This irradiation was done in November 2000 in the Ljubljana reactor to compare
the damage to the transistors for the two irradiation tubes.
In our reactor we can irradiate our samples in  2 tubes: small and big.
In the previous irradiation TEMIC transistors were irradiated in the small tube whereas
the ABCD chips on hybrids were irradiated in the big tube. There was inconsistency
between the damage of ABCD chips and the damage of transistors. Thus the
TEMIC transistors were irradiated also in the big tube to see if irradiation
in this tube gives different results.

We irradiated 6 1.2x1.2 size and 3 10x1.2 size transistors. We divided them
in 3 sets containing 2 1.2x1.2 samples and 1 10x1.2 sample.
The 3 sets were irradiated to 3 different fluences: 6,12 and 20x10**13 n/cm2.

Beta (Ic/Ib) as a function of collector current measured before irradiation is  here.

Next  plot shows beta as a function of collector current after irradiation. Added are also
measurements of transistors irradiated in the small tube in February 2000. Unfortunately
there is no plot showing the beta before irradiation of transistors irradiated in the small tube.

In the last  plot  the values of beta at collector current of 100 uA versus fluence for different
irradiation is shown. Beta values from various irradiation are put into this plot:
irradiation in big and small tube as above,  irradiation in the small tube but beta measured
by Santa Cruz (done sometimes in 1999), irradiation done at the Prospero reactor and
also irradiation done at PS (data taken from Miguels web page, hardness factor 0.62 used to get NIEL fluence).
The error bars are calculated simply from the beta vs fluence curve (linear approx) taking 10% of dosimetry error i.e. error = dBeta/dFluence*(fluence*0.1).

One can observe somewhat lower damage in the big-tube compared to the small
tube.  Damage in the reactor is always larger than at Prospero or PS.
The difference is seen more clearly if 1/Beta is ploted versus fluence as can be seen in
 http://www-f9.ijs.si/~mandic/TestStruct/Beta-1At100.eps

There is some difference between neutron spectra in big and small tube, small having
larger contribution of thermal neutrons (from R. Jeraj et al, Nuclear Energy in Cetnral Europe 2001, Protoroz,  Slovenia, September 10-13 2001):
 

Spectral  fraction (%)	Small tube	Big tube
Thermal	50.1	39.5
Intermediate	25.3	29.1
Fast	24.6	31.4

Thermal: E < 0.5 eV, Intermediate: 0.5 eV < E < 100 keV, Fast E > 100 keV

Damage factor for neutrons in the reactor such that: NIEL_fluence =  Fast_fluence * 0.9
The fluences in the reactor (in the plots above) are always NIEL_fluences.

From the table above it can be calculated that with the same NIEL fluence, samples receive
by about a factor of 2 more thermal neutrons in the small tube than in the big tube.