Johann Georg Ernst Engelhard

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Johann Georg Ernst Engelhard (born September 17, 1908 in Nuremberg , † November 10, 1984 in Braunschweig ) was a German physicist .

Live and act

Engelhard received his doctorate in 1933 in the field of precision measurement technology. First he was at the Physikalisch-Technische Reichsanstalt (PTR) in Berlin . After the Second World War he worked at the Physikalisch-Technische Bundesanstalt (PTB) on the basics of modern measurement technology. In 1951 he developed a krypton spectral lamp, which is also called the Engelhard lamp after him; it is a central part of the redefinition of the meter from 1960. This wavelength definition is based on the principles of Engelhard and Wilhelm Kösters , who have examined the suitability of different spectral lines for interferometric length measurement over several decades.

In addition, Engelhard was Executive Director at the Physikalisch-Technische Bundesanstalt in Braunschweig. In 1973 Engelhard left the PTB and was active worldwide as a consultant for the establishment of further state institutes based on the model of the PTB.

The Krypton 86 spectral lamp

A Krypton-86 lamp whose vermilion spectral (wavelength approximately 606 nm) 1960-1983 to define the SI-unit meter was used

With the spectral lamp developed by Engelhard it became possible to reproduce a wavelength that had a relative uncertainty of 10 −8 or 10 −9 . The isotope separation and a suppression of the Doppler broadening thus formed the prerequisites for the later international redefinition of the meter by means of the wavelength of the electromagnetic radiation of the orange-red spectral line of the krypton isotope 86 Kr. 1960 at the 11th General Conference on Weights and Measures (CGPM) the (to 1983 valid) wavelength definition of the meter adopted. The meter was defined as 1,650,763.73 times the wavelength of the light emitted by 86 Kr when transitioning between states 5d 5 and 2p 10 in a vacuum.

As a result, the unit meter could be represented by a factor of 10 to 100 more precisely than before with the international meter prototype of the original meter . In addition, this method had the advantage of immutability in the definition; On the other hand, the rod-shaped original meter consisting of a platinum-iridium alloy can potentially be changed (unintentionally) by external influences.

Honors

  • In 1976 he was awarded the Federal Cross of Merit, 1st Class , for his services . Engelhardstrasse was named after him in the Braunschweig district of Rüningen in 2010.
  • On his 76th birthday, the building for length measurement technology in the Brazilian state institute Inmetro was named after him.

literature

Web links

Individual evidence

  1. ↑ a b c Document Ratsinfo Braunschweig Annex 1 Prof. Dr. Johann Georg Ernst Engelhard
  2. ^ Friedrich Bayer-Helms:  Kösters, Wilhelm. In: New German Biography (NDB). Volume 12, Duncker & Humblot, Berlin 1980, ISBN 3-428-00193-1 , p. 406 f. ( Digitized version ).
  3. ↑ Chronicle of the City of Braunschweig - November 10, 1984 on braunschweig.de, accessed on September 26, 2013.
  4. ↑ a b c Harald Schnatz: Announcements 1/2012. (PDF) Specialist journal of the physical-technical federal institute. PTB, March 2012, p. 10 (PDF count 11) , archived from the original on September 28, 2013 ; accessed on August 6, 2014 : "The transition 2p 10 [...] relative uncertainty of 10 −8 can be realized"
  5. ↑ a b PTR / PTB: 125 years of metrological research p. 33. on ptb.de, accessed on December 29, 2015 (PDF; 4.5 MB)
  6. ↑ Resolutions of the CGPM: 11th meeting (October 11-20, 1960) at bipm.org, accessed on September 26, 2013. (English, French)
  7. ↑ PTR / PTB: 125 years of metrological research p. 40. on ptb.de, accessed on December 29, 2015. (PDF; 4.5 MB)
  8. ↑ Announcement by the City of Braunschweig, Department of Urban Planning and Environmental Protection, Geoinformation Department (PDF; 137 kB)
personal data
SURNAME Engelhard, Johann Georg Ernst
BRIEF DESCRIPTION German physicist
DATE OF BIRTH 17th September 1908
PLACE OF BIRTH Nuremberg
DATE OF DEATH November 10, 1984
Place of death Braunschweig