Excited level lifetime measurements following very low energy nuclear recoils

Using high resolution gamma spectroscopy it is possible to observe Doppler broadening of gamma transitions from excited states which have themselves been populated after emission of gamma photons or other low energy nuclear radiation. This allows the determination of the lifetimes of these intermediate states, providing the time dependence of the recoil velocities is known. Conversely, if the lifetime is well known, this technique may be used to study the recoil process itself (and hence the atomic interaction) at energies of only a few times the lattice binding energy.     

GRID lifetime measurements in59, 61, 63Ni following thermal neutron capture

The GRID-method has been used to measure the lifetimes of ten excited states in^{59, 61, 63}Ni following thermal neutron capture in Ni targets of natural isotopic composition. Four of the lifetimes have been determined for the first time, the other six lifetimes can be compared with the results of conventional DSA-measurements following charged particle induced reactions. Cascade feeding effects have been included in the analysis. Level energies and electromagnetic properties of negative parity states in⁵⁹Ni have been compared with the results of shell model calculations in 3p0h and 4p 1h model spaces. Statistical model estimates of the lifetimes as function of excitation energy and spin are also given.Work partially supported by Deutsches BMFT under contract 06GOE141     

Two-quasiparticle bands in72Br

High spin states in the doubly odd nucleus⁷²Br were investigated via the reaction⁵⁸Ni(¹⁶O,pn) at 52–65 MeV beam energy. A multi-element detector system consisting of ten Compton supressed Ge detectors (OSIRIS) and two NE213 neutron detectors was used to establish the yrast bands up to 5 MeV excitation energy and probable spins of 15⁺ resp. 14^?. The lifetimes of 12 states and lifetime limits of four states were measured with the recoil distance method, among them four 0.5–3.1 ns isomers. Doppler broadened line shapes obtained in an additionalγγ-coincidence experiment via the reaction⁴⁰Ca(³⁶Ar, 3pn) at 125 MeV revealed further lifetimes and (very short) side feeding times. Three rotational bands were established with deformation parameters ¦β ₂¦≈0.3 and moment of inertia parameters \(\tilde f\) /? ²=36 MeV^?1 (K ^ρ=1^?) resp. 23 MeV^?1; their quasi-particle configurations are being discussed.     

Calorimetric Investigation of Adsorption of Organic Compounds by Active Carbons

Enthalpies of wetting of two active carbons and one brown coal coke by several pure liquids (mainly homologous series) were measured at 298.15 K with two quasi-isothermal microcalorimeters. Different measuring cells with cavities of about 0.5 and 15 cm³ were used. The advantage of the larger measuring cell with three independent 15 cm³ cavities is the higher mass of active carbon, leading to a high reproducibility with standard deviations below 1% and a reduced measuring time. Experiments were carried out with n-alkanes, l-alkanols, cycloalkanes and isomers thereof, i.e. 2-propanol, methylcyclohexane, 2,2,4-trimethylpentane (isooctane and 2-ethyl-1-hexanol, and water. Like the polarity, the size and the three-dimensional expansion of the molecules, the energetic and geometric heterogeneity of the adsorbent influences the enthalpy of wetting. This revised version was published online in August 2006 with corrections to the Cover Date.     

Experimental study at the solid/liquid interface: Enthalpies of wetting of several liquids onto active carbon

Enthalpies of wetting of several pure liquids onto active carbon were measured at 298.15 K with a quasi-isothermal microcalorimeter Setaram MS 80 II. New measuring cells with three independent cavities of about 15 cm³ were created. The advantage of this new method is the high weight-in of active carbon and a reduced time per measurement for reaching a constant baseline. Experiments were carried out with n-alkanes, 1-alkanols, cyclohexane, 2,2,4-trimethyl-pentane (isooctane) and water. The experimental results for the enthalpy of wetting show a dependence of the geometric heterogeneity of the active carbon and the polarity of liquids.     

Effect of NaCl on the excess enthalpies of binary liquid systems

The excess molar enthalpies h^E₁₊₂₃ of ethanol+(water+NaCl), benzylalcohol+(water+NaCl), and cyclohexane+(methanol+NaCl) were measured at 298.15 K, those of methanol+(water+NaCl) at 298.15 and 323.15 K. An LKB flow microcalorimeter was used and a special flow-mix cell was developed with regard to the corrosive electrolyte solutions. Knowing the integral enthalpy of solution and the solution enthalpy at infinite dilution for a salt (3) in a solvent (2), the molar excess enthalpy h^E₁₂₃ can be calculated.     

Determination of an amount of gas by weighing under vacuum conditions and uncertainty analysis

For the determination of the calorific value of gases, a mass determination system for the gas burnt in the calorimeter was developed. Contrary to classical methods, which weigh the gas bottle offline, the method applied here weighs the amount of gas online and continuously. For this purpose, a commercial analytical balance with a readability of 10 µg across the entire weighing range of 205 g was modified for use under vacuum conditions.Since the gas bottle has to be permanently connected to the calorimeter by a steel capillary, an additional force is exerted to the balance. The influence of this force is investigated and determined by a special weighing procedure.In addition, an automatic calibration technique must be developed to ensure the traceability of the results to the national standard of mass. This allows an uncertainty analysis according to the Guide to the Expression of Uncertainty in Measurement (GUM) to be performed.This revised version was published online in November 2005 with corrections to the Cover Date.