Improved Limits for Violations of Local Position Invariance from Atomic Clock Comparisons.

We compare two optical clocks based on the ^{2}S_{1/2}(F=0)→^{2}D_{3/2}(F=2) electric quadrupole (E2) and the ^{2}S_{1/2}(F=0)→^{2}F_{7/2}(F=3) electric octupole (E3) transition of ^{171}Yb^{+} and measure the frequency ratio ν_{E3}/ν_{E2}=0.932829404530965376(32), improving upon previous measurements by an order of magnitude. Using two caesium fountain clocks, we find ν_{E3}=642121496772645.10(8) Hz, the most accurate determination of an optical transition frequency to date. Repeated measurements of both quantities over several years are analyzed for potential violations of local position invariance. We improve by factors of about 20 and 2 the limits for fractional temporal variations of the fine structure constant α to 1.0(1.1)×10^{-18}/yr and of the proton-to-electron mass ratio µ to -8(36)×10^{-18}/yr. Using the annual variation of the Sun's gravitational potential at Earth Φ, we improve limits for a potential coupling of both constants to gravity, (c^{2}/α)(dα/dΦ)=14(11)×10^{-9} and (c^{2}/µ)(dµ/dΦ)=7(45)×10^{-8}.

Stopping power of water for carbon ions with energies in the Bragg peak region.

The stopping power of liquid water was measured for carbon ions with energies in the Bragg peak region using the inverted Doppler shift attenuation method. Among the semiempirical data, the results of this work agree best with the data recommended in the Errata and Addendum of ICRU Report No. 73, which is based on an I value of 78 eV for water. The agreement was worse when the present results were compared to the newer recommendation of the ICRU published in ICRU Report No. 90. The srim code seems to slightly overestimate the stopping power of water for carbon ions above 3 MeV. A semiexperimental stopping power of water for α particles was derived from the present results using the theoretical ratio between the stopping powers of water for carbon ions and α particles computed by means of the casp code. These values agree well with the experimental data for α particles within the uncertainties.

Stopping power of liquid water for carbon ions in the energy range between 1 MeV and 6 MeV.

The stopping power of liquid water was measured for the first time for carbon ions in the energy range between 1 and 6 MeV using the inverted Doppler shift attenuation method. The feasibility study carried out within the scope of the present work shows that this method is well suited for the quantification of the controversial condensed phased effect in the stopping power for heavy ions in the intermediate energy range. The preliminary results of this work indicate that the stopping power of water for carbon ions with energies prevailing in the Bragg-peak region is significantly lower than that of water vapor. In view of the relatively high uncertainty of the present results, a new experiment with uncertainties less than the predicted difference between the stopping powers of both water phases is planned.