Search

A 241Am gamma (γ)-ray calibration field that meets the requirements for a γ-ray reference field as specified in the ISO 4037 standard series was established in the Facility of Radiation Standards of the Japan Atomic Energy Agency. The reference air kerma rates were measured using a reference ionization chamber calibrated by the N-80 quality X-ray calibration field of the national metrology standard in Japan and with a correction to account for differences in photon energy due to the calibration field. Conversion coefficients for the 241Am γ-ray calibration field, including those not listed in the ISO 4037 standard series, were calculated based on the measured γ-ray fluence rate spectra. [ABSTRACT FROM AUTHOR]

With the goal of developing a new type of boron neutron capture therapy (BNCT) agent, selective internalisation of submicrometer boron carbide spherical particles into cancer cells via surface transferrin conjugation is demonstrated and confirmed in vitro and in vivo. Herein, negatively charged, spherical, submicrometer boron carbide (B4C) particles were coated with positively charged poly-L-lysine and negatively charged poly-γ-glutamic acid; the particles were subsequently conjugated with transferrin. It was confirmed in vitro and in vivo by confocal laser scanning microscopy and transmission electron microscopy that the coated particles interacted with transferrin receptors that were highly expressed on the surface of cancer cells, endocytosed by tumour cells, and transferred to the proximity of the nucleus. The submicrometer size of the particles provided stronger interaction between transferrin and transferrin receptors and hence resulted in more efficient internalisation than that obtained using nanoparticles. This method might be effective for the selective internalisation of large submicrometer particles for high therapeutic effects due to the large particle size, but with small particle dosages. [ABSTRACT FROM AUTHOR]

The anisotropic emission of neutrons from a cylindrical X1 252Cf source with the spherical external casing was experimentally determined. The influence of metal materials and shapes of the external casing to the anisotropy factor, F I (θ), was assessed by the Monte Carlo calculation, before performing the measurement. The results of the calculation implied that light- and spherical-shaped external casing decreases the anisotropic emission of neutrons from a cylindrical source and the nature of the material does not affect the anisotropic emission to a large extent. The experimental results obtained when a spherical-shaped aluminum protection case was employed also revealed that the anisotropy factor was close to 1.0 with a wide zenith angle range. Considering the source handling and measures against mechanical impact to the source, we designed an SUS304-made spherical protection case for a renovated source delivering apparatus. With the SUS304-made spherical protection case, the measured anisotropy factor F I(90) was determined to be 1.002 ± 0.002 (k  = 1). Results from the experiments also indicated that the measured anisotropy factor has a flat distribution from 55 to 125° with zenith angle. [ABSTRACT FROM AUTHOR]

When considering drug delivery, the amount of drug that can be carried at a particular time and how the drug is incorporated efficiently into cells are important parameters. Transferrin (Tf)-conjugated nanocarriers have been used for the targeted delivery of drugs to cancer cells due to the availability of receptor-mediated clathrin-dependent endocytosis. In general, however, endocytosis seems to differ according to the size and shape of carriers. Large substances are generally internalized into cells by phagocytosis. We studied the internalization mechanism of Tf-conjugated nanoparticles (diameter, 522 nm). Tf-conjugated polystyrene particles were incorporated into cells by receptor-mediated endocytosis with large clathrin-coated vesicles even though their diameter was >500 nm and despite that fact that clathrin-coated vesicles have a diameter of ≍100 nm. This finding suggests that signals for internalization generated by stimulated Tf receptors (TfRs) activate clathrin-mediated endocytosis preferentially. Whether these larger particles could deliver drugs more efficiently than smaller particles was then examined. The toxicity of larger Tf-conjugated biodegradable nanoparticles (poly(lactic-co-glycolic acid)) encapsulating doxorubicin (diameter, 216 ± 38 nm) was appreciably dependent on the number of Tf molecules conjugated on a particle and the number of TfRs expressed on the cell membrane. Larger Tf-conjugated particles delivered drugs to cancer cells expressing many TfRs more selectively than their smaller counterparts (diameter, 56 ± 9 nm) if they were decorated with an appropriate number of Tf molecules. [ABSTRACT FROM PUBLISHER]

An attempt was made to estimate organ doses of a victim in a high-dose non-homogeneous exposure accident caused by a sealed 192Ir gamma-ray source. The Gilan accident was selected as a case study. Organ doses including testis, red bone marrow and so on were properly estimated by applying the Monte Carlo calculation with the state-of-the-art adult male Mesh type Reference Computational Phantom. By introducing a complicated exposure scenario, the dose distribution on the right chest of the victim in the Gilan accident could be reproduced to a certain extent., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

A dosimeter should ideally be calibrated in a reference field with similar energy and doserate to that which the dosimeter is being used to measure. Environments around nuclear reactors and radiation therapy facilities have high-energy photons with energies exceeding that of 60 Co gamma rays, and controlling exposure to these photons is important. The Japan Atomic Energy Agency and National Metrology Institute of Japan have high-energy reference fields with energies above several megaelectronvolts for different types of accelerators. Their reference fields have different fluence-energy distributions. In this study, the energy dependencies of the two-cavity ionization chambers, which are often used by secondary standard laboratories, were experimentally and computationally evaluated for each high-energy field. These results agreed well within the relative expanded uncertainties ( k = 2), and their capabilities for air kerma measurements in each high-energy reference field were confirmed. Therefore, the capabilities of the air-kerma measurements were verified in the two high-energy reference fields., (© 2024 Society for Radiological Protection. Published on behalf of SRP by IOP Publishing Limited. All rights, including for text and data mining, AI training, and similar technologies, are reserved.)

A 241Am gamma (γ)-ray calibration field that meets the requirements for a γ-ray reference field as specified in the ISO 4037 standard series was established in the Facility of Radiation Standards of the Japan Atomic Energy Agency. The reference air kerma rates were measured using a reference ionization chamber calibrated by the N-80 quality X-ray calibration field of the national metrology standard in Japan and with a correction to account for differences in photon energy due to the calibration field. Conversion coefficients for the 241Am γ-ray calibration field, including those not listed in the ISO 4037 standard series, were calculated based on the measured γ-ray fluence rate spectra., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)