Note: Neutron shutter for Kolkata superconducting cyclotron.

In particle accelerator facilities, experimental areas are isolated from active accelerator area with thick concrete walls. A neutron shutter is used to isolate the experimental areas from the active accelerator area in the beam line. These shutters are provided primarily to reduce the secondary radiations like neutrons in the experimental areas to permissible limit when the primary beam is blocked in the accelerator area. The reduced radiation level in the experimental areas makes the experimental areas accessible. The shutters should allow the primary beam to pass to the experimental caves when they retracted from the beam line. A new neutron shutter has been designed and fabricated. This shutter incorporates compact features with considerable reduction in length, surface area and volume. The attenuation of secondary radiations is evaluated using Monte-Carlo radiation transport code FLUKA. It is found that the features of the shutter are sufficiently good enough to reduce the diffused secondary radiations well within the permissible levels.

Association of leaf micro-morphological characters with powdery mildew resistance in field-grown mulberry (Morus spp.) germplasm.

BACKGROUND AND AIMS: Micro-morphological characteristics can influence fungal infectivity. We sought links between micro-morphology and resistance to powdery mildew in mulberry with the intention of assisting selection of disease-resistant lines. METHODOLOGY: Over 3 years and under field conditions, we evaluated 30 lines of mulberry with contrasting susceptibilities to powdery mildew (15 resistant and 15 susceptible). Disease severity was related statistically to stomatal area, stomatal density, stomatal index, upper and lower cuticular thicknesses, leaf thickness and trichome density. PRINCIPAL RESULTS: Differences between lines were significant (P <0.05) for all characters studied. Variation between the resistant and susceptible groups was statistically highly significant (P <0.01) for stomatal index, stomatal area and trichome density. The powdery mildew-resistant group was distinguished by  17.4 % lower stomatal density, 12.5 % smaller stomatal index per unit leaf area, 20.0 % greater trichome density and 18.0 % higher stomatal area compared with the susceptible group. Trichome density was negatively correlated with disease severity index and with the accumulative area under disease progression curves. Stomatal density was positively correlated with both measures of disease severity. Although stomatal area was negatively related to disease severity index (r = -0.28; P <0.05), the correlation was weak. There was no statistically significant relationship between stomatal area and the accumulative area under disease progression curves. The germplasm was partitioned into seven sub-groups based on hierarchical cluster analysis derived from pooled disease severity index scores and three highly significant micro-morphological characters. Eighty per cent of the resistant germplasm accumulated in three cluster components (A1, A2 and B2) characterized by high trichome densities and a high stomatal density and stomatal index. CONCLUSIONS: Resistance to powdery mildew in mulberry is associated with trichome and stomatal features rather than leaf and epidermal thicknesses. Trichome density, stomatal density and stomatal index are shown to be promising markers for screening powdery mildew resistance in breeding programmes.