The cascading 3.21 and 4.44 MeV electric quadrupole transitions have been observed from the Hoyle state at 7.65 MeV excitation energy in 12 C, excited by the 12 Cðp; p 0 Þ reaction at 10.7 MeV proton energy. From the proton-γ-γ triple coincidence data, a value of Γ rad =Γ ¼ 6.2ð6Þ × 10 −4 was obtained for the radiative branching ratio. Using our results, together with Γ E0 π =Γ from Eriksen et al. [Phys. Rev. C 102, 024320 (2020)] and the currently adopted Γ π ðE0Þ values, the radiative width of the Hoyle state is determined as Γ rad ¼ 5.1ð6Þ × 10 −3 eV. This value is about 34% higher than the currently adopted value and will impact models of stellar evolution and nucleosynthesis.

Deterministic HELIOS-2.1 and SCALE-6.1 codes are compared using pin-cell models for light water reactor (LWR) and heavy water reactor (HWR) cases. The main objective of this study is to identify the origins of any discrepancies between compared codes. The infinite multiplication factor kinf, flux distribution, absorption, fission, production reaction rates, and burn-up dependent concentrations of major fuel isotopes, are investigated herein and compared.Comparison of kinf has shown that the codes are in good agreement for both the LWR and HWR cases. The codes showed differences in the isotope number density of up to 6% in the case of prominent isotopes, and for 235 U and 239 Pu at 60 GWd/tU in the LWR case. These differences were, approximately 20% for 235 U and 30% for 239 Pu in the HWR case.It is concluded that these discrepancies are attributed to differences in the modelling of the thermalisation process in the HWR case. This needs to be investigated further to determine the root cause. Possible causes could be the neutron group structure, cross section condensation, treatment of up-scatter, angle dependence of scatter, and spatial homogenisation during source iterations.

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