Photodissociation of p-process nuclei studied by bremsstrahlung induced activation

A research program has been started to study experimentally the near-threshold photodissociation of nuclides in the chain of cosmic heavy element production with bremsstrahlung from the ELBE accelerator. An important prerequisite for such studies is good knowledge of the bremsstrahlung distribution which was determined by measuring the photodissociation of the deuteron and by comparison with model calculations. First data were obtained for the astrophysically important target nucleus 92-Mo by observing the radioactive decay of the nuclides produced by bremsstrahlung irradiation at end-point energies between 11.8 MeV and 14.0 MeV. The results are compared to recent statistical model calculations.Comment: 6 pages, 8 figures, Proceedings Nuclear Physics in Astrophysics II, May 16-20, 2005, Debrecen, Hungary. The original publication is available at www.eurphysj.or

Deterministic Partial Differential Equation Model for Dose Calculation in Electron Radiotherapy

Treatment with high energy ionizing radiation is one of the main methods in modern cancer therapy that is in clinical use. During the last decades, two main approaches to dose calculation were used, Monte Carlo simulations and semi-empirical models based on Fermi-Eyges theory. A third way to dose calculation has only recently attracted attention in the medical physics community. This approach is based on the deterministic kinetic equations of radiative transfer. Starting from these, we derive a macroscopic partial differential equation model for electron transport in tissue. This model involves an angular closure in the phase space. It is exact for the free-streaming and the isotropic regime. We solve it numerically by a newly developed HLLC scheme based on [BerCharDub], that exactly preserves key properties of the analytical solution on the discrete level. Several numerical results for test cases from the medical physics literature are presented.Comment: 20 pages, 7 figure

NEST: A Comprehensive Model for Scintillation Yield in Liquid Xenon

A comprehensive model for explaining scintillation yield in liquid xenon is introduced. We unify various definitions of work function which abound in the literature and incorporate all available data on electron recoil scintillation yield. This results in a better understanding of electron recoil, and facilitates an improved description of nuclear recoil. An incident gamma energy range of O(1 keV) to O(1 MeV) and electric fields between 0 and O(10 kV/cm) are incorporated into this heuristic model. We show results from a Geant4 implementation, but because the model has a few free parameters, implementation in any simulation package should be simple. We use a quasi-empirical approach, with an objective of improving detector calibrations and performance verification. The model will aid in the design and optimization of future detectors. This model is also easy to extend to other noble elements. In this paper we lay the foundation for an exhaustive simulation code which we call NEST (Noble Element Simulation Technique).Comment: 24 pages, 9 figures, 3 table

The Standard Model in Strong Fields: Electroweak Radiative Corrections for Highly Charged Ions

Electroweak radiative corrections to the matrix elements $<ns_{1/2}|{\hat H}_{PNC}|n'p_{1/2}>$ are calculated for highly charged hydrogenlike ions. These matrix elements constitute the basis for the description of the most parity nonconserving (PNC) processes in atomic physics. The operator ${\hat H}_{PNC}$ represents the parity nonconserving relativistic effective atomic Hamiltonian at the tree level. The deviation of these calculations from the calculations valid for the momentum transfer $q^{2}=0$ demonstrates the effect of the strong field, characterized by the momentum transfer $q^{2}=m_{e}^{2}$ ($m_{e}$ is the electron mass). This allows for a test of the Standard Model in the presence of strong fields in experiments with highly charged ions.Comment: 27 LaTex page

The convergence method to calculate particles fluxes in x rays spectrometry techniques. Application in nuclear compounds

A method to calculate particle fluxes applicable in most of the spectroscopy techniques is described. Flux intensities of backscattered or absorbed electrons and emitted photons are calculated using a method of convergence to solve the Invariant Embedding equations that are used to describe the particle trajectories inside a solid sample. Our results are found to be helpful to carry out a procedure for quantitative characterization using instrument such as Electron Probe Microanalysis or other probes. Examples of application to calculate the composition of ternary alloys are given and are compared with the same calculations using another procedure.Comment: 15 page

Measurement of the neutron lifetime using an asymmetric magneto- gravitational trap and in situ detection

The precise value of the mean neutron lifetime, $\tau_n$, plays an important role in nuclear and particle physics and cosmology. It is a key input for predicting the ratio of protons to helium atoms in the primordial universe and is used to search for new physics beyond the Standard Model of particle physics. There is a 3.9 standard deviation discrepancy between $\tau_n$ measured by counting the decay rate of free neutrons in a beam (887.7 $\pm$ 2.2 s) and by counting surviving ultracold neutrons stored for different storage times in a material trap (878.5$\pm$0.8 s). The experiment described here eliminates loss mechanisms present in previous trap experiments by levitating polarized ultracold neutrons above the surface of an asymmetric storage trap using a repulsive magnetic field gradient so that the stored neutrons do not interact with material trap walls and neutrons in quasi-stable orbits rapidly exit the trap. As a result of this approach and the use of a new in situ neutron detector, the lifetime reported here (877.7 $\pm$ 0.7 (stat) +0.4/-0.2 (sys) s) is the first modern measurement of $\tau_n$ that does not require corrections larger than the quoted uncertainties.Comment: 9 pages, 3 figures, 2 table