W (25-p) drift tubes for precision tracking in a magnetic

Transcription

1 L 1564 EEE TRANSACTONS ON NUCLEAR SCENCE, VOL. 37, NO. 5, OCTOER 199 Performace of Small-Radius Thi-Wall Drift Tubes i a SSC Radiatio Eviromet at the MT Research Reactor NG ZHOU, DAVD WARNER, JAMES ROHLF, DAVD OSORNE, ALEXANDRU MARN, WENWEN LU, GEORGE HOPKNS, THOMAS COAN, JAMES EATTY, AND STEVEN AHLEN Abstract-Drift tubes of 1.9-mm radius ad 25-p wall thickess were exposed to eutros ad associated gamma radiatio from uraium fissio at tbe MT Research Reactor. 45 hours of irradiatio, the drift tubes received a eutro fluece with eergy greater tha.5 MeV of 1.1 x 113 cm- ad accumulated a charge per wire legth of.8 coul cm-l, about that expected for three years of operatio at the SSC for a lead scitillator calorimeter at a 1-m radius ad for drift tubes at a distace of several tes of cetimeters from the beam axis. Measuremet of the pulse height, pulse shape, coutig rates, ad currets showed o degradatio i drift tube performace. Fast (few aosecod rise time), sharp (2-s width) pulses were observed at coutig rates of 5 MHz usig CF, as the drift gas. E have developed small-radius (1.9 mm) thi-wall W (25-p) drift tubes for precisio trackig i a magetic field for the purpose of lepto idetificatio i the fial states of high-eergy high-lumiosity proto- proto collisios at the Supercoductig Super Collider (SSC). We report here first results of the geeral performace characteristics of these drift tubes at high coutig rates (5 MHz) after a eutro fluece (eergy greater tha.5 MeV) of 1.1 x lo3 cmp2 ad a accumulated charge per wire legth of.8 coul cm- obtaied at the Massachusetts stitute of Techology Research Reactor (MTR-). The harsh radiatio eviromet at the SSC will impose more striget costraits o the radiatio durability of particle detectors ad associated electroics tha ay previous particle physics facility. At the SSC desig lumiosity of cm-2-1 s oe expects the rate of miimum ioizig particles from proto-proto collisios to be 7 x lo8 s- pu pseudorapidity (7 = - ta 6/2, where 6 is the agle with respect to the beam axis). For a trackig detector a distace r from depedet ad ca be a factor of two larger for a large soleoidal detector [l]. Furthermore, the aual fluece of eutros i the cetral cavity of a SSC detector due to backscatterig from a calorimeter is calculated [l] to be approximately 8 x 1 ~ (1 m/r)2 cmp2 (for uraium scitillator), where R is the ier radius of the cetral cavity. This fluece varies as a fuctio of the calorimeter material ad is calculated, for example, to be about a factor of two smaller for the case of lead scitillator ad a factor of three larger for uraium-argo [ 11. The work we describe i this paper was motivated by the realizatio that the trackig detectors that will occupy the cetral cavity of a SSC detector may be proe to damage by the eutro flux. Silico trackig detectors are well-kow examples that are quite sesitive to MeV eutros, characteristic of eutros i the cetral cavity [2]. At the other extreme would be detectors ot relyig o iate crystallie perfectio for their performace, such as gas-based trackig devices. However, the suitability of gas detectors at the large SSC rates has ot bee demostrated. A coveiet eutro source for our group i osto is the MTR-11, a 5-MW reactor with umerous exteral beam ad iteral irradiatio facilities. This work was performed at the Fast Spectrum Facility, which is well-suited for SSC radiatio simulatios. t cosists of a slab (2 x 2 m area ad.5-m thickess) of uraium slightly eriched i 235U (2%), which is irradiated by thermal eutros from the reactor core. A boro thermal shield allows high-eergy fissio eutros to uiformly irradiate the area where our detectors are laced. The prompt eutro eergy spectrum from fissio of 2kJ is well-fit by the expressio [3] particles does ot iclude the effect of trappig of low mometum particles i a magetic field, which is detector Mauscript received April 4, 199; revised May 19, 199. This work was supported i part by osto Uiversity ad the U.S. Departmet of Eergy uder grat DE-FG2-8ER177.AO13 to MT.. Zhou, D. Warer, J. Rohlf, D. Osbore, A. Mari, W. Lu, T. Coa, 3. eatty, ad S. Ahle are with osto Uiversity, Departmet of Physics, 59 Commowealth Aveue, osto, MA G. Hopkis is with the Massachusetts stitute of Techology, Nuclear Reactor Laboratory, Cambridge, MA, EEE Log Number where dn / de is i uits of eutros/mev ormalized to uity with the eergy E expressed i MeV. The peak of the spectrum is at.6 MeV ad it falls off rapidly with eergy. Each fissio produces about 2.5 fast eutros. About 8 gammas per fissio are emitted (prompt ad fissio product) with the eergy spectrum as tabulated i Table. We simultaeously exposed two types of drift tubes at the MTR-11: 1) PAR type, the same drift tube used i the PAR /9/164$1.OO 199 EEE Authorized licesed use limited to: OSTON UNVERSTY. Dowloaded o Jue 16, 29 at 8:34 from EEE Xplore. Restrictios apply.

2 ZHOU el al.: SMALL-RADUS THN-WALL DRFT TUES 1565 From [3]. TALE ENERGY SPECTRUM OF GAMMAS FROM 235U Fissio Eergy terval (MeV).1 to.4.4 to.9.9 to to to to 2.6 > 2.6 Photos /Fissio balloo experimet [4] for which the first thi-wall drift tubes were ieveloped (12.5-p mylar p polycarboate + 1 A of alumium) [5]. We moitored two tubes (PAR-1 ad PAR-2 of a 8-tube PAR prototype array for the test. The tube radius is 6.35 mm ad the legth is 2 cm. The aode wire is 2-p gold-plated tugste tesioed at 2 g. The wire aligmet is held by a cocetric precisio arragemet of a outer brass plug, delri iset, ad stailess steel ferrule [4]. 2) SSC type, a smaller-radius versio developed by our group for potetial use at the SSC. Two tubes (SSC-1 ad SSC-2) were moitored durig this experimet. The same wall material was used as for the PAR tubes, but the tube radius is 1.9 mm ad the legth of the tubes is 3 cm. The SSC detector has 2-p diameter gold-plated tugste wires tesioed at 5 g. The edplug desig is essetially a miiaturizatio of that used i PAR. However, the challege was to maitai the precisio i the wire placemet while still providig for adequate gas flow ad a practical meas for coectio of high voltage i a small space. Special attetio was take to miimize the amout of material i the ed plug desig. This was accomplished with a alumium edpiece, a delri iset, ad the same stailess steel ferrule used i PAR. The alumium iserts are glued to the isides of the tubes with coductig silver epoxy. The drift tubes are desiged to achieve 1-p spatial resolutio, so we have machied the edpieces to hold a tolerace of 25 p. We have checked the rough aligmet of the wires i this desig by recordig the electro drift times i two staggered tubes for cosmic rays passig through the middle ad ear the two eds of the drift tubes usig argo-ethae (5/5) as the drift gas. The trackig resolutio of the SSC drift tubes will be addressed by our group i a upcomig beam test. All the drift tubes were mouted parallel to oe aother ad to the uraium slab with their axis i the horizotal plae. We ote that the temperature i the Fast Spectrum Facility remais at room temperature durig the exposure. The gas used for these tests was CF,, chose for its high electro drift speed (about 1 p/s), which is highly desirable at SSC rates, although the fial choice of gas for the SSC would iclude the additio of isobutae or dimethylether to improve trackig resolutio. The gas flow was serial, first through the two SSC tubes ad the through the PAR tubes at a rather slow rate of approximately 15 cm3/mi. Two hoses 12 m i legth with a iside diameter of 4 mm were used to deliver ad receive the gas from the drift tube detectors. The iput pressure to the delivery hose was 3 cm of water, the large value of which is due to the small gas passages used i the SSC edplug desig. The output pressure of the receivig hose was regulated by a mieral oil bubbler set to 8 mm above atmospheric pressure. High voltage was delivered to the tubes ad sigals received from the tubes by a sigle 7.6-m log coaxial cable for each of the four drift tubes that were moitored. A separate power supply was used for each drift tube. The tube voltages were maitaied at 22 V for SSC-1, SSC-2. ad PAR-1, ad 25 V for PAR-2. A Fe source (producig 55 M 5.9 kev K-shell X-rays) placed at the midpoit of the tube legth yields a sigal of 1.2 mv (after amplifier gai is divided out) out of the 7.6-m log coax truk lie ito 5 Q for 22 V o a SSC tube, ad the same for 25 V o a PAR tube. Sese wire gais were measured by pulse height aalysis of the Fe source before the exposure. The performace of the drift tubes were moitored i a umber of ways. a) Currets from the high-voltage supplies (erta 375) for each drift tube were moitored throughout the ru. Currets were measured both o the supply meters ad the curret moitor outputs. The accuracy of the curret measuremet from the moitor is 1 A. Small currets ca be measured from the meter to about 2 A. b) The coutig rates of SSC-, SSC-2, ad PAR-2 were moitored at a threshold correspodig to.3 mv (3 mv after 1 x amplificatio i two stages of a LeCroy 612A) at the lie output ito SO Q. c) The coicidece rate (2-11s discrimiator width, 3-mV threshold after 1 x amplificatio) of the SSC tubes, which were mouted horizotally adjacet to oe aother, trasverse to a lie to the uraium source, was moitored. Note that the maximum drift time i CF, gas is slightly less tha 2 s for the SSC tubes at 22 V. d) Pulse waveforms from SSC- 1 ad SSC-2 were recorded (after 1 x amplificatio) for coicidece triggers throughout the exposure with a LeCroy 94 waveform digitizer (1-s time samples) ad miicomputer data acquisitio system. This eabled us to moitor ad record pulse quality ad to determie pulse height spectra throughout the exposure. e) Pulse height spectra were measured i the PAR ad SSC tubes with a 55Fe source before the exposure, after 26 h of irradiatio ad agai at the ed of the exposure. The data reported here were take i three periods of pcak reactor power of 4 MW: lj a 15.7-h iterval betwee at 3:5 ad 19:33 o December 13, ) a 1.25-h iterval betwee O:OO ad 1:15 o December 14, 1989, ad 3) a h iterval betwee 18:lO o December 2, 1989 ad 13:35 o December 21, We report first the details of our measuremets durig period 1) ad the summarize the results from the total exposure of 45.3 h. Fig. l(a) shows the curret i SSC-1 measured as the reactor was tured o for period 1) at power levels of.4,.25, 1, 2, 3, ad 4 MW. The power is moitored i the reactor cotrol room by measuremet of the eutro flux Authorized licesed use limited to: OSTON UNVERSTY. Dowloaded o Jue 16, 29 at 8:34 from EEE Xplore. Restrictios apply.

3 Authorized licesed use limited to: OSTON UNVERSTY. Dowloaded o Jue 16, 29 at 8:34 from EEE Xplore. Restrictios apply EEE TRANSACTONS ON NUCLEAR SCENCE, VOL. 37, NO. 5, OCTOER 199 s A U $ i x 9 - Y V 5l o C E CF x ar f K 1 1 OY-+---Y Reactor Power (MW) Fig. 1. (a) Curret measured i SSC-1 ad (b) coicidet rate i SSC tubes as fuctio of reactor power at begiig of experimet. Solid-lies are liear fit. A Y i! x c! P s loo t. : ---= 2 4 O 8 Fig. 2. OU 1 2 Curret i SSC Tube (ricroamps) Coicidece rate betwee SSC-1 ad SSC-2 versus curret i SSC-1 at begiig of experimet. Solid lie is liear fit. Time (5) Fig. 3 (a) Curret measured i SSC-1 (solid squares) ad SSC-2 (ope circles), (b) sigles rates, ad (c) SSC-1 ad SSC-2 coicidece rate as fuctio of time. creases i currets ad rates were observed as reactor was powered up. Small bump at about t = 7 s represets abortive attempt to power up reactor. Reactor power was 4 Mw for iterval 138 s < t < 7 38 s. At t = 7 38 s reactor shutters were closed. Last two measuremets show were made 54 s ad 192 s after closig of shutters. from the core. The curret was observed to icrease liearly with reactor power. The observed coicidece rate betwee SSC-1 ad SSC-2 icreases liearly with the reactor power as show i Fig. l(b), measured as the reactor was powered o for period 1). Fig. 2 shows the measured coicidece rate versus curret as the reactor was powered o. Fig. 3(a) shows the curret i SSC-1 ad SSC-2 as a fuctio of time, t = beig defied as : o December 13. The little bump is due to a aborted attempt to start up the reactor durig the time t = 63 s to t = 81 s. The sharp rise is due to the reactor beig powered up durig the period t = 822 to t = 13 8 s. The maximum curret of about 15 pa correspods exactly to the period of maximum reactor power. The eutro flux at our detector may fluctuate slightly durig ormal operatio as fuel is cosumed ad rods are adjusted. The slightly higher (8%) curret i SSC-2 is believed due to oe or both of the followig: a) the activatio of a alumium support stad, 27Al(,cy)24Na, which was i closer proximity to SSC-2 tha SSC-1, ad b) iteractios i SSC-1 (SSC-1 was located betwee the uraium target ad SSC-2). At t = 738 s the reactor shutters were closed, cuttig off the flux of thermal eutros to the uraium slab. The currets correspodig to the largest times i Fig. 2 were take 9 ad 32 mi after the closig of the shutters.

4 ZHOU rf al.: SMALL-RADUS THN-WALL DRFT TUES 1567 The sigles rates i SSC-1 ad SSC-2 as a fuctio of time are also show i Fig. 3(b). The rate was costat at 5 MHz maximum power ad was idetical to withi 4% i the two SSC tubes. (The sigles rate i the PAR tube at 25 V was observed to be about 2 MHz.) Whe the shutters were closed, the rate was observed to drop istatly to 2 MHz. t fell a additioal factor of te after 2 mi. The coicidece rate of the SSC tubes as a fuctio of time is show i Fig. 3(c). efore the reactor was started, this rate was measured to be 72 Hz due to a small radioactive backgroud i the Fast Spectrum Facility. A maximum power, the coicidece rate is observed to be 2 MHz or about 4% of the sigles rate. Usig Poisso statistics, we calculated the rate of accidetal pulse overlap of 2-11s width pulses at 5 MHz rates to be 36%. The accidetals rate was measured to be 42% whe SSC-2 was delayed by 55 s. We attribute the coicideces to eergetic Compto electros produced outside the tubes (because the sigles rates i SSC-1 ad SSC-2 are early idetical). The eergy of the emitted gammas (Table ) is peaked at aroud 6 kev; thus Compto electros produced by such gammas ca easily peetrate two tubes (3 kev correspods to practical electro rages of 8 mg cm-2, the tube wall thickess is about 3 mg cm-2, ad the CF, gas is about 1.3 mg er--' i a SSC tube). Neutro-iduced proto recoils are ulikely to accout for more tha a few percet of the observed coicideces because it takes more tha 2 MeV for a proto to make it through 2.5 walls plus the CF, i order to cause a coicidece. Whe the shutters are closed, the flux of eutros to our detectors is cut off immediately, but a compoet of the gamma radiatio is still preset (see Fig. 2). From the measured coicidece rate (84 khz) ad currets (.58 pa i SSC-1 ad.68 pa i SSC-2) 9 mi after the shutters were closed, we ca determie that essetially all of the curret with the reactor o was gamma iduced. Pulse height spectra were take with a "Fe source o December 9 before istallatio at the reactor i all the drift tubes at several voltages. The sigals from the drift tubes were iput to a charge sesitive preamplifier (C = 1 pf) ad a fast shapig amplifier (Ortec 575) ad the to a pulse height aalyzer (Ortec 71). At 2 V, with the fast amplifier gai set at 3, the locatio of the X-ray peak was at 6.68 V i SSC-. We had access to the drift tubes o the morig of December 19 after 26-h of irradiatio at 4 MW, at which time were measured the "Fe peak ad foud it to be at 6.58 V. O December 27, after 45 h of exposure at peak power, we had aother access to the tubes durig which the pulse height spectrum was agai remeasured to be at 6.62 V. Thus, the 5'Fe peak was observed to be uchaged withi measuremet error (1 %). The width was also observed to be uchaged (21 % stadard deviatio). The PAR tubes were measured i a similar fashio at 25 V ad the X-ray peaks were foud to be uchaged withi 1 %. The pulse waveforms from SSC-1 ad SSC-2 were carefully moitored ad recorded throughout the experimet. Fig. 4(a) shows te sequetial pulses i SSC- ad SSC-2 geerated by the Compto electro coicideces ear the begiig of the ru with the reactor at full power. The pulse height of a miimum ioizig particle is expected to be a few mv after te fold amplificatio of the drift tube sigal. The pulses typically have fast (few aosecods) rise times ad widths of about 2 s. Fig. 4(a) also gives us some measure of how difficult (or easy) it will be to do trackig i a backgroud at 5 MHz sigles rates (comparable to SSC rates). Note that there is little difficulty i idetifyig the pulse pairs, which geerated the coicidece, that occurred ear t =. The quality of the waveforms was cosistet throughout the ru. Fig. 4(b) we show 1 sequetial pulses ear the ed of period 1) with reactor at full power. For compariso, i Fig. 4(c) we show 1 sequetial pulses take after the reactor shutters were closed ad the coicidece rate has dropped to 57 khz ad the sigles rates to 2 khz. y itegratig the waveforms from 4 s before the coicidece trigger to 4 s after the trigger time, we ca obtai pulse height spectra to cotiuously moitor the gai of the tubes durig exposure. Spectra at the begiig ad the ed of period 1) durig full-power operatio are show i Fig. 5(a) ad 5(b). No obvious chages are to be oted. We emphasize that o rate problems were observed due to io clearig. t has bee stated that rates should be kept below 1' mm-'s-' (correspodig to 3 MHz for our 3-cm log tubes) to avoid such problems [6]. To illustrate this we show i Fig. 5(c) the pulse height spectra take after the reactor shutters were closed, with the coicidece rate at 57 khz ad the sigles rates at 2 khz. The low eergy side is cleaer tha with reactor o (Fig. 5(a)-(b)), but there is o serious gai degradatio durig the ru due to io clearig problems. We measured the pulse heights of chace coicideces ad foud them to be cosistet with the low pulse height compoet observed i Fig. 5(a)-(b). The larger PAR drift tubes did show a serious efficiecy problem at high rates, likely due to io clearig problems. The eutro fluece for this ru was determied by placig a ickel foil i the irradiatio area adjacet to our drift tubes for period 1) ad period 2). The ickel is activated by the reactio "Ni(,p)58Co. These foils were removed durig the access o December 19, ad gammas from 58Co decay of eergy.8 MeV (71.3 day lifetime) were couted i a calibrated detector by stadard techique. The eutro flux for eergies greater tha.5 MeV was determied to be 7 x O7 cm-'s- with a estimated error of about 1%. The eutro flux with E > 3 ev was determied to be 3.3 x O8 cm-2 - s from kowledge of the eergy depedece of the spectrum at MTR-1 from previous measuremets. The total amout of charge collected per wire is determied by measuremet of the currets. For SSC-1, this measured to be.8 coul cm-. This direct measuremet is i excellet agreemet with the charge per wire legth expected from miimum ioizig particles at the measured sigles rate of 5 MHz ad sese wire gai of 4.8 x lo5 (limited streamer mode), takig the electro yield i CF, to be 1 electros/cm. The SSC tubes whe operated with argo-ethae (5/5) have a similar gai at 175 V. Fig. 5(d) shows the pulse height spectrum for coicidece triggers obtaied from the itegrated wave forms for SSC-1 Authorized licesed use limited to: OSTON UNVERSTY. Dowloaded o Jue 16, 29 at 8:34 from EEE Xplore. Restrictios apply.

5 1568 EEE TRANSACTONS ON NUCLEAR SCENCE, VOL. 37, NO. 5, OCTOER 199 ssc-1 -~~~ ssc-1 -a ! ~ -!:F time(s) C ssc-1 time( s) Fig. 4(a). Te sequetial waveforms for both SSC-1 (first trace) ad SSC-2 (secod trace) for coicidece triggers recorded durig begiig of ru with reactor at 4 MW. Coicidece rate was 2 MHz ad sigles rates were 5 MHz. Amplificatio factor is te. Threshold for coicidece circuit correspods to 3 mv o these traces, ad trigger is at t = SSC time(s) time(s) Fig. 4@). Te sequetial waveforms for both SSC-1 (first trace) ad SSC-2 (secod trace) for coicidece triggers recorded at ed of 15 h with reactor at 4 MW. Coicidece rate was 2 MHz ad sigles rates were 5 MHz. Amplificatio factor is te. Threshold for coicidece circuit correspods to 3 mv o these traces, ad trigger is at t =.

6 ZHOU et al.: SMALL-RADUS THN-WALL DRFT TUES 1569 tire(s) tire(s) Fig. 4(c). Te sequetial waveforms for both SSC-1 (top trace) ad SSC-2 (bottom trace) for SSC tube coicideces recorded after 15.7 h of exposure with shutters closed. Coicidece rate was 57 khz ad sigles rates were 2 khz. Amplificatio factor is te. Threshold for coicidece circuit correspods to 3 mv o these traces, ad trigger is at t =. 1 d w > Fig. 5. Pulse height spectra for SSC-1 obtaied by tegratio of recorded waveforms *4 s about trigger time for evets recorded a) i first half-hour of ru with coicidece rate at 2 MHz ad sigles rates at 5 MHz, b) after 15 h of exposure, (c) after reactor shutters were closed with coicidece rate at 57 khz ad sigles rates at 2 khz, ad d) after eutro fluece of 1.1 x 1 cm-*sc ad a charge per wire legth of.8 coul cmcl with coicidece rate at 2 MHz ad sigles rates at 5 MHz. Authorized licesed use limited to: OSTON UNVERSTY. Dowloaded o Jue 16, 29 at 8:34 from EEE Xplore. Restrictios apply.

7 157 EEE TRANSACTONS ON NUCLEAR SCENCE, VOL. 37, NO. 5, OCTOER 199 Charge/wire legth TALE ssc This Experimet MeV eutro flux (U-scit., R = 1 m) 8 x 1 cm-2s-1 7 x i~~cm-~s-~ (Pb-scit., R = 1 m) 4 x io5 cm-*s- MeV eutro fluece (U-scit., R = 1 m, 1 yr) 8 x 1l2 cm x 113 (Pb-scit., R = 1 m, 1 yr) 4 x 1 cm-2 Rate i 1.9-mm (AV = 1.5, R = 1 m).6 MHz 5 MHz radius tube (Aq = 3, R =.5 m) (AV = 3, R =.25 m) (Aq = 1.5, R = 1 m, 1 yr) (Aq = 3, R =.5 m, 1 yr) (A = 3, R =.25 m. 1 vr) 2.5 MHz 5.1 MHz.2 coul cm-.8 COU cm-.3 coul cm-.8 COU er--' Compariso of rates of eutros, charged particle coutig rates, ad collected charge per wire legth betwee that expected at the SSC (for various detector cofiguratios) ad this experimet. The SSC eutro fluxes are from [l]. The drift tube legths for (&=1.5, R=lm),(Aq=3, R=.5m),ad(A~=3,R=.25m)are2.12m,2.12m,ad1.6m,respectively.the calculatio of coul cm- at the SSC it is assumed that the charge collected is due to miimum ioizig particles oly ad o magetic trappig with 1 primary electros/cm produced ad a wire gai of lo4. The SSC eutro fluece ad estimated charge/wire legth correspod to oe year. at the ed of period 3), with reactor at full power, compared ACKNOWLEDGMENT to that obtaied at the begiig of period 1). No sigificat We thak George Pisiello ad Day 9Coell for assischage is oted. The eutro fluece for the total tace i fabricatio of the drift tube parts. We ackowledge was cm-2 ad a total charge per wire legth Of the assistace of the staff of the MT Nuclear Reactor Labo- *8 cm- was 1 gives a Of ratory, especially Joh eard, Kwa Kwok, ad Professor this exposure together with that expected at the SSC. Note We would also like to thak Professor Ed that the eutro flux Of this experimet is times that ooth for suggestig to us the suitability of usig the MTR-11 expected at the SSC. Sigle-tube coutig rates are compara- for these studies. ble betwee this experimet ad loger tubes at radial distaces of several tes of cetimeters at the SSC. At the SSC, REFERENCES we would expect to operate the drift tubes at the much lower [l] Doald E. Groom, Radiatio Levels i SSC Detectors, i Report gai of approximately lo4. ech tests have determied that of the Task Force o Radiatio Levels i the SSC teractio Regios, SSC Cetral Desig Group, SSC-21, 1989; Radiatio miimum ioizig particles are clearly observable at this gai Levels i the SSC teractio Regios, ed. D. E. Groom, SSC-SR- (18 V for CF, ad 13 V for argo ethae), although 133 (1988); ad Report of the Task Force o Radiatio Effects at better electroics are required. A large charge per wire the SSC, SSC Cetral Desig Group Report SSC-SR35 (1988). [2] H. W. Kraer, Z. Li, ad K. U. Posecker, Fast eutro damage i legth has bee collected here i a short time due to the large silico detectors, Nucl. strume. Methods Phys. Res, vol. particle flux ad large sese wire gai used i these measure- A279, p. 266, mets. We ote that the exposure reported here was oly [3] H. Soodak, Ed., Reactor Hadbook, vol. 111, part A. New York: tersciece, 1962; A. E. Profio, Radiatio Shieldig ad Dosime- 45-h duratio ad that strog rate depedeces have bee try. New York: Wiley, observed i radiatio damage effects [ 11. [4] S. Ahle et al., A ew limit o the low eergy atiproto/proto t is our coclusio, based o these observatios, that drift ratio i the galactic cosmic radiatio, Phys. Rev. Lett., vol. 61, p. 145, 1988; ad A. Tomasch, Ph.D. thesis, osto Uiversity, tubes of the type used here are good cadidates for operatio [5] CLEO Collaboratio, CLEO 1 updated proposal for improvemets i the SSC radiatio eviromet. Future tests are plaed to to the CLEO detector for the study of e+e- iteractios at CESR, exted the radiatio exposure limits at the MTR-1 ad to CLNS 85/634, (Thi-wall drift tubes were developed idepedetly by a group from Ohio State Uiversity (H. Kaga et al.)). determie trackig resolutio at high rates with multiple drift [6] H. H. Williams, Desig priciples of detectors at collidig beams, tube arrays at the reactor. A. Rev. Nucl. Sri., vol. 36, p. 361, 1986.