I purchased two “Giant Super Sensitive MC6” GM tubes from Electronic Goldmine (Item Number : G18717, Unit Price: $89.95). These are Russian-made new-old-stock model MC6. They are 10.25″ long x 0.9″ diameter. I compared the sensitivity of these tubes to the other GM tubes that I use with my CDV700 Pro Geiger Counter.
For the experiment, I used a LENi CDV700, my d.i.y. counter/scaler, a Cs-137 exempt disc source, a Co-60 exempt disc source, a PM1703M radiation counter, a Geo210 pancake GM probe, a Geo310 pancake GM probe, and two DT106/PDR27G probes. Please note that this is just a comparison of gamma sensitivity, even though the pancakes may not be designed specifically for linear response to gammas because they are most useful for work with alpha sources.
I tested the DT106probes in two different configurations: 1. Perpendicular to the radiation beam, with the beta shield closed, and 2. with the beta shield open, pointing at the radiation source.
Since GM tubes are sensitive to UV light, I conducted my tests in a darkened room, taking the extra precaution of covering the tubes with a piece of Thorlabs BK5 rubberized blackout fabric.
The following table shows the results that I obtained by averaging three one-minute counts for each test configuration.
| Background | Co-60 | Cs-137 | |
| PM1703M Measurement | 5 uR/h | 7 uR/h | 20 uR/h |
| DT106 #1 closed β | 73 | 96 | 152 |
| DT106 #1 open β | 60 | 82 | 203 |
| DT106 #2 closed β | 46 | 58 | 127 |
| DT106 #2 open β | 38 | 54 | 136 |
| Geo 210 (LND7311) | 28 | 58 | 208 |
| MC6 #1 | 103 | 166 | 297 |
| MC6 #2 | 111 | 145 | 278 |
| Geo 310 | 86 | 142 | 1873 |
Indeed, the russian-made MC-6 tubes are quite sensitive to gamma and show good energy compensation (unlike the russian pancake in the Geo310 which is incredibly sensitive at the energy of Cs-137 photons, something to be expected from a tube that is designed mostly for work with alphas).
