Posts by exsafs

1) Message boards : Science : Detector behavior in high dose rate levels (Message 3047)
Posted 3339 days ago by exsafs
I have something to add here.
Just dug out my old R@H v1.5 detector recently and tested that one with a 3 GBq Be-7 source in our lab.
The actual dose rate at 1 cm distance should be around 15 mSv/h, but the detector was not capable of measuring anything above 1 mSv/h.
2) Message boards : Science : Beta versus Gamma attenuation (Message 2000)
Posted 3858 days ago by exsafs
Hello Craig,

i will try to answer your question. Unlike gammas, beta and alpha particles have a mass, and therefore, in a classical way, loose energy by collisions with the matrix material. So, a beam of mono-energetic betas would constantly loose energy by traveling through aluminum roughly staying constant in population. There will be also a spreading of the energy and the path around a mean value. Nevertheless, such term as "half value layer" does only apply to gamma radiation.

Certainly, there is a stopping range (complete energy loss) for each particle of specific energy in a desired material. However, the energy loss per traveled distance is not linear (see Bragg peak). For a deeper understanding you could try out a freeware program called SRIM (stopping & range of ions in matter), where simulations of particle behavior in many different matrixes may be performed.

Keep also in mind that beta emitters never emit mono-energetic particles.
3) Message boards : Science : Detector behavior in high dose rate levels (Message 1721)
Posted 3970 days ago by exsafs
u will indeed need a source of large activity in order to get a homogeneous radiation field at a certain distance. only this will ensure a reliable and meaningful comparison between dose rate meters.
4) Message boards : Science : Alpha and Beta radiation (Message 1339)
Posted 4229 days ago by exsafs
Only gammas are able to easily penetrate the housing of a discharge tube to generate a countable event inside it. Alphas and betas, even having similar energies, may not be detected with such a tube, as they simply are stopped before reaching the gas inside.
5) Message boards : Number crunching : OSX version required (Message 1103)
Posted 4340 days ago by exsafs
ok, it finally worked ... thanks! now lets measure real radiation!
6) Message boards : Science : detector testing with real radioactive sources (Message 1085)
Posted 4346 days ago by exsafs
Hello Krzysztof,

sure, i may do some tests with other devices too. Just send me a PM.
Concerning beta radiation - it is not possible to directly detect beta radiation with the shown device, neither with your detector. Betas emit Bremstrahlung radiation when they are stopped in matter, and only this radiation may be detected with our devices. It also depends on the beta energy - you will not detect H-3 (roughly 100 keV beta), but you will see P-32, for example (1,7 MeV beta).

7) Message boards : Science : detector testing with real radioactive sources (Message 1083)
Posted 4346 days ago by exsafs
ok,

as promised i want to share some test results with real radioactive sources with you.
Before i start, one comment - I have access to radioactive sources as i am working in a radioactive laboratory of a Swiss research Institute (http://www.psi.ch) where normal radio protection rules apply. I am working in a controlled zone, have had to pass a training course and i do wear a dosimeter. Every measurement i publish here was done by myself being aware of basic radio-protection rules.

Basically i did a comparison of the readings of a V2.01 device obtained end of March from this project with a certified one available at our laboratory. It is a 6150 AD 6/H dosimeter calibrated at the accredited dosimetry calibration laboratory at PSI, Switzerland. Furthermore, i have had the opportunity to make some preliminary tests in this laboratory with the Radioactive@home device.

First of all - here a picture of the dosimeter at our laboratory:



sorry for the crappy quality, i will try to make better pictures in future.

I tested this device with two radioactive sources from our lab. One is a 373 kBq (01.03.2006) Co-60 source, the other one is 117 kBq Cs-137 of the same date. The measurement was done with both detectors directly attached to the source (not a true scientific approach). The buzzer was on.

Co-60 with readings:



Cs-137 with readings:



you see a clear difference in the values. the readings of the Radioactive@home device are about 30% below the readings of the certified dosimeter.

some more pictures of the sources:




additionally i made a test with both sources and sample of quite high doserate just to see how much the detector may stand:



you see - the device is measuring 0.5 mSv/h where it should read 1 mSv/h. Basically one can say that the device is measuring too low dose rates (Which may not automatically apply to background measurements).
The approach i have chosen is not really meaningful as the radiation field that is generated is not homogeneous if the source has direct contact to the device (The discharge tube of the 6150 device is shorter, so there are some limitation for my measurements just from geometrical considerations).

A much better approach is to generate a homogeneous radiation field from a powerful source at a certain distance. This was possible at the certified dosimeter calibration laboratory at my institute. There, they generated radiation fields between 1 and 100 µSv/h with Co-60 and Cs-137 sources of much higher activities.
The outcome of this test is: for Co-60 (mean 1200 keV gamma line) the readings of the V2.01 device where 20% below the expected value, for Cs-137 (600 keV mean) it was already 40%. The operator said that for a self-made device, this thing performs quite well (good background statistics, reasonable results for the dose rate tests).

Congratulations, Team Poland!
8) Message boards : Science : Data analysis - What can you really measure? (Message 1081)
Posted 4346 days ago by exsafs
:)

background statistics is a complicated topic, as you are never sure where the counts are coming from. To do a correct background measurement is far more complicated than doing measurements of a radioactive sample.
just an example - leaning over the detector automatically should increase the background counts as the K-40 decay inside the body of each of us gives automatically more counts. The crucial question is - how much does each effect (radon emanation after rain, solar modulation etc.) change the mean background value?

i guess that measuring real radioactive samples with our detector will decrease the uncertainty significantly. if desired, i may provide you with the data.
9) Message boards : Science : Detector bugs (Message 1063)
Posted 4350 days ago by exsafs
Just want to share my observations in a real radiation field.
I have had the opportunity to test your device in a certified calibration laboratory for radiation detectors. There, they use Cs-137 and Co-60 sources from 70 MBq to 70 TBq to generate radiation fields between 10 µSv/h up to 10 Sv/h under well-defined geometries. With an optical camera you get the readings from the detector into the control room.

One big problem during the tests was - above 100µSv/h the LCD display was too dark to see any reading. At 10 µSv/h there was no problem to visually inspect it. My suspicion was the buzzer, which probably should be turned off at higher dose rates, because its simply needs too much juice.

The main outcome of the test: for Cs-137 (gamma-lines at around 600 keV) the detector reads 40% less than it should. At 1200 keV (mean) gamma of Co-60 it is only 20% less. Measured for dose rates between 1 and 100 µSv/h.

I have done some more testing with radioactive sources in the lab, i will post some pictures later. I will try to do a comparison test with an radioactive source (buzzer on vs. buzzer off)

10) Message boards : Number crunching : OSX version required (Message 1019)
Posted 4353 days ago by exsafs
maybe this is helpful:

Stderr output
<core_client_version>7.0.25</core_client_version>
<![CDATA[
<message>
process got signal 5
</message>
<stderr_txt>
dyld: Library not loaded: /usr/local/lib/libusb-0.1.4.dylib
Referenced from: /Library/Application Support/BOINC Data/slots/0/../../projects/radioactiveathome.org_boinc/radac_1.54_x86_64-apple-darwin
Reason: image not found

</stderr_txt>
]]>


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