Research Projects at the MAL Linac Facility
Nuclear Astrophysics p-Process Studies at the Madison Accelerator Laboratory
Principal Investigator:
Dr. Adriana Banu, Associate Professor, Department of Physics and Astronomy/JMU
The nuclear astrophysics program, currently under development at MAL, is focused on investigating experimentally ground-state photoneutron reaction rates and the respective cross sections of reactions on stable nuclei relevant to the p-process nucleosynthesis by employing the experimental photoactivation technique using bremsstrahlung photons.
Our objective is to compare to the experimental data determined at astrophysically relevant energies calculated ground-state reaction rates and cross sections in Hauser-Feshbach statistical reaction models. The goal here is to improve the knowledge of the dipole γ-strength functions. In turn, this will contribute to constraining the nuclear reaction statistical models and consequently will help put p-process nucleosynthesis calculations on a firmer ground.
The general experimental setup of photoactivation experiments, obviously limited to reactions where an unstable nucleus is produced, is fairly simple. A target sample (made of stable nuclei) is irradiated with bremsstrahlung photons. After the activation, the produced γ-ray activity is counted offline with a high-purity germanium (HPGe) detector, well-shielded against background.
Photoactivation studies using bremsstrahlung as real photon sources have been widely performed at conventional linear accelerators around the world, most notably at the superconducting Darmstadt linear electron accelerator S-DALINAC and at the superconducting electron accelerator ELBE of the Forschungszentrum Rossendorf. However, using an “off-the-shelf” medical linear electron accelerator, originally designed for clinical operations, and repurposing it for nuclear physics experiments is a novel idea.
Read more here about our first published results.
Archaeometry with Photon Activation Analysis (PAA) at the Madison Accelerator Laboratory
Principal Investigator:
Dr. Carole Nash, Associate Professor, Integrated Science and Technology (ISAT) of School of Integrated Sciences/JMU; Director, Shenandoah National Park Environmental Archaeology Program
Co-Principal Investigator:
Dr. Adriana Banu, Associate Professor, Department of Physics and Astronomy/JMU
This work, currently under development at MAL, exploits the idea that bremsstrahlung photons can induce short-lived radioactivity that can, in turn, be used to measure the elemental composition of archaeological specimens. Since this technique is non-destructive, it may prove extremely attractive to a broader “artifact” community, such as museum curators, historians, ancient art, etc.
Photon Activation Analysis (PAA) is a versatile non-destructive activation tool that provides high sensitivity for detecting the vast majority of the elements throughout the periodic table. The process of PAA entails exposing a sample with photons. As a result, many nuclei in the sample become activated and decay by emitting characteristic γ-ray radiations, which are the telltale signatures for identifying elements in the sample. They are measured with dedicated spectrometers such as high-purity Germanium detectors.
In the energy range covered by medical linear accelerators, two major nuclear processes are involved in the generation of activation products. The first one is the (γ,n) reaction, also called nuclear photoeffect. It involves the emission of a neutron from a nucleus hit by a photon of an energy that exceeds the nuclear binding energy of that nucleus. (The mean nucleon binding energy is about 8 MeV, depending on the mass of the nucleus.) The (γ,n) reaction will produce a nucleus situated one field to the left of the parent nucleus in the chart of nuclides, i.e., of the same element with the number of neutrons reduced by one. In most cases the nucleus will be a β+ emitter or decay by electron capture. The second nuclear process involved in PAA is the (n,γ) reaction, also called neutron capture, i.e., the absorption of a neutron by a nucleus, followed by the emission of the excess energy in the form of a photon. Here, neutrons are needed, which in the linac case are provided by previous (γ,n) reactions. The nucleus produced is located right from the parent nucleus in the chart of nuclides, and will be a β– emitter in most cases.
PAA is not an “absolute” method, as the samples under investigation must be irradiated along with a reference or calibrating material having a well-known elemental composition. The quantitative evaluation is performed through comparing the two resulting element spectra from the unknown sample and reference material.
PAA offers two key advantages as a research tool: it can probe materials that are difficult to treat chemically, and it is very well suited for investigating minute samples (sub-milligram) to very large ones (in the kilogram range.)
Read here about a recent review on principles, methodologies, and applications of photon activation analysis.
Archaeologists who work in Eastern North America, where soil moisture and acidity accelerate the decomposition of perishable material culture, rely on non-perishable items to understand the patterns of behavior of past Indigenous peoples. The archaeological record of the region consists largely of lithic (stone tools) and fired clay (low-fire ceramics) materials. In order to develop explanatory models of human settlement and interaction, which stretch across 15,000 years from the peoples of the continent to the complex chiefdoms that met European colonists four centuries ago, archaeologists are turning to non-destructive materials science. The archaeometric study of lithic and clay sourcing has expanded our understanding of trade and mobility among Indigenous communities. The opportunity to apply linear accelerator technology to archaeological research is exciting, and the capacity to do this at James Madison University opens new doors for student-faculty collaboration.
At James Madison University, archaeologists working in the Appalachian Mountains are using X-Ray Fluorescence (XRF) to identify and quantify the elemental composition of lithic artifacts. In tandem, we are preparing a companion database of compositions for rock outcrops that are hypothesized to be sources of the material. By matching the atomic fingerprint of artifacts to outcrops, a major question about cultural interaction and movement can be resolved. However, we have found in testing metasandstones of the region, a favored source for stone tools, that the high silica content of the rock makes it difficult to differentiate one source from another. As these outcrops extend for 100 kilometers and form the basis of a multi-millennial lithic technology, more precise elemental composition identification is needed.
It is hoped that the linear accelerator will provide this by enhancing the identification of trace elements that vary across outcrops. We are also interested in developing a testing protocol that will compare XRF test results for other lithic types (i.e. metarhyolite, jasper, soapstone) to those from the linear accelerator, as a comparison of the methodologies.
Evaluation of Oxides and Au-Supported Oxides as Potential Radiosensitizer Nanomaterials at the Madison Accelerator Laboratory
Principal Investigator:
Dr. Jessika Rojas, Associate Professor, Department of Mechanical and Nuclear Engineering/ Virginia Commonwealth University (VCU)
Co-Principal Investigator:
Dr. Adriana Banu, Associate Professor, Department of Physics and Astronomy/JMU
Radiation therapy is an important procedure for cancer treatment, nowadays up to 50% of the patients diagnosed with the disease will benefit from the use of radiation during their treatment. Nonetheless, there are some disadvantages associated with radiation therapy such as collateral damage to healthy tissue and resistance of cells to radiation. Therefore, current research is focused on targeted therapy strategies, aiming to improve the quality of life and comfort of the patients affected by the disease. Radiosensitization is one of these approaches, where nanomaterials are used to increase the sensitivity of the tumors to the effects of radiation.
This collaborative work aims to evaluate oxides and gold-supported oxides (Au@oxides) for their use as potential radiosensitizers.
Experimental Procedure: Nanomaterials such as ZnO, HfO2, Au@HfO2, Au@ZnO and Au@TiO2 were added in a concentration of 0.2 mg/ml to a 50 uM solution of Methylene Blue (MB), then the solutions were irradiated at MAL using a 6 MV X-rays, a dose rate of 8 Gy/min and an irradiation field of 10×10 cm. The MB degradation in the presence of the particles was analyzed by following the decrease of the characteristic absorbance of MB at 664 nm with a UV-Vis spectrophotometer.
Read more here about our first published results.
Oxides semiconductors and Au@oxides demonstrated great potential as radiosensitizers. The idea behind Au@oxides as radiosensitizers is based on the interaction of Au and oxides-semiconductors with ionizing radiation. Au interaction with X-rays leads to emission of photoelectrons, Compton and Auger electrons, as well as fluorescence photons. These species interact with the aqueous medium, increasing the radiation dose delivered to the dye. On the other hand, upon X-rays interaction semiconductors create electron hole-pairs that interact with the surrounding medium producing reactive oxygen species (ROS) causing accelerated dye degradation.
Future experiments at MAL will include radiosensitization testing of Au@oxides under different synthesis conditions, as well as the use of in water equivalent probe such as coumarin, in order perform pre-clinical studies that will enable the use of Au@oxides for future in-vivo and in-vitro experiments.