Phys 3650 Jesse Winner Seminar Wednesday 2.13.19 Photomultipliers Phys 3650 Jesse Winner Seminar Wednesday 2.13.19

Safety Considerations High Voltage: Photomultipliers are operated using high voltage: 1500 Volts DC Handle the Tube with care Do not allow the glass to get scratched Do not touch the tube, faceplate, or base with bare hands Do not expose the tube to strong light For other models: Silica Bulbs: Do not use in atmosphere where helium is present Use extra care with tubes that have glass bases Picture from: Hamamatsu, Photomultiplier Tubes: Photomultiplier Tubes and Related Products, Photomultiplier Tubes: Photomultiplier Tubes and Related Products. (2016). https://www.hamamatsu.com/resources/pdf/etd/PMT_TPMZ0002E.pdf (accessed February 10, 2019).

Photomultiplier Overview Go here for an interactive tutorial. Tutorial is a side-on circular cage type Photomultiplier. http://tinyurl.com/y2nn75x5 K.R. Spring, J.C. Long, Interactive Tutorials Side-On Photomultipliers, Molecular Expressions Microscopy Primer: Specialized Microscopy Techniques - Fluorescence Digital Image Gallery - Normal African Green Monkey Kidney Epithelial Cells (Vero). (2016). https://micro.magnet.fsu.edu/primer/java/digitalimaging/photomultiplier/sideonpmt/index.html (accessed February 10, 2019).

What is a Photomultiplier (PM)? A photomultiplier allows for the measurement of light that is too dim for the naked eye to see. They measure the photoelectron flux of an area of incident light. The PM amplifies the incident photon’s energy so that we can read the photoelectron flux generated by the incident particle. Used in the gamma spectroscopy lab and the photoelectric effect lab.

How does a Photomultiplier (PM) Work? The incident light enters the PM through a photocathode and is converted into a photoelectron, the primary photoelectron. The primary photoelectron hits the first Dynode and penetrates into the metal. The kinetic energy of the photoelectron causes electrons to be raised to higher energy states in the metal and excite out of the work function of the metal creating secondary electrons. The amount of secondary electrons depend on how much energy in the primary electron and the positive potential difference on the dynode. Bialkali How does a Photomultiplier (PM) Work? Picture from: Hamamatsu, Photomultiplier Tubes: Photomultiplier Tubes and Related Products, Photomultiplier Tubes: Photomultiplier Tubes and Related Products. (2016). https://www.hamamatsu.com/resources/pdf/etd/PMT_TPMZ0002E.pdf (accessed February 10, 2019). A.H. Sommer, Photoelectric tubes, 2nd ed., Methuen, London, 1951.

How does a Photomultiplier (PM) Work? Secondary Electrons can create more secondary electrons as they leave the dynode. This process is then repeated in the next dynode where the secondary electrons bombard the electrons in the subsequent dynodes and cause an avalanche of electrons leaving the metal. This continues until all the avalanched electrons reach an anode where the potential difference between photocathode and anode is measured. The multiplication factor for the PM is: M=Sn where S is the number of secondary electrons and n is the number of dynodes. How does a Photomultiplier (PM) Work? Picture from: Hamamatsu, Photomultiplier Tubes: Photomultiplier Tubes and Related Products, Photomultiplier Tubes: Photomultiplier Tubes and Related Products. (2016). https://www.hamamatsu.com/resources/pdf/etd/PMT_TPMZ0002E.pdf (accessed February 10, 2019). A.H. Sommer, Photoelectric tubes, 2nd ed., Methuen, London, 1951.

How does a Photomultiplier (PM) Work? The gain should be kept low and amplified externally to reduce dark count a nonideal PM characteristic (noise) It is important to warm up a PM by turning it on early. This allows for it to get to a “settling down” state which reduces noise in the data Single Electron Response (SER) has a poissonian probability P(n)=(µ)ne-µ/n! Where µ is the secondary emission coefficient or gain This is the probability of observing n secondary electrons How does a Photomultiplier (PM) Work? Picture from: Hamamatsu, Photomultiplier Tubes: Photomultiplier Tubes and Related Products, Photomultiplier Tubes: Photomultiplier Tubes and Related Products. (2016). https://www.hamamatsu.com/resources/pdf/etd/PMT_TPMZ0002E.pdf (accessed February 10, 2019). B.H. Candy, Photomultiplier characteristics and practice relevant to photon counting, Review of Scientific Instruments. 56 (1985) 183–193. doi:10.1063/1.1138327.

Types of Photomultipliers The side-on and head-on type photomultipliers are the most common. We are using the head-on box-and-grid type in our lab and this is the same type I passed around. Another type is the head-on venetian blind PM. Side-on Circular-cage PM Head-on box-and-grid PM Head-on venetian blind PM Pictures from: Hamamatsu, Photomultiplier Tubes: Photomultiplier Tubes and Related Products, Photomultiplier Tubes: Photomultiplier Tubes and Related Products. (2016). https://www.hamamatsu.com/resources/pdf/etd/PMT_TPMZ0002E.pdf (accessed February 10, 2019).

Spec Sheet Terminology Quantum Efficiency Probability that the photoelectric effect will result in an incident Photon causing a primary electron to be emitted. Transit Time The time it takes from the emittance of the first primary electron after the photoelectric effect to the absorption of all the secondary electrons at the anode. Dark Current The current left over in a photoelectric device when no incident light is present. Picture from: Hamamatsu, PHOTOMULTIPLIER TUBES R1307, R1307-01, PHOTOMULTIPLIER TUBES R1307, R1307-01. (2016). A.C. Melissinos, J. Napolitano, Experiments in modern physics, 2nd ed., Academic Press, San Diego, CA, 2003.

Bibliography A.C. Melissinos, J. Napolitano, Experiments in modern physics, 2nd ed., Academic Press, San Diego, CA, 2003, p.491-494. B.H. Candy, Photomultiplier characteristics and practice relevant to photon counting, Review of Scientific Instruments. 56 (1985) 183–193. doi:10.1063/1.1138327, p. 184-186. Hamamatsu, Photomultiplier Tubes: Photomultiplier Tubes and Related Products, Photomultiplier Tubes: Photomultiplier Tubes and Related Products. (2016). https://www.hamamatsu.com/resources/pdf/etd/PMT_TPMZ0002E.pdf (accessed February 10, 2019), p. 4-5, 126. Hamamatsu, PHOTOMULTIPLIER TUBES R1307, R1307-01, PHOTOMULTIPLIER TUBES R1307, R1307-01. (2016), p. 2. K.R. Spring, J.C. Long, Interactive Tutorials Side-On Photomultipliers, Molecular Expressions Microscopy Primer: Specialized Microscopy Techniques - Fluorescence Digital Image Gallery - Normal African Green Monkey Kidney Epithelial Cells (Vero). (2016). https://micro.magnet.fsu.edu/primer/java/digitalimaging/photomultiplier/sideon pmt/index.html (accessed February 10, 2019).