Dual-modulation difference stimulated emission depletion microscopy to suppress the background signal

Stimulated emission depletion(STED)nanoscopy is one of the most well-developed nanoscopy techniques that can provide subdiffraction spatial resolution imaging.Here,we introduce dual-modulation difference STED microscopy(dmdSTED)to suppress the background noise in traditional STED imaging.By applying respective time-domain modulations to the two continuous-wave lasers,signals are distributed discretely in the frequency spectrum and thus are obtained through lock-in demodulation of the corresponding frequencies.The background signals can be selectively eliminated from the effective signal without compromise of temporal resolution.We used nanoparticle,fixed cell,and perovskite coating experiments,as well as theoretical demonstration,to confirm the effectiveness of this method.We highlight dmdSTED as an idea and approach with simple implementation for improving the imaging quality,which substantially enlarges the versatility of STED nanoscopy.

Signal-background discrimination with convolutional neural networks in the PandaX-Ⅲ experiment using MC simulation

The PandaX-Ⅲ experiment will search for neutrinoless double beta decay of 136Xe with high pressure gaseous time projection chambers at the China Jin-Ping underground Laboratory. The tracking feature of gaseous detectors helps suppress the background level, resulting in the improvement of the detection sensitivity. We study a method based on the convolutional neural networks to discriminate double beta decay signals against the background from high energy gammas generated by 214Bi and 2^208 T1 decays based on detailed Monte Carlo simulation. Using the 2-dimensional projections of recorded tracks on two planes, the method successfully suppresses the background level by a factor larger than 100 with a high signal efficiency. An improvement of 62% on the efficiency ratio of Еs/√Еb is achieved in comparison with the baseline in the PandaX-Ⅲ conceptual design report.

A gaseous time projection chamber with Micromegas readout for low-radioactive material screening

Purpose Low-radioactive material screening is becoming essential for rare event search experiments,such as neutrinoless double beta decay and dark matter searches in underground laboratories.A gaseous time projection chamber(TPC)can be used for such purposes with large active areas and high efficiency.Methods A gaseous TPC with a Micromegas readout plane of approximately 20×20 cm^(2)is successfully constructed for surface alpha contamination measurements.Results We have characterized the energy resolution,gain stability,and tracking capability with calibration sources.Conclusion With the unique track-related background suppression cuts of the gaseous TPC,we have established that the alpha background rate of the TPC is(0.13±0.03)×10^(−6)Bq/cm^(2),comparable to the leading commercial solutions.

Enhanced search sensitivity to the double beta decay of ^(136)Xe to excited states with topological signatures

The double beta decay of ^(136)Xe to excited states of 136Ba(DBD-ES)has not yet been discovered experimentally.The experimental signature of such decays,one or two gamma rays following the beta signals,can be identified more effectively in a gaseous detector with the help of topological signatures.We have investigated key parameters of particle trajectories of DBD-ES with Monte Carlo simulation data of the proposed PandaX-III detector as an example.The background rates can be reduced by about one order of magnitude while keeping more than half of signals with topological analysis.The estimated half-life sensitivity of DBD-ES can be improved by 1.8 times to 4.1×10^(23) year(90%C.L.).Similarly,the half-life sensitivity of neutrinoless double beta decay of ^(136)Xe to excited states of 136Ba can be improved by a factor of 4.8 with topological signatures.