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 Tue Sep 10 15:18:20 2019, Matej Roguljic, Other, Modules 1504, 1505, 1520 irradiation report
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 Fri Sep 13 15:06:51 2019, Andrey Starodumov, Other, Modules 1504, 1505, 1520 irradiation report
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Thu Sep 19 00:52:24 2019, Dinko Ferencek, Other, Modules 1504, 1505, 1520 irradiation report 
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Message ID: 12
Entry time: Thu Sep 19 00:52:24 2019
In reply to: 10
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| Author: |
Dinko Ferencek |
| Category: |
Other |
| Subject: |
Modules 1504, 1505, 1520 irradiation report |
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| Andrey Starodumov wrote: | It was discovered that these modules were stored in Zagreb in the climatic lab where T was about +22C. These modules have been transported from Co60 irradiation facility to the lab on open air with T>30C and RH>70%. Water in the air under the cap condensated on the surface of HDIs and diluted residuals (from soldering, passivation etc), that after remains liquid or crystallised.
The irradiation itself does not course any damage. This is also confirmed by the fact that after two previous irradiations in Jan and Jul 2019 of modules and HDIs, samples remained in a good shape without any residuals on HSI surfaces. These samples have been kept in an office where T and RH were similar to the outside and not in the climatic lab.
We consider the the case is understood and closed. |
Just to clarify. The modules were not transported from Co60 the irradiation facility to the lab in open air but inside a closed Petri dish. Otherwise, there would be no risk of water condensation if the air surrounding modules was allowed to quickly mix with the air-conditioned lab air. Here the problem arose from the fact that it was not only the modules that were brought inside the lab but they were brought inside a pocket of the outside air. A closed Petri dish is not airtight but it significantly reduces mixing of the air inside the Petri dish with the surrounding lab air making it slower than the rate at which the Petri dish and the module inside it were cooling down once brought inside the lab. This could have led to water condensation if the pocket of air trapped inside the Petri dish was warm and humid and had a dew point above the lab air temperature. To prevent this from happening, the solution should be relatively simple and it would be to open the Petri dish and uncover modules before bringing them inside the lab. That way the exchange of air will be faster and the risk of condensation will be basically gone because a warm module will be quickly surrounded by the lab air which will not condense on a warmer surface.
However, there is an additional twist in this particular case. On Aug. 22, when the modules were brought in the lab, there was a thunderstorm in Zagreb in the early afternoon (https://www.zagreb.info/aktualno/zagreb-je-zahvatila-oluja-munje-i-jaka-kisa-nad-vecim-dijelom-grada/227156) with temperature around 21.5 C and RH around 75% at the time the modules were transported (around 15:20), and the whole day was relatively fresh and humid. The outside air on that day would definitely not lead to water condensation in the lab. However, before being brought in the lab, the modules were sitting in a room in the building where the Co60 irradiation facility is located so the air inside the Petri dish was likely similar to the air inside that room (the modules were sitting there for a while and there was enough time for the air temperature and humidity to equalize) and there was not much time to mix with the outside when being transported from one building to another. Unfortunately, there are no measurements of the air temperature and humidity in that room. However, it is worth mentioning that the previous day, Aug. 21, was not very hot and humid with midday temperature around 26 C and RH around 50%. It is therefore likely that the air inside that room and consequently inside the Petri dish was not very hot and humid, making the hypothesis of water condensation in the lab, if not improbable, certainly less likely.
Either way, more careful handling of modules will be needed. |
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