PMTs detect and convert light from crystal into electronic signal and amplify signal by as much as about 10^7.

PMTs detect and convert light from crystal into electronic signal and amplify signal by as much as about 10^7.

• A. 10^5
• B. 10^7
• C. 10^3
• D. 10^9

Answer: (B)

Photomultiplier tubes achieve this level of amplification by converting incoming light into electrons at the photocathode and then multiplying those electrons through a chain of dynodes. When a photon hits the photocathode, it ejects a photoelectron. That electron is accelerated toward the first dynode, and at each dynode it causes the emission of multiple secondary electrons. Those secondary electrons then strike the next dynode, producing even more electrons, and so on through the cascade. The gains at each stage multiply, so the total amplification ends up in the order of ten million, or 10^7. This high gain is what lets PMTs detect very faint light, even a single photon, by producing a sizable electronic signal from a tiny initial input. The other numbers would either undervalue the sensitivity or exceed typical PMT performance, whereas about 10^7 is a standard, well-known gain for many PMTs.

Photomultiplier tubes achieve this level of amplification by converting incoming light into electrons at the photocathode and then multiplying those electrons through a chain of dynodes. When a photon hits the photocathode, it ejects a photoelectron. That electron is accelerated toward the first dynode, and at each dynode it causes the emission of multiple secondary electrons. Those secondary electrons then strike the next dynode, producing even more electrons, and so on through the cascade. The gains at each stage multiply, so the total amplification ends up in the order of ten million, or 10^7. This high gain is what lets PMTs detect very faint light, even a single photon, by producing a sizable electronic signal from a tiny initial input. The other numbers would either undervalue the sensitivity or exceed typical PMT performance, whereas about 10^7 is a standard, well-known gain for many PMTs.