Accelerator production of Ac-225 addresses the global supply deficiency currently inhibiting clinical trials fromestablishing Ac-225's therapeutic utility, provided that the accelerator product is of sufficient radionuclidic purity for patient use. Two proton activation experiments utilizing the stacked foil technique between 40 and 200MeV were employed to study the likely co-formation of radionuclides expected to be especially challenging to separate from Ac-225. Foils were assayed by nondestructive gamma-spectroscopy and by alpha-spectroscopy of chemically processed target material. Nuclear formation cross sections for the radionuclides Ac-226 and Ac-227 as well as lower lanthanide radioisotopes Ce-139, Ce-141, Ce-143, and La-140 whose elemental ionic radii closely match that of actinium were measured and are reported. The predictions of the latest MCNP6 event generators are compared with measured data, as they permit estimation of the formation rates of other radionuclides whose decay emissions are not clearly discerned in the complex spectra collected from Th-232(p,x) fission product mixtures.

The total reaction energy (Q) of individual nuclear decays was measured using microcalorimeters with transition-edge-sensor (TES) thermometers. For alpha-decaying actinides (e.g., U-235, Pu-239, Np-237, Am-241), Q is in the 4-6 MeV range. Nearly all of this energy goes into the relatively light alpha particle, and approximately 100 keV is left over for the much heavier, recoiling daughter atom. Alpha-particle energy spectroscopy with TES-microcalorimeters has shown the ability to simultaneously resolve peaks that overlap in conventional alpha spectroscopy, with resolution now less than 1 keV full-width-at-half-maximum (FWHM) at 5.3 MeV. For total reaction energy spectroscopy, we use the same TES design as our alpha detectors, but embed a small radioactive sample (of about 1 Bq) directly inside an absorber designed to capture all the emitted particles (alpha, recoil nucleus, electrons, X-rays) with near 100% efficiency. We have measured Q-spectra of alpha-decaying isotopes with spectral resolution of 2-3 keV FWHM. For some actinide analytical problems, the Q-spectrum is simpler than the alpha-spectrum: fewer peaks, further apart, and easier to quantify. We will discuss sensor design, methods for embedding radionuclides, and spectral data.

Ultra-high resolution alpha spectrometry by microcalorimetry has demonstrated a dramatic improvement in alpha energy resolution over silicon based detectors. To characterize the optimal resolution obtained by the microcalorimeter alpha spectrometers, high quality deposits that are virtually massless are required; electrodeposition is the preferred method for the preparation of high quality deposits. In order to better understand the factors that contribute to lower alpha energy resolution and deposit yield, we have conducted a study to determine the effect of some of the parameters that are used for preparing electrodeposits. We have compared four different electrodeposition methods and four different substrate materials to determine the effect on the deposit yield and alpha energy resolution of plutonium as measured by full width at half maximum using silicon based detectors. Furthermore, we wanted to understand the effect of contaminants from environmental samples on electrodeposits. Therefore, the effect on deposit yield and alpha energy resolution with several common soil constituents (Al-3+, Eu3+, Fe3+, K+, Lu3+, Mg2+, Na+, Zn2+) have been studied.

Source term information is required for to reconstruct a device used in a dispersed radiological dispersal device. Simulating a radioactive environment to train and exercise sampling and sample characterization methods with suitable sample materials is a continued challenge. The Idaho National Laboratory has developed and permitted a radioactive response training range (RRTR), an 800 acre test range that is approved for open air dispersal of activated KBr, for training first responders in the entry and exit from radioactively contaminated areas, and testing protocols for environmental sampling and field characterization. Members from the Department of Defense, Law Enforcement, and the Department of Energy participated in the first contamination exercise that was conducted at the RRTR in the July 2011. The range was contaminated using a short lived radioactive 82 Br isotope (activated KBr). Soil samples contaminated with KBr (dispersed as a solution) and glass particles containing activated potassium bromide that emulated dispersed radioactive materials (such as ceramic-based sealed source materials) were collected to assess environmental sampling and characterization techniques. This presentation summarizes the performance of a radioactive materials surrogate for use as a training aide for nuclear forensics.

Alpha-particle spectrometry is a powerful analytical tool for nuclear forensics and environmental monitoring. Superconducting transition-edge sensor microcalorimeters have been shown to yield unsurpassed energy resolution for alpha spectrometry. With nearly an order of magnitude better energy resolution (1.06 keV FWHM at 5.3 MeV) than the current state-of-the-art silicon detectors (8-10 keV at 5.3 MeV), it is possible to measure samples containing multiple radioisotopes that would require expensive and time-consuming radiochemical separation prior to measurement with a silicon detector. This paper presents recent results from the Los Alamos four-channel microcalorimeter alpha spectrometer. We have prepared a source from weapons-grade plutonium and demonstrated the ability of microcalorimeter alpha spectrometry to simultaneously resolve alpha energies from 239 Pu, 240 Pu, 238 Pu, and 241 Am. The low-energy performance of the spectrometer system has been improved to allow measurement of energies as low as 5 keV, which gives a dynamic range of 1000. We have demonstrated this capability by simultaneously measuring the alpha particles and low-energy x-rays and internal conversion electrons emitted by an electroplated 240 Pu source.

Glass or silicon substrates functionalized with a monolayer of carbamoylmethylphosphonate (CMP) ligands effectively bind tetravalent actinides from optimized mineral acid solutions to enable rapid, high quality radiometric assay by alpha spectrometry. The observed alpha spectra compare favorably with the highest quality electroplated samples. The CMP-functionalized surfaces have been used to develop simplified analytical methods to determine plutonium from complex mixtures.

The long-lived rare earth isotopes 151 Sm (90 years, β max = 76.3 keV) and 147 Pm (2.62 years, β max = 224.6 keV) are low-yield fission products that generally require lengthy separation procedures to isolate and count by their beta emissions. We will describe novel liquid scintillation counting techniques using radioactive tracers to determine radiochemical yields from an environmental matrix. The recovery of 151 Sm is determined from the alpha decay (2.25 MeV) of 147 Sm in the natural Sm carrier and is in excellent agreement with the gravimetric recovery. The 147 Pm recovery is determined by the use of 145 Pm (17.7 years, EC) tracer, custom-produced at LANL using an isotopically enriched target of 144 Sm. We have determined the 145 Pm recovery both from the 37.4 keV k α1 X-ray, and the electron-capture emissions by LSC. A comparison of these recovery methods is presented.

Special considerations and techniques are desired for the preparation of small actinide counting sources. Counting sources have been prepared on metal disk substrates (planchets) with an active area of only 0.079 mm(2). This represents a 93.75% reduction in deposition area from standard electrodeposition methods. The actinide distribution upon the smaller planchet must remain thin and uniform to allow alpha particle emissions to escape the counting source with a minimal amount of self-attenuation. This work describes the development of micro-electrodeposition methods and optimization of the technique with respect to deposition time and current density for various planchet sizes.

Microcalorimeters have been shown to yield unsurpassed energy resolution for alpha spectrometry, up to 1.06 keV FWHM at 5.3 MeV. These detectors use a superconducting transition-edge sensor (TES) to measure the temperature change in an absorber from energy deposited by an interacting alpha particle. Our system has four independent detectors mounted inside a liquid nitrogen/liquid helium cryostat. An adiabatic demagnetization refrigerator (ADR) cools the detector stage to its operating temperature of 80 mK. Temperature regulation with similar to 15-mu K peak-to-peak variation is achieved by PID control of the ADR. The detectors are voltage-biased, and the current signal is amplified by a commercial SQUID readout system and digitized for further analysis. This paper will discuss design and operation of our microcalorimeter alpha-particle spectrometer, and will show recent results.

The long-lived rare earth isotopes Sm-151 (90 years, beta (max) = 76.3 keV) and Pm-147 (2.62 years, beta (max) = 224.6 keV) are low-yield fission products that generally require lengthy separation procedures to isolate and count by their beta emissions. We will describe novel liquid scintillation counting techniques using radioactive tracers to determine radiochemical yields from an environmental matrix. The recovery of Sm-151 is determined from the alpha decay (2.25 MeV) of Sm-147 in the natural Sm carrier and is in excellent agreement with the gravimetric recovery. The Pm-147 recovery is determined by the use of Pm-145 (17.7 years, EC) tracer, custom-produced at LANL using an isotopically enriched target of Sm-144. We have determined the Pm-145 recovery both from the 37.4 keV k(alpha 1) X-ray, and the electron-capture emissions by LSC. A comparison of these recovery methods is presented.

Identification of trace nuclear materials is usually accomplished by alpha spectrometry. Current detectors cannot distinguish critical elements and isotopes. We have developed a detector called a microcalorimeter, which achieves a resolution of 1.06 keV for 5.3 MeV alphas, the highest resolving power of any energy dispersive measurement. With this exquisite resolution, we can unambiguously identify the P240u/P239u ratio in Pu, a critical measurement for ascertaining the intended use of nuclear material. Furthermore, we have made a direct measurement of the P209o ground state decay.

A novel radiochemical separation for 48V radiotracer in no-carrier-added (NCA) form, via proton irradiation on Ti targets of natural isotopic composition has been developed. Metallic Ti targets irradiated with 21 MeV proton beam energy was submitted to a selective radiochemical separation consisting of an alkaline fusion-precipitation step, followed by column Chelex-100 chromatographic purification. Very high specific activity 48V, at levels of hundreds MBq .µg-1 was prepared. Chemical analysis of radiotracer was carried out by ET-AAS and INAA. The decontamination factor from Ti target was 5 . 105, with an overall radiochemical yield for 48V larger than 90%. The NCA 48V has used for labeling a range of chemical forms of V(III, IV, V) and applied in the study of metabolic behavior of different chemical forms in in-vivo and in-vitro experiments on rats and cell cultures.

The Isotope and Nuclear Chemistry (C-INC) Radioassay Facility at Los Alamos National Laboratory (LANL) has been in operation since 1948 to measure fission-product and actinide activities from the U.S. weapons testing program. Since the cessation of testing in 1992, the facility has remained in continuous operation by analyzing samples for environmental, bioassay and research projects. In addition to the many gamma spectroscopy systems, two independent planar germanium detectors are employed for measurement of x-rays and low-energy gsunma rays. 'These counters were used to collect data of select isotopes to support the development of a new ASTM standard, 'Standard Practice for High-Resolution Low-Energy Photon Spectrometry of Water'. This standard is being developed by ASTM Subcommittee D19.04 as a tool for measurement of low-energy gamma-rays and x-rays fiom approximately 4 keV to 150 keV. This work describes empirical counting results obtained fkom traceable sources covering the energy range of interest. Specifically, the isotopes used were 5%i, 55Fe, Am, I, Cd, and 57C0 which provide a range of 5.9 to 136 keV. Mixed nuclide sources were also counted for the purpose of providing data for coincidence summing effects. All data is presented in hardcopy and accompanying electronic form.