A data-based photonuclear simulation algorithm for determining specific activity of medical radioisotopes

For simulating more accurately neutron or proton production from photonuclear reactions,a data-based photonuclear reaction simulation algorithm has been developed.Reliable photonuclear cross sections from evaluated or experimental database are chosen as input data.For checking the validity of the use of the data-based photonuclear algorithm,benchmarking simulations are presented in detail.We calculate photonuclear cross sections or reaction yield for ~9Be,^(48)Ti,^(133)Cs,and ^(197)Au and compare them with experimental data in the region of incident photon energy below ~30 MeV.While Geant4 can hardly reproduce photonuclear experimental data,results obtained from the data-based photonuclear algorithm are found in good agreement with experimental measurements.Potential application in estimation of specific activity of radioisotopes is further discussed.We conclude that the developed data-based photonuclear algorithm is suitable for an accurate prediction of photoninduced neutron or proton productions.

Probing and possible application of the QED vacuum with micro-bubble implosions induced by ultra-intense laser pulses

The interaction of micro-bubbles with ultra-intense laser pulses has been shown to generate ultra-high proton densities and correspondingly high electric fields.Weinvestigate the possibility of using such a combination to study the fundamental physical phenomenon of vacuum polarization.With current or near-future laser systems,measurement of vacuum polarization via the bending of gamma rays that pass near imploded microbubbles may be possible.Since it is independent of photon energy to within the leading-order solution of the Heisenberg–Euler Lagrangian and the geometric optics approximation,the corresponding index of refraction can dominate the indices of refraction due to other effects at sufficiently high photon energies.We consider the possibility of its application to a transient gamma-ray lens.

Exploring fs-laser irradiation damage subthreshold behavior of dielectric mirrors via electrical measurements

With ultrafast laser systems reaching presently 10 PW peak power or operating at high repetition rates,research towards ensuring the long-term,trouble-free performance of all laser-exposed optical components is critical.Our work is focused on providing insight into the optical material behavior at fluences below the standardized laser-induced damage threshold(LIDT)value by implementing a simultaneous dual analysis of surface emitted particles using a Langmuir probe(LP)and the target current(TC).HfO_(2) and ZrO_(2) thin films deposited on fused silica substrates by pulsed laser deposition at various O_(2) pressures for defect and stoichiometry control were irradiated by Gaussian,ultrashort laser pulses(800 nm,10 Hz,70 fs)in a wide range of fluences.Both TC and LP collected signals were in good agreement with the existing theoretical description of laser–matter interaction at an ultrashort time scale.Our approach for an in situ LIDT monitoring system provides measurable signals for below-threshold irradiation conditions that indicate the endurance limit of the optical surfaces in the single-shot energy scanning mode.The LIDT value extracted from the LP-TC system is in line with the multipulse statistical analysis done with ISO 21254-2:2011(E).The implementation of the LP and TC as on-shot diagnostic tools for optical components will have a significant impact on the reliability of next-generation ultrafast and high-power laser systems.

Electron Acceleration by a radially polarised cosh-Gaussian laser beam in vacuum

In this paper,a radially polarised cosh-Gaussian laser beam(CGLB)is used to study the electron acceleration produced in vacuum.A highly energetic electron beam can be achieved by a CGLB,even with comparatively low-powered lasers.The properties of a CGLB cause it to focus earlier,over a shorter duration than a Gaussian laser beam,which makes it suitable for obtaining high energies over small durations.It is found that the energy gained by the electrons strongly depends upon the decentering parameter of the laser profile.It is also observed that for a fixed value of energy gain,if the decentering parameter is increased,then the intensity of the laser field decreases.The dependence of the energy gained by electrons on the laser intensity and the laserspot size is also studied.