166 research outputs found
On the feasibility of a nuclear exciton laser
Nuclear excitons known from M\"ossbauer spectroscopy describe coherent
excitations of a large number of nuclei -- analogous to Dicke states (or Dicke
super-radiance) in quantum optics. In this paper, we study the possibility of
constructing a laser based on these coherent excitations. In contrast to the
free electron laser (in its usual design), such a device would be based on
stimulated emission and thus might offer certain advantages, e.g., regarding
energy-momentum accuracy. Unfortunately, inserting realistic parameters, the
window of operability is probably not open (yet) to present-day technology --
but our design should be feasible in the UV regime, for example.Comment: 7 pages RevTeX, 4 figure
Neutron Halo Isomers in Stable Nuclei and their Possible Application for the Production of Low Energy, Pulsed, Polarized Neutron Beams of High Intensity and High Brilliance
We propose to search for neutron halo isomers populated via -capture
in stable nuclei with mass numbers of about A=140-180 or A=40-60, where the
or neutron shell model state reaches zero binding energy.
These halo nuclei can be produced for the first time with new -beams of
high intensity and small band width ( 0.1%) achievable via Compton
back-scattering off brilliant electron beams thus offering a promising
perspective to selectively populate these isomers with small separation
energies of 1 eV to a few keV. Similar to single-neutron halo states for very
light, extremely neutron-rich, radioactive nuclei
\cite{hansen95,tanihata96,aumann00}, the low neutron separation energy and
short-range nuclear force allows the neutron to tunnel far out into free space
much beyond the nuclear core radius. This results in prolonged half lives of
the isomers for the -decay back to the ground state in the 100
ps-s range. Similar to the treatment of photodisintegration of the
deuteron, the neutron release from the neutron halo isomer via a second,
low-energy, intense photon beam has a known much larger cross section with a
typical energy threshold behavior. In the second step, the neutrons can be
released as a low-energy, pulsed, polarized neutron beam of high intensity and
high brilliance, possibly being much superior to presently existing beams from
reactors or spallation neutron sources.Comment: accepted for publication in Applied Physics
Production of Medical Radioisotopes with High Specific Activity in Photonuclear Reactions with Beams of High Intensity and Large Brilliance
We study the production of radioisotopes for nuclear medicine in
photonuclear reactions or ()
photoexcitation reactions with high flux [()/s], small
diameter m and small band width () beams produced by Compton back-scattering of laser
light from relativistic brilliant electron beams. We compare them to (ion,np) reactions with (ion=p,d,) from particle accelerators like
cyclotrons and (n,) or (n,f) reactions from nuclear reactors. For
photonuclear reactions with a narrow beam the energy deposition in the
target can be managed by using a stack of thin target foils or wires, hence
avoiding direct stopping of the Compton and pair electrons (positrons).
isomer production via specially selected cascades
allows to produce high specific activity in multiple excitations, where no
back-pumping of the isomer to the ground state occurs. We discuss in detail
many specific radioisotopes for diagnostics and therapy applications.
Photonuclear reactions with beams allow to produce certain
radioisotopes, e.g. Sc, Ti, Cu, Pd, Sn,
Er, Pt or Ac, with higher specific activity and/or
more economically than with classical methods. This will open the way for
completely new clinical applications of radioisotopes. For example Pt
could be used to verify the patient's response to chemotherapy with platinum
compounds before a complete treatment is performed. Also innovative isotopes
like Sc, Cu and Ac could be produced for the first time
in sufficient quantities for large-scale application in targeted radionuclide
therapy.Comment: submitted to Appl. Phys.
Characterization and Tuning of Ultra High Gradient Permanent Magnet Quadrupoles
The application of quadrupole-devices with high field gradients and small
apertures requires precise control over higher order multipole field
components. We present a new scheme for performance control and tuning, which
allows the illumination of most of the quadrupole-device aperture because of
the reduction of higher order field components. Consequently, the size of the
aperture can be minimized to match the beam size achieving field gradients of
up to 500 T/m at good imaging quality. The characterization method based on a
Hall probe measurement and a Fourier analysis was confirmed using the high
quality electron beam at the Mainz Microtron MAMI
Quadrupole deformations of neutron-drip-line nuclei studied within the Skyrme Hartree-Fock-Bogolyubov approach
We introduce a local-scaling point transformation to allow for modifying the
asymptotic properties of the deformed three-dimensional Cartesian harmonic
oscillator wave functions. The resulting single-particle bases are very well
suited for solving the Hartree-Fock-Bogoliubov equations for deformed drip-line
nuclei. We then present results of self-consistent calculations performed for
the Mg isotopes and for light nuclei located near the two-neutron drip line.
The results suggest that for all even-even elements with =10--18 the most
weakly-bound nucleus has an oblate ground-state shape.Comment: 20 pages, 7 figure
Status of the REX-ISOLDE project
The radioactive beam experiment REX-ISOLDE, a pilot experiment testing a new concept of post acceleration of radioactive ions at ISOLDE/CERN is in progress. Singly charged radioactive ions delivered by the online mass separator ISOLDE are accumulated in a Penning trap (REX trap), charge bred in an electron beam ion source (EBIS), separated from the residual gas in a mass separator and then accelerated in a linac with output energies between 0.8 and 2.2 MeV /u. The REX trap is in operation, a first test beam was already injected. The design phase of the EBIS is finished and the construction has been started. The superconducting magnet is delivered. The linac consists of a radiofrequency quadrupole (RFQ) accelerator, an interdigital IH-structure and 3 seven gap resonators to vary the final energy. (12 refs)
Invariant-mass and [gamma]-ray spectroscopy using secondary, radioactive ion beams
Coulomb excitation of secondary beams (5 < Z < 20) at energies
around 250 .1 MeV was explored at GSI. For low-lying states, 7-ray spectroscopy
was utilized, while high-lying excitations were investigated by
means of invariant-mass spectroscopy
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