DC-SRF-II gun, a high-brightness continuous-wave photocathode gun, has greater potential in electron beam irradiation applications. This paper presents the in-vacuum and in-air irradiation dosimetry study of the high repetition rate electron beam from the DC-SRF-II gun with both Monte Carlo simulations and experiments. Especially, high-dose uniform irradiations with flexible and accurate tuning of dose rate across orders of magnitude are demonstrated. Good stability and repeatability of the doses are also shown. The ultra-wide tuning range and precise control of irradiation time and dose rate are expected to pave the way for innovative applications across a wide range of fields.

The silicon vacancy (VSi−) color centers in 4H-SiC are promising solid-state spin defects for quantum sensing applications, featuring long room-temperature coherence times, near-infrared photoluminescence, and an optically controllable spin–photon interface. However, it is essential to achieve high-brightness silicon vacancy color-center ensembles by different irradiations for efficient signal detection and high-fidelity quantum sensing. In this work, we conducted irradiation experiments of MeV electrons, protons, and laser-driven ions to investigate the influence of irradiation parameters on the fabrication of VSi− center ensembles, confirming the vital roles of crystal damage densities in the production yield of VSi− centers. Furthermore, the hot irradiation experiments reveal that irradiation at optimized temperatures can enhance the production yield of VSi− centers and break the inherent limitation of radiation-induced crystal damage, achieving higher-brightness ensembles. 1 MeV proton irradiation with 1013 cm−2 at 200 °C could achieve a 2–3 times stronger photoluminescence intensity enhancement than that at room-temperature irradiation. We established a controllable fabrication methodology for engineering the brightness of color-center ensembles through precise tuning of irradiation conditions, which paves the foundation for fabricating high-quality VSi− color-center ensembles and other color-center systems in wide-bandgap semiconductor materials.

The performance of ultrafast scintillators under ultrahigh dose rate is highly important for applications utilizing brilliant radiation sources. In this work, the scintillation properties of β-Ga₂O₃, a high-performance ultrafast wide-bandgap semiconductor scintillator, are systematically investigated under dose rates of 10⁷ to 10⁹ Gy/s for the first time by employing ultrashort high-charge electron bunches (bunch charge from 500 fC to 50 pC) generated from a superconducting radio-frequency accelerator. Our results show that in spite of the ultrahigh dose rate, the scintillation intensity was still linearly proportional to the electron bunch charge. Lifetime analysis reveals a fast decay component ranging from 3 to 4 ns, along with an average lifetime of 20 ns. These findings establish a solid foundation for the application of β-Ga₂O₃ as the scintillation material for high-charge electron sources such as laser-wakefield accelerated electrons.

Objective: This study aims to investigate the impact of the beam temporal profile on the radical dynamics and inter-track interactions of FLASH radiotherapy, supporting parameter optimization for the equipment development, radio-biological experiments and clinical implementation. Approach: Monte-Carlo simulations based on the independent reaction time (IRT) method were performed to analyze the dynamics after irradiation, including single-pulse or multi-pulses irradiation, pulse repetition rate, pulse width and dose. The physicochemical experiments were performed to measure the hydrated electron lifetimes for validation. The generation and recombination of hydroxyl radicals and hydrated electrons were recorded under 6 MeV electron irradiation with varying beam temporal profiles. The radial distributions of the radicals were statistically analyzed, and the inter-track interactions were assessed through a mathematical model. Main results: The spatial distribution and temporal evolution of radicals were significantly affected by the beam temporal profiles. Compared with multi-pulses irradiation, single-pulse irradiation mode with a pulse width less than 1/10 of the radical lifetime, a repetition interval longer than the radical lifetime, and a dose exceeding 1 Gy/pulse can lead to rapid consumption of radicals within the first 30% of their lifetime, hence reduced the residual radical content. Instantaneous high dose rates induced overlapping of radical tracks. When the single-pulse dose exceeded 1 Gy, the overlap probability approached 100%, aligning with the dose threshold for the instantaneous radical combination. Significance: Under a low-duty cycle and high instantaneous dose-rate temporal profile, the radicals were rapidly consumed through track overlap, affecting FLASH effect. The optimized temporal profile can be used to guide the development of equipment and parameter settings in clinical practice to maximize the FLASH effect, such as the laser accelerators and superconducting photocathode guns.