5.2.27. Event Generator Mode

For Event Generator mode [1] [2] [3] [4] , dmax(2) should be defined appropriately using information from the nuclear data library. In the special statistical decay model, detailed information on the level structure near the ground state for particle and photon emission is used, which requires setting igamma=1-3. The special statistical decay model has been developed based on GEM; to use it, the operator should specify nevap=3. The related parameters are automatically set by specifying e-mode=1, 2 or 3 (unless explicitly specified, igamma=2 is selected). For consistency reason, the combination igamma=1 and e-mode=1 is also supported.

Event generator mode Ver.2 is the improved version of the legacy version (i.e., event generator mode Ver.1). In reactions emitting multiple neutrons, the previous event generator mode sampled the first ejectile neutron from the cross-section data and emission of the subsequent particles was simulated using the statistical decay model. By contrast, ver.2 samples all ejectile neutrons from the cross-section data and the statistical decay model is used merely to simulate prompt gamma-ray production. For capture reactions, the previous event generator mode assumed that the target nucleus absorbs incident neutrons, and particle emission was simulated by the statistical decay model. In this updated version, ejectile particle species are fully determined by the statistical decay model. While ver.2 selects the ejectile particle species depending on the reaction channel (i.e., in the \((n,\alpha)\) reaction, emission of only one alpha particle and gamma-rays is allowed). In e-mode = 3, in addition to the features of e-mode = 2, event generation is performed using nuclear data that explicitly account for the excitation states of residual nuclei, when such data are available (for example, MT numbers 600?649 for (n,p) reactions). If angular distributions of emitted particles corresponding to specific excitation states are included in the nuclear data, sampling is carried out according to those distributions. As a result, it becomes possible to predict high-accuracy energy spectra and angular distributions of emitted particles based on evaluated nuclear data, as well as the total energy deposition excluding gamma rays, for applications such as detector response calculations.

Under Event Generator mode, the following new observables, which cannot be detected otherwise, are obtained:

(1). The deposition energy distribution by the low-energy neutrons below dmax(2) without the kerma approximation is available in the [t-deposit] tally by considering contributions from the secondary charged particles. When e-mode=0, the deposition energy by the low-energy neutrons in [t-deposit] is calculated with the kerma approximation [5] .

(2). In [t-yield] and [t-product], the yield and product quantities can be tallied below dmax(2).

(3). DPA values are obtained even for neutrons of energies below dmax(2).

[1]

Y. Iwamoto et al.,International Conference on Nuclear Data for Science and Technology2007, DOI: 10.1051/ndata:07417.

[2]

K. Niita et al.,International Conference on Nuclear Data for Science and Technology2007, DOI: 10.1051/ndata:07398.

[3]

Y. Iwamoto et al., Prog. Nucl. Sci. Technol. 2, 931-935 (2011).

[4]

T. Furuta et al., Nucl. Instrum. Methods Phys. Res. A, 1086, 171320 (2026).

[5]

After ver. 3.05. Before ver. 3.04, the [t-deposit] tally cannot calculate the deposition energy with the kerma approximation.