JAT7;.8 / ^>0(0 \ 30iun'48 MDDC - 886 UNITED STATES ATOMIC ENERGY COMMISSION OAK RIDGE TENNESSEE RYERSON POCKET METER Argonne National Laboratory Published for use within the Atomic Energy Commission. Inquiries for additional copies and any questions regarding reproduction by recipients of this document may be referred to the Technical Information Division, Atomic Energy Commission, P. O. Box E, Oak Ridge, Tennessee. Inasmuch as a declassified document may differ materially from the original classified document by reason of deletions necessary to accomplish declassification, this copy does not constitute authority for declassification of classified copies of a similar document which may bear the same title and authors. Date of Manuscript: Unknown Date of Release: January 17, 1947 This document consists of 4 pages. N 1 - MDDC - 886 RYERSON POCKET METER The Ryerson Pocket Meter is a hermetically sealed condenser type ionization chamber about the size and shape of a fountain pen, designed to be worn as a personnel monitoring device for X and gamma radiation. In order to properly serve the above function, a device of this type must meet certain rigid qualifications as follows: (1) sensitivity, the ability to measure within 10% accuracy, 100 milliroentgens; (2) wave-length independence,- (3) low electrical leakage; (4) inde- pendent of atmospheric temperature, pressure, and humidity; (5) sealed against entrance of dirt and alpha contamination; (6) electrical insensitivity to dropping and mistreatment; (7) rugged construction; (8) easily charged and read by unskilled personnel; (9) low cost. The Ryerson Pocket Meter is unique in that it meets all these specifications while com- mercially available meters do not. It is designed for use in conjunction with the Victoreen "Minometer" or other quartz fiber electrometers having a capacity of about 2 cm. The Ryerson Pocket Meter has an electrical capacity of approximately 4 cm, a voltage of approx- imately 20 volts per 100 milliroentgens (O.lOr) and a volume of approximately 6 cc, thus furnishing a sensitivity of 200 milliroentgens full scale. This range covers twice the pres- ently accepted permissible daily dose of 100 milliroentgens. Wavelength independence is achieved through the use of low atomic number material, such as Tenite II (cellulose acetate butyrate) for the barrel, cap,and diaphragm, (see Fig. 1) and a conducting plastic liner (lucite and graphite) for the ionization chamber. Secondary emis- sion from the insulated aluminum center collecting electrode is corrected for by coatii^ with a conducting graphite paint. By proper adjustment of the wall thickness (ca 2.4 mm) and the above construction, the meter is independent of wavelength within 10% from 40 kev to 1 Mev "effective." Low electrical leakage is achieved by the use of molded polystyrene insulators made with very highly polished molds. Machined polystyrene insulators, despite much effort on polishing, dipping, and coating have failed to give comparable results. The 0.045" 2 S alu- minum electrode, cut from commercial stock, is upset on one end to furnish a contact for the diaphragm button and dented to prevent the molded insulators from becoming loose. The above methods result in a leakage of less than 1/2% of full scale per day, i.e., less than 1 mr. This indicates an internal resistance of ca 10 ohms, Hermetical sealing of the meter, making it essentially independent of atmospheric temperature, pressure, and humidity, as well as preventing the entrance of dirt and alpha contamination, is accomplished through the use of a molded corrugated Tenite II diaphragm, again produced with very highly polished molds. The 2 S aluminum contact button is ma- chined and placed in the mold prior to the molding operation. The corrugated diaphragm serves as a retainer for the collector system and is heat-welded by a lip to the tenite case. Contact between the conducting plastic ion chamber and the aluminum outer contact sleeve is made by molding into the barrel, a star-shaped copper ring such that contact is alter- nately brought from the inside to the outside tlu-ough the ring making three points of con- tact on each member. The molded protective cap is ribbed on the inner surface for a - 2 - MDDC - 886 friction fit, thus eliminating threads which wear out in use. The long coverage of the cap helps prevent contamination of the electrometer socket. The whole of the foregoing assembly results in a very rugged device which has withstood such severe but not unreasonable tests as dropping from heights of 30 feet, throwing against a concrete wall or floor with very few electrical discharges and no broken meters. When dropped, the meters apparently never discharge if they fall on either end, but do oc- casionally, if they land flat. No explanation is offered for the latter phenomena. Equipped with a specially designed stainless steel spring clip set in a groove in the case so that the clip may be slipped down but not off the meter, few casualties are expected from dropping since the clip will tear cloth unless deliberately released. Tests have been made by soaking the meters in water without lose of charge. The dia- phragm has withstood (from the inside) 245 p.s.i. hydrostatic pressure. At this pressure, the cap stretched and protruded from the end of the barrel, but did not leak. To use the meter, it is inserted into the electrometer socket lightly making contact with the diaphragm contact. The cap is then charged to full voltage and observed for a few seconds to check leakage. If it leaks, it may be cleaned with mild soap and water using a toothbrush and dried with clean, drj' compressed air or nitrogen. Reinserted, the dia- phragm is first charged; light additional pressure allows placing a charge on central elec- trode. After exposure, the meter is reinserted, the cap charged and checked for leakage. If leakage is satisfactorily low, additional pressure obtains the reading. Excessive pres- sures will result in the generation of static charges on the diaphragm which may be re- moved by pressing on the diaphragm witli the finger. Excessive pressures will eventually peen the contact button point and damage the meter. Tenite is soluble in ketones, such as acetone,and in other aromatic hydrocarbons, and precautions should be taken accordingly. The diaphragm should not be cleaned in alcohol, absolute or otherwise, since the surface will eventually become damaged. Last but not least, the technique of molding most parts with very few machine operations, allows large scale production at low cost. 3 - MDDC -886 -4 - MDDC - 886 « u c\l (O-^ to U \a ^cvifO^^iO^NoQ NflOO* < ? or r < CI hi 2C (J o a / UNIVERSITY OF FLORIDA 3 1262 08909 7553 a