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I. UNITED STATES
.;. ATOMIC ENERGY COMMISSION
iO i: AK RIDGE
RYERSON POCKET METER
Argonne National Laboratory
.)use within the Atomic Energy Commission. Inquiries for additional copies
qtxestions regarding reproduction by recipients of this document may be referred
Sa Information Division, Atomic Energy Commission; P. 0. Box E,
w~ a declassified document may differ materially from the original classified
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Sin bear the same title and authors.
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eaas: Janary 11, 1947
of 4 pages.
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l;' le Ryerson Pocket Meter is a hermetically sealed condenser type ionization chamber
i aibouithe. size and shape of a fountain pen, designed to be worn as a personnel monitoring
S't.dOftce efor X and gamma radiation.
l:i'" n order to properly serve the above function, a device of this type must meet certain
ri'i gi..d qualifications as follows: (1) sensitivity, the ability to measure within 10% accuracy,
i:. i-100 milliroentgens; (2) wave-length independence; (3) low electrical leakage; (4) inde-
:pendent of atmospheric temperature, pressure, and humidity (5) sealed against entrance
Sof,dirt and alpha contamination; (4) 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-
:Aii iercially available meters do not. It is designed for use in conjunction with the Victoreen
ter" or other quartz fiber electrometers having a capacity of about 2 cm. The
i"D bn.l-Pocket Meter has an electrical capacity of approximately 4 cm, a voltage of approx-
4i: t .20 volts per 100 milliroentgens (0.10r) and a volume of approximately 6 cc, thus
| :.i4g. a sensitivity of 200 milliroentgens full scale. This range covers twice the pres-
i|iiii j epted .permissible daily dose of 100 milliroentgens.
Wh::a"'velength independence is achieved through the use of low atomic number lnaterial,such
:':'as T'ieite I (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-
Siasifrom the insulated aluminum center collecting electrode is corrected for by coating
*; with a conducting graphite paint. By proper adjustment of the wall thickness (ca 2.4 mm)
!'i.d .the above construction, the meter is independent of wavelength within 10% from 40 key
l I Yw'Ie'v "effective."
SLow electrical leakage is achieved by the use of molded polystyrene insulators made
hi*ih very highly polished molds. Machined polystyrene insulators, despite much effort on
polishing, dippingand coating have failed to give comparable results. The 0.045" 2 S alu-
Ai:num electrode, cut from commercial stock, is upset on one end to furnish a contact for
thle .diaphragm button and dented to prevent the molded insulators from becoming loose.
Shie above methods result in a leakage of less than 1/2% of full scale per day, i.e., less
t..an 1 mr. This indicates an internal resistance of ca 1018 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 11 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-
S nately brought from the inside to the outside through the ring making three points of con-
S tact on each member. The molded protective cap is ribbed on the inner surface for a
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casionally, if they lad flat. No explanation is loff5eed
- wita specially designed stainless steel spran l:i seCt l rUA -weh:i a
clip.may be slipped down but not off the meter;, fttwsaaMu a gef
aisne the clip will tear cloth unless deliberately e s. mu Ia :
Tests Ihav been made by soaking the meters iniwater -thaouk B fm weLt'Bl. a :
phragm has withstood (from the inside) 245 p.s.i. hrLydrs~tattin~zial
tkh.ae-a ahe+oh d and prn &tdedv firnn the and an+hlUn-e q lthd*SmiWbkillel- -
T' use the meter, it is inserted into the electromatem-s eks-inte:l a ti i Ab''
thediaphragm contact. The cap is then charged-toa. lLtvlibuwe-" hi ve t:itii:'
seconds to check leakage. If it leaks, it may be cleaed.will~iai~a lap awat ti
toothbrush and dried with clean, dry compressed.air or: nitrqpsgen aiurBt. i:" .. ;". i:
phragm is first charged; light additional pressure allows .:lPaci t..chrhIe en iin
rode. After exposure, the meter is reinserted, the cap, clge hpeed for -liglw l
If leakage is satisfactorily low, additional pressure obtaiasthr~'adi a.cesi asmH"
sures will result in the generation of static charges on.ta therdairi ugd it:lBm :t
moved by pressing on the diaphragm with the finger. Emces ssveupmsmelags im:- ll is,
peen the contact button point and damage the meter. .....
Tenite is soluble in ketones, such as acetoneaand in other aromatlllW.j,-,,m_' .-
precautions should be taken accordingly. The diaphragm shoud ut'ns~sc sbae' i itaiSa I
absolute or otherwise, since the surface will eventually become daamed- '.
Last but not least, the technique of molding most parts A.wi -i-, ftOHf
allows large scale-production at low cost, ....:
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