A note on the age of radioactive tracers

Abstract The age of a water mass is often estimated experimentally using the radio-age computed from the distribution of a radioactive tracer (radiocarbon, helium -tritium). Deleersnijder et al. [J. Mar. Syst. 28 (2001) 229.] have shown that the radioage underestimates the age of the water and is larger than the age of the radioactive tracer used for its evaluation. This result is generalized here to radio-ages computed from the ratio of two radioactive tracers. The differences between the different ages are also studied analytically and numerically as functions of the decay rate of the radioactive tracers. For small decay rates, the difference between the age of the water mass and the radio-age is shown to be proportional to the decay rate. It depends also on the level of mixing in the system; even radioactive tracers with small decay rates can provide poor estimates of the age of the water mass in a strongly diffusive flow. For small half lives, both the radio-age and the age of radioactive tracers decrease as the inverse of the square root of the decay rate. The same analysis applies to some extent to the estimates of the age of a water mass from stable tracers with known time dependent sources (e.g. chloroflurocarbons)

The Representation of Texture in Cold-Rolled Copper Sheet by an Advanced X-Ray Diffraction Technique

The influence of texture on forming properties of metals has widely been recognized [l–4]. Preferred orientation of the crystallites (grains) in polycrystalline aggregates results in anisotropy of the mechanical properties. The desired degree of, or absence of, anisotropy depends on the particular process of forming, and any subsequent manufacturing process requires certain material properties for satisfactory performance. For example, the type of texture desired in deep drawing is quite different from the one necessary for simple stamping or multiaxial bending. Thus, in-process texture monitoring is receiving increased interest, both from manufacturers and researchers [4,5].</p

Microphase separation of highly amphiphilic, low N polymers by photoinduced copper-mediated polymerization, achieving sub-2 nm domains at half-pitch

The lower limit of domain size resolution using microphase separation of short poly(acrylic acid) homopolymers equipped with a short fluorinated tail, posing as an antagonist 'A block' in pseudo AB block copolymers has been investigated. An alkyl halide initiator with a fluorocarbon chain was utilized as a first 'A block' in the synthesis of low molecular weight polymers (1400-4300 g mol -1) using photoinduced Cu(ii)-mediated polymerization allowing for very narrow dispersity. Poly(tert-butyl acrylate) was synthesized and subsequently deprotected to give very low degrees of polymerization (N), amphiphilic polymers with low dispersity (D = 1.06-1.13). By exploiting the high driving force for demixing and the well-defined 'block' sizes, we are able to control the nanostructure in terms of domain size (down to 3.4 nm full-pitch) and morphology. This work demonstrates the simple and highly controlled synthesis of polymers to push the boundaries of the smallest achievable domain sizes obtained from polymer self-assembly