Alexander Howard

Geant4 developments and applications

Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Its functionality and modeling capabilities continue to be extended, while its performance is enhanced. An overview of recent developments in diverse areas of the toolkit is presented. These include performance optimization for complex setups; improvements for the propagation in fields; new options for event biasing; and additions and improvements in geometry, physics processes and interactive capabilities

Progress in hadronic physics modelling in Geant4

Geant4 offers a set of models to simulate hadronic showers in calorimeters. Recent improvements to several models relevant to the modelling of hadronic showers are discussed. These include improved cross sections, a revision of the FTF model, the addition of quasi-elastic scattering to the QGS model, and enhancements in the nuclear precompound and de-excitation models. The validation of physics models against thin target experiments has been extended especially in the energy region 10 GeV and below. Examples of new validation results are shown.

GEANT4 Physics Lists for HEP

In GEANT4, a Physics List is a consistent set of physics models that is able to cover all combinations of incident particle type, energy, and target material. Various Physics Lists are possible and useful, according to the specific application domains (e.g. high-energy physics, shielding, space-application, medical physics, etc.), and the best compromise between accuracy and CPU time that the user can accept. Users are allowed to write their own preferred Physics List, but several pre-defined ones are available in GEANT4 for convenience, and indeed they are used by the large majority of users. We present here the Physics Lists that are of interest for high-energy physics applications.

Geant4 electromagnetic physics for high statistic simulation of LHC experiments

An overview of the current status of electromagnetic physics (EM) of the Geant4 toolkit is presented. Recent improvements are focused on the performance of large scale production for LHC and on the precision of simulation results over a wide energy range. Significant efforts have been made to improve the accuracy without compromising of CPU speed for EM particle transport. New biasing options have been introduced, which are applicable to any EM process. These include algorithms to enhance and suppress processes, force interactions or splitting of secondary particles. It is shown that the performance of the EM sub-package is improved. We will report extensions of the testing suite allowing high statistics validation of EM physics. It includes validation of multiple scattering, bremsstrahlung and other models. Cross checks between standard and low-energy EM models have been performed using evaluated data libraries and reference benchmark results.

A scalable DAQ system based on the DRS4 waveform digitizing chip

Many current and future experiments require the highest temporal resolution together with large numbers of channels in the data acquisition system (DAQ) for a minimum cost. The DRS4 waveform digitizing chip allows data sampling at up to 5 Giga-samples per second (GSPS) with high amplitude resolution. The domino wave sampling method offers a significant cost and power reduction compared to a traditional flash analog-to-digital converter (ADC). This work presents a new DAQ system based on the DRS4 chip that allows continuous digitization of analog signals at 120 Mega-samples per second (MSPS) with the possibility to sample a region of interest up to a rate of 5 GSPS, thereby allowing a long event record with small dead-time in the read-out. The signal-to-noise ratio (SNR) of the system is measured to be 9.3 bit for the 120 MSPS signal and 9.6 bit for the DRS4 readout signal. Arbitrarily complex trigger logic can be built entirely in the digital domain in the read-out field-programmable gate array (FPGA). A Gigabit Ethernet link provides high-speed connectivity from the DAQ board to the backend system. Built-in board-to-board communication and the modular design of the system offer great scalability and flexibility with respect to the number of supported data channels.

Parallel geometries in Geant4: Foundation and recent enhancements

The Geant4 software toolkit simulates the passage of particles through matter. It is utilized in high energy and nuclear physics experiments, in medical physics and space applications.

Fast neutron detection in homeland security applications

Calculations are presented to support the claim that fast neutron detection systems can achieve higher performance in detecting weak neutron sources than conventional thermal neutron detection systems involving moderators. Minimum Detectable Limits (MDL) are used as a comparative metric, more representative than the metric of absolute sensitivity, which does not take into account the influence of natural backgrounds. Monte Carlo simulations are used to show that heavily shielded neutron sources emit a substantial fraction of fast neutrons. Arguments are presented to support the claim that fast neutron detection systems are superior at defeating heavy neutron shielding than thermal systems.

New Geant4 model and interface developments for improved space electron transport simulations: First results

A review of Geant4 model and benchmark developments in the framework of an Electron Shielding project sponsored by ESA is presented. It includes extensions of electron ionisation models to lower energies, development of a new standard model of bremsstrahlung and a new angular generator of bremsstrahlung, and new standard models of Compton and Rayleigh scattering. New validation benchmarks have been developed for electron scattering and bremsstrahlung; also a simple benchmark tool has been developed for the GRAS tool. With the new benchmarks Geant4 simulation results can be compared with EGSnrc and Penelope predictions.

Gamma-insensitive fast neutron detector with spectral source identification potential

A neutron scintillation detector based on high-pressure 4He has been developed and tested. The detector responds to elastic scattering of unmoderated fast neutrons, preserving neutron energy, position, and timing information. Neutrons from three different sources, AmBe, 252Cf, and from the ambient background, have been measured with clearly distinct energy spectra. Exposing the detector to different levels of gamma radiation up to 1 mSv/h from a 60Co source has demonstrated that gamma exposure does not affect neutron detection performance within measurement statistics. Applications in the field of radiation portal monitoring are discussed.

The SAFIR project: an innovative high rate preclinical PET/MR detector towards dynamic multimodal imaging

SAFIR (Small Animal Fast Insert for mRi) is an innovative, high rate, PET detector insert for MRI, to be used for quantitative dynamic pre-clinical imaging, with very high activities injected in the animals, up to 500 MBq. The PET detector will be designed to allow for ultra short acquisition periods (of the order of a few seconds) simultaneously with the MRI, permitting unprecedented temporal resolutions in preclinical dynamic multimodal imaging. High sensitivity (~ 6%), high spatial resolution (~1.5 mm FWHM), excellent coincidence timing resolution (CTR ~ 300 ps FWHM) and a fast DAQ system able to cope with the huge data throughput are required. Parallel with the hardware efforts, dedicated 4D algorithms for image reconstruction must be developed. The overall state of the project will be presented, including ongoing activities towards the choice and characterization of the detector components (crystals, SiPMs and readout chips), MonteCarlo simulations, and first reconstruction of various simulated sources. Special emphasis will be given to the results of a recent high rate test, where the TOFPET ASIC has been tested with Hamamatsu S12642-0404PB-50 SiPM arrays coupled to matrices of LYSO:Ce crystals (3.1x3.1x12 mm3 each), exposed to a 500 MBq activity of FDG radiotracer in a volume of about 0.5 cm3.