Kaul, O N

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ROLE PLAYED BY AMMONIUM SALTS IN THE CLEARING OF NUCLEAR EMULSIONS0. N. KAULSaha I nstitute of N uclear Physics, Calcutta-9.{Received March 14, 1961)ABSTRACT. The offeot of tlio addition of variouK anmionium salts hiinmoniurn chlo­ride, ainmoiiium sidplmte, and aminoninin acetate) to the usual hypo solution on the clearing time or nuclear oniulsionH and also their inhiioncc on the c:rain size and the shrinkage factor, have biHUi investigated in  view of some' (unitradietory rt 'su lts reported by various authors in recent years. 'F Ik - addition of th<‘ atnmoniinn salts has bof'ii found to cause a decrease in the ch'nring tiiin*, and then a slight incrtui.se, afU'r attainment of the o jitiinum  concentration. The addition of ammonium salts, ho\veV(*r, has been found to have no eftcct on the grain size or tlie shrinkage factor of nuclear emulsions. Hesults obtained have also betm I'xplained on the basis of th(' current theory.Thick emulsions netjessitate longer clearing times, and this prolonged fixation leads to severe distortions in nuclear emulsions. As such, the metliods for decreas­ing the clearing time have been studied by various authors, and it has been found that the addition of ammonium salts to hypo decreases the fixation time consider­ably, because the ammonium salts of hypo arc better complex forming salts with silver halides than the sodium salts of hypo.(NH,),^,032NHiCl+Na.S203 i  H-2NaClAmmonium salt of hypoPiper worked on this problem, and investigated the change in the clear­ing time of thin plates with a change in the concentration of ammonium salts. He reported a fall in the clearing time with an increase in the concentration of the ammonium salt, till an optimum concentration is attained, after which, the clear­ing time has been reported to increase again. Also, according to him the <  < Cl> >  ion in ammonium chloride is responsible for eating up the developed grains, near the surface of the emulsion.Prakash et ah (1958) reported a contradiction to the observations made by Piper. According to them, the clearing time decreases up to an optimum concentration of the ammonium salt, after which it remains more or less constant, and does not have an appreciable rise as reported by Piper.In view of the above contradictions the author found it useful to take up some work in this direction. The observations and the results thus arrived at are reported in this paper.62662E X P E R T  M E N T  A L P K  () E  D U R EThe ammonium salts sdcrted were ammonium ohlori.le. ammonium ac-etato and ammonium sulphate. The first salt was sel.-etod. beeause in ail.lition to am- momum thiosulphate the chlorine ion eoncnitration affects the diffusion rate of t^e fixer, and therefore, may suppress the reaction and also because it offers a direct verification of the observations made by Piper and those due to Prakash et al. Ammonium sulphate an.l acetate were sele.-ted so as to st.nly the effect due of any other two suitable ammonium .salts, not tried so far.For this work Ilford K.^  plates of loo, 200, atul 400 microns, and also K„ and Gj plates of 200 micron thickiu>ss were used, so as to study the effect on the clearing time by a change in the thickness and type of the emulsion. Further, the experi- luonts were (jondiicted in the following stugos :1) Effect of the idiange in the concentration of aiuinoniiim cldoride on the clearing time of Ilford 100 micron jilatcs Kjand was studied, using different concentrations of hypo. Jdates wore directly put in the fixing solution maintained at 17 C. Care was taken to see that the level of the fixing solution is same in all the three cases. The results arc plotted as shown in Fig. J.Role Played by Amnionivm Salts in the Clearing, etc. f>63Uig. 1. T h o perctm trgo rnnonntration  o f  N H 4r i  against tho clearing tiint* in niimitt r fo r  different con coritration s o f  h y p o  fo r  100 p lates Ko & Or, (lom p ora luro 17°0).The curves show^  a fall upto an optimurYi value of concentration, and then a rise, although the rise is not as pronounced as reported by Piper. Moreover, a shift in the position of optimum concentration was oliserved wdth a (change in the hypo concentration, as shown in Fig. 1. (Change in the type of emulsion, how­ever, has been found to have no effect on the clearing time of the emulsion.2) Secondly, the change in the clearing time of Kg and 200 micron plates with a change in the concentration of the three ammonium salts was studied. A564 0» N . Knulfall, and then a rise has been observed in the ease of all the three curves, for am- moniiim chluride, ammonium sulphate and ammonium acetate. The rise is more pronouru^od in the case of ammoniiini chloride than in the case of other two am­monium salts. Results, which have further heen found to be independent of tlie type of emulsion used, are represented in Fig. 2.Fig. 2. PorcontagfJ oonoonl.ration o f \ arioiiH Hinmomnin salts (‘louring t iino in mimitos for 200 TIford Ko & Ko plat. K tempf'raiurt* during rltviring 17^ 'C hypo concen­tration in f'Hcli solution 40%3) Thirdly, the effect of the emulsion thickness over the percentage reduction in the clearing time was investigated in the case of plates for all the threeammonium slats. The eurvos weu’e found to have a fall up to 200 rni(*rons in all the cases excepting for ammonium chloride where the fall persists beyond 200 microns. These results are plotted as shown in Fig. 3.UF S UT . T P  a n d  D T S C U S S T O NTlie results may be discussed in light of the three stages of observations men­tioned above.1. The rise and fall of curves shown in Fig. 1 can be accounted for as follows :Ammonium salts of hypo being bettor complex forming salts with silver halides, as compared to sodium salts o f hypo, any increase in the concentration of the ammonium salts should dee.reaso the clearing time.2NH4Cl +Na2SA (NH4)A0a+2Naa(NH4),[Ag(S203)3lComplex formation |3 (NH4)2S203+AgBr i  + N H 4BrAg complexHole Played by Ammonium Salts in the Clearing, etc. 665The optimum concentration can he explained on the basis of the reversible nature of the reaction, and so also the shift in the position of the optimum \vith respect to different hypo concentrations. Th(^  rise in the curves may be explained as being due to the fact that higher complexes of ammonium thiosulphate and silver halides are unstable as com})ared to the higher complexes of sodium thios\ilphat(\ and silver halides. The clearing time, liow ev er. is independent of the type of tlie emulsion as is expected.T h iok iirm  o f  fcho oinimilHion in /^m 3. E m u ls ion  Uiiekno-is V s %  n otion  in tho i loarin^r tiim*.2) A fall, and then a rise in the curves is obtaimMl in case ol all the three ammonical salts, as is (‘xplained on the basis of th(‘ explanations given above. The more pronounced rise observed in the case of ammonium chloiide can be explained as being due to the prcseTiee of <  <Gb > >  ion which effects the rate of diffusion, as chlorine harden the gelatine of the emulsion, thereby increasing the clearing time by effecting th»' difhision rate. As this iactoi is al)sent in the case of other two ammonium salt s, the rise is imt as jironounecd in their ease,3 ) The percentage fall goes oir decreasing in the ease of higher thicknesses for NH4CI, whereas f(>r other salts it remains constant after 200 microns. The reason for this is that upto 200 microns the diffnsioti velocity of the hxing solution decreases with an increase in the thickness, and hence a fall in the curve. In case o f ammonium chloride this effect persists beyond 200 microns, because of the contribution of the < < 0 1  >  > ion, which, however, is not the case with other ammonium salts. Also, the diffusion velocity becomes independent of emulsion thickness beyond 200/nn. which explains the flatness o f the cuiwos beyond 200/tm.Effect on the shrinkage factor and the, gram size:Effect on the grain size was investigated so as to find out whether or not the chlorine eats away the dcvelopefl grains at the surface as reported by Piper.566 0 . tV. KaulFor this, the grain size at the top and the bottom of the plate was found in case of pure hypo, and hypo with each of the other ammonium salts. (The optimum concentration being used in each case). The plates o f the same type wei e simul­taneously put in the four different baths and the fixing carried out undei* the same experimental conditions. The observations regarding the shrinkage factor and the grain size are shown in Tables I and IITABLE 1Observations regarding the shrinkage factorP la to  th io .kn oss P u r o  b y p o  in li\u1002004002.0f>2.r>()2.7.->vSliriiikaj^ t* faotorHy, )() witL <)])tiinum oonoonl ration of*NHi (1 N1UCJ)H^2 . 10 2.00  2 .5 02 .0 52 .42 .5 02 .0 4  2 72 2 .7 5TABLE IIObservations regarding the grain sizeG ra inThioKnnsso f  tlu' plateS m ’fac(‘of Fro(' lfy|><> liav in ,; opiimum conocntmtion ofm f im (‘mill,Sion hyj)o ( N H 4 ) . S 0 ,luo Hottoni 0 5 0.75 0.5 (t.5Top 0.5 0,50 0.5 0.52(W) Mot tom 0.75 0.75 0.5 (K75Top 0.75 0.75 0 75 {) 754nn Mott-oiii 0.5 0.75 0.5 0.50T o p (1.75 (K 75 0.75 0.50The study of the shrinkage factor, and the grain size reveals that within the allowed statistics, the shrinkage and the grain size is in no way affeeded by the addition of the ammonium salts. It also contradicts the hypothesis that chlorine is responsible for eating away the emulsion at the surface. The optimum concen­tration of the various ammonium salts used by the author are 1.5% for ammo­nium chloride, 2.5% for ammonium sulphate and 2.5% for amonium acetate. Relative study of the suitability o f these salts as regards the clearing o f thick plates :For thick plates the clearing time depends predominantly upon the diffusion velocity of the fixing solution, as against the thin plates. Consequently thenpH value o f the fixing ablution becomes an important factor. To make a relative study of the usefulness o f these salts as regards the (ilearing of thick ])lates, pH values o f the various concentrations o f these solutions Mere calculated by the usual formulae, Vogel (19.58). The results are .sho^ vn in Table TTI;TABLE IIIObservations regarding clearing timeUoU Played by Ammonium Salts in the Clearing, etc. 667Corie. o famm. salt %  .5 1.0 1.5 2.0 2.5 8.n 8.5 4.0pH-or(NlT4)o SOi- (optm. conc.) -!- hypo (40%) r).8 r>.() 5. S 0.2 5.7 5.0 5.8 5.0pH  ofNHiCoOuH.r (optni, oone.)-j- 0.8 hypo (40%)().8 0.0 0.0 7.4 7.S 7.0 S.lp H -o fN H 4 n  (optrn oonf.)-I 0.1 hypo (40%)0.5 0.7 O.K 0.2 5.7 5.1 5.2The table clearly shows (liat the })H value of liy])o f ainm. .sulphate and also hypo+aniTii. chlorkle .solution is mcII vithiii the zeid region, thus ensuring a high diffusion velocity, and the ])H value ofamm. acetate being in Hk; basic region, it does not have a high diffusion velocity, 'rhercforc, amm. acetate | hypo is not as suitable for clearing as the other two salts. Amin, suljihate. however, has been found to be most' suitable, for t his ]uirpose.A C K N O W L E I) (; M E N T SThe author is grateful to Prof. B. 1). Nagchaudhiiri, Director o f the Institute, for his encouragement and guidance.Thanks are also due to Prof. D. N. Kundu, head of the Accch'm/or DmsMm for providing the laboratory facilities and to Mr. Muiiesli Puikayastha, Head of the Nuclear Chemislry Divimm, for many helpful discussions.R E F E K E N C E SPiper, “ Funelftmontals of PhotoKi-npliic TJiooiy” , ji. .''.2S.Prakash, Y., Ahmad, N., and Slianna, A. 1'.. 10.58, N uom  Crmrlo 8, 717.Vogol, A. 1., 10.78, ‘ ‘A  Text Book of Quantitiitivc Inorganic .Annlysis.”

Role Played by Ammonium Salts in the Clearing of Nuclear Emulsions

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Role Played by Ammonium Salts in the Clearing of Nuclear Emulsions

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