Experimental studies and nuclear model calculations on (p,xn) and (p,pxn) reactions on 85Rb from their threshold up to 100 MeV

Excitation functions were measured by the stacked-foil technique for the reactions Rb-85(p, pxn)Rb-89m,Rb-g83,Rb-82m.81 from their thresholds up to 100MeV. Nuclear model calculations were performed using the code ALICE-IPPE both on (p, xn) reactions reported earlier and (p, pxn) reactions described here. The experimental excitation curves and the results of nuclear model calculations were found to be qualitatively in agreement. With the exception of the (p, n) reaction above 40MeV, the theory appears to reproduce all the experimental data within deviations of about 50%. The cross section ratios for the isomeric pairs Sr-85m,Sr-g and Rb-84m,Rb-g are discussed qualitatively in terms of the spins of the states involved and the increasing projectile energy

Association of ABCB1, 5-HT3B receptor and CYP2D6 genetic polymorphisms with ondansetron and metoclopramide antiemetic response in Indonesian cancer patients treated with highly emetogenic chemotherapy.

Our study shows that in Indonesian cancer patients treated with highly cytostatic emetogenic, carriership of the CTG haplotype of the ABCB1 gene is related to an increased risk of delayed chemotherapy-induced nausea and vomiting

Proton Beam Energy Characterization

Introduction The Los Alamos Isotope Production Facility (IPF) is actively engaged in the development of isotope production technologies that can utilize its 100 MeV proton beam. Characterization of the proton beam energy and current is vital for optimizing isotope production and accurately conducting research at the IPF. Motivation In order to monitor beam intensity during research irradiations, aluminum foils are interspersed in experimental stacks. A theoretical yield of 22Na from 27Al(p,x)22Na reactions is cal-culated using MCNP6 (Monte Carlo N-Particle), TRIM (Transport of Ions in Matter), and Andersen & Ziegler (A&Z) [1] computational models. For some recent experiments, experimentally measured activities did not match computational predictions. This discrepancy motivated further experimental investigations including a direct time-of-flight measurement of the proton beam energy upstream of the target stack. The Isotope Production Program now tracks the beam energy and current by a complement of experimental and computational methods described below. Material and Methods A stacked-foil activation technique, utilizing aluminum monitor foils [2] in conjunction with a direct time-of-flight measurement helps define the current and energy of the proton beam. Theoretical yields of 22Na activity generated in the Al monitor foils are compared with experimental measurements. Additionally, MCNP, TRIM, and A&Z computational simulations are compared with one another and with experimental data. Experimental Approach Thin foils (0.254mm) of high purity aluminum are encapsulated in kapton tape and stacked with Tb foils in between aluminum degraders. Following irradiation, the Al foils are assayed using γ-spectroscopy on calibrated HPGe detectors in the Chemistry Division countroom at LANL. We use the well-characterized 27Al(p,x)22Na energy dependent production cross section [3] to calculate a predicted yield of 22Na in each foil. Details of the experimental activity determination and associated uncertainties have been addressed previously [4]. The nominally stated beam parameters are 100 MeV and 100–120 nA for the foil stack irradiation experiments. Time-of-flight measurements performed in the month of January 2014 revealed beam energy of 99.1 ± 0.5 MeV. Computational Simulations Andersen & Zeigler (A&Z) is a deterministic method and also the simplest of the three com-putational methods considered. While the mean energy degradation can be calculated using the A&Z formalism, the beam current attenuation cannot. Consequentially, A&Z will also lack the ability to account for a broadening in the beam energy that a stochastic method affords. Additionally, A&Z does not account for nuclear recoil or contributions from secondary interactions. TRIM uses a stochastic based method to calculate the stopping range of incident particles applying Bethe-Block formalisms. TRIM, like A&Z, does not include contributions from nuclear recoil or contributions from secondary interactions. Computationally, TRIM is a very expensive code to run. TRIM is able to calculate a broadening in the energy of the beam; however, beam attenuation predictions are much less reliable. TRIM determines the overall beam attenuation in the whole stack to be less than one percent, whereas 7–10 % is expected. MCNP6 is arguably the most sophisticated approach to modeling the physics of the experiment. It also uses a stochastic procedure for calculation, adopting the Cascade-Exciton Model (CEM03) to track particles. The physics card is enabled in the MCNP input to track light ion recoils. Contributions from neutron and proton secondary particle interactions are included, although their contribution is minimal. For both MCNP and TRIM, the proton beam is simulated as a pencil beam. To find the current, an F4 volumetric tally of proton flux from MCNP simulation is matched to the experimental current for the first foil in the stack. Subsequent foil currents are calculated relative to the first foil based on MCNP predictions for beam attenuation. The equation used for calculating the current from the experi-mental activity is [5]: where: is the cross section for the process, [mbarns] is the atomic mass of the target [amu] is the is the number of product nuclei pre-sent at End-of-Bombardment is the average beam current, [μA] is the density of the target material, [g/cc] is the target thickness, [cm] is the decay constant, [s−1] is the irradiation time, [s] For each foil in the experimental stack, we also have a statistically driven broadening of the incident energy. The beam energy is modeled as a Gaussian distribution, with the tallies for each energy bin determining the parameters of the fit. TABLE 1 and FIG. 3 summarize the mean energy and standard deviation of the energy for each aluminum monitor foil. To address the energy distribution, we calculate an effective or weighted cross-section. It is especially important to account for energy broadening in regions where the associated excitation function varies rapidly. In the excitation function, we see a strong variation in the energy range from 30–65 MeV, the energy region cov-ered by the last 3 foils in the stack. Cross section weighting also accounts for the mean energy variation within each foil. The excitation function will overlay the Gaussian shaped flux distribution, giving rise to a lateral distribution where incrementally weighted values of the cross section are determined by the flux tally of the corresponding energy bin. With the effective cross section and the current at each of the foils, it is straight-forward to calculate the number of 22Na atoms created and the activity of each foil using the previously stated equation. Results and Conclusion The general trend in the amount of activity produced follows the shape of the excitation func-tion for the 27Al(p,x)22Na reaction. Small shifts in the incident energy upstream trickle down to produce much more pronounced shifts in the energy range of foils towards the back of the foil stack. The characteristic “rolling over” of the activity seen in the experimental foils indicates that the 6th foil must be in the energy region below 45 MeV, where the peak of the excitation function occurs. Conservatively, computational simulations are able to accurately determine the proton beam’s energy for an energy range from 100 to 50 MeV. As the beam degrades below 50 MeV, computa-tional simulations diverge from experimentally observed energies by over-predicting the energy. This observation has been noted in past studies [6,7] that compare the stacked foil technique with stopping-power based calculations. A complement of experimental and computational predictions allows for energy determinations at several points within target stacks. While this study focuses on an Al-Tb foil stack, the analysis of a similar Al-Th foil stack resulted in the same conclusions. Although we do not have a concurrent time-of-flight energy measurement at the time of the foil stack experiments, it is reasonable to assume that the energy at the time of the stacked foil experiments was also lower than the assumed energy of 100 MeV. Computational simulations developed in this work firmly support this assumption. Various computational models are able to predict with good agreement the energy as a function of depth for complex foil stack geometries. Their predictions diverge as the beam energy distribution broadens and statistical uncertainties propagate. A careful inspection of the codes reveals that these discrepancies likely originate from minute differences between the cross sections and stopping power tables that MCNP and TRIM/A&Z use respectively

Rubidium metal target development for large scale 82Sr production: LA-UR-14-22338

Strontium-82 (t1/2 = 25.5 d) is one of the medical isotopes produced on a large scale at the Isotope Production Facility (IPF) of the Los Alamos National Laboratory (LANL), employing a high intensity 100 MeV proton beam and RbCl targets. A constant increase in the 82Sr demand over the last decade combined with an established thermal limit of molten RbCl salt targets [1,2] has challenged the IPF’s world leading production capacity in recent years and necessitated the consideration of low-melting point (39.3 °C) Rb metal targets. Metal targets are used at other facilities [3–5] and offer obvious production rate advantages due to a higher relative density of Rb target atoms and a higher expected thermal performance of molten metal. One major disadvantage is the known violent reaction of molten Rb with cooling water and the potential for facility damage following a catastrophic target failure. This represents a significant risk, given the high beam intensities used routinely at IPF. In order to assess this risk, a target failure experiment was conducted at the LANL firing site using a mockup target station. Subsequent fabrication, irradiation and processing of two prototype targets showed a target thermal performance consistent with thermal modeling predictions and yields in agreement with predictions based on IAEA recommended cross sections [6]. Target failure test: The target failure test bed (FIG. 1) was constructed to represent a near replica of the IPF target station, incorporating its most important features. One of the most vulnerable components in the assembly is the Inconel beam window (FIG. 2) which forms the only barrier between the target cooling water and the beam line vacuum. The test bed also mimicked relevant IPF operational parameters seeking to simulate the target environment during irradiation, such as typical cooling water flow velocities around the target surfaces. While the aggressive thermal effects of the beam heating could not be simulated directly, heated cooling water (45 °C) ensured that the rubidium target material remained molten during the failure test. A worst case catastrophic target failure event was initiated by uncovering an oversized predrilled pinhole (1 mm Φ) to abruptly expose the molten target material to fast flowing cooling water. Prototype target irradiations: Two prototype Rb metal target containers were fabricated by machining Inconel 625 parts and by EB welding. The target containers were filled with molten Rb metal under an inert argon atmosphere. Follow-ing appropriate QA inspections, the prototype targets were irradiated in the medium energy slot of a standard IPF target stack using beam currents up to 230 µA. After irradiation the targets were transported to the LANL hot cell facili-ty for processing and for 82Sr yield verification. During the target failure test, cooling water conductivity and pressure excursions in the target chamber were continuously monitored and recorded at a rate of 1 kHz. Video footage taken of the beam window and the pinhole area combined with the recorded data indicated an aggressive reaction between the Rb metal and the cooling water, but did not reveal a violent explosion that could seriously damage the beam window. These observations, together with thermal model predictions, provided the necessary confidence to fabricate and fill prototype targets for irradiation at production-scale beam currents. X-ray imaging of filled targets (FIG. 3) shows a need for tighter control over the target fill level. One prototype target was first subjected to lower intensity (< 150 µA) beams before the second was irradiated at production level (230 µA) beams. During irradiation, monitoring of cooling water conductivity indicated no container breach or leak and, as anticipated given the model predictions, the post irradiation target inspection showed no sign of imminent thermal failure (see FIG. 4). Subsequent chemical processing of the targets followed an established procedure that was slightly modified to accommodate the larger target mass. TABLE 1 shows that post chemistry 82Sr yields agree to within 2 % of the in-target production rates expected on the basis of IAEA recommended cross sections. The table also compares 82Sr yields from the Rb metal targets against yields routinely obtained from RbCl targets, showing an increase in yield of almost 50 %

57Co Production using RbCl/RbCl/58Ni Target Stacks at the Los Alamos Isotope Production Facility: LA-UR-14-22122

Introduction The Los Alamos Isotope Production Program commonly irradiates target stacks consisting of high, medium and low-energy targets in the “A-”, “B-”, and “C-slots”, respectively, with a 100MeV proton beam. The Program has recently considered the production of 57Co (t1/2 = 271.74 d, 100% EC) from 58Ni using the low-energy posi-tion of the Isotope Production Facility, down-stream of two RbCl salt targets. Initial MCNPX/ CINDER’90 studies predicted 57Co radioisotopic purities >90% depending on time allotted for decay. But these studies do not account for broadening of the proton beam’s energy distribution caused by density changes in molten, potentially boiling RbCl targets upstream of the 58Ni (see e.g., [1]). During a typical production with 230 µA average proton intensity, the RbCl targets’ temperature is expected to produce beam energy changes of several MeV and commensurate effects on the yield and purity of any radioisotope irradiated in the low-energy posi-tion of the target stack. An experiment was designed to investigate both the potential for 57Co’s large-scale production and the 2-dimensional proton beam energy distribution. Material and Methods Two aluminum targets holders were fabricated to each contain 31 58Ni discs (99.48%, Isoflex, CA), 4.76 mm (Φ) x 0.127 mm (thickness). Each foil was indexed with a unique cut pattern by EDM with a 0.254 mm brass wire to allow their position in the target to be tracked through hot cell disassembly and assay (see FIG. 1). Brass residue from EDM was removed with HNO3/HCl solution. The holders’ front windows were 2.87 and 1.37 mm thick, corresponding to predicted average incident energies of 17.9 and 24.8 MeV on the Ni [2]. Each target was irradiated with protons for 1 h with an average beam current of 218 ± 3 µA to ensure an upstream RbCl target temperature and density that would mimic routine production. Following irradiation, targets were disassembled and each disc was assayed by HPGe γ-spectroscopy. Residuals 56Co (t1/2 = 77.2 d, 100% EC) and 57Co have inversely varying measured nuclear formation cross sections between approximately 15 and 40 MeV. Results and Conclusion Distributions of 56,57,58,60Co were tracked as described in both irradiated targets. The distribution of activities matched expectations, with radioisotopes produced by proton interactions with the 58Ni target (56Co and 57Co) concentrated in the area struck by IPF’s rastered, annulus-shaped proton beam, and the distribution of radioisotopes produced by neutron-induced reactions (58Co and 60Co) relatively uniform across all irradiated foils. The potential range of such temperature variations predicted by thermal modeling (approx. ± 200 °C) corre-sponds to a density variation of nearly 0.2 g.cm−3, and a change in the average energy of protons incident on the low-energy “C-slot” of approximately 5 MeV, well-matched to the indi-rectly measured energy variation plotted in FIG. 3. No energy distribution in the plane per-pendicular to the beam axis has previously been assumed in the design of IPF targets. The effective incident energy measured by yields of 57Co and 56Co is, however, almost 5 MeV higher than those predicted using Anderson and Ziegler’s well-known formalism [2]. This discrepancy is supported by previous reports [3] and likely exacerbated compared to these reports by the large magnitude of energy degradation (from 100 MeV down to 30 MeV) in the IPF target stack. For more detailed discussion, refer to Marus et al.’s abstract, also reported at this meeting. While the experiments reported do confirm the potential for many Ci-scale yields of 57Co from months-long irradiations at the IPF, the level radioisotopic impurities 56Co and 58Co are concerning. Commercial radioisotope producers using U-150 (23 MeV) and RIC-14 (14 MeV) cyclotrons in Obninsk, Russia specify 56/58Co activities at levels <0.2% of available 57C