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71.
72.
H. Klewe-Nebenius D. Habs K. Wisshak H. Faust G. Nowicki S. Göring H. Rebel G. Schatz M. Schwall 《Nuclear Physics A》1975,240(1):137-170
The level scheme of 137Pr was investigated by means of the γ-rays following the β-decay of 137Nd as well as by prompt γ-rays accompanying (α, xn) reactions. We measured γ-ray single spectra, γγ coincidences (both in-beam and off-beam), angular distributions of prompt γ-rays and conversion electrons. About 100 γ-rays were assigned to the 38 min decay of 137Nd most of which fit into a scheme of 26 deduced levels. From in-beam experiments we tentatively assigned an ? level which is the basis of a strong cascade of stretched E2 transitions with a probable level sequence of ? ?? ?? ??. The interpretation of this cascade in the framework of a strong coupling model indicates a prolate deformation of 137Pr. Another indication for such a deformation was obtained from the very low energy (75 keV) of the first + level which could not be interpreted in an intermediate coupling model, but is suggested by a Nilsson scheme. 相似文献
73.
F. Grüner S. Becker U. Schramm T. Eichner M. Fuchs R. Weingartner D. Habs J. Meyer-ter-Vehn M. Geissler M. Ferrario L. Serafini B. van der Geer H. Backe W. Lauth S. Reiche 《Applied physics. B, Lasers and optics》2007,86(3):431-435
A recent breakthrough in laser-plasma accelerators, based upon ultrashort high-intensity lasers, demonstrated the generation
of quasi-monoenergetic GeV-electrons. With future Petawatt lasers ultra-high beam currents of ∼100 kA in ∼10 fs can be expected,
allowing for drastic reduction in the undulator length of free-electron-lasers (FELs). We present a discussion of the key
aspects of a table-top FEL design, including energy loss and chirps induced by space-charge and wakefields. These effects
become important for an optimized table-top FEL operation. A first proof-of-principle VUV case is considered as well as a
table-top X-ray-FEL which may also open a brilliant light source for new methods in clinical diagnostics.
PACS 41.60.Cr; 52.38.Kd 相似文献
74.
Th. Kröll T. Behrens R. Krücken V. Bildstein R. Gernhäuser P. Maierbeck I. Stefanescu O. Ivanov J. Van de Walle N. Warr P. A. Butler J. Cederkäll P. Delahaye L. M. Fraile G. Georgiev U. Köster T. Sieber D. Voulot F. Wenander P. E. Kent A. Ekström K.-H. Speidel J. Leske S. Schielke D. Habs R. Lutter P. Thirolf H. Scheit T. Davinson 《The European physical journal. Special topics》2007,150(1):127-129
We report on “safe” Coulomb excitation of neutron-rich 138,140,142Xe
nuclei.
The radioactive nuclei have been produced by ISOLDE at CERN and
post-accelerated
by the REX-ISOLDE facility. The γ-rays emitted by the decay of excited
states have been detected by the MINIBALL array. Recent results are
presented. 相似文献
75.
D. Habs B. M. Hegelich J. Schreiber P. G. Thirolf 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(2):253-264
The use is suggested of a laser-accelerated dense electron sheet with
an energy of (E=[(g)\tilde] mc2E=\tilde{\gamma} mc^2) as a relativistic mirror to reflect coherently a second
laser with photon energy ħω, generating by the Doppler boost
high-energy γ photons with $
\hbar \omega ' = 4\tilde \gamma ^2 \hbar \omega
$
\hbar \omega ' = 4\tilde \gamma ^2 \hbar \omega
and
short duration [A. Einstein, Annalen der Physik 17, 891 (1905); D. Habs et al., Appl. Phys. B 93, 349 (2008)]. Two of these counter-propagating
γ beams are focused by the parabolically shaped electron sheets into the
interaction region with small, close to diffraction-limited, spot size.
Comparing the new nγ-mγ collider with former proposed
γγ collider schemes we achieve the conversion of many
photon-pairs in a small space-time volume to matter-antimatter particles,
while in the other discussed setups only two isolated, much more
high-energetic photons will be converted, reaching in the
new approach much higher energy densities and temperatures.
With a γ-field strength somewhat below the Schwinger limit we can
reach this complete conversion of the γ bunch energy into
e+e- or quark-antiquark q[`(q)]q\bar{q}-plasmas.
For a Bose-Einstein condensate (BEC) [A. Einstein, Physikalisch-mathematische Klasse (Berlin) 22, 261 (1924); A. Einstein, Physikalisch-mathematische Klasse (Berlin) 22, 3 (1925); A. Griffin, D.W. Snoke, S. Stringari, Bose-Einstein Condensation (Cambridge University Press, 1995)] final state or for the Cooper pair ground state at higher densities [A.J. Leggett, Quantum Liquids, Oxford Graduate Texts (Oxford University Press, 2006)] the strong induced transition
into this coherent state is of special interest for single-cycle γ
pulses. Due to annihilation these cold coherent states are very
short-lived. For γ beams with photon energies
of 1–10 keV the rather cold e+e--plasma or
e+e--BEC expands to a cold dense aggregate of positronium (Ps)
atoms, where the production of Ps molecules is discussed.
For photon energies of 1–10 MeV we discuss the production of
a cold induced π0-BEC followed by the formation of molecules.
For the direct population of higher q[`(q)]q\bar{q} densities we can study
condensates of color-neutral mesons with enhanced population.
For a γγ collider with several-cycle laser pulses
the following cycles heat up the fermion-antifermion
f[`(f)]f\bar{f} system to a certain temperature.
Thus we can reach high energy densities and temperatures of an e+e-γ
plasma, where the production of hadrons in general or the quark-gluon
phase transition can be observed. Within the long-term goal of very
high photon energies of about 1 GeV in the nγ-mγ-collider,
even the electro-weak phase transition or SUSY phase transition
could be reached. 相似文献
76.
S. Ter-Avetisyan M. Schnürer T. Sokollik P. V. Nickles W. Sandner U. Stein D. Habs T. Nakamura K. Mima 《The European physical journal. Special topics》2009,169(1):117-121
The complex dynamical behavior of the electron sheath in laser driven ion acceleration leads to variations in ion beam pointing
and ion energy modulation. These processes are derived from high resolution particle spectroscopy and 2D-PIC simulations.
The phenomena arise from ion source movement if laser irradiation occurs at oblique incidence. Different laser absorption
processes act in dependence on laser parameter which determines the ion acceleration. 相似文献
77.
C. Hugenschmidt K. Schreckenbach D. Habs P. G. Thirolf 《Applied physics. B, Lasers and optics》2012,106(1):241-249
Presently, large efforts are conducted toward the development of highly brilliant γ beams via Compton back scattering of photons from a high-brilliance electron beam, either on the basis of a normal-conducting
electron linac or a (super-conducting) Energy Recovery Linac (ERL). Particularly, ERLs provide an extremely brilliant electron
beam, thus enabling the generation of highest-quality γ beams. A 2.5 MeV γ beam with an envisaged intensity of 1015 photons s−1, as ultimately envisaged for an ERL-based γ-beam facility, narrow band width (10−3), and extremely low emittance (10−4 mm2 mrad2) offers the possibility to produce a high-intensity bright polarized positron beam. Pair production in a face-on irradiated
W converter foil (200 μm thick, 10 mm long) would lead to the emission of 2×1013 (fast) positrons per second, which is four orders of magnitude higher compared to strong radioactive 22Na sources conventionally used in the laboratory. Using a stack of converter foils and subsequent positron moderation, a high-intensity
low-energy beam of moderated positrons can be produced. Two different source setups are presented: a high-brightness positron
beam with a diameter as low as 0.2 mm, and a high-intensity beam of 3×1011 moderated positrons per second. Hence, profiting from an improved moderation efficiency, the envisaged positron intensity
would exceed that of present high-intensity positron sources by a factor of 100. 相似文献
78.
For x rays the real part of the refractive index, dominated by Rayleigh scattering, is negative and converges to zero for higher energies. For γ rays a positive component, related to Delbrück scattering, increases with energy and becomes dominating. The deflection of a monochromatic γ beam due to refraction was measured by placing a Si wedge into a flat double crystal spectrometer. Data were obtained in an energy range from 0.18?MeV to 2?MeV. The data are compared to theory, taking into account elastic and inelastic Delbrück scattering as well as recent results on the energy dependence of the pair creation cross section. Probably a new field of γ optics with many new applications opens up. 相似文献
79.
F. Nebel J. Szerypo E. Zech T. Faestermann R. Groetzschel M. Groß D. Habs R. Krücken P. Maier-Komor P. G. Thirolf A. Yakushev 《The European Physical Journal A - Hadrons and Nuclei》2006,29(3):369-381
A detailed account on the distribution of radioactive nuclei in the vacuum system of the planned Munich Accelerator for Fission
Fragments (MAFF) located at the FRM-II research reactor is presented. Tools used for the simulation of spacial and temporal
distribution of radionuclides are explained. The latter allows for a detailed activity budget as well as estimates for the
mass-separated ion yields at MAFF. Additionally, a concept to reduce the activity release from the MAFF slit system due to
surface sputtering is presented. It is shown, that the use of low-density carbon foam, as a surface coating, reduces sputtering
by orders of magnitude. 相似文献
80.
Van de Walle J Aksouh F Ames F Behrens T Bildstein V Blazhev A Cederkäll J Clément E Cocolios TE Davinson T Delahaye P Eberth J Ekström A Fedorov DV Fedosseev VN Fraile LM Franchoo S Gernhauser R Georgiev G Habs D Heyde K Huber G Huyse M Ibrahim F Ivanov O Iwanicki J Jolie J Kester O Köster U Kröll T Krücken R Lauer M Lisetskiy AF Lutter R Marsh BA Mayet P Niedermaier O Nilsson T Pantea M Perru O Raabe R Reiter P Sawicka M Scheit H Schrieder G Schwalm D Seliverstov MD Sieber T Sletten G 《Physical review letters》2007,99(14):142501
Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)+ state in 78Zn could be firmly established and for the first time the 2+ --> 0(1)+ transition in 80Zn was observed at 1492(1) keV. B(E2,2(1)+ --> 0(1)+) values were extracted for (74,76,78,80)Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus 78Ni. 相似文献