Nuclear detectors

Nuclear Detectors are discussed here, important and main points published in presentation,

1. Nuclear Detectors Presented by: Muhammad Salman BSCHEM01173013 1 Muhammad Deen BSCHEM01173031 Muhammad Zeeshan BSCHEM01173036 Hafiz Muhammad Saad Ali BSCHEM01173025 Muhammad Waqas BSCHEM01173011 BS Chemistry (8 th Semester) GROUP NO II

2. CONTENTS Radiation Dosimetry Types Gas Filled Detectors Ionization Chamber GM Counter Scintillation Counter 2

3. 3 Radiation Radiation is the kind of energy, that comes from a source & travels through space & may be able to penetrate various materials Or Is the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles which cause ionization . Types of the radiation (1) CHARGED PARTICLES ( 2) UNCHARGED PARTICLES (a) Alpha Radiation ( a) Gamma Radiation (b) Beta Radiation (b ) Neutrons

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5. Dosimetry Radiation Dosimetry is a study in physics which deals with the measurement of radiation which may include Exposure, Absorbed dose etc ., Detectors that indicate the net amount of energy deposited in the detector by multiple interactions are called dosimeters Dosimetry is extensively used for radiation protection and is routinely applied to radiation workers, where irradiation is expected but regulatory levels must not be exceeded. Dosimetry contains required quantitative methods which are used to determine the dose of radiation, which helps in , a. The need of protection against ionizing radiation, b. Application of radiation in medicine. 5

6. Dosimetric quantities Activity Exposure Absorbed dose Activity : Activity refers to amount of unstable nuclei that gains stability through radio disintegration per unit time   Where dN is the number of nuclear transformation (decay) in unit time dt. Exposure: Exposure is a measure of ionization produced in air by photons (X rays or Gamma rays). X   where dQ is the absolute value of total charge of ions of one sign produced in air when all electrons (negatron's or positrons) liberated by photons in air of mass dm are completely stopped by air 6

7. SI unit of exposure is C/Kg. Special Unit of exposure is Roentgen. It is applicable only for: Photon energies below 3 MeV Interaction is only between photons and air . Absorbed dose: The Absorbed dose (D) , is the energy absorbed per unit mass. This quantity is defined for all ionizing radiation (not only for EM radiation, as in the case of the exposure) and for any material. D   where , dE is the energy imparted to matter of mass dm. The unit of absorbed dose is Gray. 7

8. Radiation Dosimeters Radiation Dosimeters are the devices used for detection of the radiation which directly or indirectly measures Exposure, Kerma , Absorbed dose, Equivalent dose or other quantities. The dosimeter along with its reader is referred to as a Dosimetry System . Two parts of Radiation measuring system are: 1. A detector 2. A measuring apparatus(electrometer) The interaction of radiation with the system takes place in the detector. The measuring apparatus takes the output of the detector and performs the function required to accomplish the measurements . 8

9. Properties of an useful dosimeter are as follows 1. High accuracy and precision 2. Linearity of signal with dose over a wide range 3. Small dose and dose rate dependence 4. Flat Energy response(Quality dependence) 5. Small directional dependence 6. High spatial resolution 9

10. Types of Detectors 10

11. 7 This instrument works on the principle that as radiation passes through air or a specific gas, ionization of the molecules in the air occur. When a high voltage is placed between two areas of the gas filled space , the positive ions will be attracted to the negative side of the detector (the cathode) and the free electrons will travel to the positive side (the anode ). These charges are collected by the anode and cathode which then form a very small current in the wires going to the detector. By placing a very sensitive current measuring device between the wires from the cathode and anode, the small current measured and displayed as a signal. The more radiation which enters the chamber , the more current displayed by the instrument. 11

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13. 21 Types of Gas Filled Detectors Ionization chamber Proportional counter GM counter Ionization chambers have wider range of physical shape (parallel plates, concentric cylinders, etc.) Proportional counters and GM counters must have thin wire anode 13

14. 21 14 “Ionization chamber measures the charge from the number of ion pairs created within a gas caused by incident radiation .” Ion-pairs move towards opposite polarity electrodes G enerating an ionization current which is measured by an electrometer circuit. The chamber cannot discriminate between radiation types (beta or gamma ). It cannot produce an energy spectrum of radiation Straight pleateu as there is no “multiplication” and also no “recombination”. Ionization chambers

15. Ionization chambers 15

16. 16 1. Nuclear industry: Used where a constant high dose rate is being measured T hey have a greater operating lifetime than standard GM tubes , which suffer from gas break down. 2. Smoke detectors: Ionization chamber contains an alpha-emitter Producing constant ion current Smoke enters, disrupts this current because ions strike smoke particles and are neutralized . This drop in current triggers the alarm 3. Medical radiation measurement: Ionization chambers are used to ensure that the dose delivered from a therapy unit. Applications

17. 11 The Geiger counter is an instrument used for measuring ionizing radiation. It detects ionizing radiation such as alpha particles, beta particles and gamma rays using the ionization effect produced in a Geiger–Müller tube. It is perhaps one of the world's best-known radiation detection instruments. Geiger counter / Geiger-Müller Operating Principle A Geiger counter consists of a Geiger-Müller tube, the sensing element which detects the radiation, and the processing electronics – Results in Display Geiger-Müller tube is filled with an inert gas such as helium, neon, or argon at low pressure, to which a high voltage is applied Tube briefly conducts electrical charge when a particle or photon of incident radiation makes the gas conductive by ionization 17

18. 12 The ionization is considerably amplified within the tube by the Townsend Discharge effect to produce an easily measured detection pulse This large pulse from the tube makes the G-M counter cheap to manufacture, as the subsequent electronics is greatly simplified. The electronics also generates the high voltage, typically 400–600 volts 18

19. 13 Application For the detection of alpha and beta particles To detect radioactive rocks and minerals in the course of mineral prospecting or as a mineral collector To check for environmental levels of radioactivity For Fire and Police first responders to a analysis for making an initial determination of radiation risk. 19

20. 14 Scintillation counter scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillator material , and detecting the resultant light pulses. 20

21. 15 Structure of Scintillation counter It consists of a scintillator which generates photons in response to incident radiation. a sensitive photomultiplier tube (PMT) which converts the light to an electrical signal and electronics to process this signal. Scintillator consists of a transparent crystal, usually a phosphor, plastic or organic liquid . 21

22. 16 Principle When high energy atomic radiations are incident on a surface coated with some fluorescent material, then flashes of lights are produced. The scintillations are detected with the help of a photomultiplier tube that gives rise to an equivalent electric pulse. 22

23. 17 Working When an ionizing particle passes into the scintillator material, atoms are ionized along a track. The photon from the scintillation strikes a photocathode and emits an electron which accelerated by a pulse and produce a voltage across the external resistance This voltage is amplified and recorded by an electronic counter. 23

24. 19 Application Scintillation counters are used to measure radiation in a variety of applications including hand held radiation survey meters, personnel and environmental monitoring for radioactive contamination, medical imaging , radiometric assay, nuclear security and nuclear plant safety. Scintillation counters designed for freight terminals, border security, ports , weigh bridge applications, scrap metal yards and contamination monitoring of nuclear waste. 24

25. 19 References C Baldock , Y De Deene , S Doran, G Ibbott , A Jirasek , M Lepage , KB McAuley , M Oldham, LJ Schreiner 2010. Polymer gel dosimetry. Physics in Medicine and Biology 55 (5) R1   Feinendegen LE. The cell dose concept; potential application in radiation protection. 1990 Phys. Med. Biol. 35 597 Senthil Srinivasan, V.S.; Pandya, Arun (2011). "Dosimetry aspects of hafnium oxide metal-oxide-semiconductor (MOS) capacitor". Thin Solid Films. 520 (1): 574–577.  Bibcode : 2011TSF...520..574S .  doi : 10.1016/j.tsf.2011.07.010 . Curran , Samuel C. (1949).  Counting tubes, theory and applications . Academic Press (New York). p. 235 . ^   Oxford Dictionary of National Biography ^   "Automatic Radiation Detection and Monitoring System" . Archived from  the original  on 2014-08-14. ^   "Automatic Radiation Detection Vehicles" . Archived from  the original  on 2014-08-14 . ^   Portable MicroR Survey Meters   Archived  2009-12-07 at the  Wayback Machine 25

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