arXiv subjects

M. Jentschel

Publications and source records attributed to M. Jentschel.

26 records · Page 2Linked to original sources

arXiv2012

Seeded quantum FEL at 478 keV

We present for the first time the concept of a seeded γ quantum Free-Electron-Laser (QFEL) at 478 keV, which has very different properties compared to a classical. The basic concept is to produce a highly brilliant γ beam via SASE. To produce highly intense and coherent γ beam, we intend to use a seeded FEL scheme. Important for the production of such a γ beam are novel refractive γ -lenses for focusing and an efficient monochromator, allowing to generate a very intense and coherent seed beam. The energy of the γ beam is 478 keV, corresponding to a wavelength in the sub-Ångstrøm regime (1/38 Å). To realize a coherent γ beam at 478 keV, it is necessary to use a quantum FEL design. At such high radiation energies a classical description of the γ-FEL becomes wrong.

physics.acc-ph↗

arXiv2012

Nuclear Photonics

With new gamma-beam facilities like MEGa-ray at LLNL (USA) or ELI-NP at Bucharest with 10^13 g/s and a bandwidth of Delta E_g/E_g ~10^-3, a new era of g-beams with energies <=20 MeV comes into operation, compared to the present world-leading HIGS facility (Duke Univ., USA) with 10^8 g/s and Delta E_g/E_g~0.03. Even a seeded quantum FEL for g-beams may become possible, with much higher brilliance and spectral flux. At the same time new exciting possibilities open up for focused g-beams. We describe a new experiment at the g-beam of the ILL reactor (Grenoble), where we observed for the first time that the index of refraction for g-beams is determined by virtual pair creation. Using a combination of refractive and reflective optics, efficient monochromators for g-beams are being developed. Thus we have to optimize the system of the g-beam facility, the g-beam optics and g-detectors. We can trade g-intensity for band width, going down to Delta E_g/E_g ~ 10^-6 and address individual nuclear levels. 'Nuclear photonics' stresses the importance of nuclear applications. We can address with g-beams individual nuclear isotopes and not just elements like with X-ray beams. Compared to X rays, g-beams can penetrate much deeper into big samples like radioactive waste barrels, motors or batteries. We can perform tomography and microscopy studies by focusing down to micron resolution using Nucl. Reson. Fluorescence for detection with eV resolution and high spatial resolution. We discuss the dominating M1 and E1 excitations like scissors mode, two-phonon quadrupole octupole excitations, pygmy dipole excitations or giant dipole excitations under the new facet of applications. We find many new applications in biomedicine, green energy, radioactive waste management or homeland security. Also more brilliant secondary beams of neutrons and positrons can be produced.

physics.acc-ph↗

arXiv2012

Nuclear photonics at ultra-high counting rates and higher multipole excitations

Next-generation gamma beams beams from laser Compton-backscattering facilities like ELI-NP (Bucharest)] or MEGa-Ray (Livermore) will drastically exceed the photon flux presently available at existing facilities, reaching or even exceeding 10^13 gamma/sec. The beam structure as presently foreseen for MEGa-Ray and ELI-NP builds upon a structure of macro-pulses (~120 Hz) for the electron beam, accelerated with X-band technology at 11.5 GHz, resulting in a micro structure of 87 ps distance between the electron pulses acting as mirrors for a counterpropagating intense laser. In total each 8.3 ms a gamma pulse series with a duration of about 100 ns will impinge on the target, resulting in an instantaneous photon flux of about 10^18 gamma/s, thus introducing major challenges in view of pile-up. Novel gamma optics will be applied to monochromatize the gamma beam to ultimately Delta E/E~10^-6. Thus level-selective spectroscopy of higher multipole excitations will become accessible with good contrast for the first time. Fast responding gamma detectors, e.g. based on advanced scintillator technology (e.g. LaBr3(Ce)) allow for measurements with count rates as high as 10^6-10^7 gamma/s without significant drop of performance. Data handling adapted to the beam conditions could be performed by fast digitizing electronics, able to sample data traces during the micro-pulse duration, while the subsequent macro-pulse gap of ca. 8 ms leaves ample time for data readout. A ball of LaBr3 detectors with digital readout appears to best suited for this novel type of nuclear photonics at ultra-high counting rates.

physics.ins-det↗

arXiv2010

Measurement of the neutron electric dipole moment via spin rotation in a non-centrosymmetric crystal

We have measured the neutron electric dipole moment using spin rotation in a non-centrosymmetric crystal. Our result is d_n = (2.5 +- 6.5(stat) +- 5.5(syst)) 10^{-24} e cm. The dominating contribution to the systematic uncertainty is statistical in nature and will reduce with improved statistics. The statistical sensitivity can be increased to 2 10^{-26} e cm in 100 days data taking with an improved setup. We state technical requirements for a systematic uncertainty at the same level.

hep-ex↗

arXiv2009

Soft gamma-ray optics: new Laue lens design and performance estimates

Laue lenses are an emerging technology based on diffraction in crystals that allows the concentration of soft gamma rays. This kind of optics that works in the 100 keV - 1.5 MeV band can be used to realize an high-sensitivity and high-angular resolution telescope (in a narrow field of view). This paper reviews the recent progresses that have been done in the development of efficient crystals, in the design study and in the modelisation of the answer of Laue lenses. Through the example of a new concept of 20 m focal length lens focusing in the 100 keV - 600 keV band, the performance of a telescope based on a Laue lens is presented. This lens uses the most efficient mosaic crystals in each sub-energy range in order to yield the maximum reflectivity. Imaging capabilities are investigated and shows promising results.

astro-ph.IM↗

arXiv2009

Measurement of the neutron electric dipole moment by crystal diffraction

An experiment using a prototype setup to search for the neutron electric dipole moment by measuring spin-rotation in a non-centrosymmetric crystal (quartz) was carried out to investigate statistical sensitivity and systematic effects of the method. It has been demonstrated that the concept of the method works. The preliminary result of the experiment is $d_{\rm n}=(2.5\pm 6.5)\cdot 10^{-24}$ e$\cdot $cm. The experiment showed that an accuracy of $\sim 2.5\cdot 10^{-26}$ e$\cdot $cm can be obtained in 100 days data taking, using available quartz crystals and neutron beams.

nucl-ex↗

arXiv2008

R&D progress on second-generation crystals for Laue lens applications

The concept of a gamma-ray telescope based on a Laue lens offers the possibility to increase the sensitivity by more than an order of magnitude with respect to existing instruments. Laue lenses have been developed by our collaboration for several years : the main achievement of this R&D program was the CLAIRE lens prototype. Since then, the endeavour has been oriented towards the development of efficient diffracting elements (crystal slabs), the aim being to step from a technological Laue lens to a scientifically exploitable lens. The latest mission concept featuring a gamma-ray lens is the European Gamma-Ray Imager (GRI) which intends to make use of the Laue lens to cover energies from 200 keV to 1300 keV. Investigations of two promising materials, low mosaicity copper and gradient concentration silicon-germanium are presented in this paper. The measurements have been performed during three runs on beamline ID15A of the European Synchrotron Radiation Facility, and on the GAMS 4 instrument of the Institute Laue-Langevin (both in Grenoble, France) using highly monochromatic beam of energy close to 500 keV. Despite it was not perfectly homogeneous, the presented copper crystal exhibits peak reflectivity of 25% in accordance with theoretical predictions, and a mosaicity around 26 arcsec, the ideal range for the realization of a Laue lens such as GRI. Silicon-germanium featuring a constant gradient have been measured for the very first time at 500 keV. Two samples showed a quite homogeneous reflectivity reaching 26%, which is far from the 48% already observed in experimental crystals but a very encouraging beginning. This results have been used to estimate the performance of the GRI Laue lens design.

astro-ph↗

arXiv2005

Precision Measurement of the 29Si, 33S, and 36Cl Binding Energies

The binding energies of 29Si, 33S, and 36Cl have been measured with a relative uncertainty $< 0.59 \times 10^{-6}$ using a flat-crystal spectrometer. The unique features of these measurements are 1) nearly perfect crystals whose lattice spacing is known in meters, 2) a highly precise angle scale that is derived from first principles, and 3) a gamma-ray measurement facility that is coupled to a high flux reactor with near-core source capability. The binding energy is obtained by measuring all gamma-rays in a cascade scheme connecting the capture and ground states. The measurements require the extension of precision flat-crystal diffraction techniques to the 5 to 6 MeV energy region, a significant precision measurement challenge. The binding energies determined from these gamma-ray measurements are consistent with recent highly accurate atomic mass measurements within a relative uncertainty of $4.3 \times 10^{-7}$. The gamma-ray measurement uncertainties are the dominant contributors to the uncertainty of this consistency test. The measured gamma-ray energies are in agreement with earlier precision gamma-ray measurements.

nucl-ex↗