Foil Targets Research Articles

Preventing damage to floating foils caused by Rayleigh-Taylor instabilities

An evaporated metal foil target is often produced on a layer of water-soluble parting agent previously applied to a massive substrate. The foil is then floated onto a water surface by immersing the substrate into a water bath. and is picked up later if the foil survives. During the foil's release, a significant fraction of the dissolved parting agent may remain close to the floating foil, as a "heavy" thin layer of solution having higher density than water. This layer of parting agent solution and the lower-density water bath below it form a gravitationally unstable configuration known as a Rayleigh-Taylor instability. If the foil is sufficiently thin, its mass and elastic properties can be ignored, and the motion of the liquids is determined by only the liquids' properties. This system can spontaneously adjust itself toward stability in several ways, one of which involves rotating a cylindrical liquid cell having a horizontal axis, and its cylindrical surface tangent to the surface. This motion moves part of the heavy layer from the top surface downward. The target maker detects this occurrence by the motions of the foil floating on the top of the bath; if the foil is frail, these motions may result in the crumpling, wrinkling, or tearing of the foil. We have observed such behavior with aluminum foils having thickness of 37 nm and diameter of 920 mm on NaCl parting agent, and have successfully implemented methods to prevent such damage.

Boosted acceleration of protons by tailored ultra-thin foil targets

We report on a detailed experimental and numerical study on the boosted acceleration of protons from ultra-thin hemispherical targets utilizing multi-Joule short-pulse laser-systems. For a laser intensity of 1 × 1020 W/cm2 and an on-target energy of only 1.3 J with this setup a proton cut-off energy of 8.5 MeV was achieved, which is a factor of 1.8 higher compared to a flat foil target of the same thickness. While a boost of the acceleration process by additionally injected electrons was observed for sophisticated targets at high-energy laser-systems before, our studies reveal that the process can be utilized over at least two orders of magnitude in intensity and is therefore suitable for a large number of nowadays existing laser-systems. We retrieved a cut-off energy of about 6.5 MeV of proton energy per Joule of incident laser energy, which is a noticeable enhancement with respect to previous results employing this mechanism. The approach presented here has the advantage of using structure-wise simple targets and being sustainable for numerous applications and high repetition rate demands at the same time.

Improvement of proton acceleration via collisionless shock acceleration by laser-foil interaction with an external magnetic field

Effects of the external intense axial magnetic field on collisionless shock acceleration (CSA) are investigated by using two-dimensional particle-in-cell simulations. Proton beams accelerated by CSA show different properties when left-hand circularly polarized (LHCP) or right-hand circularly polarized (RHCP) lasers are individually applied to a foil target with or without the magnetic field. It can be attributed to the difference of the dispersion relationship for the laser propagating in a plasma. Protons achieve more efficient acceleration when magnetized plasma is irradiated by the RHCP laser compared with the LHCP laser. Furthermore, the effect of different amplitudes of the magnetic field is studied numerically. It shows that the induced electrostatic charge-separation field arises deep in the target with huge strength of the magnetic field. Protons in the upstream are accelerated before the shock arrives, leading to less efficient acceleration. As a result, an appropriate magnetic field should be applied to enhance the CSA regime.

Separation of Ac-225 from Lanthanide Fission Products using a Reverse Phase Chromatographic Process Incorporating a Solvent Impregnated Resin

Targeted α-particle therapy (TAT) has been shown in recent years to be a promising route for the treatment of various forms of cancer, and may serve as an alternative to more traditional cancer treatment options. TAT takes advantage of an α-emitting radionuclide’s ability to deliver cytotoxic doses of radiation to tumor cells while causing minimal damage to surrounding healthy tissue. This is possible because of the short path length and high linear energy transfer associated with α -particles, which are on the order of 100 μm or less and around 100 keV/μm, respectively. To this end, a number of α-emitting radionuclides have explored for therapeutic applications including Ac-225, Bi-213, Bi-212, At-211, and Ra-223 with others currently in development. Of these, Ac-225 in particular has proven itself to be an especially appealing isotope for the treatment of some cancers. The value of Ac-225 is derived in part from its four alpha decay chain, which includes Bi-213 (t1/2 = ∼46 minutes), which is in itself a desirable isotope for TAT. The targeted delivery of Ac-225 to tumor sites has been shown in a number of instances to be highly effective for the treatment of several forms of cancer when a conjugate with an antibody, peptide, or protein is produced which can carry the isotope to the target site. One of the more notable instances of the successful treatment of human cancer with Ac-225 has been in the treatment of prostate cancer, for which Ac-225 may be conjugated with Prostate Specific Membrane Antigen for targeted doses to prostate cancer tumor cells. Because of the proven efficacy of Ac-225-containing conjugate species in anticancer treatment applications, demand for this isotope is expected to rise above current production capabilities. The work presented herein describes a new method for the separation of Ac-225 from radiolanthanide impurities resulting from fission of proton irradiated Th-232 target foils. The process incorporates a solvent impregnated resin to achieve the separation, and is the first in a series of resins to be tested as alternatives to current technologies incorporating branched DGA resin. The current resin is comprised of an Amberlite XAD7HP resin that has been loaded with the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonamide ([Bmim][NTf2]) and the extractant N,N-dioctyldiglycolamic acid (DODGAA). Going forward, the resin will be tuned to achieve optimum results by loading the Amberlite scaffold with varying combinations of ionic liquids and extractants. Data presented will include batch extraction experiments including the solvent impregnated resin with complex matrices of metals (La-Lu, Sc, Y, U, Th, Ac) in HCl, HNO3, and citrate-phosphate buffer media over a range of pH. Additionally, results of dynamic column experiments will be presented, and comparisons will be made to separations technologies currently in use.

Simulation and Experimental Comparison of Laser Impact Welding with a Plasma Pressure Model

In this study, spatial and temporal profiles of an Nd-YAG laser beam pressure pulse are experimentally characterized and fully captured for use in numerical simulations of laser impact welding (LIW). Both axisymmetric, Arbitrary Lagrangian-Eulerian (ALE) and Eulerian dynamic explicit numerical simulations of the collision and deformation of the flyer and target foils are created. The effect of the standoff distance between the foils on impact angle, velocity distribution, springback, the overall shape of the deformed foils, and the weld strength in lap shear tests are investigated. In addition, the jetting phenomenon (separation and ejection of particles at very high velocities due to high-impact collision) and interlocking of the foils along the weld interface are simulated. Simulation results are compared to experiments, which exhibit very similar deformation and impact behaviors. In contrast to previous numerical studies that assume a pre-defined deformed flyer foil shape with uniform initial velocity, the research in this work shows that incorporation of the actual spatial and temporal profiles of the laser beam and modeling of the corresponding pressure pulse based on a laser shock peening approach provides a more realistic prediction of the LIW process mechanism.

Controlling energy distribution of fast ions and X-ray emission via target reliefs in ultrafast and relativistic laser plasma interaction

Secondary emission from laser produced plasma is governed by the electron distribution function. Therefore, its control is of utmost importance to steer the emission, e.g., of ultrashort bursts of high energy photons and ions for decisive application. Maximum gain is achieved if the laser light absorption by plasma is also maximized. In our theoretical analysis including comparison to recent experiments, we follow this route and study how the energy is transferred from a short laser pulse to the energy of fast ions and X-rays. We make use of ion and K-α emissions, which respond differently to branches of the electron distribution function when we optimize the laser light absorption via structuring of the target surface. Our investigation comprises laser intensities up to 5 × 1020 W/cm2 produced with femtosecond near infrared laser pulses and titanium foil targets of a few micrometer thicknesses. In particular, we reveal an energy relaxation process of hot electrons, which determines the observed laser intensity dependence of secondary emission and points to the benefit of target surface structuring in different optimization scenarios.

Determination of the 193Ir(n, 2n) reaction cross section and correction methodology for the 191Ir(n,$ \gamma$) contamination

The cross section of the 193Ir(n, 2n)192Ir reaction has been determined by means of the activation technique, relative to the 27Al (n,$ \alpha$) and 197Au(n, 2n) reference reactions cross sections, at neutron beam energies ranging from 10 to 21 MeV. The quasi-monoenergetic neutron beams were produced at the 5.5 MV Tandem T11/25 Accelerator Laboratory of NCSR “Demokritos” via the 2H(d, n) and 3H(d, n) reactions. The induced $ \gamma$-ray activity of the irradiated target and reference foils was measured with high resolution HPGe detectors. In order to correct for the contribution of the 191Ir(n,$ \gamma$)192Ir reaction, which is open to low energy parasitic neutrons, a recently developed analysis method was implemented and it is presented in great detail. Furthermore, cross section theoretical calculations were carried out using the EMPIRE and TALYS codes over a wide energy range.

Laser-driven acceleration of quasi-monoenergetic, near-collimated titanium ions via a transparency-enhanced acceleration scheme

Laser-driven ion acceleration has been an active research area in the past two decades with the prospects of designing novel and compact ion accelerators. Many potential applications in science and industry require high-quality, energetic ion beams with low divergence and narrow energy spread. Intense laser ion acceleration research strives to meet these challenges and may provide high charge state beams, with some successes for carbon and lighter ions. Here we demonstrate the generation of well collimated, quasi-monoenergetic titanium ions with energies ∼145 and 180 MeV in experiments using the high-contrast (<10−9) and high-intensity () Trident laser and ultra-thin (∼100 nm) titanium foil targets. Numerical simulations show that the foils become transparent to the laser pulses, undergoing relativistically induced transparency (RIT), resulting in a two-stage acceleration process which lasts until ∼2 ps after the onset of RIT. Such long acceleration time in the self-generated electric fields in the expanding plasma enables the formation of the quasi-monoenergetic peaks. This work contributes to the better understanding of the acceleration of heavier ions in the RIT regime, towards the development of next generation laser-based ion accelerators for various applications.

The differential cross section in deuteron-proton elastic scattering at 500, 750 and 900 MeV/nucleon

The results on the differential cross section of dp elastic scattering obtained at the Internal Target Station at the Nuclotron JINR at the energies of 500, 750 and 900MeV/nucleon are presented. The measurements have been performed using an unpolarized deuteron beam and polyethylene foil target. The data have been obtained in the angular range of $ 70^{\circ}$ - $ 120^{\circ}$ in the cms. The angular dependences of the data from the present experiment are compared with the world experimental data obtained at nearby energies as well as with the theoretical calculations performed within the relativistic multiple scattering theory. The behavior of the differential cross section at the fixed scattering angles covering the total cms energy region of $ \sqrt{s} = 3.1 -3.42$ GeV is in qualitative agreement with the s power-law dependence.

Isolation and quantification of a 93Mo isotope solution from proton irradiated niobium

93Mo (4000 y half-life) formed through the 93Nb(p,n)93Mo reaction was isolated from a niobium target foil previously used in a low energy medical cyclotron. 93Mo has identical characteristic x-ray emission and mass as the isomer 93mNb and stable Nb present in the target foil at much higher concentrations. This makes distinction between 93Mo, 93mNb and stable Nb difficult using radiometric or mass spectrometric methods. An anion exchange method in combination with x-ray spectrometry and ICP-MS/OES enabled quantitative isolation of about 0.4 μg 93Mo (14 kBq) from 93mNb with a separation factor >104 on a single column. An extraction chromatography column (TEVA) was used to reach a93mNb/93Mo activity ratio of <10−6 and an atom ratio 93Nb/93Mo <1% making the 93Mo suitable for both radiometric and mass spectrometric testing. 93Mo is the only radioisotope of molybdenum with a long enough half-life suitable for this purpose. Calibration of the 93Mo isotope solution was done through x-ray spectrometry using a characterized BEGe-detector in combination with a99mTc solution. This is the first reported isolation of a93Mo solution in the literature and the first time a LSC-spectrum of 93Mo is shown.

A platform for nuclear physics experiments with laser-accelerated light ions

A novel platform for nuclear physics experiments has been developed on the high-energy, short-pulse OMEGA EP Laser System. Planar foil targets are irradiated with a 10-ps, 1-kJ infrared beam focused to an intensity of the order of 1018 W/cm2. Relativistic electrons generated in the laser–target interaction escape the target, generating a very large electrostatic field, which extracts ions from the target’s back surface and accelerates them to MeV energies. The energetic ion flow from the back side of this primary target creates neutrons and charged particles through nuclear reactions in a secondary target placed in the ion flow. Charged-particle detectors were used to measure the energy spectra of the ions. The energy spectrum of the neutrons generated in the secondary target was measured using scintillator-based neutron time-of-flight detectors. First experiments to validate the performance of this setup studied d(d,n)3He and 9Be(d,n)10B reactions. This experimental platform is suitable especially for survey-type studies of nuclear reactions and for reactions that involve rare or radioactive ions like tritium.

Study of laser produced plasma in a longitudinal magnetic field

Laser produced plasma embedded in a longitudinal magnetic field was studied using a 1 MA pulsed power generator coupled with a 50 TW laser. Half turn coil loads with an internal diameter of 2.5–3.5 mm generate a 50–70 T axial magnetic field near the load. A subpicosecond laser pulse with an intensity of 1018–1019 W/cm2 irradiates a thin Si foil target in the magnetic field of the coil load. A laser produced plasma plume collimates within the longitudinal field to a narrow jet 0.2–0.3 mm in diameter with a length of 3–4 mm and an electron plasma density of (0.2–1) × 1020 cm−3 on the jet axis. The jet propagates with a velocity of 160–200 km/s in general agreement with magnetohydrodynamic simulations. X-ray spectral measurements show an increase in the plasma electron density resulting from the magnetic confinement of the jet.

FLUKA simulation yields in a comparison with theoretical and experimental yields relevant to 89Zr produced in the 89Y(p,n) reaction

Abstract The high importance of zirconium-89 (T1/2 = 78.41 h) is related to its applications in medical imaging. It can be produced at low-energy cyclotrons by the reaction 89Y(p,n)89Zr. There exist several publications on its production at low and intermediate energies but there is discrepancy with simulated data. In this study we considered the experimental parameters for four different types of yttrium foil targets reported in literature. The experimental parameters considered were the target geometry, beam profile, and angle of the target relative to the beam during irradiation. The Monte-Carlo code FLUKA was used to calculate production yields. The resulting values obtained by FLUKA from pencil beam or spread energy beam were compared to the theoretical yields obtained from the excitation function and the experimental ones. The FLUKA prediction for 89Z-yield reached ≈50 MBq/μA · h which agrees to a high extent with experimental and theoretical yields reported for the different targets.

Photonuclear production, chemistry, and in vitro evaluation of the theranostic radionuclide 47Sc

BackgroundIn molecular imaging and nuclear medicine, theranostic agents that integrate radionuclide pairs are successfully being used for individualized care, which has led to rapidly growing interest in their continued development. These compounds, which are radiolabeled with one radionuclide for imaging and a chemically identical or similar radionuclide for therapy, may improve patient-specific treatment and outcomes by matching the properties of different radionuclides with a targeting vector for a particular tumor type. One proposed theranostic radionuclide is scandium-47 (47Sc, T1/2 = 3.35 days), which can be used for targeted radiotherapy and may be paired with the positron emitting radionuclides, 43Sc (T1/2 = 3.89 h) and 44Sc (T1/2 = 3.97 h) for imaging. The aim of this study was to investigate the photonuclear production of 47Sc via the 48Ti(γ,p)47Sc reaction using an electron linear accelerator (eLINAC), separation and purification of 47Sc, the radiolabeling of somatostatin receptor-targeting peptide DOTATOC with 47Sc, and in vitro receptor-mediated binding of [47Sc]Sc-DOTATOC in AR42J somatostatin receptor subtype two (SSTR2) expressing rat pancreatic tumor cells.ResultsThe rate of 47Sc production in a stack of natural titanium foils (n = 39) was 8 × 107 Bq/mA·h (n = 3). Irradiated target foils were dissolved in 2.0 M H2SO4 under reflux. After dissolution, trivalent 47Sc ions were separated from natural Ti using AG MP-50 cation exchange resin. The recovered 47Sc was then purified using CHELEX 100 ion exchange resin. The average decay-corrected two-step 47Sc recovery (n = 9) was (77 ± 7)%. A radiolabeling yield of > 99.9% of [47Sc]Sc-DOTATOC (0.384 mg in 0.3 mL) was achieved using 1.7 MBq of 47Sc. Blocking studies using Octreotide illustrated receptor-mediated uptake of [47Sc]Sc-DOTATOC in AR42J cells.Conclusions47Sc can be produced via the 48Ti(γ,p)47Sc reaction and separated from natural Ti targets with a yield and radiochemical purity suitable for radiolabeling of peptides for in vitro studies. The data in this work supports the potential use of eLINACs for studies of photonuclear production of medical radionuclides and the future development of high-intensity eLINAC facilities capable of producing relevant quantities of carrier-free radionuclides currently inaccessible via routine production pathways or limited due to costly enriched targets.

Fabrication of thin 130Te target foils for sub-barrier fusion studies

Abstract Thin 130Te target foils of thickness 139– 260 μ g /cm 2 have been prepared on 12C backing using resistive evaporation technique for sub-barrier fusion studies in heavy-ion induced nuclear reactions. The deposition thickness of both 12C and 130 Te has been measured using profilometer , and the thickness of a few target foils has been measured using α -transmission method. Target foils fabricated in the present work have been characterized using the Rutherford Backscattering Spectrometry (RBS), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDXS) for impurity and to estimate the thickness. 130 Te is known to be brittle with the low melting point, and it quickly degrades if bombarded with energetic heavy-ion beams. In the present work, 130Te target foils fabricated on carbon backing were bombarded with 70 MeV 32S and 114–155 MeV 35 , 37 Cl beams to vet the stability of the targets. It has been observed that 130Te target foils fabricated on 12C backing survived the bombardment with energetic 32S, and 35 , 37 Cl beams without any degradation for the entire duration of sub-barrier fusion measurement at different energies.

Measurement of spallation cross sections for the production of terbium radioisotopes for medical applications from tantalum targets

We present new measurements of cumulative cross sections for the production of 139Ce and 149Tb by proton-induced spallation of tantalum foil targets at different proton energies between 300 and 1700 MeV, using the COSY synchrotron at FZ Jülich. Those measurements are presented in the context of the production of medically-relevant radioisotopes for medical applications.

Target fabrication for laser-ion acceleration research at the Technological Laboratory of the LMU Munich

The Technological Laboratory of LMU Munich supplies various types of solid-state target for laser plasma experiments at the Centre for Advanced Laser Applications in Garching. Our main focus here is on the production of free-standing, thin foil targets, such as diamond-like-carbon foils, carbon nanotube foams (CNFs), plastic, and gold foils. The presented methods comprise cathodic arc deposition for DLC targets, chemical vapor deposition for CNFs, a droplet and spin-coating process for plastic foil production, as well as physical vapor deposition that has been optimized to provide ultrathin gold foils and tailored sacrifice layers. This paper reviews our current capabilities, which are a result of a close collaboration between target production processes and experiment, using high-power chirped pulse amplification laser systems over the past eight years.

Excitation function of the [formula omitted] reactions within the energy range of 10-22 MeV

The production cross-sections of the V48, S47c, S46c, and S44mc residues were measured in the proton induced Tnati reactions using the stack foil activation technique followed by the off-line γ−ray spectrometry. The present work was carried out at 14UD BARC-TIFR Pelletron accelerator, Mumbai, India. The proton beam of 22 MeV was used for the irradiation of the samples and was degraded along the stack of target foils using aluminum (Al) degraders. The measured cross-section data were compared with the existing literature data available in EXFOR data library. The results were also compared with the theoretical values from the TALYS-1.9 and the ALICE-2014 nuclear model codes using the suitable input level density models. The pre-equilibrium contribution has also been estimated for the populated reaction residues in the present work. The present work offers a comparison between the two theoretical model codes using a similar input level density model. The reaction product S44mc also has some practical medical applications in nuclear medicine.

Transparent capacitive micromachined ultrasonic transducers (CMUTs) for photoacoustic applications

Integration of acoustic and optical techniques prompted the need for transparent ultrasonic transducers to guide the light through the transducer and improve the signal to noise ratio. In the presented paper, capacitive micromachined ultrasound transducers (CMUTs) using glass substrate and indium-tin-oxide electrodes were fabricated by adhesive wafer bonding technique presenting a transparency of up to 82% in the visible range. A receive sensitivity of 65.5 μV/Pa was measured with noise equivalent sensitivity of 95 Pa. Capacity of the produced CMUTs for photoacoustic imaging was also demonstrated by successfully detecting the photoacoustic signal from an aluminum foil target, which was irradiated by a 532-nm pulse laser transmitted through the CMUT. The centre frequency of the detected photoacoustic signal was at 2 MHz with 52.3% -6-dB fractional bandwidth.

Characteristics of the preplasma formation using an uncompressed picosecond-long laser pulse with a large spot size on Al and mylar targets

A preplasma plays a very important role in laser-driven proton acceleration, where it can increase the proton energy significantly. In this research, we generated a nearly planar preplasma intentionally by sending an uncompressed picosecond-long Ti:sapphire laser pulse with a large spot size onto a thin foil target (Al and mylar) and investigated the characteristics of the preplasma by using a space-time-resolved Nomarski interferometer. In this paper, a simple analytical approach employing the one-dimensional collisional plasma concept was also developed and its result is compared with the experimental results. This work reveals the detailed characteristics of the behavior of the planar preplasma, which is very important in laser-driven proton acceleration, X-ray laser, etc., employing laser-solid interactions.