Generation of fast protons by interaction of modest laser intensities with H2O “snow” nano-wire targets

We report on the generation of protons with energies of 5.5 MeV when irradiating an H₂O nano-wire layer grown on a sapphire plate with an intensity of 5×10¹⁷ W/cm². A theoretical model is suggested in which plasma near the tip of the wire is subject to enhanced electrical fields and protons are accelerated to several MeVs.     

The response of a CsI(Tl) scintillator with photodiode readout to light particles and heavy ions

The response of a small (1 cm³) CsI(Tl) crystal coupled to a silicon photodiode to light particles and heavy ions has been investigated using proton, alpha and oxygen beams in the energy range 10–25 MeV/n.Pulse-height resolution of 1.2 and 2.9% [fwhm] have been measured for 98 MeV ⁴He and 278 MeV ¹⁶O. The use of CsI(Tl)-photodiode assembly in nuclear physics experiments with intermediate energy heavy-ions beams is envisaged     

Development of a cryogenic gas target for intense RI beam production at CRIB

Nuclear reactions of astrophysical interest, especially those under high-temperature and high-density conditions, require high-intensity low-energy radioactive ion beams, because the cross-sections are very small for the direct method study. Production of high-intensity radioactive ion beams is, therefore, one of the key developments for RI beam facilities.We report the development of a new cryogenic RI beam production gas target, along with its characteristics and performance. Some of its advantages are the increased stability against high-current primary beams and the increased thickness due to the cooling by liquid nitrogen.The target is being tested with heavy-ion beams. Measures by energy loss of the beam indicate that a thickness of about 2.4 mg/cm² of H₂ gas has been attained and a secondary beam of ⁷Be⁴⁺ at 4.0 MeV/u of more than 2×10⁸ pps was produced.     

A storage ring for the JULIC cyclotron

The storage ring COSY is planned to provide higher intensity and resolution for nuclear structure experiments using the light heavy ion beams (p, d, τ, α) of the JULIC cyclotron and the magnet spectrograph BIG KARL. The ring contains the measuring target of BIG KARL as an internal target, two rf cavities for compensating the mean energy loss in the target and providing additional acceleration of the stored beam and an e^?-cooling section. In the recirculator mode, i.e., without e^?-cooling, a luminosity of L = 3.64 × 10³⁰ particles/(cm² s) is obtained for an experiment with 41 MeV protons and a 50 μg/cm²¹²C target at a spectrograph resolution p/dp = 10⁴ and 100% duty factor. This corresponds to a gain in L of 546.5 in comparison with the same experiment without a storage ring. In the recirculator mode with acceleration L = 1.17 × 10³² p/(cm² s) and 98.8% duty factor results for 1500 MeV protons on the same target at the same resolution. Using e^?-cooling L and the feasible p/dp can be enhanced, however, at a reduced duty factor.     

Estimation of the impurity levels in polyimide foils and the life-time of the foils irradiated by charged projectiles

The life-time of thin polyimide foils (prepared by in-situ polymerisation) in beams of 2.0 MeV helium ions and 1.5 MeV protons has been studied, irradiating foils with beams of different intensities. The impurity levels of the foils measured by PIXE and RBS were found to be in order of ng/cm².     

PIXE detection limits for dental enamel from some human teeth by excitation with protons and He ions from a 3 MeV Van der Graaff accelerator

A technique has been developed to measure elemental content in human teeth using H⁺ and ⁴He²⁺ ion beam analysis. Teeth of Oradea inhabitants were sampled in two stomatological clinics in Oradea in the period of 2004 and 2005 years. Tooth samples were irradiated in vacuum with 2 MeV proton and 3 MeV alpha beams from a Van der Graaff electrostatic accelerator of EG-5 experimental facility in FLNP, JINR. The particle induced X-ray emission (PIXE) analysis, apart from determination of Ca, allowed an optimised detection of Cr, Cu, Fe and Zn above the detection limits by the use of Al and Mylar filters. The detection limits for K_α X-rays using proton and alpha beams are determined and discussed.     

Neutronic design and simulated performance of Peking University Neutron Imaging Facility (PKUNIFTY)

The Peking University Neutron Imaging Facility (PKUNIFTY) is a Radio Frequency Quadruple (RFQ) accelerator based system. The fast neutrons are produced by 2 MeV deuterons bombarding beryllium target. The moderator, reflector, shielding and collimator have been optimized with Monte-Carlo simulation to improve the neutron beam quality. The neutrons are thermalized in water cylinder of Φ26×26 cm² with a polyethylene disk in front of Be target. The size of deuteron beam spot is optimized considering both the thermal neutron distribution and the demand of target cooling. The shielding is a combination of 8 cm thick lead and 42 cm thick boron doped polyethylene. The thermal neutrons are extracted through a rectangular inner collimator and a divergent outer collimator. The thermal neutron beam axis is perpendicular to the D⁺ beam line in order to reduce the fast neutron and the γ ray components in the imaging beam. When the neutron yield is 3×10¹² n/s and the L/D is 50, the thermal neutron flux is 5×10⁵ n/cm²/s at the imaging plane, the Cd ratio is 1.63 and the n/γ ratio is 1.6×10¹⁰ n/cm²/Sv.     

Modifications induced by silicon and nickel ion beams in the electrical conductivity of zinc nanowires

This paper presents the modification in electrical conductivity of Zn nanowires under swift heavy ions irradiation at different fluences. The polycrystalline Zn nanowires were synthesized within polymeric templates, using electrochemical deposition technique and were irradiated with 80 MeV Si⁷⁺ and 110 MeV Ni⁸⁺ ion beams with fluence varying from 1 × 10¹² to 3 × 10¹³ ions/cm². I–V characteristics of exposed nanowires revealed a decrease in electrical conductivity with increase in ion fluence which was found to be independent of applied potential difference. But in the case of high fluence of Ni ion beam (3 × 10¹³ ions/cm²), electrical conductivity was found to increase with potential difference. The analysis found a significant contribution from grain boundaries scattering of conduction electrons and defects produced by ion beam during irradiation on flow of charge carriers in nanowires.     

Ag and O ion irradiation induced improvement in dielectric properties of the Ba(Co1/3Nb2/3)O3 thin films

We present the preliminary results of temperature and frequency dependent dielectric measurements on Ba(Co_1/3Nb_2/3)O₃ (BCN) thin films. These films were prepared on indium tin oxide (ITO) coated glass substrates by the pulse laser deposition (PLD) technique. It exhibits single-phase hexagonal symmetry. These films were irradiated with Ag¹⁵⁺ (200 MeV) and O⁷⁺ (100 MeV) beams at the fluence 1 × 10¹¹, 1 × 10¹², and 1 × 10¹³ ions/cm². On irradiating these films, its dielectric constant (?′) and dielectric loss (tan δ) parameters improve compared to un-irradiated film. Compared to O⁷⁺ irradiation induced point/cluster defects Ag¹⁵⁺ induced columnar defects are more effective in reducing/pinning trapped charges within grains. The present paper highlights the role of swift heavy ion irradiation in engineering the dielectric properties of conductive samples to enable them to be useful for microwave device applications.     

Experimental modeling of fast neutron-beam impact on Pt using Ar+ beams

Using the methods of field ion microscopy, we studied radiation-induced defects on an atomically clean surface and within a subsurface volume of platinum initiated by the interaction of neutron (E > 0.1 MeV) and Ar⁺ beams (E = 30 keV). It is shown that interaction of fast neutrons (E > 0.1 MeV, F = 6.7 × 10²¹ m^?2, and 3.5 × 10²² m^?2) with platinum leads to the same radiation damage in the volume of Pt as that produced by beams of Ar⁺ ions (E = 30 keV, F = 10¹⁶ ion/cm²) and is observed at a depth of about 1.5–2 nm beneath the irradiated Pt surface. Thus, we have carried out modeling of neutron impact with matter when replacing the neutron beam by an ion beam that causes the same radiation damage in the bulk of the material.     

High-fidelity MCNP modeling of a D-T neutron generator for active interrogation of special nuclear material

Fast and robust methods for interrogation of special nuclear material (SNM) are of interest to many agencies and institutions in the United States. It is well known that passive interrogation methods are typically sufficient for plutonium identification because of a relatively high neutron production rate from ²⁴⁰Pu [1]. On the other hand, identification of shielded uranium requires active methods using neutron or photon sources [2]. Deuterium-deuterium (2.45 MeV) and deuterium-tritium (14.1 MeV) neutron-generator sources have been previously tested and proven to be relatively reliable instruments for active interrogation of nuclear materials [3] and [4]. In addition, the newest generators of this type are small enough for applications requiring portable interrogation systems.Active interrogation techniques using high-energy neutrons are being investigated as a method to detect hidden SNM in shielded containers [4] and [5]. Due to the thickness of some containers, penetrating radiation such as high-energy neutrons can provide a potential means of probing shielded SNM. In an effort to develop the capability to assess the signal seen from various forms of shielded nuclear materials, the University of Michigan Neutron Science Laboratory’s D-T neutron generator and its shielding were accurately modeled in MCNP. The generator, while operating at nominal power, produces approximately 1×10¹⁰ neutrons/s, a source intensity which requires a large amount of shielding to minimize the dose rates around the generator. For this reason, the existing shielding completely encompasses the generator and does not include beam ports. Therefore, several MCNP simulations were performed to estimate the yield of uncollided 14.1-MeV neutrons from the generator for active interrogation experiments. Beam port diameters of 5, 10, 15, 20, and 25 cm were modeled to assess the resulting neutron fluxes. The neutron flux outside the beam ports was estimated to be approximately 2×10⁴ n/cm² s.     

Carbon-silicon stripper foils

TRIUMF operates several high power industrial cyclotrons for the commercial production of isotopes for radiological diagnostics and therapy. Two of these accelerators, TR30-1 and TR30-2, are capable of delivering H⁻ beams of 30 MeV and beam currents in excess of 1000 μA. For many years, in-house produced diamond-like carbon (DLC) foils of various compositions have been utilized to extract proton beams from these cyclotrons (Zeisler and Jaggi, 2008) [1].The TRIUMF Carbon Foil Laboratory, now incorporated as Micromatter^TM, uses pulsed laser deposition to fabricate DLC films in a wide thickness range (from 10 nm to ∼10 μm). More recently, we reported the production of DLC foils containing boron (Zeisler and Jaggi, 2010) [2]. Carbon-boron multilayer foils have outstanding mechanical stability and show an extended lifetime in high intensity proton beams. In an attempt to further enhance the quality of our beam strippers, we investigated the production of carbon-silicon multilayer foils.     

UV photoconductivity characteristics of ZnO nanowire field effect transistor treated by proton irradiation

We investigated the UV photoconductivity characteristics of ZnO nanowire field effect transistors (FETs) irradiated by proton beams. After proton beam irradiation (using a beam energy of 10 MeV and a fluence of 10¹² cm^− 2), the drain current and carrier density in the ZnO nanowire FETs decreased, and the threshold voltage shifted to the positive gate bias direction due to the creation of interface traps at the SiO₂/ZnO nanowire interface by the proton beam. The interface traps produced a higher surface barrier potential and a larger depletion region at the ZnO nanowire surface, affecting the photoconductivity and its decay time. The UV photoconductivity of the proton-irradiated ZnO nanowire FETs was higher and more prolonged than that of the pristine ZnO nanowire FETs. The results extend our understanding of the UV photoconductivity characteristics of ZnO nanowire devices and other materials when irradiated with highly energetic particles.     

High resolution X-ray diffraction studies on unirradiated and irradiated strontium hexaferrite crystals

High-resolution X-ray diffraction technique, employing a three-crystal monochromator?Ccollimator combination is used to study the irradiation induced defects in flux grown Sr-hexaferrite crystals irradiated with 50?MeV Li³⁺ ion beams at room temperature with a fluence value of 1 × 10¹⁴ ions/cm². The diffraction curves of the irradiated crystals suggest the possibility of creation of low angle grain boundaries and other point/clusters of defects causing amorphization in the irradiated crystals. The perfection of the irradiated and unirradiated (0001) cleaved surfaces of the crystals is studied using the bulk method of X-ray topography. The topographs supplement the findings suggestive of modifications in the crystalline quality of SrFe₁₂O₁₉ on irradiation with SHI of Li^3?+?. Etching of the (0001) cleaved surfaces in H₃PO₄ at 120°C suggests that the dissolution characteristics of the surfaces get affected on irradiation with SHI of Li^3?+?, besides supporting the findings of HRXRD and X-ray topography regarding modifications in the perfection of SrFe₁₂O₁₉ on irradiation.     

Continuous measurement of radiation damage of standard CMOS imagers

In this work we have irradiated a standard CMOS VGA imager with a 24 MeV proton beam at INFN Laboratori Nazionali del Sud, up to a nominal fluence of 10¹⁴ protons/cm². The device under test was fabricated with a 130 nm technology without radiation hardening. During the damaging the detector was fully operational to monitor the progressive damaging of the sensor and the associated on-pixel electronics in terms of detection efficiency, charge collection and noise. We found that the detector is still working at 10¹³ protons/cm², with a moderate increase of the noise (20%).     

Crystallinity and electrical conductivity of sulfur-containing microcrystalline diamond thin film

Hydrogen sulfide (H₂S) was introduced into a microwave plasma chemical vapor deposition of microcrystalline diamond thin film. Secondary-ion mass spectroscopy showed that sulfur concentration was controlled from 2 × 10¹⁵ to 9 × 10¹⁷ cm^− 3 by controlling the H₂S/CH₄ ratio, while that of hydrogen concentration was around 5 × 10²⁰ cm^− 3 and was independent of the H₂S/CH₄ ratio. Electrical conductance increased linearly as the S concentration increased from 2 × 10¹⁵ to 3 × 10¹⁶ cm^− 3 without significant deterioration of film crystallinity, i.e., the amount of sp² phase did not increase. Non-ohmic conduction was converted to ohmic conduction when the S concentration reached 9 × 10¹⁷ cm^− 3 by increasing the H₂S/CH₄ ratio to 30,000 ppm. This modification was consistent to the formation of a graphitic phase by heavy S-doping, which was identified by Raman spectra and surface morphology.     

Transient optical phenomena in quartz fibers under high-power pulsed reactor irradiation

Measurements of the intensity of emission and induced optical absorption at 400–750 nm in KU-1 quartz fibers were performed under pulsed irradiation in a BARS-6 reactor (pulse duration, 80 μs; dose per pulse, up to 5×10¹² neutrons/cm² (E>0.2 MeV); dose rate, up to 10⁵ Gy/s). The nondelayed emission component is due to the Cerenkov radiation, the weak relaxation component has a relaxation time of ∼150±50 μs, and the radiation-induced optical absorption reaches a value of 2.5×10⁻⁴ cm⁻¹ (relaxation time, 600–1200 μs). A nonlinear dependence of the Cerenkov radiation on the dose rate and the presence of the relaxation emission component and the transient optical absorption may be associated with an optical inhomogeneity of glass induced by the high-power reactor irradiation.     

High current, high energy proton beams accelerated by a sub-nanosecond laser

The sub-nanosecond laser system available at PALS facility in Prague has been used in order to produce MeV proton beams with typical current density approaching 1 A/cm² at few tens of centimeters from the target surface. In spite of the relatively long pulse duration (0.3 ns) and low intensity (∼10¹⁶ W/cm²), far away from the forefront laser facilities used for advanced proton beam acceleration in the recent years (from tens of femtoseconds to few picoseconds), the obtained results are promising both in terms of maximum proton energy and fast proton current. Real-time diagnostics systems, mainly in time-of-flight (TOF) configuration, have been used in order to estimate maximum and peak energy of the plasma fast proton component, peak current density, total number of fast protons and conversion efficiency of laser energy into accelerated fast proton total energy. Optimization of the maximum attainable proton energy and current has been carried out by irradiating targets of different composition as well as varying the laser energy and the focal spot diameter. Experimental results, as well as possible applications in material science and nuclear physics, are discussed and compared with literature data.     

DC sputter deposition of amorphous indium-gallium-zinc-oxide (a-IGZO) films with H2O introduction

Amorphous indium-gallium-zinc-oxide (a-IGZO) films were deposited by dc magnetron sputtering with H₂O introduction and how the H₂O partial pressure (P_H2O) during the deposition affects the electrical properties of the films was investigated in detail. Resistivity of the a-IGZO films increased dramatically to over 2 × 10⁵ Ωcm with increasing P_H2O to 2.7 × 10^− 2 Pa while the hydrogen concentration in the films increased to 2.0 × 10²¹ cm^− 3. TFTs using a-IGZO channels deposited under P_H2O at 1.6-8.6 × 10^− 2 Pa exhibited a field-effect mobility of 1.4-3.0 cm²/Vs, subthreshold swing of 1.0-1.6 V/decade and on-off current ratio of 3.9 × 10⁷-1.0 × 10⁸.