Proton Beam Bombardment Research Articles

Effects of Simulated Solar Wind on Polymethyl Methacrylate Thin Film.

Space exploration missions are currently becoming more frequent, due to the ambition for space colonization in sight of strengthening terrestrial technologies and extracting new raw materials and/or resources. In this field, the study of the materials’ behaviour when exposed to space conditions is fundamental for enabling the use of currently existing materials or the development of new materials suitable for application in extra-terrestrial environments. In particular, the versatility of polymers renders them suitable for advanced applications, but the effects of space radiation on these materials are not yet fully understood. Here, to shed light on the effects of simulated solar wind on a polymeric material, polymethyl methacrylate (PMMA) was produced through radical bulk polymerization. The PMMA in the form of a thin film was subjected to proton beam bombardment at different fluences and in a high vacuum environment, with structural changes monitored through real-time FT-IR analysis. The structure of the residual material was investigated through MALDI-TOF mass spectrometry and 1H-NMR spectroscopy. The collected data allowed us to hypothesize the structural modifications of the PMMA and the related mechanisms.

Strong and durable fluorine-implanted targets developed for deep underground nuclear astrophysical experiments

Nine fluorine targets of various types were developed for the 19F(p, α)16O experiment to be performed at the Jinping Underground Nuclear Astrophysics Experiment (JUNA), China. Two targets were produced by evaporating CaF2 on Ta backings: one was produced by sputtering MgF2 on the Cr+Fe backings, and six were produced by implanting 20–80 keV 19F ions into pure Fe and Cu backings. Thin Cr protective layers were covered over these targets. We assessed each target’s stability by monitoring the γ-ray yields of the 19F(p, αγ)16O reaction over the well-known 340 keV resonance. Our results indicate that the traditional evaporated and sputtered targets exhibit 0.6%–6% deterioration (or 19F material loss) per Coulomb, while the implanted targets exhibit relatively small deterioration due to the proton beam bombardment. For the optimum target #8, the 19F target material loss is only approximately 0.05% per Coulomb proton beam bombardment, and such target is much more stable than the traditional targets. The fluorine depth distribution of the implanted target #8 was precisely analyzed by the atom probe tomography (APT) technique. The obtained depth distribution can well reproduce the experimental γ-ray yield curve. Furthermore, as test experiment, the 19F(p, αγ)16O cross section was measured with the implanted target #8 in a center-of-mass energy region of Ec.m. = 174–358 keV, which is consistent with the previous results. In conclusion, traditional fluorine targets produced with the evaporation and sputtering techniques are not suitable for the high-current experiment even with a protective layer. For the upcoming high-current JUNA experiment, this work offers an optimum target scheme: first, implanting 19F ions into the pure Fe backings with an implantation energy of 40 keV, and then sputtering a 50 nm thick Cr layer to further prevent the fluorine material loss.

Facile Synthetic Route to a Nitrogen‐doped Titanium Oxide with Enhanced Photoelectrochemical Property via Proton Beam Irradiation

A layered titanate with a light harvesting property only in a UV region was irradiated with a proton beam in the presence of nitrogen source like ammonium cation, in order to modify its band gap from UV to visible region. According to X‐ray diffraction and X‐ray absorption spectroscopy results, a protonic titanate maintains its lamellar structure even after proton beam bombardment, showing that the crystal structure of layered titanate was preserved even after the ammonium adsorption and successive proton beam irradiation for nitrogen doping. However, UV–vis and X‐ray photoelectron spectra clearly show that the proton beam irradiation could provide enough energy to introduce ~0.5 at. % of nitrogen atoms into the titanium oxide for absorbing not only UV but also visible light. Photocurrent measurement clearly reveals that the nitrogen‐doped titanium oxide via the proton beam treatment shows highly enhanced photocurrent in comparison with that of the bare titanium oxide, suggesting that the proton beam irradiation could be a potential method for band gap engineering of a wide variety of semiconducting materials.

Numerical Simulation on Molten Metal Collision Behavior Using SPH Method Combined with Fractal Analysis on Morphology of Stacking Pattern

The developments of the high power proton accelerators become a worldwide interest to provide various applications, where the targets are demanded to efficiently produce secondary beams and to survive intensive MW class proton beam power supplied by the accelerators. Solid metal targets might be melted by very high heat flux that is caused by the intensive proton beam bombardment. In fact, the incident occurred at J-PARC (Japan Proton Accelerator Research Complex), in which the gold solid target was locally melted to explosively jet molten gold. The molten gold jet collided with a structural beryllium flange plate that has a function of vacuum boundary. Some parts of molten gold were splashed and the other stuck on the flange plate. The relationship between the impact velocity and the morphology of the sticking pattern on the plate was quantitatively evaluated by introducing fractal analysis. It was found that the fractal dimension is correlated with the impact velocity and might be a useful factor to indicate the localized impact force and behavior.

Cavitation damage prediction for the JSNS mercury target vessel

The liquid mercury target system for the Japan Spallation Neutron Source (JSNS) at the Materials and Life science experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC) is designed to produce pulsed neutrons. The mercury target vessel in this system, which is made of type 316L stainless steel, is damaged by pressure wave-induced cavitation due to proton beam bombardment. Currently, cavitation damage is considered to be the dominant factor influencing the service life of the target vessel rather than radiation damage. In this study, cavitation damage to the interior surface of the target vessel was predicted on the basis of accumulated damage data from off-beam and on-beam experiments. The predicted damage was compared with the damage observed in a used target vessel. Furthermore, the effect of injecting gas microbubbles on cavitation damage was predicted through the measurement of the acoustic vibration of the target vessel. It was shown that the predicted depth of cavitation damage is reasonably coincident with the observed results. Moreover, it was confirmed that the injection of gas microbubbles had an effect on cavitation damage.

Monte carlo simulation of a radiation shielding carrier for proton-beam-irradiated sample

Two target rooms, TR23 and TR103, will be constructed for the utilization of the 20-MeV and the 100-MeV linear proton beams, and hot cells will be installed at these target rooms to handle samples that are highly activated by proton beam bombardment. The sample transport methods depend on the sample size because of the limited size of the penetration hole between the target room and the treatment room. For small samples that can be transported through the penetration hole, we can use a remotely-operated sample transport system, but for large-size samples will have to be moved through the shielding door opening, so a lead-shielded carrier has to be used for radiation protection. The carrier can be used to transport the samples from hot cell to another radiation worker’s areas in the accelerator building. In this research, we designed a lead-shielded carrier and evaluated its radiation shielding capability for the expected samples and their radioactivities by using Monte Carlo code simulations. We also calculated the shielding capability of the hot cell.

Coupling between the protons and PO4 tetrahedra in H+-ion-irradiated TlH2PO4

We studied hydrogen-bonded TlH2PO4 (TDP) ferroelectrics treated with proton-beam bombardment. The TDP material was irradiated with a 1-MeV proton beam at a dose of 1015/cm2. To analyze the local microscopic structure of TDP, we conducted 1H combined rotation and multiple pulse spectroscopy (CRAMPS), nuclear magnetic resonance (NMR), and high-resolution 31P NMR measurements. The isotropic chemical shifts of hydrogen and phosphor nuclei exhibited displacive features throughout the antiferroelectric, ferroelastic, and paraelastic phases that were attributed to the interplay of PO4 lattice deformation and the microscopic hydrogen bond network. The temperature dependence of the isotropic chemical shift σiso in 1H and high resolution 31P NMR revealed that the electronic charge redistribution was induced by proton-beam irradiation and the material’s elastic properties. We examined the proton-lattice relationship in terms of the proton’s location in a local double minimum well and the displacive character of the PO4 lattice.

Reliability Study of the Liquid Target Chamber for <sup>18</sup>F Production at the BATAN’s Cyclotron Facilities

The liquid target chamber for 18 F production at the Cyclotron Division, Centre for Radioisotopes and Radiopharmaceuticals (PRR) of the National Nuclear Energy Agency of Indonesia (BATAN) has been analysed for its reliability in enduring high pressures and heat transfer requirements during proton beam bombardment as well as the recommended irradiation parameters for effective 18 F production. The target chamber was subject to house the 18 O-enriched water bombarded with high energy proton beam to produce 18 F. A range of SRIM-computer simulations have also been conducted to calculate the ranges of several energetic proton beams (of up to 20 MeV) into pure water target. A study of radioactive impurities which might be produced from the proton-irradiated chamber’s materials was also included based on some references. Due to concern over the heat produced during target irradiation, a heat transfer analysis - particularly for the target’s cavity - was also included in the presented studies to obtain a brief preliminary calculation of the heating impacts prior to irradiation tests. The calculation was performed for various proton beam currents and energies of up to 30 μA and 20 MeV respectively. It was found that the chamber was reliable for production of 18 F from proton irradiated- 18 O enriched-water target by maintaining the chamber’s pressure of up to 3.6 bar if the proton beam current was kept below 16 μA for all energies or the proton beam energy was kept to or below 10 MeV for any employed beam currents. The overall heat transfer coefficient was also found to depend on the power deposited into the water target. Received: 25 June 2010; Revised: 20 March 2011; Accepted: 08 April 2011

Application of CRAMPS for a Phase Transition in H+-ion irradiated TlH2PO4

We studied the hydrogen-bonded <TEX>$TlH_2PO_4$</TEX> (TDP) ferroelectrics treated with the proton-beam bombardment. The TDP material was irradiated with 1-MeV proton beam at a dose of <TEX>$10^{15}/cm^2$</TEX>. In order to analyze the hydrogen environment in TDP, we carried out the <TEX>$^1H$</TEX> high resolution nuclear magnetic resonance (NMR) - i.e., Combined Rotation And Multiple Pulse Spectroscopy (CRAMPS) measurement. The isotropic chemical shift of hydrogen indicates its displacive property is related to the <TEX>$PO_4$</TEX> lattice deformation which occurs throughout the antiferroelectric-, the ferroelastic- and the paraelastic-phase transitions. The temperature dependence of <TEX>$\sigma_{iso}$</TEX> reveals the electronic charge redistribution is induced by the proton-beam irradiation and the elastic property.

Properties of 23Na implanted targets

Ten types of 23Na implanted targets have been fabricated for the purposes of investigating the effects of proton beam bombardment on the implanted sodium distribution. Targets were implanted at energies of E Na = 10–30 keV using copper, tantalum, and nickel as host materials. Thin layers (100–200 Å) of chromium and gold were also evaporated over some of the targets to provide a protective layer for the implanted sodium. The 23Na( p, γ) resonance at a lab proton energy of E p = 309 keV was used to determine the implanted distribution. Successive resonance profile measurements are presented for each implanted target, and the concurrent loss of 23Na resulting from beam bombardment is reported. The calculated temperature rise of the targets indicates that beam heating has a negligible effect on the implanted sodium distribution, and that the principal mechanism for 23Na loss during beam bombardment is sputtering.

Study of the Hyperthermal Proton Bombardment Effects on Self-Assembled Monolayers of Dodecanethiol on Au(111)

Proton bombardment on self-assembled monolayers (SAMs) of dodecanethiol formed on a gold surface is performed and its effect is studied by scanning tunneling microscope (STM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). STM gives clear evidence that a relatively uniform layer of organic nanoclusters with different sizes and densities can be created on the surface. Analysis of the mass spectra collected from the SAM samples reveals that large hydrocarbon fragments from the bombarded sample area show higher intensity than those from the virgin area, which is a strong indication that selective C-H bond cleavage and cross-linking are induced by the proton beam bombardment. We demonstrate that the size and density of the clusters can be harnessed by controlling the proton beam energy and fluence. The clusters grow bigger, at the expense of a decreasing number density, with increasing proton energy or fluence.

Measurement of response functions of organic liquid scintillator for neutron energy range up to 390 MeV

The neutron response functions of 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator have been measured in the energy range up to 390 MeV at the Research Center for Nuclear Physics (RCNP) of Osaka University. The continuous energy neutrons were produced by the 392 MeV proton bombardment on a 20-cm thick aluminum target and the response functions of the time-of-flight (TOF)-gated monoenergetic neutrons in a wide energy range up to 390 MeV were simultaneously measured. The quasi-monoenergetic neutrons were also produced via 7Li(p,n) 7Be reaction by the 392-MeV proton beam bombardment on a 1.0-cm thick 7Li target, and the TOF-gated 388-MeV peak neutrons were used to obtain the response function at this energy. The measured results show that the response functions for monoenergetic neutrons below 100 MeV have a recoil proton plateau and an edge around the maximum light output which increases with increasing neutron energy, while on the other hand, for energies above 100 MeV, the plateau and the edge become unclear because the proton range starts to exceed the detector size allowing protons to escape.

Measurements of the response functions of a large size NE213 organic liquid scintillator for neutrons up to 800 MeV

The response functions of 25.4 cm (length) x 25.4 cm (diameter) NE213 organic liquid scintillator have been measured for neutrons in the energy range from 20 to 800 MeV at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) and at the Research Center for Nuclear Physics (RCNP) of Osaka University. At HIMAC, white (continuous) energy spectrum neutrons were produced by the 400 MeV per nucleon carbon ion bombardment on a thick graphite target, whose energy spectrum has already been measured by Kurosawa et al., [Nucl. Sci. Eng. 132, 30 (1999)] and the response functions of the time-of-flight-gated monoenergetic neutrons in a wide energy range from 20 to 800 MeV were simultaneously measured. At RCNP, the quasi-monoenergetic neutrons were produced via 7Li(p,n)7Be reaction by 250 MeV proton beam bombardment on a thin 7Li target, and the TOF-gated 245 MeV peak neutrons were measured. The absolute peak neutron yield was obtained by the measurement of 478 keV gamma rays from the 7Be nuclei produced in a Li target. The measured results show that the response functions for monoenergetic neutrons < 250 MeV have a recoil proton plateau and an edge around the maximum light output, which increases with increasing incident neutron energy, on the other hand > 250 MeV, the plateau and the edge become unclear because the proton range becomes longer than the detector size and the escaping protons increase. It can be found that the efficiency of the 24.5 cm (diameter) x 25.4 cm (length) NE213 for the 250 MeV neutrons is -10 times larger than the 12.7 cm (length) x 12.7 cm (diameter) NE213, which is widely used as a neutron spectrometer.

Analysis of deuterium and lithium on titanium surface by NRA method

Concentrations of deuterium (D) and lithium (Li) in titanium (Ti) were measured with nuclear reaction analysis (NRA) method. With ΔE& E-counter-telescope, proton peaks by the D(d,p)T and 6Li(d,p) 7Li reactions were well resolved from continuous spectrum of α-particles by the 7Li(d,α + n)α reaction. The yields of these protons were obtained and densities of deuterium and lithium isotopes on the Ti surfaces were obtained. Isotopic ratio of lithium was determined by comparing the yield of 6Li(p,3He)α, 6Li(p,α) 3He and 7Li(p,α)α reactions with proton beam bombardment. Deviation among the experimental values was about 9%.

Ion beam radiation effects on InAs semiconductor quantum dots

AbstractSelf-assembled quantum dots (QDs) have attracted significant attention because of their potential applications in novel semiconductor devices. In this work, we investigated radiation effects induced by 1.0 MeV proton ion beams on InAs self-assembled quantum dots. In particular, we emphasized the effects of lattice environments of QDs on their luminescence emission after ion beam irradiation. Photoluminescence (PL) spectroscopy was used to characterize the optical properties of QDs subjected to proton irradiation and post-irradiation annealing. Compared to the single-layer QDs grown in GaAs films, the QDs embedded in an AlAs/GaAs superlattice exhibited much higher PL degradation resistance to proton beam bombardment, e.g., at the highest dose (1.0×1014 cm−2) used in this work, a difference of ~ 20-fold in PL intensity was found between the QDs configured in these two different lattice structures. After thermal annealing of irradiated QD samples, ion beam enhanced blueshift of PL was observed to be much more pronounced for the single-layer QDs. We discuss mechanisms that may result in the differences in optical response to ion beams between QDs with different lattice surroundings.

High energy proton beam bombardment of polyaniline

Irradiation effects of 35 MeV proton beam bombardment on polyaniline (PAn) have been studied. PAn was made by standard MacDiarmid method, and the irradiation was performed at ambient temperature lower than 20°C. A 511 keV γ photon was detected by γ spectrum analysis, and a nuclear reaction 14N(p,α) 11C in collaboration of 12C(p,pn) 11C took place. By means of chemical ionization, mass spectra of samples before and after ion bombardment were recorded. Experimental results showed that products such as ▪ and cyclic compounds like ▪ and ▪ were produced. IR spectra and SEM micrographs gave results of vibrational frequency shifts and morphology consistent with mass spectrometry. Finally we conclude that high energy proton beam bombardment resulted in main-chain scission and carbonization of PAn. Although the electrical conductivity reduced from 0.72 to 0.62 S cm -1, it retained at the same level. This implies that PAn might be used under the influence of high energy radiation.

Radiation damage in PIXE analysis of museum paper-like objects

Paper discoloration and its tensile strength degradation caused by 2.1 MeV external proton beam bombardment under low beam current density ( < 10 nA/cm 2) were measured as a function of the number of incident protons. The target temperature reached during bombardment was measured using an infrared thermometer. Under low beam current density, paper heating is negligible and the paper deterioration depends only on the total beam fluence. Some of the experimental results are presented and discussed for several types of paper, including one used for traditional Chinese paintings.

Relative intensity database of L-Shell lines of lanthanides and analysis of the PIXE spectra

The PIXE spectra resulting from proton beam bombardment in the energy range of 1 to 2.5 MeV of the thin targets of 14 lanthanides were measured using a Ge detector to obtain a relative intensity database of the L-shell lines. The database utilizes the relativistic Hartree-Slater (RHS) emission rates reported by Scofield. To correct the other quantities affecting the relative intensities such as L-subshell ionization cross sections etc., empirical factors are introduced and the values are determined by the least squares method. The reduced chi-squared value is 0.85 ± 0.4 for 90 spectra. The relative intensities of Nd, Dy and Yb obtained at 2 MeV are compared with the recent ECPSSR approach by Cohen and Harrigan, and it is found that these results are in fairly good agreement. The PIXE spectra of the mixtures of lanthanides and the crude rare-earth chlorides from monazite are analyzed by use of the database. The reasonable analytical results obtained confirm the practical utility of this approach. The performance of a program, PIXS, developed for doing the analysis on a personal computer is also reported.

Proton activation analysis of trace impurities in purified cobalt

Nondestructive activation analysis by proton beam bombardment has been applied to cobalt specimens. Thick target yields were measured on 18 elements for the purpose of quantitative analysis. In order to detect precisely the radionuclides with different half-lives, gamma-ray spectrometry was repeated three times after different cooling times of 1, 15 and 250 hrs from the finish of bombardment for 1 hrby 10.4 MeV proton beam. It was found that Ti, Cr, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Zr, Nb, Mo, Cd, Sn, Sb, and Te of the order of ppm or less could be detected accurately. Using the proton activation analysis developed, the purification effects of anion exchange, electrolytic extraction, and floating zone-refining have been examined. It was confirmed that the concentrations of the impurity elements contained in the starting material decreased stepwise upon the application of each purification method.

Isomeric γ-ray transitions in 98Tc

Delayed γ-rays from 98Tc have been observed following pulsed proton beam bombardment of an enriched 98Mo target. The energies of the delayed γ-rays are 43.5 ± 0.5 keV and 21.8 ± 0.1 keV. Also seen are delayed Tc X-rays. These radiations all have the same half-life which has been measured to be 14.6 ± 0.7 μs. The 21.8 keV γ-ray is identified as the first excited state to ground state transition. An estimate of the internal conversion coefficients of the 21.8 and 43 keV decays suggests that both transitions are M1.