51 research outputs found
Reaction rate sensitivity of 44Ti production in massive stars and implications of a thick target yield measurement of 40Ca(alpha,gamma)44Ti
We evaluate two dominant nuclear reaction rates and their uncertainties that
affect 44Ti production in explosive nucleosynthesis. Experimentally we develop
thick-target yields for the 40Ca(alpha,gamma)44Ti reaction at E(alpha) = 4.13,
4.54, and 5.36 MeV using gamma-ray spectroscopy. At the highest beam energy, we
also performed an activation measurement that agrees with the thick target
result. From the measured yields a stellar reaction rate was developed that is
smaller than current statistical-model calculations and recent experimental
results, which would suggest lower 44Ti production in scenarios for the
alpha-rich freeze out. Special attention has been paid to assessing realistic
uncertainties of stellar rates produced from a combination of experimental and
theoretical cross sections, which we use to develop a re-evaluation of the
44Ti(alpha,p)47V reaction rate. Using these we carry out a sensitivity survey
of 44Ti synthesis in eight expansions representing peak temperature and density
conditions drawn from a suite of recent supernova explosion models. Our results
suggest that the current uncertainty in these two reaction rates could lead to
as large an uncertainty in 44Ti synthesis as that produced by different
treatments of stellar physics.Comment: Comments: 45 pages, 19 postscript figures Minor corrections from
Referee and Proof Editors Figs 9 & 10 now in colo
Identification of the New Isotope \u3csup\u3e244\u3c/sup\u3eMd
In an experiment performed at Lawrence Berkeley National Laboratory\u27s 88-inch cyclotron, the isotope Md244 was produced in the Bi209(Ar40,5n) reaction. Decay properties of Md244 were measured at the focal plane of the Berkeley Gas-filled Separator, and the mass number assignment of A=244 was confirmed with the apparatus for the identification of nuclide A. The isotope Md244 is reported to have one, possibly two, α-decaying states with α energies of 8.66(2) and 8.31(2) MeV and half-lives of 0.4-0.1+0.4 and ∼6 s, respectively. Additionally, first evidence of the α decay of Bk236 was observed and is reported
Report on 241,242Am(n,x) surrogate cross section measurement
The main goal of this measurement is to determine the {sup 242}Am(n,f) and {sup 241}Am(n,f) cross sections via the surrogate {sup 243}Am. Gamma-ray data was also collected for the purpose of measuring the (n,2n) cross-sections. The experiment was conducted using the STARS/LIBERACE experimental facility located at the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory the first week of February 2011. A description of the experiment and status of the data analysis follow
Identification and shell model calculation of high spin states in 137,138Cs nuclei
High spin states of have been studied by measuring \ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma} coincidences from the spontaneous fission of with the LBNL Gammasphere detector array. The high spin level scheme of the neutron-rich Cs () isotope, , built on the {6}^{\ensuremath{-}} isomeric state, has been established for the first time up to a 4626 keV level, assigned (). The level scheme of has been expanded up to a 5495 keV level, assigned (31/{2}^{\ensuremath{-}}). Spins, parities, and configurations are assigned based on the agreement between experimental level energies and shell model calculations and level systematics. Similarities are observed in the isotones, and , up to as well as in the isotones, and , up to {12}^{\ensuremath{-}}. The shell model calculations indicate the important role played by interactions between the excitation of the valence protons outside the major shell and the valence neutron outside the major shell
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Synthesis of the isotopes of elements 118 and 116 in the 249Cf and 245Cm+48Ca fusion reactions
The decay properties of {sup 290}116 and {sup 291}116, and the dependence of their production cross sections on the excitation energies of the compound nucleus, {sup 293}116, have been measured in the {sup 245}Cm({sup 48}Ca,xn){sup 293-x}116 reaction. These isotopes of element 116 are the decay daughters of element 118 isotopes, which are produced via the {sup 249}Cf+{sup 48}Ca reaction. They performed the element 118 experiment at two projectile energies, corresponding to {sup 297}118 compound nucleus excitation energies of E* = 29.2 {+-} 2.5 and 34.4 {+-} 2.3 MeV. During an irradiation with a total beam dose of 4.1 x 10{sup 19} {sup 48}Ca projectiles, three similar decay chains consisting of two or three consecutive {alpha} decays and terminated by a spontaneous fission (SF) with high total kinetic energy of about 230 MeV were observed. The three decay chains originated from the even-even isotope {sup 294}118 (E{sub {alpha}} = 11.65 {+-} 0.06 MeV, T{sub {alpha}} = 0.89{sub -0.31}{sup +1.07} ms) produced in the 3n-evaporation channel of the {sup 249}Cf+{sup 48}Ca reaction with a maximum cross section of 0.5{sub -0.3}{sup +1.6} pb
Electromagnetic signals related to incidence of a teleseismic body wave into a subsurface piezoelectric body
Observation of rotational bands in the neutron-rich 107Ru nucleus
Levels in the neutron-rich, odd-mass 107Ru nucleus have been reinvestigated with Gammasphere by measuring high-fold, prompt coincidence events following spontaneous fission of 252Cf. The ground state band has been extended up to 27/2ℏ. The structure associated with the h11/2 excitation has been confirmed and extended to higher spin. The h11/2 band head has been established to lie at 301.8 keV. These results clear up differences between our earlier work and results from another experiment published recently. A new collective band based on a 9/2- level has been identified for the first time. Some distinct features of the level scheme are discussed
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Thick target measurement of the 40Ca(alpha,gamma)44Ti reaction rate
The thick-target yield for the {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction has been measured for E{sub beam} = 4.13, 4.54, and 5.36 MeV using both an activation measurement and online {gamma}-ray spectroscopy. The results of the two measurements agree. From the measured yield a reaction rate is deduced that is smaller than statistical model calculations. This implies a smaller {sup 44}Ti production in supernova compared to recently measured {sup 40}Ca({alpha},{gamma}){sup 44}Ti reaction rates
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