This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

Cox, B.M.

DuPlantis, D.

Eads, A.

Opper, A.K.

Sawafta, R.

Schwandt, P.

Solberg, K.A.

Stephenson, E.J.

Wissink, S.W.

English

IUScholarWorks

THE K6OO FOCAL PLANE POLARIMETER 
B.M. Cox, D. DuPlantis, A. Eads, A.K. Opper, R. Sawafta, P. Schwandt, 
K.A. Solberg, E.J. Stephenson, and S.W. Wissink 
Construction has begun on a high-efficiency polarimeter for intermediate-energy 
charged particles. This device, which will initially be located downstream from the 
medium-dispersion focal plane of the K600 spectrometer system, has now been fully de- 
signed. All components of the dedicated electronics have been ordered, materials for wire 
chamber and scintillator fabrication are in-house, and an adjustable mounting/shielding 
platform for alignment and integration into the existing K600 system is under construction. 
The polarimeter consists of a thick carbon block, followed by two sets of paired x-y 
multiwire proportional chambers, and two planes of plastic scintillator. The high-density 
(1.74 g/cm2) carbon target serves as the polarization analyzer, and can be varied in thick- 
ness from 1.27 cm to 5.08 cm in 1.27 cm increments. For incident proton energies between 
120 and 200 MeV, the p-12 c analyzing powers are large in magnitude, and have been care- 
fully studied for both elastic and inelastic scattering processes.1 The needed carbon blocks 
are now complete, and associated mounting structures have been designed and submitted 
for fabrication. 
The MWPC designs were finished by mid-1987, and all necessary materials have been 
procurred. The printed circuit boards used to transmit signals from the actual wires to the 
pre-amplifier cards were designed and etched, and several sections of the required G-10 
have been machined. Readout of the wire chamber information will occur via the LeCroy 
PCOS I11 system, which offers several advantages over either direct coincidence register 
or highly multiplexed configurations. A crucial feature is the rapid encoding time (< 500 
ns), with presentation of the encoded output at an ECLport. This information will be 
used as input to a second-level trigger processor for on-line rejection of events in which 
the particle underwent no significant scattering in the analyzer target. We estimate that 
I this should increase our data-taking speed by approximately a factor of twenty. Other features include programmable chamber card thresholds, computer control of latch delays, 
clusterization of adjacent wire hits, and minimal word transfer over the (slow) CAMAC 
dataway. By the end of 1987, all the MWPC cards and most of the PCOS electronics were 
in-house, with all remaining modules expected by the end of February 1988. 
The scintillator planes will be 0.64 cm and 7.62 cm thick NE102 stock. Depending on 
the incident particle type and energy, these will serve as either a AE-E pair or as a AE- 
high-resolution-AE combination. The 0.64 cm scintillator will be a single sheet, viewed by 
four low-gain 2" photomultiplier tubes (Hamamatsu R329), while the 7.62 cm thick plastic 
will be segmented into six vertical non-overlapping sections, each viewed by two similar 
2" tubes. This segmentation was considered necessary in light of the high background 
rates that arise under certain spectrometer running conditions and the large volumes of 
scintillator involved. The sixteen anode signals will be discriminated and fed into another 
second-level trigger processor which allows for user-selectable logic levels to be generated 
for all possible 16-bit inputs. Thus, the high-voltage bias applied to the photomultiplier 
tubes, the discriminator thresholds, and even the 16-fold scintillator coincidence logic will 
all be under remote computer control. All the PMT bases are transistor-stabilized, and 
have been built and tested. A prototype E detector has been constructed, and preliminary 
measurements suggest that pulse-height resolutions of 2-3% should be readily attainable, 
with a uniformity over the entire active surface of better than 1%. More extensive tests are 
planned, and will be compared to Monte Carlo calculations for the particular light-guide 
geometry chosen. 
With the above polarimeter, our goal is to calibrate and measure the normal com- 
ponent of outgoing proton polarizations by mid-1988, and to complete measurements of 
the induced polarization P and the polarizat ion-transfer coefficient DNN' for experiment 
E306 by the end of the year. During this time, we will also be involved in the commission- 
ing of additional equipment that will be required for full polarization transfer capabilities 
at IUCF. This includes installation of two spin-precession solenoids in the high-energy 
~ beamlines, development and calibration of associated in-beam transmission polarimeters, 
, and the 'addition of two horizontal drift chambers to the K600 focal plane system for com- 
plete vertical trajectory information. Most of these tasks are part of general laboratory 
development, and will benefit many other users beyond the spin-transfer group. Operation 
of the focal plane detectors at locations other than the medium-dispersion mode may also 
be required before complete sets of all polarization-transfer observables can be obtained. 
1. see, for example, IUCF Scientific and Technical Report 1982, p. 182-188. 
TARGET LAB TECHNICAL STATUS 
W. Lozowski 
A new design for an electrolysis cell was used to produce 66967~n foils of very high 
purity with 94.7% material efficiency. The cell was constructed of teflon machined so that 
a retangular bar of mirror-polished tungsten carbide (the cathode) could be compression- 
sealed in the side. In this way the Zn could deposit only on one vertical surface of the 
WC bar. A P t  screen was used for the anode. Argon gas was bubbled through the 
plating solution of ZnO dissolved in 3 ml of acetic acid. The argon helped to achieve 
a more uniform Zn deposit. The Zn peeled easily in one piece from the cathode. With 
this method, followed by rolling between stainless steel packs, targets of 7.3, 5.0, and 1.7 
mg/cm2 were produced. 
Large area (1/2" x 1 1/2") pressed powder targets of 'OI"B (150-200 mg/cm2), 
32134S (16 mg/cm2) and Si (16 mg/cm2) were developed. For the B and Si, the binder 
was partially decomposed styrene. The new binding technique involved preparation of 
a solution of styrene in sylene to which enough ETOH was added to precipitate styrene 
powder fine enough to be suspended in the liquid i.e., the solution became cloudy. After 
the concentration was determined, 1-2% by weight was mixed (wet) with the target powder 
and allowed to dry. 


The K600 Focal Plane Polarimeter

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The K600 Focal Plane Polarimeter

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