549 research outputs found
Algorithmic decidability of Engel's property for automaton groups
We consider decidability problems associated with Engel's identity
( for a long enough commutator sequence) in groups
generated by an automaton. We give a partial algorithm that decides, given
, whether an Engel identity is satisfied. It succeeds, importantly, in
proving that Grigorchuk's -group is not Engel. We consider next the problem
of recognizing Engel elements, namely elements such that the map
attracts to . Although this problem seems intractable in
general, we prove that it is decidable for Grigorchuk's group: Engel elements
are precisely those of order at most . Our computations were implemented
using the package FR within the computer algebra system GAP
γ spectroscopy of 25 , 27 Ne and 26 , 27 Na
The γ spectroscopy of 25, 27 Ne and 26, 27 Na was studied from the reaction of 26 Ne with a deuterium target in inverse kinematics at 9.7 MeV/nucleon. The selectivity of the (d,p), (d,t), and (d,n) transfer reactions provides new spectroscopic information on low-lying states. The validity of the sd shell-model space for these nuclei isdiscussed
Direct mass measurements of 19B, 22C, 29F, 31Ne, 34Na and other light exotic nuclei
We report on direct time-of-flight based mass measurements of 16 light
neutron-rich nuclei. These include the first determination of the masses of the
Borromean drip-line nuclei B, C and F as well as that of
Na. In addition, the most precise determinations to date for N
and Ne are reported. Coupled with recent interaction cross-section
measurements, the present results support the occurrence of a two-neutron halo
in C, with a dominant configuration, and a
single-neutron halo in Ne with the valence neutron occupying
predominantly the 2 orbital. Despite a very low two-neutron separation
energy the development of a halo in B is hindered by the 1
character of the valence neutrons.Comment: 5 page
Investigation of the ground-state spin inversion in the neutron-rich 47,49Cl isotopes
A first γ -ray study of 47,49Cl spectroscopy was performed at the Radioactive Isotope Beam Factory with 50Ar projectiles at 217 MeV/nucleon, impinging on the liquid hydrogen target of the MINOS device. Prompt
deexcitation γ rays were measured with the NaI(Tl) array DALI2+. Through the one-proton knockout reaction 50Ar(p, 2p), a spin assignment could be determined for the low-lying states of 49Cl from the momentum
distribution obtained with the SAMURAI spectrometer. A spin-parity Jπ = 3/2+ is deduced for the ground
state of 49Cl, similar to the recently studied N = 32 isotope 51K. The evolution of the energy difference
E(1/2+
1 ) − E(3/2+
1 ) is compared to state-of-the-art theoretical predictions.Ministerio de Ciencia de España, Innovación y Universidades y fondos FEDER. FIS2017-88410-PFondo Nacional de Investigación, Desarrollo e Innovación de Hungría. Proyecto No. K128947.The Office of Nuclear Physics, U.S. Department of Energy. De-sc0018223The United Kingdom Science and Technology Facilities Council (STFC). ST/L005816/1Natural Sciences and Engineering Research Council of Canada (NSERC). SAPIN-2016-00033, SAPIN-2018- 00027 y RGPAS-2018-522453
Structure of unbound neutron-rich He studied using single-neutron transfer
The 8He(d,p) reaction was studied in inverse kinematics at 15.4A MeV using
the MUST2 Si-CsI array in order to shed light on the level structure of 9He.
The well known 16O(d,p)17O reaction, performed here in reverse kinematics, was
used as a test to validate the experimental methods. The 9He missing mass
spectrum was deduced from the kinetic energies and emission angles of the
recoiling protons. Several structures were observed above the neutron-emission
threshold and the angular distributions were used to deduce the multipolarity
of the transitions. This work confirms that the ground state of 9He is located
very close to the neutron threshold of 8He and supports the occurrence of
parity inversion in 9He.Comment: Exp\'erience GANIL/SPIRAL1/MUST
Investigation of the 6He cluster structures
The 4He+2n and t+t clustering of the 6He ground state were investigated by
means of the transfer reaction 6He(p,t)4He at 25 MeV/nucleon. The experiment
was performed in inverse kinematics at GANIL with the SPEG spectrometer coupled
to the MUST array. Experimental data for the transfer reaction were analyzed by
a DWBA calculation including the two neutrons and the triton transfer. The
couplings to the 6He --> 4He + 2n breakup channels were taken into account with
a polarization potential deduced from a coupled-discretized-continuum channels
analysis of the 6He+1H elastic scattering measured at the same time. The
influence on the calculations of the 4He+t exit potential and of the triton
sequential transfer is discussed. The final calculation gives a spectroscopic
factor close to one for the 4He+2n configuration as expected. The spectroscopic
factor obtained for the t+t configuration is much smaller than the theoretical
predictions.Comment: 10 pages, 11 figures, accepted in PR
Elements Discrimination in the Study of Super-Heavy Elements using an Ionization Chamber
Dedicated ionization chamber was built and installed to measure the energy
loss of very heavy nuclei at 2.7 MeV/u produced in fusion reactions in inverse
kinematics (beam of 208Pb). After going through the ionization chamber,
products of reactions on 12C, 18O targets are implanted in a Si detector. Their
identification through their alpha decay chain is ambiguous when their
half-life is short. After calibration with Pb and Th nuclei, the ionization
chamber signal allowed us to resolve these ambiguities. In the search for rare
super-heavy nuclei produced in fusion reactions in inverse or symmetric
kinematics, such a chamber will provide direct information on the nuclear
charge of each implanted nucleus.Comment: submitted to NIMA, 10 pages+4 figures, Latex, uses elsart.cls and
grahpic
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