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Aging properties of Kodak type 101 emulsions

Brian Dohne, Uri Feldman, and Werner Neupert

The aging characteristics for several batches of Kodak type 101 emulsion during storage prior to exposure

have been tested. We have found that storage conditions significantly influence how well the film will main-

tain its sensitometric properties. During this period the sensitivity and maximum density increase to amaximum level. Any additional aging may result in higher fog levels and loss of sensitivity. By keeping thefilm in an environment free of photographically active compounds it is possible to use this storage intervalto optimize the films' properties. Batches of filny with different sensitivities age differently. Of the cur-

rently available emulsions, those with maximum sensitivity (measured at 1700 A) are 2.5 times faster than

those at the low end of the sensitivity scale. Significantly accelerated changes in aging properties were mea-

sured for the more sensitive emulsions. The successful use of such emulsions in space applications will re-

quire that careful consideration be given to time and temperature profiles. When the control of these fac-tors is limited the use of less sensitive emulsions should be considered.

1. Introduction

Instruments which use photographic film requiredetectors with good spatial and temporal resolution,properties that depend upon the sensitivity and struc-ture of the silver halide emulsion. The structure of thephotographic emulsion also makes it sensitive toproblems of contamination: silver halide grains and thelatent image formed by an exposure to light are avail-able for reactions and are subject to alterations otherthan those of development.

Schumann emulsions, which are used as detectors ofthe UV, have a unique structure characterized by theirlow gelatin content and by the absence of any protectivegelatin overcoat. This structure, which makes thesefilms sensitive below the gelatin transmission cutoff at2200 A, also results in increased sensitivity to environ-mental conditions and to handling. Instrumentspresently under development for Spacelab and otherSpace Shuttle missions will use Kodak Special Filmtype SO-652 previously known as Kodak 101. Theseare the most sensitive of the Schumann-type emulsionsavailable.

Kodak 101 film is produced by special order on anintermittent basis within the Research Laboratories ofthe Eastman Kodal Co. It is shipped in containers

Werner Neupert is with NASA Goddard Space Flight Center,Laboratory for Astronomy & Solar Physics, Greenbelt, Maryland20771; the other authors are with U.S. Naval Research Laboratory,Washington, D.C. 20375.

Received 15 July 1983.

maintained below the ambient temperature by dry ice.After arrival at the Naval Research Laboratory (NRL)it is stored at -221C. At this temperature the shelf lifeis extended, that is, emulsions stored for periods ofseveral years under this condition show little or nochange. These same films, when stored at temperaturesof -20'C, show temperature-induced changes over in-tervals as short as one or two weeks.

Experience with these films and tests conducted atNRL prior to the NASA manned orbiting spacelabmission (Skylab) suggest a correlation between extremeultraviolet (XUV) sensitivity and sensitivity to envi-ronmental degradation.1 Millikan and Altman haveindicated that a priori statements concerning the effectsof specific chemical agents are not always possible. 2

The silver halide emulsion is sensitive to both oxidizingand reducing agents. Under the conditions of spaceexperiments within which the type 101 emulsion is ex-posed (10-5-10- 7 -Torr vacuum) the presence of elec-trons, ions, and neutral species might induce changesin the silver halide.3

As an example, it is well established that both oxygenand water vapor are important to the mechanism oflatent image fading and affect film sensitivity. Someother reported photographically active compounds in-clude aldehydes, hydrogen sulfide, hydrogen, ammonia,amines, peroxides, sulfur dioxide, and many other sulfurcompounds. Trace amounts of residual atmosphericgases and untreated aluminum surfaces, the presenceof which may result in the formation of hydrogen per-oxide, have been observed to fog Schumann emulsionsused in vacuum. This has been reported in the litera-ture as the Russell effect.4 5

15 February 1984 / Vol. 23, No. 4 / APPLIED OPTICS 589

To define appropriate handling conditions for ex-periments using Kodak type 101 emulsion, an evalua-tion of the integrated effects of various environmentsprior to, during, and after its exposure has been un-dertaken. The testing which we undertook had as ob-jectives not only criteria for assessing the effects of filmhandling but also criteria for flight film selection.Testing was based on conditions that would be en-countered by the film from the time of installation intoa flight spectrograph until recovery after flight. It isexpected that for the Shuttle the complete cycle frominstallation through film processing will require fromfour to six weeks, during which time the film could beexposed to many environments. During this intervalthe experimenter will have limited opportunities toprovide the most favorable conditions for the film.

II. Photometric Techniques

The sensitometric curve was used to evaluate changesin sensitivity and changes in the latent image. Reso-lution measurements were also made to evaluatechanges in image structure. The density vs log expo-sure curve depends upon the wavelength of the exposingradiation, duration of the exposure (reciprocity failure),and size and spatial distribution of the image (Eberhardand Kostinsky effects). For the purposes of these tests,consideration was given primarily to a convenient andreproducible exposure. Therefore, sensitometric ex-posures were made using an Eastman model 101 processcontrol sensitometer. This device provides an exposureof 0.20 sec through a calibrated step tablet. Its tungstensource was filtered with a blue Corning Glass Filter5113. Two important variables have been omitted bythis approach-the effects of vacuum exposure onsensitivity and dependence of sensitivity changes on thewavelength of the radiation used. Inferences aboutthese effects can be made from calibrations performedat 3600 and 1700 A. Some results and comments onthese measurements are included in a later section.

Because Kodal 101 does show variations in sensitivity,maximum density, and fog density, it was important toevaluate several emulsions and to establish any corre-lation between these characteristics and changes in-duced by testing. The relative sensitivity of the fiveemulsions tested here is shown in Table I; these will bereferred to by the consecutively assigned numbers (onethrough five); they are further identified by a Kodakassigned number. Type 101 emulsion is presentlydesignated Kodak Special Film type SO 652. Emul-sions identified as test emulsions were supplied to us by

Table I. Emulsions Which Were Tested, Identified by Their KodakAssigned Numbers; Values of Relative Sensitivity are Equal to the Wedge

Density X100 Which Gave a Density of 0.3 Above Base Plus Fog

Relative KodakEmulsion sensitivity identification

1 184 10107 062 187 SO 642 test3 190 SO 652 024 192 101 07 125 219 101 07 test

Kodak for our evaluation purposes. These filmsbracket the median values of currently availableemulsions. They provide useful comparative test re-sults.

To obtain accurate sensitometric curves for eachemulsion, under the variety of test conditions, it wasnecessary to account accurately for the contribution offog density to the measured densities at all levels. Acorrection of measured densities is necessary whenprocedures which result in increased fog levels are to beevaluated for their effect on the input-output rela-tionships used to establish film speeds or when emul-sions with initially different fog densities are to becompared. The corrections adopted here are suggestedby Miller. 6 For a zero point correction,

D -D ~~Dmax -DmeasuredDcorrected- Dmeasured - . DfogDmax - Dfog

(1)

was applied. When a test resulted in increased foglevels for the same emulsion another form of equationwas used:

Dcorrected , Dmeasured D ax- Dmeasured . (Df, test - Dfog). (2)Dmax - Dfog test

This equation gives a curve which preserves informationsuch as initial densities, fog levels, and curve shape.These corrections should be considered an approxi-mation.

Densities were measured using a MacBeth model TD100A densitometer having a circular aperture of 2 mm.The measurement if diffuse densities using this aperturefor large areas of exposure modulated by a step tabletcannot necessarily be applied to line spectra. Com-pared to the narrow aperture of a microdensitometer,an aperture of 2-mm diam represents a large areatransmission density measurement and does not havethe same signal-to-noise characteristics.

One requirement for spectrographic emulsions is theability to maintain the resolving power of the instru-ment. Measured resolution increases with increasingexposure, passes through a maximum, and decreases asthe number of developed grains in areas not directlyexposed increases. Measured resolution also increaseswith increasing target contrast and is influenced by theshape of the characteristic curve. Resolution is af-fected, therefore, when fog levels and low densities in-crease more rapidly than high densities as exposure isincreased; that is, the density scale is compressed. Thistypically occurs under the conditions that have beenused in our tests.

The exposures for the evaluation of resolution weremade using a slightly modified Bausch & Lomb micro-scope with an integral camera. An Air Force typehigh-contrast positive resolution target on glass wasmounted in the camera image plane. A forty times re-duced image was formed at the microscope stage by theobjective-camera lens combination. The target wasilluminated by a tungsten source through condensersusing a Corning 5113 filter. Samples of film were heldon the microscope stage by a platen having equallyspaced apertures. Vernier adjustments to the me-

590 APPLIED OPTICS / Vol. 23, No. 4 / 15 February 1984

3.02 2.70 2.41 2.12 1.82 1.53 1.24 .98 .71 .38 .06WEDGE DENSITY

(a)

1.50 >

z0

1.00 a

S

.50

.00

I I I I I I I I I I I

- -

_ X ~~~~~~~~~~~~~~~~~~~~~Emulsion I

3.02 2.70 2.41 2.12 1.82 1.53 1.24 .98 .71 .38 .06WEDGE DENSITY

4,K

3.02 2.70 2.41 2.12

I I I I I I I I I I I

1.82 1.5 .2 7Emulsion 5

I~ ~ ~ I I I I I I I_ 1.82 1.53 1.24 .98 .71WEDGE DENSITY

(C)

.38

1.50

1.00

.50

.00

(-z

crSC)4LU

I I I .003.02 2.70 2.41 2.12 1.82 1.53 1.24 .98 .71 .38 .06

WEDGE DENSITY

(d)

Fig. 1. Sensitometric curves for two of the emulsions tested based on measured and corrected densities. The solid curves show results for

sensitometric exposures processed 2 h following exposure. The broken curves show the changes which occurred after the exposed films were

placed in vacuum for 6 h at 21C before development. The dashed curves show the effect on latent image of 36'C temperature excursion starting

at 211C for 6 h. The additional curve [dash-dot line in (a)] shows a typical effect of unspecified contamination in the vacuumsystem.

chanical stage were used to position the film for eachexposure. The microcamera exceeded the acceptedstandard for performance which requires resolution bythe optical system, which is at least twice that of thephotographic emulsion.

Ill. Environmental Effects

A. Short-Term Temperature Increases

Varying conditions which the film will encounterinclude those of preflight, in-flight, and reentry.During these phases of a mission the film may be af-fected by its thermal environment, controlled gaseousenvironments, and the Shuttle-induced environment.This investigation was concerned primarily with thefirst of these, the thermal environment. This is ofconcern, because solar exposure or reentry and the as-sociated thermal soak-back in the Shuttle bay may re-sult in a short-term temperature excursion. To avoidpossible latent image fading due to oxygen and watervapor, evaluation of the effects of temperature increaseswas made for films held in a 10- 6 -Torr vacuum.

Exposed samples of the film were loaded into ventedstainless steel containers and outgassed in the vacuumchamber for 2 h. The samples were then heated forperiods of up to 6 h. The results for a temperature ex-cursion of 360 starting at 210 under a vacuum of 10-7

Torr are shown in Fig. 1. Two control exposures werealso carried out at 210C. In one, the control film washeld in air and developed 2 h after exposure, as previouswork at NRL has shown that most latent image fadingoccurs within 2 h of exposure. In the other, the expo-sure was subject to a vacuum of 10-6 Torr but with noincrease in temperature above the ambient of 21'C.Results of both controls are also shown.

B. Results of Short-Term Temperature Excursions

There are consistent changes in the sensitometriccurves for films held in vacuum following exposure inair; for the slower emulsion (emulsion 1) the displace-ment of the curves to the left indicates latent imageintensification [see Figs. 1(a) and (b)]. A similar resulthas been reported in the literature.7 The fact that thesechanges do not appear to have occurred in the more


- ;- Emulsion I

I I I I I I I I I I

.50 >-

zW

1.00 -C.)

0C.)

.50

.00

U)z

c

'M

U

LU

0U.

.06

sensitive emulsion (emulsion 5) [see Figs. 1(c) and (d)]is probably a result of the greater increase in fog density.If measured on a finer time scale, similar changes wouldbe evident. Table II includes changes in fog density andfilm resolution for all the 6-h temperature excursionswhich included the third emulsion (emulsion 4), whichhas a sensitivity intermediate to the other two. Theseresults clearly show greater increases in fog density dueto exposure to elevated temperatures with increasingemulsion sensitivity.

In all the tests the decrease in the maximum densityand the change in the shape of the shoulder of the sen-sitometric curve when the film is exposed to highertemperatures indicate some loss of information due todecreased separation of densities. Loss of maximumdensity often occurs and was particularly evident in thetype 104 films flown on Skylab. Although the high-density portion of the curve may have poor signal-to-noise characteristics, it must be well defined to obtainthe widest possible usable dynamic range, which can beimportant for solar experiments where correct expo-sures are uncertain and where transient events or rela-tive line intensities may require a greater exposurelatitude.

The lower portion of the sensitometric curve foremulsion 1, when held in vacuum following exposure,shows in addition to the latent image intensification[Fig. 1(b)] an extension of the toe [Fig. 1(a)]. Thesechanges were also evident for emulsion 4. Emulsion 5shows a measurable loss of density in the toe of thesensitometric curve due to the increased temperature[Fig. 1(c)]; there is no latent image intensification in thecorrected curves [Fig. 1(d)]. These results should beverified for shorter wavelengths. The tests were madeboth with and without the ionization gauge in operation.Its operation at this pressure (10-7 Torr) produced nochange in the sensitometric measurements for the timeinterval involved in these tests.

The reduced density scale and loss of image contrastresult in a loss of resolution which is greatest for thefilms having the highest sensitivity. Decreases in res-olution parallel increases in fog density. Areas of thethree-bar target not directly exposed to light do notshow, when examined under the microscope, any greaterchanges than the unexposed film outside the targetarea.

C. Some Observed Contamination EffectsDespite efforts to maintain consistent conditions

within the vacuum chamber between tests, someunexpected results were observed. Although either drynitrogen or a vacuum can provide an inert condition inwhich to study effects of increased temperature, it wasfound that maintaining this environment depends onthe outgassing characteristics of the container, the in-tegrity of seals, or the quality of a vacuum. In a firstattempt to raise the temperature of the film containerby using a shroud that heated the entire vacuumchamber, higher than expected fog densities resulted.Outgassing from the shroud apparently had resulted inchanges in the gaseous environment which could not bedetected on an ionization gauge under conditions of a10-7-Torr vacuum. The temperature was measuredremotely by a thermistor placed in the film container.The test was repeated in the same vacuum system fol-lowing the same thermal profile by heating only thecontainer of film with an electric resistor. In this ex-periment fog densities were lower.

The loss of maximum density and increased fogdensity at elevated chamber temperatures are inter-preted as a further indication of the combined effectsof increased temperature and of residual gases. Theionization gauge (which was in continuous operation)may also have contributed to the presence of photo-graphically active substances. For example, atomichydrogen generated by the action of a hot filament onhydrocarbons (or on molecular hydrogen) in oil pumpedsystems is adsorbed at a very significant rate onto me-tallic surfaces; its adsorption is reduced by increasedtemperatures. 8 The fogging effect of such a mechanismon photographic film has been observed.3 Atomicoxygen generated by a microwave discharge source hasbeen reported to fog type 101 film and to reduce maxi-mum density.9

Similar changes of calibrations made at 1700 A havealso been observed as a result of conditions in the vac-uum system. In such cases, in addition to changes inthe shape of the sensitometric curve, there is a reducedcorrelation between results of calibrations done at dif-ferent times.

In subsequent testing we have found that introduc-tion of ambient atmosphere, oxygen, or hydrogen intoa well-evacuated chamber with the ionization gauge in

Table II. Fog Densities and Resolution in Line Pairs per Millimeters Before (Stock) and After 6-h Temperature Excursions, Resolution Results are inParentheses; Stock emulsion was held at a temperature of -22 0 C

Relative speedEmulsion type at 4600 Aa Stock 210C 32 0C 49 0C 540 C 600C 820 C

101 07 06 188 0.07 0.09 0.10 0.12 0.12 0.14 0.60(112) (112) (112) (99) (88) (79) -

101 07 12 192 0.08 0.10 0.11 0.14 0.17 0.22 0.82(99) (99) (99 (99) (79) - -

101 07 T'est 210 0.12 0.16 0.15 0.26 0.32 0.48 1.36(88) (88) (79) (62) -

a Wedge density 100 (corresponding to an output density of 0.3, 0-point corrected).


operation results in a significantly greater increases infog density and greater changes in the sensitometriccurve for emulsions having higher UV sensitivities.

D. Long-Term Storage Tests

The integration of payloads into the Space Shuttleorbiter will take place from two to four weeks prior toa mission. Tests were initiated, therefore, to evaluatesensitometric changes in films stored for periods up toeight weeks at the expected orbiter temperatures.Millikan2 has speculated that the film should not showsignificant changes during periods of up to six weeks ifconditioned by vacuum and stored under nitrogen at200C. However, it is anticipated that a temperature of250 C could be possible for extended periods.

Nitrogen has been commonly used as an inert atmo-sphere for the storage of silver halide emulsions, par-ticularly for spectrographic emulsions in astronomicalapplications. To avoid possible atmospheric contam-inants it was selected as a standard test environment.Two approaches, using either continuously purged orhermetically sealed containers, were taken to evaluatethe effects of film storage. In the first, steel cans withfriction lids replaced the tape seal on the containers inwhich the film is originally received from Kodak.Copper and Teflon tubing were added to provide acontinuous nitrogen purge. A molecular sieve was usedto reduce contamination. Some outgassing fromcomponents (which had been vapor degreased andbaked at 1000C to eliminate traces of chlorinated hy-drocarbons) and leakage through the nonhermetic sealswere expected. In the second approach, hermeticallysealed containers of 304 stainless steel were used. Thismaterial has in previous tests been demonstrated tohave no effects on type 101 film and is being used in asmall self-contained Shuttle payload to determine insitu the integrated effects of the Shuttle environment.To further evaluate its compatability with such film, thecontainers were used under conditions which parallelthe laboratory work. These containers were passivated,vapor degreased, and vacuum baked (10-6 Torr) at1500C. Film samples for these tests were conditionedby placing them in a 10- 6-Torr vacuum for 2 h in thestainless steel cylinders, which were then backfilled witha high grade of nitrogen.

The results from tests performed under these twoconditions have been evaluated for changing film sen-sitivity, fog level, and maximum density.

E. Results and Long-Term Storage Tests

Three comparisons will be discussed: (1) thermaleffects on five different emulsions; (2) thermal effectsat two different temperatures on three of the emulsions;and (3) changes for two of the emulsions related to thegaseous environment under the two conditions of con-tainment previously described.

In the first of these comparisons we have found thattemperature-induced changes in fog levels for fiveemulsions held under nitrogen at 260 C have a signifi-cant correlation with initial sensitivity (Figs. 2-6). Theleast sensitive emulsions showed the smallest changes

over a period of eight weeks (0.08 and 0.06 densityunits). The films with intermediate sensitivitiesshowed a slightly larger increase (0.11 and 0.16 densityunits). The most sensitive emulsion showed thegreatest change (0.47 density units); this emulsion hadinitially a higher level of fog density (0.12) than theother four emulsions (0.08-0.10).

Changes in the sensitivity of the film with durationof storage were also observed. Increases in sensitivitywith time for this emulsion are to be expected. For thefive emulsions under discussion, sensitivities on a rel-ative scale were derived from the corrected D-logEcurves [Eq. (1)] at a density of 0.3 units above base plusfog. Changes in sensitivity within each emulsion rela-tive to the control were derived using Eq. (2). Only theleast sensitive emulsion showed little or no increase insensitivity at the end of eight weeks. Taken in orderof initial emulsion sensitivity, the next three emulsionsshowed approximately the same increases (0.13, 0.18,and 0.12 relative log exposure units) over a period ofeight weeks. The most sensitive emulsion showed thegreatest change (0.25 relative log E units) after only fourweeks. In the following four-week period its sensitivitydecreased (-0.13 units). Although this emulsion re-mained high on the sensitivity scale, its resolution andability to record low densities were significantly de-graded due to high fog levels (see Table II). Generally,values of maximum density also increased with time. InFigs. 2-6, changes in fog level, sensitivity, and maximumdensity for the five emulsions which were used in thesetests are presented.

These results indicate that there is a correlation be-tween initial sensitivity and the amount of increasedsensitivity that can be expected. Assuming a mea-surement error of ±0.02 log exposure units, note thatthe two least sensitive films are separated by an amountjust equal to this error.

In the second set of comparisons three of the emul-sions were evaluated for their response after storage attwo temperatures, 20 and 260C. The range of emulsionsensitivities- is well represented by these samples. Ineach case storage at the higher temperature causedgreater or more rapid increases in sensitivity. For twoof the emulsions, 2 (Fig. 3) and 3 (Fig. 5), we founddefinite increases in sensitivity but not necessarily in-creases in fog levels. The results for emulsion 5 (Fig.6) at 260 C have already been discussed. These samechanges occur at 20'C, but at a reduced rate, that is,after four weeks at 260C, the sensitivity has peaked andis beginning to decline while at 20'C it is still increasingafter six weeks. Temperature-induced increases in foglevel, like chemical reactions, are assumed to double inrate for an increase of 100C.10 These results indicateapproximately such a change for this film. For long-term storage tests, resolution measurements were madefor emulsion 5. Values, which decreased with increas-ing fog density, are shown in Table III. These resultsindicate that the ability to select films with optimumsensitivity will be strongly dependent on the selectionof appropriate time and temperature profiles for the.space mission.


|i90 200 1.70 1.75 1.80 1.85SENSITIVITY MAXIMUM DENSITY

Emulsion I

Fig. 2. Emulsion 1 aging curves showing sensitivity vs fog level andmaximum density vs fog levels for the periods indicated in weeks.

The results are for 26 0C nonhermetic storage.

U.J.0U-C 0

Fe"','-GF ,

190 200 210 I.60 1.65 1.70

SENSITIVITY

1.75

MAXIMUM DENSITY

zE.0

220 230 1.60 1.70

SENSITIVITY MAXIMUM DENSITY

Emulsion 5

Fig. 6. Emulsion 5 aging curves showing sensitivity vs fog levels andmaximum density vs fog levels for the periods indicated in weeks.The results are for nonhermetic storage at 26 0C (broken lines) and

nonhermetics storage at 20'C (solid lines).

Emulsion 2Fig. 3. Emulsion 2 aging curves showing sensitivity vs fog level andmaximum density vs fog levels for the periods indicated in weeks.The results for hermetic storage are shown by the squares. Resultsfor nonhermetic storage are shown by circles. Solid lines are for 20'C

storage. Broken lines are for 26 0C storage.

.30

.25

.15

.10

I I I

I I

i 6, to 4am -I

190 200 210

SENSITIVITY1.50 1.55 1.60 1.65

MAXIMUM DENSITY

Emulsion 3

Fig. 4. Emulsion 3 aging curves showing sensitivity vs fog level andmaximum density vs fog levels for the periods indicated in weeks.

The results are for 260C nonhermetic storage.

.20

LE .1 5E 0

.10

I- I I .

IA -11 II

S _ ti) _I-G) I1,I9O 200

SENSITIVITY

Emulsion

Fig. 5. Emulsion 4 aging curves showing smaximum density vs fog levels for the pei

The results are for 260 nonheri

Table I. Fog Densities, Maximum Density, and Resolution (Expressed inLine Pair per Millimeter) of Emulsion 5 as a Function of Storage Time at

the Temperature Shown

Temperature Period Fog Maximum Resolution(0C) (weeks) density density (lp/mm)

26 4 0.36 1.70 6020 6 0.34 1.71 7820 2 0.18 1.63 8826 2 0.23 1.65 88Controla 0.14 1.56 99

a The emulsion was checked immediately after it came out ofstorage (-22 0C).

The last of the comparisons involves measurementsof changes in film sensitometry for two of the testemulsions stored under hermetic and nonhermetic seals(Figs. 3 and 4). The changes for an emulsion keptunder hermetic seals, for a period of up to eight weeks,show significant increases in speed, minimum increasesin emulsion fog, and improved maximum density. Forthe first four weeks of nonhermetic storage we haveobtained similar results. However, beyond four weeks,there are signs of deterioration in the film. There is alsoa greater increase in fog levels and simultaneous de-crease in growth of maximum density or in one case anactual loss of maximum density (Fig. 3).

IV. Film Calibration Values, The Kodak Research Laboratory will provide a cali-

bration number with each of the 101 films they manu-- i -J facture; these numbers usually fall between 80 and 100.

This calibration is performed at a wavelength of 36001 1 A. Six recently acquired emulsions have been cali-

MAXIMUM DENSITY brated by us for the following wavelengths: 4600, 3600,and 1700 A. There is a good correlation between the4 Kodak calibration and our VUV calibration (see Fig. 7).ensitivity vs fog level and As previously described, these six films were maintainedriods indicated in weeks. at low temperatures, except for the interval required tometic storage. bring films to room temperature and to remove a sam-


I

N

0

these factors-sensitivity, granularity, and slope-tophotographic efficiency is expressed as detectivequantum efficiency (DQE). DQE is directly propor-tional to the square of the slope, inversely proportionalto the second power of the granularity, and directlyproportional to the sensitivity:

(dDd logE)2

. / The decreased efficiency introduced by changes in(05) +(02) -~ the gradient term due to aging is significant and can

+. (03) negate any increase in sensitivity. Given the aging, , , , , , , , , characteristics of the most sensitive emulsions, their

20 25 30 35 40 45 50 55 60 selection should be based on a requirement for short

NRL 1 700 A Relative Calibration (Log T x I 00) photographic exposure times in experiments of shortimparison of the Kodak vs NRL calibrations for the six duration and under conditions which are, by design, freet S0652 (type 101) emulsions received at NRL. The po- of contamination. Such emulsions have been fre-ur of the five emulsions tested and described in the paper quently used successfully on sounding rocket. For goodit the top of the figure; 101 07 test, the fifth emulsion, is results under conditions of long exposure to uncon-

well outside this range. trolled conditions, say four to eight weeks, an emulsionhaving average sensitivity which has previously beenstored under conditions free of photographically active

s minimizes any effect of film aging. A second substances can be used.variable, the effect of the gaseous environment (inparticular oxygen and water vapor) for a 3600-A cali-bration, was also established. A calibration at 3600 Awas made following evacuation of the spectrograph andbackfilling with a high grade of nitrogen and comparedwith a calibration made in ambient air. It showed thesame increases in sensitivity for all the films. There isalso a direct correlation between measurements at 4600and 3600 A (see Table IV).

V. Criteria for Film Selection

This investigation of Kodak 101 film has shown thatthe selection of films for applications requiring optimumsensitivity is limited by the duration and conditions offilm storage. We have observed a significantly greaterincrease in sensitivity and fog density for the moresensitive emulsions. Increases in fog density contributea constant noise level (measured as granularity) andcompressed density scale which results in a reductionin the slope of the D-logE curve. The contribution of

Table IV. A Comparison of Film Calibrations at Various Wavelengths.

Correlationcoefficientsa Comparison

0.98 NRL at 1700 A to Kodak at 3600 A0.97 NRL at 3600 A to Kodak at 3600 A0.97 NRL at 3600 A to Kodak at 4600 A

a The correlation coefficient r is given by the following equation:r = (mU.)/Ur", where

N2L K -( - Ki)

2 i=l IUK N

N N NXi , .- N L XiYi

M=N i2 NEXi -NYEX2

M == i=

for more details see Fig. 7.

VI. Conclusions

To achieve the maximum performance from Kodaktype 101 emulsion, an understanding of its sensitivityto the environment in which it is stored is essential.Our tests demonstrated that the aging process is asensitive function of temperature. A significant cor-relation between sensitivity to the gaseous environmentand to UV sensitivity has been demonstrated by thesetests. Although aging under well-controlled conditionswill result in increased sensitivity with minimal in-creases in fog density, the best combination of sensi-tivity and low initial fog density is achieved by usingfilms as they are manufactured which have been storedat low temperatures. This is true for all but the leastsensitive type 101 emulsions.

As they are received from the Research Laboratoriesof Eastman Kodak, batches of type 101 show variationsin sensitivity. For the emulsions which we have re-cently acquired and calibrated, the maximum differencein sensitivity between the least and most sensitiveemulsion is a difference of 0.4 log exposure units or afactor of 2.5 measured at 1700 A. Emulsions above themedian value were observed to have significantly greaterincreases in fog density.

Elevated storage temperatures as well as exposure toradiation may produce a latent image. Testing has alsodemonstrated the ability of 101 film to withstandtemperature excursions in a vacuum free of photo-graphically active substances. However, during thesetemperature excursions the introduction into the en-vironment of previously absorbed substances due tothermal desorption is an important consideration. Theoutgassing rate of materials is important under allconditions. Where an ionizing source is present re-sidual or desorbed atmospheric gases may producephotographically active substances. The same con-siderations that apply to high-vacuum chamber design


N0

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100

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Yo

010

X

104 -

I I .I . I . I . I I I I

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95

90

85

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ple. Thi

and appropriate vacuum techniques are essential to thesuccessful use of this film.

We wish to express our deep appreciation to C.Stouffer from Goddard Space Flight Center for his in-terest and support during all phases of the research.We would also like to thank A. G. Millikan, J. H. Alt-man, and S. Phillips from Kodak as well as J.-D. F.Bartoe from NRL for helpful discussions.References1. T. C. Winter, Jr., and M. E. VanHoosier, "Schumann-Type

Photographic Film Preliminary Environmental Test Results,"NRL Report 7072, Naval Research Laboratory, Washington, D.C.(14 July 1970).

2. A. Millikan, and J. Altman, Research Laboratories, EastmanKodak Co.; private communication (1980).

3. V. Zhelev, Photogr. Sci. Eng. 26, 118 (1982).4. J. H. Underwood, Rev. Sci. Instrum. 47, 644 (1977).5. R. P. Clifford, Rev. Sci. Instrum. 48, 491 (1977).6. W. C. Miller, AAS Photobull. No. 16, 3 (1977).7. K. Kuge, S. Fujiwara, and H. Hada, Photogr. Sci. Eng. 25, 197

(1981).8. I. Langmuir, J. Am. Chem. Soc. 34, 1310 (1912).9. W. M. Burton, A. T. Hatter, and A. Ridgeley, Appl. Opt. 12,1851

(1973).10. H. W. Cleveland, "Latent Image: Formation and Properties in

Silve Halide Emulsions," in SPSE Handbook of PhotographicScience and Engineering, W. Thomas, Jr., Ed. (Wiley, New York,1973).

APPLIED OPTICS SUMMER COURSE

July 2nd - 13th 1984

The Optics SectionImperial College

London

This two week course is intended for scientists, engineersand managers whose training is in fields other than optics andit is also suitable as a refresher course for opticalspecialists. It consists of approximately 40 lecturesemphasising basic concepts in applied optics and laser physicsand includes demonstration experiments and visits to relevantlaboratories in the Optics Section. The lectures are all givenby the staff of the Optics Section and printed lecture notesare provided for participants.

The fee for the course is 450 (approx.$700).Accommodation is available in local hotels. For furtherinformation and registration forms, please contact Professor JC Dainty, Optics Section, Blackett Laboratory, ImperialCollege, London SW7 2BZ, England, telephone (01)589 5111ext2307.
