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In theories of the minor phase (domain) formation in polyblends rendered as emulsions it is usually assumed that the size and shape of the domains are the result of melt viscosity effects (Taylor, Wu) or viscoelasticity effects (VanOene, Elmendorp) being balanced by interfacial tension. This assumption would predict a monotonic decrease of the domain size to a final limiting size with increasing energy of mixing. However, a systematic study of the dependence of domain morphology on industrial mixing processes which was carried out on a "model" LDPE/PS (2/1) mixture and the related polyalloy (i.e., the same mixture with a corresponding block copolymer as compatibilizer) does not support this expectation. Domain size was found to go through a minimum a s mixing energy was increased. A similar minimum was seen in data on specific volume of the melt vs. mixing energy, which indicates a correlation between melt specific volume and domain size. Calculation of the approximate surface area of the domains using a simple model of domain shape indicated that total interfacial energy in the polyblend and/or polyalloy is a trivial part of the mixing energy introduced. These calculations also indicated that if compatibilizer was located entirely at the interface, the surface layer would have a thickness of about 90 nm. Some micrographs seem to show such a surface layer. We propose that a n abrasion mechanism is responsible for the early stage of the dispersion process, and that the final domain size may be controlled by a dispersion-coalescence equilibrium. This is compared with the theories of final particle size proposed by VanOene and Wu. A. P. Plochocki, S. S. Dagli, a n d R. D. A n d r e w s groups the larger domains in the vicinity of the extrudate courtesy of M . J . Doyle, Exxon Corp. center (right hand side of the photograph) (cf. 31 b).

Using the on-line mass separator at the Gesellschaft fur Schwerionenforschung Unilac we produced Ba through the Ni( Ni, 2n) Ba reaction and measured its production cross section to be 0.20+o 09 pb. The new isotope Ba represents the heaviest N = Z+ 2 nucleus known to date. With KE-E telescopes we measured the total (P-decay) half-life to be Tp = 0.43+o~s s and the partial o.-decay half-life to be T ) 1.2 x 10 s (1 Mev( E' ( 4 MeV) for Ba. With track detectors we found a half-life for spontaneous C emission T& & 1.1 x 10 s based on three carbon events. PACS number(s): 23.70. +j, 23.60.+e, 25.70.Jj, 27.60. +jCluster radioactivity is now a well established, although rare, decay mode of heavy nuclei. Intense experimental research in the last decade has led to the detection of 20 cases of spontaneous emission of clusters ranging from C to Si from trans-lead nuclei, with branching ratios relative to o, decay &om 10 down to 10 and partial half-lives from 10~u p to 10 s [1]. The general features of this new radioactive decay mode have been established; above all, its strong dependence on the barrier penetration factor and consequently on the Q value, which must be large in order to compensate for the small preformation factors typical of such complew clusters [2]. For this reason, all heavy residual nuclei resulting &om cluster emission have been found so far to differ &om the doubly magic Pb by three nucleons at most. Analogously, a new island of cluster radioactivity having residual nuclei close to doubly magic Sn has been predicted by Greiner et al. and Poenaru et al. [3,4]. They found the most favorable case to be C emission from Ba and calculated the decay rate using various mass predictions [5] for the then unknown Ba nucleus. The results of their predictions strongly depend on the adopted Q value: a 2-MeV spread in the Q values results in a factor 10 spread in the partial half-lives. More recently others [6 -10] have taken up the challenge of calculating the decay rate for C emission from~~Ba; their results for the same choice of Q value span more than eight orders of magnitude. This situation is in complete contrast with what is found in the translead region of cluster radioactivity, where Q values are generally known and all models predict half-lives for the same decay mode that typically agree within an order of magnitude [11]. It is clear that the possible island of cluster radioactivity in the trans-tin region would be interesting to ex-plore. Apart &om the possibility of discriminating among different theoretical approaches, the mere detection and measurement of the partial C decay rate of 4Ba could shed light on the behavior of cluster radioactivity in this region of the Chart of the Nuclides far below Pb, possibly providing information on the interplay with o. decay and on the role of the nearly double shell closure in a nucleus such as Sn far from the stability line. The first searches for