RCA 1P21  
Written by Accutron on 2017-05-10  

The RCA 1P21 is an early derivative of the 931A, optimized for extreme low-light applications. The 1P21 specification is similar to the 931A, with a S-4 spectral response and a peak sensitivity of 400nm, but the 1P21 has a much higher sensitivity and a much lower maximum anode current. This increased sensitivity is sufficient for detecting individual photons. The 1P21 revolutionized the science of astronomical photometry, as it was capable of precisely measureing a star's intensity. While the earliest 1P21 tubes were specially binned 931A devices, later examples of the 1P21 were purpose-built as a separate part number.

RCA 1P21 Datasheet (PDF)
Gerald E. Kron: The 1P21 (PDF)
RCA Photomultiplier Manual (PDF)


RCA 1P21 nine-stage photomultiplier.

This article is part of the [Detection & Imaging Tubes] exhibit.

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