482 research outputs found
Cross Section Limits for the Pb(Kr,n)118 Reaction
In April-May, 2001, the previously reported experiment to synthesize element
118 using the Pb(Kr,n)118 reaction was repeated. No
events corresponding to the synthesis of element 118 were observed with a total
beam dose of 2.6 x 10 ions. The simple upper limit cross sections (1
event) were 0.9 and 0.6 pb for evaporation residue magnetic rigidities of 2.00
and 2.12 , respectively. A more detailed cross section calculation,
accounting for an assumed narrow excitation function, the energy loss of the
beam in traversing the target and the uncertainty in the magnetic rigidity of
the Z=118 recoils is also presented. Re-analysis of the primary data files from
the 1999 experiment showed the reported element 118 events are not in the
original data. The current results put constraints on the production cross
section for synthesis of very heavy nuclei in cold fusion reactions.Comment: 7 pages, 2 figures. Submitted to EPJ
On Semiclassical Limits of String States
We explore the relation between classical and quantum states in both open and
closed (super)strings discussing the relevance of coherent states as a
semiclassical approximation. For the closed string sector a gauge-fixing of the
residual world-sheet rigid translation symmetry of the light-cone gauge is
needed for the construction to be possible. The circular target-space loop
example is worked out explicitly.Comment: 12 page
Search for the Production of Element 112 in the 48Ca + 238U Reaction
We have searched for the production of element 112 in the reaction of 231 MeV
48Ca with 238U. We have not observed any events with a "one event" upper limit
cross section of 1.6 pb for EVR-fission events and 1.8 pb for EVR-alpha events.Comment: 6 pages, 3 figures, submitted to Phys. Rev.
The STACEE-32 Ground Based Gamma-ray Detector
We describe the design and performance of the Solar Tower Atmospheric
Cherenkov Effect Experiment detector in its initial configuration (STACEE-32).
STACEE is a new ground-based gamma ray detector using the atmospheric Cherenkov
technique. In STACEE, the heliostats of a solar energy research array are used
to collect and focus the Cherenkov photons produced in gamma-ray induced air
showers. The large Cherenkov photon collection area of STACEE results in a
gamma-ray energy threshold below that of previous detectors.Comment: 45 pages, 25 figures, Accepted for publication in Nuclear Instruments
and Methods
Nuclear Half-Lives for Alpha Radioactivity of Elements with 100 Z 130
Theoretical estimates for the half lives of about 1700 isotopes of heavy
elements with Z from 100 to 130 are tabulated using theoretical Q-values. The
quantum mechanical tunneling probabilities are calculated within a WKB
framework using microscopic nuclear potentials. The microscopic nucleus-nucleus
potentials are obtained by folding the densities of interacting nuclei with a
density dependent M3Y (DDM3Y) effective nucleon-nucleon interaction. The
alpha-decay half lives calculated in this formalism using the experimental
Q-values were found to be in good agreement over a wide range of experimental
data spanning about twenty orders of magnitude. The theoretical Q-values used
for the present calculations are extracted from three different mass estimates
viz. Myers-Swiatecki [MS], Muntian-Hofmann-Patyk-Sobiczewski [M] and
Koura-Tachibana-Uno-Yamada [KUTY].Comment: 57 pages, 2 tables, 1 figur
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