Evaluation of a therapeutic carbon beam using a G2000 glass scintillator.

A G2000 glass scintillator (G2000-SC) was used to determine the carbon profile and range of a 290-MeV/n carbon beam used in heavy-ion therapy because it was sensitive enough to detect single-ion hits at hundreds of mega electron Volts. An electron-multiplying charge-coupled device camera was used to detect the ion luminescence generated during the irradiation of G2000-SC with the beam. The resulting image showed that the position of the Bragg peak can be determined. The beam passes through the 112-mm-thick water phantom and stops 5.73 ± 0.03 mm from the incident side to the G2000-SC. Additionally, the location of the Bragg peak was simulated when irradiating G2000-SC with the beam using the Monte Carlo code particle and heavy ion transport system (PHITS). Simulation results show that the incident beam stops at 5.60 mm after entering G2000-SC. The beam stop location obtained from images and the PHITS code is defined at 80% distal fall-off from the Bragg peak position. Consequently, G2000-SC provided effective profile measurements of therapeutic carbon beams.

Development of the Dual-Beam Ion Irradiation Facility for Fusion Materials (DiFU).

The Dual-beam ion irradiation facility for Fusion materials (DiFU) has been developed and installed at the Ruder Boskovic Institute with the purpose to perform irradiation of samples of fusion materials by one or two ion beams. Ion beams are delivered to the DiFU chamber by a 6 MV EN Tandem Van de Graaff and a 1 MV HVE Tandetron accelerator, enabling irradiation of areas up to 30 × 30 mm2. The sample holder enables the three-dimensional positioning of samples that can be irradiated while being heated, cooled, or kept at room temperature. Ion fluxes are measured indirectly by the insertion of two large Faraday cups. Besides, the ion flux is monitored continuously by two sets of horizontal and vertical slits, which, in turn, define the limits of the irradiation area on the sample. Sample temperature and conditions during irradiation are additionally monitored by a set of thermocouples, an IR camera, and a video camera. Particular care is dedicated to the mitigation of carbon contamination during ion irradiation.

All-Optical Wide-Field Selective Imaging of Fluorescent Nanodiamonds in Cells, In Vivo and Ex Vivo.

Fluorescence imaging is a critical tool to understand the spatial distribution of biomacromolecules in cells and in vivo, providing information on molecular dynamics and interactions. Numerous valuable insights into biological systems have been provided by the specific detection of various molecular species. However, molecule-selective detection is often hampered by background fluorescence, such as cell autofluorescence and fluorescence leakage from molecules stained by other dyes. Here we describe a method for all-optical selective imaging of fluorescent nanodiamonds containing nitrogen-vacancy centers (NVCs) for wide-field fluorescence bioimaging. The method is based on the fact that the fluorescence intensity of NVCs strictly depends on the configuration of ground-state electron spins, which can be controlled by changing the pulse recurrence intervals of microsecond excitation laser pulses. Therefore, by using regulated laser pulses, we can oscillate the fluorescence from NVCs in a nanodiamond, while oscillating other optical signals in the opposite phase to NVCs. As a result, we can reconstruct a selective image of a nanodiamond by using a series of oscillated fluorescence images. We demonstrate application of the method to the selective imaging of nanodiamonds in live cells, in microanimals, and on a hippocampal slice culture obtained from a rat. Our approach potentially enables us to achieve high-contrast images of nanodiamond-labeled biomolecules with a signal-to-background ratio improved by up to 100-fold over the standard fluorescence image, thereby providing a more powerful tool for the investigation of molecular dynamics in cells and in vivo.

Optimization of Wide-Field ODMR Measurements Using Fluorescent Nanodiamonds to Improve Temperature Determination Accuracy.

Fluorescent nanodiamonds containing nitrogen-vacancy centers have attracted attention as nanoprobes for temperature measurements in microenvironments, potentially enabling the measurement of intracellular temperature distributions and temporal changes. However, to date, the time resolution and accuracy of the temperature determinations using fluorescent nanodiamonds have been insufficient for wide-field fluorescence imaging. Here, we describe a method for highly accurate wide-field temperature imaging using fluorescent nanodiamonds for optically detected magnetic resonance (ODMR) measurements. We performed a Monte Carlo simulation to determine the optimal frequency sweep range for ODMR temperature determination. We then applied this sweep range to fluorescent nanodiamonds. As a result, the temperature determination accuracies were improved by a factor ~1.5. Our result paves the way for the contribution of quantum sensors to cell biology for understanding, for example, differentiation in multicellular systems.

Triple nitrogen-vacancy centre fabrication by C5N4Hn ion implantation.

Quantum information processing requires quantum registers based on coherently interacting quantum bits. The dipolar couplings between nitrogen vacancy (NV) centres with nanometre separation makes them a potential platform for room-temperature quantum registers. The fabrication of quantum registers that consist of NV centre arrays has not advanced beyond NV pairs for several years. Further scaling up of coupled NV centres by using nitrogen implantation through nanoholes has been hampered because the shortening of the separation distance is limited by the nanohole size and ion straggling. Here, we demonstrate the implantation of C5N4Hn from an adenine ion source to achieve further scaling. Because the C5N4Hn ion may be regarded as an ideal point source, the separation distance is solely determined by straggling. We successfully demonstrate the fabrication of strongly coupled triple NV centres. Our method may be extended to fabricate small quantum registers that can perform quantum information processing at room temperature.

Annihilation gamma imaging for carbon ion beam range monitoring using Si/CdTe Compton camera.

In this study, we performed on-beam monitoring of 511 keV annihilation gamma emissions using a Compton camera. Beam monitoring experiments were conducted using carbon ion beams of 290 MeV/u irradiated on a polymethyl methacrylate (PMMA) phantom. The intensity of the beams was 3 × 109 particles per pulse, with 20 pulses per minute. A Compton camera based on a silicon/cadmium telluride (Si/CdTe) detector was used to monitor the annihilation gamma rays emitted from the phantom. We successfully reconstructed the energy events of 511 keV annihilation gamma rays and developed Compton images using a simple back-projection method. The distribution of the annihilation gamma ray generation traced the beam trajectory and the peak intensity position was a few millimeters shorter than the Bragg peak position. Moreover, the effect of the beam range shifter with 30, 60, and 90 mm water equivalent thickness (WET) was clearly visualized in the reconstructed Compton images. The experimentally measured values of the corresponding range shifts in the PMMA phantom (28.70 mm, 52.49 mm, and 76.77 mm, respectively) were consistent with the shifts of the Bragg peak position (25.50 mm, 51.30 mm and 76.70 mm, respectively) evaluated by Monte Carlo simulation. The results show that the Si/CdTe Compton camera has strong potential for on-beam monitoring of annihilation gamma rays in particle therapy in clinical situations.

Visualization of focused proton beam dose distribution by atomic force microscopy using blended polymer films based on polyacrylic acid.

A simple and sensitive sub-micrometer scale method for visualization of the dose distribution of a focused proton beam (FPB) was developed, taking advantage of the formation of a bulky crosslinked structure induced by FPB irradiation of a common polymer and cross-linker, polyacrylic acid-N, N'-methylene bisacrylamide, blend film surface. The irradiated part of the film swelled as a peak, and the height of swelling increased with increasing FPB fluence. The film was used as a proton beam-sensitive polymer film by analysis of the irradiated film surface using atomic force microscopy. The method was successfully applied to confirm the FPB pattern. Typical misaligned spot shape of FPB gave clear 3-dimensional structures, and the half-solenoidal nanostructures are visualized clearly by use of crescent shaped beam.