Model 265A Photomultiplier Base Operating and Service Manual
Contents
1. DER RI UERBO ee tg bel qr nv ib E RE S 1 2 5 RELATED EQUIPMENT ane EE ned bee es beer uh ted Dried eode t orco aeg 2 2 6 MECHANIGAL DATA os winters eR ek eb ieee alee wk c XXE D Pee px 2 3 INSTALLATION et re ER Refer etn Ime t ees der de ean es 2 3 1 DETECTOR 2 3 2 PHOTOMULTIPLIER INSERTION 2 3 9 INITIAE ADJUSTMENTS eR ERR UR EX a 2 3 4 CONNECTION INTO A SYSTEM 2 3 4 EE SERIA EUER EE IY EPA 4 4 1 TIMING WITH 4 4 4 2 APPLICATIONS eb oat ae ee ban ees stew RR CE SEE Rie ee 4 5 CIRCUIT DESCRIPTION 1 1 7 0 10 SAFETY INSTRUCTIONS AND SYMBOLS This manual contains up to three levels of safety instructions that must be observed in order to avoid personal injury and or damage to equipment or other property These are DANGER Indicates a hazard that could result in death or serious bodily harm if the safety instruction is not observed WARNING Indicates a hazard that could result in bodily harm if the safety instruction is not ob2. 452 460 and 485 are typical shaping amplifiers for the linear signals The timing signal from the anode can be connected through 500 cable terminated to an ORTEC 436 Fast Discriminator or 437A 447 or 457 Time to Pulse Height Converter Either output connector can be left with no external connection if its signal is not required 4 OPERATION Once the steps outlined in Section 3 of this manual have been performed the unit is ready for use Negative high voltage may be applied and adjusted for the appropriate gain associated with the specific experiment The gain will vary by a factor of approximately 2 with a high voltage change of 100 V 4 1 TIMING WITH PHOTOMULTIPLIERS Timing with photomultipliers implies some type of coincidence measurement This measurement may be performed with standard coincidence circuits such as the pulse overlap type which are essentially single channel time analyzers or with time to pulse height converters which are differential type or with multichannel analyzers The response of the coincidence system to a prompt cascade always has finite width which comes from a variety of sources The most important of these are as follows 1 Variation of time of interaction of radiation with the scintillator and the amount of energy deposited therein 2 Finite decay time of light emitting states in the phosphor and variation of times of photon arrival at the multiplier cathode 3 Variation of tran
3. in Figs 4 6 4 9 for the aid of the user TIMING SHAPING PREAMP ANALYZER ADC 1 ADC 2 STILBENE DISC LEVELS 1 i 3 5 l TIMING SCA Fig 4 6 Fast Fast Coincidence Photomultiplier Tube with Pulse Shape Discrimination PULSE GENERATOR TIMING SCA semicono OET 7A source Start ZA PM TUBE 265A or 269 PM BASE LINEAR GATE TIMING SCA ANALYZER SCING SHAPING PREAMP AMP Optional Not Needed If Crossover Timing 15 Chosen Fig 4 7 Fast Timing System Semiconductor Detector Photomultiplier Tube for Coincidence Using Crossover Pickoff Techniques Power TIMING SCA SCINC SHAPING PREAMP AMP 265A or 269 PM BASE ZA source MQ PM TUBE 265A or 269 PM BASE PHOSPHOR ANALYZER PHOSPHOR Stop SCINC SHAPING PREAMP AMP Fig 4 8 Semiconductor PM Coincidence Using Conventional Crossover Timing TIMING SCA LINEAR AMP CONSTANT FRACTION 58 DETECTOR DISCRIMI WITH NATOR TIMING PREAMP PULSE GENERATOR TIME TO PULSE HEIGHT CONVERTER DETECTOR 265A or 269 PM BASE 100 MHz DISCRIMI NATOR Fig 4 9 Subnanosecond Timing System Semiconductor Photomultiplier Tube SLOW COINCIDENCE LINEAR GATE ANALYZER 10 5 CIRCUIT DESCRIPT
4. laboratory conditions using the ORTEC 265A and other appropriate equipment It is important to remember that the resolution obtainable varies as 1V n where nrepresents the number of photoelectrons created by the event and is therefore representative of the amount of energy deposited in the scintillating phosphor and is strongly influenced by PM optics A Schwarmhild A Survey of the Latest Developments in Delayed Coincidence Measurements Nuct Instr Methods 21 1 1 1963 2G Present et al Fast Delayed Coincidence Technique The XP1020 Photomultiplier and Limits of Resolving Times Due to Scintillator Characteristics Nucl Instr Methods 31 l 71 1964 E Gatti and V Svelto Revised Theory of Time Resolution in Scintillation Counters Nuct Instr Methods 30 213 1964 D A Godcke and C W Williams High Resolution Time Spectroscopy 1 Scintillation Detectors ORTEC publication August 1968 5 with Ge Li Detectors ORTEC Application Note 31 1970 Typical Fast Slow Coincidence Using Nal TI The block diagram of Fig 4 1 applies equally well here The difference in the two systems is the scintillator and its decay characteristic This decay time constant is 0 25 usec whereas the same time constant for Naton 136 is approximately 2 nsec With Nal Tl much more total light is produced per equivalent energy event but the collection of this light is over such a wide period of time as indicated
5. the same procedure and ORTEC will provide a quotation Damage in Transit Shipments should be examined immediately upon receipt for evidence of external or concealed damage The carrier making delivery should be notified immediately of any such damage since the carrier is normally liable for damage in shipment Packing materials waybills and other such documentation should be preserved in order to establish claims After such notification to the carrier please notify ORTEC of the circumstances so that assistance can be provided in making damage claims and in providing replacement equipment if necessary Copyright 2005 Advanced Measurement Technology Inc All rights reserved ORTEC is a registered trademark of Advanced Measurement Technology Inc All other trademarks used herein are the property of their respective owners CONTENTS SAFETY INSTRUCTIONS AND SYMBOLS 2 iv SAFETY WARNINGS AND CLEANING INSTRUCTIONS TA DESCRIPTION 54g acted eurer IULIUS 1 2 SPECIFICATIONS Le PE E ERE Boe eat perde is 1 24 PERFORMANCE ue ce eb uh bed deu pue vea Eee is 1 2 2 CONTROLS dar PERDE EX Her Eu RR en M E e tes 1 2 34 INPUTS Dax cete pei Ld rV eS 1 234 OUTPUTS ori cR repr
6. 65A PHOTOMULTIPLIER BASE 1 DESCRIPTION The ORTEC 265A Photomultiplier Base structure provides a mechanical assembly and resistive voltage divider network with appropriate capacity decoupling for operation of the Burle 8850 or Hamamatsu R1332 photomultiplier This tube is a bi alkali photocathode device with very good timing and energy resolution characteristics The tube is capable of relatively high pulse currents when used in timing applications and this base structure complements the tube characteristics by maintaining good pulse fidelity over a wide range of signal currents see Fig 1 1 The unit provides two outputs the negative anode signal for timing applications and the linear signal from the ninth dynode This linear signal is of special importance in any experiment in which energy measurements are desired Conditions High Voltage 2200 V Phosphor Naton 136 Horizontal Cal 5 nsec cm Vertical Cal 10 mA cm Source 80 Fig 1 1 Typical Anode Output Pulse 2 SPECIFICATIONS 2 1 PERFORMANCE All photomultiplier tube specifications are furnished by the manufacturer The 265A Base accom modates the RCA 8575 or 8850 tube and includes an appropriate voltage divider network for the tube elements 2 2 CONTROLS Internal adjustments are included for the focus electrode and for the second and twelfth dynodes 2 3 INPUTS HIGH VOLTAGE 3 kV maximum at 2 mA maximum for bleeder network T
7. ION The divider is a graded resistance divider whose The last four dynodes are directly available at J4 for gain and signal quality have been carefully external dc control or additional capacitance if considered R15 and R17 perform the function of desired optimizing the input optics An open view of the 265A showing these controls is given in Fig 5 1 R26 Fig 5 1 Open Unit Showing Picture of Controls
8. Model 265A Photomultiplier Base Operating and Service Manual Printed in U S A ORTEC Part No 733110 0905 Manual Revision C Advanced Measurement Technology Inc a k a ORTEC a subsidiary of AMETEK Inc WARRANTY ORTEC warrants that the items will be delivered free from defects in material or workmanship ORTEC makes no other warranties express or implied and specifically NO WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ORTEC s exclusive liability is limited to repairing or replacing at ORTEC s option items found by ORTEC to be defective in workmanship or materials within one year from the date of delivery ORTEC s liability on any claim of any kind including negligence loss or damages arising out of connected with or from the performance or breach thereof or from the manufacture sale delivery resale repair or use of any item or services covered by this agreement or purchase order shall in no case exceed the price allocable to the item or service furnished or any part thereof that gives rise to the claim In the event ORTEC fails to manufacture or deliver items called for in this agreement or purchase order ORTEC s exclusive liability and buyer s exclusive remedy shall be release of the buyer from the obligation to pay the purchase price In no event shall ORTEC be liable for special or consequential damages Quality Control Before being approved for shipment each ORTEC instrument must pass a stringen
9. and requires that the anode be operated at ground potential This means thatthe photocathode is at negative HV Assure that this high voltage is not dropped across the glass envelope of the photomultiplier Be careful to preventthe scintillator from imposing a ground at the front surface of the photocathode A drawing of the suggested method of mounting a simple detector is shown in Fig 3 1 Scotch Type 33 is recommended forthe two layers of electrical tape shown in Fig 3 1 that are to be applied over the photomultiplier tube This product not only affords the necessary electrical insulation but also minimizes noise that would be present because of extraneous light that could reach the tube structure This tape wrapping should be extended beyond the physical body of the photomultiplier tube to include the tapered surface of the tube socket within the light shielded configuration 3 2 PHOTOMULTIPLIER INSERTION Remove the magnetic shield if used The tube may now be inserted directly into the light tight socket Place the felt washers around the photomultiplier and remount the magnetic shield 3 3 INITIAL ADJUSTMENTS Remove the high voltage divider cover The controls of the unit are trimmed for optimum operation with a specific PM at the factory However the unit will probably need trimming again when a different PM is used These adjustments need to be performed rarely more than once with a specific PM unless the operating HV i
10. e 4 4 kHz Stop 1 x l in Naton 136 8575 Rate 2 8 kHz Source 2300 V C R 5 T ch 28 8 psec Width of E Windows 20 FWHM 270 psec 10 FWTM z 521 psec Counts Channel 10 10 150 160 170 180 190 200 210 Channel Number Fig 4 2 Typical Coincidence Spectrum Using Plastic Scintillators Counts Channel 10 Start 1 x 140 Naton 136 XP 1021 Rate 4 4 kHz Stop 1 x 1 Naton 136 8575 Rate 2 8 kHz Source Co 2300 V C R 5 T ch 28 8 psec Width of E Windows 20 FWHM 270 psec 10 FWTM 521 psec Start 8 cm Coaxial Ge Li Drifted Coax 2 Stop 1 1 2 x 1 on RCA 8575 Channel Width 1 32 nsec Source 22 uncollimated Det Bias 450 V Start Threshold 30 keV Counts Channel 10 10 60 70 30 90 100 110 120 ks T T 3 ae Channel Number Channel Number Fig 4 3 Typical Coincidence Spectrum Using Fig 4 5 Timing Spectrum with Ge Li Drifted Nal TI Scintillator Detector Energy LINEAR DELAY Power TIMING SCA 1K ON source TIME TIME PICKOFF LINEAR Nal TI pickorF CONTROL GATE SCINTILLATOR Analyzer Time or Energy PM BASE TPHC ANALYZER Stop DELAY Power SHAPING PREAMP AMP SCA Fig 4 4 Gamma Gamma Coincidence System with a Ge Li Drifted Detctor System Block Diagrams A number of experimental systems are shown
11. s varied more than 200 V MAGNETIC SHIELD ALUMINUM SOCKET CIRCUIT RING TWO LAYERS OF ELECTRICAL TAPE 10 kV PER LAYER PRINTED ALUMINUM STYROFOAM TUBE OPTIONAL ALUMINUM ALUMINUM FOIL AT CATHODE POTENTIAL c PHOTO MULTIPLIER EPOXY CEMENT TUBE SCINTILLATING CRYSTAL Fig 3 1 Cutaway Drawing of PM Scintillator Mounting WARNING he voltages used in this network are dangerous so adjust the controls cautiously Observe the Anode output on a fast rise time osciloscope terminate the coaxial cables properly Apply negative 2200 V or the voltage at which the tube is to be operated to the high voltage connector Place a radiation source appropriate to the chosen scintillator near the detector Observe the output waveform and adjust the two bleeder string controls i e the Focus R17 and Dynode R15 for maximum output signal This assures that the input optics are adjusted properly for the specific photomultiplier used see Fig 3 1 5 Adjust R26 for maximum signal output without pulse shape distortion 6 Turn off the high voltage and replace HV divider cover The unit is now ready for operation 3 4 CONNECTION INTO A SYSTEM The linear dynode signal should be coupled through a scintillation preamplifier such as the ORTEC 113 to a shaping amplifier if linear energy information is desired The ORTEC 410 450 451
12. served CAUTION Indicates a hazard that could result in property damage if the safety instruction is not observed Please read all safety instructions carefully and make sure you understand them fully before attempting to use this product In addition the following symbol may appear on the product ATTENTION Refer to Manual DANGER High Voltage Please read all safety instructions carefully and make sure you understand them fully before attempting to use this product SAFETY WARNINGS AND CLEANING INSTRUCTIONS DANGER Opening the cover of this instrument is likely to expose dangerous voltages Disconnect the instrument from all voltage sources while it is being opened WARNING Using this instrument in a manner not specified by the manufacturer may impair the protection provided by the instrument Cleaning Instructions To clean the instrument exterior e Unplug the instrument from the ac power supply e Remove loose dust on the outside of the instrument with a lint free cloth e Remove remaining dirt with a lint free cloth dampened in a general purpose detergent and water solution Do not use abrasive cleaners CAUTION To prevent moisture inside of the instrument during external cleaning use only enough liquid to dampen the cloth or applicator e Allow the instrument to dry completely before reconnecting it to the power source vi HIGH NEG w P ONLY ORTEC MODEL 2
13. sit time of photoelectrons in the photomultiplier due to different path lengths and to variation of initial energy and angle of the secondary electrons 4 Jitter and uncertainties of triggering times of the associated electronics The variation of the time of interaction can be minimized by appropriate geometry and small scintillators at a corresponding loss in efficiency and average energy deposition For a complete discussion of timing with photomultipliers the reader is referred to some of the excellent literature available on the subject 4 2 APPLICATIONS The different specific applications for the ORTEC 265A are essentially limitless but since the unit was designed primarily for timing applications a number of system block diagrams utilizing this unit are given Some typical resolution curves for three of the systems are given separately from which operational characteristics of other systems may be implied Typical Fast Slow Coincidence System Using Plastic Scintillators Figure 4 1 is a block diagram of a system that might be used to perform lifetime measurements or to study the time dispersion associated with some prescribed coincidence events It does not represent an optimum system if clean slopes ofthe coincidence curves are required to four or five decades but will give clean spectra to at least three decades at moderately high count rates The time spectrum shown in Fig 4 2 represents what may be obtained under
14. t set of quality control tests designed to expose any flaws in materials or workmanship Permanent records of these tests are maintained for use in warranty repair and as a source of statistical information for design improvements Repair Service If it becomes necessary to return this instrument for repair itis essential that Customer Services be contacted in advance of its return so that a Return Authorization Number can be assigned to the unit Also ORTEC must be informed either in writing by telephone 865 482 4411 or by facsimile transmission 865 483 2133 of the nature of the fault of the instrument being returned and of the model serial and revision Rev on rear panel numbers Failure to do so may cause unnecessary delays in getting the unit repaired The ORTEC standard procedure requires that instruments returned for repair pass the same quality control tests that are used for new production instruments Instruments that are returned should be packed so that they will withstand normal transit handling and must be shipped PREPAID via Air Parcel Post or United Parcel Service to the designated ORTEC repair center The address label and the package should include the Return Authorization Number assigned Instruments being returned that are damaged in transit due to inadequate packing will be repaired at the sender s expense and it will be the sender s responsibility to make claim with the shipper Instruments not in warranty should follow
15. that the time resolution is poorer than that of plastic Figure 4 3 is a typical spectrum taken with 1 7 in by 1 in Nal on one side of the coincidence system Fast Coincidence Using Ge Li Drifted Detectors Some recent experiments have been performed using a 1 by 1 in Nal TI ina gamma gamma coincidence arrangement with an ORTEC 10 cm Ge Li drifted coaxial detector as shown in Fig 4 4 In this case the radiant energy from the source was not collimated at all so that the time is given by collection from all parts of the detector The source viewed one end of a germanium detector Side channels selected the energy region of interest which was the photopeak on each side The full time spectrum is given in Fig 4 5 Full width at half maximum and full width at one tenth maximum are indicated This when compared with published timing curves indicates a very good detector design for timing purposes R L Graham et al Timing Characteristics of Large Coaxial Ge Li Detertors for Coincidence Experiments Trans Nucl Sci 5 13 1 72 1966 TIMING SCA Power SCINC SHAPING PREAMP AMP ORTEC 436 100 MHz DISC SCINTILLATOR NY source scinticcator NSN PM TUBE LINEAR GATE ORTEC 436 265A or 269 PM BASE 100 MHz DISC TIMING SCA ANALYZER Fig 4 1 Simple Fast Slow Timing System 10 Start 1 x 140 Naton 136 1021 Rat
16. ype SHV connector AUXILIARY Last four dynodes are available at pins in the Auxiliary connector for optional external voltage stabilization type MS3112E12 10S or Bendix PTO2E 12 10S connector 2 4 OUTPUTS ANODE Negative timing signal 500 dc coupled back terminated very good pulse quality for signal currents to 0 5 A type BNC connector DYNODE Positive linear signal from 9 dynode capacity coupled high impedance Z 1 MQ type BNC connector 2 5 RELATED EQUIPMENT The Anode timing signal can be furnished to a fast discriminator such as the ORTEC 453 or 436 when using either a Nal TI or plastic scintillator For plastic scintillators only the Anode signal can be fed directly to the Start or Stop input of an ORTEC 437A 447 or 457 Time to Pulse Height Converter The linear output from the 9 dynode is normally processed through an ORTEC 113 Scintillation Preamplifier and a shaping amplifier such as the ORTEC 410 450 451 452 460 or 485 2 6 MECHANICAL DATA WEIGHT Shipping 265A PM Base 3 lb 1 37 kg 218 Shield 2 Ib 0 9 kg C36 12 Cable lt 1 Ib 0 46 kg WEIGHT Net 265A PM Base 1 4 Ib 0 63 kg 218 Shield 1 Ib 0 46 kg C36 12 Cable lt 1 Ib 0 46 kg DIMENSIONS 265A PM Base 3 dia x 8 in long 218 Shield 3 in dia assembled 265A and 218 13 in long C36 12 Cable 12 ft long 3 INSTALLATION 3 1 DETECTOR MOUNTING The ORTEC 265A is designed for the best in pulse fidelity
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