A mgh ENERGY NEUTRON DETECTOR USING PROPORTIONAL WIRE CHAMBERS (Ii 727) Presented by M. Atac National Accelerator Laboratory* Batavia, Illinois

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1 A mgh ENERGY NEUTRON DETECTOR USNG PROPORTONAL WRE CHAMBERS (i 727) Presented by M. Atac National Accelerator Laboratory* Batavia, llinois An exeriment to study the roerties of negative hyerons roduced by the Brookhaven 1 National Laboratory Alternating Gradient Synchrotron required a neutron detector to identify the fast (t5-z0 GeV/c) neutrons resulting from hyeron decays of interest, e.g., ~ - n~". Figuret shows a schematic of the aaratus. The extracted roton beam (about 5 ><tot 1 rotons er ulse at Z8 GeV/c) is allowed to strike a small target at the entrance of the magnetic channel. Negative hyerons, ~ -, ;::-. n -. roduced in the forward direction traverse the channel and have their 2 osition recorded by a secial high-resolution sark chamber and the channel exit. Most of the hyerons that decay downstream of this chamber have their charged decay articles momentumanalyzed by the two sectrometer magnets and four clusters of magnetostrictive sark chambers. The fast forward neutrons roduced in some decays are then detected by the device described here. A measurement of the neutron osition and hence angle, along with a rough measurement of its energy. is desired. As shown in Fig. 2 the detector consists of two arts. the neutron osition detector and the neutron calorimeter. The first section contains alternating layers of 3.2 -em thick steel late em thick lastic scintillator. and a air of orthogonal roortional wire chambers. There are five such layers each having a Cross section of about 60 cm>< 60 em. The detector consists of 10 roortional wire chambers, 5 steel lates, and 6 scintillation counters. The active area of the roortional chambers is 48 cm>< 48 em. Each chamber (see Fig. 3) contains 48 signal wires (25 micron diameter gold -lated tungsten) which are t -em aart. The sacing between the wire lane and the outer electrodes is 8 mm. The outer electrodes are made of 50 micron coer foils on t. 5 -mm thick eoxy glass sheets. The same material is also used around the 3 chamber as an electromagnetic shield. The calorimeter was built by the University of Michigan grou and consists of alternating layers of steel lates (3.8 -em thick) and lastic BcintUlators (0.6 -em thick). t contained over four interaction lengths of material. Neutrons of momentum 13 to 21 GeV/ c interact in the steel lates to give charged hadronic and electromagnetic cascades. The osition of these cascades is given by the roortional wire chambers. The scintillators in both the osition detector and the calorimeter are Bummed to give ulse -height information, hence a measurement of the energy deosited. This ulse height is used in the trigger and also recorded by the data-collection system. 4 A similar tye of detector with a single converter late was reorted. G. Coignet et al obtained ±2.2 mm accuracy in determining the interaction vertex of neutrons in a carbon converter with an efficiency of 6.50/. *Oerated by Universities Research Association, nc. for the United States Atomic Energy Commission. -4t 3

2 A tyical icture of a hadronic and electromagnetic cascade resulting in the detectorrrom the interactions of a 1.5 GeV/c ion and neutron resectively is shown in Figs. ~a) and (b). n this icture each row of a vertical rojection or a horizontal rojection corresonds to a roortional chamber lane and each (f) reresents a wire ulse. These data alonr; with all other relevant data concerning the event were recorded on magnetic tae by our 1Jl<;C PDP-15 \:omuter. Even a cursory erusal of these rojection lots indicated that showers were indeed being detected, and a measurement of the neutron interaction was ossible. A satial resolution uf a " 7 mm with a 610/0 total detection efficiency in determining the neutron ositions was achieved. See Fig. S. The exact determination of this osition is a attern -recognition roblem which is discussed in a searate aer. 6 Better satial resolutions can be obtained with roortional chambers having smaller wire sacing. The energy resolution of the detector is determned to be about 20% for hadrons of 15 to 20 GeV/c. The resolution of the roortional chambers was 35 nsec at HWHM. Figure 4(c/ shows a icture of a,.. track obtained from the detector. Muons are used for determining the relative alignment of the roortional chambers. An obvious identification of the muons is that they leave straight tracks or single tracks with a 6-ray branch formation in the detector. This idea may be alied to detection of all neutral articles and gammas. High reetitionrate caability, high multi -track efficiency, and good time resolution are some of the advantages of this neutron detector over detectors using otical sark chambers. 7 The satial and energy resolutions of this tye of detector are exected to be imroved at higher energies since the forward <:one angle of the hadronic and electromagnetic cascades will be narrower. The authors would like to exress their areciation to J. Lach, J. Marx, A, Roberts, J. Sandweiss, and W. J. Willis for very useful discussions and to J. 8loomquist, 8. Lombardi, E. Steigmeyer, and 1. J. Winters for their hel in constructing the detector and the readout system. References 1AGS Proosal # 430, Study of Production and Decay of High Energy ~ 2W. J. Willis eta1.. Nucl. ostr. and Methods 91,33 (1971). 3 L. W. Jones etal., Phys. Letters 36B, 509 (1971). 4G. Coignet et al., Nucl. ostr. and Methods 99, 1. 9 (1972/. 5. W. Slach et a1., Nuc1. lnstr. aod Methods 91, 211 (1971.), 6W. Tanenbaum, to be Ublished in Nucl. lnst;-and Methods. 7J. Engler et a., Phys. Letters 29B, 321 (1969), and

3 Proton Steering ~~nei, ± '" 8eo..~ High Resolution Sark Sark Sark Chamber Chamber Chamber "~ Neutro~ ~B S - eam - ~-~ ~ Muon Sark Cerenkov U-Down Charged Shieidino Chamber Counter Counters. Beam Hodoscoe Veto Counters o Feet (s.counters) Scale Neutron Colorimeter Neutron Position Detector Fig. t. Schematic view of the exerimental layout,

4 NeulronPosilion DeleCMiNeutron 'COlorimeteri -r- r... ~r-~ - '7' '7'... '/ ~ ~ ~ '/./ V ~.. /. V V ~ ' ~ ~ ~ V.. V ~ ~ ~. ~. V../..../ ~ V.. / /. ~ ~. ~ ~. v / / ;' ~.. ~ / r; '/. / '/ 1/ l'/. '/ V / '/ '/ " ~ ~ 1.1' V ~ 1/ '/ ~ ;/ ~ ~ / '/ ~ ' ~ V l'/ V... u... l..l ~ '/ i/... " ~1 1 " \ \ ~~ \ \ Steel Plastic A Pairof Plastic Steel Plate Scintillator Orthogonal Scintillator Plate Proortional Chambers Neutrons ~ ~. ~ c) ~ Fig. 2. To view of the neutron detector.

5 Amlifier Card Guard Stris Eleetrostotic Shield (Outside) 25 micron Au- Plated Tungsten Wire ;t... Aluminum Shielding BOl( CU clad GO Electrode GO Sacer Fig. 3. A simlified cross -sectional view of the roortional chamber.

6 Vertical Projection Horizontal Projection ~Beom ~B.om \ " l " (a) ' ,," Jll 1/ ' 11"'1 \ \ 111 (b), (c) Fig. 4. A tyical icture of a hadronic and electromagnetic cascade resulting in the detector from the interaction of a) a 15 Gev/c n; bl a neutron; c) icture of J. track.

7 100 E o an N...: en c Q) > tjj o - o z Fig. 5. A robability distribution of the reconstruction of a neutron-interaction oint. -4t9