• Simulation Data.

• Run simulation with detector length ~2.5“.
• Print casing for Sodium Iodide detector.

We use a P-type coaxial High Purity Germanium (HPGe) detector with a cylindrical Boride filled shield. Figure shown below.

• More information on the detector can be found here and with the user manual.
• A Plot of the detector's efficiency, taken from the user manual, is here.
• A figure with more dimensions shown is here.

We ran the detector with a ¹³³Ba source on the other side of a ~1/4 in gap made with lead bricks. The data was recorded for 15 min and then the detector was moved (along its cylindrically symmetric axis) and this was repeated.

• z represents the distance out from the base of the endcap.

• Now we plot the total counts from each peak together.
• The plot is weighted by the production rate of the source (81.0keV is produced 34.06% of the time and 356keV is 62.05%).

To test the accuracy of the efficiency plot given in the user manual, we ran the detector with the ¹³³Ba source placed 8in from the end of the detector

• The 81.0keV and 356keV peaks can clearly be seen.
• After calculating the production rate of the source and the geometry of the setup, the efficiency of the detector is estimated to be 98% for the 81keV peak and 46% for the 356keV peak.

This result matches with an N-type coaxial detector but not a P-type.

Data taken over ~2.75 days with Plutonium/Beryllium source, with and without Boron shielding.

• Energy scale calibrated from a ²²Na source.
• There is a 511keV peak from pair production background and a 477keV peak from neutron captures within the Boron shield.

From a Gaussian fit of the peak, A total of ~95,000 counts/day is estimated.

From a rough estimate of the geometry, we expect to have measured ~190,000 counts/day. The Calculation is shown below.

Anthony has updated the “k100Sim” so that it can simulate a situation where the South Wall of the K100 shield is removed (that was the wall where we mounted the NaI detectors). In the place of that wall we have the dewar and HPGe setup with the ability to add/remove the Boron shielding.

The data from a first run of 790M primaries of the Pu/Be source in the barrel position of Run 68 is here (Note: this is with HPGe length of 3 3/8”) :

/data/chocula/villaa/k100Sim_Data/boron/Run68_boron_PuBe_0x0000_1M_*_000_000.txt

This data has the format where each of the columns are as such below:

EV  DT  TS  P Type  E1  D3  PX3 PY3 PZ3 X3  Y3  Z3  time3 PX1 PY1 PZ1 X1  Y1  Z1  time1 nCap

The definitions are:

Here is an example of a Macro for the “k100Sim” that can do this:

#make a generic generator
/gps/particle neutron
#/gps/position 0.0 1197.31 -565.15 mm
#updated position for in-barrel source
/gps/position 0.0 1197.31 -646.79 mm 
/gps/pos/type Point
/gps/ang/type iso
/gps/ene/type Arb
/gps/hist/type arb
/gps/hist/file sources/pube_skim.dat
/gps/hist/inter Lin

/CDMS/Zip1/IsGe False
/CDMS/detector/activate Walls
/CDMS/detector/activate Floor
/CDMS/detector/activate Frame
/CDMS/detector/activate IceBox
/CDMS/detector/activate PuBeSourceAndShield
/CDMS/PuBe/Barrel True
/CDMS/detector/activate Shields

#this is needed to place the HPGe detector on the South wall
/CDMS/Shield/HPGeboron True
#this is needed to put the boron case shielding around the HPGe
/CDMS/Shield/HPGeboron_shield True
/CDMS/updateGeometry

#run naming stuff
/run/k100/OnlyNCapOut false
/run/k100/OFPrefix /where/you/want/the/files/prefix_

/run/beamOn NEVENTS

From the simulation:

• Number of events with neutrons passing through shield: 169864
• Total number of neutrons captured by shield: 73542 (43% of above number)
• Number of events with gammas produced from neutron capture: 68917 (93.7% of above number)
• Number of events with energy deposited into HPGe within energy range (0.45-0.5 MeV): 1020 (1.5% of above number)

We obtain the correct result (~94%) for the production probability of gammas.

Using 1.5% as the geometrical and detector efficiency, the shield efficiency estimate becomes ~ 125%.

Below is a plot of the Neutron captures in the Boron powder. Colored by density of points.

Taking the cross section of 120<z<140 (plot changed to histogram to more accurately show distribution).

Below is a histogram of the simulated deposited energy into the HPGe detector.