In this paper, X‐ray and γ‐ray propagation in crystals having a constant strain gradient and flat or cylindrical surfaces is investigated. When a displacement field is present, the Takagi–Taupin ...equations are solved either by the Riemann–Green method or by a numerical method. The results are applied to study the operation of a double‐crystal Laue–Laue diffractometer having a flat collimating crystal followed by a bent analyzer crystal. In particular, the effect of the analyzer strain on the location of the diffraction peaks in the dispersive and non‐dispersive set‐up is examined, thus confirming the previously reported peak location as being set only by the diffracting‐plane spacing on the analyzer entrance surface.
Polarization encoding and phase modulation allow the optical interferometer to be precisely set on a specific position of
the interference fringe—the null point setting. The null point settings in ...the interference fringe field correspond to dark
or bright fringes. Null measurement ensures maximum possible noise rejection. However, polarization encoding makes the interferometer
nonlinear, but all nonlinearity effects are effectively zero at the fringe set point. The X–ray interferometer provides the
means for linear subdivision of optical fringes. Each X–ray fringe corresponds to a displacement that is equal to the lattice
parameter of silicon, which is ca .0.19 nm for the (220) lattice planes. For displacements up to 1 m the measurement uncertainties
at 95% confidence level are ± 30 pm, and for displacements up to 100 m and 1 mm the uncertainties are ± 35 and ± 170 pm, respectively., The requirement for calibrating transducers having subnanometre displacement sensitivities stimulated the development of an
instrument in which the displacement is measured by a combination of optical and X–ray interferometry. The need to combine
both types of interferometry arises from the fact that optical interferometry enables displacements corresponding to whole
numbers of optical fringes to be measured very precisely, but subdivision of an optical fringe may give rise to errors that
are significant at the subnanometre level. The X–ray interferometer is used to subdivide the optical fringes. Traceability
to the meter is achieved via traceable calibrations of the lattice parameter of silicon and of the laser frequency., Important features of the instrument, which is located at the National Physical Laboratory, are the silicon monolith interferometer
that both diffracts X–rays and forms part of the optical interferometer, a totally reflecting parabolic collimator for enhancing
the usable X–ray flux and the servo–control for the interferometers.
We have analyzed data of the DISTO experiment on the exclusive
pp
→
K
+
Λ
p
process at
T
p
= 2.85 GeV to search for a
K
−
pp
( ≡
X
) nuclear bound state to be formed in the
pp
→
K
+
+
X
...reaction. The deviation spectra of the
K
+
missing-mass Δ
M
(
K
+
) and Λ
p
invariant-mass
M
(Λ
p
) with selection of large-angle proton emission revealed a structure with
M
X
= 2265 ±2 MeV/
c
2
and
Γ
X
= 118 ±8 MeV.
The ratio of the total exclusive production cross sections for
η' and
η mesons has been measured in the
pp reaction at
p
beam=3.67 GeV/
c. The observed
η
′/
η ratio is (0.83±0.11
+0.23
−0.18)×10
−2 ...from which the exclusive
η
′ meson production cross section is determined to be (1.12±0.15
+0.42
−0.31) μb. Differential cross section distributions have been measured. Their shape is consistent with isotropic
η
′ meson production.
The p¯ stopping power in helium from 1 keV kinetic energy is evaluated. Contrary to the effect observed around and below the maximum, Obelix data indicate a p¯ stopping power higher than that for ...proton, the difference being of the order of 15±5% at ≈700 keV. The result contributes to assert the fundamental difference between p¯ stoppings in the simplest gases (He, H2) and in solid targets below some MeV.
The total cross section of the reaction
pp→
ppK
+
K
− has been determined for proton–proton reactions with
p
beam
=3.67
GeV/c
. This represents the first cross section measurement of the
pp→
ppK
−
K
...+ channel near threshold, and is equivalent to the inclusive
pp→
ppK
−
X cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive
pp→
ppK
+
X meson production at the same CM energy above the corresponding threshold. This large difference in the
K
+ and
K
− meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.
Barkas effect for antiproton stopping in H2 Lodi Rizzini, E; Bianconi, A; Bussa, M P ...
Physical review letters,
2002-Oct-28, 20021028, Letnik:
89, Številka:
18
Journal Article
Recenzirano
We report the stopping power of molecular hydrogen for antiprotons of kinetic energy above the maximum (approximately 100 keV) with the purpose of comparing with the proton one. Our result is ...consistent with a positive difference in antiproton-proton stopping powers above approximately 250 keV and with a maximum difference between the stopping powers of 21%+/-3% at around 600 keV.
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