It has been reported that detectors made of lanthanum-cerium halides (LaBr3:Ce and CeBr3) have superior energy resolution for gamma-radiation detection compared to what is offered by conventional sodium iodide (NaI:T1) detectors. Although superior energy resolution may be observed, one major barrier that has hindered the rapid adaptation of lanthanum halides is their self-activity, due primarily to the presence of isotope 138La, and the α contamination, due to the trace amount of actinides. It has also been observed that the lanthanum-cerium halides contain a substantial amount of self-activity caused by the radioactive isotope 138La. Additionally, LaBr3:Ce spectra are also affected by β contaminations in the low-energy region. To use either LaBr3:Ce or CeBr3 for high-sensitivity gamma detection, it may be necessary to have the self-activity as well as α and β contaminations removed or reduced. This paper describes a novel algorithmic approach for self-activity and contamination reduction for LaBr3:Ce and CeBr3 detectors using a third reference NaI:T1 detector. We present a computational procedure for separating self-activity from the gamma spectra obtained by LaBr3:Ce detectors. With the self-activity spectra precalculated, it is possible to perform real-time self-activity removal. This procedure can be implemented as an automatic self-activity subtraction module for gamma-radiation detectors made of LaBr3:Ce and/or CeBr3 crystals. With this approach, it is possible to develop a new generation of LaBr3:Ce detectors capable of producing spectra as clean as those obtained by conventional NaI:T1 detectors, but with much improved energy resolutions.
Neutron flux from linear accelerators is conventionally monitored using ionization chambers containing one or
more foils thinly coated with a fissionable or fissile material. Due to the long pulse rise times resulting from the
ionization mechanism, fission chambers are prone to pulse pile-up in high-neutron-flux environments. In addition,
their relatively low efficiencies result in extremely long counting times in low-flux environments. To ameliorate
these effects, a novel type of neutron flux monitor, consisting of fissionable material loaded in a liquid scintillator,
has been developed, characterized, and tested in the beam line at the Los Alamos Neutron Science Center. This
is a rugged, cost-efficient detector with high efficiency, a short signal rise time, and the ability to be used in low
neutron-flux environments. Compared with a conventional fission chamber, the fissionable scintillator displays a
significantly higher event rate. Related research on nanocomposite scintillators for gamma-ray detection suggests
the possibility of extending this approach by synthesizing fissionable material nanoparticles and loading them
into an organic scintillator. We will present results of the design and characterization process and an analysis of
the results of the beam line experiments.
In recent years, composite scintillators consisting of nanosize inorganic crystals in an organic matrix have been
actively developed. Ideally these scintillators would have efficiency and resolution similar to inorganic crystals,
but at the same time would be inexpensive and easy to manufacture. In order to make composite scintillators
optically transparent, McKigney et al. finds that nanosize inorganic crystals should be used in order to reduce
optical scattering. One way to produce these nanosize inorganic crystals is through wet milling, where inorganic
crystals are ground with microsize beads in an organic solvent to achieve size reduction. Milling is relatively
simple in terms of preparation and equipment; however, milling is also known to introduce defects into the
ground material. Therefore, a new light yield measurement technique is developed to evaluate the degree to
which milling alters the light yield of the milled inorganic crystals. In this work, the light yield measurement
technique is applied to samples containing BaFCl:Eu inorganic crystals milled in a tributyl phosphate (TBP)
and cyclohexane mixture.
Nanocomposites may enable the use of scintillator materials such as cerium-doped lanthanum fluoride (LaF3:Ce) and
cerium bromide (CeBr3) without requiring the growth of large crystals. Nanostructured detectors may allow us to
engineer immensely sized detectors of flexible form factors that will have a broad energy range and an energy resolution
sufficient to perform isotopic identification. Furthermore, nanocomposites are easy to prepare and very low in cost. It is
much less costly to use nanocomposites rather than grow large whole crystals of scintillator materials; with
nanocomposites fabricated on an industrial scale, costs are even less. Nanostructured radiation scintillator detectors may
improve quantum efficiency and provide vastly improved detector form factors. Quantum efficiencies up to 60% have
been seen in photoluminescence from silicon nanocrystals in a densely packed ensemble. We have fabricated
nanoparticles with sizes <10 nm and characterized their nanocomposite radiation detector properties. This work
investigates the properties of the nanostructured radiation scintillator in order to extend the gamma energy response on
both low- and high-energy regimes by demonstrating the ability to detect low-energy x-rays and relatively high-energy
activation prompt gamma rays simultaneously using nanostructured lanthanum bromide, lanthanum fluoride, or CeBr3.
Preliminary results of this investigation are consistent with a significant response of these materials to nuclear radiation.
Evolution of c-axis oriented YBa2Cu3O7-y (YBCO) thin films under 200 MeV Ag ion irradiation at 79 K is studied by in-situ
temperature dependent resistivity and in-situ low temperature x-ray diffraction. The electronic energy loss (25.18
keV nm-1) of these ions is shown to induce secondary electrons, which create oxygen disorder selectively in the CuO
basal planes of fully oxygenated YBCO in a cylindrical region of radius 97 nm around the ion induced latent tracks of
radius 1.9 nm. This technique provides a unique way of creating oxygen disorder in a fully oxygenated YBCO, which
was not possible earlier.
The National Ignition Facility at Lawrence Livermore National Laboratory is the world's leading
facility to study the physics of igniting plasmas. Plasmas of hot deuterium and tritium, undergo
d(t,n)α reactions that produce a 14.1 MeV neutron and 3.5 MeV a particle, in the center of mass.
As these neutrons pass through the materials surrounding the hot core, they may undergo
subsequent (n,x) reactions. For example, 12C(n,n'γ)12C reactions occur in remnant debris from
the polymer ablator resulting in a significant fluence of 4.44 MeV gamma-rays. Imaging of these
gammas will enable the determination of the volumetric size and symmetry of the ablation; large
size and high asymmetry is expected to correlate with poor compression and lower fusion yield.
Results from a gamma-ray imaging system are expected to be complimentary to a neutron
imaging diagnostic system already in place at the NIF. This paper describes initial efforts to
design a gamma-ray imaging system for the NIF using the existing neutron imaging system as a
baseline for study. Due to the cross-section and expected range of ablator areal densities, the
gamma flux should be approximately 10-3 of the neutron flux. For this reason, care must be taken
to maximize the efficiency of the gamma-ray imaging system because it will be gamma starved.
As with the neutron imager, use of pinholes and/or coded apertures are anticipated. Along with
aperture and detector design, the selection of an appropriate scintillator is discussed. The volume
of energy deposition of the interacting 4.44 MeV gamma-rays is a critical parameter limiting the
imaging system spatial resolution. The volume of energy deposition is simulated with GEANT4,
and plans to measure the volume of energy deposition experimentally are described. Results of
tests on a pixellated LYSO scintillator are also presented.
The large fluence of 14-MeV neutrons produced in high-yield inertial confinement fusion (ICF) experiments creates a
variety of backgrounds in x-ray imagers viewing the implosion. Secondary charged particles produce background light
by Cherenkov emission, phosphor screen excitation and possibly scintillation in the optical components of the imager. In
addition, radiation induced optical absorption may lead to attenuation of the signal. Noise is also produced directly in the
image recorder itself (CCD or film) via energy deposition by electrons and heavy charged particles such as protons and
alphas. We will present results from CCD background measurements and compare them to Monte Carlo calculations. In
addition we show measurements of luminescence and long-term darkening for some of the glasses employed in imagers.
X-ray imaging is integral to the measurement of the properties of hot plasmas. To this end, a suite of gated x-ray imagers
have been developed for use in a wide range of experiments at the National Ignition Facility (NIF). These instruments
are sensitive to x-rays over the range of 0.7-90keV and can acquire images at 20ps intervals for source intensities
ranging over several orders of magnitude. We review the design, technology, and construction of these instruments and
present recent results obtained from NIF experiments in which gated x-ray imagers have played a key role.
The radiation environment associated with Inertial Confinement Fusion (ICF) experiments presents unique challenges
for x-ray imaging. We report on the performance of gated imagers that have been optimized for this harsh environment
and describe diagnostics to be deployed in the near future that will provide x-ray images of imploding ICF capsules in
the presence of backgrounds associated with neutron yields above 1016. Such images will provide crucial data that will
enable even higher neutron yields and successful ignition.
Currently there is a significant amount of interest in standoff radiation detection. One of the biggest challenges is to
separate small radiation signals from large varying background radiation. Many systems have been developed to address
this problem that rely on coded-aperture and/or Compton imaging. These imaging systems tend to be large, heavy,
complex, and therefore expensive. In this paper we report on the development of a self-occluding directional gamma
radiation sensor that is relatively small (<40 kg), inexpensive, and simple in design. Laboratory and field measurements
suggest that these sensors will work as well as the gamma imaging systems for many radiation detection applications at a
fraction of the cost, weight, and complexity. An azimuth can be resolved with a standard deviation of 7° in 10 seconds
for a source yielding 45 CPS at the detector in a 300 CPS background radiation field. This paper describes the self-occluding
quad NaI directional gamma radiation detector, the impact of gamma energy and distance on angular precision
and accuracy, and potential applications.
A compact neutron generator is being developed based on a novel coaxial dipole permanent magnet electron cyclotron
resonance (ECR) ion source. The ion source is capable of generating a high fraction of atomic ion species and can operate
at low pressure. Multiple deuterium ion (D+) beamlets are extracted from the plasma ion source and accelerated to a beam-loaded
titanium target creating 2.4 MeV neutrons as a result of the D-D fusion reaction at the target surface. This paper
describes the design of the ECR-based neutron generator as well as reports on preliminary simulation and experimental
results of the ion source performance.
The Calliope plant, a pool-type irradiation facility located at the Research Centre ENEA-Casaccia (Rome), is
equipped with the 60Co γ source in a high-volume shielded cell. Calliope facility is involved in radiation processing
research on materials (polymers and optical components) and on devices to be used in hostile radiation environment
such as nuclear plants, aerospace experiments and High Energy Physics experiments. The aim of this work is to give
an overall picture of the activity we are carrying on at our laboratories with a mention to the possible applications in
the field of scintillators and glasses, like doping effect to induce radiation resistance in scintillators, glasses for safe
nuclear fuel disposal, suitable substitute oxides which can replace PbO in the preparation of lead-free glasses
complying environmental regulations.
In this paper we describe a new nondestructive evaluation (NDE) technique called Compton Imaging Tomography (CIT)
for reconstructing the complete three-dimensional internal structure of an object, based on the registration of multiple
two-dimensional Compton-scattered x-ray images of the object. CIT provides high resolution and sensitivity with
virtually any material, including lightweight structures and organics, which normally pose problems in conventional
x-ray computed tomography because of low contrast. The CIT technique requires only one-sided access to the object,
has no limitation on the object's size, and can be applied to high-resolution real-time in situ NDE of large
aircraft/spacecraft structures and components. Theoretical and experimental results will be presented.
Polypropylene is irradiated by 6 MeV electrons in presence of Iodine and subsequently characterized by the techniques
such as weight gain, weight loss, Energy Dispersive Spectroscopy (EDS), Scanning Electron microscopy (SEM),
Ultraviolet Visible Spectroscopy (UV-Vis), Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray diffraction
(XRD). It is unambiguously observed that the electron beam assists the doping and trapping of volatile Iodine in
Polypropylene. Presence of the Iodine during irradiation strongly supports the radiation-induced decrease in the band gap
up to almost visible region. Further, the doped Iodine strongly interacts and decreases the crystalline structure of the
Polypropylene. It is also observed that the nanoclusters of Iodine having size around 100 nm are formed on the surface of
Polypropylene due to electron irradiation.
Passive and active detection of gamma rays from shielded radioactive materials, including special nuclear
materials, is an important task for any radiological emergency response organization. This article reports on the
current trends and status of gamma radiation detection objectives and measurement techniques as applied to
nonproliferation and radiological emergencies. In recent years, since the establishment of the Domestic Nuclear
Detection Office by the Department of Homeland Security, a tremendous amount of progress has been made in
detection materials (scintillators, semiconductors), imaging techniques (Compton imaging, use of active
masking and hybrid imaging), data acquisition systems with digital signal processing, field programmable gate
arrays and embedded isotopic analysis software (viz. gamma detector response and analysis software
[GADRAS]1), fast template matching, and data fusion (merging radiological data with geo-referenced maps,
digital imagery to provide better situational awareness). In this stride to progress, a significant amount of inter-disciplinary
research and development has taken place-techniques and spin-offs from medical science (such as
x-ray radiography and tomography), materials engineering (systematic planned studies on scintillators to
optimize several qualities of a good scintillator, nanoparticle applications, quantum dots, and photonic crystals,
just to name a few). No trend analysis of radiation detection systems would be complete without mentioning the
unprecedented strategic position taken by the National Nuclear Security Administration (NNSA) to deter,
detect, and interdict illicit trafficking in nuclear and other radioactive materials across international borders and
through the global maritime transportation-the so-called second line of defense.
To improve the resolution and field of view of high-energy Compton-scattered x-ray and gamma-ray imaging systems,
we have developed and tested apodized imaging optics based on apertures with depth-dependent cross sections
fabricated in an x-ray-absorbing material. Through ray-tracing modeling, we determined the optimum aperture shapes
(apodizations) that maximize the field of view and/or resolution of the system. Such apodized apertures can be used
either in single-aperture optics, or in coded-aperture arrays. Potential applications of this technology include
nondestructive evaluation (NDE) of materials and structures, in particular Compton imaging tomography (CIT), x-ray
and gamma-ray astronomy, and medical imaging.
X-ray imaging instruments will operate in a harsh ionizing radiation background environment on implosion experiments
at the National Ignition Facility. These backgrounds consist of mostly neutrons and gamma rays produced by inelastic
scattering of neutrons. Imaging systems based on x-ray framing cameras with film and CCD's have been designed to
operate in such harsh neutron-induced background environments. Some imaging components were placed inside a
shielded enclosure that reduced exposures to neutrons and gamma rays. Modeling of the signal and noise of the x-ray
imaging system is presented.
Silicon-based photodetectors offer several benefits relative to photomultiplier tube-based scintillator systems. Solid-state
photomultipliers (SSPM) can realize the gain of a photomultiplier tube (PMT) with the quantum efficiency of silicon.
The advantages of the solid-state approach must be balanced with adverse trade-offs, for example from increased dark
current, to optimize radiation detection sensitivity. We are designing a custom SSPM that will be optimized for green
emission of thallium-doped cesium iodide (CsI(Tl)). A typical field gamma radiation detector incorporates thallium
doped sodium iodide (NaI(Tl)) and a radiation converter with a PMT. A PMT's sensitivity peaks in the blue wavelengths
and is well matched to NaI(Tl). This paper presents results of photomultiplier sensitivity relative to conventional SSPMs
and discusses model design improvements. Prototype fabrications are in progress.