UNIVERSITY OF MICHIGAN Ann Arbor FINAL REPORT OF RADIATION

Transcription

1 4 UNIVERSITY OF MICHIGAN Ann Arbor FINAL REPORT HIGH RESOLUTION DETECTION OF RADIATION By HENRY J GOMBERG Principl Investigtor FEARGHUS FOGLUDGHA JACOB 1 TROMBKA REUBENA WEYANT PFOJECT AT(ll1)7ONo 3 Mroh, 1959 p

2 TABLES OF CONTENTS Pge LISTOFFIGU?JS..., iii 7\TnmTrrmT(T j.js.., o o o o o o o o e o.. o o o o o RESEARCHRESULTS 3 I.. HIGH DENSiTY THIN SILVER HALIDE FILMS e 3 II.. MOLECULAR 11 DYE FO?IVIING FILMS 12 III.. NEW TECHNIQUES TESTED WITH INDEFINITE OR NEGATIVERESULTS A.. Monomoleculr Silver Hlide Film Experiments, e e o 24 B.. Distse Experiments 29 C.. Continuous Medi, 38 D.. Geltin Bichromte Films e o o o 4]. BIBLIOGRAPHY 42 APPENDIX ± 43 ii

3 LIST OF FIGURES Figure Pge 1 Autordogrphs of Chlorell Tgged With Cltt p p 11 2 Use of Moleculr Dye Forming Films for Recording Ptterns Creted by Electrons 23 3 Arrngement for Forming Monolyer 27 4 Showing Apprent Improvement in Resolution When The Geltin Concentrtion in the Auto rdiogrphic Emulsion is Reduced by i s solving s 27 5 Effect of Finite Object Thickness on Apprent Resolution in Very Thin Emulsions 37 ii

4 INTRODUCTION The objectives of our project hve been l Cretionof new systems of detecting rdition in which there re incorported such properties s:. very high sptil resolution b. low sensitivity to non-ionizing rdition c. low inherent bckground d. high sensitivity to ionizing rdition 2, Cretion of new devices to fcilitte detection of rdition with dequte sptil resolution but with less mnipultion necessry thn is the cse with existing methods. As result of objective (1), cme the development of wet process utordiogrphy nd lter the perfection of protective lyer techniques for use with the commercilly vilble stripping films. Wet process utordiogrphy hs been widely dopted(1) for solution of specil rdition detection problems. The bet ry microscope cme s result of work on objective (2). A bibliogrphy of rticles nd reports to which workers Appendix I. on this project contributed is given in In this report re descriptions of dditionl new processes which hve been used successfully in high sptil resolution detection of rdition. 1.

5 It is our belief tht the techniques now vilble pro vide dequte support for reserch work in which precise loction of rdioctive trcers is needed, This ws not true t the time the project ws strted, It is therefore our conclusion tht our efforts should be used in other res where more significnt problems exist, For us, these re primrily in the study of fundmentl mechnisms in the interction of rdition nd mtter, In this finl report, we re presenting the results of experiments in which new types of films, suitble for high resolution utordiogrphy were produced. In one group, the bsic silver hlide system ws retined, but incorported into films in such wy s to mximize resolution despite the presence of visible grin structure. In others, moleculr rection systems were used so s to eliminte the grin structure problem. Some illustrtive pplictions of the successfully developed systems re shown, Finlly, some of our unsuccessful ttempts t new film development re discussed. 2

6 RESEARCH RESULTS 1 HIGH DENSITY THIN SILVER HALIDE FILMS The technique described below ws the finl development of n effort to mke very thin (1 micron) but dense film of silver hlide grins The principles of ction of such film re well known but the technique for mnufcture hd to be creted, The film produced is considered quite stisfctory for ppliction to problems involving smll specimen res (I squre centimeter or less,) Method For Mklng Silver Bromide Thin Film A Ag-KOH Solution. l Mke up l silver nitrte in distilled wter 2, Add few drops of dilute mmonium hydroxide The solution will turn drk brown, 3, Add more mmonium hydroxide very slowly until the brown precipitte is lmost gone 4 Mke up 1 KOH solution nd dd to the bove mixture in (If l2 proportion using 1 ml, AgNO 3 solutions dd 5 ml, KOH solution) The mixture will gin precipitte. 5 Add few more drops very slowly of dilute 4H NH but do not let the solution become 3

7 entirely cler, If the solution should cier then dd more AgNO forms, B, Reducing Solution, 3 until permnent precipitte This solution should be prepred one week prior to using 7 ml, distilled wters 8 gm, sugr When dissolved dds 175 ml, ethnol 3 ml, nitric cid Wter to mke 1 ml, Use 1/25 s much reducing solution s Ag-KOH solution, The reducing solution is poured into the AgKH solution nd quickly stirred nd poured into contct with substnce to be silvered, Method For Mking Plstic Film The plstic film is mde for 2 solution of prlodion in myl cette, The film is formed by plcing drop of the 2 prlodion in lrge wtch glss contining distilled wter, nd The plstic spreds over the surfce of the wter thin film is formed, When the film hs formed tke one prt of the reducing solution nd pour into beker contining 25 prts of the AgKH solution nd stir quick1y As soon s this is well mixed quickly decnt the distilled wter out from under the plstic film nd replce it with the silvering solution, This is esily ccomplished by pouring the silvering solution 4

8 towrds the edge of the film the solution will flow under the film As this is llowed to stnds the solution underneth the film will turn first blcks then drk brown, then golden grey color, When the film is uniformly coted with silver, decnt the silvering solution out from under the film nd replce with severl chnges of distilled wter until the distilled wter remins cler The silver grins re now on the wter side of the floting film The film my now be picked up on whtever crrier one wishes (slides, etce) merely by plcing the crrier over the film nd then quickly inverting so the film is picked up grin side It is necessry tht the grins be in this position s the processing solutions needed lter will not penetrte the plstic support Also, in this wy, the plstic support cts s protective lyer between the smple nd the film, thus in some mesure helping to prevent chemicl rection between the film nd the object to be utordiogrphed, After the film hs dried well hot ir blower my be used to hsten this the silver is redy to be converted to silver bromide All steps from here on must be crried out in hood with red light illumintion only (wrtten filter #2 t two or three feet distnce from the film is stisfctory) The silver grins re converted to silver bromide grins merely by plcing the film in continer holding few 5

9 drops of liquid bromides Here one must experiment until the correct mount of bromine is used to fill the continer with fumes just sufficient to convert the silver to silver 2 without giving n overdose of bromine nd burning bromide the plstic When this procedure hs been performed correctly the film will turn n even white color nd will still be 2 trnsprent. The yellow color of the bromide is just brely perceptible After the film hs hd sufficient exposure to the bromine it is removed from the bromine nd ired in the hood to get rid of ny excess free bromine 2 nd then the film is coted with geltin by dipping the film in 5 geltin 2 drining solution 2 nd llowing the film to dry slowly in the ir The geltin is necessry 2 mong other things 2 to help hold the grins in plce during processing 2 s well s cting s sensitizer on the silrer bromide gri 4is Discussion A6 Film Formtion Forming the film directly on the silvering solution insted of on wter first 2 ws tried It ws found tht smoother film ws chieved in this mnner 9 due minly to 6 However lrge smooth film is not less hndling necessity s the re of film needed for most specimens is smll, Also 2 forming the plstic film directly over the silvering solution gve much hevier silver deposit 2 6

10 in fct too hevy deposit, while t the sme time some of the silver grins were deposited within the plstic during its formtion, nd these grins could not be reched by the processing solutions. On the other hnd, forming the film first on distilled wter nd then replcing the distilled wter with silvering solution resulted in films with thinner lyer of silver extremely tightly pcked nd the grins on this film were completely clered by fixing solutions indicting no grins could be deposited within the plstic itself, but only on the surfce of the plstic. And finlly, film formed in this mnner hlogented more rpidly, uniformly nd completely. B. Film Processing. Film development ws tried with vrious commercij. developers s well s with the physicl development technique. All methods of development worked with the most stisfctory being D-l9 used undilute for 2 seconds. Fixtion ws crried out with i -6 for one minute. Actully the film clers grossly in four or five seconds. Following fixtion the film is rinsed in severl chnge of wter nd dried. C. Film Sensitiztion. Film sensitiztion ezperiments were crried out testing the effect of: 1. Combined helogention - specificlly bromine nd iodine. This ws crried out by briefly shortening the film s exposure to bromine nd 7

11 following this exposure with n exposure to iodine fumes, Although vrious combintions in timing were tried no conclusive evidence ws obtined to indicte this method to be either benevicil or detrimentl to the process 2. Different types of geltin were tried nd here gin the results were not consistent enough to indicte ny increse in sensitivity. However the use of Kodk pure geltin gve much clener results, Although ll geltins were filtered before use. some of them showed minute frgments which were not present in the Kodk geltin. 3, Experiments were lso crried out to determine if the use of NH 4OH would ct s sensitizer to the film Aginthe evidence ccumultedwsnot conclusive one wy or nother, 4. The fourth method tested ws the dditon of known sensitizer to the geltin. rhis ws ccomplished by dding the sensitizer to the melted geltin before the film ws dipped. Results of tests run with this sensitizer indicted n increse in sensitivity of the film, LC3\ KE c CC \i 3 B

12 5. The effect of temperture on the film during its exposure time ws tested nd this hd no effect on sensitivity. However, when tempertures bove 25 C. were used, the geltin becme too brittle nd did not process well, if t ll. These experiments were ll run using rdioctive chlorell s test source. The chlorell ws incorported in the geltin coting used merely by dding mesured mount to the geltin before dipping the film in the geltin. Inctive chlorell ws used s control. Very good results were obtined using this s test orgnism, quite con sistent results being obtinble. Test results re shown in Fig. 1. The film ws lso tested on rdioctive metls, nd x-ry. Good response ws obtined to thllium nd to x-rys. Experiments run with rdioctive nickel would not give con sistent results, lthough some good utordiogrphs were obtined, they could not lwys be duplicted. Much diffi culty ws encountered trying to prevent overexposure of the metl to the bromine, lthough hevy (5/i) plstic pro tective lyers of vyns were used between the metl nd the film, the bromine would still penetrte the film nd etch the metl. The film ws lso tried on rt thyroid tissue. Stis fctory results were not obtined s system hd to be worked out to keep the tissue from drying out while under 9

13 the film, s wter soluble plstic wshed out from under the film during photogrphic processing, nd plstios which were not wter soluble fogged during photogrphic processing. Obviously some entirely different system for mintining the tissue integrity would hve to be developed before redble utordiogrph cn be obtined using this silver bromide film. The thickness of this silver bromine film ws determined by bet bsorption nd results indicted tht the film is 1.4 microns thick. 1

14 O OH F-b--d C CDHcn & (C COp (( H CD o( OH po o& H R) D H. C) & Pd - WCO) CJ) 1Op C) H O o F- (Ud CO ) - - H Q F-b o P) ( (JQ c-to F- H CDHOD F- PQF-bH H H I) H ) d & H H QF) HO CD 4: CD ( H 3 bri F- Q CD H 4:- c-i ) F-b P P) H c-i CD ( b ) ( CI CD ) C) c-i-

15 Tie IoLc:LAR idye FQJJMfG FiLVI The importnt chrcteristics of deecting lyer which determines resolution in utordiogrohy nd micrc rdiogrphy re the foilowin, thickness ot : iliii; b, sensitivity of the detecting lyer to ionizing rdition; c, density of ocking of the ensltive mteril; d, prticle size of the sensitive system Up to the present time, silver hlide systems hve yielded the bet results, Much excellent work hs been done to optimize the bove mentioned chrcteristics But mjor limittion of ny silver system is the prticle size. In order to imprt photosensitivity to silver emulsion, some kind of crystlline structure is necessry. When enlrgement of the order of 1 x or greter is desired, there will be ioss in resolution due to the finite size of the silver grins, In order to optimize the chrcteristics listed in, c, nd d, film ws rrepred in which dye molecule rther thn reduced silver grin ws produced upon exposure to ionizing rdition, The sensitive system is moleculr rther thn crystlline in size Furthermore since the systemis solid solution rther thn suspension, the film hs no insensitive regions See Reference 173 Appendix I 12

16 While c nd d hve been optimized d) the sensitivity of the dye films is lower thn the silver hlide emulsions Becuse of the low sensitivity of the films produced to dte when compred with sensitized utordiogrphic emulsions the mjor ppliction of this system will be in micrordiogrphy nd possibly dosimetry In micrordiogrphy becsue of extreme resolution requirements even the silver hlide films used re usully of low sensitivity Exposure time for the dye to chieve stisfctory imge is comprble to the exposure time required for the fine grined silver hlide films usully used 9 One thousnd dimeter nd greter enlrgements of the rdiogrphs using dye forming films cn be mde directly without resolution loss due to prticle Both x-rys nd electron bems hve been used to size produce micrordiogrph on these films Development Of Dye Films A Films Contining Hlides And Dye Forming Regents 1 Interction Process The use of dye forming regents nd hlides for rdition sensitive films ws suggested by the work of Mr J Grsou who is studying the rdiochemistry of such systems on nother project t our lbortories(2) Ionizingrdition tends to cuse the relese of free hlogens from certin If dye forming regent is dded to the systems hlides the free hlogen produced upon irrdition will interct with the regent to form dye molecule The regent is 13

17 trnsprent in olution nd turns its chrcteristic color upon oxidtion 2 Choice of Hlide Both metllic nd orgnic hlides were tried nd PPhenylenedimine (PPD) ws used s the dye forming regent, Either solutions or suspension of the hlide nd (PPD) in myl cette were mde nd then irrdited using xry diffrction unit t 3 PKV nd 15 m Metllic bromides nd iodides nd lso orgnic iodides were investigted The metllic hlides were found to be completely unstisfctory becuse of either strong drk rections or becuse of extremely low yield fter rther lrge doses The yield could be mesured roughly by the discolortion produced Iodoforrn ws found to be the most stisfctory of the orgnic hlides 3 Choice p eformi Regent Polystyrene ws used s the plstic to contin the rdition sensitive system The nextproblemwsto find the best dye forming regent to use for imge formtion Solutions of po1ystyrene iodoform myl cette nd vrious dye forming regents such s ppheny1enedimine crystl violet 1ctonebenzoyl leuco methy1ene, nd p p ph methylidy nitris (MDT) were used Films were then llowed to dry These films were then exposed for given time to collimted xry bem from n x=ry diffrction unit operting t 3 PKV nd 15 m MDTws found to yield the best imge in terms of opticl opcity 14

18 4 Prqportion of Constituents Used nd Film tionprecution Up to this point the constituents which produce the most stisfctory system were the following orgnic hlide iodoform O6 gm b dye forming regent p p p methylidynitris (MDT) 4 gm c solvent myl cette 2 gm d plstic polystyrene 1 gm Other polymers nd solvents such s vinyl cette in bsolute methyl lcohol were used nd found stisfctory The following precutions must be tken in pre pring the films These precutions hold for the films to be discussed lter The solvents must be reltively dry becuse of the instbility of the orgnic hlide nd dye forming regent due to the presence of moisture b Impurities in either polymers or monomers nd solvents must not be of such nture s to interct with either the orgnic hlide nd dye forming regent c The films should be dried in reltively dry tmospheres becuse of the instbility of the orgnic hlide nd dye forming regent to moisture 15

19 d The drying should lso be done in dust free tmosphere becuse dust prticles incorported into the emulsion interfere with imge detection e The film must be completely dried so tht very little solvent be left in the film The films will tend to crck if they re not completely dried Films described bove were prepred Micro rdiogrph using both soft x rys nd collimted electron bems were produced s follows A 2 copper wire mesh (n electron microscope screen) ws plced in intimte contct with the film The film is exposed to either n xry bem from n xry diffrction unit or n electron bem from n electron diffrction unit. The enlrgements in Fig 2 re mde from micrordiogrph produced by using n electron bem Direct microscopic enelrgements were mde t 5 x, l24 x nd 2 x The fourth photogrph is 4 x enlrgement of the 2 x microscopic enlrgement. The imperfections in the enlrgements re due primrily to mechnicl breks nd scrtches in the polystyrene films to the presence of undissoived orgnic hlides nd dye forming regents nd to dust prticles incorported into the film during the drying process lso been mde, been observed Microscopic observtions t 97 x hve nd no perceptible grnulr structure hs The drkening in the bckground cn be 16

20 ttributed to the sensitivity of the film to light There fore during the opticl enlrgement process the film tends to drken 5 Film InstbiJ4 It ws t this point tht the instbility under light of this system ws observed The imge tended to be lost in bckground fter sustined observtion under microscope The film ws sensitive to light in the opticl regions to moistures nd to het Sensitivity to rdition in the visible prt of the spectrum ws now considered A spectrophotometer ws used s source of monochromtic light The film ws found to be sensitive to light In the ultrviolet blues nd green regions while it ws reltively insensitive to light in the yellow nd red regions. It is known tht free iodine Is relesed from iodoform under exposure to lights hets nd moistures nd therefore it ws believed tht if the iodoform could be eliminted fter exposures the film would be more stble. B. Double Emulsion Films In order to find method of eliminting the iodoform fter exposures. double emulsion system ws investigted MDT ws included in plstic polystyrene film, nd iodoform ws included in vinyl cette film After csting nd drying the polystyrene film contining MDT the vinyl cette contining the iodoform film ws cst on 17

21 top of the polystyrene film Vinyl cette is soluble in bsolute methyl lcohol while polystyrene is reltively in soluble in bsolute methyl lcohol Thus the film contining the iodoform could be removed fter exposure by immersion in bsolute methyl lcohol Such films were prepred exposures mde nd imges were formed in the emulsion contining MDT The sensitivity ws much lower thn the single lyer films It ws then decided to try to increse the sensitivity by Incresing the concentrtion of MDT in the polystyrene lyer The sensitivity incresed, but this system ws not too stisfctory becuse of the extr steps in hndling nd becuse of the necessity of incresing the emulsion thickness C Dye Forming Film With Dye Forming Regent Alone 1 Film_Sensitivit Constituents nd Prprtion Previously the sensitivity of the films con tming rther low concentrtions of MDT without ny orgnic hlide were tested nd the films seemed reltively insensitive to both xrys nd electrons Now it ws decided to try the films with MOT lone but with n incresed concentrtion of MOT The films were found to be sensitive to both xrys nd electrons, lthough the sensitivity with respect to the first described system is somewht lower This system is much more stble thn the system contining iodoform. These films re lmost completely insensitive to light in the opticl region s shown in tests using. spectrophotometer s n irrdition source 18

22 The following system using MDT is the mot stis fctory system developed up to the present time, dye forming regent MDT 1 gm b, solvent myl cette 1 gm, plstic polystyrene 2 gm The thickness of the emulsions will depend on the mount nd nture of the solvent nd pistic nd on the method of drying The film preprtion is the sme s described in (B), 2, Alternte Fin1ly n lternte film preprtion technique hs been investigted, This method elimintes the necessity of drying out the solvents, nd llows control of the im purities dded to the system In this technique the MOT is dded to the monomer, The monomer is polymerized using either het or ctlytic gents, A solid solution of IVIOT in plstic block is then obtined, This technique hs been tried nd found successful with foming urthne plstics This plstic is not trnsprent so tht styrene nd methyl methcrylte monomer were tried, The following difficulties were encountered with these monomers, A strong drk 1 rection occurred due to the concentrtion of regents oxidtion by ct1yst nd oxidtion due to het, Most ctlytic gents contin peroxides which tend to oxidize the dye forming regent, One 9 ctlyst 9 bis-zoisobutyrlnitrite does not form peroxides nd thus will not oxidize the system upon If this polymeriztion 19

23 ctlyst cn be obtined this my prove to be the proper gent for polymeriztion mrfresu its And ictions A Results. Enlrgements of micrordiogrph of copper electron diffrction screens re shown in Fig 2 These enlrgements were mde from micrordiogrphs using the film prepred with the orgnic hlide Micrordiogrph hve lso been mde with the films contining MDT lone yielding similr results This ltter film shows greter stbility to hets, moisture The exposure times required to produce detectble nd light imges using collimted electron bems re from 3 minutes to one hour Exposure times to produce detectble imges using xry bems from n xry diffrction units copper trgets 3 PKV 15 m t bout 6 inches from the trget re lso bout 3 minutes to one hour These exposure times re bout of the sme order of mgnitude tht is required for the extremely fine grined silver hlide films such s the 548 spectroscopic films which re usully used in micrordlogrphy developed The films using T lone hve only recently been Therefore time hs not permitted us to investi gte quntittively the sensitivity of the films Tests were crried out for the films using both iocloform nd MDT Becuse of the instbility of the systems the results of this investigtion were rther meningless The opticl opcity 2

24 produced in the film by given irrdition is used s Knowing the rdition dose for mesure of sensitivity given irrdition the film sensitivity s function of dose cn be found by mesuring the opticl opcity using The films spectrophotometer for the vrious irrditions contining iodoform re sensitive to the light used in mesuring the opticl opciity thus the opticl opcity of the films chnged during these mesurements So the originl ttempt to mesure the film sensitivity ws perturbed by the method of detection Thesemesurements shouldbe ble to be performed with the new film contining the dye forming regent lone Boththe energy dependence nd dose dependence should be investigted B Appliction To Dosimetry And Irrdition Pttern Studies An ppliction of these rdition sensitive lyers is their use s dosimeters Investigtion could be crried out to mesure the film opcity s function of dose If liner reltion holds between opticl opcity nd dose nd if the reproducibility of the system is good enough this ppliction could be directly mde There is lso possibility of mking lrge plstic blocks contining T in solid solution with which dose ptterns could be mesured Upon irrdition these blocks will chnge color outlining the irrdition pttern in the plstic block Such blocks hve been mde but rther lrge 21

25 l!drk rection h occurred in their production Sti11 irrdition pttern hve been observed in the blocks fter exposure to collimted xry bems These ptterns re not too esily observed of courses becuse of the bckground but it is believed tht this drk rection cn be gretly reduced so tht its effect will be negligible 22

26 5 x l2 x 2x BOOx Fig. 2: Use of moleculrtdye Forming films for recording ptterns creted by electrons. Shown re 7 x, l2t. x, 2 x, nd 8 x opticl projection enlrgements mde with microscope. Imge is mde with 2 mesh electron microscope screen resting on Dye Forming film illuminted with collimted electron bem. No grin structure in originl imge is pprent. 23

27 ill NEW TECHNI TiES TESTED WITH INDEFiNITE OR NEGATIVE RESULTS in ny explortory progrm such s this one, there re mny experiments which end in filures For those with interest in this field, the following re presented so tht they my void our errors nd filures A Monomoleculr Silver Hlide Film Experiments. In n ttempt to develop sensitive silver hlide mteril fulfilling the requirements essentil to high resolution utordiogrphy, of l. extreme thinness 2. dense pcking of hlide grins efforts were mde to produce true monomoleculr lyers or monolyers of silver hlide (the word monolyer is here used in its strict sense, mening one molecule thick, rther thn in the sense of one reports of this project) thick, s in some previous The production of these lyers hs been studied f or mny yers nd the technique hs been described dequtely in the literture (see 3 for exmple, Blodgett(3) nd Sobotk( 4)). The principle of the method is to deposit minute quntity of ftty cid or other polr substnce on wter surfces The wter ttrcts the soclied hydrophiliccooh groups of the ftty cid molecules strongly enough to prevent their escpe from the wter surfce nd consequent evportion of the film but not strongly enough to cuse dissolution of the film in the wter substrte in these circumstnces the film 24

28 resembles two-dimensionl gs but if lterl pressure is pplied to it by suitble brriers; the intermoleculr distnce cn be mde less thn the rnge of the Inter moleculr forces nd the lyer of molecules then behves s twodimenionl liquid which resists compression troflglyq The compressed film cn be withdrwn from the wter surfce onto suitble metl plte; nd the mounted film then con slts of true monolyer with the smllest thickness nd densest pcking possible Metllic Ions cn be incorported into these films by floting the ftty cid on substrte consisting of wter dulterted with slt of the desired metl If the ph of the substrte is properly djusted; the hydrophilic heds of the ftty cid molecules; protruding little below the wter surfce; combine with free ctions which remin ttched to the cid molecules during subsequent withdrwl of the film from the liquid surfce In this wy monolyer consisting of metllic slt of ftty cid my be built Ue Chemicl tretment of the monolyer cn be undertken to limited extent nd in certin cir cumstnces the long-chin group cn be replced by hlogen or other toms In the present experiments; it ws proposed to form film of steric cid on substrte contining silver The resulting film of silver sterte molecules would; ion fter removl on chromed plte; s described by Sobotk( 4) 25

29 nd others, be converted to silver hlide by tretment with chemicl solutions or by direct exposure to hlide vpor. The difficulty of this scheme is tht some kind of crystlline structure is necessry to imprt photogrphic sensitivity to the lyer However, by depositing multilyer of twenty or thirty superimposed lyers, film with regulr structure cn be mde, nd it is resonble to ssume tht it would exhibit photogrphic sensitivity, This view is supported by the work of Bikermnn(5), Astbury t nd Stenhgen(), which ttributes qusi-crystlline structure to multi-lyers of vrious kinds, nd by Fnkuchen( 8) nd Bikermnn nd Schulmn(9), who observed x-ry diffrction ptterns comptible with the existence of micro-crystls in the lyers The films were mde by dissolving some steric cid in tiny drop of benzene nd depositing it lfl the center of loop of wxed thred floting on the liquid surfce, Com pression of the film which remined fter evportion of the benzene ws chieved by depositing nother benzene drop, contining oleic cid, in the spce between the thred nd the wlls of the continer (Fig. 3), The oleic cid cts s piston oil becuse of its higher surfce pressure, nd compresses the loop nd its contined film until the sterte lyer ssumes it condensed form The film is removed from the substrte by inserting smll chrome plted plte verticlly in the liquid nd withdrwing it slowly. The 26

30 Metl which removed plte film is on thred oleic cid here steric cid here substrte contining silver ion Fig. 5: Arrngement for forming monolyers. () (b) Fig. i-i-: Showing pprent improvement in resolution when the geltin concentrtion in the utordiogrphic emul dissolving. Undissolved t (), dissolved t (b). sion is reduced by 1-llbelled Chiorell. The emulsion test-object is C-l 27

31 film ttches itself to the plte nd ny number of lyers cn be plced on top of ech other by moving the plte up nd down slowly The progress of the opertion cn be followed by noting the diminution in re of the wxed 1oop The wter ws 1 N in AgNO 3 nd ws buffered t ph of 8,,, The silver sterte lyer ws successfully withdrwn nd ws converted to hlide by exposure to the vpors of iodine nd bromine After exposure to light the films were developed nd fixed with Dl9 nd F 6 but without ny blckening being pprent under the microscope. A remrkble feture ws the extreme resistnce of the films to these mnipultions, in shrp distinction to commercil emulsions which re sometimes severely dmged in processing. This gret strength is not gined t the expense of permnent ttchment to the mounting p1te, for removl is esily effected by lowering the plte gently into dilute H2S 4 when the film flots off the plte. If such removl were not possible it is difficult to envisge ny lrge scle ppliction to uto rdiogrphy since the dvntge of extreme thinness would be offset by the difficulty of chieving intimte contct between biologicl specimen nd p1temounted emulsion, Filure to observe response to light could be due to 1. Absence of crystlline structure in the lyers; 2 Presence of ion other thn Ag in the substrte. This is known to hve profound effect on the nture of the resultnt film, 28

32 3 Insufficient ttention to clenliness Mny of the precutions (triplydistilled wters sterte coted dishes etc ) dvised by the stndrd texts. were not observed - nd indeed would render routine preprtion of the films in the drk n excting process The possible effects on the chrcter of the films were not investi gted Though the preliminry experiments met with no success the method should be investigted further s it offers the utlimte in thinness nd dense pcking The points which re uncertin re the existence of sufficient crystlline structure to imprt sensitivity nd the possibility of ctstrophic spred of whtever photogrphic effects occur through n essentilly continuous lyer of hlide The hndling properties of the films re very ttrctive feture, B Distse Experiments Though it is reltively simple mtter to obtins by the techniques developed in this project. silver hlide lyer of lmost vnishing thickness it is considerbly more difficult to rrnge sufficiently dense pcking of grins within the lyer. Experiments crried out by Corner nd Skipper() suggested the following pproch. Estmn Kodk Permeble-Bse Stripping Flrn (experi mentl) with sensitive lyer of 5)thick ws mounted 29

33 emulsion side downwrds on 3 x 1 glss slides which hd been subbed in solution contining 25 gr geltin nd 25 gr chromelum in 5 ml wter t 2l C The sections to be utordiogrphed hd been previously mounted on these slides The films were llowed to dry thoroughly nd were then immersed for 4 minutes in freshly mde queous solution of the enzyme distse (2 gr commercil distse trde nme Tk-distse in 3 ml wter) After dissolving the pltes were immersed in distilled wter for 5 minutes nd were llowed to dry thoroughly They were then stored in the drk for time pproprite to the rdioctive properties of the object being utordlogrphed 3 fter which they were processed in the usul wy (1 minute undiluted D-l9 1 minute wsh 1 minutes ll t l8 c) full-strength F-6 2 minutes wsh; The enzyme solution dissolves some of the geltin in which the hlide grins re suspended nd s result the uppermost grins settle downwrds nd film of diminished thickness nd greter grin-density is produced The dis solving technique ws used by Corner nd Skipper to mke film thin enough to be exmined in the electron microscope The work of these uthors ws concerned with the detection of -prticles emitted by minerl grins embedded in the emulsion nd the ttinment of dequte resolution ws therefore not serious problems since the most intimte contct possible between emulsion nd specimen ws lwys 3

34 mintined Further 4, the origin of the-prticies could be determined to high order of ccurcy by trcing bck the chrcteristiclly stright nd dense trcks In the present experiments 4, 4, however where one is in the min concerned with emitters concentrted in tissue sections mounted outside the sensitive lyer 4, reducing the geltin content should improve the resolution not only by reducing the film thickness 4, but lso 4, importntly 4, by reducing the men grin spcing; f or the sme number of grins s before will be present in the diminished emulsion volume remining fter dissolution The incresed grin-density my be expected to ffect the resolution by 1 incresing-trck recognisbility ( jective entity) in trck utordiogrphy; or 2 in contrst utordiogrphy 4, by incresing the interction probbility in the vicinity of the source Among the possible dvntges of this technique re the fct tht it employs redymde grins whose dequcy in detecting 4, s trcks 4, -prticles with energies up to 15 kev# is well known 4, nd renders unnecessry the complex processes of ripening 4, etc Considerble difficulty ws experienced In crrying out the experiments nd in interpreting the results: 1 In the beginning the slides were coted with * But see comment on Pge 38 31

35 solution of prlodion in methy1ethyl-ketone (MEK) since Corner nd Skipper hd indicted tht n impermeble bselyer of some kind ws vluble if the film ws to be removed lter from the mounting plte for electron microscope exmin TheprlodionM tion EK coting hd to be bndoned eventully in fvor of the subbing solution mentioned bove s the sticking qulities of the film were very poor unless the composition nd thickness of the prlodionm E.K coting were crefully controlled Eventhe conventionl subbing method ws sometimes unrelible but it is interesting to note tht films which hd been dissolved survived processing better thn the undissolved ones This ws presumbly becuse the geltin bonded firmly onto the glss slide when reduced to tcky stte by the dissolving gent The presence of 5pgeltin bcking on the permeble-bse stripping film is disdvntgeous in dissolving experiments since greter volume of geltin must be removed in order to obtin the given totl film thickness. As we shll sees the prolonged immersion necessry to remove lrge volume of geltin hs undesirble effects on the strength nd uniformity of the resulting films, nd bcking less thn thick would therefore be usefui though it would undoubtedly mke routine hndling more difficult 2 The concentrtion of the enzyme bth is im If too little distse is present the quntity of portnt geltin removed is inpprecible, 9 while if the dissolving 32

36 process is too vigorous film of uneven thickness results 3 s shown by the ptchy bckground density in films which were first processed nd then dissolved in very concentrted enzyme solution Experiments showed tht the Q7 (pproxi mtely) by weight concentrtion finlly chosen gve thinning effect redily pprecited by the nked eye 3 without dversely ffecting the uniformity of the film or its mechnicl strength during processing Unfortuntely the optimumcon centrtion depends on the type of emulsion employed nd on its ges. Thus 9 British Kodk AR1O stripping-plte emulsion needed only one-hlf the dissolving time* of the Estmn Kodk film 9 presumbly becuse different geltin is used Now chnges in the geltin re usully ccompnied by chnges in the photogrphic sensitivity, nd since the pprent resolution is dependent on the sensitivity 3 t constnt 9 both the exposure time nd the enzyme concentrtion exposure must be chnged for ech emulsion type 6 There ws some evidence tht these djustments re necessry for different btches of the sme emulsion if they hve been mnufctured on different dtes or stored for vrying lengths of time 3 It is very importnt tht ll slides remin in horizontl position during the dissolving 3 rinsing nd drying processes Otherwise the finl film is very uneven nd my contin voids where the emulsion hs run off the edge of the plte, In the present work the slides were mounted on *though its bcking is loy thick 33

37 glss rck with shelf-like supports which ws lowered rid rised gently y hnd but in more elborte experiments screw mechnism for lowering the rigidlyheld slides into the regent bths would be helpful 4 The test-object used in these experiments ws the plnt Chlorell pyroidos lbeled with C-l4 supplied t n ctivity of 2c/mg through the courtesy of Nucler- Chicgo Corportion In order to mke this rther tenuous orgnism visible it ws prestined with eosin This led to confusing rtifct which ws not recognised s such in the beginning nd whose cuse therefore escped detection for some considerble time It ws esily estblished fterwrds tht the eosin stining must be crried out fter ll processing is completed 5 Erly experiments concerned with the possible effects of dissolving on photogrphic sensitivity were confused by inttention to the vrible swelling of stripping film when floted on wter The bckgroundgrin-density of control films processed fter dissolving ws compred with tht of similr films dissolved fter processing in the hope of detecting ny decresed sensitivity or greter fogging ttributble to the dissolving process The results were vitited by the fct tht the degree of swelling nd hence the bckground density depend on the wter tempertures the floting times nd the drying conditions Inneffort to stndrdizes, ll films were therefter floted for four 34

38 minutes (if possible - occsionlly film sinks) before mountings, but we believe tht there is still vrition in the degree of swelling 8 6 The results obtined with Estmn Kodk Stripping Film were difficult to interpret stisfctorily though there ws n pprent Improvement in resolution (Fig., 4) The principl difficulty ws the high bckground which mde suspect ny estimte not bsed on grincounts., An effort ws mde to obvite this difficulty by using the erdiction techniques fmilir in nucler emulsion work 8 Attempts to erdicte 5,JI emulsions by heting in moist tmosphere resulted either in n pprently permnent loss of sensitivity or in melted emulsion., Finlly Albouy nd Frggis scheme of exposure to the vpor of 4 hydrogen peroxide ws resorted to., At first erdiction ws crried out when the emulsion hd dried t the end of the mounting process but it ws still difficult to drw ny conclusions bout the difference in resolution between dissolved nd undissolved films f or though the bckground ws undoubtedly reduced it ws not entirely removed., In films contining no rdio ctive chlorell 3 however erdiction ws complete nd it therefore ppered likely tht some t lest of the bckground ws cused by movement during the dissolving process of grins exposed in the drying period following mounting In lter work erdiction ws crried out when the mounting nd dissolving opertions were complete Roughly 24hours fter 35

39 removl from the peroxide vpor the films ppered to recover their norml speed nd this time ws therefore dded to the exposure periods which with unerdicted emulsions nd the chlorell SctIvity uoted here ws bout 48 hours 7 Experiments long these lines were bndoned for two resons: A film (described previously) of vstly superior resolution hd been mde b Chlorell is n unstisfctory test-object for work of this kind Its min disdvntge is Its considerble dimeter ( 2p.) which is greter thn the thickness of the dis solved films As result the treted films present lumpy surfce to the viewers ech lump corresponding with group of orgnisms over which the film is snugly drped (Fig 5) The exposed grins immeditely bove the chlorell re therefore in plne different from those in the min body of the film Now the depth of focus of the objective used (95 x9 NA l3) is less (i/j) thn the chiorell dimeter nd n objective focused t level A in Fig 3 sees lrge number of grins directly over the chloreli nd very few in the interstices; n objective focused t level B on the other hnd sees 36

40 Viewer Level Level B. Autordiogrphic emulsion Chiorell () (b) (c) Fig. 5: Effect of finite object thickness on pprent very thin emulsions. resolution in () (b) (c) Cross section (not to scle) showing how the emulsion presents lumpy surfce to n observer viewing from bove. Typicl ppernce when the microscope is focussed t level A in Fig. 5 (). Typicl ppernce when the microscope is focussed t level B in Fig. 5 (). it 57

41 the interspces dotted with grins The true resolution could therefore be determined only t lrge depths of focus which in prctice excludes high-power exmin tion CO Continuous Medi The possibility of individul prticle detection using continuous nonsilver medium ws investigted con currently with the experiments reported bove One of the principl dvntges of silver systems is the existence of multiplictive effect tending to enhnce the primry photogrphic event., No mplifiction ws nticipted in ny of the systems described below nd the dvntges expected to ccrue from their use must there f ore be gret in order to outweigh the serious drwbck of non-multipliction The single dvntge of continuous medium is tht it is potentilly sensitive long the entire trck of -prticle rther thn t intervls of the order of the grin-spcing There is therefore possibility tht the entire pth, however. tortuous my be rendered visible s trcks circumstnce leding to n extreme resolution which offsets the bsence of multipliction It lso lowers the contrst requirements since continuous trck 15 visible ginst denser bckground thn is the cse for trck composed of isolted grins (We my here remrk tht fter considerble work with -14 p-prticles using Estmn Kodk 38

42 emulsions consulttion of published informtion(1 3) gve rise to serious doubt bout the sensitivity of the films to electrons with energies bove 8 key If s suspected the emulsion will not record such prticles s treks then frction of the Cl4prticles cnnot be detected t ll* in the vicinity of the emitting toms, where in the interests of resolution high sensitivity is needed Correspondencewiththemnu fcturers did not dispel this doubt nd BritLh Kodk AR1O emulsion ws used subsequently AR1O emulsion is known to record -prticles of ll energies s trcks The first chemicl system tried ws the clssicl ferrous-ferric dosimeter incorported in solidified l queous solution of geltin Though the oxidtion yield is extremely smll the quntity of ferric ion formed during the pssge of (sy) single ThB-prticle is lrge enough to be microscopiclly visible () if it is suitbly compounded nd (b) if it is loclized long the trck of the prticles An inert mteril cn be incorported in the ferrous-geltin lyer to increse the stopping power nd thus improve the chnces of visulizing the trck The pltes were exposed toot- nd p-prticles nd to 2 KV x-rys Theywere then differentited with potssium ferrocynide which gives rection with ferric but not with ferrous ion Oxidtion by tmospheric oxygen prevented stisfctory evlution of the experiments 5, nd the sme difficulty ws encountered in * Unless the contrst is extremely high 39

43 FeSO-geltin system employing 2-pentne-dione s complexing gent for Fe 3 ion,, No complex is formed when the iron is in the reduced sttes while the ferric complex is of high moleculr weight nd deeply colored Both systems might hve been successful in n inert tmospheres but this would mke routine use difficult nd it ws not ttempted Compounds exhibiting steric hindrnce were then investigted the supposition being tht n tom which is prohibited by its size from remining t the norml seprtion from its neighbors in the molecule is correspondingly wekly bound nd therefore more vulnerble to dislodgment by rdi tion The compounds tried were bromoform nd iodoform nd It ws proposed to use the leucobse of prphenylenedimine (PP,D ) to detect the hlogen set free from them by rdition The bromoform system ws mde by dissolving P6P.D in bromo form nd incorporting the solution in queous geltin with ddition of myl lcohol for stbiliztion of the emulsion The queous geltin ws omitted in the iodoform system nd re plced by myl cette No sensitivity to prticulte or xrdition ws observed A system using stoichimetric quntities of sodium iodide nd iodte with PPD ws lso unsuccessful s trck detector in the solid form Similr negtive results were obtined with solutions of photogrphicthypo in Deposition of sulphur linked to themolecule by geltin vulnerble double bond ws expected but not observed The 4

44 mercuriochloride mmonium oxlte system lso filed s did ttempts to produce the chioroform-bromoresol green system in solid form Lstly the light-sensitive dizosystem of Alnk 9 Kennig nd oippei(14) ws tried in some detil using the double slt p-diethylminobenzene - dizonium chloride - pphi by Antr Chemicls of New York response ws elicited nd Dr No rdition Dippel lter confirmed tht he hd hd similr experience with ionizing rditions.. Geltin Bichromte Films These films were mnufctured by using 5% geltin in wter with smll mount of mmonium bichromte. Slides were dipped in this solution nd llowed to dry slowly These films were exposed to slit of light nd then developed by rinsing in wrm wter The geltin wshed off the slides except for the re which hd been exposed to light The results were nice nd clen nd there ws bsolutely no bckground 9 However the systems smybe expected is not very sensitive It took 5-1 minutes exposure to light to give relly shrp results Exposures of only l2 minutes could be seen on the geltins but would dispper with development no mtter how little development ws used. Also when exposed to x-ry this film showed only suggestion of n utordiogrph - relly shrp grin ws never obtined. The system ws not pursued further 4].

45 BIBLIOGRAPHY N, Plkin et l; Micrordiogrphic Study of Action of Flottion Agents Trnsctions of the Institution of Mining nd Metllurgy 9 Prt I (l ), (A report on work in Russi published in Englnd.) 2. Gomberg 3 H. J. nd Grsou 3 J,; Studies With An X-Ry Monochromter University of Michign AEC AT(l1l)-434 (1958). 3 Finl Report 3 Blodgett; J. Amer. Chem. Soc (1935). 4, Sobotk; Article on Monomoleculr Films in Glsers Medicl Physics. 11 5, Bikermnn; Proc. Roy. Soc (l939) 6. Astbury 3 Bell 3 Gorter 3 vn Orrnondt; Nture (1938). 7. Stenhgen; Trns. Frdy Soc (1938), 8, Fnkuchen; Phys. Rev, (1938), 9 Bikermnn nd Schulmn; Phys. Rev, (1938). 1 Corner nd Skipper; Science (1954). 11, Albouy nd Frggi; Rev, Sci, Instr, 12. Stevens; Photogrphic Journ, Brit, J, Rdiol, (1952) lll3 (1944); O9195O)O 13. According to the Estmn Kodk circulr on utordiogrphic nd nucler emulsions the sensitivity of EK experimentl permeb1ebse stripping film is between tht of EK nd NTB emulsions. According to Tble 14 (p. 73) of Boyd s Autordiogrphy (Acdemic Press 3 New York NTA ) the stripping film could not therefore register electrons bove 8 key s trcks, 14, Alink 3 Kennig nd Dippel; Philips Techn, Rev, (l94 rl948),

46 APPENDIX I Publictions By Prticipnts In Study Of High Resolution Detection Of Rdition 1 Wet Process Autordiogrphy Report COO Henry J Gomberg 49 (1951) Februry ABC 2 Wet Process Autordiogrphy (Abstrct) 83, No Rev 6 H J Gomberg 4 (1951) August, Pge A New HighReso1ution System of Autordiogrphy Henry J Gomberg, Nucleonics9, 2843 (1951) October 4, High Resolution Detection of Rdition AEC Report AECU 2485, Jnury 1952, Henry J. Gomberg 5 High Resolution Detection of Rdition ABC Jnury l953 Report Henry J Gomberg, 6 High Resolution Autordiogrphy in Metllurgy H J, Gomberg et l, Project 229, Interim Report, Engineering Reserch Institute Februry, ,. Theoreticl Aspects of Autordiogrphy Conference on Autordiogrphy Proceedings - Ok Ridge Institute for Nucler Studies. June, i953 8 HighReso1ution Detection of Rdition ABC Report, Jnury 1954 Henry J Gomberg 9 A BetRy Microscope, Willim Kerr nd Henry J Gomberg. Science 119, No 38, (1954) Jnury 1O High-Resolution Autordiogrphy for Study of Grin Boundries in Metls F, Engineering Reserch Institute, Februry, 1954, H J, Gomberg et 1 Project 11 High Resolution Autordiogrphy George C Towe, Henry J Gomberg, nd J W Freemn. Ntionl Advisory Committee For Aeronutics Technicl Note 329 July, l High Resolution Loction of Rdiolsotopes -- The Bet-Ry Willim Kerr nd H J Gomberg Microscope Pper No, , delivered t the First Interntionl Instrument Congress nd Exposition of the Instrument Society of Americ, Sept, 13-23, 1954, Phildelphi, Pennsylvni 43

47 APPENDIX I (continued) 13 An Autordiogrphic Study of Sintered Tungsten Crbide- Nickel Compcts Yukw H J Gomberg M J Sinnott nd S Project 22O4-4-F EngineeringReserchInstitute For Crboloy Deprtment of Generl Electric Compny November l4 WetProcess Autordiogrphy Modified for Studying Metls George C Towers Henry J Gomberg nd J W, Freemn Nucleonics l3, No 1,, (19555 Jnury i5 High Resolution Rdition Detectors in Reserch Gomberg H J Pper presented t Genev Conference on Peceful Uses of Atomic Energy P/159 August (1955) i6 Autordiogrphy s Testing Technique Schlesinger 9 Jr for Testing Mterils 9 nd Henry J Gomberg Milton J. AmericnSociety l7 The Use of Dye Forming Films in Micrordiogrphy nd Autordiogrphy J L, Trombk Gomberg 3 J Grsou nd H J Delivered t the Americn Nucler Society Meeting 9 October 283l Henry Hudson Hotel 9 New York York 3 New l8 Studies of the Response of Orgnic Solid nd Liquid Solutions to Monochromtic X nd T Rys Doctorl Disserttion 3 University of Liege J Grsou 3 Belgium 44