<p>The <a href="https://en.wikipedia.org/wiki/Photoelectric_effect" rel="nofollow noreferrer">photoelectric effect</a> produces an electrical current when light strikes a surface with an energy per photon greater than the work function of the material.</p>
<p>Since it's one charge unit per photon, the current produced by a photoelectric detector can be quite linearly proportional to the incident intensity of the light striking it, independent of wavelength as long as their energy is above the work function but not <em>twice</em> the work function. Beyond that you have to start thinking about double ionization.</p>
<p>@PeterErwin has linked to <a href="http://articles.adsabs.harvard.edu/full/1966ApJ...144..921W" rel="nofollow noreferrer">Scanner Observations of λ 4430</a> which discusses two types of specroscopic measuring techniques; <em>photographic</em> and <em>photoelectric</em>, and it was photoelectric that is discussed at length.</p>
<p><strong>For</strong> <em><strong>photographic</strong></em> <strong>spectroscopic measurements</strong> in the early 1960's a photographic plate would be placed at the dispersive focal plane of a spectrograph, and exposure made, the plate developed, and then the plate would be scanned by a <em>measuring machine</em> that shone a slit of light through the spectrum and scanned that across it. A photoelectric cell (or possibly a photomultiplier used in current mode, see below) on the other side of the film would receive the light, change it to an electrical current and then (likely) drive a chart recorder. This is my best guess, there were other electronic recording technologies available at the time.</p>
<p><strong>For</strong> <em><strong>photoelectric</strong></em> <strong>spectroscopic measurements</strong> in the early 1960's either a photoelectric cell (no gain, just a photocathode and an anode) or more likely a <a href="https://en.wikipedia.org/wiki/Photomultiplier_tube" rel="nofollow noreferrer">photomultiplier tube</a> would be used. These have substantial gain (often in the 1E+06 to 1E+09 range) so each photon detected through the spectrograph's slit would produce a burst or pulse of electrons at the output of the photomultiplier.</p>
<p>Instead of collecting the whole spectrum on film then scanning it, only a single slit of light at a certain wavelength was used from the telescope at a given time. They would have to scan the grating slowly to bring the spectrum across the slit.</p>
<p>From the paper:</p>
<blockquote>
<p>Scanning is accomplished by driving the grating with a stepping motor. A Digitron counter, rigidly coupled to the grating drive gear train, provides visual and electrical readout of the wavelength. The wavelength of the scanner is capable of being calibrated to better than 1 Â in the first order although in practice temperature changes, guiding errors, etc., will sometimes shift the entire spectra by several angstroms. For the λ 4430 observations the scanner was used in a pre-programmed spectrophotometer mode. That is, instead of continuous scanning, the scanner was used as a spectrophotometer, automatically observing in sequence a set of predetermined wavelength regions. The heart of the programmer consists of a coincidence circuit that compares the electrical reading of the Digitron counter with the location of a set of pins in a programming pinboard. The scanner drive motor slews the scanner at a 100 Â/sec scan rate until a coincidence is found. The motor is then stopped and an integration is started. At the end of the integration period the data are recorded and the grating is moved to next position</p>
<p>Pulse counting was used, and in general an observation was continued until at least 5 X 10<sup>4</sup>  counts were obtained at each of the predetermined wavelength points. The integration time was set so that a minimum of ten “passes” or scans were obtained for each observation. For stars brighter than about eleventh magnitude this procedure resulted in a relative accuracy of about 0.6 per cent for the individual points. Two programs were used; one with a 6-Â exit slot provided several continuum points, sampled the λ 4430 feature every 5 Â, and provided a wavelength check by measuring Hy. The other used a 3-Â exit slot, sampled the wings of λ 4430 every 5 Â, and sampled the λ 4410-4440 region every 2 Â.</p>
</blockquote>
<p>The paper links to <a href="http://adsabs.harvard.edu/full/1964ApJ...139..240S" rel="nofollow noreferrer">On the Interstellar λ 4430 Line.</a> by R. Stoeckly, R. &amp; K. Dressler (1964). I once knew a <em>Thomas</em> R. Stoeckly who might fit into the right timeline, but not sure if it's the same.</p>
<p>The paper mentions the photomultiplier tube itself:</p>
<blockquote>
<p>c) Electronics</p>
<p>RCA 6199 photomultipliers were used at dry-ice temperature. The voltage was 1200 V; the cathodes were grounded to reduce the background count, which was of order 10<sup>3</sup>/min. The pulse-counting equipment is that described by Rogerson et al. (1959). The discriminator level used rejected an  estimated 20 per cent of the pulses from the photocathodes.</p>
</blockquote>
<p>That one looked like this:</p>
<p><a href="https://i.sstatic.net/Tc0zn.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Tc0zn.jpg" alt="RCA 6199 Photomultiplier Tube with Custom Connector" /></a></p>
<p><strong>above:</strong> <a href="https://socotek.co/media/rca-6199-photomultiplier-tube-with-custom-connector-nm0031247/" rel="nofollow noreferrer">Source</a> &quot;RCA 6199 Photomultiplier Tube with Custom Connector&quot; <strong>below:</strong> <a href="https://reverb.com/item/14192987-4-vintage-rca-6199-photomultiplier-pmt-photocathode-vacuum-tube-valve-bangybang-tubes" rel="nofollow noreferrer">Source</a> &quot;4 Vintage RCA 6199 Photomultiplier PMT Photocathode Vacuum Tube&quot;</p>
<p><a href="https://i.sstatic.net/uXfQS.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/uXfQS.jpg" alt="6199-photomultiplier-pmt-photocathode-vacuum-tube-valve-bangybang-tubes) &quot;4 Vintage RCA 6199 Photomultiplier PMT Photocathode Vacuum Tube" /></a></p>

CC BY-SA 4.0
2021-11-08T10:05:26.437Z
2021-11-08T10:05:26.437Z
uhoh
<p>I am reading <a href="https://ui.adsabs.harvard.edu/abs/1967PASP...79..351W/abstract" rel="nofollow noreferrer">this article by  Wing, Peimbert and Spinrad</a>, where they mention the use of a photoelectric scanner. By searching online, I find that <a href="https://encyclopedia2.thefreedictionary.com/photoelectric+scanner" rel="nofollow noreferrer">photoelectric scanners are used to scan punchcards</a>, but I doubt this is the kind of device that they are referring to.</p>
<p>What is a photoelectric scanner? How is it used and what does it do? What does it look like?</p>

CC BY-SA 4.0
2021-11-07T18:58:51.667Z
A description that particular instrument can be found here: 
https://ui.adsabs.harvard.edu/abs/1966ApJ...144..921W/abstract
Peter Erwin
<observational-astronomy><instruments>
What is a photoelectric scanner?
usernumber
# What is a photoelectric scanner?

(Asked by: username_0 on 2021-11-07)

I am reading [this article by Wing, Peimbert and Spinrad](https://ui.adsabs.harvard.edu/abs/1967PASP...79..351W/abstract), where they mention the use of a photoelectric scanner. By searching online, I find that [photoelectric scanners are used to scan punchcards](https://encyclopedia2.thefreedictionary.com/photoelectric+scanner), but I doubt this is the kind of device that they are referring to.

What is a photoelectric scanner? How is it used and what does it do? What does it look like?

**Tags:** observational-astronomy, instruments

> **Comments:**
> **username_1**: A description that particular instrument can be found here:  https://ui.adsabs.harvard.edu/abs/1966ApJ...144..921W/abstract  

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## 1 answers

### Answer by username_2 on 2021-11-08. Score: 3

The [photoelectric effect](https://en.wikipedia.org/wiki/Photoelectric_effect) produces an electrical current when light strikes a surface with an energy per photon greater than the work function of the material.

Since it's one charge unit per photon, the current produced by a photoelectric detector can be quite linearly proportional to the incident intensity of the light striking it, independent of wavelength as long as their energy is above the work function but not *twice* the work function. Beyond that you have to start thinking about double ionization.

@PeterErwin has linked to [Scanner Observations of λ 4430](http://articles.adsabs.harvard.edu/full/1966ApJ...144..921W) which discusses two types of specroscopic measuring techniques; *photographic* and *photoelectric*, and it was photoelectric that is discussed at length.

**For** ***photographic*** **spectroscopic measurements** in the early 1960's a photographic plate would be placed at the dispersive focal plane of a spectrograph, and exposure made, the plate developed, and then the plate would be scanned by a *measuring machine* that shone a slit of light through the spectrum and scanned that across it. A photoelectric cell (or possibly a photomultiplier used in current mode, see below) on the other side of the film would receive the light, change it to an electrical current and then (likely) drive a chart recorder. This is my best guess, there were other electronic recording technologies available at the time.

**For** ***photoelectric*** **spectroscopic measurements** in the early 1960's either a photoelectric cell (no gain, just a photocathode and an anode) or more likely a [photomultiplier tube](https://en.wikipedia.org/wiki/Photomultiplier_tube) would be used. These have substantial gain (often in the 1E+06 to 1E+09 range) so each photon detected through the spectrograph's slit would produce a burst or pulse of electrons at the output of the photomultiplier.

Instead of collecting the whole spectrum on film then scanning it, only a single slit of light at a certain wavelength was used from the telescope at a given time. They would have to scan the grating slowly to bring the spectrum across the slit.

From the paper:

> Scanning is accomplished by driving the grating with a stepping motor. A Digitron counter, rigidly coupled to the grating drive gear train, provides visual and electrical readout of the wavelength. The wavelength of the scanner is capable of being calibrated to better than 1 Â in the first order although in practice temperature changes, guiding errors, etc., will sometimes shift the entire spectra by several angstroms. For the λ 4430 observations the scanner was used in a pre-programmed spectrophotometer mode. That is, instead of continuous scanning, the scanner was used as a spectrophotometer, automatically observing in sequence a set of predetermined wavelength regions. The heart of the programmer consists of a coincidence circuit that compares the electrical reading of the Digitron counter with the location of a set of pins in a programming pinboard. The scanner drive motor slews the scanner at a 100 Â/sec scan rate until a coincidence is found. The motor is then stopped and an integration is started. At the end of the integration period the data are recorded and the grating is moved to next position
>
> Pulse counting was used, and in general an observation was continued until at least 5 X 104 counts were obtained at each of the predetermined wavelength points. The integration time was set so that a minimum of ten “passes” or scans were obtained for each observation. For stars brighter than about eleventh magnitude this procedure resulted in a relative accuracy of about 0.6 per cent for the individual points. Two programs were used; one with a 6-Â exit slot provided several continuum points, sampled the λ 4430 feature every 5 Â, and provided a wavelength check by measuring Hy. The other used a 3-Â exit slot, sampled the wings of λ 4430 every 5 Â, and sampled the λ 4410-4440 region every 2 Â.

The paper links to [On the Interstellar λ 4430 Line.](http://adsabs.harvard.edu/full/1964ApJ...139..240S) by R. Stoeckly, R. & K. Dressler (1964). I once knew a *Thomas* R. Stoeckly who might fit into the right timeline, but not sure if it's the same.

The paper mentions the photomultiplier tube itself:

> c) Electronics
>
> RCA 6199 photomultipliers were used at dry-ice temperature. The voltage was 1200 V; the cathodes were grounded to reduce the background count, which was of order 103/min. The pulse-counting equipment is that described by Rogerson et al. (1959). The discriminator level used rejected an estimated 20 per cent of the pulses from the photocathodes.

That one looked like this:

[![RCA 6199 Photomultiplier Tube with Custom Connector](https://i.sstatic.net/Tc0zn.jpg)](https://i.sstatic.net/Tc0zn.jpg)

**above:** [Source](https://socotek.co/media/rca-6199-photomultiplier-tube-with-custom-connector-nm0031247/) "RCA 6199 Photomultiplier Tube with Custom Connector" **below:** [Source](https://reverb.com/item/14192987-4-vintage-rca-6199-photomultiplier-pmt-photocathode-vacuum-tube-valve-bangybang-tubes) "4 Vintage RCA 6199 Photomultiplier PMT Photocathode Vacuum Tube"

[![6199-photomultiplier-pmt-photocathode-vacuum-tube-valve-bangybang-tubes) ](https://i.sstatic.net/uXfQS.jpg)](https://i.sstatic.net/uXfQS.jpg)


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