Physics:Niel scaling

According to NIEL (non-ionizing energy loss) scaling, any particle fluence can be reduced to an equivalent 1 MeV neutron fluence producing the same bulk damage in a specific semiconductor. The scaling is based on the hypothesis that generation of bulk damage is due to non-ionizing energy transfers to the lattice.

Given an arbitrary particle field with a spectral distribution and of fluence , the 1 MeV equivalent neutron fluence is:

is called the hardness parameter and is defined as:

with EDK the energy spectrum averaged displacement KERMA ( Radiation Measures and Units):

where is the differential flux, and

is the displacement KERMA or the damage function for the energy E of the incident particle, the cross-section for reaction k, the probability of the incident particle to produce a recoil of energy in reaction k, and the partition function (the part of the recoil energy deposited in displacements). EDK (1MeV) = 95MeVmb ASTM93. The integration is done over the whole energy range.

A few damage functions are available for neutrons up to 18 MeV in silicon ( Lazo86, Ougouag90 and have been standardized in ASTM93.

Ougouag90 also gives displacement function tables for GaAs.

A review and analysis for neutrons can be found in Vasilescu97 ( Angelescu96).

For neutrons above 18 MeV and for other particles, the situation is still controversial. Results on neutrons are available from Ginneken89, who also studied electron, muon, pion, gamma and proton NIEL, and Konobeyev92 and Huhtinen93b. For protons, the energy region up to 200 MeV is covered by Summers93 (also giving tabulations for GaAs and InP, for protons and electrons). Above 200 MeV the only extrapolations are those from Huhtinen93b and Ginneken89. For pions, damage function calculations are presented in Ginneken89, Huhtinen93b, Lazanu97. These results should be treated with some care. New calculations are needed, based on detailed simulation and comparison to the experiment, as in Huhtinen93a, Aarnio95. Work is in progress in further analysis of the NIEL, due to its importance especially for damage estimates in collider radiation environments and the operational scenario of the 10 years of experiments planned at the LHC at CERN.