SOLID SCINTILLATION WRITE UP.docx
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The document provides a detailed analysis of solid scintillation counters, discussing the principles, types, workings, and applications of this radiation detection instrument. It explains the differences between solid and liquid scintillation counters, their historical development, as well as their advantages and disadvantages in various fields such as cancer research and border security. Key points include the mechanisms of detecting ionizing radiation, the materials used in scintillation, and the significance of different radiation types.
SOLID SCINTILLATION WRITE UP.docx
- 1. 1 GOVERNMENPT NAGARJUNA P.G. COLLEGE OF SCIENCE RAIPUR (C.G.) M.Sc. MICROBIOLOGY SEMESTER - 2 2022-23 WRITE UP ON SOLID SCINTILLATION COUNTER SUBMITTED BY :- SUBMITTED TO:- SNEHA AGRAWAL DEPT.OF MICROBIOLOGY
- 2. 2 INDEX RADIOACTIVITY EXPERIMENT FOR RADIOACTIVITY MEASUREMENT OF RADIOACTIVITY SCINTILLATION COUNTER HISTORY TYPES DIFFERENCE BETWEEN SOLID AND LIQUID SCINTILLATION COUNTER SOLID SCINTILLATION COUNTER PRINCIPLE INSTRUMENTATION WORKING APPLICATION ADVANTAGES DISADVANTAGES REFERENCE
- 3. 3 RADIOACTIVITY The phenomenon in which the nucleus of the atom of an element undergoes spontaneous and uncontrollable disintegration or decay and emit alpha, beta, or gamma rays It is the property of some unstable atoms to spontaneously emit nuclear radiation to gain stability. The heavy elements are called radioactive elements and rays emitted these elements are called radioactive rays. The phenomenon of radioactivity is discovered by HENRI BACQUEREL IN 1896. Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha decay (α-decay), beta decay (β-decay), and gamma decay (γ-decay), all of which involve emitting one or more particles. EXPERIMENT FOR RADIOACTIVITY In this experiment a radioactive substance is kept between the two plates one is positively (+ve) charged and other is negatively (-ve) charged. It was observed that some radiations are attracted towards negative (-ve) plate because they will have positive (+ve) charge and are knows as alpha (α) rays. Some are attracted towards positive (+ve) plate because they will have negative (-ve) charged and are knows as beta (β) rays.
- 4. 4 Some radiation are neither attracted towards positive (+ve) or negative (-ve) plate i.e. they are neutral charge and are known as gamma (γ) rays MESUREMENTS OF RADIOACTIVITY The radioactivity of a substance can be measured by Becquerel is the SI unit for measurement of radioactivity. It is defined as the number of disintegration per second. The radioactivity of radioactive substance is measured or detected by instruments like :- 1. SCINTILLATION COUNTER 2. GAS FILLED CHAMBER SCINTILLATION COUNTER A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillating material, and detecting the resultant light pulses or it can be defined as it is used to detect gamma rays and the presence of a particle. It can also measure the radiation in the scintillating medium, the energy loss, or the energy gain. The medium can be solid and liquid. TYPES OF SCINTILLATION COUNTER There are two types of scintillation counter based on the fluorescent material used. They are: 1. solid scintillation counter 2. Liquid scintillation counter
- 5. 5 DIFFERENCE BETWEEN SOLID AND LIQUID SCINTILLATION COUNTER S.NO . SOLID SCINTILLATION COUNTER LIQUID SCINTILLATION COUNTER 1. IT IS A RADIATION DETECTOR WHICH INCLUDES A SCINTILLATION CRYSTAL TO DETECT RADIATION AND PRODUCES LIGHT PULSES. IT IS A INSTRUMENT FOR DETRMINING ACTIVITY OF A LIQUID SAMPLE 2. USEFUL FOR GAMMA (γ) EMITTING ISOTOPES. USEFUL FOR QUANTIFYING ALPHA (α) AND WEAK BETA (β) EMITTERS. 3. MOSTLY SCINTILLATOR USED ARE INORGANIC SCINTILLATORS AND ORGANIC SCINTILLATORS. HERE, IT CAN BE EITHER LIQUID (ORGANIC SOLVENTS) OR SOLID FORM (PLASTICS) SOLID SCINTILLATION COUNTER SOLID SCINTILLATION COUNTER (SSC) is an attractive alternative and conventional instrument . With this method, a sample is deposited directly onto a solid scintillating material, dried, and counted in a scintillation counter. Solid scintillators have several advantages. They are non volatile, toxic, or flammable, and hence are safer to use. Waste disposal costs are reduced since the sample is dried onto the solid scintillating material and may be disposed of as solid waste. The light emitted in scintillation can be detected by coupling it to photomultiplier which convert the photon energy into an electrical
- 6. 6 pulse whose magnitude remains proportional to the energy of the original radioactive event. The crystal normally used are: 1. Sodium iodide : For gamma emitters 2. Zinc sulphide crystal : For alpha emitters 3. Anthracene : For beta emitters HISTORY The modern electronic scintillation counter was invented in 1944 by sir samuel curran(UK). Previously scintillation events had to be laboriously detected by eye using a spinthariscope which was a simple microscope to observe light flashes in the scintillator. PRINCIPLE When high energy atomic radiations are incident on a surface coated with some fluorescent material, then flashes of light (called scintillation) are produced. The scintillation are detected with the help of a photomultiplier tube , that gives rise to an equivalent electric pulse. These output electrical pulse can then be analyses and counted electronically and gives rise to information regarding the incident radiation. A solid scintillation counter is a radiation detector which includes a scintillation crystal to detect radiation and produce light pulses. In the solid scintillation counters, the sample is placed in a vial, just adjacent to a crystal or fluorescent material. Crystals are in turn
- 7. 7 placed near to the photomultiplier connected to a high voltage supply and a scaler. The solid scintillation counter is especially useful for gamma emitting isotopes as these rays are electromagnetic radiation and can collide well with the densely packed atoms of solid crystals. The high atomic number and density of certain inorganic crystals make them suitable for gamma spectroscopy with high detection efficiencies. SCINTILLATORS MAY BE CHARACTERISED INTO 2 MAIN TYPES 1. ORGANIC SCINTILLATORS:- A) Pure organic scintillators :- Anthracene, etc. B) Liquid organic solutions :- pure organic scintillators are dissolved in a suitable solvent &then we obtain liquid organic scintillators. C) Plastic scintillators :- pure organic scintillators after dissolving in the solvent are subsequently polymerized. 2. INORGANIC SCINTILLATORS :- NaI(Tl) :- Thallium activated Sodium Iodide CsI(Tl) :- Thallium activated Cesium Iodide CsI(Na) :- Sodium activated Cesium Iodide INSTRUMENTATION RADIATION- The high energy ionizing radiation strike the crystal.
- 8. 8 SCINTILLATORS- It consist of a scintillator which generates photons in response to incident radiation. LIGHT FLASHES- Flash or rays of light produced in a transparent material by passing a particle PHOTOMULTIPLIER TUBE (PMT) –A sensitive photomultiplier tube (PMT) which converts the light to an electrical signal and electronics to process this signal. PHOTOCATHODE- A photocathode is a surface that convert light (photons) into electrons by photoelectric effect. ELECTRICAL PULSE- A pulse may last from a fraction of a nanosecond upto several seconds or even minutes. AMPLIFIER- It is an electronic device that measures the peak of potential pulse. COUNTER- It measures the voltage of potential drop created by the electrons. WORKING When ionizing incident radiation enters the scintillator, it interacts with the material of the scintillator due to which the electrons enter an excited state. Charged particles follow the path of the particle itself. The energy of gamma radiation (uncharged) is converted to a high energy electron either through the photoelectric effect. The excited atoms of the scintillator material gradually undergo de-excitation and emit photons in the visible range of light. This emission is directly proportional to the energy of the incident ionizing particle. The material shines or flows brightly due to fluorescence. The pulse of light emitted by the scintillator hits the photocathode of the photomultiplier and releases at most one photoelectron for each photon. These electrons are accelerated
- 9. 9 through electrostatic means by applying a voltage potential and are targeted to hit the first dynode called the primary electrons. And having enough energy to produce further electrons, these released electrons are called secondary electrons. They strike the second dynode, thereby releasing further electrons. This process occurs in a photomultiplier tube. Each subsequent impact on the dynode releases further electrons, and hence a current amplifying effect occurs on the dynodes. Each subsequent dynode is at a higher potential than the previous one, and so helps in enhancing the acceleration. Likewise, the primary signal is multiplied throughout 10 to 12 stages. At the final dynode, highly sufficient numbers of electrons are present to produce a pulse of high magnitude to develop amplification. This pulse carries information about the energy of the incident ionizing particle. The number of pulses per unit time gives the significance of the intensity of radiation. And finally counted in counter where it measures the voltage of potential drop created by the electrons and saved the data for future use. APPLICATION It is widely used in screening technologies, RIA alternative technologies, cancer research, scientists, physicians, engineers & technicians. It also has its applications in protein interaction and detection, academic research and pharmaceutical. Border security ,nuclear plant safety, national and homeland security Used for the detection of alpha, beta and gamma emitters.
- 10. 10 ADVANTAGES Its counting rate is very fast. This instrument is also used to detect X-rays. It can detect lower levels of radiation. DISADVANTAGES Hygroscopicity- A disadvantage of some inorganic crystals, e.g. sodium iodide, is their hygroscopicity, a property which requires them to be housed in an airtight container to protect them from moisture. The cost per sample of scintillation counter is significantly higher. The high voltage applied to the photomultiplier gives rise to electronic events in the system which are not dependent on radioactivity but which contribute to a high background count. This effect is known as photomultiplier noise and can be reduced by cooling the photmultiplier. REFERANCE BIOPHYSICAL CHEMISTRY PRINCIPLES AND TECHNIQUES BY UPADHYAYA AND UPADHYAY AND NATH. A TEXTBOOK OF MICROBIOLOGY BBY R.C. DUBEY & DR. D. K. MAHESHWARI. https://www.researchgate.net/publication/263209531_Liquid_a nd_solid_scintillation_principles_and_applications
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