Primary Radiation Damage:
from nuclear reaction to point defects

Technical Meeting (F4-TM-43223), 1 - 4 October 2012, IAEA Headquarters, Vienna, Austria
is followed by CRP F44003 (2013-2017)

Motivations

   The displacement cross section is a reference measure used to characterize and compare the radiation damage induced by neutrons and charged particles in crystalline materials. To evaluate the number of displaced atoms Norget, Torrens and Robinson proposed in 1975 a standard (the so-called NRT-dpa), which has been widely used from that time.
   Nowadays this formulation is recognized as suffering from some limitations: it is not applicable for compound materials, does not account for the recombination of atoms during the cascade evolution, cannot be directly validated and has no uncertainties/covarincies as evaluated cross sections usually have now.
   Upgrading of the dpa-standard means the inclusion of the results of the Molecular Dynamics (MD), Binary Collision Aproximation (BCA) or other simulations for primary radiation defects (PRD), i.e. Frankel pairs (FP) and Interstitial Clusters, which survive after relaxation of the Primary Knockout Atoms (PKA) cascade.
   The essential advantages of the upgraded dpa-standard will be:
- non-dependence on the energy distribution of incident neutrons - this means more correct inter-comparison of radiation damage in the different facilities on the basis of the accumulated dpa-fluence
- it also becomes more feasible for comparison of neutron and charged particles or ion induced damage
- empirical validation against frozen defects at cryogenic temperature (NRT-dpa can never be observed)
- prediction of damage in polyatomic materials and alloys (NRT treats dpa in compounds by mathematical weighting of separated elements)

Purpose of the Meeting

   To find ways to overcome the drawbacks of the NRT standard and benefit from the recent developments in primary radiation damage simulations, the Technical Meeting has the objectives to discuss:

• revisiting the NRT standard with the purpose of improving it by the evaluation of uncertainties
connected with recoil spectra and the energy partitioning model;
• proposal of a new upgraded standard that will capture the annealing of defects in the recoil cascade on the basis of MD, BCA and other models.

   As an outcome of discussions the definition of objectives and participating organisations for a new Coordinated Research Project (CRP) on this topic are expected.

Specific issues to be addressed

   Cross sections, evaluated data libraries and the NRT standard

• PKA spectra - availability in libraries, methods of calculation, agreement and uncertainties
• processing of cross section files to derive KERMA, damage energy and dpa
• gas (helium, hydrogen) production cross sections
• uncertainties/covariances for these quantities
• others

   MD, BCA and other simulations of survived primary point defects in mono- and poly-atomic materials and thermal-spike-enhanced recombination

• scope of materials - pure metals, Fe-xC, semiconductors (Si, Ge), insulators and ceramics (Al2O3, SiC ...)
• PKA energy range covered by different simulation methods
• calculation outputs - survived Frankel Pairs (FP), simple interstitial clusters
• dependence on temperature and material composition
• incorporation of MD/BCA results in processing codes (NJOY) or storage in a separate cross section database
• empirical validation
• applications
• others

TM Summary Report

INDC(NDS)-0624

Presentations

Crocombette, Dudarev, Fukahori, Griffin, Inozemtsev, Kahler, Konobeev, Kwon, Mota, Nordlund, Pechenkin, Ryazanov, Simakov, Simakov, Simeone, Stoller, Vila

Illustrative Examples (pure Iron)