nurmi, I., Kaihola, L. Simultaneous counting of low alpha-and beta-particle activities with liquid scintillation spectrometry and pulse-shape analysis. Appl. Radial Isot 38A, 875-878 (1987)... 

Liquid scintillation counting of high-energy beta emitters - beta particles with energies greater than 1 MeV can be counted in water (Cerencov radiation), with no requirement for additional fluors (e.g. 52P). 

Rutherford and his students used a screen coated with zinc sulfide to detect the arrival of alpha particles by the pinpoint scintillations of light they produce. That simple device has been developed into the modern scintillation counter. Instead of a ZnS screen, the modern scintillation counter uses a crystal of sodium iodide, in which a small fraction of the Na ions have been replaced by thallium (TH) ions. The crystal emits a pulse of light when it absorbs a beta particle or a gamma ray, and a photomultiplier tube detects and counts the light pulses. 

Radiation from radioactive sources can be detected and measured in essentially Ihe same way as X-radialioii (Sections l2B-4and 12B-S). Gas-filled chambers, scintillation counters, and semiconductor detectors are all sensitive to alpha and beta particles and to gamma rays because absorption of these particles produces ionization or photoelectrons, which can in turn produce thousands of ion pairs. A detectable electrical pulse is thus produced for each particle reaching the transducer. 

Three types of radiation detectors are in common use the gas-ionization detector, the scintillation detector, and the solid-state (or semiconductor) detector. Generally, the type used depends on the specific application. Gas-ionization detectors are commonly used for inexpensive detection of charged particles, scintillation detectors for beta- and gamma-ray detection, and solid-state detectors for x-ray and gamma-ray detection. The operation and properties of these detectors will be briefly described. 

In a liquid scintillation (LS) system, the sample is mixed with a cocktail that consists of an organic scintillator dissolved in an organic solvent. The cocktail and the usual aqueous sample form an emulsion. The radiation emitted by the intimately mixed radionuclide deposits its energy in the solvent, which transfers it to the scintillator. The scintillations are then detected by the PMT. The LS counter is useful for detecting alpha particles and low-energy beta particles from samples that... 

As discussed in Chapter 7, a source may also be deposited by volatilization or electrodeposition for alpha or beta particle counting by Si diode or proportional counter, or added as a solution or suspension to scintillation cocktail for liquid scintillation counting. For electrodeposition, as indicated by Eq. (3.20), the... 

Counting Alpha and Beta Particles with a Liquid Scintillation Detector... 

In an LS counter, the cocktail is about a thousand times as dense as counter gas, hence most beta particles and all alpha particles deposit their full energy in it. This energy deposition produces enough scintillations for all but near-zero-energy beta particles to be recorded. 

The radiation type guides selection of the detection system and sample size, which in turn affect the magnitude of the radiation background and the detection limit, as discussed in Section 8.2. The gas-filled proportional and liquid scintillation (LS) counter respond efficiently to alpha and beta particles. Low-energy X rays can also be detected in them, while energetic gamma rays pass through with little interaction. Thin silicon diodes respond efficiently to alpha particles and low-... 

Low-background alpha/beta particle gas proportional counters can be placed anywhere if a dedicated counting-gas cylinder is provided for each unit. If a central supply of counting gas is used, the units should be placed in direct access to the gas supply manifold. Liquid scintillation counters can be placed anywhere in the counting room because they can be operated as stand-alone instruments. 

Quantities of plutonium-241, a beta-particle emitter, can be quantified from (1) assumed isotopic abundance ratios, (2) estimated in-growth of its progeny americion-241 by gamma spectrometry, or by (3) mass spectrometry (Bernhardt 1976). Americium-241 is produced from the beta decay of plutonium-241 and, therefore, can be used to indirectly measure the concentration of plutonium-241 (Metz and Waterbury 1962). Direct determination of plutonium-241 by measurement of its low energy beta-particle decay has been reported using liquid scintillation analysis (Martin 1986). 

The lower energy and short penetration ability of beta particles requires a scintillator in direct contact with the decaying isotope. This is accomplished by dissolving or suspending the sample in a liquid fluor. Counters which use this technique are called beta counters or liquid scintillation counters. 

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