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Atomic nucleus - Wikipedia, the free encyclopedia The liquid-drop model is able to reproduce many features of nuclei, including the general trend of binding energy with respect to mass number, as well as the phenomenon of nuclear fission. Nuclei with certain numbers of neutrons and protons (the magic numbers 2, 8, 20, 50, 82, 126,...) are particularly stable, because their shells are filled. Nuclei may also have extreme shapes (similar to that of american footballs) or extreme neutron-to-proton ratios. en.wikipedia.org /wiki/Atomic_nucleus   (895 words)

Superheavy Nuclei   (Site not responding. Last check: 2007-11-07) These newly discovered nuclei are shown as tiny red egg-shaped objects in the first figure, positioned according to the number of neutrons and the number of protons that they contain. The large electrostatic forces cause heavy nuclei to decay rapidly by the emission of alpha particles (helium nuclei) and by spontaneous fission. Most magic nuclei are spherical in shape, but some nuclei can lower their energy somewhat, and hence increase their stability, by rearranging their protons and neutrons into deformed shells accommodating a different number of nucleons. t2.lanl.gov /tour/shn.html   (717 words)

Exotic nuclei: why and how to make them?   (Site not responding. Last check: 2007-11-07) Chart of the nuclides representing the nuclei according to their number of protons Z and of neutrons N. The clear outline shows the limit of the nuclei observed experimentally, and the outline of the brown zone indicates the theoretical limit of nuclear cohesion. An approach to the description of nuclei, which seems obvious and which is entirely satisfactory for atomic physics, consists in trying to consider the nuclear force as the sum of the forces between the individual nucleons. At the moment, the dependence of independent-particle orbits as a function of the neutron excess and of the binding energy is the most commonly used explanation for the disappearance of magic numbers valid for the nuclei close to stability and for the appearance of new shell closures. www.europhysicsnews.com /full/28/article3/article3.html   (3642 words)

Nuclei reveal novel decay (September 2002) - News - PhysicsWeb Nuclei decay when they contain either too many neutrons or too many protons to be stable. In these nuclei the protons and neutrons are bound together by a "pairing" force, which causes emission of two protons at the same time. These nuclei were then separated out from the rest of the impact debris, slowed down and captured in a series of silicon detectors, where they quickly decayed via two-proton emission. physicsweb.org /article/news/6/9/8   (586 words)

The Nucleus The convention for designating nuclei is by atomic number, Z, and mass number, A, as well as its chemical symbol. The nuclei of some atoms are spherical, while others are stretched or flattened into deformed shapes. The time required for half of a population of unstable nuclei to decay is called the half-life. www.lbl.gov /abc/wallchart/chapters/02/2.html   (357 words)

Medical Neurosciences The two cochlear nuclei lie dorsal lateral (dorsal cochlear nucleus) and ventral lateral (ventral cochlear nucleus) to the inferior cerebellar peduncle at the rostral pole of the medulla (they “drape” the inferior cerebellar peduncle). The primary input to both cochlear nuclei is from the auditory portion of C.N. The axons making up this division of C.N. VIII consist of the central processes of neurons that lie in the spiral or cochlear ganglion (lies in the modiolus [bony core] of the cochlea). As far as neurological deficits involving lesions of the auditory nuclei and pathways, you should know that a lesion of the auditory portion of the C.N. VIII (nerve) results in deafness in the IPSILATERAL ear. www.neuroanatomy.wisc.edu /virtualbrain/BrainStem/12Cochlear.html   (518 words)

Basic Histology -- Nuclei and Cytoplasm   (Site not responding. Last check: 2007-11-07) Nuclei always stain blue, with at least a rim of dark blue at their edges. The nuclei of the island cells are quite more-or-less and rather large. The cytoplasm of the cells tends to be purple near the nuclei, more pink toward the center of the unit. www.pathguy.com /histo/005.htm   (231 words)

Physics News Update 686 Strontium-76 is one of the most deformed nuclei in its ground state and is the most deformed of all nuclei in which the number of protons (Z) equals the number of neutrons (N). The newly made Sr nuclei then diffused out of the target, ionized, and were swept away and sent to the heart of a spectrometer called "Lucrecia." There the fragile nuclei are directed up a slender hole in the world's largest crystal of pure sodium iodide. It is in that sanctum that gamma rays from the disintegration of the Sr-76 nuclei are observed. www.aip.org /pnu/2004/split/686-3.html   (322 words)

Basic Histology -- Looking at Nuclei   (Site not responding. Last check: 2007-11-07) The epidermis renews itself by division of cells at the dermal border, and shedding of cells from the surface. This epidermis is somewhat abnormal, since its nuclei are retained in the upper layers of the epidermis. In the middle of the epidermis, the cells are actively synthesizing keratin to protect the surface. www.pathguy.com /histo/013.htm   (222 words)

ORNL discovers superdeformed light nuclei   (Site not responding. Last check: 2007-11-07) In the 1960s, it was discovered experimentally that nuclei of very heavy atoms called actinides, such as plutonium-240, assume elongated shapes and have a good chance to break up, or fission spontaneously, into two fragments. The nuclei of interest are typically synthesized by bombarding a nickel-58 target with beams of silicon-28 or sulfur-32 ions (electrically charged atoms). The measured properties of these nuclei are in reasonable agreement with the predictions of theory, but some puzzles remain. www.ornl.gov /info/press_releases/archive/mr19960611-01.html   (609 words)

Nuclei put a new spin on quantum computing (January 2002) - News - PhysicsWeb Now Smet and colleagues have brought these devices a step closer with the discovery that the spins of nuclei in a gallium arsenide semiconductor can be controlled with a gate voltage. Moreover, the changes in the spins of the nuclei were reversible and reproducible, which suggests that they could be used to store information. According to the German team, this phenomenon is also a novel probe of the interactions between the spins of electrons and nuclei. physicsweb.org /article/news/6/1/8   (561 words)

The Deformed Proton - Deformed nuclei 06/98   (Site not responding. Last check: 2007-11-07) Atomic nuclei are composed of protons and neutrons. Many nuclei are spherical, but a large number also are found to be deformed spheroids-squeezed in two directions like a football or in one direction like a gibbous moon. The nuclei observed by Cary Davids and a multinational research team have an excess of protons, are already in their ground (lowest) states, and are viewed as having highly deformed football shapes with length 1.5 times that of their width. www.pnl.gov /er_news/06_98/file1.htm   (348 words)

DNA Replication in Quiescent Cell Nuclei: Regulation by the Nuclear Envelope and Chromatin Structure -- Lu et al. 10 ... Nuclei were isolated and stained for total DNA (DNA) and with Texas Red-streptavidin to detect biotin-dUTP incorporation into nascent DNA (Biotin). Intact nuclei were incubated in extract for 4 h, diluted, sedimented, and treated with 0.1 or 0.5% Triton X-100 before fixation or with 0.5% Triton X-100 after fixation. The chromatin-associated proteins from unincubated nuclei (XEN) and from incubated nuclei were isolated and analyzed as described in Figure 4. www.molbiolcell.org /cgi/content/full/10/12/4091   (8486 words)

How Things Work - Nuclear Weapons Because deuterium and tritium are both gases, and because tritium is unstable and gradually decays into the light isotope of helium, some hydrogen bombs form the tritium during the explosion by exposing lithium nuclei to neutrons from the fission trigger. Neutrons are uncharged subatomic particles that are found in the nuclei of all atoms except the normal hydrogen atom. Building large nuclei is a curiosity in modern science, not a sensible scheme for synthesizing elements. howthingswork.virginia.edu /nuclear_weapons.html   (2823 words)

Number and spatial distribution of nuclei in the muscle fibres of normal mice studied in vivo -- Bruusgaard et al. 551 ... Since nuclei are usually distributed close to the surface of the fibre, the statistical evaluation of the distribution was based on a projection of the nuclei onto an idealized surface. The EDL nuclei were also strictly aligned parallel to the long axis of the fibre, with an average deviation of only 4 deg between the long axis of the nuclei and that of the fibre (Fig. In the soleus the extrasynaptic nuclei were as round as the synaptic nuclei, although synaptic nuclei were quite varied in orientation (Fig. jp.physoc.org /cgi/content/full/551/2/467   (7768 words)

Cdc6 protein causes premature entry into S phase in a mammalian cell-free system   (Site not responding. Last check: 2007-11-07) After incubation for 3 h with biotin-16-dUTP, nuclei were washed, fixed in paraformaldehyde and stained with propidium iodide to reveal DNA (red) and with fluorescein−streptavidin (green) to detect biotin incorporation resulting from DNA synthesis. nuclei incubated in S phase cytosol alone was not influenced by permeabilization of the nuclear envelope with lysolecithin (b and d). Note that the histogram summarizes quantitative data for (a−e) and that impermeable and permeable nuclei are represented by dark-blue and light-blue columns respectively. www.nature.com /emboj/journal/v17/n24/fig_tab/7591410ft.html   (1016 words)

Accelerated beams of radioactive nuclei   (Site not responding. Last check: 2007-11-07) A chart of the nuclides with the fl squares, representing the stable nuclei, plotted as a function of the number of protons and neutrons in the nucleus. Interactions with the target nuclei can result in fission or fragmentation, with the nuclei which are produced leaving the target with velocities close to those of the projectiles. Beams of radioactive nuclei will allow us to narrow the range of guesses if not decide where the neutron-rich nuclei come to an end by precise measurements of nuclear masses and the separation energies for the last neutron. www.europhysicsnews.com /full/06/article2/article2.html   (2281 words)

Effects of altered tonicity by sodium chloride on L-tryptophan binding to hepatic nuclei -- Sidransky et al. 278 (6): ... H]tryptophan binding to rat hepatic nuclei assayed in vitro. Rat hepatic nuclei were prepared as described by Blobel and Potter (3). Nuclei from rat liver: isolation method that combines purity with high yield. ajpcell.physiology.org /cgi/content/full/278/6/C1237   (4683 words)

The Most Tightly Bound Nuclei   (Site not responding. Last check: 2007-11-07) The four most tightly bound nuclides are listed in the table below with a tabulation of the binding energy B divided by the mass number A. The curve adapted from Fewell shows those nuclides that are close to the peak. The curve drawn through the cluster of nuclei above is just to show the nature of the trend with mass number. A similar kind of trend is observed with even-odd nuclides at a lower range of binding energy, and then by odd-odd nuclei at the least-bound extreme. hyperphysics.phy-astr.gsu.edu /hbase/nucene/nucbin2.html   (209 words)

Structure of Exotic Nuclei - Forschungszentrum Rossendorf Exotic Nuclei are nuclei with an extraordinary ratio of protons and neutrons. The structure of nuclei close to the proton drip line is expected to present a sensitive probe for nuclear models. All nuclei were produced in fusion-evaporation reactions where the b-delayed protons were detected by a DE-E Silicon detector telescope and b-delayed g rays were detected with the Rossendorf Germanium Cluster Detector and the GSI Segmented Clover Detector. www.fz-rossendorf.de /pls/rois/Cms?pNid=313   (967 words)

Science News: Deformed nuclei spit out protons.(new type of p... @ HighBeam Research   (Site not responding. Last check: 2007-11-07) By determining the rate at which the unstable nuclei of two elements emit protons, researchers have for the first time obtained experimental evidence that these particular nuclei look more like flattened globes than true spheres. Many nuclei are unstable, however, because they contain too many protons for the number of neutrons present. Davids and his team aim to detect proton radioactivity in unstable isotopes of other elements that contain an odd number of protons, from which a single proton is most likely to escape. www.highbeam.com /library/doc0.asp?DOCID=1G1:20406294&refid=ip_encyclopedia_hf   (525 words)

Doubly Strange Nuclei Studies of these nuclei will help scientists explore the forces between nuclear particles, particularly within so-called strange matter, and may contribute to a better understanding of neutron stars, the super dense remains of burnt-out stars, which are thought to contain large quantities of strange quarks. To create the nuclei, the scientists aim the world's most intense proton beam - produced at one of Brookhaven's particle accelerators, the Alternating Gradient Synchrotron - at a tungsten target. The experiment to produce doubly strange nuclei and investigate the interaction between two lambda particles was conceived, designed, and built in Japan, and brought to Brookhaven Lab to take advantage of the world's most powerful kaon beam, produced at the Lab's Alternating Gradient Synchrotron (AGS). www.bnl.gov /bnlweb/pubaf/pr/2001/bnlpr082001.htm   (955 words)

PROBING EXCITED STATES IN NUCLEI   (Site not responding. Last check: 2007-11-07) As a result, the gamma rays emitted from these nuclei after they are produced in a heavy-ion fusion reaction are impossible to identify using only Gammasphere because they are completely obscured by the gamma rays from other isotopes produced with much larger cross-sections. This is accomplished by allowing the nuclei produced at the target position to pass through the FMA and implant in a pixilated silicon detector. For heavy nuclei, this is extremely difficult due to the fact that the production cross sections are very small and the gamma-ray spectrum is dominated by nuclei which fission. www.phy.anl.gov /dnp/current/gamma/gs@limits.html   (708 words)

Isolation of nuclei In addition it was possible to determine the buoyant density of the nuclei accurately, since the colloidal silica particles are coated with polyvinylpyrrolidone to which the nuclear membrane is impermeable. The biological material in the gradient, in this case nuclei, bands isopycnically, so that the sample particles reach a position where their densities and that of the surrounding Percoll medium are equal. The nuclei banded to one region of the gradient but the band was not homogeneous: the upper part was relatively disperse, the center was dense and homogeneous, and the lower part exhibited some clumps. www.fgsc.net /methods/talbot37.html   (714 words)

Superdeformation of Nuclei ORME theory is that one is dealing with high-spin, superdeformed nuclei, whose electrons form Cooper pairs, and thus the monoatomic elements become a beam of light, a superconducting medium. In strongly rotating, superdeformed nuclei, Shimizu and Broglia [4] have suggested that “superconductivity should disappear for particles in the quantal size effects (QSE’s) regime, when the energy difference between two discrete one-electron states is comparable to the energy gap of the superconducting state. electrons as, e.g., atomic nuclei should be strongly affected by quantal size effects.” Conversely, with fewer and fewer electrons, as one approaches the microcluster, and ultimately the monoatomic state, the superdeformed rotational bands contribute to the pairing correlations in nuclei. www.halexandria.org /dward164.htm   (1070 words)

The Two Nuclei of Giardia Each Have Complete Copies of the Genome and Are Partitioned Equationally at Cytokinesis -- Yu ... of nuclei, analogous to the equational partitioning of chromatids For most of the trophozoites, both nuclei were labeled, but the arrows demonstrate a trophozoite in which one nucleus appears partially degraded (A5) and shows no probe signal (B5). The arrows indicate the nuclei of a trophozoite in which the p4F11 probe demonstrated hybridization to only one of the two nuclei. ec.asm.org /cgi/content/full/1/2/191   (4750 words)

Super-heavy nuclei take shape in 'extreme' new theories Experiments performed at GSI in Germany, RIKEN in Japan, in Dubna, Russia, and elsewhere have bolstered theories that the lives of nuclei become longer as certain configurations of protons and neutrons are achieved. Computationally intense theoretical modeling indicates that a large difference in the shapes of a "parent" nucleus, which decays by emitting an alpha particle, and that of its "daughter" isotope will hinder the rate of decay to that daughter. In terms of existence for extremely heavy nuclei, a half-minute is an eternity. www.physorg.com /news3089.html   (1196 words)

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