Kodak Nuclear Track Platesrecord tracks of mesons from 5 MEV down.*. . tracks of electrons from 50 KEV down

Kodak Nuclear Track Plates, TypeNTB, bring certain specific advan-tages to the field of nuclear research.In addition to recording meson andelectron tracks, they may be used torecord alpha particle tracks from400 MEY down; proton tracks from50MEY down; deuteron tracks from100 MEV down.Now made to a standard emulsion

uniformity, these plates offer a par-ticle recording medium of continu-ous sensitivity; one that providesthe possibility of evaluating energy

Photomicrograph at left from a Kodak NuclearTrack Plate, Type NTB, is the track of a 7r-mesonhaving a negative charge and mass equal to 313electron units. This mass is converted into energywhich explodes a nucleus, the fragments of whichmake the star at the end of the track.

Photomicrograph at right shows a hook-shaped track of an electron in a KodakNuclear Track Plate, Type NTB. Thistrack was obtained by very slight exposureto filtered 190-KV x-raysl and strongdevelopment.The exposure was so slight that only a

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2 It is now believed that all x-ray-proI materials consists of a homogeneousI by photo-electrons knocked out of at

3 Ordinarily, electrons affect emulsionI has dropped to the point where theI grains to go before stopping. Therefi

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On the original plate, the meson trackwas 400p. long. Exposure was made bybombardment of a carbon target with380-MEV alpha particles, produced in thecyclotron of the Radiation Laboratory ofthe University of California.

its kinetic energy was still as high as 50electron kilovolts.3

as produced by x-ray bombard-be interested in electron tracks

duced density in photographicmass of such tracks produced

toms.

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Nutritional Biochemist, Bacteriologist, Ph.D. Sigma Xi. PhiKappa Phi. Publications. Teaching experience. Desires researchposition. Box 400-A, SCIENCE. 8-6

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Research and Medical Director: Age 38, Ph.D. Harvard, taughtat Harvard, 10 years biochemical, nutritional and endocrinologicalresearch, 65 publications, available for appointment with smallhighly ethical pharmaceutical firm, salary desired about $12,000.For further information, write to Patricia Edgerly, Director, NewYork Medical Exchange, 489 Fifth Avenue, New York City. XZoologist: M.S. (B.A. in Chemistry), 2 years college teaching,desires position teaching zoology, or work in biological or bio-chemical research laboratory in or near New York City. Box410A, SCIENCE. X

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broad integrated program including bio- and organic chemistry,bacteriology and pharmacology. Qualified individual will haveopportunity to advance to Research Director within two years.Desirable age 28-38. Applicant should submit details of educa-tion, experience, and other qualifications together with age, maritalstatus, and salary desired. Write: Box 411A, SCIENCE. XAssociate Nutritionist: University of Hawaii Agricultural Experi-ment Station, Honolulu. Ph.D. Nutrition and Biochemistry.Salary $4380 to $5280 according to training and experience.Write: Nutrition Department, University of Hawaii, PO Box 18,Honolulu 10, TH. X

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* Complete bibliography on phase microscopy.* Numerous photomicrographs and other il-

lustrations.

Much of this information hasnrbeen available befote. For your£rcecopy write Dept. H1 ' '; Phase Microscope

>- No. i8MAV

American 4O3ptica1COM ANY.

Scientiffi9 Instrtiment .DtvisionBuffalo, 15,NeW YQrk'