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GE innovator Robert N. Hall most proud of Hyper-pure Germanium Detector

When we interviewed what is perhaps General Electric’s greatest innovator of the 60s “Bob” Hall at the Edison Tech Center we had him tell us about his career and inventions. Bob Hall is known for developing the power rectifier, lasers and a practical lithium drift detector. Bob Hall’s most famous invention is the semiconductor laser which became the basis of hundreds of thousands of devices including the optical disk player (CDs and DVDs) and of course… the laser pointer!

Our video How the Laser Works is an excerpt of the whole interview with Mr. Hall and is by far the most popular.

 

Hyper-pure detectors (intrinsic detectors):

Despite lasers being very popular and easy for the public to understand the importance of Mr. Hall’s personal opinion was that his hyperpure germanium detector (an instrument!) was the greatest invention. Why did he feel that this obscure detector which no regular person has heard of was the best addition to our technological history? Well, it’s because this detector allowed for the advancement of nuclear science and better understanding of our universe!

How it works:

Take a p/n junction and put a reverse bias on it, now you will get a space charge layer that will catch any ionized particles and give you a pulse of current. This detector will catch a gamma ray coming in (off a nuclear source for example) and create a pulse of current that will tell you the energy of the incoming gamma ray.

Mr. Hall was first approached on a ski trip by a colleague at General Electric who complained that nuclear researchers were having a lot of trouble with germanium because the Eagle Picture germanium mine in Oklahoma had a change in processing that resulted in a world-wide crisis with those working with the element.

Eric Pell at the GE Research lab initially discovered the lithium drift process. The nuclear physicists then figured out how to make massive lithium drift detectors (space charge layer 1cm thick).  These large drift detectors were not stable at room temperature and had to be kept at liquid nitrogen temperatures.

Bob began the task with the target of creating germanium with 1 part in 10 to the 13th of active impurities. This ultra pure germanium allowed detectors to be made more cheaply, smaller, more robust and stable at room temperature. This had an enormous impact on the development of nuclear physics. Today we use Bob’s intrinsic detectors in nuclear labs everywhere and even on satellites.

Here is the video:

 

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