Gd Targets Research Articles

E2 decay strength of the M1 scissors mode of ^{156}Gd and its first excited rotational state.

The E2/M1 multipole mixing ratio δ_{1→2} of the 1_{sc}^{+}→2_{1}^{+} γ-ray decay in ^{156}Gd and hence the isovector E2 transition rate of the scissors mode of a well-deformed rotational nucleus has been measured for the first time. It has been obtained from the angular distribution of an artificial quasimonochromatic linearly polarized γ-ray beam of energy 3.07(6)MeV scattered inelastically off an isotopically highly enriched ^{156}Gd target. The data yield first direct support for the deformation dependence of effective proton and neutron quadrupole boson charges in the framework of algebraic nuclear models. First evidence for a low-lying J^{π}=2^{+} member of the rotational band of states on top of the 1^{+} band head is obtained, too, indicating a significant signature splitting in the K=1 scissors mode rotational band.

High-k gadolinium scandate on Si obtained by high pressure sputtering from metal targets and in-situ plasma oxidation

This article studies the physical and electrical behavior of Gd2−xScxO3 layers grown by high pressure sputtering from metallic Gd and Sc targets. The aim is to obtain a high permittivity dielectric for microelectronic applications. The films were obtained by the deposition of a metallic nanolaminate of Gd and Sc alternating layers, which is afterwards in-situ oxidized by plasma. The oxide films obtained were close to stoichiometry, amorphous and with minimal interfacial regrowth. By fabricating metal–insulator–semiconductor capacitors we found that a moderate temperature annealing is needed to enhance permittivity, which reaches a high value of 32 while keeping moderate leakage. Finally, the feasibility of interface scavenging in this material with Ti gate electrodes is also demonstrated.

Beyond Extreme Ultra Violet (BEUV) Radiation from Spherically symmetrical High-Z plasmas

Photo-lithography is a key technology for volume manufacture of high performance and compact semiconductor devices. Smaller and more complex structures can be fabricated by using shorter wavelength light in the photolithography. One of the most critical issues in development of the next generation photo-lithography is to increase energy conversion efficiency (CE) from laser to shorter wavelength light. Experimental database of beyond extreme ultraviolet (BEUV) radiation was obtained by using spherically symmetrical high-Z plasmas generated with spherically allocated laser beams. Absolute energy and spectra of BEUV light emitted from Tb, Gd, and Mo plasmas were measured with a absolutely calibrated BEUV calorimeter and a transmission grating spectrometer. 1.0 x 1012 W/cm2 is the optimal laser intensity to produced efficient BEUV light source plasmas with Tb and Gd targets. Maximum CE is achieved at 0.8% that is two times higher than the published CEs obtained with planar targets.

Recent target development activities at Inter-University Accelerator Centre

The target development laboratory at Inter-University Accelerator Centre (IUAC) is one of the main facilities for the fabrication of nuclear physics targets in India. Vacuum evaporation and cold rolling technique are mainly used for the production of isotopically pure targets at IUAC. Targets of Gd, Pt, W, Mo, Ta, Ni, Ag and Sn have been developed in the form of self-supporting targets and with thin carbon backing. Recent progress in target development laboratory at IUAC will be discussed in the report.

Experimental research on laser-produced Gd target plasma source for 6.7 nm lithography

Extreme ultraviolet (EUV) lithography at λ =6.7 nm is a challenging subject for next generation semiconductor lithography beyond 13.5 nm. The availability of strong radiation at the operating wavelength and low-debris of the plasma source are the two most important aspects for the development of laser-produced Gd plasma source at 6.7 nm. In this paper, experimental research on the extreme ultraviolet source based on the laser-produced Gd plasma is performed. Strong radiation near 6.7 nm from the source has been obtained, which is attributed to the n=4-n=4 transitions in Gd ions that overlap to yield an intense unresolved transition array (UTA). Dependence of spectral variation near the strong emission region of Gd plasma on the incident laser power density and detection angles is given. It is found that the intensity of EUV radiation around 6.7 nm is increased with increasing laser power density, and the emission peak around 7.1 nm increases faster than that of emission peak around 6.7 nm after the laser intensity reaching 6.4×1011 W/cm2, which is ascribed to the unique spectroscopic behavior of Gd ions. In addition, the energy of the ion debris from laser-produced Gd plasma source as well as the angular distribution of the ion yield off the target normal are measured with Faraday cup. Results show that the ion energy corresponding to the peak position of Gd ion energy distribution is about 2.6 keV at 10° off the target normal, and the yield of Gd ions decreases with the increase of the angle from the target normal. Furthermore, the stopping ability of an ambient magnetic field for ion debris from laser Gd plasma source is evaluated, and the result shows that the energetic Gd ion can be effectively mitigated by applying a 0.9 T magnetic field.

(Invited) High Pressure Sputtering for High-K Dielectric Deposition. Is It Worth Trying

Our research group studies the deposition of high permittivity dielectrics by a non-standard method: high-pressure sputtering. The dielectrics studied here are gadolinium scandate deposited from dielectric targets, and gadolinium oxide deposited from a metallic target, with an in situ plasma oxidation. The stoichiometric gadolinium scandate presents a slight permittivity boost after annealing, but with gadolinium-rich scandate (grown with an annealing of a nanolaminate) the dielectric shows a high effective permittivity of 21 and no noticeable SiO2 layer at the interface with Si. On the other hand, the stacks fabricated with the metallic Gd target have a SiO2 interface less than 0.7 nm thick that can be further reduced by scavenging with Ti gates. In fact, this scavenging effect is also demonstrated for the first time with indium phosphide substrates, obtaining a low capacitance equivalent thickness of only 2.1 nm.

Characterization onpH sensing performance and structural properties of gadolinium oxide post-treated by nitrogen rapid thermal annealing

A detail investigation on the pH sensing performance of Gd2O3 layer was proposed in this work. Electrolyte–insulator–semiconductor (EIS) structure with Gd2O3 layer deposited directly on silicon by reactive radio frequency sputtering with Gd target was chosen as the testing platform. The postdeposition rapid thermal annealing (RTA), performed at various temperatures for 1 min in N2 ambience, was first used to improve the pH sensing performance of Gd2O3. With RTA treatment at 800 °C, pH sensitivity of Gd2O3 EIS structure can be increased from 35.5 mV/pH to 55 mV/pH. This behavior can be explained by the increase of surface sites, which is supported by atomic force microscopy analysis. With RTA treatment at 700 °C and 800 °C, the drift coefficient for Gd2O3 layer was reduced to 0.03 and 1.2 mV/h, which is resulted from the densification of Gd2O3 layer supported by x-ray photoemission spectrometry. Therefore, Gd2O3 layer with RTA in N2 ambience at 700 °C or 800 °C could be a potential candidate for pH-sensitive membrane.

Photon strength functions in Gd isotopes studied from radiative capture of resonance neutrons

The experimental spectra of γ rays following radiative neutron capture on iso- lated resonances of stable 152,154−158 Gd targets were measured by the DANCE calorime- ter installed at the Los Alamos Neutron Scattering Center in New Mexico, USA. These spectra were analyzed within the extreme statistical model to get new information on the photon strength functions. Special emphasis was put on study of the scissors vibrational mode present in these isotopes. Our data show that the scissors-mode resonances are built not only on the ground states but also on the excited levels of all studied Gd iso- topes. The scissors mode strength observed in 157,159 Gd products is significantly higher than in neighboring even-even nuclei 156,158 Gd. Such a difference indicates the existence of an odd-even effect in the scissors mode strength. Moreover, there exists no universal parameter-free model of the electric dipole photon strength function describing the ex- perimental data in all of the Gd isotopes studied. The results for the scissors mode are compared with the (γ, γ � ) data for the ground-state transitions and with the results from 3 He-induced reactions.

Strength of the scissors mode in odd-mass Gd isotopes from the radiative capture of resonance neutrons

Radiative neutron capture reaction was measured in the resolved resonance region for ${}^{152,154,156,158}$Gd targets with the Detector for Advanced Neutron Capture Experiments $\ensuremath{\gamma}$-ray calorimeter at the Los Alamos Neutron Science Center. The $\ensuremath{\gamma}$-ray energy spectra for different multiplicities were obtained for several $s$-wave resonances in each nucleus. These spectra were analyzed within the extreme statistical model to provide unique information on the photon strength functions and especially on the scissors mode in odd Gd isotopes. The main result of this analysis is that in all nuclei scissors-mode resonances are built on excited levels and not only on their ground states. The strength of the mode found in ${}^{153}$Gd and ${}^{155}$Gd is comparable to the strength observed in well-deformed even-even Gd isotopes while it is substantially higher in ${}^{157,159}$Gd. The difference in observed strengths of the scissors mode indicates an existence of an even-odd effect in this quantity.

Extreme ultraviolet spectra from highly charged gadolinium and neodymium ions in the Large Helical Device and laser produced plasmas

We have observed extreme ultraviolet spectra from highly charged gadolinium (Gd) and neodymium (Nd) ions produced in two different types of light sources for comparative studies. Only broad quasicontinuum feature arising from unresolved transition array was observed in high-density laser produced plasmas of pure/diluted Gd and Nd targets at the University College Dublin, and the spectral feature largely depends on electron temperature in optically thin plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The difference in spectral feature among a number of spectra can be qualitatively interpreted by considering dominant ion stages and opacity effects in the plasmas.

High longitudinal relaxivity of ultra-small gadolinium oxide prepared by microsecond laser ablation in diethylene glycol

Ultra-small gadolinium oxide (Gd2O3) can be used as T1-weighted Magnetic Resonance Imaging (MRI) contrast agent own to its high longitudinal relaxivity (r1) and has attracted intensive attention in these years. In this paper, ultra-small Gd2O3 nanoparticles of 3.8 nm in diameter have been successfully synthesized by a microsecond laser ablating a gadolinium (Gd) target in diethylene glycol (DEG). The growth inhibition effect induced by the large viscosity of DEG makes it possible to synthesize ultra-small Gd2O3 by laser ablation in DEG. The r1 value and T1-weighted MR images are measured by a 3.0 T MRI spectroscope. The results show these nanoparticles with a high r1 value of 9.76 s−1 mM−1 to be good MRI contrast agents. We propose an explanation for the high r1 value of ultra-small Gd2O3 by considering the decreasing factor (surface to volume ratio of the nanoparticles, S/V) and the increasing factor (water hydration number of the Gd3+ on Gd2O3 surface, q), which offer a new look into the relaxivity studies of MRI contrast agents. Our research provides a new approach to preparing ultra-small Gd2O3 of high r1 value by laser ablation in DEG and develops the understanding of high relaxivity of ultra-small Gd2O3 MRI contrast agents.

Ligand-free gadolinium oxide for in vivo T1-weighted magnetic resonance imaging

Gadolinium oxide (Gd2O3), which can be used as a T1-weighted magnetic resonance imaging (MRI) contrast agent, has attracted intense attention in recent years. In this paper, ligand-free monoclinic Gd2O3 nanocrystals of 7.1 nm in diameter are synthesized by a simple and green approach, namely microsecond laser ablation of a gadolinium (Gd) target in deionized water. These nanocrystals obtain high r1 relaxivity of 5.53 s(-1) mM(-1), and their low toxicity was demonstrated by the cell viability of S18 cells and apoptosis in RAW264.7 cells. In vitro and in vivo MR images show these particles to be good T1-weighted MRI contrast agents. Base on the experimental results and theoretical analysis, we suggest that the purity of the Gd2O3 contributes to its high r1 relaxivity value, while the low toxicity is due to its good crystallinity. These findings show that laser ablation in liquid (LAL) is a promising strategy to synthesize ligand-free monoclinic Gd2O3 nanocrystals for use as high efficient T1-weighted MRI contrast agents.

High pressure sputtering as a viable technique for future high permittivity dielectric on III–V integration: GdOx on InP demonstration

The electrical properties of metal–oxide–semiconductor devices based on GdOx obtained by high pressure sputtering on InP substrates are studied. In order to prevent damage of the semiconductor substrate, an optimized two-step sputtering procedure has been used for the high permittivity dielectric deposition. First, a thin metallic Gd film was sputtered using a metallic Gd target and a pure Ar plasma. Then, without extracting the sample from the system, the GdOx films were obtained by plasma oxidation using an Ar/O2 mixed atmosphere and reducing plasma power to minimize damage and interfacial regrowth. The resulting devices show fully functional capacitance curves. After forming gas annealing, the capacitors do not show interface regrowth up to a temperature of 500 °C and the gate leakage stays within reasonable limits, below 2 × 10−4 Acm−2 at a gate voltage of 1.5 V. In addition, the interface trap density remains roughly constant with annealing temperature up to 400 °C, in the low 1013 eV−1cm−2 range, decreasing for higher temperatures. At 550 °C, the trap density is very low, under the detection limit of the conductance technique, but the devices show a severe capacitance reduction.

A Unique Matched Quadruplet of Terbium Radioisotopes for PET and SPECT and for α- and β−-Radionuclide Therapy: An In Vivo Proof-of-Concept Study with a New Receptor-Targeted Folate Derivative

Terbium offers 4 clinically interesting radioisotopes with complementary physical decay characteristics: (149)Tb, (152)Tb, (155)Tb, and (161)Tb. The identical chemical characteristics of these radioisotopes allow the preparation of radiopharmaceuticals with identical pharmacokinetics useful for PET ((152)Tb) and SPECT diagnosis ((155)Tb) and for α- ((149)Tb) and β(-)-particle ((161)Tb) therapy. The goal of this proof-of-concept study was to produce all 4 terbium radioisotopes and assess their diagnostic and therapeutic features in vivo when labeled with a folate-based targeting agent. (161)Tb was produced by irradiation of (160)Gd targets with neutrons at Paul Scherrer Institute or Institut Laue-Langevin. After neutron capture, the short-lived (161)Gd decays to (161)Tb. (149)Tb, (152)Tb, and (155)Tb were produced by proton-induced spallation of tantalum targets, followed by an online isotope separation process at ISOLDE/CERN. The isotopes were purified by means of cation exchange chromatography. For the in vivo studies, we used the DOTA-folate conjugate cm09, which binds to folate receptor (FR)-positive KB tumor cells. Therapy experiments with (149)Tb-cm09 and (161)Tb-cm09 were performed in KB tumor-bearing nude mice. Diagnostic PET/CT ((152)Tb-cm09) and SPECT/CT ((155)Tb-cm09 and (161)Tb-cm09) studies were performed in the same tumor mouse model. Carrier-free terbium radioisotopes were obtained after purification, with activities ranging from approximately 6 MBq (for (149)Tb) to approximately 15 MBq (for (161)Tb). The radiolabeling of cm09 was achieved in a greater than 96% radiochemical yield for all terbium radioisotopes. Biodistribution studies showed high and specific uptake in FR-positive tumor xenografts (23.8% ± 2.5% at 4 h after injection, 22.0% ± 4.4% at 24 h after injection, and 18.4% ± 1.8% at 48 h after injection). Excellent tumor-to-background ratios at 24 h after injection (tumor to blood, ≈ 15; tumor to liver, ≈ 5.9; and tumor to kidney, ≈ 0.8) allowed the visualization of tumors in mice using PET ((152)Tb-cm09) and SPECT ((155)Tb-cm09 and (161)Tb-cm09). Compared with no therapy, α- ((149)Tb-cm09) and β(-)-particle therapy ((161)Tb-cm09) resulted in a marked delay in tumor growth or even complete remission (33% for (149)Tb-cm09 and 80% for (161)Tb-cm09) and a significantly increased survival. For the first time, to our knowledge, 4 terbium radionuclides have been tested in parallel with tumor-bearing mice using an FR targeting agent. Along with excellent tumor visualization enabled by (152)Tb PET and (155)Tb SPECT, we demonstrated the therapeutic efficacy of the α-emitter (149)Tb and β(-)-emitter (161)Tb.

Fabrication of epitaxial zirconia and ceria thin films with arbitrary dopant and host atom composition

Epitaxial zirconia and ceria thin films have been of interest recently as components of solid oxide fuel cells and other devices as well as means to study interfacial and strain effects on ion motion. These films are typically fabricated by one of a variety of physical vapor deposition methods. One difficulty in these studies is that the film composition is fixed by the composition of a ceramic or metal alloy target. Here, we demonstrate a means to produce epitaxial films with arbitrary dopant composition and Zr–Ce ratio. Reactive co-sputtering was performed using pure elemental targets of Zr, Ce, Y, and Gd onto (100) MgO substrates. The use of metal targets allowed for high purity and, by varying the relative sputtering powers and deposition time, the composition and thickness of single or multi-layer thin films was controlled. X-ray diffraction and transmission electron microscopy showed that yttria-stabilized zirconia (YSZ) films deposited on (100) MgO substrates at a substrate temperature of 400°C were epitaxially grown along the (100) direction, while gadolinium doped ceria (GDC) films had no epitaxial relationship. Still, it was found that a YSZ film could be used as a buffer layer on the MgO substrates to enable epitaxial growth of the GDC film in the (100) orientation.

Optimizing conversion efficiency and reducing ion energy in a laser-produced Gd plasma

We have demonstrated an efficient extreme ultraviolet (EUV) source at 6.7 nm by irradiating Gd targets with 0.8 and 1.06 μm laser pulses of 140 fs to 10 ns duration. Maximum conversion efficiency of 0.4% was observed within a 0.6% bandwidth. A Faraday cup observed ion yield and time of flight signals for ions from plasmas generated by each laser. Ion kinetic energy was lower for shorter pulse durations, which yielded higher electron temperatures required for efficient EUV emission, due to higher laser intensity. Picosecond laser pulses were found to be the best suited to 6.7 nm EUV source generation.

Extreme ultraviolet source at 6.7 nm based on a low-density plasma

We demonstrate an efficient extreme ultraviolet (EUV) source for operation at λ = 6.7 nm by optimizing the optical thickness of gadolinium (Gd) plasmas. Using low initial density Gd targets and dual laser pulse irradiation, we observed a maximum EUV conversion efficiency (CE) of 0.54% for 0.6% bandwidth (BW) (1.8% for 2% BW), which is 1.6 times larger than the 0.33% (0.6% BW) CE produced from a solid density target. Enhancement of the EUV CE by use of a low-density plasma is attributed to the reduction of self-absorption effects.

The low-energy β− and electron emitter 161Tb as an alternative to 177Lu for targeted radionuclide therapy

The low-energy β(-) emitter (161)Tb is very similar to (177)Lu with respect to half-life, beta energy and chemical properties. However, (161)Tb also emits a significant amount of conversion and Auger electrons. Greater therapeutic effect can therefore be expected in comparison to (177)Lu. It also emits low-energy photons that are useful for gamma camera imaging. The (160)Gd(n,γ)(161)Gd→(161)Tb production route was used to produce (161)Tb by neutron irradiation of massive (160)Gd targets (up to 40 mg) in nuclear reactors. A semiautomated procedure based on cation exchange chromatography was developed and applied to isolate no carrier added (n.c.a.) (161)Tb from the bulk of the (160)Gd target and from its stable decay product (161)Dy. (161)Tb was used for radiolabeling DOTA-Tyr3-octreotate; the radiolabeling profile was compared to the commercially available n.c.a. (177)Lu. A (161)Tb Derenzo phantom was imaged using a small-animal single-photon emission computed tomography camera. Up to 15 GBq of (161)Tb was produced by long-term irradiation of Gd targets. Using a cation exchange resin, we obtained 80%-90% of the available (161)Tb with high specific activity, radionuclide and chemical purity and in quantities sufficient for therapeutic applications. The (161)Tb obtained was of the quality required to prepare (161)Tb-DOTA-Tyr3-octreotate. We were able to produce (161)Tb in n.c.a. form by irradiating highly enriched (160)Gd targets; it can be obtained in the quantity and quality required for the preparation of (161)Tb-labeled therapeutic agents.

Rare-earth plasma extreme ultraviolet sources at 6.5–6.7 nm

We have demonstrated a laser-produced plasma extreme ultraviolet source operating in the 6.5–6.7 nm region based on rare-earth targets of Gd and Tb coupled with a Mo/B4C multilayer mirror. Multiply charged ions produce strong resonance emission lines, which combine to yield an intense unresolved transition array. The spectra of these resonant lines around 6.7 nm (in-band: 6.7 nm ±1%) suggest that the in-band emission increases with increased plasma volume by suppressing the plasma hydrodynamic expansion loss at an electron temperature of about 50 eV, resulting in maximized emission.

Performances and stability of a 2.4 ton Gd organic liquid scintillator target for ν̄e detection

In this paper we report the performance and the chemical and physical properties of a 2 × 1.2 ton organic liquid scintillator target doped with Gd up to ∼ 0.1%, and the results of a 3 year long stability survey of the target. In particular we have measured and monitored the optical and fluorescent properties of the Gd-doped liquid scintillator (LS), the amount of both Gd and primary fluor in solution, and the performance of the two Gd doped targets as neutron detectors, namely neutron capture efficiency and average capture time. The experimental survey is ongoing, the targets being continuously monitored. From the spectrophotometric measurements performed on samples periodically extracted along the three years, we can exclude, at 99% C.L. level, a degradation of the light transmittance of the Gd-doped liquid scintillator larger than 1% y-1; from the in-tank measurements no significant decrease of the neutron capture efficiency and neutron capture time is observed. This is the largest stable Gd-doped organic liquid scintillator target ever produced and continuously operated for a long period.