Resonances in 28Si+28Si. I

A molecular model developed for resonances observed in medium light heavy-ion collisions is described. At high spins in 28Si+28Si (oblate-oblate system), a stable dinuclear configuration is found to be equator-equator touching one. The normal modes around the equilibrium are investigated. These modes are expected to be the origin of a large number of resonances observed. Furthermore, due to the axially asymmetric shape of the stable configuration of 28Si+28Si, the system rotates preferentially around the axis with the largest moment of inertia, which gives rise to wobbling motion ($K$-mixing). Energy spectra for the normal modes and for the extended model including the wobbling motion are given.Comment: 46 pages, 13 figures. PTP in press (vol.127, No.5

Resonances in 28Si+28Si. II

Resonances observed in the 28Si+28Si collision are studied by the molecular model. In the preceding paper, it is clarified that at high spins in 28Si+28Si (oblate-oblate system), the stable dinuclear configuration of the system is equator-equator touching one, and that the axially asymmetric shape of the stable configuration of 28Si+28Si gives rise to a wobbling motion ($K$-mixing). There, the normal modes around the equilibrium have been solved and various excited states have been obtained. Those states are expected to be the origin of a large number of resonances observed. Hence their physical quantities are analyzed theoretically. The results are compared with the recent experiment performed in Strasbourg and turn out to be in good agreement with the data. Disalignments between the orbital angular momentum and the spins of the constituent 28Si nuclei in the resonance state are clarified. Moreover the analyses of the angular correlations indicate characteristic features for each normal-mode excitation. Thus it is possible to identify the modes, and a systematic experimental study of angular correlation measurements is desired.Comment: 29 pages, 12 figures. PTP in press (vol.127, No.5

Fusion Hindrance in the Heavy Ion Reactions -- Border Between the Normal and Hindered Fusions

The fusion hindrance in heavy ion collisions is studied in the framework of the two-center liquid drop model. It appears that the neck and the radial degrees of freedom might both be hampered by an inner potential barrier on their path between the contact configuration to the compound nucleus. Heavy ion reactions with and without the two kinds of fusion hindrance are classified through systematic calculations. It is found that the number of reactions without radial fusion hindrance is much smaller than that without neck fusion hindrance, and for both kinds of fusion hindrance the number of reactions without fusion hindrance at small mass-asymmetry parameter $\alpha$ is smaller than that at large $\alpha$. In the formation of a given compound nucleus, if a reaction with $\alpha_c$ is not hindered, then other reactions with $\alpha > \alpha_c$ are also not hindered as it is well known experimentally.Comment: 14 pages, 7 figure

Theory of fusion hindrance and synthesis of the superheavy elements

The two-step model for fusion reactions of massive systems is briefly reviewed.By the use of fusion probabilities obtained by the model and of survival probabilities obtained by the new statistical code, we predict residue cross sections for 48Ca+actinide systems leading to superheavy elements with Z=114, 116 and 118.Comment: 7 pages, 4 figures, Halong Bay meeting proceedin

On the predictions of the models for the Super-Heavy Elements

Nuclear structure calculations predict the existence of super-heavy elements (SHE) that are tentatively synthesized through heavy-ion collisions. A complete description of the reaction to synthesize Super-Heavy Elements is necessary to bridge these predictions with the experimental results on the fission time and residue cross sections. In this contibution, we will present the constraints that can be given on the shell correction energy from experimental data and the developments that are needed for the dynamical models

KEWPIE: a dynamical cascade code for decaying exited compound nuclei

A new dynamical cascade code for decaying hot nuclei is proposed and specially adapted to the synthesis of super-heavy nuclei. For such a case, the interesting channel is the tiny fraction that will decay through particles emission, thus the code avoids classical Monte-Carlo methods and proposes a new numerical scheme. The time dependence is explicitely taken into account in order to cope with the fact that fission decay rate might not be constant. The code allows to evaluate both statistical and dynamical observables. Results are successfully compared to experimental data.Comment: 15 pages, 3 Figures, Submitted to Comp. Phys. Co

Two-Step Model of Fusion for Synthesis of Superheavy Elements

A new model is proposed for fusion mechanisms of massive nuclear systems where so-called fusion hindrance exists. The model describes two-body collision processes in an approaching phase and shape evolutions of an amalgamated system into the compound nucleus formation. It is applied to $^{48}$Ca-induced reactions and is found to reproduce the experimental fusion cross sections extremely well, without any free parameter. Combined with the statistical decay theory, residue cross sections for the superheavy elements can be readily calculated. Examples are given.Comment: 4 pages, 4 figure

Analysis of the Fusion Hindrance in Mass-symmetric Heavy Ion Reactions

The fusion hindrance, which is also denominated by the term extra-push, is studied on mass-symmetric systems by the use of the liquid drop model with the two-center parameterization. Following the idea that the fusion hindrance exists only if the liquid drop barrier (saddle point) is located at the inner side of the contact point after overcoming the outer Coulomb barrier, the reactions in which two barriers are overlapped with each other are determined. It is shown that there are many systems where the fusion hindrance does not exist for the atomic number of projectile or target nucleus $Z\leq43$, while for $Z>43$, all of the mass-symmetric reactions are fusion-hindered.Comment: 6 pages, 4 figures. to be published in Sci. in China

Impacts of Dry Season and Forest Fire 1997-1998 Episodes on Mixed Dipterocarp Forest at Bukit Bangkirai, East Kalimantan*[pengaruh Musim Kering Dan Kebakaran Hutan Episode 1997-1998 Terhadap Hutan Dipterocarp Campuran Di Bukit Bangkirai, Kalimantan Timur]

Kawasan Kalimantan Timur mengalami musim kemarau panjang yang merangsang terjadinya kebakaran hutan yang luas pada 1982-1983 dan 1997-1998.Naskah ini mengemukakan hasil penelitian di Bukit Bangkirai, Kalimantan Tengah mengenai dampak dari kemarau panjang dan kebakaran hutan 1997-1998 terhadap diversitas tumbuhan pohon hutan dipterokarp campuran.Penelitian dilakukan dengan cara memperbandinkan hasil pencacahan tumbuhan pohon berlingkar batang setinggi dada lebih daripada 15cm yang terdapat dalam tiga petak penelitian, masing-masing: lha di hutan alam yang tidak terbakar (K-plot), 0,3 ha di hutan yang terbakar ringan (LD) dan lha di hutan yang terbakar berat (HD).Hasil penelitian menunjukkan bahwa musim kemarau panjang 1997-1998 menyebabkan 12,02% mortalitas individual pohon di hutan alam yang tidak terbakar, yang terlihat dari pohon mati berdiri tegak akibat kekeringan, atau kehilangan 21,67% dari total basal area. Secara keseluruhan terlihat bahwa kebakaran hutan menyebabkan kerusakan berat terhadap struktur dan komposisi hutan. Secara kumulatif, kemarau panjang dan kebakaran hutan menyebabkan mortalitas individual pohon berkisar 36-70% dan kehilangan total basal area antara 45-85% dan menyebabkan lantai hutan terbuka terhadap penyinaran matahari langsung karena menurunnya penutupan tajuk sebesar 23-79%.Kebakaran hutan juga berdampak terhadap penurunan biodiversitas tumbuhan pohon sebesar 23-79% pada tingkat jenis, 53-66% pada tingkat marga dan 18-21% pada tingkat suku.Tercatat Perubahan komposisi jenis pada hutan yang terbakar; dominasi jenis Dipterocarpaceae dipetak hutan tak terbakar (K) menjadi dominasi pionir sekunder Macaranga gigantea-Vernonia arborea di petak terbakar berat (HD) dan dominasi Macaranga gigantea-Shorea smilhiana di petak terbakar ringan (LD).Beberapa jenis seperti Durio acutifolius dan Syzygium incarnaium mungkin dapat digolongkan sebagai jenis yang relative lebih tahan terhadap api

Diffusion over a saddle with a Langevin equation

The diffusion problem over a saddle is studied using a multi-dimensional Langevin equation. An analytical solution is derived for a quadratic potential and the probability to pass over the barrier deduced. A very simple solution is given for the one dimension problem and a general scheme is shown for higher dimensions.Comment: 13 pages, use revTeX, to appear in Phys. Rev. E6