Beard, K.B.

Benenson, W.

Kashy, E.

Plicht, J. van der

Yurkon, J.

English

We have constructed an MWPC for detection of low ionizing particles at high count rates in the focal plane of an Enge split pole spectrograph. The general method is suitable for any spectrograph with non-normal incidence. A unique feature of the detector is that the cathodes and anode wires are parallel to the incident particles

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   University of GroningenThe MIW Detector - An MWPC for Inclined TrajectoriesBeard, K.B.; Benenson, W.; Kashy, E.; Plicht, J. van der; Yurkon, J.Published in:Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors andAssociated EquipmentIMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite fromit. Please check the document version below.Document VersionPublisher's PDF, also known as Version of recordPublication date:1986Link to publication in University of Groningen/UMCG research databaseCitation for published version (APA):Beard, K. B., Benenson, W., Kashy, E., Plicht, J. V. D., & Yurkon, J. (1986). The MIW Detector - An MWPCfor Inclined Trajectories. Nuclear Instruments and Methods in Physics Research Section A AcceleratorsSpectrometers Detectors and Associated Equipment, 249(2).CopyrightOther than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of theauthor(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license.More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne-amendment.Take-down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons thenumber of authors shown on this cover page is limited to 10 maximum.Download date: 20-06-2022296	Nuclear Instruments and Methods in Physics Research A249 (1986) 296-298North-Holland, AmsterdamTHEMIW DETECTOR - AN MWPC FOR INCLINED TRAJECTORIESK.B . BEARD, W. BENENSON, E. KASHY, J. VAN DER PLICHT AND J. YURKONNational Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USAReceived 7 April 1986We have constructed an MWPC for detection of low ionizing particles at high count rates in the focal plane of an Enge split polespectrograph. The general method is suitable for any spectrograph with non-normal incidence. A unique feature of the detector isthat the cathodes and anode wires are parallel to the incident particles.1 . IntroductionA magnetic spectrograph distributes particles on itsfocal plane according to their charge to mass ratio. Avariety of detectors have been built to measure thepositions of these particles and to identify them . Specialproblems arise when the particles have low ionizationand when they hit the focal plane at non-normal angles .The limitation of the spatial resolution of a single wiredetector has been shown to be due to fluctuations in theionization of the traversing particles, for both the chargedivision [1] and delay line readout [2] method . Thisproblem is made more difficult when the particles areclose to minimum ionizing or have ionization apprecia-bly lower than other reaction products with the samerigidity.A high count rate limits the usefulness of a counterwith a single wire since all the ionization collects onthat wire, and pileup can occur at the preamplifiersconnected to it . In addition, the ionization tends tospread out along the wire, reducing the position resolu-tion of that counter. The multiwire proportional cham-ber (MWPC) [3] overcomes these difficulties by usingmany wires (with individual readout) instead of a singlewire .In a standard MWPC, the anode wires are vertical inthe focal plane. The distance between anode wires andcathode planes is typically three to four times the anodewire spacing [4]. Particles which have been transmittedby an Enge spectrograph [5] enter the focal plane atincident angles ranging from 36° to 54°, and thereforein a conventional ]MWPC, the particle track wouldbe collected by a single wire . This configuration isshown in fig . 1 and is called the multi-inclined wire(MIW) counter.2. Construction and operationAn exploded view of the MIW detector is shown infig . 2. The detector operates in air rather than in vacuum.A 75 pm thick kapton window foil mounted betweendipole and camera box of the Enge spectrograph sep-arates the spectrograph vacuum from the camera boxwhich was at atmospheric pressure. The detector oper-ates at 1 atm of CF,, or Ar/CZH6 (50-50%) gas. Thedetector gas box (see fig . 2) has 75 pm thick kaptonentrance and exit pressure windows. The active detec-tion area is 48 cm x 1 .8 cm. The anode wires are 12 .5pm diameter gold-plated tungsten with a spacing of 5mm along the focal plane (and 3.5 mm normal to thewires due to the inclination of 45°) . The cathodes arealuminum plates at a distance of 20 mm (primary) andCATHODE 2BOX TOPMHV HIGH VOLTAGECONNECTORSADAPTER BOARDSECONDARYCATHODEGAS BOXFig . 2. Exploded view of the MIW detector box .CARD EDGE CONNECTORS1 .5 mm (secondary). Typical voltages are 5 .5 kV for theprimary, and 2.0 kV for the secondary cathode. Theanode wires are at ground potential . Behind the anodewires in the focal plane, a second anode wire plane isplaced at a distance of 28.5 mm in the same gas volume.Thus the MIW consists basically of two independentdetectors, each with 96 wires per plane, one behindthe other. The MIW therefore measures the angle ofincidence to permit trajectory reconstruction.The MIW was designed to be used with the LeCroyPCOS III readout system [6). This system consists of 16channel integrated circuit boards with amplifiers andprogrammable discriminators. The readout system isone reason why the detector is used in air rather than invacuum, since each amplifier/discriminator card dis-sipates about 5 W. The connections between the wiresand the PCOS cards outside the gas box were madeusing mating Samtec [7] model TS-132-G-A male con-nectors on the anode board with every other pin re-moved (to provide the correct spacing) and an adapterprinted circuit board with similarly modified femaleSS-132-G-2 connectors . The adapter board runners con-nected the pins of the Samtec connectors to the pins ofthe wire-wrap style 36 pin card edge connectors epoxiedto the lid of the gas box . In this way, a large number ofreliable, gas tight connections were made to the PCOScard . This consideration was important, since the detec-tor has nearly 200 wires to feed through a gas tight seal.Each cathode is connected to a 1 MS2 resistor forKB. Beard et al. / The MIWdetector3 . ResultsPHENOLIC SPACERSCOPPER GROUNDING PLATES-MALE 98 PIN CONNECTORS_LEXAN CONNECTOR SUPPORT--LEXAN SPACERSWINDOW FRAMES-BOX BOTTOM297current limiting and a 0.01 gF capacitor for signalpickoff.The PCOS cards can be replaced by printed circuitboards containing delay lines . These cards connect eachof the 16 wires to a tap on a delay line, each wire beingseparated by 5 ns. The printed circuit boards have theadvantage of being simple and inexpensive, and requir-ing no cooling, and they are therefore very useful fortesting purposes.The MIW detector was designed for detection ofparticles such as protons, diprotons ( 2He) and chargedpions produced in heavy ion induced reactions . Thusfar, the detector has been tested and used extensivelywith a particles, protons, electrons and positrons pro-duced in nuclear reactions, and 3.54 MeV electronsfrom a 106Ru source . Since the MIW is a transmissiondetector for these particles, scintillator and/or Cheren-kov counters can be placed behind the MIW for particleidentification purposes and additional range measure-ments .Results from the reactions (a, a') and (a, p) on a12C target of 30 mg/cm2 thickness are shown in fig. 3 .The beam energy was 80 MeV, and the spectrographwas set at a laboratory angle of 0 = 100 . In this case,the MIW is followed by a 6.3 mm thick DE and a 7529812C+a0 20 40 60 80 100wire numberFig. 3. Spectra for the reactions (a, a') and (a, p) on 12C at abeam energy of 80 MeV, measured with the MIW detector .mm thick E scintillator detector . The first excited stateof 15N is about 5.3 MeV above the ground state [8] .Elastically scattered a-particles, however, have nearlythe same momentum to charge ratio as the ground stateprotons but much smaller range. These a's were numer-ous enough that reactions taking place within the AEscintillator were triggering the E scintillator as often asprotons were. The use of particle identification with thescintillators, however, allowed the complete eliminationof the a-particle background and produced a clean 15Nspectrum (bottom part of fig. 3) despite the large num-ber of a's passing through the MIW. In the plots shownin fig . 3, one channel corresponds to the wire spacing ofthe MIW (which is 5 mm), which in turn corresponds toabout 380 keV.The MIW detector has also been used recently fordetection of high energy electrons and positrons, pro-duced in medium energy nucleus-nucleus colisions [9] .The MIW detector was in this case backed by a plasticscintillator and two Cherenkov counters for electron/positron identification . Fig. 4 shows a plot of the num-ber of wires in the front detector prevent for positronswith energies ranging from 20 to 30 MeV. Most eventscorrespond to a single wire firing . The positrons re-sulted from conversion of high energy gamma rays,which were produced by stopping a 560 MeV 14 N beamK.B . Beard et al. / The MIW detectorOU100020 - 30 MeV e+1 2 3 4 5 6 7 8 9 10wire multiplicityFig. 4 . Wire multiplicity for 20-30 MeV positrons .in a 770 mg/cm2 Cu target . This experiment yieldedinteresting results for high energy photon production inintermediate energy nucleus-nucleus collisions [9,10] .In summary, we have shown that a detector with anovel geometry, the MIW, can make MWPC type coun-ters useful for high count rate, non-normal incidencelow ionizing particles on the focal plane of a magneticspectrograph. Although the detector has not been usedthis way, it maintains the multiparticle detection capa-bility of an MWPC and would make a good correlatedparticle device, for example for 2 He detection.AcknowledgementThis work was supported in part by the NationalScience Foundation under Grant no. PHY83-12245.References[1] J.C.L . Ford, Nucl . Instr . and Meth. 162 (1979) 277.[2] R.G. Markham, Nucl. Instr. and Meth. 162 (1979) 327 .[3] F. Sauli, CERN 77-09, unpublished .[4] G. Charpak, G. Peterson, A. Pohcarpo and F. Sauli, Nucl.Instr. and Meth. 148 (1978) 471 .[51 J.E . Spencer and H.A . Enge, Nucl. Instr. and Meth. 49(1967) 181 .[6] LeCroy, Inc., Spring Valley, NY 10977, USA.[71 Samtec, Inc ., New Albany, IN 47150, USA.[8] J.E . Glenn, C.D . Zafiratos and C.S . Zaidins, Phys . Rev.Lett. 26 (1971) 328 .[9] K. Beard, W. Benenson, C. Bloch, E. Kashy, J. Stevenson,D.J . Morrissey, J. van der Plicht, B. Sherrill and J.S .Winfield, Phys . Rev. C32 (1985) 1111 ; K. Beard, PhD.Thesis, Michigan State University (1986).

The MIW Detector - An MWPC for Inclined Trajectories

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The MIW Detector - An MWPC for Inclined Trajectories

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