CHARACTERISATION OF RADIOPHOTOLUMINESCENCE DOSIMETRY SYSTEM FOR INDIVIDUAL MONITORING.

Performance evaluation is typically assessed as part of the approval procedure to verify that a dosimetry system fulfils specified national or international type-test requirements under representative exposure conditions that are expected to mimic workplace fields from the radiological activities being monitored. The International Atomic Energy Agency Radiation Safety Technical Services Laboratory has recently implemented an integrated radiophotoluminescence (RPL) personal dosimetry system developed by Chiyoda Technol Corporation. This paper reports on the successful verification of dosimetric performance properties of the RPL dosimetry system to IEC 62387:2020, in which the badges were exposed to a range of radiation energies and angles of incidence as well as other influence parameters. Characteristics under test included the coefficient of variation, non-linearity of response due to dose dependence as well as the energy and angular response to photon and beta radiation.

Dose limits to the lens of the eye: International Basic Safety Standards and related guidance.

The International Atomic Energy Agency (IAEA) safety requirements: 'General Safety Requirements Part 3--Radiation protection and safety of radiation sources: International Basic Safety Standards' (BSS) was approved by the IAEA Board of Governors at its meeting in September 2011, and was issued as General Safety Requirements Part 3 in July 2014. The equivalent dose limit for the lens of the eye for occupational exposure in planned exposure situations was reduced from 150 mSv year(-1) to 20 mSv year(-1), averaged over defined periods of 5 years, with no annual dose in a single year exceeding 50 mSv. This reduction in the dose limit for the lens of the eye followed the recommendation of the International Commission on Radiological Protection in its statement on tissue reactions of 21 April 2011. IAEA has developed guidance on the implications of the new dose limit for the lens of the eye. This paper summarises the process that led to the inclusion of the new dose limit for the lens of the eye in the BSS, and the implications of the new dose limit.

Essential dynamics of DNA containing a cis.syn cyclobutane thymine dimer lesion.

Conformational properties of a UV-damaged DNA decamer containing a cis.syn cyclobutane thymine dimer (PD) have been investigated by molecular dynamics (MD) simulations. Results from MD simulations of the damaged decamer DNA show a kink of approximately 21.7 degrees at the PD damaged site and a disruption of H bonding between the 5'-thymine of the PD and its complementary adenine. However, no extra-helical flipping of the 3'-adenine complementary to the PD was observed. Comparison to two undamaged DNA decamers, one with the same sequence and the other with an AT replacing the TT sequence, indicates that these properties are specific to the damaged DNA. Essential dynamics (ED) derived from the MD trajectories of the three DNAs show that the backbone phosphate between the two adenines complementary to the PD of the damaged DNA has considerably larger mobility than the rest of the molecule and occurs only in the damaged DNA. As observed in the crystal structure of T4 endonuclease V in a complex with the damaged DNA, the interaction of the enzyme with the damaged DNA can lead to bending along the flexible joint and to induction of adenine flipping into an extra-helical position. Such motions may play an important role in damage recognition by repair enzymes.

Monte Carlo simulation of 252CF dose distribution brachytherapy.

The calculation of absorbed dose rate of photons and neutrons for the linear source of 252Cf with the active length of 2 cm is presented. Monte Carlo code and neutron cross-section data processed from ENDF/B-6 library were used. The achieved values of the absorbed dose rates are in good agreement with those published by other authors. The results of the calculation are applied to the gynecological configuration used in brachytherapy.

Molecular dynamics (MD) simulation of DNA dodecamer with 5-hydroxy-6-cytosinyl radical.

Molecular dynamics (MD) simulation of DNA dodecamer d (CGCGAATTC*GCG)2 with a primary radiation damage represented by 5-hydroxy-6-cytosinyl radical (C*) in position 9 was performed with AMBER 4.0 force field with periodic boundary conditions for the solvent. The temperature, potential energy of the system, energetic contributions from groups and RMS deviation from original positions were examined throughout the course of the simulation up to 140 ps. The stabilized structure (after 100 ps) was distorted and bent near the damaged site, which is similar to that observed in the MD of DNA with thymine glycol (Miaskiewicz, K. et al (1994) Radiat. Protection Dosimetry, 52, 149-153). The results suggest that a small and local damage in DNA may cause a large and global conformational change in DNA. Water molecules form two layers at distance 2.5 A and 5.5 A around the DNA. The MD simulation is a new approach to study radiation damages in molecular level.

Energy deposition in structural parts of DNA by monoenergetic electrons.

The Monte Carlo simulation of energy deposition in structural parts of DNA based on "Structural Model" is described. This model takes under consideration space positions of atoms in B-form of DNA and clearly defines sensitive volumes of each nucleotide (phosphodiester bonds, sugar, base, hydrogen bonds). ETRACK code producing the positions of energy deposition events in water vapor medium is used for simulation of electron track structure. The electron production points are chosen randomly within the sphere containing cell nucleus. DNA segments are randomly distributed in cell nucleus. Each energy deposition point is tested if it occurs in any element of any DNA part. The highest probability of energy deposition is found for phosphodiester bonds area, whereas the lowest for deoxyribose area. Electrons of initial energies from 5 keV to 10 keV have higher probability of energy deposition in structural part in comparison with lower and higher energy electrons.