THE STATUS OF THE SCINTILLATION CHAMBER

MartinUniversityAnn Arbor,

Summary

Several successful experiments car-ried out with the scintillation chamber aresummarized to show what can be done withthe systems which can be built now. Therehave been no developments in scintillationchamber components in the last year whichallow radical improvements of these presentsystems. Many of the high energy nuclearexperiments envisaged for the scintilla-tion chamber can be done better with sparkchambers. As a result of these two fac-tors, there are only a few areas where ascintillation chamber is now the best in-strument to use. Examples of such areasare space physics experiments, high energybeam imaging, high energy gamma ray detec-tion and particle decays.

The scintillation chamber has apeculiar status today. It is now a work-ing and useful device. This is demonstra-ted by a number of experiments which havebeen performed using it; these experimentsI will list later. Yet its use is notwidespread, and some of its developers,such as myself, are using another technique,the spark chamber, for some of their pres-ent experiments. In fact in describingthe status of the scintillation chamber,its usefulness in relation to the sparkchamber must be considered, and the firstpart of my talk will do just that. Thenbefore briefly describing experimentswhich have used the scintillation chamber,I will describe those experimental areaswhere the luminescent chamber remains use-ful. Finally I will mention a few devel-opments in the technique.

The interest of the high energy nuc-lear physicist in the scintillation cham-ber is based upon the need for a trackvisualization device with microsecond timeresolution and which allows counter prese-lection of the events to be photographed.Since the spark chamber has these prop-erties it is also of interest. But thespark chamber has some additional prop-erties which have led to its use or toplans for its use being much greater thanfor the scintillation chamber. In ourhigh-energy work the most valuable prop-erty of the spark chamber is that it canbe made much larger than the scintillation

L. Perlof MichiganMichigan

chamber. This enables larger solid anglesto be covered, larger liquid hydrogen tar-gets to be used, and greater angular ac-curacy to be achieved. The last effectcomes only from the greater size becauseboth instruments have spatial resolutionsof about 1 mm. A second valuable propertyin some experiments is that the spark cham-ber can be made with very low average den-sity. Other reasons which have beengiven for the greater usefulness of thespark chamber compared to the scintill-ation chamber are that the former iseasier to build and more reliable in op-eration and that the latter is more expen-sive because of the image tubes. I havenot found these other reasons to be ofultimate importance, although they cer-tainly are influencing choices of exper-imental methods at present. I believethat most high energy nuclear experimentswhich can make use of a fast track vis-ualization device, will use the sparkchamber, and they will use it primarilybecause it can be built so large. Isthere then an area left in high energynuclear physics where the scintillationchamber is more useful than the sparkchamber? I believe that there is; andthis area includes those experiments wherethe sensitivity of the scintillation cham-ber to ionization, its ability to measureranges well, its ability to provide ahigh density medium with continuous spa-tial sensitivity are needed, and wherethe volume need not be large. Such ex-periments as the study of rare decay modes,or where it is necessary to detect highenergy gamma with close to 100% efficiencyare examples. Let me give you an examplewith respect to the range question. Re-cently I was considering an experiment inwhich I wanted to measure the energy of20 to 160 Mev protons by their range in alead plate spark ch4mber and I wanted toget a precision of -5 Mev. Now a 10 Mevproton will stop in .33gr/cm2 of lead.But a 160 Mev proton has a range of36gr/cm2 of lead. Therefore to do this Iwould have needed 110 lead plates, which,using 1 cm spacing, is a chamber 1.1 meterslong. Now in a recent experiment Peck,Jones and myself did just this kind ofmeasurement in a four inch thick sodium

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iodide luminescent chamber. I would haveused the luminescent chamber again, exceptthat the experiment is on a large scaleand we can't at present make a chamber bigenough. I think the trend of my thoughtis clear. The status of the scintillationchamber in high energy nuclear physics isthat it is a working device with uniqueproperties; its use will never be wide-spread as is the use of the bubble chamberand no doubt will also be the use of thespark chamber; but physics has been donewith it and I believe much more will bedone.

Now what about the status of thescintillation chamber outside of highenergy nuclear experiments? First let memention its use as a method of seeing theshape of and local intensity variationsacross a low intensity, high energy,charged particle beam. A bundle of para-llel scintillation filaments is placedagainst the photocathode of a large dia-meter image tube, with the axis of thecharged particle beam paralled to the fila-ments. This instrument in its simplestform, using a Westinghouse 5 in. diametersingle stage image tube and 4 in. long,1 mm. diameter plastic scintillator fila-ments, was first described by Jones andmyself.1 We also described its use in highenergy X radiography. The instrument hasbeen further developed by us2, but the mostbeautiful demonstration has been given byReynolds, Scarl, Swanson, Waters andZdanis 3,4 at Princeton University. Theyused an 8 in. diameter, single stage R.C.A.image tubeIand 1 1/4 in. long filaments.This image tube was coupled to an R.C.A.single stage image intensifier orthicon.Single minimum ionizing beam particleswere clearly seen with a resolution ofabout 1 mm.

Another much larger area where thescintillation chamber has a unique role isin studying radiation in space. Doolittleand Graves 5 of Space Technology Labora-tories are now planning space-experimentswith the scintillation chamber. One cansummarize their arguments for this asfollows. If you are going to send up any-thing into space to study the radiation,why not send up something that sends backa maximum amount of information. Thescintillation chamber gives angles, ranges,and ionization; it can detect neutrons and6 rays, and it has several microsecondtime resolutions. Putting it into a spaceprobe is feasible. As a first experiment,Doolittle and Graves are using a highaltitude balloon flight for a study of thefrequency, angular distribution and energyof primary cosmic ray nuclei heavier thanhelium. They use a sodium iodide lumines-cent chamber which is viewed by two mag-

netically focussed, three stage R.C.A.image tubes, and they record directly onfilm.

As for the status of the scintill-ation chamber in low energy nuclearphysics, because of my ignorance I willask you a question. Are there uses forthe cIamber in that field?

Returning to high energy nuclearphysics the following four successfulexperiments have been done with thescintillation ch9mber. Lande, Mann,Reibel and White0 at the University ofPennsylvania have studied the spectrum ofthe Kp3 decay mode of the K+ meson. Themethod consisted of stopping the K+ mesonsin a scintillation counter. The energyof the p. is determined by its range in afilamentary chamber consisting of 52 lay-ers, each made up of a row of 1 mm plasticscintillator filaments and a slightlythinner gold plate. No results of thisexperiment have been published. Reynoldset. al. 3 have studied the reaction- + C12 -- B12 + y with subsequent decayof the B12 in order to obtain the coupl-ing constant for the universal Fermiinteraction in mu meson capture. Theyused a plastic filamentary chamber, athree stage R.C.A. electrostaticallyfocussed image tube and a single stageR.C.A. intensifier image orthicon. Theyhave excellent results.7 Peck, Jones andmyself have published results8 on 1Y- vinteractions below the'765 Mev resonance,which were obtained using a sodium iodidechamber and a liquid hydrogen target.With the same target and a double sodiumiodide chamber, Lai, Jones and myself ob-tained detailed data9 on large angle elas-tic scattering of n- mesons on protons at1.5, 2.0 and 2.5 Bev/c. We have extendedthe elastic scattering experiment from3.0 to 5.0 Bev/c 1T-tP and also for Vt4e,but we then used spark chambers, becausethis is an experiment where very large lowdensity chambers are best.

These are the experiments which havebeen done; for those which will be doneone is interested in new developments inthe scintillation chamber technique. Inthe past year there have been no radicaldevelopments in the design or constructionof chambers. A very good review of thepresent chamber construction limitationshas been civen by Hill, Caldwell andSchluter.'° The new developments of in-terest are all in image tube design andconstruction. First of all, all of theimage tubes used in the aforementionedexperiments are obsolete.1 From 20thCentury Electronics and English ElectricValve Co. in Great Britain and from Wes-tinghouse in the United States there arenow available magnetically focussed,

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multistage image tubes with gains of io5and uniformly good resolution. This meansthat through a single tube one can photo-graph single photoelectrons, and thereforeone of these tubes alone provides all theamplification necessary for a scintillationchamber. A beautiful magnetically focus-sed three stage image tube is now beingmade by R.C.A. Gildemeister and Ciese atthe Universtat Bonnll have built a veryfine four stage, magnetically focussed,image tube with which they have photo-graphed the best sodium iodide luminescentchamber tracks I have ever seen. The fieldenhanced transmission secondary emissiontechnique described by Stexilass and Goetzat this meeting has also been used withgreat success in image tubes13 and prom-ises to give us an even simpler very highgain image tube. One problem that con-tinues to bother us is that whereas all ofthese high gain tubes have photocathodesof 1 to 2 in. diameter, that for most ex-periments the first photocathode must be5, 8, or 10 in. in diameter. This necces-sary demagnifying tube sometimes decreasesthe total resolution inordinately. A so-lution to this problef has been proposedby Zacharov of CERN.1 He has designed ademagni fy ing tube using converging para-llel electric and magnetic fields.

I am sorry to say that from the USSRI have heard nothing about developments intechnique or of experiments with scintil-lation chambers. Their publications onthis subject are clear and when you meetsomeone in this field he tells you freelywhat they are doing, but they seem to havean aversion to answering letters. If Icould speak Russian I think I would callthem on the telephone and I think theywould provide all the information, and afew Russian proverbs.

As you see, there have been no rad-ical developments in the scintillationchamber technique. With the new tubes youcan do experiments much more easily andyou can use more complicated setups. Butfor the near future the kinds of experi-ments I have talked about are the onlykinds that can be done. But as I said be-fore, this includes some very useful andinteresting things.

While writing this paper, some of usat Michigan were considering how to studythe newly discovered IY-17 resonances witha spark chamber. As we- worked over the

problems, it seemed to us that a hydrogenbubble chamber was perhaps a better way todo this sort of thing. The spark chamberhad so many problems and the bubble cham-ber so few. Then suddenly an opportunitycame to possibly obtain some hydrogenbubble chamber pictures on a related ex-periment. In an afternoon we discoveredall sorts of hydrogen bubble chamber prob-lems we had not known about. This leadsto two American proverbs: "The other fel-lows technique is always easier and better"and "We still need a new kind of chamber"'.Well, the scintillation chamber develop-ment exhausted my ingenuity and I am look-ing to others for a new kind of chamber.I have a list of required properties inmy pocket but it would be too discouragingto show them at any meeting on techniques.

References

1. L. W. Jones and M. L. Perl, NuclearInstruments and Methods 10, 345 (1961)2. D. Dickinson and M. L. Perl, TechnicalReport No. 5, University of Michigan3. G. T. Reynolds, D. B. Scarl, R. A.Swanson, J. R. Waters, and R. A. Zdanis,Advances in Electronics, Vol. 16, AcademicPress (New York, 1962)4. J. R. Waters, G. T. Reynolds, D. B.Scarl, and R. A. Zdanis, Princeton-Pennsylvania Acceleration Report PPAD435D5. R. F. Doolittle and C. D. Graves, Ad-vances in Electronics, Vol 16, AcademicPress (New York, 1962)6. K. Lande, prive communication7. D. B. Scarl, G. T. Reynolds, R. A.Swanson, J. R. Waters and R. A. Zdanis,Bull. Am. Phys. Soc. II 7, 48 (1962)8. C. C. Peck, L. W. Jones and M. L. Perl,Technical Report No. 4, University ofMichigan; and in press of the Phys. Rev.9. K. W. Lai, L. W. Jones, and M. L. Perl,Phys. Rev. Letters 7, 125 (1961)10. D. A. Hill, D. 0. Caldwell and R. A.Schluter, Advances in Electronics, Vol 16Academic Press (New York, 1962)11. 0. Gildemeister and R. Ciese, Advancesin Electronics, Vol 16, Academic Press(New York, 1962)12. B. Zacharov, Advances in Electronics,Vol 16, Academic Press (New York, 1962)13. G. W. Goetz, Private communication

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