Rate Capability Measurement for UIUC RPC
test RPC performance (efficiency and position/timing resolution) at different rates.
Monte Carlo method
The program simulates a photon coming from a random point of the source travelling in random direction; the place where the photon set off an ionization is determined by the free mean path of the photon (the distance the photon travels follows a decaying exponential distribution). According to the location of the ionization, we can then determine which RPC strip should have a response.
Calculation for radiation level
the name of the program is now "new-radiation.C"
check out the code, first point to my CVS repository
export CVSROOT=/home/npl/yangrz/cvsthen go to an empty directory
cvs co rpc-cosmic/radiationrun the code like this:
root -l new-radiation.C+note the "+" means ROOT will compile the code so that it will run faster
Result of the program (2007-06-04)
Using a Fe55 source with activity 100 micro-Ci, photon rate on each strip are: (in Hz/cm^2)
strip #1 : 1386.41 Hz/cm2 strip #2 : 513.73 Hz/cm2 strip #3 : 245.891 Hz/cm2 strip #4 : 133.95 Hz/cm2 strip #5 : 77.7117 Hz/cm2 strip #6 : 47.0663 Hz/cm2 strip #7 : 30.1433 Hz/cm2 strip #8 : 19.5168 Hz/cm2 strip #9 : 12.9791 Hz/cm2 strip #10 : 8.84459 Hz/cm2 strip #11 : 6.14312 Hz/cm2 strip #12 : 4.24214 Hz/cm2 strip #13 : 3.06341 Hz/cm2 strip #14 : 2.19281 Hz/cm2 strip #15 : 1.08907 Hz/cm2
The source has been assumed to be a thin (cross section 1mm x 1mm), long (10cm) rod placed 1cm away from the nearest strip. The source also has 1mm offset from the strip plane in the vertical direction (z). The geometry is shown below.
So the rate coverage goes from ~1Hz/cm^2 to ~10kHz/cm^2, PHENIX RPC will be expected to have rate capability ~100Hz/cm^2. Therefore, we can change our rate range to the order of 100Hz~1kHz if we put the source a little further and use a stronger source.
This is an illustration of the radiation levels at RPC strips using the geometry described above:
Parameters in the program
Some important parameters: location (sx, sy, sz) and dimensions of the source (sdx, sdy, sdz):double sx = 3.0*CM; double sy = -1.0*CM; double sz = 0.1*CM; double sdx = 10.0*CM; double sdy = 0.1*CM; double sdz = 0.1*CM;
Other parameters for RPC
double edge = 0.0*CM; double rpc1x1 = 0 - edge; double rpc1y1 = 0 - edge; double rpc1x2 = 6.0*CM + edge; double rpc1y2 = 17.8*CM - edge; double rpc1z = 0; double rpc1dxy = 0.1*CM;
Note that right now the final plots shows the photon rates for a surface at height rpc1z = 1mm
References
presentation by Nathan Sparks (ACU) ppt
Fe55 source
http://www.ornl.gov/sci/isotopes/r_fe55.html
http://www.gmu.edu/research/labsafety/RHAS-Resources/55Fe.pdf
photon cross section (for photon free mean path calculation)
