Excited state evolution of DNA stacked adenines resolved at the CASPT2//CASSCF/Amber level: from the bright to the excimer state and back

La and excimer state population exchange, along the common puckering decay coordinate, explains the longest DNA lifetime component.

Encapsulation of Natural Flavors in Cyclodextrins: Free Volume Studies by PALS

Positron annihilation lifetime spectroscopy (PALS) is used to study the free-volume in β-cyclodextrin (CD) with the encapsulation of two different essential oils: garlic (Allium sativum) and marjoram (Origanum majorana). The data reveal the presence of a long lifetime component related to the o-Ps. It is observed that the addition of garlic (or marjoram) oil to β-CD results in a decrease of the o-Ps lifetime which was ascribed to a reduction of the free volume holes from 83.6 to 67.7 Å3 (79.1 to 72.6 Å3). Different mechanisms for the encapsulation of garlic and marjoram oils in β-CD are suggested by the PALS parameters.

Recombination at Oxide Precipitates in Silicon

Transient and quasi-steady-state photoconductance methods were used to measure minority carrier lifetime in p-type Czochralski silicon processed in very clean conditions to contain oxide precipitates. Precipitation treatments were varied to produce a matrix of samples, which were then characterised by chemical etching and transmission electron microscopy to determine the density and morphology of the precipitates. The lifetime component associated with the precipitates was isolated by preventing or factoring out the effects of other known recombination mechanisms. The lifetime component due to unstrained precipitates could be extremely high (up to ~4.5ms). Recombination at unstrained precipitates was found to be weak, with a capture coefficient of ~8 x 10-8cm3s-1at an injection level equal to half the doping level. Strained precipitates and defects associated with them (dislocations and stacking faults) act as much stronger recombination centres with a capture coefficient of ~3 x 10-6cm3s-1at the same level of injection. The lifetime associated with strained precipitates increases with temperature with a ~0.18eV activation energy over the room temperature to 140°C range. The shape of the injection level dependence of lifetime was similar for all the specimens studied, with the magnitude of the lifetime being dependent on the precipitate density, strain state and temperature, but independent of precipitate size.

Preliminary Positron Lifetime Results on Free Volumes in Cyclodextrins

Positron annihilation lifetime spectroscopy was used to study the free-volume parameters in various pure -, - and -cyclodextrins samples and, in the case of β-cyclodextrin, with inclusion of S-carvone and thymoquinone. The results clearly indicate the presence of long lifetime components related to Ps-formation. The data show that the addition of S-carvone to β-cyclodextrin results in a decrease of o-Ps lifetime that we ascribe to a reduction of free volume holes from 81.8 to 63.7 Å3. The long lifetime component disappears when thymoquinone is added to -cyclodextrin, indicating this substance acts as an o-Ps quencher. For all samples studied, a decrease in the long lifetime component values was observed with increasing source in situ time, a result that might be attributed to the irradiation of the sample by the 22Na positron source.

Positron Annihilation in Undercooled Water and Ice

Positron lifetime and Doppler broadened annihilation line at wide temperature range 15-300 K was measured. The phase transition at melting temperature and its temperature shift in undercooled water was observed. The change in temperature dependence of long lifetime component in region 150 K was observed. The lifetime distributions (by program MELT) were calculated in full temperature range with an accent for the phase transition temperature range.

4-Channel Digital Positron Lifetime Spectrometer for Studying Biological Samples

In this work a novel detector setup for PALS-studies on biomolecular materials is presented. When pursuing optimal detecting efficiency and lifetime component resolution one must make compromises when using only one detector pair. With smaller scintillation heads the resolution is higher, but the detecting efficiency decreases and vice versa. When measuring biological materials that do not withstand long measurement periods, sacrifices are made for gaining efficiency. The price of this optimization is low resolution of the lifetime components, namely separating the always present water’s lifetime component of ~1.8 ns from the actual material’s lifetime component, typically >2 ns. A solution to this problem is measuring the annihilation spectra with two individual detector pairs simultaneously. Using analog setup, it would require duplicate ADC-hardware that are both expensive and degrade by time. With a fully digital setup, the need for hardware is smaller and the precision of the setup is constant during its service life.

Enhanced product functionality with life cycle units

Cycle economy is not only ecologically reasonable but also a chance for new business. Selling utilization instead of selling products is advantageous once additional costs for information processing and logistics are less than costs for underutilized capacity. A competitive provider offers product functionality in quality, time and location as required by the user. Lifetime component monitoring is conditional for this performance. Modern microelectronic technology enables the acquisition of component deterioration with sensorial devices, information processing and storing with microcontrollers and initiating appropriate actions such as maintenance. The architecture of a microsystem called the life cycle unit (LCU) for product and component monitoring is introduced and specified. Product examples illustrate some application areas.

Undoped gallium antimonide studied by positron annihilation spectroscopy

ABSTRACTPositron lifetime spectroscopy has been used to study the vacancy type defects in undoped gallium antimonide. Temperature dependent positron trapping into the VGa-related defect having a characteristic lifetime of 310ps was observed in the as-grown sample. The lifetime data were well described by a model involving the thermal ionization (0/-) of the VGa-related defect and its ionization energy was found to be E(0/-)=83meV. For the electron irradiated sample, the VGa-related defect with lifetime of 310ps that was found in the non-irradiated samples was also identified. Moreover, another lifetime component (280ps) was only observed in the electron irradiated sample but not in the non-irradiated sample. It was also attributed to the VGa-related defect. The two identified VGa-related defects should have different microstructures because of their difference in characteristic lifetimes. The 280ps component remains thermally stable after the 500°C annealing while the 310ps component anneals at 300°C.

COLD DARK MATTER AND PRIMORDIAL SUPERHEAVY PARTICLES

The hypothesis that cold dark matter consists of primordial superheavy particles, the decay of short lifetime component of which led to the observable mass of matter while long living component survived up to modern times manifesting its presence in high energetic cosmic rays particles is investigated.