65 research outputs found
Longitudinal spin-relaxation in nitrogen-vacancy centers in electron irradiated diamond
We present systematic measurements of longitudinal relaxation rates ()
of spin polarization in the ground state of the nitrogen-vacancy (NV) color
center in synthetic diamond as a function of NV concentration and magnetic
field . NV centers were created by irradiating a Type 1b single-crystal
diamond along the [100] axis with 200 keV electrons from a transmission
electron microscope with varying doses to achieve spots of different NV
center concentrations. Values of () were measured for each spot as a
function of .Comment: 4 pages, 8 figure
Preliminary results of fast neutron treatments in carcinoma of the pancreas
A group of 30 patients with adenocarcinoma of the pancreas including some patients with very advanced disease, were treated with the so-called mixed beam modality employing photon treatments three times per week and neutron treatments twice a week. Two hundred Rads or equivalent Rads (RBE 3.3) were given in daily fractions aiming at a total dose of 6000 Rads in 6 to 8 weeks. The treatments were well tolerated and significant palliation was achieved in 26 to 30 cases. Twelve months survival was 33 percent with a median survival of 7 months or 210 days. Treatment techniques and localization procedures are discussed
Detailed studies of non-linear magneto-optical resonances at D1 excitation of Rb-85 and Rb-87 for partially resolved hyperfine F-levels
Experimental signals of non-linear magneto-optical resonances at D1
excitation of natural rubidium in a vapor cell have been obtained and described
with experimental accuracy by a detailed theoretical model based on the optical
Bloch equations. The D1 transition of rubidium is a challenging system to
analyze theoretically because it contains transitions that are only partially
resolved under Doppler broadening. The theoretical model took into account all
nearby transitions, the coherence properties of the exciting laser radiation,
and the mixing of magnetic sublevels in an external magnetic field and also
included averaging over the Doppler profile. Great care was taken to obtain
accurate experimental signals and avoid systematic errors. The experimental
signals were reproduced very well at each hyperfine transition and over a wide
range of laser power densities, beam diameters, and laser detunings from the
exact transition frequency. The bright resonance expected at the F_g=1 -->
F_e=2 transition of Rb-87 has been observed. A bright resonance was observed at
the F_g=2 --> F_e=3 transition of Rb-85, but displaced from the exact position
of the transition due to the influence of the nearby F_g=2 --> F_e=2
transition, which is a dark resonance whose contrast is almost two orders of
magnitude larger than the contrast of the bright resonance at the F_g=2 -->
F_e=3 transition. Even in this very delicate situation, the theoretical model
described in detail the experimental signals at different laser detunings.Comment: 11 pages, 9 figure
Conversion of bright magneto-optical resonances into dark at fixed laser frequency for D2 excitation of atomic rubidium
Nonlinear magneto-optical resonances on the hyperfine transitions belonging
to the D2 line of rubidium were changed from bright to dark resonances by
changing the laser power density of the single exciting laser field or by
changing the vapor temperature in the cell. In one set of experiments atoms
were excited by linearly polarized light from an extended cavity diode laser
with polarization vector perpendicular to the light's propagation direction and
magnetic field, and laser induced fluorescence (LIF) was observed along the
direction of the magnetic field, which was scanned. A low-contrast bright
resonance was observed at low laser power densities when the laser was tuned to
the Fg=2 --> Fe=3 transition of Rb-87 and near to the Fg=3 --> Fe=4 transition
of Rb-85. The bright resonance became dark as the laser power density was
increased above 0.6mW/cm2 or 0.8 mW/cm2, respectively. When the Fg=2 --> Fe=3
transition of Rb-87 was excited with circularly polarized light in a second set
of experiments, a bright resonance was observed, which became dark when the
temperature was increased to around 50C. The experimental observations at room
temperature could be reproduced with good agreement by calculations based on a
theoretical model, although the theoretical model was not able to describe
measurements at elevated temperatures, where reabsorption was thought to play a
decisive role. The model was derived from the optical Bloch equations and
included all nearby hyperfine components, averaging over the Doppler profile,
mixing of magnetic sublevels in the external magnetic field, and a treatment of
the coherence properties of the exciting radiation field.Comment: 9 pages, 7 figure
Composition of Primary Cosmic-Ray Nuclei at High Energies
The TRACER instrument (``Transition Radiation Array for Cosmic Energetic
Radiation'') has been developed for direct measurements of the heavier primary
cosmic-ray nuclei at high energies. The instrument had a successful
long-duration balloon flight in Antarctica in 2003. The detector system and
measurement process are described, details of the data analysis are discussed,
and the individual energy spectra of the elements O, Ne, Mg, Si, S, Ar, Ca, and
Fe (nuclear charge Z=8 to 26) are presented. The large geometric factor of
TRACER and the use of a transition radiation detector make it possible to
determine the spectra up to energies in excess of 10 eV per particle. A
power-law fit to the individual energy spectra above 20 GeV per amu exhibits
nearly the same spectral index ( 2.65 0.05) for all elements,
without noticeable dependence on the elemental charge Z.Comment: Accepted for publication in the Astrophysical Journal (3-Jan-08), 37
pages, 15 figure
Level-crossing spectroscopy of the 7, 9, and 10D_5/2 states of 133Cs and validation of relativistic many-body calculations of the polarizabilities and hyperfine constants
We present an experimental and theoretical investigation of the
polarizabilities and hyperfine constants of D_J states in 133Cs for J=3/2 and
J=5/2. New experimental values for the hyperfine constant A are obtained from
level-crossing signals of the (7,9,10)D_5/2 states of 133Cs and precise
calculations of the tensor polarizabilities alpha_2. The results of
relativistic many-body calculations for scalar and tensor polarizabilities of
the (5-10)D_3/2 and (5-10)D_5/2 states are presented and compared with measured
values from the literature. Calculated values of the hyperfine constants A for
these states are also presented and checked for consistency with experimental
values.Comment: 12 pages, revtex4, 11 figure file
Nonlinear magneto-optical resonances at D1 excitation of 85Rb and 87Rb in an extremely thin cell
Nonlinear magneto-optical resonances have been measured in an extremely thin
cell (ETC) for the D1 transition of rubidium in an atomic vapor of natural
isotopic composition. All hyperfine transitions of both isotopes have been
studied for a wide range of laser power densities, laser detunings, and ETC
wall separations. Dark resonances in the laser induced fluorescence (LIF) were
observed as expected when the ground state total angular momentum F_g was
greater than or equal to the excited state total angular momentum F_e. Unlike
the case of ordinary cells, the width and contrast of dark resonances formed in
the ETC dramatically depended on the detuning of the laser from the exact
atomic transition. A theoretical model based on the optical Bloch equations was
applied to calculate the shapes of the resonance curves. The model averaged
over the contributions from different atomic velocity groups, considered all
neighboring hyperfine transitions, took into account the splitting and mixing
of magnetic sublevels in an external magnetic field, and included a detailed
treatment of the coherence properties of the laser radiation. Such a
theoretical approach had successfully described nonlinear magneto-optical
resonances in ordinary vapor cells. Although the values of certain model
parameters in the ETC differed significantly from the case of ordinary cells,
the same physical processes were used to model both cases. However, to describe
the resonances in the ETC, key parameters such as the transit relaxation rate
and Doppler width had to be modified in accordance with the ETC's unique
features. Agreement between the measured and calculated resonance curves was
satisfactory for the ETC, though not as good as in the case of ordinary cells.Comment: v2: substantial changes and expanded theoretical model; 13 pages, 10
figures; accepted for publication in Physical Review
Cascade coherence transfer and magneto-optical resonances at 455 nm excitation of Cesium
We present and experimental and theoretical study of nonlinear
magneto-optical resonances observed in the fluorescence to the ground state
from the 7P_{3/2} state of cesium, which was populated directly by laser
radiation at 455 nm, and from the 6P_{1/2} and 6P_{3/2} states, which were
populated via cascade transitions that started from the 7P_{3/2} state and
passed through various intermediate states. The laser-induced fluorescence
(LIF) was observed as the magnetic field was scanned through zero. Signals were
recorded for the two orthogonal, linearly polarized components of the LIF. We
compared the measured signals with the results of calculations from a model
that was based on the optical Bloch equations and averaged over the Doppler
profile. This model was adapted from a model that had been developed for D_1
and D_2 excitation of alkali metal atoms. The calculations agree quite well
with the measurements, especially when taking into account the fact that some
experimental parameters were only estimated in the model.Comment: small changes to text of previous version; 12 pages, 8 figure
- …