Low keV Energies Research Articles

Early detection of hypervascularization in hepatocellular carcinoma (≤2 cm) on hepatic arterial phase with virtual monochromatic imaging: Comparison with low-tube voltage CT.

This study aims to assess the diagnostic value of virtual monochromatic image (VMI) at low keV energy for early detection of small hepatocellular carcinoma (HCC) in hepatic arterial phase compared with low-tube voltage (80 kVp) CT generated from dual-energy CT (DE-CT). A total of 107 patients with 114 hypervascular HCCs (≤2 cm) underwent DE-CT, 140 kVp, blended 120 kVp, and 80 kVp images were generated, as well as 40 and 50 keV. CT numbers of HCCs and the standard deviation as image noise on psoas muscle were measured. The contrast-to-noise ratios (CNR) of HCC were compared among all techniques. Overall image quality and sensitivity for detecting HCC hypervascularity were qualitatively assessed by three readers. The mean CT numbers, CNR, and image noise were highest at 40 keV followed by 50 keV, 80 kVp, blended 120 kVp, and 140 kVp. Significant differences were found in all evaluating endpoints except for mean image noise of 50 keV and 80 kVp. Image quality of 40 keV was the lowest, but still it was considered acceptable for diagnostic purposes. The mean sensitivity for detecting lesion hypervascularity with 40 keV (92%) and 50 keV (84%) was higher than those with 80 kVp (56%). Low keV energy images were superior to 80 kVp in detecting hypervascularization of early HCC.

Development of Cryogenic Detectors for Neutrinoless Double Beta Decay Searches with CUORE and CUPID

Searching for neutrinoless double beta decay is a top priority in particle and astroparticle physics, being the most sensitive test of lepton number violation and the only suitable process to probe the Majorana nature of neutrinos. In order to increase the experimental sensitivity for this particular search, ton-scale detectors operated at nearly zero-background conditions with a low keV energy resolution at the expected signal peak are required. In this scenario, cryogenic detectors have been proven effective in addressing many of these issues simultaneously. After long technical developments, the Cryogenic Underground Observatory for Rare Events (CUORE) experiment established the possibility to operate large-scale detectors based on this technology. Parallel studies pointed out that scintillating cryogenic detectors represent a suitable upgrade for the CUORE design, directed towards higher sensitivities. In this work, we review the recent development of cryogenic detectors, starting from the state-of-the-art and outlying the path toward next-generation experiments.

Ionization and electron capture for H+ collisions at low keV energy with CCl4 molecules

Relative total ionization cross sections and fragment target ions have been measured for proton impact on CCl4 molecules for the first time, namely associated with the formation of CCl3+, CCl2+, CCl+, Cl2+, Cl+ and C+ ions. The experiment was conducted by crossing a proton beam of 2.5 to 10 keV with a CCl4 vapor target where the fragment ions were measured employing the time of flight technique. Relative fragment cross sections were added leading to the total relative cross section. All relative cross sections seem to be independent of the collisional energy. A qualitative comparison was conducted with previous measurements of electron impact experiments. Ratios of CCl3+/CCl2+, CCl3+/CCl+, CCl3+/C+ and CCl3+/Cl+ were compared to those obtained from electron impact experiments.

Characterization of a plastic dosimeter based on organic semiconductor photodiodes and scintillator.

Measurement of dose delivery is essential to guarantee the safety of patients undergoing medical radiation imaging or treatment procedures. This study aimed to evaluate the ability of organic semiconductors, coupled with a plastic scintillator, to measure photon dose in clinically relevant conditions, and establish its radiation hardness. Thereby, proving organic devices are capable of being a water-equivalent, mechanically flexible, real-time dosimeter. The shelf-life of an organic photodiode was analyzed to 40kGy by comparison of the charge-collection-efficiency of a 520nm light emitting diode. A non-irradiated and pre-irradiated photodiode was coupled to a plastic scintillator and their response to 6 MV photons was investigated. The dose linearity, dose-per-pulse dependence and energy dependence was characterized. Finally, the percentage depth dose (PDD) between 0.5 and 20cm was compared with ionization chamber measurements. Sensitivity to 6 MV photons was (190±0.28) pC/cGy and (170±0.11) pC/cGy for the non-irradiated and pre-irradiated photodiode biased at -2 V. The response was independent of the dose-per-pulse between 0.031 and 0.34mGy/pulse. An energy dependence was found for low keV energies, explained by the energy dependence of the scintillator which plateaued between 70keV and 1.2MeV. The PDD was within ±3% of the ionization chamber. Coupling an organic photodiode with a plastic scintillator provided reliable measurement of a range of photon energies. Dose-per-pulse and energy independence advocate their use as a dosimeter, specifically image-guided treatment without beam-quality correction factors. Degradation effects of organic semiconducting materials deteriorate sensor response but can be stabilized.

Ionization and electron capture for H+ collisions at low keV energy with a water-vapor target

We have investigated the total relative ionization and dissociative electron capture cross section for proton collisions with water-vapor molecules within the energy range of 2.5–10 keV. Time of flight mass spectroscopy was employed in the measurements of the atomic and molecular singly charged particles H+, H2+, O+, OH+ and H2O+ as well as the doubly charged particles O++, H2O++, OH++, and the contribution of the different channels was evaluated. Ionization was found to be the dominant reaction channel as expected. The contribution of the singly charged particles was found to be one order of magnitude higher than that of the doubly charged particles.

Relationship between Carotid Computed Tomography Dual-Energy and Brain Leukoaraiosis

The purpose of this study was to assess if there is a correlation between the carotid computed tomography (CT) Hounsfield unit (HU)-based plaque attenuation values measured using dual-energy CT (DECT) scanner and brain leukoaraiosis (LA). Fifty consecutive patients (34 males, 16 females; mean age, 69 years; age range, 46-84 years) who underwent carotid CT and brain magnetic resonance imaging were included in the study. CT examinations were performed with a DECT scanner, and LA lesion volume quantification was performed using a semiautomated segmentation technique. We found an inverse statistically significant correlation between the HU-based carotid artery plaque attenuation and the LA lesion volume. Because of the presence of calcified plaques, a second model was calculated at low kiloelectron volt levels from 66 to 100 and 100 kV by taking into consideration the fatty and mixed plaques, and this further led to the associations between HU-based attenuation and LA volume in brain and vascular territories. The results of our study suggest that the associations between HU attenuation of the carotid artery plaques (with the exclusion of calcified plaques) and the volume of LA are emphasized at low keV energy levels.

Ionization and Electron Capture for H+ Collisions with CO at low keV Energy

We have investigated the total relative ionization and dissociative electron capture cross section for proton collisions with CO within the energy range of 2 keV to 10 keV. Time of flight mass spectroscopy was employed in the measurements of CO+, O+ and C+ and the contribution of the different channels was evaluated. Ionization was found to be the dominant reaction channel as expected, while the C+ ionic fragments intensity was found to be higher than those of O+.

Decreased stage migration rate of early gastric cancer with a new reconstruction algorithm using dual-energy CT images: a preliminary study

ObjectivesTo evaluate the potential value of advanced monoenergetic images (AMEIs) on early gastric cancer (EGC) using dual-energy CT (DECT).Methods31 EGC patients (19 men, 12 women; age range, 38–81 years; mean age, 57.19 years) were retrospectively enrolled in this study. Conventionally reconstructed polyenergetic images (PEIs) at 120 kV and virtual monoenergetic images (MEIs) and AMEIs at six different kiloelectron volt (keV) levels (from 40 to 90 keV) were evaluated from the 100 and Sn 140 kV dual energy image data, respectively. The visibility and stage migration of EGC for all three image data sets were evaluated and statistically analyzed. The objective and subjective image qualities were also evaluated.ResultsAMEIs at 40 keV showed the best visibility (80.7 %) and the lowest stage migration (35.5 %) for EGC. The stage migration for AMEIs at 40 keV was significantly lower than that for PEIs (p = 0.026). AMEIs at 40 keV had statistically higher CNR in the arterial and portal phases, gastric-specific diagnostic performance and visual sharpness compared with other AMEIs, MEIs and PEIs (all p < 0.05).ConclusionsAMEIs at 40 keV with MPR increase the CNR of EGC and thus potentially lower the stage migration of EGC.Key Points• AMEIs benefits from the recombination of low-keV images and medium energies.• AMEIs could receive better CNR results than MEIs.• AMEIs at 40 keV potentially lower the stage migration of EGC.

Large increase in the electron capture and excitation cross sections for Li+ colliding with atomic H under UV laser assistance

Neutralization and ash products due to electron capture processes in plasmas reduce the efficiency of energy generation in fusion Tokamak reactors. Therefore, lithium ions have been used to improve the efficiency of energy generation where good control of the electron capture process is required. Here, we show that an intense ( W cm−2), ultra-short (1 fs at full width half-maximum) Gaussian laser pulse in the UV region can enhance the electron capture process on in the low collision keV energy region. We find a factor of 10 enhancement in electron capture cross-section at impact energies lower than 10 keV amu−1 for an 80 nm wavelength laser and a factor of 2 for the excitation process in the hydrogen atom as compared to the laser-free case. In contrast, for a 200 nm wavelength laser the increase of the electron capture cross-sections takes place around 1 keV amu−1 by a factor of 3 and no enhancement for the excitation process. Our results show that the UV assisted production of Li can be controlled, particularly for short UV wave-length for a specific collision energy range. We anticipate that our findings will facilitate UV laser control of the Li production in Tokamak reactors and encourage further experimental work in this system.

Image plate characterization and absolute calibration to low kilo-electron-volt electrons.

We report on the characterization of an image plate and its absolute calibration to electrons in the low keV energy range (1-30 keV). In our case, an Agfa MD4.0 without protection layer was used in combination with a Fuji FLA7000 scanner. The calibration data are compared to other published data and a consistent picture of the sensitivity of image plates to electrons is obtained, which suggests a validity of the obtained calibration up to 100 keV.

Development delay induced by low-keV energy ions in early larva of the nematode Caenorhabditis elegans

Ionizing radiation influences animal growth and early development. We have studied bio-effects of low-keV energy argon ion (LKE-AI) using Caenorhabditis elegans focusing on the effects of LKE-AI on larval development. The results showed that LKE-AI of 2–5 keV energy with fluences ranging from 2 × 1014 to 5 × 1014 ions/cm2 induced developmental delay and a decrease in mean brood size, compared to the control group. Under trypan blue staining, some damage to the cuticle was detected. Moreover, C. elegans L1 larvae of hus-1(op241), mek-2(n1989) or sos-1(cs41) deletion mutants showed higher sensitivity to exposure to LKE-AI, and dimethyl sulphoxide could rescue the developmental delay induced by LKE-AI. Our results give an initial insight in the effect of LKE-AI-induced abnormal development via cuticle damage and the generation of reactive oxygen species.

Configuration interaction calculations of cross sections for proton stopping reactions

Purpose: To illustrate the role of quantum mechanical electronic structure methods in providing accurate predictions of the cross sections for ionization and electron capture processes that occur as a result of proton collisions in the high-eV to low-keV energy region.Methods: Calculations are carried out to compute potential curves and non-adiabatic coupling elements for a variety of collision partners employing the ab initio multireference single- and double-excitation configuration interaction (MRD-CI) method. These results are used as input for the electronic-state close-coupling (ESCC) method in order to compute cross sections for various transitions that occur because of collisions.Results: Emphasis is placed on proton-molecule collisions that play a key role in various medical applications as well as in astrophysics and nano-scale materials manufacturing. Examples discussed include the Na-He pair of atoms of interest in recent astrophysical observations, proton collisions with various hydrocarbons and also with water and oxygen, and key ionic products such as H2O+ and H3O+ .Conclusions: The computed cross sections provide a detailed picture of radiation damage dynamics in Monte Carlo simulations. This information can potentially enhance the efficiency of proton beam focusing and also reduce undesirable side effects on body tissues.

Application of low energy ion blocking for adsorption site determination of Na Atoms on a Cu(111) surface

Ion blocking in the low keV energy range is demonstrated to be a sensitive method for probing surface adsorption sites by means of the technique of time-of-flight scattering and recoiling spectroscopy (TOF-SARS). Adsorbed atoms can block the nearly isotropic backscattering of primary ions from surface atoms in the outmost layers of a crystal. The relative adsorption site position can be derived unambiguously by simple geometrical constructs between the adsorbed atom site and the surface atom sites. Classical ion trajectory simulations using the scattering and recoiling imaging code (SARIC) and molecular dynamics (MD) simulations provide the detailed ion trajectories. Herein we present a quantitative analysis of the blocking effects produced by sub-monolayer Na adsorbed on a Cu(111) surface at room temperature. The results show that the Na adsorption site preferences are different at different Na coverages. At a coverage θ = 0.25 monolayer, Na atoms preferentially populate the fcc threefold surface sites with a height of 2.7 ± 0.1 Å above the 1st layer Cu atoms. At a lower coverage of θ = 0.10 monolayer, there is no adsorption site preference for the Na atoms on the Cu(111) surface.

Charge-transfer processes inF2++H→F++H+collisions and the reverse process at low-keV energies

Charge-transfer processes inF2++H→F++H+collisions and the reverse process at low-keV energies

He+ scattering on a TiO2(1 1 0) surface

We present measurements of energy-losses and neutralisation of helium ions on a TiO2(110) surface at low keV energies. Measurements were performed in the 1–4keV energy range. The target azimuthal orientation dependence of total scattering intensity profiles, energy-losses and probability of electron capture or loss were determined. On the basis of Marlowe simulations it is concluded that ion scattering intensities give indications about defects regarding surface bridging O atoms. Variations in energy losses for different scattering directions are reported. Ion fraction measurements were made using both incident ions and neutrals. Similar ion fractions were found indicating that He is efficiently neutralised and ions result from reionisation. These ion fractions are found to depend on the azimuthal orientation and have a minimum along the main crystallographic directions.

DNA strand breaks induced by low keV energy heavy ions

We present some results on the interaction of low energy atomic ions with DNA. Experiments consist of irradiation of dried DNA in vacuum with Ar ions at low keV energies for different time intervals. The DNA is placed back in solution and analysed by agarose gel electrophoresis. These experiments demonstrated the production of single and double strand breaks. The induction of these lesions could be due to several processes: direct collisions with DNA constituent atoms resulting in displacements, cascade recoil collisions of the constituent atoms, electron transfer processes between the ion and the DNA as well as breaks induced by molecular excitation and secondary electron interactions. Here we briefly discuss some aspects of direct and recoil collision processes.

Channelling and stopping of hydrogen and fluorine ions in grazing scattering on an Ag(1 1 0) surface at low keV energies and effects of oxygen adsorption

We present measurements of energy-loss spectra of hydrogen and fluorine ions, which are scattered off an Ag(1 1 0) single-crystal surface for primary energies between 1 and 6 keV. The effect of oxygen adsorption, which leads to an added row reconstruction of the surface is investigated. We performed measurements for grazing angles in chanelling conditions. Experimental results are discussed in the light of trajectory calculations of hydrogen and fluorine atoms scattered under grazing incidence conditions on the surface. Different trajectory classes are found by the calculations and assigned to different contributions in the energy-loss spectra. These data on ion stopping allow us to deduce the values of friction coefficients as a function of atom–surface distance.

Formation of autoionizing Ne ∗∗ in grazing collisions with an Al(111) surface

We present a study of the production of neon autoionizing states during glancing scattering of 3–50 keV Ne + on an Al(111) surface of varying degree of roughness. The projectile energy dependence of the intensity of neon autoionization peaks in the electron spectra indicates that the various autoionizing states fall into two main groups. At low keV energies, Ne(2p 43s 2) autoionizing states are formed, while at higher energies other peaks appear in the electron spectra with similar intensity. Some of these peaks may be due to low-lying 2p 4nln′l′ states, whose population is aided by the motion of the projectile. Other peaks can be assigned to 2s2p 5nl, 2s2p 6nl and 2p 3nln′l′ states. A study of the effect of surface roughness shows that the production of excited states in grazing scattering is favored at rougher surfaces. For flat surfaces the peaks become broader and less intense, an effect that we ascribe to autoionization decay closer to the surface, based on previous numerical simulations of peak shapes.

Absolute detection efficiency of a microchannel plate detector for neutral atoms

The absolute detection efficiency (ADE) of microchannel plates for neutral sodium and potassium atoms is measured in the low keV energy range. It is shown that ADE is primarily a function of the particle energy. This result is compared to measurements made by other authors for ionic particles.

Adsorption site determination of light elements on heavy substrates by low-energy ion channeling

Ion channeling in the low-keV energy range is demonstrated by means of the technique of time-of-flight scattering and recoiling spectrometry. The predictions of the Lindhard string model of ion channeling are compared with the experimental findings. Qualitative agreement was obtained between the experimentally measured critical angles and the predictions of the model. The technique of low-energy ion channeling is shown to be capable of quantitatively probing the positions of light elements on heavy substrates with analysis by simple geometrical constructs. Classical ion trajectory simulations using the scattering and recoiling imaging code were used to observe the details of the ion trajectories. Quantitative analysis of the Pt(111)-(1×1)-H surface using 5 keV Ne+ shows that the hydrogen atoms preferentially populate the threefold fcc sites with a height of 0.9±0.1 Å above the first-layer Pt atoms and a corresponding Pt–H bond length of 1.9±0.1 Å.