The CR-39 nuclear track detector is used in many nuclear diagnostics fielded at inertial confinement fusion (ICF) facilities. Large x-ray fluences generated by ICF experiments may impact the CR-39 response to incident charged particles. To determine the impact of x-ray exposure on the CR-39 response to alpha particles, a thick-target bremsstrahlung x-ray generator was used to expose CR-39 to various doses of 8 keV Cu-Kα and Kβ x-rays. The CR-39 detectors were then exposed to 1–5.5 MeV alphas from an Am-241 source. The regions of the CR-39 exposed to x-rays showed a smaller track diameter than those not exposed to x-rays: for example, a dose of 3.0 ± 0.1 Gy causes a decrease of (19 ± 2)% in the track diameter of a 5.5 MeV alpha particle, while a dose of 60.0 ± 1.3 Gy results in a decrease of (45 ± 5)% in the track diameter. The reduced track diameters were found to be predominantly caused by a comparable reduction in the bulk etch rate of the CR-39 with x-ray dose. A residual effect depending on alpha particle energy is characterized using an empirical formula.

The experimental work presented in this article deals with the study of low-frequency high-amplitude pressure wave attenuation in a cavity when boiling takes place on the inside. The working fluid was HFE7100. Regarding the flow regime, the study considered two different situations: pool boiling and flow boiling in the low to moderate Reynolds number regime. Regarding the operating parameters, the study considered: (a) the type of evaporator, (b) the temperature of the evaporator, and (c) the frequency of the pressure waves. Three different types of evaporators were manufactured and tested: a flat one and another two based on a micro pin fin structure. Pin fin sizes for these two evaporators were 500 u.m x 500 u.m x 500 u.m and 1000 u.m x 1000 u.m x 1000 u.m respectively. The temperature of the evaporators was varied between 40 °C and 80 °C. Frequency of the pressure waves changed between 35 Hz and 75 Hz. An additional isothermal reference case (no boiling) was used for comparison purposes. The typical order of magnitude of the peak-to-peak applied pressure amplitudes was 0.2 bar. Regarding the results, it was found that boiling causes a significant attenuation of the peak-to-peak amplitude of the pressure waves in the cavity. The main parameter acting on this attenuation was the temperature of the evaporator (related to the input electrical power), while the actual micro-structure of the evaporator played a nearly negligible role. Also, it was found that while a small electrical power input of about 5 W achieves an attenuation factor of about 0.5, four times as much power (20 W) is needed to halve again the attenuation factor to 0.25. This suggests a scaling law relating attenuation and power which could be used for engineering design purposes.

The nuclear track detector CR-39 is used extensively for charged particle diagnosis, in particular proton spectroscopy, at inertial confinement fusion facilities. These detectors can absorb x-ray doses from the experiments in the order of 1-100 Gy, the effects of which are not accounted for in the previous detector calibrations. X-ray dose absorbed in the CR-39 has previously been shown to affect the track size of alpha particles in the detector, primarily due to a measured reduction in the material bulk etch rate [Rojas-Herrera et al., Rev. Sci. Instrum. 86, 033501 (2015)]. Similar to the previous findings for alpha particles, protons with energies in the range 0.5-9.1 MeV are shown to produce tracks that are systematically smaller as a function of the absorbed x-ray dose in the CR-39. The reduction of track size due to x-ray dose is found to diminish with time between exposure and etching if the CR-39 is stored at ambient temperature, and complete recovery is observed after two weeks. The impact of this effect on the analysis of data from existing CR-39-based proton diagnostics on OMEGA and the National Ignition Facility is evaluated and best practices are proposed for cases in which the effect of x rays is significant.