13 research outputs found
APDs as single-photon detectors for visible and near-infrared wavelengths down to Hz rates
For the SPECTRAP experiment at GSI, Germany, detectors with Single-Photon
counting capability in the visible and near-infrared regime are required. For
the wavelength region up to 1100 nm we investigate the performance of 2x2 mm^2
avalanche photo diodes (APDs) of type S0223 manufactured by Radiation
Monitoring Devices. To minimize thermal noise, the APDs are cooled to
approximately -170 deg. C using liquid nitrogen. By operating the diodes close
to the breakdown voltage it is possible to achieve relative gains in excess of
2x10^4. Custom-made low noise preamplifiers are used to read out the devices.
The measurements presented in this paper have been obtained at a relative gain
of 2.2x10^4. At a discriminator threshold of 6 mV the resulting dark count rate
is in the region of 230/s. With these settings the studied APDs are able to
detect single photons at 628 nm wavelength with a photo detection efficiency of
(67+-7)%. Measurements at 1020 nm wavelength have been performed using the
attenuated output of a grating spectrograph with a light bulb as photon source.
With this setup the photo detection efficiency at 1020 nm has been determined
to be (13+-3)%, again at a threshold of 6 mV.Comment: 14 pages, 9 figures, submitted to Journal of Instrumentatio
Polarization-dependent disappearance of a resonance signal: Indication for optical pumping in a storage ring?
We report on laser spectroscopic measurements on Li ions in the
experimental storage ring ESR at the GSI Helmholtz Centre for Heavy Ion
Research. Driving the 2s\,^3\!{S}_1\;(F=\frac{3}{2})
\,\leftrightarrow\,2p\,^3\!P_2\;(F=\frac{5}{2}) \leftrightarrow
2s\,^3\!{S}_1\;(F=\frac{5}{2}) -transition in Li with two
superimposed laser beams it was found that the use of circularly polarized
light leads to a disappearance of the resonance structure in the fluorescence
signal. This can be explained by optical pumping into a dark state of polarized
ions. We present a detailed theoretical analysis of this process that supports
the interpretation of optical pumping and demonstrates that the polarization
induced by the laser light must then be at least partially maintained during
the round trip of the ions in the storage ring. Such polarized ion beams in
storage rings will provide opportunities for new experiments, especially on
parity violation.Comment: 14 pages, 8 figures, new version with small adjustments, closest to
final publication in PRA
Nuclear Charge Radii of B
The first determination of the nuclear charge radius by laser spectroscopy
for a five-electron system is reported. This is achieved by combining
high-accuracy ab initio mass-shift calculations and a high-resolution
measurement of the isotope shift in the 2s^2 2p\, ^2\mathrm{P}_{1/2}
\rightarrow 2s^2 3s\, ^2\mathrm{S}_{1/2} ground state transition in boron
atoms. Accuracy is increased by orders of magnitude for the stable isotopes
B and the results are used to extract their difference in the
mean-square charge radius . The result is
qualitatively explained by a possible cluster structure of the boron nuclei and
quantitatively used as a benchmark for new ab initio nuclear structure
calculations using the no-core shell model and Green's function Monte Carlo
approaches
Hyperfine structure and nuclear magnetic moments of the praseodymium isotopes
International audienceCollinear Laser spectroscopy was applied to measure the hyperfine structure ofPr at ISOLDE/CERN. Combined with measurements of the stable isotopePr at the TRIGA-SPEC setup in Mainz we were able to determine the magnetic moments of the neutron-deficient isotopesPr,Pr andPr for the first time
Spin and magnetic moment of Mg
A negative magnetic moment of <sup>23</sup>Mg has been determined by collinear laser spectroscopy at CERN-ISOLDE. The absolute value is in agreement with previous measurements by nuclear magnetic resonance while the sign points at high-seniority configurations. The result is consistent with shell-model predictions for nuclei with valence nucleons in the sd shell
Status of CRYRING@ESR and preparations for first experiments
Synopsis CRYRING was moved from Stockholm to Darmstadt, modernized and integrated into the GSI/FAIR beamline topology behind ESR. As CRYRING@ESR, it will receive and store heavy, highly charged ions from all species the present accelerator chain is capable of producing. An extensive research program on low-energy atomic collisions, spectroscopy and nuclear reactions was proposed. The facility is gradually completing commissioning, ion beams from the local injector branch have already been stored and prototype experiments performed. We present the machine status and highlight some planned experiments