Run 5

1. Placed two Am-241 sources of activity 37 kBq in source holder mounted in tower.
   • Collimation performed by means of a lead disk of thickness 1/16“ and outer diameter 1”, with a hole of diameter 0.008“ drilled through the its centre.
   • Hole covered with Cu tape to prevent alphas from contaminating the data.
     • Unable to see peaks at energies < 30 keV due to copper's high atomic number (Z = 29) and density (8.92 g/cm³).
     • Lesson: use Al tape in future (Z = 13, density = 2.7 g/cm³).
2. Tower assembled using threaded rods and side coax 4.
   • One connector found to have a damaged pin.
   • One connector gave strange results when an electrical check was performed.
   • Both sides have been labelled so as not to be used again.
3. Base temperature is slightly higher than before at 40 mK.
4. Could not get DCRCv2 to work for phonon channels, so switched to DCRCv1.
   • Known problem in DCRCv2, which will be fixed in DCRCv3.
   • 8 keV line from Cu fluorescence not visible due to higher energy threshold of DCRCv1.
5. Performed overnight (approximately 11-hour) Am-241 run on 28/29 July 2010.
   • See 60 keV line clearly and position of sources through reconstruction.
   • No degredation in neutralisation.
   • Ambient neutron rate is 2.5 ± 0.3 mHz.
6. Performed 1-hour Cf-252 (& Am-241) runs to test shielding effects of polyethylene sheets on 29 July 2010.
   • Tested shielding thicknesses of 0”, 2“, 4” & 8“.
   • Neutrons selected with Total Phonon Energy (Pt) between 20 and 60 keV, and Yield 0 to 0.6.
   • 8” of polyethylene reduces neutron flux by a factor of 6.
   • Drilled holes in polyehthylene shield and line-of-sight only coverage of shielding between detector and source means these values are fairly conservative.
7. Performed overnight (approximately 8-hour) Ba-133 (& Am-241) run on 30/31 July 2010.
   • Ideal position of Ba-133 source is 13“ below top of metal shield.
   • Am-241 peak visible at 60 keV.
   • Ba-133 peaks visible at 303 keV, 356 keV and 384 keV.
   • No degredation in neutralisation.
   • Ambient neutron rate is 2.1 ± 0.2 mHz, which agrees within errors with that obtained from the overnight Am-241 run.

Data summary

The eps, matlab fig and png files of all the following plots can be found here

% position cut
cQin = 0.93 <= Qpart & Qpart <=1.07;
cDel = (-50 < Xdel & Xdel <50) & (-50 < Ydel & Ydel <50 );
cAmDel1 = ((-7.86 < Xdel & Xdel < -1) & (-29.1 < Ydel & Ydel < -20.5));
cAmDel2 = ((3.4 < Xdel & Xdel < 10.5) & (15.7 < Ydel & Ydel < 25.5));
cAmDel = cAmDel1 | cAmDel2;
 
% fitting quality cut
cQchi2 = QSOFchisq(detnum,0) < 9000 + Qsum.^2*0.21;
 
% energy cut
cE = 5 < Qsum & Qsum < 100;
cPt = Pt > 5;
cQsum = Qsum >5;

Neutron rates and fluxes in Figure 7 obtained with data taken in 1 hour Cf-252 runs with 0", 2", 4", & 8" of polyethylene shielding. Ambient neutron rate and flux obtained with data from the overnight Am-241 run.

Figure 7: Neutron rate and flux as a function of polyethylene neutron shield thickness
Matlab fig, eps
Matlab fig, eps

Neutrons are selected as events with Total Phonon Energy (Pt) between 20 and 60 keV, and Yield 0 to 0.6. An ambient neutron rate of 2.5 ± 0.3 mHz is found from the overnight Am-241 run:

Figure 8: Yield Y as a function of Total Phonon Energy Pt from overnight Am-241 run
Matlab fig, eps, data set 07100728_2249: link to all plots

The ambient neutron rate obtained from the overnight Ba-133 and Am-241 run of 2.1 ± 0.2 mHz lies within errors:

Figure 9: Yield Y as a function of Total Phonon Energy Pt from overnight Ba-133 & Am-241 run
Matlab fig, eps, data set 07100731_0111: link to all plots

Polyethylene sheets of approximate height 6” and width 2' were placed between the source and detector such that the line-of-sight was covered. However, neutrons, unlike gamma-rays, do not necessarily follow a straight path to the detector. Additionally, drilled holes in the polyethylene also means that shielding does not provide a uniform coverage. Therefore, the reduction in neutron rate by a factor of 6 with 8“ of polyethylene shielding is fairly conservative, and hence should be assumed to be a lower limit. The neutron castle will better cover the detector, and hence will improve this result.

Figure 10: Yield Y as a function of Total Phonon Energy Pt from 1 hour Cf-252 & Am-241 runs with 0”, 2“, 4” & 8“ of polyethylene shielding
Matlab fig, eps, data set 07100729_2305: link to all plots
Matlab fig, eps, data set 07100729_2138: link to all plots
Matlab fig, eps, data set 07100729_1856: link to all plots
Matlab fig, eps, data set 07100729_2305: link to all plots