7D10.80-u1 - Cosmic Ray Telescope
Demonstrate detection of muons from the upper atmosphere and also other high energy particles that meet the coincidence requirement established by the instrumentation.
TEK O-Scope settings saved under Save/Recall Setting 3 (Sept. 2005)
InstructionsThe muon detector is built with several dedicated components. There is a processor (the bin assembly) which consists of an amplifier, discriminator, and coincidence tray; this is preassembled on a rack. The bin processes the signals from the two photomultiplier tubes (PMT) which are mounted at different elevations (in our case separated by ~3 feet). The bin outputs to an oscilloscope where comparisons can be made about the different rates of muon detection at different altitudes. Additionally, we include a speaker so that the sound of coincident muons can be heard by the class.
To assemble the demonstration, most electronic components are placed on the bottom of a 4’ cart. These include: the processor rack, the Tektronix scope, the high voltage power supply (HVPS), and the optional amplifier and speaker. On the top of the cart, place one PMT. Build a shelf with 4 bench clamps and 4 cross bars, and place the second PMT on top of that, about 3 feet above the other PMT.
Connecting the PMT to power Plug the PMTs into the HVPS with the provided coaxial cables via a distribution switch. The power supply inputs are labeled (w/ color 6). The mini-coax outputs are labeled with color 7. The outputs go to the processor rack. Caution: Incorrect connection to the HVPS can destroy the detectors!
Input to the processor The inputs to the processor rack are from the 2 PMT. The lower elevation detector is “Input 1” and the higher one is “Input 2” to the amplifier on the rack.
Output from the processor The processor has five outputs, four to the oscilloscope and one to the optional speaker. We organize the scope inputs so the first two channels simply measure the number of incident muons on each plate. These channel inputs are labeled (color 1 &amp;amp;amp;amp; 2). They come from the amplifier. The third and fourth channels measure the number of coincident muons. The third channel, input color (color 3), displays coincident muons from the coincidence tray. The fourth input (color 4) shows a processed muon coincidence from the amplifier tray.
Optionally, we can output the signal of coincident muons to a speaker. Route the (color 5) coaxial cable from the coincidence tray’s output to a mini Radio Shack Amplifier, which is in turn output to a standard speaker.
Programming the Oscilloscope Make the following settings to the TEK scope (most are found in the Quickmenu): DC Coupled (all), Impedance 50 Ohm (all), Ch1 @ 100mV, Ch2 &Ch3 @ 500mV, M(Hor)= 100ns, Trigger(Source) on Ch3, Set bandwidth to 20MHz, Trigger to Normal, Sample, Neg Slope, LF reject, Edge Trigger, Horizontal Resolution: Normal, Aquire: Wave Alert. (April 2009) SET TRIGGER LEVEL TO NEGATIVE!! to view negative pulse!
Turning on the devices First turn on the bins (the processor rack) and the optional amplifier. Only after the other devices are on will you turn on the HVPS. To turn on the HVPS, flip the switch and allow to warm up for 15 seconds. Switch to KV output, and VERY slowly dial in 1800 VDC. To turn the PS off, reverse those directions (dial down, turn off).
Optimizing the scope The scope usually needs some tweaking to get it to trigger properly. Just adjust the trigger level until stable, then make sure that the display is properly indicating on the screen.
Analyze the output on the oscilloscope, and explain what the students are hearing on the speaker. They are hearing coincident muons. The oscilloscope is shows three significant things: the number of incident muons on the top and bottom PMTs, and the coincident muons (muons incident on both tubes). The electronics are designed to measure "coincident" muons, i.e. a single muon that passes through both plates.