Americium Run with ~ 13 mm Sample

A smaller sized scintillator sample was machined to about 10 mm thick. This sample was tested with background and Am-241 in the new dark room with PMT R1332. The full-scale used was 0.8V.

Table 1: Run Information
Run	Source	Threshold	Bias Voltage	Number Events	Total Time	Saturation	Data File
1	background	30 mV	1800 V	10002	2869 s	13.47%	20140728_R1332_1800V_background2.dat
2	Am-241	30 mV	1800 V	13439	333 s	0.156%	20140728_R1332_1800V_am241.dat
3	background	30 mV	2000 V	10015	925 s	6.67%	20140729_R1332_2000V_background.dat
4	Am-241	30 mV	2000 V	10255	227 s	0.897%	20140729_R1332_2000V_am241.dat
5	Am-241	30 mV	2200 V	10001	214 s	2.190%	20140729_R1332_2200V_am241.dat
6	background	90 mV	2200 V	9998	627 s	3.901%	20140729_R1332_2200V_background_90mV-threshold.dat
7	Am-241	90 mV	2200 V	10005	229 s	2.009%	20140729_R1332_2200V_am241_90mV-threshold.dat
8	Am-241	90 mV	2200 V	187843	3965 s	0.5212%	20140730_R1332_2200V_am241_90mV-threshold.dat

Figure 1: Example Am-241 Histogram from Ovechkina (2009).

1800V Bias

Figure 2: Pulse Area Spectra for Both Runs at 1800V

Figure 3: Pulse Area Comparison weighted by run time (at 1800V)

Comparing the background spectra to the Americium-241 spectra, it appears that perhaps the Compton continuum and peak are visible. The Am-241 peak would be around 2 nVs, and the Compton continuum would sit right on top of the background.

2000V Bias

Figure 4: Pulse Area Spectra for Both Runs at 2000V

Figure 5: Pulse Area Comparison weighted by run time (at 2000V)

Assuming the Compton continuum and peak are as labeled for the run at 1800V, it appears that at 2000V, the Americium-241 spectra has separated from the noise peak. The Compton continuum might sit from around 0.5 to 3 V and the Am-241 peak around 4.5 V.

There are some very strange pulses that were noticed in only the last half of the run. An example is given in Figure 6. From watching the pulses appear as they were taken, I would estimate that there are maybe 50 or so of these pulses in the run. I am unsure of how to cut these pulses out by the variable we currently record from each pulse.

Figure 6: Example of Bad Pulse

Figure 7: Example of a Good Pulse for Comparison

2200V Bias

Figure 8: Comparison of Americium-241 pulse area spectra for all voltage biases.

Figure 9: Comparison of Artificially Imposed Thresholds.

Higher Threshold at 2200 V

The 2200 V bias runs were rerun with a higher threshold of 90 mV and double fullscale.

Figure 10: Pulse Area Spectra for Both Runs at 2200V with 90 mV threshold

Figure 11: Pulse Area Comparison weighted by run time (at 2200V and 90 mV threshold)

Figure 12: Comparison between the two runs at 2200V bias

The run with the “artificially” set threshold of 90mV (run 5) has been scaled to match run 7. The scale factor was calculated by the area under the curve between 1.0 nVs and 4.5 nVs (the range of the energy peak) and is about 3.76.

Long Run at 2200 V

The long run at 2200 V had a discriminator set threshold of 90 mV; however, this didn't seem to work, as many good events below threshold were recorded as well. Table 2 shows the events cut by an “artificially” added threshold in the analysis.

Table 2: Events cut by the “artificially” added threshold
imposed threshold	Number of events	Number of events cut	Number of events cut in energy peak
0 mV	186864	0	0
30 mV	186863	1	0
60 mV	187849	15	0
70 mV	186660	204	0
80 mV	181864	5000	0
90 mV	164472	22392	0
100 mV	123889	62975	1
110 mV	91220	95644	3
120 mV	66064	120800	20

The pulses within the energy peak are defined by having a peak area greater than 1.5 nVs.

Figure 13: Example of pulse cut by imposed threshold in energy peak.

Figure 14: Americium-241 spectra at 2200 V with a 90mV threshold

Figure 15: Comparison of Americium-241 runs at 2200 V

The run with the “artificially” set thresholds of 90mV (run 5) and 120 mV (run 8) have been scaled to match run 7. The scale factor was calculated by the area under the curve between 1.5 nVs and 4.5 nVs (the range of the energy peak past the noise).