Low Background Counting Facility

The SNOLAB Low Background Counting Group performs low background counting utilizing two ultra-low background germanium detectors, located in the underground laboratory at the 6800 foot level (6000 m.w.e) at SNOLAB.


Detector Properties

Detectors	SNOLAB Gamma Counter 1 (PGT)	SNOLAB Gamma Counter 2 (Canberra Well)	SNOLAB Gamma Counter 3 (Lively)	SNOLAB Gamma Counter 4 (Vue des Alpes)	SNOLAB Gamma Counter 5 (Gopher)
Detector Characteristics	PGT Coaxial Detector	Canberra Well Detector	Canberra Coaxial Detector	Eurisys-Mesures Coaxial Detector	Canberra Coaxial Detector
Manufacturer Details	Princeton Gamma-Tech 1992	Canberra 2011	Canberra 2011	Eurisys-Mesures 2001	Canberra 2007
Operational Dates at SNOLAB	2005	2013	2019	2017	2017
Detector Volume	210 cm3	300 cm3	400 cm3	400 cm3	400 cm3
Detector Type	p-type	p-type	p-type	p-type	p-type
Endcap Diameter	83 mm	105 mm	100 mm	105 mm	105 mm
Relative Efficiency	55% wrt standard NaI(Tl) detector	80% wrt standard NaI(Tl) detector	107% wrt standard NaI(Tl) detector	120% wrt standard NaI(Tl) detector	120% wrt standard NaI(Tl) detector
Shielding	Cubic shielding of 2 inches of Cu + 8 inches of Pb	Cylindrical shielding of 2 inches of Cu + 8 inches of Pb	Cubic shielding of 3 inches of Cu + 10 inches of Pb	Cubic shielding of 6 inches of Cu + 8 inches of Pb	Cubic shielding of 2 inches of Cu + 12-14 inches of Pb
Radon Suppression	Purge rate at 2 L/min	Purge rate at 2 L/min	Purge rate of 2 L/min	Purge rate of 2 L/min	Purge rate of 2 L/min
Muon Suppression	6000 m.w.e. overburden	6000 m.w.e. overburden	6000 m.w.e. overburden	6000 m.w.e. overburden	6000 m.w.e. overburden
Detection Region	Energy: 90-3000 keV	Energy: 10-900 keV	Energy: 40-3000 keV	Energy: 40-3000 keV	Energy: 40-3000 keV
Sample Size	Nominal: 1L (max ~4L)	Nominal: 8 mL	Nominal: 1L (max ~4L)	Nominal: 1L (max ~4L)	Nominal: 1L (max ~4L)
Detector Chamber 3-D Schematic	PGT Schematic	Not Available	Lively Schematic	VDA Schematic	Not Available

Detector Sensitivities

Isotope	SNOLAB Gamma Counter 1 (mBq)	SNOLAB Gamma Counter 2 (mBq)	SNOLAB Gamma Counter 3 (mBq)	SNOLAB Gamma Counter 4 (mBq)	SNOLAB Gamma Counter 5 (mBq)
238U	0.11 mBq	0.02 mBq	0.05 mBq	0.09 mBq	0.17 mBq
235U	0.16 mBq	0.01 mBq	0.02 mBq	0.06 mBq	0.08 mBq
232Th	0.10 mBq	0.02 mBq	0.06 mBq	0.08 mBq	0.21 mBq
40K	1.42 mBq	0.92 mBq	0.45 mBq	1.22 mBq	1.01 mBq
60Co	0.04 mBq	0.03 mBq	0.02 mBq	0.02 mBq	0.04 mBq
137Cs	0.13 mBq	0.02 mBq	0.02 mBq	0.05 mBq	0.08 mBq
54Mn	0.043 mBq	0.033 mBq	0.021 mBq	0.034 mBq	0.044 mBq
210Pb	N/A	0.55 mBq	31.53 mBq	7.71 mBq	16.49 mBq

Detector Sensitivities in Standardised Units

Isotope	SNOLAB Gamma Counter 1 [cts/(d-kg)] (PGT)	SNOLAB Gamma Counter 2 [cts/(d-kg)] (Canberra Well) [Obsolete DAQ Settings - Results to be Updated]	SNOLAB Gamma Counter 3 [cts/(d-kg)] (Lively)	SNOLAB Gamma Counter 4 [cts/(d-kg)] (Vda)	SNOLAB Gamma Counter 5 [cts/(d-kg)] (Gopher)
210Pb 46.5 keV	N/A	0.151 +- 0.071	5.47 +- 0.26	1.33 +- 0.21	N/A
226Ra 186.2 keV	0.22 +- 0.21	0.176 +- 0.080	0.600 +- 0.088	0.40 +- 0.13	1.11 +- 0.28
212Pb 238.2 keV	0.40 +- 0.14	0.710 +- 0.074	1.138 +- 0.093	1.08 +- 0.15	4.67 +- 0.28
214Pb 242.0 keV	< 1.04	0.173 +- 0.061	0.390 +- 0.080	0.67 +- 0.14	1.86 +- 0.25
214Pb 295.2 keV	0.31 +- 0.16	0.103 +- 0.044	0.528 +- 0.066	0.48 +- 0.11	2.61 +- 0.19
212Pb 300.1 keV	< 0.22	< 0.14	< 0.16	0.24 +- 0.11	0.59 +- 0.19
228Ac 338.0 keV	0.40 +- 0.14	0.070 +- 0.033	0.127 +- 0.053	0.38 +- 0.10	0.81 +- 0.14
214Pb 351.9 keV	0.59 +- 0.14	0.107 +- 0.031	1.038 +- 0.069	1.19 +- 0.13	4.74 +- 0.19
208Tl 583.2 keV	0.403 +- 0.082	0.020 +- 0.010	0.876 +- 0.058	0.440 +- 0.083	1.465 +- 0.088
214Bi 609.0 keV	0.584 +- 0.083	0.041 +- 0.010	1.030 +- 0.061	1.40 +- 0.11	2.96 +- 0.11
137Cs 662.0 keV	1.74 +- 0.11	< 0.007	< 0.090	0.422 +- 0.077	0.079 +- 0.040
54Mn 834.8 keV	< 0.12	< 0.021	< 0.048	< 0.058	< 0.065
228Ac 911.0 keV	0.209 +- 0.049	< 0.009	0.749 +- 0.050	0.422 +- 0.071	0.626 +- 0.052
228Ac 968.0 keV	0.145 +- 0.046	< 0.009	0.528 +- 0.045	0.244 +- 0.059	0.324 +- 0.037
214Bi 1120.0 keV	0.141 +- 0.046	< 0.013	0.329 +- 0.035	0.371 +- 0.059	0.300 +- 0.036
60Co 1173.2 keV	0.198 +- 0.050	< 0.009	0.165 +- 0.026	0.104 +- 0.047	0.031 +- 0.017
60Co 1332.2 keV	0.219 +- 0.043	< 0.009	0.118 +- 0.027	0.059 +- 0.044	0.085 +- 0.021
40K 1460.8 keV	1.400 +- 0.085	< 0.008	0.571 +- 0.042	1.295 +- 0.095	0.298 +- 0.034
214Bi 1764.0 keV	0.141 +- 0.034	< 0.007	0.337 +- 0.035	0.461 +- 0.059	0.173 +- 0.026
208Tl 2614.5 keV	0.498 +- 0.048	< 0.007	0.940 +- 0.050	0.508 +- 0.058	0.050 +- 0.014

Technical Details of Counter #1 (PGT) HPGE detector and material containers

• Drawing of the Geometry of the Ge detector and 1 litre Marinelli beaker, courtesy of James Loach.
• Description of the standard 1L Marinelli beaker from Ga-Ma Associates.
• Description of the 4 L Marinelli beaker from Ga-Ma Associates.
• Description of the 500 mL Marinelli beaker from Ga-Ma Associates.
• Description of the 180mL Marinelli beaker from Ga-Ma Associates.

Technical Details of Counter #2 Canberra Well detector and material containers

• Specification of the 3mL Cowie sample bottle.
• Specification of the 8mL sample vial and photo