Memorandum from Newton Underwood to Clifford Beck

%MurNBionchambers092652; ]> Memorandum from Newton Underwood to Clifford Beck Machine readable transcription Underwood, Newton Creation of machine-readable version: Russell S. Koonts Creation of digital images: Russell S. Koonts Conversion to TEI.2-conformant markup: Russell S. Koonts ca. 9 kilobytes NCSU Libraries Raleigh, NC Modern English, MurNBionchambers092652

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5 November, 2000

Nuclear Reactor Digitization Project

Raymond L. Murray Reactor Project Notebook

Illustrations have been included from the print version. Scanned by Russell Koonts with Photoshop 5.0 software. Memorandum from Newton Underwood to Clifford Beck Newton Underwood

1 p. Manuscript copy consulted UA 105.16

Prepared for the North Carolina State University Science and Technology Electronic Text Center

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Library of Congress Subject Headings September 26, 1952 English LCSH manuscript 24-bit color: 400 dpi Memorandum from Newton Underwood to Clifford Beck Typescript 1 p. September 26, 1952 MurNBionization091052

September 26, 1952 To Clifford Beck From Newton Underwood Subject - Ion Chambers

The basic specifications for the linear integrated ion current systems which Dr. Waltner, myself, and the Reactor Committee arrived at after much discussion and several meetings are.-

1. At 10,000 watts, the neutron flux should produce a current of approximately 100 micro-amperes. According to computations of neutron flux at the location of the ion chambers by Menius and Murray, this maybe translated as about 1 micro- ampere per 108 neutrons per cm2 per sec.

2. The automatic controls should function at as low a power level as feasible.

3. The calibration should be as stable as possible.

4. The power level safety trips should release the rods within 20 milliseconds of a 20 to 30 percent overshoot of the predetermined level.

The lower level limit of power at which the linear systems will operate satisfactorily is determined by many factors. The more important ones are.- 1. Sensitivity of the amplifier. 2. Current output of the ion chambers per neutron flux. 3. Insulation resistance which can be maintained. 4. Current output of the ion chambers when there is no neutron flux.

We have assumed that the input insulation resistance can be maintained sufficiently high so that it is possible to use a maximum input resistance in the amplifier of 109 ohms. In this case the smallest current that will give full scale deflection is 10-8 amperes. In accord with the previous assumptions this will correspond to a reactor power of 1 watt.

It is evident that the current in the ionization chamber caused by residual activity must be negligible in comparison to 10-8 amperes. This implies a very careful choice of constructional material (Carbon, Magnesium, and lead, and quartz insulation) and the use of Boron 10 instead of U235 as the surface coating for the electrodes. The α current from 1 gm of U235 (about 2 micro curies) spread over 1000 cm2 would theoretically be of the order of 10-9 amperes. Also gas must flow through the chamber to sweep out activated atmosphere.

If for any reason the ion current obtained when the reactor is operating at 10 KW should turn out to be less than 100 micro- amperes then the above numbers would have to be modified according.