Author: Ranjini Unnikrishnan

Original story here by Laura Simmons.

The NRSB serves to organize and oversee studies on safety, security, technical efficacy and other policy and societal issues arising from the application of nuclear and radiation-based technologies. Dewji’s research focuses primarily on radiation protection and dosimetry and nuclear material assay for nuclear safeguards and security, making her an expert addition to the board.

Dewji is moderating the Fourth Gilbert W. Beebe Webinar: Health Effects from Chernobyl and Fukushima on April 7, hosted by the NRSB of the NASEM, which will feature presentations and discussions on radiation and nonradiation induced health effects to populations impacted by the accidents as well as potential transgenerational effects.

“Working with the NRSB is an invaluable opportunity to apply my diverse background and technical experience towards providing scientific leadership in technical and policy guidance applied to the safe and secure use of nuclear materials and technologies,” said Dewji.

Dewji is also the department’s only ADVANCE Scholar. The ADVANCE Scholars Program is Texas A&M’s unique faculty mentoring program designed to advance the success of tenure-track faculty who have been historically underrepresented in higher education. Scholars are able to engage in professional networking opportunities, develop a career plan, share with research experts in their field and heighten their professional visibility.

“I see great value in Dr. Dewji’s participation in this program by providing her the opportunity to access the academic and professional development experiences, which will clearly promote and support her personal and professional growth,” said Dr. Michael Nastasi, head of the nuclear engineering department.

Dewji leads a research laboratory as well, the Radiological Engineering, Detection and Dosimetry laboratory. Her team focuses on harnessing both computational capabilities in radiation transport modeling and experimental measurements using radiation detection for applications in radiation protection, dosimetry, health physics and nuclear materials accounting.

Three Center for Nuclear Security Science and Policy Initiatives (NSSPI) students have been selected for the National Nuclear Security Administration (NNSA) Graduate Fellowship Program (NGFP), including RED² graduate student, Audrey Nguyen. The NGFP is administered by Pacific Northwest National Laboratory and provides students with a year-long, salaried fellowship that offers training and practical experience in nuclear security and nonproliferation.

Nguyen is a Master of Science student working with Dr. Shaheen Dewji. Her research interests include dose quantification and modeling for emergency response following radiological or nuclear detonation events. Her current project involves using Monte Carlo techniques and source term fallout modeling, in conjunction with physiological models, to quantify radiation contamination and dose from uptakes in the eye. Nguyen earned her Bachelor of Science in radiological health engineering from Texas A&M with a minor in mathematics. Congratulations Audrey!

Read the full story about NSSPI students selected for this competitive opportunity on the NSSPI website (story here by K. Ragusa).

Written by Sena Dalak and Muruvet Kalay

Originally posted here authored by Laura Simmons. 

Dr. Shaheen Dewji, assistant professor in Texas A&M University’s Department of Nuclear Engineering, will participate in an expert panel webinar on January 21, 2021 hosted by the American Nuclear Society. The webinar, titled “Talking About Low-dose Radiation Risk,” will include a panel of five experts who will discuss how to communicate the risk of low-dose radiation to the general public.

Dewji is a faculty fellow for the Center for Nuclear Security Science and Policy Initiatives, where she oversees the Radiological Engineering, Detection and Dosimetry (RED²) research group. Her research interests include radiation protection and dosimetry, nuclear medicine, emergency response and defense, and Monte Carlo computational detector validation.

As Dewji will discuss with her colleagues, it is well known that high levels of radiation exposure can prove fatal or lead to the development of cancer. However, researchers are still trying to understand the effects of low-dose radiation on the human body. Americans are exposed to trace amounts of radiation every day, about half of which comes from natural background radiation from the Earth. The other half comes from medical, commercial and industrial sources such as x-ray examinations or the natural radiation in food. The small amounts of radiation that humans are exposed to have not been shown to cause any harm, but the data are still inconclusive.

The webinar will discuss the efforts of a sustained low-dose radiation research program and how to improve risk communications practices with the public. The panelists include Dr. Amir Bahadori from Kansas State University, Dr. Donald Cool from the Electric Power Research Institute, Dr. Paul Locke from Johns Hopkins University Bloomberg School of Public Health, and Mary Lou Dunzik-Gougar from Idaho State University and American Nuclear Society president.

Check out a double feature from RED² led by collaborators at the University of Florida‘s College of Medicine and Department of Biomedical Engineering. The two companion papers are published (ahead of print) in the journal, Physics in Medicine and Biology:

PAPER 1: Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal photon sources

Assessment of radiation absorbed dose to internal organs of the body from the intake of radionuclides or, in the medical setting through the injection of radiopharmaceuticals, is generally performed based upon reference biokinetic models or patient imaging data, respectively. Biokinetic models estimate the time course of activity localized to source organs. The time-integration of these organ activity profiles are then scaled by the radionuclide S value, which defines the absorbed dose to a target tissue per nuclear transformation in various source tissues. S values are computed using established nuclear decay information (particle energies and yields), and a parameter termed the specific absorbed fraction (SAF). The SAF is the ratio of the absorbed fraction (AF) – fraction of particle energy emitted in the source tissue that is deposited in the target tissue – and the target organ mass. While values of the SAF may be computed using patient-specific or individual-specific anatomic models, they have been more widely available through the use of computational reference phantoms. In this study, we report on an extensive series of photon SAFs computed in a revised series of the UF/NCI pediatric reference phantoms which have been modified to conform to the specifications embodied in the ICRP reference adult phantoms of Publication 110 (e.g., organs modeled, organ ID numbers, blood contribution to elemental compositions). Following phantom anatomical revisions, photon radiation transport simulations were performed using MCNPX v2.7 in each of the 10 phantoms of the series – male and female newborn, 1-year-old, 5-year-old, 10-year-old, and 15-year-old – for 44 different source and target tissues. A total of 25 photon energies were considered from 10 keV to 10 MeV along a logarithm energy grid. Detailed analyses were conducted of the relative statistical errors in the Monte Carlo target tissue energy deposition tallies at low photon energies and over all energies for source-target combinations at large intra-organ separation distances. Based on these analyses, various data smoothing algorithms were employed, including multi-point weighted data smoothing, and log-log interpolation at low energies (1 and 5 keV) using limiting SAF values based upon target organ mass to bound the interpolation interval. The final dataset is provided in a series of 10 electronic annexes in MS Excel format. The results of this study were further used as the basis for assessing the radiative component of internal electron source SAFs as described in our companion paper for this same pediatric phantom series.

PAPER 2: Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal electron sources

In both the ICRP and MIRD schemata of internal dosimetry, the S-value is defined as the absorbed dose to a target organ per nuclear decay of the radionuclide in a source organ. Its computation requires data on the energies and yields of all radiation emissions from radionuclide decay, the mass of the target organ, and the value of the absorbed fraction – the fraction of particle energy emitted in the source organ that is deposited in the target organ. The specific absorbed fraction (SAF) is given as the ratio of the absorbed fraction and the target mass. Historically, in the early development of both schemata, computational simplifications were made to the absorbed fraction in considering both organ self-dose (r_S=r_T) and organ cross-dose (r_S≠r_T). In particular, the value of the absorbed fraction was set to unity for all “non-penetrating” particle emissions (electrons and alpha particles) such that they contributed only to organ self-dose. As radiation transport codes for charged particles became more widely available, it became increasingly possible to abandon this distinction and to explicitly consider the transport of internally emitted electrons in a manner analogous to that for photons. In this present study, we report on an extensive series of electron SAFs computed in a revised series of the UF/NCI pediatric phantoms. A total of 28 electron energies – 0 to 10 MeV – along a logarithmic energy grid are provided in electronic annexes, where 0 keV is associated with limiting values of the SAF. Electron SAFs were computed independently for collisional energy losses (SAFCEL) and radiation energy losses (SAFREL) to the target organ. A methodology was employed in which values of SAFREL were compiled by first assembling organ-specific and electron energy-specific bremsstrahlung x-ray spectra, and then using these x-ray spectra to re-weight a previously established monoenergetic database of photon SAFs for all phantoms and source-target combinations. Age-dependent trends in the electron SAF were demonstrated for the majority of the source-target organ pairs, and were consistent to values given for the ICRP adult phantoms. In selected cases, however, anticipated age-dependent trends were not seen, and were attributed to anatomical differences in relative organ positioning at specific phantom ages. Both the electron SAFs of this study, and the photon SAFs from our companion study, are presently being used by ICRP Committee 2 in its upcoming pediatric extension to ICRP Publication 133.

Congratulations to RED² Ph.D. students, Ethan Asano and Alexander Perry for receiving the 2020-2021 Health Physics Society Fellowships. Both Asano and Perry jointed RED² in 2019, where both bring excellent and unique interests into their graduate careers and the RED² group. Asano, a student in the Center for Nuclear Security Science and Policy Initiatives (NSSPI), is investigating environmental decontamination in the event of a radiological release and involves the assessment of ground and surface contamination using experimental gamma-ray detector response validation with hybrid radiation transport simulations. Perry, a recipient of the J. Newell Stannard Health Physics Society Fellowship, is investigating machine learning applications in computational dosimetry.

Congratulations to both RED² students!

The American Nuclear Society (ANS) fosters professional development and educational advancement among the nuclear community, playing an especially important role in the development of the future generation of nuclear engineers. As an active member of the American Nuclear Society – Texas A&M University (TAMU) Student Branch and doctoral student in the Department of Nuclear Engineering, Alexander Perry was honored to be elected to the Executive Committee of the Radiation Protection and Shielding Division (RPSD). Completing his B.S. in Nuclear Engineering from TAMU and enrolling in their fast track Ph.D. in Nuclear Engineering, Mr. Perry states that “the faculty and staff in the [TAMU] Nuclear Engineering Department promoted involvement in [ANS], helping me attend and present research at my first national meeting during my undergraduate degree … and I have attended every meeting since then.” Furthermore, Mr. Perry claims that “unparalleled mentorship from my adviser, Dr. Shaheen Dewji, helped prepared me for this role.” As part of the Executive Committee, Mr. Perry’s responsibilities to the ANS RPSD involve assisting in the planning of topical meetings for the national conferences and aiding in the execution of the International Conference on Radiation Shielding. With research interests in dosimetry, radiation therapy, and machine learning, Mr. Perry hopes to provide unique perspectives to the organization while also expanding his own knowledge from the experts in radiation protection and shielding.

 

After completing her Master’s degree with an emphasis in radiation detection and nonproliferation, Sagadevan was keen on pursuing an education that focused on deterring the spread of nuclear weapons. NSSPI was at TAMU was a huge draw as it was the premier institute for this field. It is the first U.S. academic institution that focused on technical graduate education and research to safeguarding nuclear materials and the reduction of nuclear threats.

While at TAMU, Sagadevan had the opportunity to take classes in nuclear security, safeguards and policy that broadened her horizons and shaped her views on this topic under the supervision of her adviser and NSSPI Director, Dr. Sunil Chirayath. She also had the opportunity to intern at Oak Ridge National Laboratory and Los Alamos National Laboratory. “The education I received was beyond the classroom – for instance, to study the nuclear fuel cycle, I was sent to the UK (as a part of the nuclear field experience) to visit an enrichment plant, a fuel fabrication facility, a reactor, etc. Experiences like that translate to developing an immeasurable lifelong impact”, said Sagadevan. Armed with the knowledge and experience she has gained, Sagadevan wants to pursue a career in developing cutting edge technologies that can safeguard spent nuclear fuel. “This is a critical challenge that the world faces today, and I am in a position to help with that, thanks to my education at Texas A&M”.

Sagadevan’s journey in the American Nuclear Society started in 2014 when she joined as a national member. Since then she has been actively involved- She served as the Vice President for the ANS University of Michigan Student Chapter 2014 – 2015 where she oversaw community outreach and scholarships. She raised $12,000 for the student chapter to send 15 undergraduate students to the 2015 ANS Student Conference. Sagadevan has presented at student conferences and ANS meetings. In 2019, she was one of four who received the Diversity and Inclusion Award at the ANS Winter Meeting.

This year, Sagadevan has been elected as the Secretary for the Nuclear Nonproliferation Policy Division (NNPD) of ANS. She hopes to utilize this opportunity to improve and exploit her technical skills as well as develop her leadership skills to be well rounded. “I am excited to take on this role and look forward to promoting the peaceful use of nuclear technology through safeguards, security, and nuclear nonproliferation policies.” Sagadevan hopes to graduate with her PhD and work at a national lab where she can actively contribute to the development of safeguarding technologies.

Athena’s Linked In: www.linkedin.com/in/athena-sagadevan-  Email: athenaas92@tamu.edu

Congratulations to both students and we wish them both successful terms as future leaders of the American Nuclear Society!

Computational models of the human body for use in estimation of radiation dose have improved greatly with computational capabilities over the decades. Models have improved from simple geometric shapes representing the human body (#sphericalcow) to physiological models based on CT-based scans of actual humans. As advances have been made to more accurately model the behavior of radiation in more physiologically realistic models of the human body, the better these models can inform radiation regulation and better associate radiation risks and effects.

When conducting the update from the Environmental Protection Agency’s Federal Guidance Report No. 12: External Exposure to Radionuclides in Air, Water, and Soil (1993) to Report No. 15 (2019), Dr. Shaheen Dewji sought to quantify the differences between older generation mathematical stylized phantoms used in Report No. 15 with the latest models offered by the International Commission on Radiological Protection in their published voxel phantoms in Publication 110 and their pediatric counterparts. Results from Monte Carlo radiation transport simulations of a phantom submersed in an infinite cloud of gamma radiation demonstrated the differences in the stylized and voxel models, which were reported by Dr. Dewji and colleagues for the adult male, adult female, and pediatric series (newborn, 1-, 5-, 10-, 15-year old ages), highlighting limitations for differently defined organ sizes, organ resolution vis-a-vis the thickness of thin-walled organs smaller than the voxel resolution, and energy dependence of the source radiation to penetrate the body to reach internal organs. Dr. Dewji and TAMU RED² researcher, Thomas Cuthbert, under a scientific collaboration with the National Cancer Institute’s Division of Cancer Epidemiology & Genetics Radiation Epidemiology Branch scientists, Dr. Choonsik Lee and Keith Griffin, sought to quantify why these fundamental differences were observed. Overall, it was observed that the 100 keV-5 MeV range of gammas in the cloud yielded comparable results between the two phantom generations (within 5%-20%). But what were so different about these two generations of phantom models that explained variations in results (rather than just take them at face value)?

In their most recent publication, RED² and NCI investigated the guts of the details, literally. In their recently published investigation in the Journal of Physics in Medicine and Biology, “Stylized versus voxel phantoms: a juxtaposition of organ depth distributions,” simulations were conducted to quantify the organ depth distributions in each of the phantom models for adult and pediatric models, to determine the effect of organ depth distribution to the exterior surface of the body in 8 vector planes: antero-posterior, postero-anterior, left and right lateral, rotational, isotropic, cranial and caudal directions.

In essence: All models are wrong, some are useful… and more useful, if we are able to quantify our known unknowns.

Read the full details of his study here.

On January 13-15, 2020, Dr. Shaheen A. Dewji of the Department of Nuclear Engineering at Texas A&M University joined the esteemed American Nuclear Society (ANS) delegation to discuss the concept of “reasonableness” in the radiation protection philosophy of “ALARA” (As Low as Reasonably Achievable) at a workshop held by the Organization for Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA) in Lisbon, Portugal. The objective of this workshop, entitled, “NEA Workshop on Optimization: Rethinking the Art of Reasonableness”, was to identify a regulatory and practical approach for assessing radiological protection circumstances, and for developing, with appropriate stakeholder participation, the best radiological protection choices under the prevailing circumstances.  Workshop participants came from a wide variety of perspectives regarding effects of radiation exposure, radiation protection regulation and the implementation of that regulation from a selected invited group of international scientific and policy subject matter experts.

Radiological protection decisions are informed by science, but are based on judgement as to what level of protection is “reasonably achievable”. The science of radiological protection continues to evolve and advance, but seems not likely to quickly and definitively resolve the issue of what level of exposure can cause harm. However, the need to take radiological protection decisions remains, and input is needed to help to assure that protection choices are reasonable. Taking a broad view of assessing and balancing responses to the risks associated with any particular prevailing circumstance in practice can be very difficult to achieve.

The ANS delegation included past, present, and future ANS Presidents, in addition to esteemed subject matter experts in radiation protection sciences, regulation, and policy.

Under the supervision of Dr. Dewji, a series of curated case studies evaluating the application and interpretation of “reasonableness” were presented on each of the topics developed by Texas A&M Nuclear Engineering Undergraduate Students with selected subject matter experts from the American Nuclear Society:

Case 1: Appropriate Radiological Risk-Based Limitations for a Geological Repository Jordan Hillis (with Rob Hayes, NCSU; Jim Conca, UFA Ventures, Inc.; Alan Waltar, PNNL-Ret.)

Case 2: Safe Drinking Water Regulations Andrea Macias, Estefany Martinez (with Dan Stout, TVA)

Case 3: Implications of Evacuation at Fukushima Megan Frisbey, Alex de Rochemont (with Alan Waltar, PNNL-Ret.)

Case 4: Zahn’s Corner Middle School Closure Wyatt Smither, Morgan Ho (with Craig Piercy and John Starkey, ANS)

The presentation was prepared by Dr. Dewji and delivered to the Workshop audience on behalf of the ANS delegation by President Marilyn Kray. The ANS delegation is continuing to advance the discussion of “reasonableness” in the USA in the purview of resurrection of the Department of Energy Low Dose Research Program, which has impacts in all areas of Nuclear Engineering (power, public health, emergency response, defence, medicine, risk communication).

The workshop was organized by the NEA’s Committee on Radiological Protection and Public Health (CRPPH) event was hosted by the Service de Radiologie, Institut Portugais and held at the Portuguese Institute of Oncology.

Also in attendance were esteemed leadership from the NEA, Director General, William Magwood, IV, and Head of the Division of Radiological Protection and Human Aspects of Nuclear Safety, Yeonhee Hah.

Dewji (left) and Magwood (right).

Dewji (left) and Hah (right).