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

Highly efficient ultrathin plasmonic insulator-metal-insulator-metal solar cell

Nano-porous ultrathin plasmonic insulator-metal-insulator-metal (IMIM) solar cell with high power conversion efficiency up to 7% in broad wavelength range from 300 to 750 nm was theoretically studied. The proposed IMIM design allows to choose various bottom insulators with desired barrier height of metal-insulator interface due to independence of the total absorbance on the bottom insulator. IMIM structure shows 73.8% difference in the average absorbance between the top and bottom metal layers with 1-nm bottom insulator. Moreover, the incident light decreases the absorbance negligibly up to 35 degrees for both TE and TM modes and by 17.5% at 70 degrees. Furthermore, the absorption between TE and TM modes differs by less than 5%, which indicates the structure as polarization independent. Our results indicate IMIM design benefit in plasmonic solar cells demanding low thickness, flexibility, low-cost, and polarization independence. Moreover, this structure can be implemented for integrated optical circuits as well as for solar thermoelectric generator

Energy efficiency of rotary digesters

In this paper, a new technical solution is introduced for the substrate mixing in a digester. The novelty content lies in the direction changes of the gravitational forces that influence the movement of organic and mineral biomass fractions. Digester case is designed as a horizontal cylinder rotating around a horizontal axis. Digester rotates in water that is in the outer casing. This design creates a lift force for rotating digester which reduces the load on the bearings. The friction is reduced and therefore it reduces the energy loss of digester rotation and mixing of the substrate

Optoelectronic performance of AgNW transparent conductive films with different width-to-height ratios and a figure of merit embodying an optical haze

Transparent conductive films (TCFs) based on rectangularly shaped silver nanowires (AgNWs) with different width-to-height ratios were theoretically studied. We show that tall AgNWs (height > width) possess higher transmittance and lower sheet resistance compared to other configurations of AgNWs. Moreover, tall AgNWs possesses significantly higher optical haze, which makes them a transparent conductor of choice for thin solar cell applications. For applications requiring low haze such as displays and touch screens, we propose an updated figure of merit embodying transmittance, sheet resistance and haze, allowing tuning width-to-height ratio to achieve a reasonable AgNW TCF performance trade-off. Obtained results offer a means for deeper analysis of AgNW properties for many optoelectronic applications

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

Tsuchime-like Aluminum Film to Enhance Absorption in Ultra-Thin Photovoltaic Cells

Ultra-thin solar cells enable materials to be saved, reduce deposition time, and promote carrier collection from materials with short diffusion lengths. However, light absorption efficiency in ultra-thin solar panels remains a limiting factor. Most methods to increase light absorption in ultra-thin solar cells are either technically challenging or costly, given the thinness of the functional layers involved. We propose a cost-efficient and lithography-free solution to enhance light absorption in ultra-thin solar cells—a Tsuchime-like self-forming nanocrater (T-NC) aluminum (Al) film. T-NC Al film can be produced by the electrochemical anodization of Al, followed by etching the nanoporous alumina. Theoretical studies show that T-NC film can increase the average absorbance by 80.3%, depending on the active layer’s thickness. The wavelength range of increased absorption varies with the active layer thickness, with the peak of absolute absorbance increase moving from 620 nm to 950 nm as the active layer thickness increases from 500 nm to 10 µm. We have also shown that the absorbance increase is retained regardless of the active layer material. Therefore, T-NC Al film significantly boosts absorbance in ultra-thin solar cells without requiring expensive lithography, and regardless of the active layer material

Effect of silver nanowire length in a broad range on optical and electrical properties as a transparent conductive film

Optical and electrical properties of silver nanowire transparent conductive films with a broad range of nanowire lengths were studied. A proposed simulation model demonstrated similar behavior with experimental results for 30 and 90 μm nanowires, and thus it was used to expand the range of nanowire lengths from 10 to 200 μm. Theoretical results show that a lengthening of silver nanowires results in an increase of their optoelectronic performance; 200 μm long nanowire possess 13.5 times lower sheet resistance compared to 10 μm ones, while the transmittance remains similar for coverage densities of nanowires up to 25%. Moreover, the dependence of the sheet resistance on the length of nanowires changes non-linearly; from 10 to 20 µm, 20 to 80 µm and 80 to 200 µm the sheet resistance drops by a factor of 5, 2.25 and 1.2 respectively. Furthermore, a thickening of nanowire diameters from 30 to 90 nm decreases the sheet resistance to 5.8 times. Obtained results allow a deeper analysis of the silver nanowire transparent conductive films from the perspective of the length of nanowires for various optoelectronic applications

CO2 Capture by Absorption with Potassium Carbonate

The objective of this work is to improve the process for CO{sub 2} capture by alkanolamine absorption/stripping by developing an alternative solvent, aqueous K{sub 2}CO{sub 3} promoted by piperazine. The best solvent and process configuration, matrix with MDEA/PZ, offers 22% and 15% energy savings over the baseline and improved baseline, respectively, with stripping and compression to 10 MPa. The energy requirement for stripping and compression to 10 MPa is about 20% of the power output from a 500 MW power plant with 90% CO{sub 2} removal. The stripper rate model shows that a ''short and fat'' stripper requires 7 to 15% less equivalent work than a ''tall and skinny'' one. The stripper model was validated with data obtained from pilot plant experiments at the University of Texas with 5m K{sup +}/2.5m PZ and 6.4m K{sup +}/1.6m PZ under normal pressure and vacuum conditions using Flexipac AQ Style 20 structured packing. Experiments with oxidative degradation at low gas rates confirm the effects of Cu{sup +2} catalysis; in MEA/PZ solutions more formate and acetate is produced in the presence of Cu{sup +2}. At 150 C, the half life of 30% MEA with 0.4 moles CO{sub 2}/mole amine is about 2 weeks. At 100 C, less than 3% degradation occurred in two weeks. The solubility of potassium sulfate in MEA solution increases significantly with CO{sub 2} loading and decreases with MEA concentration. The base case corrosion rate in 5 M MEA/1,2M PZ is 22 mpy. With 1 wt% heat stable salt, the corrosion rate increases by 50% to 160% in the order: thiosulfate&lt; oxalate&lt;acetate&lt;formate. Cupric carbonate is ineffective in the absence of oxygen, but 50 to 250 ppm reduces corrosion to less than 2 mpy in the presence of oxygen

Silver nanowires as transparent conductive films in the near-infrared spectral range

Transparent conductive films (TCFs) comprise a crucial component of optoelectronic devices, such as displays, light-emitting diodes, solar cells and touch screens. Indium tin oxide (ITO) currently dominates among TCFs in the visible spectral range due to the high transmittance at low resistivity. However, the remarkable decrease of the transmittance in the near-infrared range (NIR) restricts from using ITO as highly efficient NIR TCF. Here we show that silver nanowires (AgNWs) possesses up to 95% transmittance for whole 0.75-2.5|jm near-infrared spectral range

Pola Sebaran dan Kelimpahan Hiu Berjalan Halmahera (Hemiscyllium halmahera) di Teluk Weda Maluku Utara, Indonesia

The Halmahera walking shark is a nocturnal species that lives at the bottom of waters and is a species endemic to North Maluku. Weda Bay is one of the largest bays on the island of Halmahera and contains marine resources and high diversity. The aims research was analyze the distribution pattern and abundance of Halmahera walking shark at that location. The research was conducted in September - November 2020. The sampling in Weda Bay, is carried out in two methods, (1) catch of nets with a mesh size of 2,5 cm stretched from the mangrove ecosystem, seagrass to coral reefs with a length of ± 50 meters and a height of 1,5 meters, (2) hand sampling equipment namely the sample catch it by hand with transect area (50x50m2) or 0,25 ha using basic diving equipment (snorkeling) to a depth of 3 meters at high tide in the night. Distribution pattern data analysis used Morisita Index and abundance analysis used reef fish abundance equation. Results the research found 28 individuals, namely 17 females and 11 males. There are 2 distribution patterns of the Halmahera epaullette shark, namely Grouping and Random. The clustered distribution pattern is found at stations 1, 2 and 4, while the random distribution pattern is found at station 3. Overall the distribution pattern of the Halmahera walking shark in Weda Bay is grouped. The highest abundance of Halmahera walkingshark was at station 1, namely 17,33 ind/ha and the lowest abundance at stations 3 and 4 was 5,33 ind/ha. The highest abundance is at station 1, this is because the habitat is still very good from the mangrove, seagrass and coral reef ecosystems to find food and the growth of the Halmahera walking shark.Hiu Berjalan Halmahera merupakan spesies nokturnal yang hidup di dasar perairan dan merupakan spesies endemik Maluku Utara. Teluk Weda merupakan salah satu teluk terluas di pulau Halmahera dan menyimpan sumberdaya perairan serta keanekaragaman tinggi. Penelitian ini dilakukan untuk mengetahui analisis pola sebaran dan kelimpahan Hiu Berjalan Halmahera, yang dilaksanakan pada September - November 2020. Pengambilan sampel di Teluk Weda, dilakukan dengan dua cara yaitu (1) menggunakan jaring dengan ukuran mata jaring 2,5 cm yang dibentangkan dari ekosistem mangrove, lamun sampai terumbu karang sepanjang ± 50 meter dan tinggi 1,5 meter, dan (2) menggunakan metode hand sampling equipment yaitu sampel ditangkap menggunakan tangan dengan luasan transek jelajah (50x50m2) atau 0,25 ha menggunakan alat selam dasar (snorkeling) sampai kedalaman 3 meter pada saat pasang di waktu malam hari. Analisis data pola sebaran menggunakan Indeks Morisita dan kelimpahan menggunakan persamaan kelimpahan ikan karang. Hasil penelitian dapat ditemukan 28 individu, yaitu 17 individu betina dan 11 individu jantan. Terdapat 2 pola sebaran dari Hiu Berjalan Halmahera, yaitu mengelompok dan acak. Pola sebaran mengelompok ditemukan pada stasiun 1, 2 dan 4, sedangkan pola sebaran acak terdapat pada stasiun 3. Secara keseluruhan pola sebaran Hiu Berjalan Halmahera di Teluk Weda adalah mengelompok. Kelimpahan Hiu Berjalan Halmahera tertinggi berada di stasiun 1 yaitu 17,33 ind/ha dan kelimpahan terendah pada stasiun 3 dan 4 yaitu 5,33 ind/ha. Kelimpahan tertinggi berada pada stasiun 1, hal ini dikarenakan habibat yang masih sangat baik dari ekosistem mangrove, lamun dan terumbu karang untuk mencari makan dan pertumbuhan Hiu Berjalan Halmahera