Is neutron radiation exposure always detrimental to metals (steels)?
It is well established that irradiated metals and alloys exhibit increased mechanical strength accompanied by reduced ductility, commonly referred to as irradiation strengthening and embrittlement. We talk about radiation damage and environmental degradation of metals following radiation exposure. Indeed, there have been numerous conferences and symposia held and planned on this subject, which include research work and discussions with the central theme being the damage created in materials by neutron radiation exposure. Radiation embrittlement in metals is believed to be due mainly to (1) changes in flow properties because of the interaction of dislocations with irradiation-produced defects1, and (2) precipitation of transmutation-produced gases and irradiation-induced segregation at grain boundaries which are potential fracture sites2. Contrary to the previously observed radiation embrittlement in metals, I report here that neutron irradiation of mild steel improved both the mechanical strength and ductility at 373 K even at relatively high (∼1018 neutrons cm−2), fast (>1 MeV) neutron doses. To my knowledge, such improvement has never been observed before.
Phytoplankton Bloom Produced by a Receding Ice Edge in the Ross Sea: Spatial Coherence with the Density Field
Measurements of chlorophyll, particulate carbon, and biogenic silica concentrations near a receding ice edge off the coast of Victoria Land, Antarctica, indicated the presence of a dense phytoplankton bloom. The bloom extended 250 kilometers from the ice edge and was restricted to waters where the melting of ice had resulted in reduced salinity. The region involved was one of enhanced vertical stability, which may have favored phytoplankton growth, accumulation, or both. Epontic algae released from melting ice may have served as an inoculum for the bloom. Ratios of organic carbon to chlorophyll and biogenic silica to carbon were unusually high, resulting in high biogenic silica concentrations despite only moderately high chlorophyll levels.
Yield Point Phenomena in Metals and Alloys
1 Yield Point Phenomena and their Theoretical Background.- The effects of tensile machine and specimen stiffness.- Types of yield point effects.- The upper yield point-experimental.- The upper yield point-theoretical.- The lower yield point.- Strain ageing.- Pseudo yield points.- 2 Iron and its Alloys.- Effects of carbon, nitrogen and other elements.- Quench ageing.- Yielding behaviour.- Strainageing kinetics.- Effects of radiation damage-Single crystals.- Steels.- 3 The Group Va and VIa Metals.- Vanadium.- Chromium.- Niobium.- Molybdenum.- Tantalum.- Tungsten-Alloys of these metals.- Discussion.- 4 Hydrogen in Metals.- Hydrogen embrittlement.- Solubility of hydrogen in metals.- Mild steel.- Group Va and VIa metals.- Nickel.- Palladium.- Titanium and zirconium.- 5 Aluminium and its Alloys.- The unloading yield point effect.- 'Commercially pure' aluminium.- Aluminium-copper alloys - Aluminium-magnesium alloys.- Other aluminium alloys.- Theories of yield points in aluminium alloys.- 6 Other Face-Centred Cubic Metals and Alloys.- Copper and its dilute alloys.- Brass.- Silver and its alloys.- Nickel and its alloys.- Thorium.- Ordered alloys.- 7 Miscellaneous Materials.- Whiskers.- Ionic crystals.- Semiconducting materials.- Hexagonal metals and alloys.- 8 Discussion.