Lecture

Photomultiplier Tubes: Principles and Applications

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Description

This lecture covers the principles and applications of photomultiplier tubes (PMTs), focusing on their structure and operation. It begins with an overview of vacuum tubes, explaining the roles of the photocathode, anode, and the vacuum environment in electron extraction. The instructor discusses the importance of high voltage in creating a current and the use of transimpedance for measuring output voltage. The lecture then introduces the concept of gain in PMTs, detailing how primary quantum efficiency and secondary emission ratios contribute to signal amplification. The process of electron acceleration through dynodes is explained, highlighting the generation of additional electrons and the resulting high output signal. The instructor provides examples of PMT gains and compares the efficiency of PMTs to standard photodiodes, emphasizing the significant amplification achievable with PMTs. The lecture concludes with practical data on responsivity and sensitivity, illustrating the advantages of PMTs in optical detection applications.

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Related concepts (32)

Photomultiplier tube

Photomultiplier tubes (photomultipliers or PMTs for short) are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. They are members of the class of vacuum tubes, more specifically vacuum phototubes. These detectors multiply the current produced by incident light by as much as 100 million times or 108 (i.e., 160 dB), in multiple dynode stages, enabling (for example) individual photons to be detected when the incident flux of light is low.

Secondary emission

In particle physics, secondary emission is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The term often refers to the emission of electrons when charged particles like electrons or ions in a vacuum tube strike a metal surface; these are called secondary electrons. In this case, the number of secondary electrons emitted per incident particle is called secondary emission yield.

Vacuum tube

A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as a thermionic tube or thermionic valve utilizes thermionic emission of electrons from a hot cathode for fundamental electronic functions such as signal amplification and current rectification.

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. It consists of a scintillator which generates photons in response to incident radiation, a sensitive photodetector (usually a photomultiplier tube (PMT), a charge-coupled device (CCD) camera, or a photodiode), which converts the light to an electrical signal and electronics to process this signal.

Anode

An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ACID, for "anode current into device". The direction of conventional current (the flow of positive charges) in a circuit is opposite to the direction of electron flow, so (negatively charged) electrons flow out the anode of a galvanic cell, into an outside or external circuit connected to the cell.

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