Detection of special nuclear materials (SNMs) is of vital importance in the prevention of nuclear terrorism and to secure states' national security. Neutron detection is a particularly useful tool to identify SNM, and neutron-sensitive scintillators have many promising properties, such as ease of use, good time resolution, and high detection efficiency. In this work, we develop highly stable, self-oriented, ultrafast 1D ZnO:Li (and codoped with Al, Ga, and In) nanorods (NRs) as thermal neutron-sensitive scintillators. Lithium-6 has high thermal neutron cross section for the (n, α) reaction in ZnO:Li scintillators which have a vertical nano array design greatly increasing the effective surface area and scintillation efficiency. Cost-effective low-temperature (95 °C) hydrothermal growth is used to obtain highly crystalline ZnO:Li nano scintillators by combining nuclear range data and electron transport mechanisms. Among the studies using low-temperature hydrothermal synthesis and a relatively low annealing temperature (≈350 °C) along with optimized NRs (length ≈ 5-8 μm, mean diameter ≈ 700 nm) for thermal neutron detection, this study reports the shortest scintillation decay time (≈ 470 ps) so far to the best of our knowledge. This nano array scintillator combines the advantages of a low-cost growth technique with environmentally friendly and widely available materials.

Abstract We report the photon (PL), electron (CL) and X-ray (XEL) induced luminescence characteristics of high aspect ratio ultra-long (~ 50 µm) ZnO nanorods (NRs) and discuss the potential for fast X-ray detection based on the consistent and efficient visible emission (~ 580 nm) from ZnO NRs. Nanostructured ZnO scintillators were rearranged to form a vertically well-aligned NR design in order to help light absorption and coupling resulting in luminescent and fast scintillation properties. The design of the nanorod array combines the key advantages of a low-cost growth technique together with environmentally friendly and widely available materials. A low temperature hydrothermal method was adopted to grow ZnO NRs in one cycle growth and their structural, optical and X-ray scintillation properties were investigated. The relatively short (~ 10 µm) ZnO NRs emitting in the near-band-edge region were found to be almost insensitive to X-rays. On the other hand, the higher XEL response of long ZnO NRs, which is a key parameter for evaluation of materials to be used as scintillators for high quality X-ray detection and imaging, along with a decay time response in the order of ns confirmed promising scintillation properties for fast and high-resolution X-ray detector applications.

The study of One Million U.S. Radiation Workers and Veterans, the Million Person Study (MPS), examines the health consequences, both cancer and non-cancer, of exposure to ionizing radiation received gradually over time. Recently the MPS has focused on mortality patterns from neurological and behavioral conditions, e.g., Parkinson’s disease, Alzheimer’s disease, dementia, and motor neuron disease such as amyotrophic lateral sclerosis. A fuller picture of radiation-related late effects comes from studying both mortality and the occurrence (incidence) of conditions not leading to death. Accordingly, the MPS is identifying neurocognitive diagnoses from fee-for-service insurance claims from the Centers for Medicare and Medicaid Services (CMS), among Medicare beneficiaries beginning in 1999 (the earliest date claims data are available). Linkages to date have identified ∼540,000 workers with available health information. Such linkages provide individual information on important co-factor and confounding variables such as smoking, alcohol consumption, blood pressure, obesity, diabetes and many other health and demographic characteristics. The total person-level set of time-dependent variables, outcomes, organ-specific dose measures, co-factors, and demographics will be massive and much too large to be evaluated with standard software. Thus, development of specialized open-source software designed for large datasets (Colossus) is nearly complete. The wealth of information available from CMS claims data, coupled with individual dose reconstructions, will thus greatly enhance the quality and precision of health evaluations for this new field of low-dose radiation and neurocognitive effects.

The materials which compose the ICRP Voxel phantoms used in the computation of conversion coefficients involve neutron interaction cross-sections that have resonances at specific energies. Depending on the energy bin structure used in the computations, these cross-section resonances may occur at energies that fall between energies at which dose coefficients are computed, thus their effects may not be completely accounted for in the reported coefficients. In the present study, a highly refined energy grid that closely follows the resonance structure in the phantom material cross-sections was identified and used to calculate dose coefficients. Both the equivalent organ/tissue doses for male and female voxel phantoms were computed as well as their summation to obtain the effective dose coefficients. The used refined energy grid tracks very closely the cross-sections in the vicinity of the resonances. The resulting refined energy grid coefficients are compared to coefficients for the coarser energy grid used in ICRP Publication 116. Additionally, reference spectra have been folded with both the fine and coarse sets of conversion coefficients. The resulting total effective doses for these reference spectra are used to assess the adequacy of the dose coefficients calculated on the original ICRP 116 energy grid. The dose coefficients were similarly computed for the local skin dose on the trunk of the body using the ICRU Report 95 phantom. The overall impact of the resonances on the organ/tissue equivalent dose, the effective dose, and the local skin dose are presented and discussed. In general, it was found that resonances can impact neutron dose coefficients, but in most cases the wide range of neutron energies encountered minimized this effect. The impact of resonances was further limited when computing effective dose due to organ/tissue summing and sex-averaging. For the neutron fields studied here, the impact was below 5%.

Abstract Organ dosimetry data of the atomic bomb survivors and the resulting cancer risk models derived from these data are currently assessed within the DS02 dosimetry system developed through the Joint US–Japan Dosimetry Working Group. In DS02, the anatomical survivor models are limited to three hermaphroditic stylized phantoms—an adult (55 kg), a child (19.8 kg), and an infant (9.7 kg)—that were originally designed for the preceding DS86 dosimetry system. As such, organ doses needed for assessment of in-utero cancer risks to the fetus have continued to rely upon the use of the uterine wall in the adult non-pregnant stylized phantom as the dose surrogate for all fetal organs regardless of gestational age. To address these limitations, the Radiation Effects Research Foundation (RERF) Working Group on Organ Dose (WGOD) has established the J45 (Japan 1945) series of high-resolution voxel phantoms, which were derived from the UF/NCI series of hybrid phantoms and scaled to match mid-1940s Japanese body morphometries. The series includes male and female phantoms—newborn to adult—and four pregnant female phantoms at gestational ages of 8, 15, 25, and 38 wk post-conception. In previous studies, we have reported organ dose differences between those reported by the DS02 system and those computed by the WGOD using 3D Monte Carlo radiation transport simulations of atomic bomb gamma-ray and neutron fields for the J45 phantoms series in their traditional “standing” posture, with some variations in their facing direction relative to the bomb hypocenter. In this present study, we present the J45 pregnant female phantoms in both a “kneeling” and “lying” posture and assess the dosimetric impact of these more anatomically realistic survivor models in comparison to current organ doses given by the DS02 system. For the kneeling phantoms facing the bomb hypocenter, organ doses from bomb source photon spectra were shown to be overestimated by the DS02 system by up to a factor of 1.45 for certain fetal organs and up to a factor of 1.17 for maternal organs. For lying phantoms with their feet in the direction of the hypocenter, fetal organ doses from bomb source photon spectra were underestimated by the DS02 system by factors as low as 0.77, while maternal organ doses were overestimated by up to a factor of 1.38. Organs doses from neutron contributions to the radiation fields exhibited an increasing overestimation by the DS02 stylized phantoms as gestational age increased. These discrepancies are most evident in fetal organs that are more posterior within the mother’s womb, such as the fetal brain. Further analysis revealed that comparison of these postures to the original standing posture indicate significant dose differences for both maternal and fetal organ doses depending on the type of irradiation. Results from this study highlight the degree to which the existing DS02 system can differ from organ dosimetry based upon 3D radiation transport simulations using more anatomically realistic models of those survivors exposed during pregnancy.

During the early response to large-scale radioactive contamination events, people who are potentially affected need to be screened for radioactive contamination and public health staff need to triage individuals who may need immediate decontamination. This is typically done by screening individuals for external contamination using ionising radiation detection equipment. In this study, spatially and temporally dependent isotopic compositions from a simulated nuclear detonation and Monte Carlo methods were used to relate contamination activity levels to the measurable radiation levels at select distances away from an individual with whole-body contamination. Radionuclide-specific air kerma rate coefficients and Geiger-Mueller instrument response coefficients at five select distances from contaminated individuals are presented for 662 radionuclides. Temporally and spatially dependent incident-specific coefficients are presented for a hypothetical surface detonation of a 235U-fueled device.

ZnO nanoarrays were grown via a low-temperature hydrothermal method. Solutions, each with different additive combinations, were prepared and evaluated. The effects of the additives involved in the growth procedure, i.e., ammonium hydroxide and sodium citrate, were studied in terms of the morphological, optical and scintillation properties of the ZnO nanostructures. Measurement of the nanorod (NR) length, corresponding photoluminescence (PL) and scintillation spectra and their dependence on the additives present in the solution are discussed. ZnO NRs grown on a silica substrate, whose UV transmission was found to be better than glass, showed high-quality structural and optical properties. It was found that the addition of sodium citrate significantly reduced defects and correspondingly increased the intrinsic near-band-edge (NBE) UV emission intensity at ~380 nm. To obtain high-quality nanostructures, samples were annealed in a 10% H2 + 90% N2 atmosphere. The anneal in the forming gas atmosphere enhanced the emission of the UV peak by reducing defects in the nanostructure. NRs are highly tapered towards the end of the structure. The tapering process was monitored using time growth studies, and its effect on PL and reflectance spectra are discussed. A good alpha particle response was obtained for the grown ZnO NRs, confirming its potential to be used as an alpha particle scintillator. After optimizing the reaction parameters, it was concluded that when ammonium hydroxide and sodium citrate were used, vertically well-aligned and long ZnO nanoarrays with highly improved optical and scintillation properties were obtained.

A significant source of information on radiation-induced biological effects following in-utero irradiation stems from studies of atomic bomb survivors who were pregnant at the time of exposure in Hiroshima, and to a lesser extent, from survivors in Nagasaki. Dose estimates to the developing fetus for these survivors have been assigned in prior dosimetry systems of the Radiation Effects Research Foundation as the dose to the uterine wall within the non-pregnant adult stylized phantom, originally designed for the dosimetry system DS86 and then carried forward in DS02. In a prior study, a new J45 (Japanese 1945) series of high-resolution phantoms of the adult pregnant female at 8 weeks, 15 weeks, 25 weeks, and 38-weeks post-conception was presented. Fetal and maternal organ doses were estimated by computationally exposing the pregnant female phantom series to DS02 free-in-air cumulative photon and neutron fluences at three distances from the hypocenter at both Hiroshima and Nagasaki under idealized frontal (AP) and isotropic (ISO) particle incidence. In this present study, this work was extended using realistic angular fluences (480 directions) from the DS02 system for seven radiation source terms, nine different radiation dose components, and five shielding conditions. In addition, to explore the effects of fetal position within the womb, four new phantoms were created and the same irradiation scenarios were performed. General findings are that the current DS02 fetal dose surrogate overestimates values of fetal organ dose seen in the J45 phantoms towards the cranial end of the fetus, especially in the later stages of pregnancy. For example, for in-open exposures at 1000 m in Hiroshima, the ratio of J45 fetal brain dose to DS02 uterine wall dose is 0.90, 0.82, and 0.70 at 15 weeks, 25 weeks, and 38-weeks, respectively, for total gamma exposures, and are 0.64, 0.44, and 0.37 at these same gestational ages for total neutron exposures. For organs in the abdominal and pelvic regions of the fetus, dose gradients across gestational age flatten and later reverse, so that DS02 fetal dosimetry begins to underestimate values of fetal organ dose as seen in the J45 phantoms. For example, for the same exposure scenario, the ratios of J45 fetal kidney dose to DS02 uterine wall dose are about 1.09 from 15 to 38 weeks for total gamma dose, and are 1.30, 1.56, and 1.75 at 15 weeks, 25 weeks, and 38 weeks, respectively, for the total neutron dose. Results using the new fetal positioning phantoms show this trend reversing for a head-up, breach fetal position. This work supports previous findings that the J45 pregnant female phantom series offers significant opportunities for gestational age-dependent assessment of fetal organ dose without the need to invoke the uterine wall as a fetal organ surrogate.

A radiation workforce of sufficient size and capacity is necessary to meet our nation’s current and future needs for energy production, health care, and other vital areas. Over the long term, workforce shortages have the potential to compromise our nation’s capabilities in these strategic sectors and, if sustained, would result in degradation of economic competitiveness and national security. In 2015,a multidisciplinary team began reviewing a selection of professional radiation workforces in the United States with the goal of developing a resource that would contain information of relevance to employers, policy makers, educational institutions, students contemplating radiation-related careers, and the public. This approach was taken because ionizing radiation is used for a wide array of applications, and these frequently involve multidisciplinary teams. Indeed, the various radiation disciplines comprise a synergistic ecosystem,with many interdependencies,and this motivated us to review disciplines individually, as well as in the context of the larger multidisciplinary ecosystem. The team members were drawn from those professions that are chiefly responsible for the radiation protection of workers, patients, and the public: health physics, medical physics, medicine (including diagnostic radiology, interventional radiology, nuclear medicine, and radiation oncology), nuclear engineering, radiation biology, and radiochemistry and nuclear chemistry. Due to practical considerations, this selection was limited; nonetheless, the authors emphasize the importance of other worker cohorts, including technologists who work in medical radiation therapy and imaging, and radiation epidemiologists and ecologists, who draw on the basic sciences of physics, chemistry, mathematics, and biology and play a significant role in radiation protection. It is hoped that these and other groups will be considered in future works. The methods used to prepare this review included surveying relevant information on each workforce,using data from the literature and other resources, such as information from professional societies. All data were evaluated by teams of subject matter experts, comprised of leaders in each of the respective professions. However, it must be emphasized that some of the professions have few to no means of surveilling their

Health physics is an applied science field focused on the protection of workers, patients, the general public, and the environment from ionizing and nonionizing radiation sources. The role of the health physicist (HP), and the recognition of health physics as a distinct field, may be traced to the advent of nuclear power and its application after the Manhattan Project in the 1940s. The field grew steadily in size to meet the growing uses of nuclear technology until reaching a peak in the mid-1990s.1 Subsequent shrinkage has been attributed mainly to attrition due to retiring baby boomers, a chronic decline in the number of replacement workers emerging from health physics education programs, and a reduced demand for health physics work in the nuclear power industry. Workforce shortages have been predicted,2, 3 although not confirmed in the literature. The discipline of health physics is devoted to the protection of people and their environment from the harmful effects of ionizing and nonionizing radiation while enabling its beneficial uses. Broadly, health physics may be considered an allied health profession with a diverse scope of practice, including essential activities in medicine, research, industry, education, emergency preparedness, radioactive waste management, environmental protection, regulation, and many other niche fields, such as radiation protection for national defense, civil aviation, and spaceflight. The International Labour Organization has recognized health physics professionals as radiation protection experts,4 and several radiation protection organizations, such as the Health Physics Society (HPS)5 and the International Radiation Protection Association, have articulated the basic aspects of the profession.6 The exact size of the domestic professional health physics workforce has been estimated at 3200 and 7000 persons, depending on the definition used for HP and other factors. It is common for professionals from other radiation and nuclear disciplines, as well as industrial hygienists, to hold health physics positions. In 2004, the HPS estimated that ∼6700 radiation protection professionals are involved in radiation safety activities in the United States, with as many as 50% of these individuals being in activities associated with nuclear energy production.7 A later article from the Bureau of Labor Statistics in 2011 referenced an HPS estimate of the health physics workforce as being "more than 6500." 8 The Oak Ridge Institute for Science and Education estimated that 4800 HPs were employed in the United States in 2009 (excluding medical facilities and other industries). "Based on very rough estimates," another 2000 HPs may be employed in medical and health-care facilities and other industries.9 Limited data are available on the variation of professional qualifications of radiation protection staff employed in the United States. For example, a survey by the Nuclear Energy Institute of all nuclear electric-generating stations in the United States revealed that only 10% of 3800 radiation protection staff (including permanent and temporary, as well as professional and other types) required a 4-year college degree in health physics or a related field. Only the position of RPM (HP) at each facility required a 4-year degree (there are methods available to obtain the equivalent of a degree to satisfy this requirement) and a minimum of 5 years of experience, including 3 years of nuclear power plant experience directly related to the radiation protection program.10 The DOE's National Laboratories and its contractors have a total of ∼400 full time professional HPs employed at their facilities; these positions generally require a 4-year degree in health physics or a related discipline. These data of professional requirements should be interpreted with caution because they are based on limited data. Neither the U.S. Department of Labor nor the Census Bureau collects employment data specifically for HPs but includes them in the broader category of physicists. Data are available on the distribution of the health physics workforce by worker age, with over 50% of the HPS members being over 50 years of age, and with many planning to retire within 10 years.1, 11 Thus, many workers are close to, or already eligible for, retirement. The exact numbers of practicing HPs is not available, but the membership size of HPS (3100 in 2020) and the number of holders of board certification (1300) provide surrogate data. The HPS membership has decreased by 14% since 2003; this has been mainly attributed to a wave of retiring baby boomers and a comparatively small number of replacements entering the profession. Interestingly, over the same time period, the number of board-certified health physicists has remained constant, that is, with ∼1300 holders of certificates from the American Board of Health Physics (ABHP). The decline in membership in the HPS is more severe than in societies of closely related professions; for example, the membership of the American Nuclear Society shrank by only 5% over the past 15 years.1 The current declared membership of HPS of ∼3100 is likely an underestimate, as not all HPs are members of the HPS.12 Health physics is an applied branch of physics that is highly multidisciplinary (see Section 2.2). HPs enter the profession through traditional degree programs in health physics or a variety of alternate pathways. The educational entry pathways vary considerably with subspecialty, employer, and job responsibilities. As defined in Section 2.2, all types of professional HPs require at least a BS degree or higher in health physics or related science, with some positions requiring an MS or PhD degree. The Accreditation Board for Engineering and Technology (ABET) provides standards for higher education. The ABET health physics standards for education outcomes and objectives were developed by the HPS. There is considerable overlap between health physics and medical physics, especially in the subspecialty of medical health physics. The HPS lists health physics–related academic programs, including 31 schools offering a range of degrees from the BS to the PhD degrees (https://hps.org). A professional HP holds a bachelor's (BS) or higher degree in physics, health physics, nuclear engineering, or in another biological or physical science. There are ∼18 regionally accredited colleges or universities in the United States that offer bachelor degree programs in health physics,13, 14 three of which are accredited by the ABET (Idaho State University, Oregon State University, and the University of Massachusetts at Lowell).15 Undergraduate programs in health physics are generally located within physics and nuclear engineering departments. Some programs offer an optional undergraduate concentration in health physics or nuclear science. Undergraduate curricula focus on breadth of knowledge and, typically, students interested in health physics will take only a few courses specifically related to health physics. Graduate education available in health physics includes MS and PhD degree programs, as well as related degrees programs in biological or physical sciences and engineering. All graduate degrees in health physics count toward the requirements of an HP (see Section 2.4). Approximately 23 programs grant MS degrees and 17 grant PhDs.14 The curricula for MS degree programs vary substantially across the United States, although minimum standards for accreditation of an MS and PhD degree programs in health physics have been established by ABET (www.abet.org). These include classes in radiation physics, radiation biology, radiation detection and measurements with laboratory experience, internal and external radiation dosimetry, principles of radiation safety and health physics, and contemporary issues in health physics. As of 2020, only six graduate programs in health physics in the United States were ABET-accredited (Clemson University, Colorado State University, Idaho State University, University of Massachusetts at Lowell, Oregon State University, and the University of Nevada at Las Vegas). In 2016, ∼20 accredited colleges and universities granted 66 master's degrees and 23 doctoral degrees in health physics or radiological sciences.16 Table 1 lists health physics graduates by degree and post-graduation status, showing relative stability in the number of master's degrees conferred, but a drop in the number of doctoral degrees to 13.17 Currently, accreditation is not available for doctoral health physics curricula. Formal postgraduate training programs in health physics are scarce. A limited number of postgraduate training opportunities in health physics are available from US national laboratories. It is worth noting that this situation comprises a radical change with past practices; postgraduate training was used extensively from the 1950s to the 1970s, especially by the U.S. Public Health Service. Consensus requirements for alternative pathways into the profession of health physics are lacking, and the subject is controversial. Multiple alternative pathways exist, including the promotion of radiation control technicians, the U.S. Navy Nuclear Propulsion program, the Army public health training program, USAF Bioenvironmental Engineer training programs, DOE national laboratory training programs, and civilian training programs at nuclear power plants and shipyards. Alternative training in radiation protection may be obtained through courses offered by Oak Ridge Associated Universities (ORAU) and a number of commercial vendors, as well as courses sponsored by other federal agencies. Since 1948, ORAU has trained more than 30 000 scientists, physicians, engineers, educators, regulators, and personnel in a variety of radiation safety and health physics topics through its Professional Training Programs. It currently offers 16 courses at its training facility at Oak Ridge, TN. The NRC also offers 27 online and classroom radiation safety and health physics courses for staff employed by the NRC and NRC Agreement States. Course topics range from fundamental and advanced health physics to diagnostic and therapeutic nuclear medicine. These types of courses augment a 4-year degree as an alternate pathway into the field of health physics. Basic RSO courses are commercially available that meet federal and state regulations and range from 8 to 40 h each. Associate degree programs typically prepare graduates for careers as health physics technicians. Through the industry-initiated Nuclear Uniform Curriculum Program, the commercial nuclear power industry has developed partnerships with multiple 2-year degree programs, including one in radiation safety.18 In addition to a BS or higher degree, an HP must obtain applied radiation protection experience by working under the supervision of an experienced HP, although the type and amount of experience needed varies considerably. For example, the requirements for an RSO at a panoramic sterilization irradiation facility include just 3 months of supervised occupational experience, whereas the requirements for a hospital RSO include 5 years of professional experience in health physics. At a U.S. nuclear power plant, no prior work experience or on-the-job training is required, whereas an RPM in the same facility requires a minimum of 5 years of related experience, which must include 3 years of nuclear power plant experience and 1 year of supervisory or management experience.10 Some positions in health physics require additional professional board certification and/or licensure. The ABHP is the main certification body for the practice of professional health physics in the United States, and it is responsible for establishing the qualifications for designation as a certified health physicist (CHP), as well as examining applicants. Requirements to become a CHP include education, work experience, and successful completion of a two-part certification examination. HPs with a graduate degree can also apply to become a "Certified Medical Health Physicist" by the American Board of Medical Physics (ABMP). The ABMP19 offers certification in Medical Health Physics for diplomates that have, by examination, been issued certificates with the words "RSO Eligible" on their certificate. Similarly, the American Board of Radiology currently provides "RSO Eligible" status to diplomates in the Diagnostic Medical Physics and the Nuclear Medical Physics subspecialties (this certification will cease in 2023). The American Board of Science in Nuclear Medicine offers certificates in the Radiation Protection Specialty. CHPs are required to obtain 80 h of continuing education every 4 years. CHPs have many options to obtain continuing education, as detailed on the American Academy of Health Physics (AAHP) website.20 The HPS, AAHP, and other organizations provide continuing education courses. The current status of the health physics workforce is difficult to discern because of insufficient data on the supply and demand for health physics services. Despite apparent declines in the number of HPs, the current workforce appears to meet the needs for radiation protection across all sectors, mainly because eligible workers have delayed their retirements due to the uneven performance of the economy since 2008. However, it is generally accepted that the number of HPs will decline significantly in the near future due to the retirements of baby boomers. Predictions for future sustainability of the workforce are less certain. The NCRP concluded in its Statement 123 that the nation will face a severe shortage of radiation professionals that could jeopardize national security without mitigation. A 2017 HPS publication pointed out that the number of health physics graduates had declined by 55% from 1995 to 2015 and predicted that future supply will not meet demand.20 On the other hand, one author suggested that the health physics profession may be a victim of its own success in that radiation protection programs have become so effective as to be capable of functioning with safety generalists replacing (higher cost) HPs.21 Further, this author referenced the public's aversion to radiation and nuclear technology, along with the closure of numerous civilian nuclear power plants, as reasons to predict a stagnant or diminished demand for radiation protection specialists in the future. He did cite three potential areas for growth—decommissioning, environmental protection, and medicine—and recommended a strengthening of standards for health physics education, training and experience, and improved outreach to attract students to the field. The field of radiological emergency preparedness has taken on increased importance since the events of 9/11, as the threat of intentional destruction and widespread contamination with radiological or nuclear devices has increased. The nuclear disaster in Fukushima, along with the earlier accidents at Chernobyl and Three Mile Island, illustrate the need to maintain a viable cadre of highly trained radiation specialists to respond to the effects of such radiologic accidents. However, the low probability of these types of incidents creates a conundrum for employers and government leaders, as it is generally not cost-effective to maintain staff for the sole purpose of responding to such emergencies. Therefore, emergency preparedness and response are typically collateral duties for HPs. However, the lack of surge capacity for large-scale incidents represents a significant gap in the safety and security of the nation and highlights the need for specialized training. With respect to the civilian nuclear power industry, power plants require a total of ∼3700 radiation protection specialists, 400 of whom would be classified as HPs.7 A recent study revealed that current needs are being met for full-time nuclear power utility staffing, that is, professional HPs and technicians. This finding was based on human resource data from a 2015 survey, using projected retirement and attrition data and the projected supply from 2-year institutions and 4-year advanced degree programs.22 The apparent adequacy of the workforce differed from earlier predictions of possible shortages.2, 3 A possible explanation is that the long-anticipated renaissance of the nuclear industry did not occur; only two new nuclear power reactors are under construction in the United States in 2021. In addition, since 2013, 13 nuclear power plants have permanently ceased operations, and several utilities have announced that additional units, including Byron 1 and 2, Dresden 1 and 2, Palisades, and Diablo Canyon 1 and 2, will close by 2025. As plant construction, closures, and decommissioning significantly impact the demand for HPs, the future needs in the nuclear power industry are difficult to forecast with certainty. The US Bureau of Labor Statistics predicts that employment in the nuclear sector will decline by ∼20% over the current decade; however, some of these losses may be offset by an increased demand for decontamination and decommissioning services.23 The status of the health physics workforce employed in the medical sector is unclear. It is difficult to estimate the number of HPs with specialization in medical health physics because of overlapping job responsibilities with medical physicists (see Chapter 3). Demand for medical health physics is difficult to forecast because it is driven by regulatory requirements, the size and age of the population, the utilization of radiation in medicine, productivity, and health-care economics. However, due to technological innovations and the medical needs of an aging population, it can be expected that this sector would experience stable or slightly increased employment. The federal government, the largest single employer of HPs, decreased its ranks from 451 HPs in 2004 to 418 HPs in 2016, with two thirds of these losses occurring at the NRC (Table 2).24 More recent data from this site indicate a stable federal workforce since 2016. The NRC reductions were attributed, in part, to staff downsizing associated with the cancellation of new reactor projects and the closing of 13 power plants since 2013. Of note, some federal departments, such as DOE, have used outsourcing to augment the capacity of their professional HP staff. State radiation control programs, which are monitored and periodically reviewed by the NRC, appear to currently have an adequate health physics workforce. These programs employ ∼1000 full-time equivalent employees, although the actual number of employees is uncertain as personnel are assigned across multiple public health duties simultaneously.7 In addition, these programs are challenged by attrition due to staff leaving state service for higher paying federal or private sector positions, which in turn necessitates the training of replacement staff to qualify for licensing, inspection or compliance work. The NRC provides the training and travel funds needed to meet these radiation control program requirements. A representative of the Conference of Radiation Control Program Directors echoed the concern of many at the 2013 NCRP WARP Workshop regarding the impact of large-scale retirements without an adequate pool of replacements and concluded that it may be necessary in the future to train general science graduates to perform radiation protection duties.25 A workshop explored areas of health physics expertise that will be required to fulfill research needs.26 This focused on research needs and did not cover workforce issues. It was observed that, across many academic programs, alternative, non-radiological technologies have significantly reduced the use of radioactive materials in biomedical research, decreasing the need for health physics staff. Recent unpublished data from Little and Johnson compiled job announcements from Colorado State University alumni, as well as from the "Indeed" website from June 2020 to February 2021 (Little and Johnson, email communication, 5 May, 2022) (Table 3). A period of 8 months of data collection yielded 643 unique job announcements for HPs. Of these, only 125 were specifically denoted as technician level positions. A total of 194 were specifically announced as jobs for "HP," with 39 others titled "RSO." Other job titles varied from "Environmental Scientist" (typically for state level health physics positions, n = 27 announcements) to "Physicist" (n = 20). Job descriptions were carefully examined to ensure that nuclear engineering and medical physics positions were not misclassified as health physics. The preliminary analysis indicated an average of 80 unique postings per month, with ∼16 for technicians and 64 for professional HPs. Analysis of previous years is ongoing; however, based on the quantity of data, similar numbers are expected for 2019 and 2018. These data suggest a robust demand for HPs, and anecdotal information indicates that competition for the limited pool of graduates is high. We conclude that the demand for HPs is sector- and specialty-specific and subject to varied and multiple factors and external influences. One example of this is driven by the shuttering of nuclear power plants; as they cease generating power, new and different works are necessary for the decontamination and decommissioning phase, requiring a reallocation of HP resources. This makes the assessment of workforce needs very challenging. Although a review of the published literature revealed a lack of evidence in support of earlier predicted shortages,3 new data suggest that there may in fact be current pent-up demand for radiation protection specialists that had not previously been recognized. It is quite possible that major shortages were averted by a drop in demand in certain sectors (e.g., nuclear power) and the delayed retirements of a significant segment of the workforce. However, the data available on the demographics of the professional health physics workforce indicate that the profession will experience an unprecedented wave of attrition as baby boomers leave the workforce. The future impacts of the COVID-19 pandemic are unknown. The demand for recent graduates demonstrates the need to provide continued support for health physics training programs. In addition, although certain radiation protection operations may be performed by generalists under ideal conditions, it is clear that professional HPs are needed for accidents or other emergencies involving radiological or nuclear activities. Furthermore, it must be acknowledged that institutional knowledge, once lost, is difficult to regain, and efforts should be made to retain and transfer this knowledge to the next generation of professional HPs. More and better quality data on the health physics workforce are needed. In particular, more frequent and focused studies are needed to adequately characterize the supply and demand for health physics professionals to ensure that the nation's future needs will be met. Although data are collected annually on health physics education and employment, longer range forecasting of changes in supply (e.g., due to attrition) and demand (e.g., due to changes in utilization of radiation sources) are notoriously difficult because of the large impact of unpredictable factors, such as economic conditions. Hence, annually updated, short-term forecasts are indicated to inform decision-making regarding the workforce. The recommendations later represent consensus expert opinions on actions needed to ensure that the health physics profession will be able to meet the nation's future needs. The Committee intentionally declined to recommend detailed methods, timelines, responsibilities of individual organizations, and funding sources. These complex subjects are outside the scope of this Review and, indeed, the Committee was prohibited from activities that could be construed as advocacy. Provide support for alternate training programs and pathways. Increase funding for health physics workforce development activities, including support for higher education programs, fellowships and scholarships for students (undergraduate and graduate level), research, curriculum development, and faculty development (hiring). Foster increased utilization of university–employer partnerships, for example, co-op and internship and externship opportunities, to increase alignment of university curricula with the employers' current and future needs. We thank the following colleagues for helpful discussions and suggestions in the preparation of this chapter: Jacqueline P. Williams, Dustin A. Gress, Michael D. Mills, David W. Jordan, Steven G. Sutlief, Melissa Martin, Edward Jackson (deceased), Edward I. Bluth, Donald P. Frush, M. Elizabeth Oates, Jeanne LaBerge, Hubert Young Pan, Seth A. Rosenthal, Phillip Costello, Lawrence W. Townsend, Lori Brady, Janice Lindegard, Howard L. Hall, Elizabeth McAndrew-Benavides, John Poston, Eric Abelquist, Lydia B. Zablotska, Ruth A. Kleinerman, Diana L. Miglioretti, Daniel Stram, Mitchell S. Anscher, Marcelo Vazquez, Amy Kronenberg, Jeffrey S. Willey, Theodore Lawrence, Gayle E. Woloschak, Brian Marples, Rosemary Wong, Michael Story, Roger W. Howell, Tom K. Hei, Sergey Y. Tolmachev, John D. Auxier, II, Thomas L. Rucker, Mikael Nilsson, Ralf Sudowe, Brian A. Powell, and Mark P. Jensen. All the authors listed have contributed directly to the intellectual content of the manuscript. No conflict of interest.

Implementation of a systematic program for galactic cosmic radiation (GCR) countermeasure discovery will require convenient access to ground-based space radiation analogs. The current gold standard approach for GCR simulation is to use a particle accelerator for sequential irradiation with ion beams representing different GCR components. This has limitations, particularly for studies of non-acute responses, strategies that require robotic instrumentation, or implementation of complex in vitro models that are emerging as alternatives to animal experimentation. Here we explore theoretical and practical issues relating to a different approach to provide a high-LET radiation field for space radiation countermeasure discovery, based on use of compact portable sources to generate neutron-induced charged particles. We present modeling studies showing that DD and DT neutron generators, as well as an AmBe radionuclide-based source, generate charged particles with a linear energy transfer (LET) distribution that, within a range of biological interest extending from about 10 to 200 keV/mu m, resembles the LET distribution of reference GCR radiation fields experienced in a spacecraft or on the lunar surface. We also demonstrate the feasibility of using DD neutrons to induce 53BP1 DNA double-strand break repair foci in the HBEC3-KT line of human bronchial epithelial cells, which are widely used for studies of lung carcinogenesis. The neutron-induced foci are larger and more persistent than X ray-induced foci, consistent with the induction of complex, difficult-to-repair DNA damage characteristic of exposure to high-LET (>10 keV/mu m) radiation. We discuss limitations of the neutron approach, including low fluence in the low LET range (<10 keV/ mu m) and the absence of certain long-range features of high charge and energy particle tracks. We present a concept for integration of a compact portable source with a multiplex microfluidic in vitro culture system, and we discuss a pathway for further validation of the use of compact portable sources for countermeasure discovery.

Abstract Specific absorbed fractions (SAFs) are key components in the workflow of internal exposure assessment following the intake of a radionuclide, allowing quick conversion of particle energy released in a source region to the expected absorbed dose in target regions throughout the body. For data completeness, SAFs for spontaneous fission neutron emitters are currently needed for the recently adopted ICRP reference pediatric voxel phantom series. With 77 source regions within each reference individual and 28 radionuclides decaying via spontaneous fission, full Monte Carlo simulation requires significant computation time. In order to reduce this burden, a novel method for neutron SAF estimation was undertaken. The Monte Carlo N-Particle version 6.1 (MCNP6) simulation package was chosen to simulate the 252Cf Watt fission neutron spectrum originating from 15 source regions in each phantom; dose estimation within 41 target tissues allowed for assessment of the SAF value for each source-target pair. For the remaining source regions, chord length distributions were computed using MATLAB code to determine the separation between the source-target pairs within the pediatric phantom series. These distance distributions were used in conjunction with a 252Cf neutron dose point kernel calculated in soft tissue, which was modified to account for the source region’s depth from the surface of the body. Lastly, the 252Cf SAF dataset was extended to the other 27 spontaneous fission neutron emitters based on differences in the Watt fission spectrum parameters of each radionuclide. This methodology has been shown to accurately estimate spontaneous fission neutron SAFs to within 20% of the Monte Carlo estimated value for most source-target pairs in the ICRP reference pediatric series.

Monte Carlo (MC) methods are considered the gold-standard approach to dose estimation for normal tissues outside the treatment field (out-of-field) in proton therapy. However, the physics of secondary particle production from high-energy protons are uncertain, particularly for secondary neutrons, due to challenges in performing accurate measurements. Instead, various physics models have been developed over the years to reenact these high-energy interactions based on theory. It should thus be acknowledged that MC users must currently accept some unknown uncertainties in out-of-field dose estimates. In the present study, we compared three MC codes (MCNP6, PHITS, and TOPAS) and their available physics models to investigate the variation in out-of-field normal tissue dosimetry for pencil beam scanning proton therapy patients. Total yield and double-differential (energy and angle) production of two major secondary particles, neutrons and gammas, were determined through irradiation of a water phantom at six proton energies (80, 90, 100, 110, 150, and 200 MeV). Out-of-field normal tissue doses were estimated for intracranial irradiations of 1-, 5-, and 15-year-old patients using whole-body computational phantoms. Notably, the total dose estimates for each out-of-field organ varied by approximately 25% across the three codes, independent of its distance from the treatment volume. Dose discrepancies amongst the codes were linked to the utilized physics model, which impacts the characteristics of the secondary radiation field. Using developer-recommended physics, TOPAS produced both the highest neutron and gamma doses to all out-of-field organs from all examined conditions; this was linked to its highest yields of secondary particles and second hardest energy spectra. Subsequent results when using other physics models found reduced yields and energies, resulting in lower dose estimates. Neutron dose estimates were the most impacted by physics model choice, and thus the variation in out-of-field dose estimates may be even larger than 25% when considering biological effectiveness.

Polyvinyltoluene-based plastic scintillators with thermally activated delayed fluorescence (TADF) dyes were explored for radiation detection.

, medicine, nuclear engineering, radiation biology, and radiation and nuclear chemistry. Chapters 2 through 7 of this special issue review the characteristics of each profession and its workforce, as well as recommending actions to ensure their future adequacy to meet the nation’s needs.

The radiation exposure estimates for the atomic bomb survivors at Hiroshima and Nagasaki have evolved over the past several decades, reflecting a constant strive by the Radiation Effects Research Foundation (RERF) to provide thorough dosimetry to their cohort. Recently, a working group has introduced a new series of anatomical models, called the J45 phantom series, which improves upon those currently used at RERF through greater age resolution, sex distinction, anatomical realism, and organ dose availability. To evaluate the potential dosimetry improvements that would arise from their use in an RERF Dosimetry System, organ doses in the J45 series are evaluated here using environmental fluence data for 20 generalized survivor scenarios pulled directly from the current dosimetry system. The energy- and angle-dependent gamma and neutron fluences were converted to a source term for use in MCNP6, a modern Monte Carlo radiation transport code. Overall, the updated phantom series would be expected to provide dose improvements to several important organs, including the active marrow, colon, and stomach wall (up to 20, 20, and 15% impact on total dose, respectively). The impacts were especially significant for neutron dose estimates (up to a two-fold difference) and within organs which were unavailable in the previous phantom series. These impacts were consistent across the 20 scenarios and are potentially even greater when biological effectiveness of the neutron dose component is considered. The entirety of the dosimetry results for all organs are available as supplementary data, providing confident justification for potential future DS workflows utilizing the J45 phantom series.

The International Commission on Radiation Units and Measurements (ICRU) Report Number 95 (2020 Operational quantities for external radiation exposure ICRU Rep. 95 J. ICRU 20) recommends new definitions ffor operational quantities as estimators of the International Commission on Radiological Protection radiation protection quantities. As part of this report, dose coefficients for neutron fluences are included for energies from 10−9–50 MeV. For lens of the eye dosimetry, several changes in the ICRU recommended quantities are of particular interest. First, an updated eye model is used that includes segmentation of the sensitive lens region. In addition, the use of absorbed dose instead of dose equivalent has been selected as the appropriate operational quantity since deterministic (i.e. non-stochastic) effects are of primary importance for the lens of the eye. The ICRU report also addresses computational parameters, such as absorbed dose tally volumes, depths, source areas and source rotational angles. In this work, neutron dose coefficients calculated for the lens of the eye in support of the ICRU report are presented. Dose coefficients for mono-energetic neutrons and reference neutron spectra are presented. The source is a parallel beam, and the mono-energetic dose coefficients are provided for rotational angles with respect to the front face of the head ranging from 0°–90°. In addition, monoenergetic dose coefficients for the parallel beam incident on the back of the head (180°) and for a rotational source geometry where the head is irradiated from all angles are reported. For all scenarios, absorbed doses to the complete lens and the sensitive volume of each eye were calculated. Eye lens absorbed dose coefficients, Dp,slab(3,0)/Φ, were also calculated in an ICRU tissue slab phantom at a depth of 3 mm for a parallel beam irradiating the slab perpendicular to the front face, and these results are compared to the values determined using the eye phantom.

Georgia Institute of Technology Atlanta, GA The author declares no conflicts of interest. (Manuscript accepted 3 September 2020)

A draft report by the International Commission on Radiation Units and Measurements (ICRU) Report Committee 26 (RC26) will recommend alternative definitions of the operational quantities that are better estimators of radiation protection quantities. Dose coefficients for use with physical field quantities-fluence and, for photons, air kerma-are given for various particle types over a broad energy range. For the skin dosimetry, several changes are of particular interest. Specifically, the use of absorbed dose instead of dose equivalent has been selected as the operational quantity since deterministic effects are of primary interest in the skin. In addition, newly recommended phantoms are specified for computing the operational dose coefficients. The report also addresses computational approaches such as tally volumes, depths, source areas, and rotational angles. In this work, dose coefficients calculated for local skin in support of the ICRU report are presented. Energy-dependent dose coefficients were calculated in phantoms specified for the trunk (slab), the ankle or wrist (pillar), and the finger (rod). The phantom specifications in this work were taken directly from the draft report. Full transport of secondary charged particles from neutron interactions was performed and an analysis of the depth-dose profiles in the slab phantom is presented, The last complete set of neutron dose coefficients for the extremities was published more than 25 years ago. Given the limited data available, it is difficult for many facilities to obtain clear guidance on how monitoring should be performed and how dosimeters should be calibrated so spectra from commonly encountered neutron sources were used to generate source-specific dose coefficients in each of the phantoms. Both energy-dependent and source-specific dose coefficients are provided for rotational angles up to 180 degrees for the rod and pillar phantoms and up to 75 degrees for the slab phantom.