RadMon thermal neutron cross-section calibration D.Kramer for the RadMon team L.Viererbl, V.Klupak NRI Rez 1

SEU induced by thermal neutrons  Thermal neutrons: E <~0.5eV  Interaction with Boron 10  10 B + n -> 4 He (1.47MeV) + 7 Li(0.84) + γ  The α is highly ionizing and has a long range  Range in Si = 5.15 um  Can produce max 65 fC  Li has shorter penetration depth and lower energy  Range in Si = 2.46 um  Can produce max 37 fC  Both ions can contribute if C crit is low enough  C crit decreases ~linearly with voltage 2 B-10 Cd

2 data sets with / without Cadmium - raw data 3 With Cd No Cd  Neutron flux assumed constant during the tests  High reproducibility for repeated tests  Clear difference if wrapped in Cd -> impact of thermals is the “difference” of the two plots  Steep sensitivity increase for low voltages

Irradiation conditions 4  BNCT has a wide spectrum neutron beam  Beam turned off for accesses (Cd wrapping) with reactor ON  Online monitoring of relative flux  Absolute flux calibration with activation foils after irradiation With Li6 filter!

Measured SEU cross section per bit for different voltages 5  Thermal x-section compared to proton beam calibration (60MeV)  Exponential voltage dependence not observed with high energy hadrons neither with 14MeV neutrons  At 5V x-sect ratio = 9.5  At 3V x-sect ratio = Cross section [cm 2 /bit]

Measured inverse SEU cross section for different voltages 6  Thermal x-section compared to proton beam calibration (60MeV)  Exponential voltage dependence not observed with high energy hadrons neither with 14MeV neutrons  At 5V x-sect ratio = 9.5  At 3V x-sect ratio = Fluence required for 1 SEU [cm -2 /SEU]

Estimation of the thermal n 0 and E>20MeV hadron fluence using the Fluka spectra 7  Ratio of fluences is obtained from Fluka spectra  Number of SEUs obtained at 3V (S 3V ) is used for the calculation of the high energy hadron fluence  The cross sections are known  Thermal fluence is obtained with a similar equation  The ratio r can be obtained if both voltages are measured

Example of use of the previous equations to the CNGS case  Ratio r garter than 1 even in the line of sight of TSG45  Fluences normalized to 1h  Station 4 wrongly placed in Fluka model  R=1000 is more realistic  Usability of the r calculation seems limited 8 1e18pot/week th/HE ratio r Hadron flux>20MeV [cm -2 /h] thermal neutron flux [cm -2 /h] Calculated r 5V3V5V3V TSG45 (floor) E+082.8E+09 TSG45 Around corner E+076.3E+063.2E+081.9E Station E+041.4E+041.5E+071.1E Station E+042.8E+042.1E+074.2E H>20MeV flux using 5V HE cross section [cm-2/h] FLUKA HE flux [cm-2/h] TSG45 (floor) 1.13E+09 TSG45 Around corner 4.46E E+07 Station E E+05 Station E E+04 The assumption that epithermal neutrons do not contribute to SEUs is not valid