An Infrared Stimulable Phosphor Dosimeterwith Time Lapse Indication

Miriam Sidran

A novel procedure for radiation dosimetry that indicates both the magnitude of the dose and the timeelapsed since exposure is described herein. It was tested using an ir stimulable ZnS phosphor to recordgamma doses in the range 10-4 R to 104 R. When the phosphor is exposed to two successive ir bands,the dose and time information are separated and retrieved by means of the two stimulated luminescencepeaks. Time lapse indicating dosimetry is applicable to particle radiation, as well as electromagneticradiation. Readout can be performed by other means than ir, and energy detected in other forms thanluminescence. The method should prove useful in tracing the causes of large accidental dose exposures ofpersonnel.

1. Introduction

A procedure for using an ir stimulable ZnS phosphorto measure gamma doses in the range 10-4 R to 104 R isdescribed.* In such a phosphor, energy stored in theform of trapped electrons and holes can be released asvisible light by ir stimulation. Previous attemptsto use an ir stimulable phosphor for dosimetryl"2 havebeen hindered by poor storage stability due to the pres-ence of many shallow traps.3

We have overcome this difficulty by using two suc-cessive ir bands for readout instead of one. The twoexposures separate two kinds of stored information, themagnitude of the dose, and the time elapsed betweendose and readout. The time decay of stored energynow yields additional time information instead of de-grading the dose information. In a variant procedure,the time and dose information are retrieved from theshape and size of the light pulse stimulated by a singleir exposure.

These experiments have demonstrated the use of anir stimulable phosphor as a time lapse indicating do-simeter for gamma radiation. In principle, the methodhas much broader applications. Other stimulablephosphors may be used, and the information retrievedby other means than ir, e.g., heat or applied potentials.Time indicating dosimetry for protons, alpha and betaparticles, x rays, uv, and visible light is easily envisaged.

The author was with Grumman Aircraft Engineering Corpora-tion when this work was done; she is now with the Physics De-partment, New York Institute of Technology, New York, NewYork 10023.

Received 29 April 1966; revised manuscript received 29 July1968.* Patent application No. 601,393, 13 December 1966.

Thermal neutrons could be measured provided the do-simeter were mixed with a secondary alpha emitter suchas lithium or boron, or with a gamma emitter such ascadmium. The ability to give the time lapse since ex-posure should prove useful in tracing causes of largeaccidental dose exposures ol personnel, and also in spacedosimetry.

11. Information Storage and Retrieval

Information is stored in a calibrated sample of thephosphor by a dose of electromagnetic or particle radia-tion. During exposure, both shallow and deep trapsfill with charge carriers in numbers depending on thedose. After exposure, the shallow trap population de-cays with time, due to thermal stimulation. The pop-ulation deficit is used to specify the time elapsed sinceexposure.

The two ir exposures used for readout stimulate twobursts of luminescence, whose peak intensities give thedose and time information. The first ir exposure con-sists of relatively long wavelengths that empty the shal-low traps rapidly and the deep traps slowly. Thisfirst exposure also stimulates a luminescence spike thatcontains combined time and dose information, separa-ble by means of calibration curves.

The second ir exposure consists of relatively shortwavelengths that can empty all traps efficiently. Sinceall shallow traps (as well as some deep traps) have al-ready been cleared, the second exposure empties theremaining occupied deep traps. The luminescence in-tensity depends on their number, which is proportionalto the dose and independent of decay time.

Ill. Experimental Procedure

A ZnS Fonda phosphor,4 activated with 0.003% (byweight) Cu and 0.04% Pb was used in these experi-

January 1969 / Vol. 8, No. 1 / APPLIED OPTICS 79

100

BAND AEd800

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a< 40BAND SX

a BAND B 20~ \

BAND S

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5WAVELENGTH, MICRONS

Fig. 1. Infrared bands used for stimulating luminescence:band S = ir lamp + 7-69 filter, intensity 0.046 W/cm2 ; bandA = ir lamp + 7-56 filter, intensity 0.240 W/cm 2 ; band B =

ir lamp + 7-56 + 4-72 filter, intensity 0.070 W/cm2.

INFRARED

i FFIL TER

Fig. 2. Sample geometry in photometer.

ments. The measured trap density is 2 X 1015 per cm3 ,of which about 80% are shallow traps with lifetimes of15 min to one week at room temperature. The remain-der are deep triaps with lifetimes of a year or more. Therecombinations of trapped charge carriers under infraredare practically 100% radiative. The ir stimulationspectrum of this phosphor (stimulated intensity vs irwavelength) has maxima at 0.75 4 and 1.35 and aminimum at 1.09 Au (Ref. 5).

The samples were microcrystalline powders depositedin an inert binder on glass slides. They were excited atvarious distances from a 1-mC or a 100-mC gammasource (radium needle) for 15 min, and after a darkdecay interval they were stimulated by radiation from a250-W ceramic ir lamp through Corning glass filters.The spectra and intensities of three ir bands used tostimulate the phosphor are shown in Fig. 1; these bandsare designated as Bands S, A, and B. Information wasread out by means of successive exposures to two ofthese bands in order of decreasing wavelength. Ex-posure to the first ir band lasted 30 see and was followedby a 30-sec dark interval. The exposure time for thesecond band exceeded the 2-sec rise time of the lumi-nescence.

The peak intensities of the two stimulated lumines-cence spikes were measured by a 1P28 photomultiplier.The average deviation of the measurements was i 15%,

the chief source of error being the nonreproduciblesample position in the photometer (Fig. 2). Resultsof measurement on a 15-mg/cm2 sample are shown inFigs. 3-6, and described in Sec. IV. Simila resultswere obtained using other samples.

IV. Results

To show the feasibility of this method, the sampleswere excited using different gamma doses, and aftervarious decay periods, they were stimulated succes-sively with bands A and S. The dependence of the firstspike peak on dose and decay time, and the dependenceof the second peak on decay time were thus determined.

The variation with dose of the peaks stimulated byband A (after a 15-min decay time) is shown in Fig.3. The peak intensity increases supralinearly withdose up to 103 R. By extrapolation, the saturationdose is found to be at least 104 R. (The saturation dosedepends to some extent on the dose rate or intensity,the decay time, and the ir band used.)

The low dose limit is set by background radiation.A deexcited sample stored in the dark for 15 h yields ameasured spike peak of 0.2 light intensity units withband A stimulation. In Fig. 3, the dose correspondingto this peak value is about 4 X 10-4 R, in good agree-ment with the dose rate of about 0.2 R per year in anaverage concrete building.6 The minimum detectableapplied dose increases with decay time because of thecumulative background level. Other effects limitingthe lowest detectable dose are phosphor excitation bystray light, ir stimulability of glass filters, and tribo-luminescence. However, these can be measured or elim-inated.

The variation with dark decay time of the spike peaksstimulated by band A is shown in Fig. 4 for two gammadoses. The luminescence spikes are shown schemati-cally. The solid curves are the loci of peaks obtainedafter decay times of 15 min to 24 days. The peaks di-

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Fig. 3. Calibration curve: band A stimulated luminescencepeaks vs gamma dose.

80 APPLIED OPTICS / Vol. 8, No. 1 / January 1969

10 11. 0io< r NORMALIZED TIME DECAY

'- CALIBRATION CURVE

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Fig. 4. Band A stimulated luminescence peaks vs dark decaytime.

minish during the first week and then level off when theshallow traps are depleted. Thus, the ability of thismethod to specify decay time is limited to one week.

Since the decay curves for the two doses are similar,they can both be represented by the dashed curve ofFig. 4, with peak values normalized to the 15-minvalues. This can be used as a time decay calibrationcurve. Decay curves for higher doses are also similarto these, while those for very low doses are somewhatsteeper.

The spike peaks stimulated by the second (band )exposure are constant with respect to decay time, asshown in Fig. 5. They increase supralinearly withdose having an average value of 1400 light intensityunits at 11 R, and 16,500 units at 100 R. To calibratefor dose readout, we plot spike peaks against dose overthe range of interest. When the dose is known, thetime is found from Figs. 3 and 4.

Whenever charge carriers are released from traps, afraction f are retrapped in deep traps.7 If the frac-tion fi retrapped during dark decay were not equal tothe fractionf2 retrapped during the first ir exposure, thedeep trap population after the first exposure would de-pend on decay time. However, this population is in-dependent of decay time, as shown by the constantspike peaks in Fig. 5. Thus fi = f2 = f.

Let N, and Nd be the initial populations of shallowand deep traps, respectively. If q is the fraction ofoccupied deep traps emptied by the first exposure, thedeep trap population after the first exposure is

N = ( - q + fq)Nd + fN,,which is independent of decay time.

V. Methods of Improving Sensitivityand Linearity

Figure 6 shows the variation with decay time of spikepeaks stimulated in different ways after an 11 R dose.The sample was stimulated once with each band to ob-tain curves S, A, and B. These spike peaks decay with

time. The sample was stimulated with band S afterfirst having been stimulated with band A or B to ob-tain curves AS and BS. These peaks are constant withtime.

After a week of decay, a spike peak of about 3500light intensity units was obtained with band S (curveS). This spike peak level represents the deep trap pop-ulation, which is stimulated efficiently by band S only.To maximize the response for dose readout, a prior ex-posure should leave this level intact, i.e., q = 0 in Eq.(1). This has been done using band B for the preex-posure; thus, curve BS is a horizontal line at about thedeep trap level. In contrast, a preexposure to band Aleaves only 40% of this level (curve AS). To maximizedose response, a band A preexposure should last only1 or 2 see instead of 30 sec, thus emptying only a mini-mum number of deep traps.

The effect of sample thickness was investigated. Theresponse to a constant gamma dose increases linearlywith sample thickness up to 270 mg/cm 2 using band Aor band S readout. For alpha or beta doses, the re-sponse saturates at smaller thicknesses, due to failureof the exciting radiation to penetrate the deeper layers.

The upper dose limit could be increased by using astimulable phosphor with a larger trap density (or a

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Fig. 5. Band S stimulated luminescence peaks, after preex-posure to band A vs dark decay time.

BAND B ONLY

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10° 10' 102TIME, HOURS

Fig. 6. Stimulated luminescence peaks vs dark decay time.

January 1969 / Vol. 8, No. 1 / APPLIED OPTICS 81

1 0 lo-

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smaller trapping probability). Thus the upper doselimit for NaCl:Ag stimulated by visible light" 9 is 10' R.Infrared stimulable ZnS:Cu, Cr, Cl (Ref. 8) probablyhas an even higher dose limit, since it has 10'7 traps/cm 3 .CdS phosphors with 10"8 traps/cm3, stimulable by heat,have also been synthesized. 0

VI. Time and Dose from a Single Band Readout

Using the procedure described below, time and doseinformation can be retrieved by one ir exposure insteadof two. The rise time of ir stimulated luminescencevaries with dark decay period, ir band, and ir intensity.By selecting the ir band and intensity, a convenientrange of rise times can be found to specify the darkdecay periods.

With the stimulating band S intensity reduced to0.0015 W/cm2 , luminescence rise times of 0.5 min, 2min, 3 min, 6 min, and 10 min were observed with thisphosphor after dark decay periods of 0.5 h, 1, 2, 4, and7 days, respectively. Thus during the first week afterexcitation, the rise time can be calibrated to specify thedark decay time. The dose can then be found from thespike peak, and a time decay calibration curve such asin Fig. 3.

VIl. Limitations on the Method

This method does not distinguish a short weak radia-tion pulse from a constant background; the latter yieldsan accurate dose indication, but a spurious time indica-tion. For this reason, the background should probablybe sampled by another technique at appropriate inter-vals.

The method is only useful in cases for which the con-cept of time lapse indication is meaningful. Its use formultiple dose exposures is therefore limited to a fewcases in which convenience must then be sacrificed.Thus, two or more short radiation pulses give an inter-mediate time lapse indication. If the interval betweenthem is long, a dosimeter with two shallow trap levels, ortwo dosimeters with different shallow trap levels mightprovide the time lapse information.

Since this method depends on the thermal release oftrapped energy during storage, it is temperature de-pendent. Laboratory temperature fluctuations of morethan 50 C should be avoided, or at least monitored,so that the results may be corrected for this effect.

For any given application, the dosimeter must becalibrated under the conditions of use. It must ofcourse have a flat response to dose rate and photonenergy for the type of radiation measured.

Vil. Alternative Readout

Any scheme which empties shallow and deep trapsseparately can give time and dose information.' 1 Trapscan be emptied by heat, electromagnetic radiation,electric fields, mechanical stress, or other means. In-stead of luminescence, one could use voltage, current,or electric charge to measure the energy released.

We have emptied shallow traps without disturbingdeep traps, using moderate heating instead of band A

or band B; samples in light proof containers heated byan ir lamp in a fixed geometry have yielded time in-dependent spike peaks on subsequent dose readout withband S.

Silver-activated NaCl has both shallow and deeptraps, stimulable by visible and uv light. The stimu-lated response varies linearly with beta and gammadoses from 10-2 R to 104 (Refs. 1 and 9). Thus, thismaterial could be used for dosimetry, with readout bytwo suitable bands.

Thermoluminescent materials with two glow peaks8

give time and dose information when heated at a uni-form rate. The low temperature peak representscharges released from the shallow traps, and the hightemperature peak those from the deep traps. Appliedelectric fields could also be used for readout, with dcfields emptying the shallow traps, and ac fields the deeptraps. 12

IX. Summary and Conclusions

A procedure using an ir stimulable ZnS phosphor forgamma dosimetry in the range 10-4 R to 104 R has beendemonstrated. In addition to the dose magnitude,the time elapsed since exposure is also indicated by thisdosimeter. The unique time indication feature shouldbe valuable in dosimetry for space exploration and forpersonnel protection.

This phosphor stores dose information in its deeptraps. Both dose and time information are stored inits shallow traps. Successive exposures to two ir bandsseparate and retrieve the information by means of twostimulated luminescence peaks. The method has thefollowing advantages.

(1) The first ir exposure makes the second lumines-cence peak independent of decay time. The dose in-formation can thus be stored for a long time (at leastone month) without decay.

(2) During the first week, the time interval betweendose and readout is obtained, in addition to the dosemagnitude.

(3) Samples are easily prepared and calibrated.(4) Measurements are made with simple equipment.

An inexpensive lamp bulb and filters replace the ovenused for readout of conventional thermoluminescentdosimeters.

(5) The low dose limit is set only by background ra-diation.

The procedure can be modified for special purposes.(1) The upper dose limit could be increased by using

a stimulable material with more traps.(2) Two other spectral bands could be used instead

of ir.(3) Other forms of stimulation such as heat, mechan-

ical stress or electric fields could be used instead of ir.(4) Voltage, current, or charge could be measured

instead of luminescence.(5) A single ir band could read out both time and

dose.(6) Doses of neutrons, protons, alpha and beta par-

ticles, x rays, uv, and visible light could be measuredwith time lapse indication.

82 APPLIED OPTICS / Vol. 8, No. 1 / January 1969

The author is grateful to H. P. Kallmann and toPaulina Jaszczyn-Kopec and Bernard Kramer for valu-able discussions.

References

1. H. Kallmann, M. Furst, and M. Sidran, Nucleonics 10, 15(1952).

2. V. V. Antonov-Romanovskii, I. D. Keirim-Marcus, M. S.Poroshina, and Z. A. Trapeznikova, Conference of the U.S.S.R.Academy of Sciences on the Peaceful Uses of Atomic Energy,July 1965; translated by U.S. Atomic Energy Comm. 1956,Vol. 4, pp. 239-249.

3. J. H. Schulman and W. D. Compton, Color Centers in Solids(The Macmillan Company, New York, 1962), p. 334.

4. G. R. Fonda, J. Opt. Soc. Amer. 36, 382 (1946).5. D. E. Mason, Rev. Mod. Phys. 37, 743 (1965).6. J. A. S. Adams and W. M. Lowder, Eds., The Natural Radia-

tion Environment (University of Chicago Press, Chicago,1964), pp. 781-796, 912.

7. D. Curie, Luminescence of Crystals (John Wiley & Sons, Inc.,New York, 1960), pp. 142, 154, 266.

8. P. Jaszczyn-Kopec, J. Gallagher, H. Kallmann, and B.Kramer, Phys. Rev. 140, 1309 (1965).

9. M. Furst and H. Kallmann, Phys. Rev. 91, 1356 (1953).10. R. H. Bube, E. L. Lind, and A. B. Drebeen, Phys. Rev. 128,

532 (1962).11. M. Sidran, Dosimetry with Time-Lapse Indication, to be

submitted for publication.12. H. Kallmann and P. Mark, Phys. Rev. 105, 1445 (1957).

Meeting Reports continued from page 78

active media. In the same session, B. B. Snavely Kodak pre-sented the results of experimental work done with 0. G. Peterson.D. J. Bradley explained the use of dye lasers as a tunable sourcefor nanosecond absorption spectroscopy in recent experimentsperformed at Queen's University in Belfast with A. Durrant,G. Gale, M. Moore and P. D. Smith. In the Plenary session,F. P. Schafer University of Marburg, enthusiastically related newdevelopments in dye lasers and predicted a bright future for thisfield. Professor Schafer mentioned three new classes of laser-active compounds and combinations including fluorescent charge-transfer complexes.

Photochromic materials for use with lasers in memory, display,or printing applications were presented by Zoltan Kiss and hiscolleagues at RCA. Inorganic photochromic materials includingCaF2 with Sm and Eu and doped SrTiO3 were described in whicha color change in the material can be both written in with onewavelength of radiation and erased with another. A sensitivityof 5 X 108 J per spot to effect an optical density change of unityin a 10-g film was reported. This is within a factor of four of themaximum theoretical sensitivity for an oscillator strength ofunity and the impurity density of 1018/cm3. No fatigue hadbeen detected in 107 reversals.

The application of Hg radiation activated photochromic filmto holographic memories was described by A. L. Mikaelian of thePopov Society.

The main recreational event of the Conference, an eveningboat cruise, was aptly described by one of its survivors, "Imagineyour dining room on a hot night, take out the chairs, put in it 100people and a table of food. Now rock it for two hours." Therewere few complaints that it was briefer than scheduled.

The next International Quantum Electronics Conference istentatively scheduled for Japan in 1970.

69th Meeting of the Deutsche Gesellschaft furangewandte Optik, Baden, 47 June 1968.

Reported by K. Rosenhauer,Physikalisch-Technische Bundesanstalt

The Sixty-ninth DGaO meeting was held as usual during theWhitsun week. In consideration of friends and members in Aus-tria, and following an invitation by Messrs. Eumig of Vienna,Baden near Vienna was selected as the venue for the meetingwhich was sponsored by Messrs. Reichert of Vienna and Messrs.Swarowski of Hall, Innsbruck.

The official opening was held in the congress hall of the city ofBaden. Next day the scientific discussions were opened in thesame hall with a welcoming address from H. K6hler, Zeiss chair-man of the DGaO, who talked about the advantages of the asso-ciation in DGaO of scientists working the field of scientific optics.

He welcomed Mr. Hirsch, deputy of the Landesregierung Nieder-osterreich, Dr. Spiesser, Bezirkshauptmann of Baden, and Mr.Ftirst, deputy of the city of Baden. The greetings of the Oster-reichische Physikalische Gesellschaft were delivered by ProfessorGabler.

The general topic of this year's meeting was coherent and par-tially coherent imaging (degree of coherence, holography, inter-ferometry), and some thirty-six lectures were given. Apart fromthose dealing primarily with the general topic, others were held oninstrumentation, measuring techniques, computations, and phys-iology. It is hoped that these papers will be published in Optik.

In accordance with the DGaO by-laws, the annual general meet-ing was held on 7 June 1968. The chairman read his annual re-port and informed the meeting about the association with theDeutsche Physikalische Gesellschaft.

The treasurer, Dr. Rosenhauer, read his financial report whichwas audited by Dr. Deutscher and, in the absence of Mr. Steg-lich, by Prof. Dr. Gg. Franke. A new board was elected for twoyears made up of:

ChairmanVice chairmanSecretary and

treasurerFirst associateSecond associate

Prof. Dr. H. Kohler, OberkochenProf. Dr. F. Gabler, WienReg. Dir. Dr. K. Rosenhauer, Braunschweig

Dr. H. Schluge, OberkochenDr. J. Hertel, Berlin

It was agreed that the 1969 meeting (the Seventieth) would beheld at Lfubeck and Dr. Hartwig of Liubeck was appointed asmeeting organizer.

The DGaO unanimously appointed Prof. Dr. Ernst Lau ofBerlin an honorary member of the Association.

SPSE Annual Conference, Boston, 10-14 June 19681. A general report by P. J. Hillson, Kodak Limited

The Rome Air Development Center of the U.S. Air Forcewas a co-sponsor of the SPSE meeting and, as usual at meetingsof this kind, the papers covered a very wide field, both technicaland scientific. In all, one hundred and eight papers werepresented in eighteen sessions, most of which were held in parallelwith other sessions. In these circumstances, any descriptionof the meeting is bound to be incomplete and idiosyncratic.The sessions devoted to the science of the conventional photo-graphic process were grouped under the headings: develop-ment, chemical sensitization, and spectral sensitization. Inthe first, considerable emphasis was placed on developmentby diffusion transfer and the last section was the most coherentand complete.

In the sessions devoted to development, H. J. Price EastmanKodak showed that in the development of silver halides bymetal ions, other factors are important besides the redox potential

January 1969 / Vol. 8, No. 1 / APPLIED OPTICS 83

of the solution. It was found that inner-sphere redox reactions,in which the coordination spheres of the metal ions were changedin such a way that a ligand is held in common between thetwo metal ions involved in the reaction, were much more selectivebetween the development of the latent image and of fog thanwere outer-sphere reactions, in which the coordination spheresof the reactants are unchanged before the electron transfer.A large number of papers were concerned with developmentby diffusion transfer. G. R. Bird, M. Morse, H. Rodriquez,and J. Johnson Polaroid found that the color of silver imagesproduced by this process could not be satisfactorily explainedby applying the Mie scattering formulas to silver particles.In addition to the size and shape of the particles, the inclusionof impurities, which reduced the mean free path of an electronin the silver, had a profound effect on the color of the image.

The sessions on spectral sensitization confirmed the sub-stantial progress that has been made in this field in recentyears. Improved experimental techniques and improved modelsfor molecular orbital calculations have allowed the energy levelsin dye molecules and the effects of aggregation and substrateupon these levels to be evaluated in a fairly quantitative manner.Although the mechanism of simple spectral sensitization hasbeen clarified, the phenomenon of supersensitization remainsobscure. It appears likely that several mechanisms can beoperative.

A paper by W. C. Lewis and T. H. James Eastman Kodakdemonstrated the surprisingly large effect of chemical environ-ment on photographic sensitivity. Exposing a film in a highvacuum substantially eliminated low intensity reciprocity-failure, even on unsensitized emulsions. With spectrallysensitized emulsions, exposing in a vacuum eliminated the de-sensitizing action of the dye and revealed the spectral sensitiza-tion conferred by such a strongly desensitizing dye as pheno-safranine.

The meeting reflected modern trends in the photographicindustry by spending a considerable time dealing with uncon-ventional systems; both the unconventional use of silver halidesand the use of nonsilver systems. R. E. Bacon and R. S. ColtEastman Kodak described a new photo-developable silverhalide emulsion in which the emulsion could be stabilized againstthe formation of print-out silver in unexposed areas by a heattreatment after the latent-image forming exposure and beforephotodevelopment.

E. H. Land Polaroid, in a special evening session, describedhow the incorporation of a substance which forms an insolublecompound with silver ions into a normal diffusion transferdeveloper can lead to the formation of a negative transferredimage. In the unexposed areas of the original negative, a shellof insoluble silver compound is formed around the grains thatprevents silver being transferred to the receiving sheet. Theonset of development disrupts the insoluble layer and permitssilver to be transferred, so that the development of a negativeimage in the exposed layer is accompanied by the developmentof a negative image in the receiving sheet. The photographicspeed of the negative transferred image is considerably higherthan that of the positive transferred image obtained by con-ventional diffusion transfer development.

A further series of papers were given on a process first describedat the SPSE symposium at Washington last year, in which theelectronic changes produced in a photoconductive layer byexposure to light were made permanent by reducing silver ionsto silver. This primary image could then be developed by con-ventional physical development methods. Another seriesof papers described fresh work on a photographic process thatdepends on the formation of dyes by a free radical mechanismand in which the initial dye formation could be amplified bysubsequent exposure to light of longer wavelength.

As would be expected from the co-sponsors of the meeting,there were a number of technological papers with special refer-ence to aerial photography.

2. Progress in Photographic Science Symposium report byAlbert J. Derr, Franklin Institute Research Laboratories

)uring their 1968 conference SPSE presented a one-day sym-posium on the progress in photographic science. This symposiumwas repeated after a successful introduction in 1967; it hasbeen structured to present a series of progress reports concerningthe gain in technology that has been accomplished in variousfields of application of photographic systems. These symposiahave featured invited speakers, many of whom represent otherprofessional societies and industries where photographic systemsand material are used in support of many other technologies.The interdisciplinary line of communication represented bysuch presentations has resulted in additional sources of feed-back information concerning the extent of influence as wellas direction for developments in the photographic industry.

This year's symposium included progress in radiology. Themedical aspects were presented by Robert P. Moseley, Jr. Univer-sity of Chicago. Industrial radiography was discussed by RoyWysnewski GAF Corporation, and C. James Bartleson MacbethCorporation reviewed the advances that had been made inpsychophysical techniques applied to photographic research.

The afternoon session covered progress in graphic arts. J.Winton Lemen Eastman Kodak discussed the advances thathad been made in photojournalism. Progress in the plate-making aspect of the industry was presented by Bernard R.Halpern DuPont Photo Products, and Eugene Coleman Miehle-Goss-Dexter discussed the influence of advances in photographicsystems on the mechanical processes of mass reproduction.

Consideration is being given by SPSE to continuing theseprograms to cover other areas of application of photographictechnology.

8th International Conference on High SpeedPhotography, Stockholm, 23-29 June 1968Reported by George H. Lunn, British National Delegate

International congresses are becoming so large and involvedthat a truly concise report is no longer practical. This particularone, organized by the Royal Swedish Academy of EngineeringSciences (IVA), the Research Institute of National SwedishDefence (FOA) and their National Committee for High SpeedPhotography (HSP) had 130 or so papers, with titles from 2to 20 words and in some cases 6 authors. Merely to list allthese requires over 2000 words so I shall restrict myself tosome personal and general impressions and the mention ofsome notables present.

The specially invited lectures were very well chosen to high-light the modern innovations and interests, provide a momentfor reflection on the past, and, adding a unique paper, reflectingthe advances in international cooperation these meetings shouldand do make. The three invited subject lectures were Photo-electronic Image Devices by J. D. McGee Imperial College,London, Fiber Optics by Walter Siegmund American Optical,and Introduction to Holography and its Applications by W.Martienssen Frankfurt. No doubt these authoritative andpossibly definitive papers will be read and quoted many times;they will be a very valuable part of the weighty proceedingsthat the organizers plan to have available by October this year.

On the Friday morning, Rudi Schall, the German NationalDelegate, spoke of the late Hubert Schardin, a father-figure

continued on page 89

84 APPLIED OPTICS / Vol. 8, No. 1 / January 1969