The human health risks posed by any given type of radioactive material depend on its activity level, or intensity; how long exposure lasts; and the way in which the body is exposed to it—via inhalation, ingestion, or external exposure. The different types of radiation—including alpha, beta, gamma, and neutron—vary in how easy or difficult they are to block or shield, which, in turn, affects the health threat posed by a particular type of radiation. Depending on the radioactive material’s intensity and the length and manner of exposure to it, health effects range from death, to severe injury, to the development of cancer, to no discernable damage. For example, alpha radiation poses little threat to human health from external exposure, but poses considerable health risks if inhaled or ingested. Gamma radiation is more penetrating and, if not properly shielded, can cause injury or death through external exposure. Neutron radiation, like gamma radiation, if not shielded, can also cause injury or death through external exposure. Although sources of neutron radiation are less common, neutron radiation is emitted from some materials that are used to make nuclear weapons. NRC oversees licensees of radiological material through three regional offices located in Illinois, Pennsylvania, and Texas; radiological material licensing responsibilities for the region II office in Georgia are handled by the region I office in Pennsylvania. NRC has relinquished regulatory authority for licensing and regulating certain radioactive material to 37 states that have entered into an agreement with NRC (agreement states). Figure 1 shows which states are agreement states and in which states NRC has maintained all regulatory authority (NRC states). NRC and agreement states issue two types of licenses authorizing the possession and use of radioactive materials: specific licenses and general licenses. Specific licenses, which are the focus of this report, are issued for devices that contain relatively larger sealed radioactive sources. These devices, such as medical equipment used to treat cancer, cameras used for industrial radiography, and moisture and density gauges used in construction, generally require training to be used safely and may also need to be properly secured to avoid misuse. An organization or individual seeking to obtain a specific license must submit an application and gain the approval of either NRC or the appropriate agreement state prior to receiving and using licensed radioactive materials. According to NRC, of the approximately 21,000 specific radioactive materials licenses in the United States, NRC administers about 2,900, and agreement states administer the rest. Our prior work on security of radioactive materials found that NRC could do more to ensure the security of these materials. Specifically, we recommended in 2008 that among other things NRC take steps to develop and implement the systems it was then planning to better track, secure, and control radioactive materials. These systems are the National Source Tracking System (NSTS), the Web-based Licensing System (WBL), and the License Verification System (LVS). NSTS, deployed in January 2009, tracks category 1 and 2 sources of the 20 radionuclides that NRC determined are sufficiently attractive for use in an RDD or for other malicious purposes and warrant national tracking. NSTS is a transaction-based system that tracks each major step that each tracked radioactive source takes within the United States from “cradle to grave.” Licensees are responsible for reporting the manufacture, shipment, arrival, disassembly, and disposal of all nationally tracked sources. A nationally tracked source is a source containing a category 1 or 2 quantity of certain radioactive materials specified in NRC’s regulations. More specifically, NSTS includes the radionuclide, quantity (activity), manufacturer, manufacture date, model number, serial number, and site address. The licensee has until the close of the next business day after a transaction—such as the sale of a source from a vendor to a customer—takes place to enter it into the system. As a result, the location of all such sources are accounted for and closely tracked. While NSTS is presently configured to track larger and potentially more dangerous radioactive sources, NRC’s WBL—deployed in August 2012— provides quick access to up-to-date information on all NRC and four agreement states’ specific licenses for all radioactive materials and sources in all five IAEA categories, enabling the user to enter, maintain, track, and search radioactive material licensing and inspection information. WBL also includes pdf images of all paper copies of category 1 and 2 licenses for both NRC and agreement state licensees. NRC also developed a third system—LVS, deployed in May 2013—which draws on the information in NSTS and WBL and provides information to regulators and vendors and other would-be transferors on whether those applicants seeking to acquire category 1 and 2 sources are legitimately licensed to do so. This is particularly important because paper licenses issued by NRC and agreement states can be altered or counterfeited. LVS provides a means to mitigate the risks of using paper licenses. While NRC and agreement states have taken steps to improve their licensing programs and better ensure that radiological materials are safe and secure, concerns about the theft of radioactive materials and the possible consequences of a dirty bomb attack persist. In 2012, for example, we identified security weaknesses at some U.S. medical facilities that use high-risk radioactive materials, such as cesium-137, and in 2014, we found that challenges exist in reducing the security risks faced by licensees using high-risk radioactive materials for industrial purposes. NRC periodically evaluates NRC regional offices’ and agreement states’ programs for licensing radioactive materials through its Integrated Materials Performance Evaluation Program (IMPEP). NRC implemented IMPEP in 1995 to periodically review NRC regional office and agreement state radioactive materials programs to ensure that they are adequately protecting public health and safety from the potential hazards associated with the use of radioactive materials, and that agreement state programs are compatible with NRC’s program. As part of IMPEP, each NRC regional office and agreement state regulatory program is typically expected to undergo a program review every 4 years; reviews may occur more or less frequently depending on a program’s past performance. The IMPEP reviewers examine a regional office’s or an agreement state’s performance in areas such as licensing and inspections to determine if the regional office’s program is adequate to protect public health and safety and if the agreement state’s program is adequate to protect public health and safety and compatible with NRC requirements. NRC also has the option to employ greater oversight of agreement state programs if it discovers performance issues. Specifically, if performance problems are found, a Management Review Board (MRB)—comprised of NRC officials and an agreement state liaison—may decide to (in ascending order of seriousness) institute Monitoring, Heightened Oversight, Probation, Suspension, or Termination. The MRB may decide to place an agreement state on Monitoring if weaknesses in the program have resulted in or could result in less than satisfactory performance in one or more performance areas. If an agreement state program is found to have more serious problems (i.e., one or more performance indicators are found to be unsatisfactory), the MRB may opt to place a program on Heightened Oversight. Under Heightened Oversight, a program may be requested to submit a program improvement plan, which involves establishing a plan to address all recommendations to eliminate unsatisfactory performance as well as frequent contact with NRC to closely monitor progress. If the program under IMPEP review does not correct performance weaknesses under Heightened Oversight the MRB/NRC may place the program on Probation or even suspend or terminate the agreement and reassert regulatory authority. Probation is a formal process and requires approval of the Commission and notification of the state’s governor, congressional delegation, and public. NRC and agreement states have taken several steps since 2007 to help ensure that radioactive materials licenses are granted only to legitimate organizations and that licensees can only obtain such materials in quantities allowed by their licenses, but have not taken some measures for better controlling category 3 quantities of radioactive materials. In 2008, NRC developed revised screening criteria and a checklist covering all five IAEA categories of radioactive materials and now directs regions and agreement states to conduct prelicensing site visits for all unknown applicants. NRC and agreement states performed IMPEP reviews to assess whether licensing guidance was being met and took corrective actions when it was not. NRC also developed and deployed NSTS, WBL, and LVS to better control such materials, although these systems are focused on category 1 and 2 quantities. NRC does not require that category 3 quantities be tracked in NSTS nor does it require all category 3 licenses be included in WBL. LVS, which queries NSTS and WBL, provides information to regulators and vendors on whether a license is valid. By not including category 3 materials in NSTS nor most agreement state licenses in WBL, NRC has not taken an important step that could better track and control these materials. Further, including all category 3 materials in these systems could help address the risk that paper licenses issued by NRC and agreement states could be altered or counterfeited or that a licensee could obtain radioactive materials in quantities greater than what is allowed by their license. NRC has taken a number of steps to address the vulnerabilities in its licensing process identified by GAO and others. Specifically, in September 2007, NRC approved its Action Plan to respond to recommendations to address security issues its and agreement states’ radioactive materials programs raised in NRC Inspector General, Senate subcommittee, and GAO reports. NRC also established prelicensing and materials working groups and the Independent External Review Panel to assess the security of NRC and agreement programs and develop recommendations to address any vulnerabilities identified.