Assessment of apple core collections constructed using phenotypic and genotypic data.

Several types of information can be used to select core collections, including passport data, agronomic data, and molecular data. However, little is known about the ability of core collections to retain the genetic diversity and structure of the whole collection for characters that were not considered during the selection, particularly when molecular markers are used. In this study, two core subsets were established for the apple (Malus spp) germplasm bank curated at the Apple Research Station, National Institute of Horticultural and Herbal Science, Korea, based upon genetic diversity estimated with 14 simple sequence repeat markers, and phenotypic diversity based on 23 traits. Comparisons between these two subsets and with the whole collection were used to determine the effect of the data used in the selection on phenotypic and genetic diversity, and population structure. The two subsets had a similar diversity and did not differ from the original collection, according to the Nei and Shannon diversity indices. Allele and class frequencies were also maintained in the two subsets. Overall, the type of data used to construct the core collection had little influence on the phenotypic and genetic diversity retained. Therefore, in the case of apple collections, the use of molecular markers is preferable, because they allow rapid and reliable characterization.

Arrangement of high-energy neutron irradiation field and shielding experiment using 4 m concrete at KENS.

An irradiation field of high-energy neutrons produced in the forward direction from a thick tungsten target bombarded by 500 MeV protons was arranged at the KENS spallation neutron source facility. In this facility, shielding experiment was performed with an ordinary concrete shield of 4 m thickness assembled in the irradiation room, 2.5 m downstream from the target centre. Activation detectors of bismuth, aluminium, indium and gold were inserted into eight slots inside the shield and attenuations of neutron reaction rates were obtained by measurements of gamma-rays from the activation detectors. A MARS14 Monte Carlo simulation was also performed down to thermal energy, and comparisons between the calculations and measurements show agreements within a factor of 3. This neutron field is useful for studies of shielding, activation and radiation damage of materials for high-energy neutrons, and experimental data are useful to check the accuracies of the transmission and activation calculation codes.

Physical evaluation of a system for direct digital intra-oral radiography based on a charge-coupled device.

OBJECTIVES: To determine technical properties of a direct digital intra-oral radiographic system, the Dixel(R) (J Morita Corporation, Kyoto, Japan). METHODS: A dose response function and the dark current were calculated from two series of exposures to a homogeneous radiation field. The line spread function (LSF) and the modulation transfer function (MTF) were determined from radiographs of an edge. The noise power spectrum (NPS) was determined at three exposures from radiographs exposed to homogeneous radiation fields. Noise equivalent quanta (NEQ) were calculated from the one-dimensional NPS and the MTF. The detective quantum efficiency (DQE) was determined from the NEQ and a representative value of the photon fluence. Signal-to-noise ratios (SNR) were calculated from the NEQs and different signal contrasts. RESULTS: The dose response function demonstrated a slight curvature. There was no effect of the dark current. NPS ranged from 10-5 - 10-7 mm2 depending on exposure and frequency. At a peak of about 2 cycles/mm the DQE is on an average about 30 per cent. SNRs are favorable. CONCLUSION: The technical properties found in this study indicate that the Dixel(R) system is suitable for intra-oral dental radiography.

Absorbed dose measurements and calculations in phantoms for 1.5 to 50 keV photons.

A Monte Carlo code EGS4 expanded for low energy photon transport was validated by measuring absorbed doses in a phantom for 30 and 10 keV monoenergetic photons from synchrotron radiation. Using the EGS4 code, depth doses at 0.07 mm, 0.02 to 0.1 mm, and 10 mm in the ICRU slab phantoms were calculated for 1.5 to 50 keV photons using the updated photon cross section data PHOTX. The results show that the doses at 0.02 to 0.1 mm below 10 keV are practical indices of effective dose as calculated by others, based on the 1990 ICRP recommendations (1991).

Measurement of absorbed dose in water irradiated by 2.5-GeV bremsstrahlung.

Plane shields made of Pb with a water tank behind them were irradiated by 2.5-GeV bremsstrahlung. The longitudinal distribution of the absorbed dose in water was measured using a scintillation counter. The results are compared with Monte Carlo calculations and published depth dose tables.