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High time resolution detecting systems for MeV pulsed radiation are essential for inertial confinement fusion diagnostics. Traditional detection of system time resolution is restricted by cable bandwidth. Based on recording excess carrier dynamics in semiconductors, a new detecting mechanism, called RadOptic, was developed by Lawrence Livermore National Laboratory (LLNL). The variation of intensity of pulsed radiation with time was converted into the variation of intensity of infrared laser probe by using this mechanism. The sensing material was InGaAsP quantum wells with severalmicrometer thickness. Picosecond time resolution for several keV pulsed radiation has been demonstrated. The reported system is not suitable for MeV pulses due to its low efficiency to MeV photons. Multiple cascaded structure for MeV photon to electron transformation was proposed by LLNL. Applying bulk material with several-hundredmicrometer thickness is an alternative. Based on transient free carrier absorption, a system recording bulk materials' instantaneous refractive index change is established. The system consists of a probe laser, an interferometer module, a signal transmission module and a signal recording module. The probe is a tunable infrared continuous wave laser whose wavelength is ~1453 nm, guided by single mode fiber to the interferometer. The interferometer consists of a single mode fiber head coupled directly with the polished face of a bulk semiconductor. The interference pattern forms by multiple beams reflected from the front face and the back face of the bulk. Part of interference light is coupled to the single mode fiber and forms the output signal. Pulsed radiation will deposit energy and generate excess carriers in the bulk material. The refractive index of the bulk material changes therewith according to the Drude model. The interference pattern and the light coupled to the single mode fiber also change therewith. The signal is transmitted by a long single mode fiber. The signal recording module consists of photoelectric detectors and a digital oscilloscope. The signal generation process and the time resolution of the system are analyzed. Intrinsic GaAs refractive index change is exploited under electron pulses and X ray pulses. The analysis of signal generation process shows that when the excess carriers recombine much faster/much slower than the pulse width, the output signal/output signal differential can be viewed as a measure of intensity variation with time of the incident pulse. For this prototype system, the time resolution is restricted by the digital oscilloscope to 1 GHz. Bulk intrinsic GaAs demonstrates 30 ns refractive index response time, which is longer than the incident pulse width. The differential signal can be viewed as a measure of incident pulse intensity when GaAs is exposed to 1 ns~0.2 MeV electrons pulses. The differential signal width is shorter than the pulse width when GaAs is exposed to 5 ns~0.2 MeV electrons pulses. Auger recombination process may occur in the pulse duration under this situation. The differential signal width is longer than the pulse width when GaAs is exposed to 1 ns~0.2 MeV X ray pulses. The poor signal to noise ratio affects the signal. The excess carrier generation process may be longer than theoretically estimated one under X ray pulse incident situation. The generation process and recombination process of excess carriers in GaAs show very different characteristics compared with optical excitation. The relationship between the system output signal and the incident pulsed radiation depends on the type of the incident radiation. With carefully considering the effects from incident pulse type and transient carriers density, the system can be used to detect ~MeV pulsed radiation. With an upgraded recording module, the system would demonstrate much higher time resolution.

Time response and light yield are two of the most important features of a scintillation detector, and are mostly determined by the luminescence properties of the scintillator.

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A novel magnetic spectrometer for Inverse-Compton X-ray source is proposed. Compton recoil electrons are generated by a lithium converter, and then confined by a complex collimator and spectrally resolved by a sector-shaped double-focusing magnet. A method of optimization for the converter is investigated, and the dependence of the best energy resolution on converting efficiency is quantitatively revealed. The configuration of the magnet is specially designed to cover a wide range of electron energy and to achieve a large collecting solid angle. The efficiency and relative energy resolution of the designed spectrometer, according to Monte-Carlo simulation using Geant4, are 10-4 e/p and about 5% respectively for 3 MeV photons.

We fabricated a liquid scintillator capillary array (LSCA) for gamma imaging with the aim of developing a one-dimensional detector system utilizing a streak camera for high temporal and spatial resolution pulsed gamma radiation detection. The detector's performance was studied in a simulation and via an experiment. The maximum efficiency of the LSCA's emission was at a wavelength of 420 nm. To establish a high fidelity representation of the detector's edge spread function and modulation transfer function (MTF), a slanted edge algorithm was introduced to calculate the edge spread function of the discrete sampling array's image screen. The simulation results showed that the spatial resolution of the LSCA was better for 14 MeV neutrons than for 1.25 MeV gamma radiation. The experimental results show that in comparison with a 6-mm-thick LaBr image plate, the LSCA had a higher temporal and spatial resolution when used as a gamma detector. The spatial resolution was 1.1 lp/mm (MTF = 0.1) for the LSCA. In addition, when an ultra-violet streak camera was coupled with the LSCA, it had a comparable sensitivity to that of a 6-mm-thick LaBr image plate.