SIMPLIFIED MUON LIFETIME EXPERIMENT lectron leaves an ionization trail in the scintilla. Muon flux tor, and as a consequence, the decay of the muon Mu ti- Channel causes another input signal to go to the discrimi- nator. This pulse at the stop input of the TAC causes it to measure the time since the last start scintil pulse and to produce a bipolar output pulse of 2 sec width with an amplitude linearly propor- turn recorded by the PhA. The read out process Amplitude takes much longer than the propagation of the decay electron signal from the stop to the start inputs, and as a result, the corresponding start pulse will be ignored etup used for this experiment. The The only piece of equipment needed to per- follows: photomultiplier tube: RCA 7264; discriminator form the experiment which is not available as Ortec model 417; TAC: Ortec model 437; Multichannel standard unit is the seintillator-photomultiplier analyzer: Nuclear Data Corp. model ND]30A tube assembly. because the natural cosmic ray flux is not very intense, approximately 1x10-2 tape. Finally, an aluminum frame was constructed muons/cmsr sec at sea level, and about twice to support and protect this assembly and hold this value at the 5000-ft elevation of the Uni- the photomultiplier tube base versity of Colorado, the need for a scintillator After the components of the system have been with a large horizontal area is indicated. Also, connected, the PM tube high voltage, the dis since the energy spectrum of the muon flux criminator level, and the TAC time range must reaches a maximum in the neighborhood of 1 Bev, be adjusted. The high voltage was selected by the scintillator should be as thick as possible. setting the discriminator to its lowest threshold, These considerations and the availability of a about -0.18 V and then increasing the voltage large piece of scintillator plastic resulted in a applied to the PM tube until a reasonable trigger 68X24X23 cm rectangular block being cut for rate was obtained for the discriminator. At he apparatus. An RCA 7264 photomultiplier -2010 V, a trigger rate of 150/ sec was obtained tube was optically coupled to one of the small To obtain a clear decay curve, the discriminato ends of the scintillator block. The entire assembly setting must be raised. A discriminator setting was then wrapped with aluminum foil and black of -0.8 v was found to give the highest possible TAC output rate and yet provide data repre- senting a smooth decay curve Coincidence III. RESULTS Circuits A long experimental run was made for a period Time to of 695 h with a TAC range of 20 usec and a dis- Conolruder criminator setting of -0.8 V to see where the decay curve merges into the background which is due to discriminator pulses randomly occurring Absorb within 20 usec of each other. This same run was che muon. For the 695-h experimental run,a pulser capable of producing pulse pairs was used along with an oscilloscope to establish a time to Muti- PHA channel gain of 0.112+0.003 usec/ch Analyzer After 695 h, the spectrum of Fig. 3 resulted. Both FiG.I.A typical muon lifetime experimental setup. the muon decay curve and the background are Details of its operation are discussed in the text. clearly evident. Channels 160-180 were average