Stationary molecules in well-defined internal states are of broad interest for physics and chemistry. In physics, this includes metrology 1-3 , quantum computing 4,5 and manybody quantum mechanics 6,7 , whereas in chemistry, stateprepared molecular targets are of interest for uni-molecular reactions with coherent light fields 8,9 , for quantum-stateselected bi-molecular reactions 10-12 and for astrochemistry 12. Here, we demonstrate rotational ground-state cooling of vibrationally and translationally cold MgH + ions, using a lasercooling scheme based on excitation of a single rovibrational transition 13,14. A nearly 15-fold increase in the rotational ground-state population of the X 1 + electronic groundstate potential has been obtained. The resulting ground-state population of 36.7 ± 1.2% is equivalent to that of a thermal distribution at about 20 K. The obtained cooling results imply that cold molecular-ion experiments can now be carried out at cryogenic temperatures in room-temperature setups. At present there is a strong interest within the scientific community to produce and experiment with cold molecules. As standard laser-cooling schemes developed for atomic species cannot be applied to molecules, in the recent past tremendous effort has been put into developing schemes to cool molecules by other means. Several schemes for producing translationally cold and strongly bound neutral molecules in a single quantum state have been demonstrated. These include buffer-gas cooling of magnetic dipolar molecules in magnetic traps 15 , Stark deceleration and trapping of molecules with permanent 16,17 or induced 18 electric dipole moments, formation of molecules through Feshbach resonances followed by transfer to the vibrational ground state of electronic molecular potentials by stimulated Raman adiabatic passage schemes 19 and photoassociative molecule formation directly in the rovibrational ground state 20 or by transfer to the vibrational ground state through the application of shaped femtosecond laser pulses 21. With respect to molecular ions, the well-established technique of buffer-gas cooling is the only method that has so far led to the production of translationally as well as internally cold molecular ions 22. Although buffer-gas cooling is simple and generally applicable, it limits both the effective internal and translational temperature to the kelvin range, and owing to frequent collisions with the buffer-gas atoms it prevents strong spatial localization as well as utilization of internal coherences. Sympathetic cooling of trapped molecular ions, through the Coulomb interaction with laser-cooled atomic ions, has, on the other hand, proven highly effective for reaching translational temperatures in the millikelvin range, where the ions become spatially localized in the form of so-called Coulomb crystals 23. The sympathetic cooling scheme does, however, not significantly influence the molecular ion's internal degrees of freedom, owing to the very distant Coulomb interactions within the crystalline structures. ...

Three dimensional radiation dosimetry has received growing interest with the implementation of highly conformal radiotherapy treatments. The radiotherapy community faces new challenges with the commissioning of image guided and image gated radiotherapy treatments (IGRT) and deformable image registration software.A new three dimensional anthropomorphically shaped flexible dosimeter, further called 'FlexyDos3D', has been constructed and a new fast optical scanning method has been implemented that enables scanning of irregular shaped dosimeters. The FlexyDos3D phantom can be actuated and deformed during the actual treatment. FlexyDos3D offers the additional advantage that it is easy to fabricate, is non-toxic and can be molded in an arbitrary shape with high geometrical precision.The dosimeter formulation has been optimized in terms of dose sensitivity. The influence of the casting material and oxygen concentration has also been investigated. The radiophysical properties of this new dosimeter are discussed including stability, spatial integrity, temperature dependence of the dosimeter during radiation, readout and storage, dose rate dependence and tissue equivalence.

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Comprehensive dose verification, such as 3D dosimetry, may be required for safe introduction and use of advanced treatment modalities in radiotherapy. A radiochromic silicone-based 3D dosimetry system has recently been suggested, though its clinical use has so far been limited by a considerable dose-rate dependency of the dose response. In this study we have investigated the dose-rate dependency with respect to the chemical composition of the dosimeter. We found that this dependency was reduced with increasing dye concentration, and the dose response was observed to be identical for dosimeters irradiated with 2 and 6 Gy min(-1) at concentrations of 0.26% (w/w) dye and 1% (w/w) dye solvent. Furthermore, for the optimized dosimeter formulation, no dose-rate effect was observed due to the attenuation of the beam fluence with depth. However, the temporal stability of the dose response decreased with dye concentration; the response was reduced by (62  ±  1)% within approximately 20 h upon irradiation, at the optimal chemical composition and storage at room temperature. In conclusion, this study presents a chemical composition for a dose-rate independent silicone dosimeter which has considerably improved the clinical applicability of such dosimeters, but at the cost of a decreased stability.