Fission decay of N = Z nuclei at high angular momentum: 60^{60}Zn

Using a unique two-arm detector system for heavy ions (the BRS, binary reaction spectrometer) coincident fission events have been measured from the decay of $^{60}$Zn compound nuclei formed at 88MeV excitation energy in the reactions with $^{36}$Ar beams on a $^{24}$Mg target at $E_{lab}(^{36}$Ar) = 195 MeV. The detectors consisted of two large area position sensitive (x,y) gas telescopes with Bragg-ionization chambers. From the binary coincidences in the two detectors inclusive and exclusive cross sections for fission channels with differing losses of charge were obtained. Narrow out-of-plane correlations corresponding to coplanar decay are observed for two fragments emitted in binary events, and in the data for ternary decay with missing charges from 4 up to 8. After subtraction of broad components these narrow correlations are interpreted as a ternary fission process at high angular momentum through an elongated shape. The lighter mass in the neck region consists dominantly of two or three-particles. Differential cross sections for the different mass splits for binary and ternary fission are presented. The relative yields of the binary and ternary events are explained using the statistical model based on the extended Hauser-Feshbach formalism for compound nucleus decay. The ternary fission process can be described by the decay of hyper-deformed states with angular momentum around 45-52 $hbar$.Comment: 23 pages, 25 figure

Alpha-cluster Condensations in Nuclei and Experimental Approaches for their Studies

The formation of alpha-clusters in nuclei close to the decay thresholds is discussed. These states can be considered to be boson-condensates, which are formed in a second order phase transition in a mixture of nucleons and alpha-particles. The de Broglie wavelength of the alpha-particles is larger than the nuclear diameter, therefore the coherent properties of the alpha-particles give particular effects for the study of such states. The states are above the thresholds thus the enhanced emission of multiple-alphas into the same direction is observed. The probability for the emission of multiple-alphas is not described by Hauser-Feshbach theory for compound nucleus decay.Comment: 21 pages, 12 figures

Coplanar Ternary Cluster Decay of Hyper-deformed 56^{56}Ni

Coincidences between two heavy fragments have been measured from fission of 56Ni compound nuclei, formed in the 32S + 24Mg reaction at Elab(32S) = 163.5 MeV. A unique experimental set-up consisting of two large area position sensitive (x, y) gas-detector telescopes has been used allowing the complete determination of the observed fragments, and their momentum vectors. In addition to binary fission events with subsequent particle evaporation, narrow out-of-plane correlations are observed for two fragments emitted in purely binary events and in events with a missing mass consisting of 2$\alpha$ and 3$\alpha$ particles(12C). These events are interpreted as ternary cluster decay from 56Ni-nuclei at high angular momenta through hyper-deformed shape

Clusters in Light Nuclei

A great deal of research work has been undertaken in the alpha-clustering study since the pioneering discovery, half a century ago, of 12C+12C molecular resonances. Our knowledge of the field of the physics of nuclear molecules has increased considerably and nuclear clustering remains one of the most fruitful domains of nuclear physics, facing some of the greatest challenges and opportunities in the years ahead. In this work, the occurence of "exotic" shapes in light N=Z alpha-like nuclei is investigated. Various approaches of superdeformed and hyperdeformed bands associated with quasimolecular resonant structures are presented. Results on clustering aspects are also discussed for light neutron-rich Oxygen isotopes.Comment: 12 pages, 5 figures. Invited Talk presented by C. Beck at the Zakopane Conference on Nuclear Physics "Extremes of the Nuclear Landscape" XLV in the series of Zakopane Schools of Physics - International Symposium - Zakopane, Poland, August 30 - September 5, 2010.To be publihed in Acta Physica Polonica B42 no 3, March 201

Binary fission and coplanar cluster decay of 60Zn compound nuclei at high angular momentum

Fission decays with two heavy fragments in coincidence have been measured from 60Ni compound nuclei, formed in the 36Ar 24Mg reaction at Elab 36Ar 195MeV 5.4 MeV A . The experiment was performed with a unique kinematic coincidence set up consisting of two large area position sensitive x,y gas detector telescopes with Bragg ionisation chambers. Very narrow out of plane correlations are observed for two heavy fragments emitted in either purely binary events or in events with a missing mass consisting of 2,3 and 4 particles. The broad out of plane distribution correspond to binary fission with the evaporation of particles or nucleons from excited fragments. The narrow correlations are interpreted as ternary coplanar cluster decay from compound nuclei at high angular momenta through elongated shapes with large moments of inertia, and the lighter mass remains with very low momentum in the centre of mass frame. It is shown in calculations of shapes, that the large moments of inertia of the hyper deformed configurations excepted in these nuclei, will lower the ternary fission barrier so as to make a competition with binary fission possibl

Extra lightweight mechanical support structures with the integrated cooling system for a new generation of vertex detectors

The performance of new extra lightweight mechanical support structures with the integrated liquid cooling system for monolithic silicon pixel detectors has been investigated. These detectors will be used to upgrade the inner tracking system in the ALICE experiment at the CERN Large Hadron Collider. The extra lightweight mechanical support structures, together with the novel pixel detectors, provide a record-breaking total radiation length of 0.3% X 0 per layer, which will make it possible to considerably extend the physical program of investigations of the quark-gluon plasma in ultra-relativistic heavy-ion collisions at the Large Hadron Collider. This is particularly important in measuring the yields of heavy-flavor hadrons and low-mass dileptons with low transverse momenta. The experimental results of the thermal tests and the comparative analysis of five samples of extra lightweight mechanical support structures for monolithic silicon pixel detectors are presented. The high efficiency of heat drain using the liquid cooling system for a power density as high as 0.5 W/cm2 is show

Investigations of the new generation pixel detectors for ALICE experiment at LHC

We present the results from testing Monolithic Active Pixel Sensors of the detector ALPIDE (ALICE Pixel Detector). The purpose of these tests was to measure the pixel threshold and noise distributions in each of the four sectors of the detector, as well as the analysis of the hit maps produced by different radioactive sources