Irradiation of ABCD3T hybrid with gammas from reactor

The ABCD3T barrel kapton hybrid which was irradiated with neutrons in
our reactor (see  neutron irradiation  ) was irradiated also with gammas in
the reactor.

Idea: when the reactor is not operating there is no neutron flux but
the secondary radioactivity of the core is very high so that it could be used for
irradiating the electronics with ionization dose.

Dosimetry: dose (dose rate) is measured with RADFETs. RADFETs are
MOS FET transistors designed for dosimetry (i.e. thick oxide under
the gate electrode (0.93 microns)).  In response to the total dose received
the threshold voltage of the FET changes due to the charge trapped
in the oxide. Thus the effect used for dosimetry is the one that also causes
damage to the electronics. This means that there is a good reason to believe that
the difference between the gamma spectra used for calibration and for
irradiation should not be a problem i.e.: the  damage done by the reactor
gammas is equal to the damage that would be caused by N rads of
gammas from calibration source.

We calibrated RADFETS with Co60 (1.2MeV) source wtih dose rate of
the same order as in the reactor. Here is the calibration curve.

RADFETs were also used to measure the ionization dose received during
neutron irradiation because  FETs are not sensitive to bulk damage.

Irradiation: the dose rate in the reactor core changes with time after
a 24h run at full power. In the plot you can see some measurements of
dose rate vs. time after a 24h run and get an idea about the dosimetry errors.

We irradiated the hybrid for few hours in days 1, 2 and 3 after the reactor was
switched off  and have done 2 irradiation periods up to now.
The dose rates were: 48 rad/s in day 1, 30 rad/s in day 2 and 21 rad/s in day 3.
During irradiation the hybrid was biased and configured and the temperature
on the hybrid was 30+-1C.

The dose that the hybrid received during neutron irradiation was ~200krad.

We monitored the hybrid performance during irradiation. We observed:
 

       Idd was measured at Udd=4V, Vth =   500.
       In the last part of irradiation we masured also Idd when clock frequency was 0.

      There are 6 annealing drops in the plot:
       - first 2 (starting at 0 dose) are ~20h each  at RT, no bias and clock
       - third is 283hours at RT, no bias, no clock
       - the next 2 are also ~20h each at RT with hybrid biased and clocked
       - the last one is 619 hours, no bias, no clock
       In the annealing plot the evolution of Idd with time after irradiation is show. The red
       curve shows the first long annealing (283 hours) and the blue one the second
       long annealing (619 hours). In the plot Idd is normalized to the Idd immediately
       after irradiation.