Chapter 3 Basic Instrumentation for Nuclear Technology Outline of experiment 1. Accelerators get particles(e.g. protons,.) 2. Detectors accelerate them throw them against each other observe and record what happens 3. Reactors analyse and interpret the data
Chapter 3. Basic Instrumentation for Nuclear Technology 1. Accelerators 2. Detectors 3. Reactors Outline of experiment: • get particles (e.g. protons, …) • accelerate them • throw them against each other • observe and record what happens • analyse and interpret the data
1. Accelerators History-Why Particle sources Acceleration stage Space charge Diagnostics Application
• History-Why • Particle Sources • Acceleration stage • Space charge • Diagnostics • Application 1.Accelerators
2. Detectors Gas-Filled Radiation Detectors ionization chambers proportional counters Geiger-Muller counters Scintillation Detectors Photomultiplier tube Semiconductor detectors photographic films Personal dosimeters photographic emulsion plates Others Cloud and bubble chambers Particle identification E-△E.TOF Measurement theory Detection Equipment
Gas-Filled Radiation Detectors Scintillation Detectors Semiconductor Detectors Personal Dosimeters Others Particle identification Measurement theory Detection Equipment ionization chambers proportional counters Geiger-Muller counters E-ΔE, TOF photographic films photographic emulsion plates Cloud and Bubble Chambers Photomultiplier tube 2. Detectors
lonization chambers Key Components in a Simple ionization Chamber lonizing Battery the voltage must be radiation sufficiently high for effective collection of Ⅰoad electrons +? resister 109(eVs1)×1.6×109( C per ion Detector 34(ev per ion Ampere chamber meter ≈5×10-12A The average energy required to Current(A) is proportional to charges collected ionize a gas atom 30 eVion If particles entering an air-filled on electrode in ionization chambers detector deposit an average of The current registered in the ionization chamber is 1 GeV S-1 in the gas, the average current flowing through proportional to the number of ion pairs generated by the chamber radioactivity
Ionization Chambers Key Components in a Simple Ionization Chamber ??? +? ? + – Amperemeter Detector chamber Ionizing radiation Battery Load resister Current (A) is proportional to charges collected on electrode in ionization chambers. The current registered in the ionization chamber is proportional to the number of ion pairs generated by radioactivity the voltage must be sufficiently high for effective collection of electrons. The average energy required to ionize a gas atom 30 eV/ion. If particles entering an air-filled detector deposit an average of 1 GeV S-1 in the gas, the average current flowing through the chamber
How can the sensitivities of ionization chambers be improved? What happens when the voltage is increased? Proportional Counters Gas Multiplication Key Components in a Simple lonization Chamber Io XOO V Load 一十-+十 Detector Amp chamber meter 十一十一十+十一+一十+一 Proportional counters +-+-+-+-+-+-+-+-+-+-+ Gas multiplication due to +-+-+-+-+-+-+-+-+-+-+-+-secondary ion pairs when the +-+-+-+-+-+-+-+-+-+-+-+-ionization chambers operate at 十 higher voltage not only collect but also accelerate electrons
5 Proportional Counters Key Components in a Simple Ionization Chamber ??? +? ? + – Amperemeter Detector chamber Ionizing radiation Battery Load resister Gas Multiplication –+ –+–+–+ –+–+–+–+–+–+–+–+–+ –+–+–+–+–+–+–+–+–+–+–+– +–+–+–+–+–+–+–+–+–+–+–+– +–+–+–+–+–+–+–+–+–+–+–+– + Proportional counters Gas multiplication due to secondary ion pairs when the ionization chambers operate at higher voltage. X00 V How can the sensitivities of ionization chambers be improved? What happens when the voltage is increased? not only collect but also accelerate electrons
It should be noted however that the small mass and high energy of electrons make them drift 100,000 times faster than ions. Thus, the current is mainly due to the drifting electrons with only a small fraction due to the drift of ions Despite the multiplication due to secondary ion pairs, the ampere-meters register currents proportional to the numbers of primary electrons caused by radiation entering the detectors. Thus, currents of proportional chambers correspond to amounts of ionization radiation entering the proportional chamber
It should be noted, however, that the small mass and high energy of electrons make them drift 100,000 times faster than ions. Thus, the current is mainly due to the drifting electrons with only a small fraction due to the drift of ions. Despite the multiplication due to secondary ion pairs, the ampere-meters register currents proportional to the numbers of primary electrons caused by radiation entering the detectors. Thus, currents of proportional chambers correspond to amounts of ionization radiation entering the proportional chamber
Key Components in a simple lonization Chamber Geiger-Muller Counters Battery Working Components of a Geiger Muller Counter ?? Load resister Detector Am ere Geiger-Muller Counter: chamber mter Pulse counting electronics Dead Time in Pul;e Counting Dead time 1500V SunDler De etector Geiger counters count pulses Source After each pulse, the voltage has to return to a certain level before the next pulse can be counted Every ionizing particle causes a discharge in the detector of G-M counters
7 Geiger-Muller Counters Key Components in a Simple Ionization Chamber ??? +? ? + – Amperemeter Detector chamber Ionizing radiation Battery Load resister 1X00 V Working Components of a Geiger Muller Counter 1500 V supplier – + Detector Source Geiger-Muller Counter: Pulse counting electronics Dead Time in Pulse Counting Dead time Every ionizing particle causes a discharge in the detector of G-M counters. Geiger counters count pulses. After each pulse, the voltage has to return to a certain level before the next pulse can be counted
high sensitivity No characterization of radioactivity When the source has a very strong radioactivity, the pulses generated in the detectors are very close together. As a result, the geiger counter may register a zero rate. In other words, a high radioactive source may overwhelm the Geiger counter, causing it to fail keep this in mind. The zero reading from a Geiger counter provides you with a(false) sense of safety when you actually walk into an area where the radioactivity is dangerously high
high sensitivity No characterization of radioactivity. When the source has a very strong radioactivity, the pulses generated in the detectors are very close together. As a result, the Geiger counter may register a zero rate. In other words, a high radioactive source may overwhelm the Geiger counter, causing it to fail. keep this in mind. The zero reading from a Geiger counter provides you with a (false) sense of safety when you actually walk into an area where the radioactivity is dangerously high
Iimited propor tionality 10 onization or tional chamber counter III discha a par ticle article recombination before collection 250 50o 750 1000 Volt age (volts) Operational regions for gas filled radiation detectors
Operational regions for gas 9 -filled radiation detectors
Scintillation Counters not based on ionization but based on light emission The Key Components of a Typical Scintillation Counter Photo- y rays cathode e supple tande sodium iodide ( Nal)crystal, analyzer/ contains 0.5 mole percent of o spstem thallium iodide(Tl)-activator Photomultiply tube Photons cause the emission of a short flash in the na(ti)l crystal The flashes cause the photo-cathode to emit electrons
10 Scintillation Counters The Key Components of a Typical Scintillation Counter High voltage supplier and multi-channel analyzer / computer system Photomultiply tube Photocathode Na(Tl)I crystal Thin Al window X- or rays Photons cause the emission of a short flash in the Na(Tl)I crystal. The flashes cause the photo-cathode to emit electrons. not based on ionization, but based on light emission. sodium iodide (NaI) crystal, contains 0.5 mole percent of thallium iodide (TlI) - activator,
