Nuclear reaction cross-section structure

The Importance of Level Structure In Nuclear Reaction Cross-Section Calculations... 

The theoretical forecasts of the neutrino fluxes used to compare with experimental observations are those from the so-called standard solar model (SSM). This model relies on the values of the solar mass, radius, luminosity, and age (4.7 billion years) and on the best-considered values of the nuclear reaction cross sections. In addition, there are some special assumptions. It is presumed that the sun is not rotating, or differentially rotating, rapidly enough in its interior to affect its internal structure or dynamics. Processes that could mix the solar interior, such as diffusion or periodic hydrodynamic oscillation, are not taken into... 

Another limit of nuclear stability is the extreme of the neutron to proton ratio, N/Z. For certain very neutron-rich nuclei, such as Li, an unusual halo structure has been observed. In halo nuclei, a core of nucleons is surrounded by a misty cloud, a halo of valence nucleons that are weakly bound and extend out to great distances, analogous to electrons surrounding the nucleus in an atom. Halo nuclei are fragile objects, are relatively large, and interact easily with other nuclei (have enhanced reaction cross sections). The halo nucleus Li, which has a Ti core surrounded by a two-neutron halo is shown in Figure 1. Li is as large as ° Pb. Li and other... 

CP-1 was assembled in an approximately spherical shape with the purest graphite in the center. About 6 tons of luanium metal fuel was used, in addition to approximately 40.5 tons of uranium oxide fuel. The lowest point of the reactor rested on the floor and the periphery was supported on a wooden structure. The whole pile was surrounded by a tent of mbberized balloon fabric so that neutron absorbing air could be evacuated. About 75 layers of 10.48-cm (4.125-in.) graphite bricks would have been required to complete the 790-cm diameter sphere. However, criticality was achieved at layer 56 without the need to evacuate the air, and assembly was discontinued at layer 57. The core then had an ellipsoidal cross section, with a polar radius of 209 cm and an equatorial radius of309 cm [20]. CP-1 was operated at low power (0.5 W) for several days. Fortuitously, it was found that the nuclear chain reaction could be controlled with cadmium strips which were inserted into the reactor to absorb neutrons and hence reduce the value of k to considerably less than 1. The pile was then disassembled and rebuilt at what is now the site of Argonne National Laboratory, U.S.A, with a concrete biological shield. Designated CP-2, the pile eventually reached a power level of 100 kW [22]. 

Fig. 3.4. A two-dimensional cross-section of the structure diagram for an ABC system. The full lines, denoting the catastrophe set, partition nuclear configuration space into its structural regions. The structure associated with each region is indicated by a representative molecular graph. The two broken lines indicate two possible reaction mechanisms for changing the structure A-B-C into the structure B-C-A.

National Nuclear Data Center — Maintains databases on nuclear structure and reactions, including neutron cross sections. The NNDC is the US. node in an international network of nuclear data centers. Address Brookhaven National Laboratory, Upton, NY 11973-5000 [www.nndc.bnl.gov]. 

Palladium and Palladium Alloys Applications. Palladium and palladium alloys are important constituents of catalysts of chemical reactions and automobile exhaust gas cleaning, of electrical contacts, capacitors, permanent magnetic alloys, thermocouples, and for the production of high purity hydrogen. The low thermal neutron cross section permits their use in solders and brazes of nuclear structural parts. Classical applications are jewelry and dentistry alloys. 

The first step in the production of nuclear data for applied purposes is measurement. Nuclear theory cannot provide accurate nuclear data. Nevertheless theory plays an important part in the interpretation of measurements, and is used for interpolation and extrapolation of measured data. Theory also provides much of the data for reactions of lesser importance, such as secondary energy and angular distributions of inelastically scattered neutrons, and also capture cross-sections for materials which are difficult to measure, such as radioactive fission products and minor actinide isotopes. If the resonance structure of a cross-section needs to be known, when... 

Darmstadtium (Z = 110) was first synthesized in 1994 at GSI with the SHIP apparatus, used to isolate Ds (ri/2 = 180 ps), produced in the Pb( Ni,n) reaction with a cross section of 2.6 pb [267]. Later, the heavier IV = 161 isotope Ds (ri/2 =1.1 ms) was produced using the Pb( Ni,n) reaction [195]. Here, an increase in the neutron number of the projectile enhanced the production cross section by a factor of 5 to 15 pb. This work has been confirmed [270, 279, 280] as has the existence of a second a-decaying state with Ty2 — 70 ms, which is probably an isomer [67, 270]. The intermediate even-even isotope Ds (Ti/2 = 100 ps) was produced in the reaction Pb( Ni,n) reaction with a cross section of 13 pb [281]. This nuclide may have a high-spin two-quasiparticle K isomer with Ty2= 6 ms [281, 282], which has interesting implications for structure effects on nuclear stability [98,283]. Production of a single atom of Ds (Ty2 = 3 ps) via the Bi( Co,n) reaction was reported tentatively in 1995 [284] the unusual decay sequence proposed for the isotope needs further experimental elucidation. The a decay of Cn results in Ds (Ty2 =170 ps) [190, 263, 271]. All cold-fusion darmstadtium isotopes have very short half-Uves, though the isomeric state in Ds has a hatf-Ufe approaching 0.1 s [270]. 

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