Planned Irradiation Tests page

LjublJana : Irradiation Test in Ljubljana (06.06.05-10.06.05,08.06.05,23.06.05)

Igor Mandic, Vladimir Cindro and Cigdem Issever irradiated the VCSELs and PINs at the research reactor in Ljubljana. The energy spectrom of the neutrons at this facility can be found at this link of Igor: More information about the reactor is at

The fluences and the probes used are listed below:

1) VCSEL Irradiations

date time put in probe tpye fluence [n(1MeV)/cm^2] ~irradiation time [sec] channel time taken out comment
06.06.2005 14:45 1a VCSEL 7 1E+14 52 F19 - -
06.06.2005 15:23 2 VCSEL 3 5E+14 260 F19 15:27 -
06.06.2005 15:28 3a VCSEL 5+6 1E+15 280 TI 15:36 Reactor tripped as we took the probe out of the reactor core
23.06.2005 10:05 11 VCSEL 9+11 3E+15 840 TI - -
08.06.2005 10:30 6 VCSEL 8+4 5E+15 2640 F19 - -
07.06.2005 9:50 10 VCSEL 10+2 1E+16 2820 TI - Reactor did not trip because power was adjusted accordingly while we were pulling the probe out.

2) PIN Irradiations

date time put in probe tpye fluence [n(1MeV)/cm^2] acc. fluence ~irradiation time [sec] channel time taken out comment
23.06.2005 9:30 8 PIN 16 3.00E+14 6.00E+14 156 F19 - -
06.06.2005 16:45 3b PIN 17 1.02E+15 1.02E+15 530 F19 16:55 - -
23.06.2005 10:00 9 PIN 2+3+7 1.35E+15 1.5E+15 702 F19 - -
06.06.2005 16:58 4 PIN 8+11 2E+15 3.05E+15 560 TI 17:08 Reactor tripped as we took the probe out of the reactor core
07.06.2005 9:50 5 PIN 14 3E+15 3.0E+15 1560 TI - -
08.06.2005 10:35 7 PIN 9+6+13 6E+15 6E+15 1680 TI - -

The reactor at Ljubljana has two tubes (channel F19 and TI) which we used to let the probes down into the reactor core. F19 is futher out in radius and its fluence uncertainity is 10% where as TI has an uncertainity on the fluence of 15%. Channel TI has roughly half of the thermal neutrons than channel F19.

We tripped the reactor twice as we were pulling probes out of channel TI. We must have had neutron absorber in the probes. The recordings show that the power of the reactor is decreasing when we let the probe into the reactor and increasing when we pull it out again. In case of the TI the power increase is high enough to trip the reactor. The reason why the trips occur at the channel TI is thought to be that this channel is closer to the core and closer to a monitoring device than F19.

Activation of Probes

Before the irradiations on the 23th of June we measurered the activation of the sample of probes. 7 days after the irradiation we measured 2mSv/h @ 10-15cm and 16 days after the irradiation it dropped to 100muSv/h @ 10-15cm. The probe with the maximum fluence in this bunch of probes was 6E+15 n(1MeV)/cm^2. The activation level of the sample (including the newly irradiated ones on the 23th) may reach 10muSv/h in 4 weeks from now onwards. The table below shows the activation levels of some probes shortly after their irradiation.

Probe Fluence Activation [muSv/h] time after irradiation distance channel
1a 1E+14 350 1h10min 20cm F19
1a 1E+14 255 1h20min 20cm F19
1a 1E+14 220 1h30min 20cm F19
2 5E+14 2200 55min 30cm F19
3a 1E+15 >5000(off scale) 1h10min 30cm TI
3b 1E+15 1500 17h30min 10-20cm F19
4 2E+15 1500 17h 10-20cm TI

Channel TI has 50% less thermal neutrons than channel F19, which is the reason for the lower activation of probe 4 than probe 3b though probe 4 got twice the fluence of probe 3b.

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-- CigdemIssever - 22 Jul 2005

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