A method to estimate gas magnification of multi-gap resistive plate chamber

Available online at www.sclencedirect.comNUCLEARSCIENCEScienceDirectANDTECHNIQUESNuclear Science and Techniques, VoL18, No.S (200) 298 301A method to estimate gas magnification of multi-gapresistive plate chamberWU Yuelei' HU Huasil’QIN Juan’WANG Xiaolian2 ZHENG Xiangyang' XU Zizong2( Nuclear Engineeing Depanment ,Schoo of Energy and Power Engineering. Xi'an Jaotong Untversity, X'an 710049, China;2 Deparment of Modem Physie, Univenity of Science & Technologv of Chin Hefel 230026 China)Abstract The gas magnification of multi-gap resistive plate chamber (MRPC) is very difficult to be measured usingthe present instruments thoroughly in the world. The gas magnifcations about ~107 were obtained in the various op~eration-high-voltages of muli-gap resistive plate chamber MRPC) by means of Monte-Carlo simulatio and the pre-sented experiment method.Key words MRPC; Magnification; Monte-Carlo simulationCLC number 0572.21*21 IntroductionMRPC before the gas avalanche magnification, Noisobtained by Monte Carlo simulation as the primaryA multi-gap resistive plate chamber (MRPC) is acharge is too small to be measured under sensitivity ofnew type of gas detectort". Being of good time reso-the present instruments in the world, and N is the totallution, high detection eficiency, insensitive to mag-charge of electrons after the avalanche magnificationnetic fields and lower cost23; MRPC can well be ain the six gaps of MRPC, deduced ftom current of thesubstitution of traditional TOF plastic scintillators,outpot loop of MRPC.which should be coupled to expensive phototubes, inhigh energy nuclear and particle experiments. Gas2 Monte Carlo simulation on primarymagnification is an important parameter of MRPC,electrons in the six gaps of MRPCwhich works in a sealed aluminum box flushed by gasmixture of iso-C4H]o and C2H2F4 and is biased withThe primary charge was deduced from the Y rayover ten thousand volt voltage. The gas mixture hasenergy deposit in the six gaps of MRPC. The enengyoptimum quenching properties to keep effectively thedeposit was calculated in the Monte Carlo simulationMRPC work at an avalanche mode and enable theMCNPCode).MRPC to bave large enough gas magnification 4. TheBased on geometic distribution of the experi-gas ectron avalanche amplification formula is N =mental setup shown in Fig.1, the mathematic simula-Noe"= NoM, wbere N is the toal number of electronstion model was built in the program. The source is aafter avalanche, No is the number of primary electrons,中0.9 mmx10mm Co wire sealed in a φ3mmxl5 mma is Townsend cofficient, D is the distance an ava-stainless steel tube (with the inner diameter of 2mm),lanche covers, and M is the gas magnification.which is placed into a cylindrical lead block of 100This paper describes a new method to obtain Mmm in diameter. Details of the system, such as theby using M=NINo, where No is the total change of pmi-Co source, the lead collimator, the aluminum win-mary electrons produced by Y rays in the six gaps ofdow中国煤化工S are properlyTYHCNMHGSupported by National Natural Scitnce Foundation of China (10576022)●E-mail: huasi Jua@ail.i.du.cRoceived duatc: 2007-0405No.5WU Yuelei et al: A method to estimate gas magnifcation of muli gap resistive plate chamber299described in the MCNP's mathematic simulationgas mixture of 5.3% isoCH1o and 94.7% C2H2F4model.(operation gas of the MRPC). The rate of primaryelectron-ion pair produced by tbe γ-ray source isOperation gas气(5.8+0.9)x10' pairs/s, which equals to a primary cur-rent of (9.2+1.4)x10"16A.^.10mmAluminum box100m15mm3 Experiment setupLead∞lmaterThe next step is to obtain the magnified curentsafter the avalancbe magnification using the experi-mental method,Fg.1 Schematics of the MRPC systemThe Monte Carlo simulation program traces each3.1 Output current loops of MRPCisotropic Y photon in the system model and samplesThe circuit diagram and the structure of MRPCuniformly from the decaying "Co nuclides, whichare shown in Fg.2. There are three parallel curentemit 1.173 and 1.332MeV photons in equal probabili- loops, the first curent loop in+ starts from the +HVties. The decay scheme of °OCo is used to look forbias, passing through the monitor meter (A+), the an-conversion point of a r photon. If the conversion pointode(C-fim), the Mylar layers and the readout pads,is outside the MRPC, the program gives up the decayand getting to the ground. The second curent i2 loopevent, and returns to the beginning. If the conversionstarts from the +HV, passing through the monitor me-point occurs at the middle glass plates of the MRPC,ter (A4), the anode (C-flm), the sandwich of gapglassthe program traces the conversion electrons to the end.plates, the cathode (C-flm), the monitor meter (A)All the energy deposit in the working gas in one of theand the -HV, and going to the ground. The third loopsix gaps of MRPC is added for the gap. If the conver-i. starts from the ground, the readout pads, the Mylarsion point is in the gap, energy deposit of the conver-layers, the cathode (C-film) via the monitor meter (A)sion electrons is added to the gap, too. After fnishingto the -HV, and the ground. The it and i. amplitudesa y photon tracking loop, sampling of a new Y photondepend on the Mylar layers' insulation property. Insu-begins. A total of 10° decays are randomly sampled inlation property of the Mylar layers can be determinedthe &Co wire, and the average energy deposits fromby shielding the Y-rays and measuring the currents ofthe first sensitive gap (bottom in Fg.1) to the sixthmonitor meters A and A . Magnitude of the currentsensitive gap are given in Table1.represents the resistance between the anode and theTable 1 Encrgy deposit (旧) in he sensitive gaps by samplingcathode of MRPC. If the MRPC works in just the1050Co decaysbackground of cosmic rays, (i+ + iz) or(i. + i2) is theLocationEKeVRelative erorleak curent. With the Co r-rays imadiating theGapl1.8460.0090MRPC, primary ionization charges are generated inGap21.8280.0092the gas gaps, electron avalanche grows in the opera-Gap31.809.0091Gap41.799tion gas, and the total current of(i1++ izori. + 2) isGap51.788dominated by iz, which is the operation current.Gap61.7660.00910.836 .0.02243.2 Monitoring system of currentsA PCF-1714 AD card is used. It has four inde~The sum of energy deposit in the six sensitivependent single-ended analog input channels and eachgaps in Table 1 is (1.0836+0.0224)x10'eV. As the in-input中国煤化工-) it has four ADtensity of the DCo source is 6.8 MBq (0.183 mCi), theconvenThe data card isresult should be 6.8 times larger (6x10*/10) and en-scaledYHC N M H Gvoltage N471A"ergy deposit rate of the 0Co source is (6.8+1.0)x10*calibrated in CERN. The total operation currents A4,A.eV/s. The average ionization energy is 11.8 eV in the300NUCLEAR SCIENCE AND TECHNIQUESVol.18and leak curents in h are monitored by PC-1714. current loops, i.e. b2+ =A+- it andi2. zA.-i. seeThe work current i2 is independently measured in two Fig.2 and Table 2.MylarPC boardPad_HV9C◆心-0ElectrodeGlassyrayFIg.2 The skech of MRPC and the diagnam of the lops of MRPC.Table2 All kinds of curents in various HVs/ ACurrent上6500V16750V+7000V+7250V+7500V+7750VA44.053+0.0495.879+0.0587.242+0.0589.179+0.06413.027+0.16422.870+0.1844.542+0.0225.903+0.0217. 193:0.0299.239+0.03113.13340.15323.024+0.0391+0.001+0.0240.003+0.0240.022+0.0380.011+0.0290.012+0.0370.024x0.051i.0.104+0.0210.015+0.0230.021+0.0370.007+0.0280.003+0.0340.00140.1842+4.052+0.0555.87620.0637.220+0.0699.168+0.07013.015+0.16822.870+0.191iz.4.438+0.0305.888t0.0317.172+0.0479.232+0.04213.130+0.15723.023+0.188b4.425+0.0315.882+0.0357.186x0.0429.200+0.041 。13.073.+0.11522.947+0.1344 Estimation of the gas magnification ofwere measured in dfferent HVs. The current spectra atthe MRPC14 kV are shown in Fg.3. Fitting the histograms byGauss function, the means and the variances are output.The MRPC shall be operated at ~20C in relativeThe output currents and errors under other HVs arebumidity of ~60% 4.6. As described in Section 2, theshown in Table 2. The work current iz (+,-) and theirprimary current is i= (9.2+1.4)x10^16 A induced byaverage i in various operation HVs are shown in the6.8MBq Co source, before the gas electron ava-last three lines of Table 2.lanche magnification. The currents of A.. A.. i. and i.18-Center 1.23100Caner 06514114LSigma 0.1514sigma 0.12581。1Current/MACurent/nA20 r20Center 7.89348Center B42378sgrme 0.1878Sigmna 0.1184A.中国煤化工MYHCNMHGFg3 Curent spectra of A, A., i+o i at 14000 (t7000)V.No.5WU Yuelei et al: A method to estimate gas magnification of multi-gap resistive plate chamber301The curnent produced by the r-ays became largercluster (~12 pairs of primary ion) in the MRPC tested.after gas magnification, varying with operation highThe iradiation from the 0Co which produces the pri-voltages. At the normal working conditions, the gasmary change Io= 9.21x10*C/s is equivalent to themagnifications M of MRPC is calculated (see Fg.4):counting rates of ~3Hz per cm2 of MIP iradiation.M= NINo=I1IoThe conclusion is that using the "Co source of36.8MBq iradiating the MRPC, under ~3Hz/cm2counting rate level, the gas magnification factors oforder ~10' have been obtained by means of the simula-tion and the experimental method.References1 Zballs E C, Crotty I, Wiliams M C S, et al. Nucl hnstrMeth, 1996, A 374; 132.2 Addcndum t切the Time of Fight ALICE Technical DesignRepot CERNLHCC 4, 24 2004.3 Akindinov A, Anselmo E, Basile M, et al. Nucl Inst Meth,1300 13500 1400 14500 15000 155002000, A456: 16.Opetnton voltageV4 Shao M, Ruan LJ, Chen H R, et al. Nucl Instr Mcth, 2002,Fig.4 M-V chanacters in normal operation.A 492: 344.5 Chen Hongfang, Li Cheng, Wang Xiaolian, et al. HEP &5 Discussions and conclusionNP (in Chinese), 2002, 26: 201.It is well known that the gas magnification of6 Williamns M C s. Nuclear Physics B (Proc. Suppl) 1998,61B: 250-257.avalanche is of counting rate's dependence.4 Accord-ing to the simulation", it shows that the minimum7 Riegler W, Lippmann C, Veenbot R Nucl Instr Meth, 2003,A 500: 144 162.ionization particle (MIP) of the gas-mixture of 5.3%iso-CJH1o and 94.7% CH2F should produce about 12中国煤化工MYHCNMHG