Tandem Accelerator Research Articles

Development of a negative helium ion source with non-metallic charge exchange

Negative helium ion (He−) beams are required for tandem accelerators used at research centers and implanter facilities. The common production method of such beams involves charge exchange between a positive helium ion (He+) source or beam, with a low pressure alkali metal vapour. However, the efficiency of this reaction is poor (only a small percentage) and the alkali metal vapour increases the potential flammability of the interior surfaces of the reaction chamber, as well as contributing to unwanted electrostatic discharge and target contamination downstream. In this paper we describe initial results from experiments using a focused He+ ion microscope (HIM) to measure charge uptake efficiencies after transmission through carbon membranes. The He+ beam (15 keV to 30 keV, 50 fA to 10 pA) collides with a non-metallic foil, and transmitted particles (He+, He0, and He−) are separated electrostatically into discrete beam spots and detected using a radiation camera (AdvaCam MiniPIX). A He− percentage uptake of 0.05 was observed using a 20 nm exfoliated graphite membrane consistent with previous reports. Future work will investigate the efficiency of charge exchange through other suitable membrane materials.

Medical radionuclide research activities at JRC-Geel

A programme to study photon- and neutron-induced reactions of medical interest, as well as accelerator-based methods of medical radionuclide production, has been instituted at JRC-Geel, making use of both existing and new infrastructure. A new electron beamline that can deliver quasi-monoenergetic beams has been commissioned at the GELINA electron linac and will be primarily dedicated to the study of photonuclear reactions and for medical radioisotope production studies via photon irradiation. The recently renewed MONNET 3.5 MV Tandem accelerator provides light ion beams for reactionbased quasi-mono-energetic neutron production and has been used for the study of 99Mo production via neutron irradiation of molybdenum nanoparticles. In this work we present an overview of the medical radionuclide activities at JRCGeel, with particular attention to aspects of the design, development and operational challenges of the new GELINA electron beamline. Some future perspectives of the programme are also discussed.

Exotic collective excitation patterns in triaxially deformed <sup>131</sup>Ba

<sec>In the last two decades, several unique phenomena in triaxially deformed nuclei, such as chiral doublet bands and wobbling motion have been revealed. Up to now, there are still many open questions which require further experimental and theoretical studies. To explore the collective motion in <sup>131</sup>Ba, an experiment was performed using the XTU Tandem accelerator in the Legnaro laboratory, Italy. High-spin states of <sup>131</sup>Ba have been populated via the heavy-ion fusion-evaporation <sup>122</sup>Sn(<sup>13</sup>C, 4n) reaction. <i>γ</i>-rays, charged particles and neutrons emitted from the residues were detected by the GALILEO array, EUCLIDES silicon ball, and the Neutron Wall, respectively. A total of 1.2<inline-formula><tex-math id="M12">\begin{document}$ \times $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20240212_M12.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20240212_M12.png"/></alternatives></inline-formula>10<sup>9</sup> triple- or higher-fold events were collected by the GALILEO data acquisition system. The <i>γ</i>-<i>γ</i>-<i>γ</i> coincidence events were sorted into a three-dimensional histogram (cube) and the analysis was carried out with the RADWARE and GASPWARE software packages.</sec><sec>Through analysis of the coincidences between <i>γ</i>-rays, the most comprehensive level schemes of <sup>131</sup>Ba to date was deduced from the present work. The extended level-scheme consists of 15 rotational bands, and newly observed transitions are marked in red. Three nearly degenerate pairs of doublet bands (Band 3–8) are identified in <sup>131</sup>Ba. Two pairs of chiral doublets (Band 3–6) with configuration <inline-formula><tex-math id="M20">\begin{document}$ {\textit{\pi}}h_{11/2}(g_{7/2},d_{5/2}){\otimes}{\nu}h_{11/2} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20240212_M20.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20240212_M20.png"/></alternatives></inline-formula> are interpreted as a set of pseudospin-chiral quartet bands. The quartet bands are fed by another pair of chiral doublet bands (Band 7–8) built on a <inline-formula><tex-math id="M21">\begin{document}$ {\textit{\pi}}h^2_{11/2}{\otimes}{\nu}h_{11/2} $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20240212_M21.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20240212_M21.png"/></alternatives></inline-formula> configuration via a series of enhanced E1 transitions. We extracted the energy displacement <i>δ</i>E and the B(E1)/B(E2) branching ratios between the positive-parity band 3 and the negative-parity band 7 in <sup>131</sup>Ba and in comparison with those in <sup>124</sup>Ba, <sup>224</sup>Th, <sup>133</sup>Ce and <sup>135</sup>Nd. The energy displacement <i>δ</i>E and the B(E1)/B(E2) branching ratios in <sup>131</sup>Ba are comparable with those in <sup>124</sup>Ba but deviate appreciably from those in <sup>224</sup>Th which has been reported to have stable octupole deformation. The results indicate the existence of octupole correlations in <sup>131</sup>Ba without stable octupole deformation. A new rotational band (Band 10) discovered in the low-spin region exhibits a level structure similar to a wobbling band. Assuming it as a wobbling band, the wobbling frequency was extracted and compared with other reported wobbling bands in the neighboring nuclei. The wobbling frequency of this band decreases with increasing angular momentum, and even exhibits negative value at the highest spin. Considering that the wobbling phonon should contribute a positive amount to the excitation energy, this band is unlikely to be explained by this mechanism. The band may originate from other collective excitation mechanisms such as <i>γ</i> vibration. The newly identified rotational band (Band 9) composed of M1 transitions is tentatively assigned as a magnetic rotational band through a systematic analysis of the level structure. Finally, the configurations of other 4 bands, Band 12-15, are also suggested based on previous researches and the extracted quasiparticle alignments.</sec>

Development and Testing of a High-Frequency Driver for a Charge-Exchange Source of Negative Hydrogen Ions

A source of negative hydrogen ions based on the recharging of a beam of positive ions in a gas target is being developed at the Institute of Nuclear Physics. G.I. Budker SB RAS. The charge exchange source can be used to inject into the tandem accelerator a neutron source intended for boron neutron capture therapy. One of the important elements of the source is the plasma emitter, which creates positive ions for primary acceleration. As an emitter, a high-frequency driver based on an induction discharge and designed for a multi-second operating mode was chosen. In this work, we measured the emission characteristics of a high-frequency driver using a moving grid probe. As a result, the parameters necessary for the use of the driver in a rechargeable source of negative ions have been achieved. The analysis of experimentally measured thermal loads in the multisecond mode is carried out.

Continuous and pulsed fast neutron beams at the CNA HiSPANoS facility

The characteristics of the fast neutron beams produced in the HiSPANoS facility at Centro Nacional de Aceleradores (CNA) are presented. The neutrons are generated by deuteron beams from a 3 MV tandem accelerator in either continuous (5 μA) or pulsed (2 ns width, 500 kHz and 4% duty cycle) mode. In this work, the pulsed mode was used in a time-of-flight characterization of the produced neutron beams in terms of yield, flux, energy resolution, and background. The results were then validated through their comparison with previously published data.Quasi-monoenergetic neutron beams between 2 and 6 MeV are produced by means of the 2H(d,n)3He reaction, featuring a neutron yield of 106 n/sr/μC at the target, with an energy resolution of about 7% at 150 cm. Neutron beams with broad energy distributions are produced by deuteron irradiation of thick beryllium and lithium targets, resulting in maximum neutron energies of 10 and 20 MeV, respectively. In this case, the neutron yields are significantly higher, reaching 1010 n/sr/μC.On the basis of these results, we consider that the HiSPANoS facility is now fully operational for the usage of fast neutrons by internal and external users of CNA.

On the accuracy of cross-section measurements of neutron-induced reactions using the activation technique with natural targets: The case of Ge at E[formula omitted] MeV

Several cross-section measurements of neutron-induced reactions on Ge found in literature, are performed utilizing natGe targets. The production of the same residual nucleus as the measured one might occur as a result of the unavoidable presence of neighboring isotopes in the same target, acting as a contamination. Corrections must be made based on theoretical calculations and models in order to resolve this problem. The accuracy and limits of a methodology for these “theoretical corrections” are investigated in this work using isotopically enriched targets, which can produce very accurate results without the need for such corrections. Experimental cross-section measurements have been made for the 76Ge(n,2n)75Ge, 72Ge(n,α)69mZn and 72Ge(n,p)72Ga reactions, via the activation technique, with the 27Al(n,α)24Na reaction used as reference, employing both a natGe and isotopically enriched Ge targets. The 3H(d,n)4He (D–T) reaction was used for producing the quasi-monoenergetic neutron beam in the 5.5 MV Tandem Accelerator Laboratory of the National Centre for Scientific Research “Demokritos” in Athens, Greece, at an incident deuteron beam energy of 2.9 MeV. Using HPGe detectors, γ-ray spectroscopy was applied to determine the induced γ-ray activity of the residual nuclei.

Monoisotopic targets production from atomic and molecular positive ion implantation in a tandem accelerator at low energies

We produced monoisotopic targets of 13C and 28,29Si with 1015−16 atoms/cm2 areal density by ion implantation in different matrices at the Accelerator Mass Spectrometry (AMS) facility in Mexico. The tandem accelerator terminal voltage was set at the lowest achievable value (200 kV) that yield beams with energy of 435 keV. It is possible to do ion implantation at lower energies in our facility through the use of molecular beams, so in this work we looked for, and successfully found, bound positively charged molecular beams, although with very low intensity. We inject 235 keV molecules into the charge of exchange canal (argon) of our tandem accelerator and detected the survival fraction of C2,3,4 molecules in 1+ and 2+ charge states or above. Our results showed that some molecules remain bound, with one or more electrons missing, after being forced through a low density gas stripper at relatively high energy. In the production process of negative molecular fluxes in the Source of Negative Ions by Cesium Sputtering (SNICS) we found an odd-even effect in their intensity that we understand as the coupling between the fragment size distribution of a dynamic fragmentation of graphite by cesium impact and the electron affinity of the molecules with n-carbon atoms. The availability of these kind of high energy molecular beams opens the door for discovery both in the study of the physics of negative and positive molecular ions.

Spectrometric performance of SiC radiation detectors at high temperature

In this work, we have investigated the performance of a 4H–SiC radiation sensor in the temperature range from 25 °C to 450 °C to explore its compatibility as detector of fast ion losses in plasma diagnostic of future nuclear fusion reactors. To simulate the escape of fusion-born alpha particles in D-T (deuterium-tritium) fusion plasmas, spectroscopic measurements were carried out in a vacuum chamber by irradiating the detector with a 3.5 MeV alpha beam from a Tandem accelerator. The detector was found to have an energy resolution ≤2% over the entire temperature range analyzed. Relevantly, the excellent spectrometric capabilities of the device have allowed us to calculate from experimental data, with unprecedented accuracy, the average energy required to create a single electron-hole pair in 4H–SiC as a function of temperature.

Physicochemical Characterization of Cullet to Glaze for Environmental Sustainability and Entrepreneurial Development

Purpose: Inability of ceramists to formulate glazes locally and the cost of importing glazes had resulted to the closure of many cottage ceramic industries in Nigeria. The study, physicochemical characterization of cullet to glaze, was conducted with the aim of recycling cullet for glazing earthen wares and the intention was to conduct elemental analysis of waste glass for glaze recipes, determine its artistic usage, lessen cullet from environment and harness the chemical properties for industrial development and economic growth.
 Methodology: Methodologies for the study involved laboratory analysis to determine oxides concentration in the cullet and studio artistic techniques to form glaze batches, batch-milling, glazes application on earthenware, and kiln firing. Four colours of windowpane cullet were used in order to determine their chromaticity effects as glaze. Cullet were pulverised with pulveriser machine (Rocklabs) and elemental analysis was carried out with tandem accelerator machine, using Particle Induce X-ray Emission to determine oxide compositions and concentrations.
 Findings: Elemental analysis revealed Na2O, MgO, K2O, Al2O3, SiO2, CaO, TiO2, PbO and FeO. SO3, P3O5, ZrO2, Rb2O, ZnO, MoO3, Sb2O5, SrO and BaO in varying concentrations as the oxides in the samples. The glass ceramic glazes gave good matt, glossy, opalescent, translucent and opaque results at 950oC kiln temperature. The reactions of additive fluxes on each formulated glaze batch with windowpane cullet assist hydrokinetics nature of their crystallisation phases in the kiln.
 Unique Contributions to Theory, Practice and Policy: The study is hinged on the circular economy theory; an approach towards designing out of waste and regenerating natural system. It explicates artists’ ideas in recycling cullet for glaze derivation and highlights recycling benefits of cullet for environmental sustainability and entrepreneurial development. The study enhances the understanding of ceramists on how cullet can be utilized for glaze production and contributes to the development of practical strategies and solutions for stakeholders in ceramic field. The adaptation will ameliorate the problem of unavailability and high cost of glazes; stimulate rapid development of the Nigerian ceramic industry and heighten economic growth of Nigeria.

Investigating the intruder states of 83Se via lifetime measurements

Quadrupole interaction involving protons and neutrons drives the nucleus into deformed configurations at low excitation energies. Intruder states appear in N=49 isotones, reaching a minimum at around 500 keV in 83Se. Since 83Se is in the mid of the proton shell (Z=28-40), it is a good candidate to study the properties of particle-hole intruder states lowered in energy by large quadrupole correlations. Moreover, it will also allow one to estimate the degree of N=50 core breaking in the ground state of Se isotopes. The lifetime of the 540-keV 1/2+ state and 1100-keV 3/2+ state of 83Se were measured using the Recoil Distance Method and the Doppler Shift Attenuation Method respectively. A beam of 82Se, with intensity 0.02 pnA, accelerated to 270 MeV from the Tandem accelerator at LNL-INFN, was sent into a deuterated polyethylene foil (C2D4), evaporated on a 6 mg/cm2 gold layer. The GALILEO γ-array was coupled to the SPIDER silicon array, allowing one to obtain the needed channel selectivity through particle-γ coincidence measurements.

Directionality for nuclear recoils in a Liquid Argon TPC

Directional sensitivity to nuclear recoils would provide a smoking gun for a possible discovery of dark matter in the form of WIMPs (Weakly Interacting Massive Particles). A hint of directional dependence of the response of a dual-phase argon Time Projection Chamber (TPC) was found in the SCENE experiment. Given the potential importance of such a capability in the framework of dark matter searches, a new dedicated experiment, ReD (Recoil Directionality), was designed by the Global Argon Dark Matter Collaboration, in order to scrutinise this hint. A small dual-phase argon TPC was irradiated with neutrons produced by the p(7Li,7Be)n reaction using the 15 MV TANDEM accelerator of the INFN - Laboratori Nazionali del Sud, Catania, Italy, so as to produce argon nuclear recoils in the range (20 - 100) keV of interest for dark matter searches. Energy and direction of nuclear recoils are inferred by the detection of the elastically-scattered neutron by a set of scintillation detectors. Events were selected by gating of the associated 7Be, which is detected by a telescope of Si detectors.

Measurement of 169Tm(n, 2n)168Tm reaction cross sections from 12 to 19.8 MeV* *Supported by the National Natural Science Foundation of China (12075216)

The cross sections of the 169Tm(n, 2n)168Tm reaction have been measured at incident energies of 12 to 19.8 MeV using the activation technique, relative to the 93Nb(n, 2n)92mNb reaction. Thulium (Tm) samples were irradiated on the surface of a two-ring orientation assembly with neutrons produced from the 3H(d, n)4He reaction at the 5SDH-2 1.7-MV Tandem accelerator in China. Theoretical model calculations were performed. The present data were then compared with previous experimental data and available evaluated data. This study provides more precise nuclear data for improvement of future evaluations.

Supervisor watchdog circuit to monitor an accelerator beam and control the safety interlock system

A supervisor watchdog circuit was developed to both monitor the dose and temperature at an accelerator beamline and provide signals to the safety interlock system of the accelerator. The implementation involved a D type flip-flop and subsequent logic gates to monitor the input and output signal states. It used a series of LEDs to inform the user about the state of the system and to enable identification of issues causing the beamline to shut down. The design allowed for a manual circuit restart to be performed to continue signal monitoring and accelerator operation. The supervisor watchdog circuit was installed at the tandem accelerator of the Reactor Materials Testing Laboratory at Queen’s University to monitor the beam properties during nuclear materials irradiation experiments. The scope for future improvements of the circuit such as automatic circuit restart in case of power fluctuations and addition of new signals is discussed.

Vacuum Insulated Tandem Accelerator for Boron Neutron Capture Therapy and Other Applications

Vacuum Insulated Tandem Accelerator for Boron Neutron Capture Therapy and Other Applications

Beam optimization of a heavy ion microbeam for targeted irradiation of mitochondria in human cells

Mitochondria, organelles of the cytoplasm, are the power plants of the cell and thus their function is important for the survival of cells. Mitochondria are known to depolarize after targeted irradiation, but the effects on cells are still unclear. The aim of this work is to investigate the effects of mitochondrial depolarization on growth and survival of cells. We performed targeted irradiation with 55 MeV C5+-ions at the ion-microbeam SNAKE at the 14 MV tandem accelerator in Garching near Munich, with a beam spot size of ∼1 µm. Approx. 6% of the mitochondrial area was irradiated in 74 cells with 5,120 carbon ions homogenously distributed over a square area of 13.2 µm2. Cell growth was investigated by observing the cells for 3.5 days via live-cell phase-contrast microscopy and evaluating the number of vital cells. While the number of irradiated cells remained constant during the observation, the unirradiated control group showed exponential growth. An additional particle track detector test with polycarbonate revealed that 4% parasitic ions hit the cells up to 500 µm away from the target, forming a so-called halo and inducing a mean parasitic dose of (2 ± 2) Gy on the cells. This dose alone, when applied in cell nuclei, is large enough to reduce the survival and growth of cells significantly and overrides any effects caused by targeted irradiation of mitochondria. Subsequently, several methods to reduce the halo were investigated. A significant reduction in halo size and number of ions in the halo could be achieved by using C6+-ions instead of C5+-ions. The slit openings, correction of lens errors, and the beam spot size had minor influence on the halo size but could achieve a reduction in halo dose. Overall, a 97% reduction in halo area and a halving of halo dose were achieved.

Fast neutron response of 6Li enriched CLYC and CLLB scintillators within 0.9–5.2 MeV

The performance of two 6Li enriched elpasolite scintillators Cs2LiYCl6 : Ce3+ (CLYC) and Cs2LiLaBr6 : Ce3+ (CLLB) were investigated using mono-energetic fast neutrons generated by a 3 MV tandem accelerator. The Pulse Shape Discrimination (PSD) ability, response and energy resolution to fast neutrons and scattered slow neutrons were studied. The 6Li enriched CLYC had excellent discrimination ability between neutron and gamma rays with the Figure of Merit (FOM) value better than 2.4. An Artificial neural network (ANN) model could discriminate fast neutrons and scattered slow neutrons effectively with an accuracy of 97%, which render the Li-6 enriched CLYC capable to detect thermal neutrons with high efficiency and the energy spectrum of fast neutrons simultaneously. The quenching factors are calculated to be 0.92 and 0.48 for the 35Cl(n, p)35S and 35Cl (n, α)32P reaction, while the detection efficiency is about 0.1%–0.75% for fast neutrons within the energy range of 0.9–5.2 MeV. Unlike CLYC, CLLB was only sensitive to slow neutrons, and the discrimination ability between neutrons and gamma rays is worse than CLYC, while the ANN model exhibit better performance which has an accuracy of 97%.

Preparation of 82Se thin films with trigonal hexagonal crystal structure for in-beam nuclear structure experiments

We report a novel approach in producing and characterizing enriched isotopic selenium-82 (82Se) thin films with trigonal hexagonal crystal structure (t-82Se), the most thermodynamically stable form of the element. The obtained t-82Se thin films are used as targets in accelerator based nuclear structure experiments. Several 82Se thin films with thicknesses around 5 mg/cm2 (10.4 μm) were deposited on 5 mg/cm2 (3 μm) tantalum (Ta) foils by vacuum evaporation-condensation method. The condensed 82Se films exhibit unstable amorphous structure (a-82Se), therefore were converted to t-82Se by means of an appropriate vacuum heat treatment developed in the target laboratory of IFIN-HH. After the thermal treatment, the microstructure, morphology and composition of the 82Se films were evaluated before and after the vacuum thermal treatment using Fourier Transform Raman Spectroscopy (FT-Raman), X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) techniques. Furthermore, an in-beam γ-spectroscopy experiment performed at the 9-MV tandem accelerator of IFIN-HH confirmed that the thermally treated t-82Se films possess high durability and high purity with no detectable contamination and no mass loss.

Sputter sample preparation for ion beam delivery of radium-223 at ATLAS.

A radium-223 ion beam was delivered to an experiment from the electron cyclotron resonance ion source, ECR2, at the Argonne Tandem Linac Accelerator System (ATLAS). The radium-223 material was in a nitrate salt form within a vial, prior to being converted to a usable sputter sample. The sputter sample was produced using a new sample preparation method, where the radium nitrate was dissolved into a solution and pipetted onto pressed aluminum powder. This sample was then allowed to dry, distributing the radium-223 material throughout the sputter sample. Ion source operation using the radium sputter sample is described with the operating parameters listed. The intensity and energy requirements for this ion beam were 1 × 106 particles/s and 1.07 GeV, respectively. Because the intensity is relatively low compared to most experiments at ATLAS, previously developed accelerator mass spectrometry methods were used Scott etal. [Rev. Sci. Instrum. 87, 02A732 (2016)] to avoid the need for tuning of the low-intensity beam of interest. Handling of the radium material, as well as loading and unloading of the sputter sample from ECR2, required collaboration with Health Physics. Procedures were used and dry runs were carried out before, during, and after the experiment to ensure the safety of the workers. The processes used and lessons learned are described within.

In-air experimental achievement of high-voltage DC power supply to be installed in a tandem electrostatic accelerator system for boron neutron capture therapy application.

The boron neutron capture therapy (BNCT) system developed by the Korea Institute of Radiological and Medical Sciences is a compact neutron source that can be installed at medical institutes. The target energy was accelerated to a maximum of 2.4 MeV-20 mA by introducing a gas stripping device that converts negative hydrogen ions into positive ions. By using the tandem-type accelerator in this way, a high-voltage DC power supply was designed with 1.2 MV-45 mA as the maximum capability. The design was improved to reduce the number of stages of a Cockcroft-Walton voltage multiplier. Hence, the ripple risk of the DC flat top resulting from unwanted stray capacitance was lowered. The overall height and volume of the Cockcroft-Walton voltage multiplier were reduced to less than half those of the existing design method, making miniaturization possible. After such advanced design and manufacturing, performance tests were performed at 750 kV-45 mA under 23 stages of the Cockcroft-Walton voltage multiplier, which is the highest level that can perform at its maximum under in-air conditions. It demonstrated stable performance under in-air conditions without breakdown for 2h, even at 620 kV-35 mA. To reach the final target of 1.2 MV-45 mA, the groundwork is laid for achieving experimental performance while satisfying the optimal requirements in SF6 gas.

Interferometric Mass Spectrometry.

Accelerator mass spectrometry (AMS) is a widely used technique with multiple applications, including geology, molecular biology, and archeology. In order to achieve a high dynamic range, AMS requires tandem accelerators and large magnets, which thus confines it to big laboratories. Here we propose interferometric mass spectrometry (Interf-MS), a novel method of mass separation which uses quantum interference. Interf-MS employs the wave-like properties of the samples and as such is complementary to AMS, in which samples are particle-like. This complementarity has two significant consequences: (i) in Interf-MS separation is performed according to the absolute mass m, and not to the mass-to-charge ratio m/q, as in AMS; (ii) in Interf-MS the samples are in the low-velocity regime, in contrast to the high-velocity regime used in AMS. Potential applications of Interf-MS are compact devices for mobile applications, sensitive molecules that break at the acceleration stage and neutral samples which are difficult to ionize.