- Published: September 6, 2022
- Updated: November 4, 2022
- University / College: Nottingham Trent University
- Language: English
- Downloads: 47
A scintillator is material which exhibits scintillation the belongings of luminescence when excited by ionising radiation.
Luminescent stuffs, when struck by an incoming ionizing radiation, absorb its energy and scintillate, i. e. reemit the captive energy in the signifier of a little flash of visible radiation in the seeable scope. If the reemission occurs quickly, i. e. within the ~10? 8s required for an atomic passage, the procedure is called fluorescence. Sometimes, the aroused province is metastable, so the relaxation back out of the aroused province is delayed the procedure so corresponds to either one of two phenomena, depending on the type of passage and therefore the wavelength of the emitted optical photon: delayed fluorescence or phosphorescence. Some belongingss desirable in a good scintillator sensor are: a low gamma end product ( i.
e. a high efficiency for change overing the energy of incident radiation into scintillation photons ) , transparence to its ain scintillation visible radiation, efficient sensing of the radiation being studied, a high fillet power, good one-dimensionality over a broad scope of energy, a short rise clip for fast timing applications, a short decay clip to cut down sensor dead-time and suit high event rates, emanation in a spectral scope fiting the spectral sensitiveness of bing photomultiplier tubing, an index of refraction near that of glass ( ? 1. 5 ) to let optimal yoke to the photomultiplier tubing window. Ruggedness and good behaviour under high temperature may be desirable where opposition to quiver and high temperature is necessary. The practical pick of a scintillator stuff is normally a via media between those belongingss to outdo tantrum a given application. the light end product is the most of import, as it affects both the efficiency and the declaration of the sensor. The light end product is a strong map of the type of incident atom or photon and of its energy, which hence strongly influences the type of scintillation stuff to be used for a peculiar application. The presence of slaking effects consequences in decreased visible radiation end product ( i.
e. reduced scintillation efficiency ) . Quenching refers to all radiation less deexcitation procedures in which the excitement is degraded chiefly to heat. The overall signal production efficiency of the sensor, nevertheless, besides depends on the quantum efficiency of the Photomultiplier tubing, and on the efficiency of light transmittal and aggregation ( which depends on the type of reflector stuff covering the scintillator and light ushers, the length/shape of the light ushers, any light soaking up, etc. ) . The light end product is frequently quantified as a figure of scintillation photons produced per keV of deposited energy. Scintillation sensors are by and large assumed to be additive. This premise is based on two demands: 1 ) That the light end product of the scintillator is relative to the energy of the incident radiation.
2 ) That the electrical pulsation produced by the photomultiplier tubing is relative to the emitted scintillation visible radiation. The one-dimensionality premise is normally a good rough estimate. The clip development of the figure of emitted scintillation photons N in a individual scintillation event can frequently be described by the additive superposition of one or two exponential decays. For two decays, we have the signifier: Where ? f and ? s are the fast and the slow decay invariables.
TYPES OF SCINTILLATORS: –
1 ) Organic crystalsOrganic scintillators are aromatic hydrocarbon compounds incorporating linked or condensed benzine pealing constructions. They typically have a really rapid decay clip. Some organic scintillates are pure crystals.
The most common types are anthracene ( C14H10, decay clip ? 30 N ) , stilbene ( C14H12, few ns decay clip ) , and naphthalene ( C10H8, few ns decay clip ) . They are really lasting, but their response is anisotropic, and they can non be easy machined, nor can they be grown in big sizes ; hence they are non really frequently used. Anthracene has the highest light end product of all organic scintillators and is hence chosen as a mention: the light end products of other scintillators are sometimes expressed as a per centum of anthracene visible radiation. 2 ) Organic LiquidsThese are liquid solutions of one or more organic scintillators in an organic dissolver.
Thse typical solutes are fluors such as p-terphenyl ( C18H14 ) , PBD ( C20H14N2O ) , butyl PBD ( C24H22N2O ) , PPO ( C15H11NO ) , and wavelength shifter such as POPOP ( C24H16N2O ) . The most widely used dissolvers are toluene, xylene, benzine, phenylcyclohexane, triethylbenzene, and decalin. Liquid scintillators are easy loaded with other additives such as wavelength shifters to fit the spectral sensitiveness scope of a peculiar Photo multiplier tubing to increase the neutron sensing efficiency of the scintillation counter itself. For many liquids, dissolved O can move as a extinction agent and lead to cut down light end product, therefore the necessity to seal the solution in an oxygen-free, airtight enclosure.
3 ) PlasticsFictile scintillators are solutions of organic scintillators in a dissolver which is later polymerized to organize a solid. Some of the common solutes are p-Terphenyl The most widely used plastic dissolvers are polyvinyl methylbenzene and polystyrene. Plastics scintillators give a fast signal and a high visible radiation end product. The figure of emitted scintillation photons is best described by the whirl of an exponential decay and a Gaussian ( instead than the exponential decay entirely ) : Where the a map degree Fahrenheit is a Gaussian.
HOW SCINTILLATOR DETECTOR OBTAINED: –
A scintillation sensor or scintillation counter is obtained when a scintillator is coupled to an electronic visible radiation detector such as a photomultiplier tubing or a photodiode. Photomultiplier tubing absorb the visible radiation emitted by the scintillator and reemit it in the signifier of negatrons via the photoelectric consequence. The subsequent generation of those negatrons consequences in an electrical pulsation which can so be analyzed and give meaningful information about the atom that originally struck the scintillator. Vacuum photodiodes are similar but do non magnify the signal while Si photodiodes accomplish the same thing straight in the Si.
SCINTILLATION COUNTER: –
A scintillation counter steps ionising radiation. The detector, called a scintillator, consists of a crystalline crystal, normally phosphor, plastic, ororganic liquid that fluoresces when struck by ionising radiation. A sensitive exposure multiplie rtube measures the visible radiation from the crystal. The Photo multiplie tubing is attached to an electronic amplifier and other electronic equipment to count and perchance quantify the amplitude of the signals produced by the photomultiplier.
Working OF SCINTILLATOR COUNTER: –
When a charged atom strikes the scintillator, a flash of visible radiation is produced, which may or may non be in the seeable part of the spectrum. Each charged atom produces a flash. If a flash is produced in a seeable part, it can be observed through a microscope and counted – an impractical method. The association of a scintillator and photomultiplier with the counter circuits forms the footing of the scintillation counter setup. When a charged atom base on ballss through the phosphor, some of the phosphor ‘ s atoms get excited and emit photons. The strength of the light flash depends on the energy of the charged atoms.
Cesium iodide ( CsI ) in crystalline signifier is used as the scintillator for the sensing of protons and alpha atoms ; Na iodide ( NaI ) incorporating a little sum of Tl is used as a scintillator for the sensing of gamma moving ridges. The scintillation counter has a bed of phosphor cemented in one of the terminals of the photomultiplier. Its interior surface is coated with a photo-emitter with less work potency. This photoelectric emitter is called as photocathode and is connected to the negative terminus of a high tenseness battery. A figure of electrodes called dynodes are arranged in the tubing at increasing positive potency. When a charged atom strikes the phosphor, a photon is emitted.
This photon strikes the photocathode in the photomultiplier, let go ofing an negatron. This negatron accelerates towards the first dynode and hits it. Multiple secondary negatrons are emitted, which accelerate towards the 2nd dynode. More negatrons are emitted and the concatenation continues, multiplying the consequence of the first charged atom.
By the clip the negatrons reach the last dynode, plenty have been released to direct a electromotive force pulsation across the external resistances. This electromotive force pulsation is amplified and recorded by the electronic counter.
APPLICATION OF SCINTILLATOR COUNTER: –
Scintillation counters can be used in a assortment of applications. Medical imaginationNational and homeland securityBorder securityNuclear safetySeveral merchandises have been introduced in the market utilising scintillation counters for sensing of potentially unsafe gamma-emitting stuffs during conveyance. These include scintillation counters designed for cargo terminuss, boundary line security, ports, weigh span applications, bit metal paces and taint monitoring of atomic waste. There are discrepancies of scintillation counters mounted on pick-up trucks and choppers for rapid response in instance of a security state of affairs due to soil bombs or radioactive waste, Hand-held units are besides normally used.
SCINTILLATOR COUNTER AS SPECTROMETER: –
Scintillators frequently convert a individual photon of high energy radiation into high figure of lower-energy photons, where the figure of photons per megaelectronvolt of input energy is reasonably changeless. By mensurating the strength of the flash, it is hence possible to spot the original photon ‘ s energy. The spectrometer consists of a suited scintillator crystal, a photomultiplier tubing, and a circuit for mensurating the tallness of the pulsations produced by the photomultiplier. The pulsations are counted and sorted by their tallness, bring forthing a x-y secret plan of scintillator flash brightness vs figure of the flashes, which approximates the energy spectrum of the incident radiation, with some extra artefacts. A monochromatic gamma radiation produces a photopeak at its energy. The sensor besides shows response at the lower energies, caused by Compton dispersing, two smaller flight extremums at energies 0.
511 and 1. 022 MeV below the photopeak for the creative activity of electron-positron braces when one or both annihilation photons flight, and a backscatter extremum. Higher energies can be measured when two or more photons strike the sensor about at the same time, looking as sum extremums with energies up to the value of two or more photopeaks added.
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