Sel Top Physical Chemistry II
Sel Top Physical Chemistry II CEM 988
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This 14 page Class Notes was uploaded by Ladarius Rohan on Saturday September 19, 2015. The Class Notes belongs to CEM 988 at Michigan State University taught by David Morrissey in Fall. Since its upload, it has received 124 views. For similar materials see /class/207690/cem-988-michigan-state-university in Chemistry at Michigan State University.
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Date Created: 09/19/15
Spring7 2009 Distributed Tues7 10 Feb 09 1 E0 00 Chemistry 988 Problem Set 2 Due Tues7 17 Feb 09 A Erisch gridded ion chamber for heavy ions is operated with methane gas at 100 mbar and 25 C The grid is 10 cm from the anode and the voltage rise between the grid and anode is 50 V The detector has a sensitive length of 50 cm along the path of incident ions NB some of the information necessary to solve this problem can be found in tables and gures in the textbook a Calculate the energy lost by an 60 MeV alpha particle in the sensitive region of this detector Be sure to indicate your source of necessary reference data b Estimate the theoretical resolution for this pulse if the Fano factor for methane is 015 c Estimate the time at which the electronic pulse from this detector reaches its maximum value d Estimate the minimum total capacitance of the electronic circuit with R509 that would be appropriate to measure this pulse e Estimate the pulse height of this signal in volts if the lumped capacitance of the circuit is actually 30 nF The empirical expression for the response of a proportional counter is written in the a i 1 L Q NIP NIP where b is a constant that depends on the energy threshold for the multiplication textbook as Calculate the Fano factor for P 10 gas if the measured resolution was found to be 132 for a 59 keV photon in a proportional counter that has b05 What is the multiplication factor for a proportional wire that has a 40 pm diameter and is operated at 500 V inside a cylindrical volume 1 cm diameter with propane gas at 100 mbar 8 96 MAM emf 4W wit 7A EHMW K0 w M Obj JO 3450 Maw 529 353815 K KmJf T 65 gt 323H54392M1 z 323 W a W Q AE AX quot 3 tilM Linn and 3 39 T243quot 5 72 E 1 Qt wul4 2 1ng T0252 j a 63961 2545 42 dzwy z 3135 34 quot 6 quot77 24w 6 W 7 CV 3 zz rgs w53 Mn laW a in g an VK At v Ax daAw n relia al tle t 2 At I UM d bt 124 LIZ 9 8a ms 14 W V N 6 V A 439 A quot ll 739 My kw MA gt G VCMWq i oo Spring7 2009 Distributed Tues7 7 Apr 09 1 5 9 4 Chemistry 988 Problem Set 4 Due Tues7 14 Apr 09 General Electric manufactures boron coated proportional counters eg7 model number RS P7 0812 117 and the speci cations indicate that the device has a capacitance of 7 pf and a resistance of 101L2 9 The manufacturer reports that the average change output is 2X10 1L3 coulombs at 600 V 1 What is the ratio of the signal current to the leakage current in this device You can leave At the time duration of the charge collection as a parameter 2 Estimate the average gain of this proportional tube You can either leave W as a parameter or assume W m 30 eVlP for the ArCOZ ll gas since the composition is not given in the speci cations Make an estimate of the ef ciency of a thermal neutron counter that is based on a gas lled proportional counter that has a boron coated wall as the active ingredient The boron coating on the wall has a effective thickness of 09 mgcmZ and is enriched to 92 1013 Attenuators for electrical circuits are often labeled in decibel units dB which can lead to confusion Formally7 dB7s were introduced in acoustics and are equal to 10 log10 PoutPm where P is the power In electronic circuits7 PV2R so a dB is also 20 log10VWtVm and many people don7t remember the factor of 2 Using the network shown in Figure 165b in the textbook7 calculate the values of the resistors that will create a 3 dB reduction of a signal with a 50 9 load The Tennelec TC 241 shaping ampli er is used in many experiments at the NSCL to amplify signals from charge sensitive preamps connected to silicon detectors of many shapes and sizes This device has one stage of differentiation followed by ampli cation and then three stages of integration Make an accurate graph of the output signal from such an ampli er if a 01 V step function eg7 a Fermi function with a1 ns is applied and all of the time constants are set to 1 us g w 3 a 2 wq in A H g ltgt m e 17233be 3 w M ii 10 31 3 33 A m 2m uwmx xmieelt4 rmzw 36 p 4 45 f f3 Ni 433 73 i k e A inn i m Mk 5a 33 My r3 x 31 nut Rim a m QR 43 253m gut w J A amp feul 4 Admwui 3V x qu n dsmhziwnmm Pampu J I J0 as is k 5 I 434 MR 9 4 dwm mdwwdg941 ad aiu L 4 we y iii d 3 md x Jaged 3 gs wwrx mw u o w newsmhie 5amp4 JauqH e e 43 33 u M mw n Sgt Rig ma kmxu u 34 IIIII tl Xb M 3 13 1 y H q H gt q nzw mag at m w aft em weir H in NE wz Z 75mm w 23b W a MAR e m wmm i wMA W lt1239edb39L VOQWWCA39 L th m39 xmm QW39 F M k r 23 W 395 39 052 j ct xlx4 P Jsa4gbuo 9 5 mm W xg w A 91 I I k 6 WW 334m 39Mz z 38gt 2 0w an g 3amp2 295 201W Vowm N g gt 3Qp W e quot V39K A f 2 lpVM Vikkg 2 Als MWTAAH39 7 u jg w cum 4 y 6 a 9o M 20243 dm2u i k ee39 L Chemistry 988 Spring7 2009 Problem Set 5 Distributed Tues7 14 Apr 09 Due Tues7 21 Apr 09 One of the most important measurements at the NSCL involves separating the pulse heights and times of ight TOF of secondary beams for event by event particle identi cation In a recent experiment a 500nm thick silicon PlN was used to identify 66Fe and 6700 ions fully stripped at the experimental endstation The two ions had the same magnetic rigidity of Bp m y q 366 Tm The TOF was measured over a distance of 2097 meters The PlN detector was connected with a very short cable to a charge sensitive preampli er with a gain of 1000 VGeV of injected charge The preamp was then connected by a 50 ns long RG58CU cable eg7 Table 161 in text to a main ampli er that split the input signal between a timing lter ampli er TFA7 CR RC network and a shaping ampli er SA7 CR RC3 network Finally7 the logic signals for the TOF measurement were created in a Tennelec TC 455 constant fraction discriminator f02 with the appropriate cable delays The rise time of the signal from the preamp was 100 ns and the time constants in the TFA were set to 250 ns H What is the value of the ENC in electrons if the RMS white noise from the preamp was observed to be 10 mV 10 What is the maximum signal to noise ratio of the tail pulse from the preamp when the 66Fe passed through the detector 9 Make an estimate of the maximum signal to noise ratio for the pulse after pass ing through the cable and splitting in the main ampli er You can assume that the white noise is not attenuated by the cable rb The TOF was measured between a fast signal from a scintillator connected to a PMT having a time width of 025 ns and the signal from the TFA What is the expected width in ns for the observed TOF for the 66Fe fragments if the TFA preserved the signal to noise ratio of the preamp signal 9quot What is the time resolution for this TOF measurement 03 This TOF was measured with a 2048 channel time to digital convertor TDC and the full scale was set to 100 ns How long did the start pulse from the scintil lator have to be delayed in ns to put the TOF in the middle of the measurement scale 5 What is the expected FWHM of the observed TOF in channels77 in the TDC was mag 5 W e b i Pm 1J3 4 E pc Lu MM 2 1 MV 33 i H 8 1 My Z5 342 W 1 Zirme IF emQsz 3923 d5 F 1997 aha use 4824 an g k a 3 4M CP 4L2 1539 than uMgt 65 A 4324 MON 4524 mm W Wm 1 826 W pun2 ad 53 1 gquot 4 16 VheY 3 Com 4PM Lawf eagt CL mmBqAM x wiMlA39j l eb 1 x 31 8MA 1 788 m a kmeaA39Co v LM 502322 N vo l an gm WM ABM 951quot J6 L33 8 39 49 Ham 1 23M MsM 3n 9534534quot r 4 wig2 PM I w Mam1 as wla m MCDTFA w 4W mu g 8821 1 39 MW W betcha tic JV3 l A z 2 2 o quot39K gt 6tjfquot Emar gm 7 5TMT 2 m 05qu WM D z m a z 39g Spring7 2009 Distributed Thurs7 19 Mar 09 1 E0 00 7 Chemistry 988 Problem Set 3 Due Thurs7 2 Apr 09 Many silicon semiconductor detectors in use at the NSCL were manufactured by Ml CRON Semiconductor Corp in England A typical recently purchased PIN device is MSX25 500 that has an area of 50x50 mm2 and a thickness of 517nm The operating bias is 90 volts for full depletion The contact layers are 05 pm each and thus can be ignored Make an estimate of the resistivity of this material if it is n type silicon A 4 Megapixel77 chip in a modern digital camera is based on a chip with 2240x1680 pixels and the data can be clocked out at 30 MHZ 1 How long does it take to record a single image if the device is readout through a single Analogue to digital convertor ADC 2 How many green photons 430 nm must be absorbed by the silicon in one pixel if the ADC has a threshold of 20 electrons What is the ratio of the mean number of photons created in a standard 377x377 NalTl detector by the photopeak of the 40K decay to that created by the average cosmic ray interaction Since uranium is an impurity in most metals7 a gas lled detector will have a low level background from alpha particles that are emitted from uranium and its daughter nuclei that leave the wall and enter the gas A typical level of contamination is 20 parts per billion Estimate the counting rate of alpha particles per square centimeter per second leaving the surface Note that the most important alpha particle will come from 235U decay and assume that one half of the alpha particles exit the surface from a layer that is equal to the 12 the range of the alpha particle CM 0amp3 mired 5 WZooq r Pf i552 1 3 m e Mow Zue4z 371 gt Al R w as 331 Va A 4 azzi b W3 Pa A few 4 z 1 WTOMRJ 39539 J 3 quot1Mm X 5 a f m fig 5 k3 WW 2 mgg quotquotr a 3 w quot4A PZ fxffvx w w 32 r MJW K2gtM 4W0 in muzzw l g z 3 x ly Z 8iev p A 1 39 M ig Wf dgg W v 2 39 4 1quot 3 T W 43 153M 139 5013 939 53 I 46K Bf M M x 3Wnev cg g y Adiqu l 1 A eb mcL webgag 95K L uz yEpOLI 1 I my 1P a szS 2 131 34 g w a i a 1 PM 3 W M my W R L4LQ Rev 1 thul iM Qr 3 1 3591 x WYZ3 L ha4 3 53 3 2 2 345 A 5 Spring 2009 Distributed Thurs 22 Jan 09 Chemistry 988 Problem Set 1 Due Thurs 29 Jan 09 1 1340s sources are often used to calibrate photon detectors In contrast to the 10 more widely available 1370s isotope available as a ssion product from uranium the lighter isotope has to made by a neutron capture reaction Be sure to cite any references that you use to answer the following questions a Give the half life the daughter nucleus and the primary radiations that are emitted by the heavier isotope 1370s A C7 V Give the half life the daughter nucleus and the primary radiations that are emitted by the lighter isotope 1340s A O V Aside from the half lifes and energies what is the most important difference between the photons emitted by these two isotopes A graduate student has a source prepared to calibrate a particular detector system Calculate the activity of a 50 mg sample of pure cesium that is exposed to a ux of 1 gtlt 1013 thermal neutronscmZs in a nuclear reactor for 100 minute at the end of the irradiation The cross section for the 717 reaction under these conditions on the target nucleus is 29 barns A barn is 100 fmz A D V Calculate the activity of this sample 23 years later when the professor is ready to retire and the student has long since graduated Estimate the nal pressure inside a stainless steel beam line at the NSCL that is 10 meters long and has an inner diameter of 10 cm This line is pumped by a 100 ls turbomolecular pump with a 10 cm aperture that is connected to the beamline with an 90 elbow with 20 cm long arms at one end of the beam line Use the estimate from lecture for the off gasing constant for the walls Table 31 Transmission Probability a for Round Pipes 10 1 1 1 1 1 1 l Id a d a quot 000 100000 16 040548 005 095240 17 039195 R 4 i 010 090922 18 037935 03 015 086993 19 036759 391 B 020 083408 20 035658 T 39 025 08012 25 031054 030 077115 30 027546 05 035 074341 35 024776 040 071779 40 022530 1 0 45 069404 45 020669 5 1 050 067198 50 019099 055 065143 60 016596 04 060 063223 70 014684 NR 065 061425 80 013175 1 070 059737 90 011951 g 075 058148 100 010938 02 4 u 080 056655 V 150 007699 5 085 055236 200 005949 090 053898 250 004851 39 095 052625 300 004097 1 1 1 1 10 051423 350 003546 0 39 39 4 5 8 11 049105 400 003127 0 1 2 3 a 12 047149 500 002529 13 045289 5000 0264791110 14 043581 50000 026643214039 Fig 310 Molecular W100 probability of an 911W Rer ed 15 042006 00 41131 with permission from J Phys 31 p 1169 D H 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