N. P. Andreeva

Topology of “white stars” in the relativistic fragmentation of light nuclei

Experimental observations of the multifragmentation of relativistic light nuclei by means of emulsions are surveyed. Events that belong to the type of “white stars” and in which the dissociation of relativistic nuclei is not accompanied by the production of mesons and target-nucleus fragments are considered. An almost complete suppression of the binary splitting of nuclei to fragments of charge in excess of two, Z > 2, is a feature peculiar to charge topology in the dissociation of Ne, Mg, Si, and S nuclei. An increase in the degree of nuclear fragmentation manifests itself in the growth of the multiplicity of singly and doubly charged fragments (Z = 1, 2) as the charge of the unexcited fragmenting-nucleus part (which is the main part) decreases. Features of the production of systems formed by extremely light nuclei α, d, and t are studied in the dissociation of the stable isotopes of Li, Be, B, C, N, and O to charged fragments. Manifestations of 3He clustering can be observed in “white stars” in the dissociation of neutron-deficient isotopes of Be, B, C, and N.

Clustering in light nuclei in fragmentation above 1 A GeV

Abstract.The relativistic invariant approach is applied to analyzing the 3.3 A GeV 22Ne fragmentation in a nuclear track emulsion. New results on few-body dissociations have been obtained from the emulsion exposures to 2.1 A GeV 14N and 1.2 A GeV 9Be nuclei. It can be asserted that the use of the invariant approach is an effective means of obtaining conclusions about the behavior of systems involving a few He nuclei at a relative energy close to 1MeV per nucleon. The first observations of fragmentation of 1.2 A GeV 8B and 9C nuclei in emulsion are described. The presented results allow one to justify the development of few-body aspects of nuclear astrophysics.

Fragmentation of 22Ne in emulsion at 4.1A GeV/c

Charge distributions of projectile fragments produced in the interactions of 22Ne beams with emulsion at 4.1A GeV/c have been studied. Correlations between projectile and target fragments and among projectile fragments are presented. The change of charge yield distribution with the violence of the collision has been shown. The present analysis contradicts theoretical calculations describing the inclusive charge yield distribution of fragments by a single process.

Radiation dose reconstruction and nuclear-explosion dating in the East-Kazakhstan region

The radioecological situation in the East-Kazakhstan region was studied by electron paramagnetic resonance (EPR), radiography and nuclear spectroscopy methods. The eastern part of this region borders the Semipalatinsk nuclear test site. Radiation doses for 33 residents of this region were measured by EPR dosimetry in tooth enamel. It was found that for 25% of the residents the measured radiation doses do not exceed the background level. The rest of the doses exceed the background level by a factor of 2–4 on the average. A new method of nuclear explosion dating was developed on the basis of the EPR measurements of the free radical concentration in annual tree rings. Their maximal concentration corresponds to the years when nuclear explosions were executed. The obtained results correlate well with the commonly accepted radiography method. Both methods show a maximum of radionuclide levels in the years of nuclear testing. The plutonium-239 content in residents hair samples was found to be equal to (0.8±0.2)·10−9 g/kg and with activity of 1.9±0.4 Bq/kg. This is by a factor of 20 higher than the permitted content for the population.

Flow effects in high-energy nucleus collisions with Ag(Br) in emulsion

Various flow phenomena observed by a unique emulsion method are reviewed. The experimental data of the emission of projectile and target fragments and relativistic particles in collisions of 1–160 A GeV/c16O, 22Ne, 28Si, 32S, 84Kr, 197Au, and 208Pb nuclei with 108Ag (80Br) targets are investigated. The transverse-momentum approach, the flow-angle analysis using principal vectors, the azimuthal correlation functions, the method of azimuthal correlations between charged secondaries, and the method of Fourier expansion of the azimuthal angle distributions are applied. Evidence of the directed flow of spectators has been obtained in the medium-impact nuclear interactions. In azimuthal distributions, with respect to the reaction plane, the signal of the elliptic flow of participants has been observed.

Coherent Dissociation

First searches for the coherent dissociation of relativistic oxygen nuclei into four a particles are reported. It is shown that reactions of this type are characterized by a significantly lower decay temperature than the conventional multifragmentation of residual projectile nuclei. The momentum spectra and correlations of a panicles are not reproduced by the simple statistical model of direct fragmentation. The possibility that the oxygen nucleus undergoing fragmentation acquires a nonzero angular momentum in the collision process is discussed.

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The full destruction (FD, that implies the disintegration into singly and doubly charged fragments only) characteristics are presented for some light nuclei ( 6 12 C, 8 16 O, 10 22 Ne, and 14 28 Si) with an energy of 3.7A GeV and heavy projectiles 79 197 Au (10.7A GeV) and 82 208 Pb (158A GeV) interacting with target nuclei in a photoemulsion. It is shown that (i) the average number of fragments, the realization of various fragmentation channels, and the degree of crushing for light projectiles substantially depend on the charge of a residual nucleus and on the mass of a target nucleus; (ii) the FD probability for residual nuclei with the same charge, as well as the multiplicity of fragments for the same impact parameter of heavy nuclei, are independent of the energy; and (iii) the integral distribution of transverse momenta of doubly charged fragments is described by two exponents (the logarithmic plot exhibits a break).

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The investigations of local concentration of alpha-decaying radionuclides in annual rings of a tree were performed. The tree cut samples were chosen from the Northern Kazakhstan, namely from the Semipalatinsk region. A retrospective study of the alpha-active radionuclide accumulation for the last 45 years was carried out.