| T O P I C R E V I E W |
| delikostidis |
Posted - 09/24/2012 : 01:48:13
Comparing GMC-300 with my old good Russian dual-tube Sosna I realized that something is wrong with the measured values.
For example, a bunch of 10 uranium marbles give a measurement of around 1.4 uSv in Sosna, and only e.g. 0.30 to 0.40 uSv in GMC-300.
Opening the case of GMC-300, I started getting values of around 2 uSV. Which means that the plastic casing of the device cuts a lot of this type of radiation from entering the tube.
Afterwards I put out one of the 2 SBM-20 tubes from Sosna (leaving it with only 1 tube) and measured on the same sample around 0.7 uSv with Sosna. Then I replaced the SBM-20 in Sosna with the pre-installed M4011 tube of GMC-300 and I got values around 50 uSv. So I decided to replace the GMC-300 tube with SBM-20.
However, the plastic casing problem would still exist.
So I installed SBM-20 a bit higher than normal (I also had to de-solder the negative pin of the tube to save length and use hot glue and extension pins) and made 7 holes across the bottom-up side of the GMC-300 where the tube is close to. Center to center: 1cm, hole size: 6mm.
The result can be seen in the attached photos.
What I got at the end, as expected, is a much higher sensitivity to uranium glass 
(GQ: Please consider adding these wholes on the casing of next versions of GMC-300).
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| 7 L A T E S T R E P L I E S (Newest First) |
| phgphd |
Posted - 10/15/2012 : 19:12:16
I must oppose adding holes to the GMC300 casing in any future improvement. I do not know what applications you are using the GMC300 for, but for health effects, the radiation levels being talked about are too low to be of concern. |
| and_kom |
Posted - 10/10/2012 : 11:05:25
Here is my version:
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| mobiusloop |
Posted - 10/03/2012 : 10:04:36
The drilling of the case will expose the m4011 glass tube to potential damage. A screen should be placed in the case to protected the tube.
Currently the top of the current case has precut slots over the tube that are covered with the relatively thin plastic labeling. This would be the target area for close proximity to a potential radiation source.
It is my understanding that the m4011 has a degree of light sensitivity and allowing unwanted photons to enter the tube by way of added holes may lead to erroneous results.
Just some thoughts. |
| ska |
Posted - 09/30/2012 : 06:51:44
quote:
Originally posted by and_kom
So SBM-20 is more sensitive than M4011?
I measured a cup of potassium salt with DIY geiger with sbm-20 and GMC-300 without case, the results were quite similar: double of backgound.
Then I measured a little piece of Tufo ( slightly radioactive magmatic rock) in same condition GMC-300 didn't measure any radiation increment, SBM-20 measured a clear step up of 50% compared to backgorund.
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| and_kom |
Posted - 09/30/2012 : 01:39:09
So SBM-20 is more sensitive than M4011? |
| ska |
Posted - 09/29/2012 : 05:44:39
I confirm your impression. The plastic case it's really bad for slightly radioactive object.
I tested a cup of potassium salt and with case there was no increase in background radiation. Without case it was better with a doubling of background radiation! |
| ZLM |
Posted - 09/24/2012 : 16:12:43
Good job! |
