Characterization of a new external neutron beam facility at the Ohio State University

A thermal neutron beam facility has been designed and implemented at the Ohio State University Research Reactor. A project is underway to construct a large vacuum chamber such that the facility could have neutron depth profiling and neutron radiography capabilities as intended. The neutron beam is extracted from the reactor through a neutron collimator emplaced in Beam Port #2. The neutron spectrum entering the neutron collimator was unfolded from foil activation analysis results and also simulated with a full reactor core model in the MCNP Monte Carlo code. The neutron collimator uses polycrystalline bismuth as a gamma ray filter and single-crystal sapphire as a fast neutron filter. The beam is defined by multiple 3.0 cm diameter apertures made of borated aluminum. Characterization of the beam was performed using foil activation to find the flux and a low-budget neutron imaging apparatus to see the beam profile. The modulation transfer function was calculated to offer insight into the resolution of the imaging system and the collimation of the beam. The neutron collimator delivers the filtered thermal neutron beam with a ~4 cm diameter and a thermal equivalent flux of (1.27 ± 0.03) × 10⁷ n/(cm²s) at 450 kW power at the end of the collimator.     

Transient absorption measurement system using pulsed energetic ion

This article reports a highly sensitive transient absorbance measurement system using pulsed energetic ions. The ions were pulsed by a beam chopper, which was synchronized with the cyclotron, and accelerated to the desired energy around 18 MeV/u. H, He, C and Ne ions can be used for the transient absorption measurement. The optical system can measure an absorbance smaller than 1.0×10⁻⁴ in the wavelength range of 400–740 nm.     

Time-resolved spectroscopy at the picosecond laser-triggered electron accelerator ELYSE

ELYSE is a fast kinetics center created for pulse radiolysis with picosecond time-resolution. The facility is a 4–9 MeV electron accelerator using a subpicosecond laser pulse to produce an electron pulse from a Cs₂Te semiconductor photocathode and RF gun technology for the electron acceleration. The pulse duration is around 5 ps at low charge (<2 nC) and high energy (9 MeV), and is under routine conditions 10 ps at higher charge (5 nC) and >8 MeV. The dark current at the target is less than 1% of the pulse photocurrent.Time-resolved absorbance measurements in cells placed in front of the electron beam are achieved using pulsed laser diodes, or a xenon flash lamp as light sources, and photodiodes connected to a 3 GHz transient digitizer or a streak camera (250–800 nm range and 3.7 ps time resolution) as detection instruments. In addition, the synchronization between the laser beam and the electron beam is exploited to measure the absorbance by a pump-probe set-up, the pump being the electron pulse produced by the laser pulse, and the probe being part of the laser beam (120 fs–3 ps) delayed by a variable optical line.     

ESR study for ion beam induced phenomena in poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP)

Trapped radicals induced in poly (tetrafluoroethylene-co-hexafluoropropylene) (FEP) were observed by X-band electron spin resonance (ESR) spectroscopy at room temperature (RT) under atmospheric field after an irradiation with various kinds of high energy ion beams (6 MeV/u). The irradiation was carried out to a stacked FEP films under vacuum (<4E?4 Pa) at RT with various fluences from 1.0×10⁹ to 1.0×10¹¹ ions/cm². All ESR spectra indicated an existence of peroxy radicals in each of the FEP films without any relation to a kind of ion and a penetration depth. Obtained depth profiles of radical concentrations induced with each ion beam almost correspond to those of stopping power. The trapped radical concentrations were strongly dependent on stopping power. It was found that G-value of trapped radicals by ion beam irradiation was decreased with increasing a stopping power, and was less than the case of gamma-rays irradiation.     

Prompt Gamma Activation Analysis with the Texas Cold Neutron Source

A Prompt Gamma Activation Analysis (PGAA) facility is being developed at The University of Texas at Austin (UT). The UT-PGAA facility will utilize a focused cold-neutron beam from the Texas Cold Neutron Source (TCNS). the TCNS consists of a cold source cryostat and a curved neutron guide. the use of a guided focused cold-neutron beam will provide a high capture reaction rate and low background. The UT-PGAA facility will be used in the nondestructive determination of B, Cd, Gd and S in biological and environmental samples.     

A new SIMS paradigm for 2D and 3D molecular imaging of bio-systems

With the implementation of focused primary ion beams, secondary ion mass spectrometry (SIMS) has become a significant technique in the rapidly emerging field of mass spectral imaging in the biological sciences. Liquid metal ion guns (LMIG) offered the prospect of sub-100 nm spatial resolution, however this aspiration has yet to be reached for molecular imaging. This brief review shows that using LMIG the limitations of the static limit and low ionization probability will restrict useful imaging to around 2 μm spatial resolution with high-yield molecules. The only prospect of going beyond this in the absence of factors of 100 increase in ionization probability is to use polyatomic ion beams such as C₆₀⁺, for which bombardment induced damage is low. In these cases sub-micron imaging becomes possible, using voxels together with molecular depth profiling and 3D imaging. The discussion shows that conventional ToF-SIMS instrumentation then becomes a limitation in that the pulsed ion beam has a very low duty cycle which results in inordinately long analysis times, and pulsing the beam means that high-mass resolution and high spatial resolution are mutually incompatible. New instrumental configurations are described that allow the use of a dc ion beam and separate the mass spectrometry for the ion formation process. Early results from these instruments suggest that sub-micron analysis and imaging with high mass resolution and good ion yields are now realizable, although the low ion yield issue still needs to be solved.     

Uses of PGAA at the Dalat reactor

A facility for neutron capture prompt -ray spectroscopy for activation analysis has been intstalled at the tangential beam tube of the 500 kW Dalat reactor. Using a single crystal of silicon for filtering the thermal neutron beam and the 73 cm³ HP-G detector shielded by common materials with flexible configurations suitable to various samples, LOD of nearly 30 elements were estimated. Applications of PGAA in the determination of elemental concentrations in biological, environmental, geological and industrial product samples are presented.     

Xenon diffusion studies with prompt gamma activation analysis

Developing a better understanding of xenon transport through porous systems is critical to predicting how this gas will enter the atmosphere after a below ground nuclear weapons test. Radioxenon monitoring is a vital part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System. This work details the development of prompt gamma activation analysis for measuring the diffusion rates of xenon and argon gases through a porous medium. The University of Texas at Austin maintains a prompt gamma activation analysis facility with a peak neutron flux of ~1.5 × 10⁷ cm⁻² s⁻¹ and a beam diameter of 1 cm. Due to the relatively large prompt gamma cross sections of many stable xenon isotopes at thermal and sub-thermal neutron energies, prompt gamma activation analysis is a suitable technique for in situ non-destructive analysis of natural xenon. A test chamber has been designed and constructed to utilize prompt gamma activation analysis to measure xenon and argon diffusion through geological materials (e.g., sand, soil, etc.). Initial experiments have been conducted to determine the detection limits for stable gas measurements. The results from these experiments will be utilized to benchmark parts of a xenon transport model that is being used to determine diffusion coefficients for xenon and argon.     

Investigation of the near surface region of chemically treated and Al-coated PMMA by Doppler-broadening spectroscopy

The positronium formation is studied in the near surface region of Polymethylmethacrylate (PMMA), which was treated with isopropanol and acetone by energy dependent Doppler-broadening spectroscopy. In addition, the variation of Ps-formation was investigated at aluminium-coated PMMA. The coincident DB (CDB) spectra reveal the fraction of positrons, which annihilate in the aluminium. All measurements were performed with mono-energetic positrons up to an energy of 31 keV at the CDB-spectrometer at the new positron beam facility NEPOMUC at FRM II.     

Activation analysis opportunities using cold neutron beams

Guided beams of cold neutrons being installed at a number of research reactors may become increasingly available for analytical research. A guided cold beam will provide higher neutron fluence rates and lower background interferences than in present facilities. In an optimized facility, fluence rates of 10⁹ n·cm^–2·s^–1 are obtainable. Focusing a large area beam onto a small target will further increase the neutron intensity. In addition, the shift to lower neutron energy increases the effective cross sections. The absence of fast neutrons and gamma rays permits detectors to be placed near the sample without intolerable background, and thus the efficiency for counting prompt gamma rays can be much higher than in present systems. Measurements made at the hydrogen cold source of the FRJ-2 (DIDO) reactor at the KFA provide a numerical evaluation of the improvements in PGAA with respect to signal-to-background ratios of important elements and matrices.     

A concept of a scanning positron microscope

The concept of a scanning positron microscope which is under construction in München and Trento will be shown. A beam with a variable energy from 1 to 30 keV and a spot diameter of 1 m, which can be scanned over an area of (0.6×0.6) mm², is formed after a double stage stochastic cooling of the positrons emitted from a radioactive source. Additionally, the beam will be pulsed to have a well-defined time base for positron lifetime measurements. The design of the microscope is dominated by special demands of positron physics. Therefore, the microscope contains electron optical elements which are well known but rarely used. These are the through the lens reflection remoderator and the optical column with a magnetic side gap lens as probe forming lens.     

Fundamental data to be obtained with the Los Alamos Fourier Transform Spectrometer

The characteristics and capabilities of the Los Alamos National Laboratory Fourier Transform Spectrometer (FTS) Facility are presented. The FTS is briefly described, including design parameters and specifications. Preliminary experiments are being carried out in a spectral window in the visible with extension into the u.v. and i.r. to be achieved in the near future. The type of fundamental data that will be obtained with the FTS facility is discussed, as well as the areas for future research.     

Comparison of experimental and computational neutron spectroscopy at a 14 MeV neutron generator facility

At any neutron production facility, the energy spectrum at any meaningful distance from the target will be modified. For the case of a facility used to provide reference irradiations of electronics and other devices at various target-to-device distances it is important to have knowledge of these spectral modifications. In addition, it is desirable to have the ability to generate near real-time measurement capability. Advances in neutron metrology have made it possible to determine neutron energy spectra in real time to high levels of accuracy. This paper outlines a series of experimental measurements and theoretical calculations designed to quantify the scattering effects for a 14 MeV neutron generator facility, and makes appropriate recommendations for near real-time measurements of these fields.     

An external helium flushed milli-beam for combined PIXE and PIGE analysis

A helium flushed external beam PIXE/PIGE facility for nondestructive multielemental analysis has been developed and tested. By using proton energies E_p4.1 MeV and simultaneous detection of X- and gamma-rays, nearly complete analysis of all elements is achieved with nondestructively low ion current of I_p1 nA (except H, He, C, O and Ne are detected in a single measurement with sensitivities from the ppm level to about one percent). For most of the elements there are at least two channels of identification, which is a special advantage in analyzing unfavourable matrices, where the radiations of certain elements may interfere with each other.     

Low-Flux NAA Applications at the Savannah River Site

Neutron activation analysis using low-flux isotopic neutron sources is put to use in addressing areas of applied interest in managing the Savannah River Site. Some of the applications are unique due the site's operating history and its chemical processing facilities. Because sensitivity needs for many of the applications are not severe, they can be accomplished using a 6 mg ²⁵²Cf neutron activation analysis facility. Overviews of the facility and several example applications are presented.     

The new prompt gamma-activation analysis facility at Budapest

Prompt gamma-activation analysis (PGAA) is an important complementary technique to conventional instrumental activation analysis that can be successfully used in a number of cases when INAA is not applicable. Therefore, a PGAA facility has been constructed at the recently refurbished and upgraded Budapest Research Reactor. It occupies the end position of a new curved themal guide of 30 m length and 2.5×10 cm² cross section which provides a clean beam of low energy neutrons. The sophisticated HPGe-BGO -ray spectrometer system can be operated in Compton-suppression and pair-spectrometer modes simultaneously. The octal splitting of the main BGO improves efficient pair mode operation when coincidences between pairs of opposite segments and the HPGe detector are required separately. Gamma-gamma coincidence measurements will also be possible when the new multiparameter data acquisition system is completed. One of the main tasks at the new facility will be the accumulation of new spectroscopic data for detector calibration and standardisation, as well as for the construction of a more accurate prompt -ray library for the chemical elements. Various applications are planned, such as the determination of hydrogen in fullerenes and of toxic trace elements in environmental samples.     

Frederick Thomas Trouton: The Man, the Rule, and the Ratio

Trouton was a multifaceted theoretician and experimentalist who left his name in several fields. Here, his many contributions to science are described and analyzed with particular emphasis on Troutons rule and its further development, his contributions to rheology (Troutons ratio), and the famous Trouton—Noble experiment, which is related to the absolute movement of the Earth through the æether.Chemists and chemical engineers are familiar with Trouton through the rule that carries his name. Troutons rule states that at the normal boiling temperature the entropy of vaporization is constant. They are generally unaware of his rich contributions in other scientific areas, such as rheology, osmotic pressure, and physics. Here we describe his personal life and career, his scientific achievements, and, in particular, how his rule has been further developed by others.     

Environmental radiation detected at Lin Shin hospital in Taichung during the Fukushima nuclear power plant accident

This work is the first evaluation of environmental gamma exposure rates by the Nuclear Medicine Department at Lin Shin Hospital (LSH) in Taichung with Thermoluminescent dosimeter (TLD-100H) during the Fukushima Nuclear Power Plant (FNPP) accident. After the 9.0 M_W strong earthquake hit northern Japan on March 11, 2011, a TLD-100H was used to monitor environmental kerma rate at Taichung (2,500 km away from northern Japan) from Mar-08 to Apr-09, 2011 and evaluated kerma rate due to global fallout of the sever FNPP accidents. Exposure rates varied widely among positions close to the PET/CT facility. Observed kerma rates of up to 4.12 ± 0.62 mSv mo⁻¹ indicated an explicit, heavy leakage of photon through the PET/CT facility. No significant contributions were detected at Taichung, Taiwan. Hence, the health effect cause by the “extra radiation” from FNPP accidents is negligible. As this was a rare case of environmental monitoring during a nuclear power plant accident, its findings are of considerable significance.     

In vivo activation analysis of organ cadmium using the Tsing Hua Mobile Educational Reactor

This work describes a nuclear facility forin vivo prompt gamma activation analysis (IVPGAA) using a moderated neutron beam from a 0.1 W Tsing-Hua Mobile Educational Reactor (THMER). The IVPGAA measurement is a new technique for toxic cadmium determination in organs, which can efficiently be used in clinical diagnosis. The low-power nuclear reactor provides a total neutron flux of 3.3·10⁴ n·cm^–2·s^–1 on the surface of the central vertical neutron beam tube to which a liquid phantom is positioned. The capability of such partial-body irradiation facility is demonstrated. The detection limit of cadmium in the left kidney for a skin dose equivalent of 1.66 mSv (166 mrem) was 1.34 mg in a 500-s irradiation/counting period, and the sensitivity in the left kidney was 103 counts mg^–1·mSv^–1. The performance of IVPGAA system using the THMER nuclear facility therefore has the advantages of mobility and feasibility with high sensitivity under low neutron and gamma doses.     

Efficient non-gated remote filament-induced breakdown spectroscopy of metallic sample

Remote filament-induced breakdown spectroscopy (R-FIBS) is a novel technique that could be applied at long distance up to a few kilometers. Our work demonstrates that by creating short and strong filaments in the atmosphere with a telescopic beam delivering system, continuum background in R-FIBS spectrum will be significantly reduced. This allows for a non-gated R-FIBS configuration for identifying solid targets. As an example, we used an aluminum plate located 50 m away from our detection system. The obtained fingerprint spectrum is so strong that the detection limit could reach 1.9 km in distance and ppm level in terms of minor element concentration.