Radioisotopes Of Interest Research Articles

Trace analysis of radioisotopes by laser spectroscopy and mass spectrometry

Trace analysis (at fg-level) of radioisotopes requires a considerable push in analytical technology. Among most sensitive are a Time-Resolved Laser-Induced Fluorescence (TRLIF) and Chemiluminescence (TRLIC) methods for detection of elemental compositions and valence states and a Resonance Ionisation Spectroscopy (RIS) in combination with mass spectrometry for isotope composition determination. The radioisotopes of interest in environmental radiochemistry and planetary science and their analysis using TRLIF/TRLIC/RIS are discussed. The aspects of the development of the new technology implementing these methods are also described.

Sci—Thur PM: Imaging — 05: Calibration of a SPECT/CT camera for quantitative SPECT with 99mTc

While quantitation is the norm in PET, it is not widely available yet in SPECT. This work's aim was to calibrate a commercially available SPECT/CT system to perform quantitative SPECT. Counting sensitivity, dead‐time (DT) constant and partial volume effect (PVE) of the system were assessed.A dual‐head Siemens SymbiaT6 SPECT/CT camera equipped with low energy high‐resolution collimators was studied. 99mTc was the radioisotope of interest because of its wide usage in nuclear medicine. First, point source acquisitions were performed (activity: 30–990MBq). Further acquisitions were then performed with a uniform Jaszczak phantom filled with water at high activity (25–5000MBq). PVE was studied using 6 hot spheres (diameters: 9.9–31.2 mm) filled with 99mTc (2.8MBq/cc) in the Jaszczak phantom, which was: (1) empty, (2) water‐filled and (3) water‐filled with low activity (0.1MBq/cc). The data was reconstructed with the Siemens's Flash3D iterative algorithm with 4 subsets and 8 iterations, attenuation‐correction (AC) and scatter‐correction (SC). DT modelling was based on the total spectrum counting rate. Sensitivity was assessed using AC‐SC reconstructed SPECT data.Sensitivity and DT for the sources were 99.51±1.46cps/MBq and 0.60±0.04µs. For the phantom, sensitivity and DT were 109.9±2.3cps/MBq and 0.62±0.13µs. The recovery‐coefficient varied from 5% for the 9.9mm, to 80% for the 31.2mm spheres.With our calibration methods, both sensitivity and DT constant of the SPECT camera had little dependence on the object geometry and attenuation. For small objects of known size, recovery‐coefficient can be applied to correct PVE. Clinical quantitative SPECT appears to be possible and has many potential applications.

The urgent requirement for new radioanalytical certified reference materials for nuclear safeguards, forensics, and consequence management

A multi-agency workshop was held from 25 to 27 August 2009, at the National Institute of Standards and Technology (NIST), to identify and prioritize the development of radioanalytical Certified Reference Materials (CRMs, generally provided by National Metrology Institutes; Standard Reference Materials, a CRM issued by NIST) for field and laboratory nuclear measurement methods to be used to assess the consequences of a domestic or international nuclear event. Without these CRMs, policy makers concerned with detecting proliferation and trafficking of nuclear materials, attribution and retribution following a nuclear event, and public health consequences of a nuclear event would have difficulty making decisions based on analytical data that would stand up to scientific, public, and judicial scrutiny. The workshop concentrated on three areas: post-incident Improvised Nuclear Device (IND) nuclear forensics, safeguard materials characterization, and consequence management for an IND or a Radiological Dispersion Device detonation scenario. The workshop identified specific CRM requirements to fulfill the needs for these three measurement communities. Of highest priority are: (1) isotope dilution mass spectrometry standards, specifically 233U, 236gNp, 244Pu, and 243Am, used for quantitative analysis of the respective elements that are in critically short supply and in urgent need of replenishment and certification; (2) CRMs that are urgently needed for post-detonation debris analysis of actinides and fission fragments, and (3) CRMs used for destructive and nondestructive analyses for safeguards measurements, and radioisotopes of interest in environmental matrices.

Radiochemistry of the 3M SBMF-40VF filter media used by the DOE CTBT Radionuclide Aerosol Sampler/Analyzer (RASA)

The Comprehensive Test Ban Treaty calls for the monitoring of aerosol radionuclides throughout the globe. Pacific Northwest National Laboratory has developed the Radionuclide Aerosol Sampler/Analyzer (RASA) for the Department of Energy to automatically collect and measure radioactive aerosols from the atmosphere. The RASA passes high volumes of air through a 3MTM Substrate Blown Microfiber Media (SBMF) specifically designated as SBMF-40VF. It then automatically moves the filter media in front of a high-purity germanium detector and collects a gamma spectrum. If further analysis on the filter is desired, the filter is sent to a laboratory and radiochemical analysis is performed. This paper discusses the method of dissolution of the SBMF-40VF filter media and the separation of the radioisotopes of interest.

Multielement comparison of instrumental neutron activation analysis techniques using reference materials

Several instrumental neutron activation analysis techniques (parametric, comparative, and ko-standardization) are evaluated using three reference materials. Each technique is applied to National Institute of Standards and Technology standard reference materials, SRM 1577a (Bovine Liver) and SRM 2704 (Buffalo River Sediment), and the United States Geological Survey standard BHVO-1 (Hawaiian Basalt Rock). Identical (but not optimum) irradiation, decay, and counting schemes are employed with each technique to provide a basis for comparison and to determine sensitivities in a routine irradiation scheme. Fifty-one elements are used in this comparison; however, several elements are not detected in the reference materials due to rigid analytical conditions (e.g., insufficient length of irradiation or activity for radioisotope of interest decaying below the lower limit of detection before counting interval). Most elements are normally distributed around certified or consensus values with a standard deviation of 10%. For some elements, discrepancies are observed and discussed. The accuracy, precision, and sensitivity of each technique are discussed by comparing the analytical results to consensus values for the Hawaiian Basalt Rock to demonstrate the diversity of multielement applications.

Application of analytical methods based on X-ray spectroscopy to the determination of radionuclides

Low levels of radionuclides are commonly determined by radiometric counting methods. However, for long lived radionuclides and for those nuclides with low energy emissions, such as soft beta emitters, non-radiometric methods can offer a more sensitive alternative. This work investigates the use of various analytical methods based on x-ray spectroscopy for the determination of low levels of radionuclides. X-ray spectroscopy cannot provide the isotopic information available from many radiometric or mass spectrometric methods but this is not always required when the radioisotope of interest is the major isotope, as could be the case with 238U or 99Tc, for example. X-ray fluorescence, total reflectance x-ray fluorescence, electron microprobe analysis, particle-induced x-ray emission and synchroton radiation-induced x-ray emission are considered in a practical intercomparison of methods. X-ray methods are relatively insensitive compared with mass spectrometric techniques but are suitable for the determination of long-lived nuclides such as 232Th and 238U.

A 3He++ Radio-Frequency Quadrupole Accelerator for Positron Emission Tomography

The feasibility of using a radio-frequency quadrupole (RFQ) accelerator to accelerate 3He++for use in positron emission tomography (PET) is shown. The 3He++ RFQ is extremely lightweight in comparison to a cyclotron, but can nevertheless produce all four radioisotopes of interest (18F, 13N, 15O, and 11C) in more than adequate quantities. Due to the neutron-poor nature of 3He++, the desired positron emitters can be produced from naturally abundant target isotopes. In addition, target reactions and collisions with the accelerating structure produce relatively small numbers of neutrons compared to proton and deuteron systems. This yields two economic advantages. Enriched 13C, 15N, and 18O target materials are not required. Also, the shielding requirements are reduced considerably, and there is no need for radiation shielding around the accelerator. This reduced shielding results in a factor of 8 reduction in total facility shielding weight compared to a proton/deuteron cyclotron facility. The order of magnitude reduction in facility weight, the virtual elimination of the accelerator weight, and the relative lack of residual induced activity gives rise to the possibility of a radiopharmaceutical production system that is less expensive than present systems and may ultimately be transportable. Such a system could make PET imaging technology far more accessible geographically and financially than it is at present.

Surface-escape corrections in “self-scintillation” measurements of beta spectra

The spectra of the escaping radiations from several materials containing beta emitters were studied, the most important case being that of K 40 contained in KI. The results indicate that the escaping radiation consists of electrons, bremsstrahlung and X-rays. It is shown how a reasonably good correction can be made for the escaping electrons in the measurement of a beta spectrum using the “self-scintillation” method. For high Z materials it is also shown that a further correction is needed for the escaping electromagnetic radiation. Such a correction would be difficult to make so that, in general, it may be better to use low Z scintillating materials containing the radioisotope of interest, particularly for those cases having a high beta end-point energy.