PMT counts over fixed time period

PMT 14 was biased to -1100V and a dual scaler (counter) NIM module is allowed to collect counts for 5 minutes. Five runs are taken for each arrangement (see table 1) of the source, scintillator, and collimator.

Table 1: experimental configuration
Config. #	Source	Scintillator	Collimator	Shielding
1	None	1-66-x	None	None
2	Am-241	1-66-x	None	None
3	None	1-66-x	Copper	None
4	Am-241	1-66-x	Copper	None
5	None	1-66-x	Copper	Lead
6	Am-241	1-66-x	Copper	Lead
7	None	None	None	None
8	Am-241	None	None	None

With Scintillator

Table 2: Counts/(5 min) with Scintillator
Run #	Am-241	No Source
1	2220	1743
2	2224	1733
3	2206	1610
4	2133	1692
5	2173	1703
Average	2191	1696
Error of Avg.	17	23

We observe a statistically significant difference in the number of counts between Am-241 and no source when the scintillator is attached to the PMT.

With Collimator, Scintillator

Table 3: Counts/(5 min) with Collimator & Scintillator
Run #	Am-241	No Source
1	1738	1685
2	1740	1727
3	1724	1700
4	1786	1688
5	1715	1691
Average	1741	1698
Error of Avg.	12	8

There is a significant difference between the Am-241 counts and background counts, but the effect is much less pronounced than with no collimator.

With Collimator, Scintillator, Shielding

For these runs, the same setup as used above is surrounded with lead bricks to shield the scintillator from cosmic rays.

Table 4: Counts/(5 min) with Collimator & Scintillator
Run #	Am-241	No Source
1	497	498
2	543	529
3	529	525
4	515	502
5	523	474
Average	521	506
Error of Avg.	8	10

No Scintillator

Table 5: Counts/(5 min) with no Scintillator
Run #	Am-241	No Source
1	0	0
2	2	3
3	3	1
4	2	2
5	2	2
Average	1.8	1.6
Error of Avg.	0.4	0.5

We observe no significant difference between Am-241 and no source when no scintillator is used.