Exotic Ions Research Articles

Study of Exotic Ions in Superfluid Helium-4 Using a Carbon Nanotube Source

We have extended our measurements of the properties of exotic negatively-charged ions in superfluid helium-4. We measured the ion mobility using the time-of-of-flight method at temperatures in the range between 1.03 and 1.16 K. Ions were generated by an electrical discharge produced by applying a voltage to sharp tips in the helium vapor above the liquid surface. Previous studies by Ihas and Sanders, Eden and McClintock, and by our group used tungsten tips and were able to detect at least twelve exotic ions in addition to the normal electron bubble. In the present work we have experimented with tips each consisting of a stainless steel wire coated with carbon nanotubes. We have found that with these tips the strength of the exotic ion signal is substantially increased making it possible to detect several ions which previously could not be seen. The present data combined with the results of the previous studies indicate that there are at least eighteen exotic ions with different mobility.

Optical and mechanical properties of electron bubbles in superfluid helium-4

A series of experiments has revealed the existence of a large number (about 18) of different types of negative ions in superfluid helium-4. Despite much effort, the physical nature of these “exotic ions” has still not been determined. We discuss possible experiments which may be able to help determine the structure of these objects.

Study of Exotic Ions in Superfluid Helium and the Possible Fission of the Electron Wave Function

An electron in liquid helium forces open a cavity referred as an electron bubble. These objects have been studied in many past experiments. It has been discovered that under certain conditions other negatively charged objects can be produced but the nature of these “exotic ions” is not understood. We have made a series of experiments to measure the mobility of these objects, and have detected at least 18 ions with different mobility. We also find strong evidence that in addition to these objects there are ions present which have a continuous distribution of mobility. We then describe experiments in which we attempt to produce exotic ions by optically exciting an electron bubble to a higher energy quantum state. To within the sensitivity of the experiment, we have not been able to detect any exotic ions produced as a result of this process. We discuss three possible explanations for the exotic ions, namely impurities, negative helium ions, and fission of the electron wave function. Each of these explanations has difficulties but as far as we can see, of the three, fission is the only plausible explanation of the results which have been obtained.

Low-Lying S-States of Two-Electron Systems

The energies of the low-lying bound S-states of some two-electron systems (treating them as three-body systems) like negatively charged hydrogen, neutral helium, positively charged-lithium, beryllium, carbon, oxygen, neon, argon and negatively charged muonium and exotic positronium ions have been calculated employing hyperspherical harmonics expansion method. The matrix elements of two-body interactions involve Raynal–Revai coefficients which are particularly essential for the numerical solution of three-body Schrődinger equation when the two-body potentials are other from Coulomb or harmonic. The technique has been applied for to two-electron ions 1H− (Z = 1) to 40Ar16+ (Z = 18), negatively charged-muonium Mu− and exotic positronium ion Ps−(e+e−e−) considering purely Coulomb interaction. The available computer facility restricted reliable calculations up to 28 partial waves (i.e. Km = 28) and energies for higher Km have been obtained by applying an extrapolation scheme suggested by Schneider.

The NSCL cyclotron gas stopper – Under construction

Rare isotopes are produced at the NSCL by projectile fragmentation at energies on the order of 100MeV/u for a wide range of research. In order to provide these exotic ions to low-energy high precision experiments such as the Penning-trap mass spectrometer LEBIT and the collinear laser spectroscopy setup, or to the NSCL’s re-accelerator (ReA), the beam must be slowed down into the eV range by solid degraders and interaction with buffer gas. A novel gas-filled reverse cyclotron is currently under construction by the NSCL and will complement a recently installed linear gas-filled cell. The new device is based on a 2.6T maximum-field cyclotron-type three-sectored magnet to confine the injected beam while it is slowed down in ≈100mbar of high-purity helium gas, cooled to liquid-nitrogen temperature. Once thermalized, the beam is transported to the center of the device by a novel RF-carpet system, extracted along the symmetry axis and accelerated to a few tens of keV of energy for delivery to the users.The device has been characterized in numerous simulations with full 3D models of its magnetic field. The beam transport has been modeled from the fragment separator to the point where they reach thermal energies. The simulations indicate that very efficient stopping and fast extraction will be possible even for light and medium-mass ions, which are difficult to efficiently thermalize in linear gas cells. Construction of the device is well underway and initial tests are planned for later this year. The design and the predicted performance of the machine is discussed and its construction status is given.

Experimental Investigation of Exotic Negative Ions in Superfluid Helium

We have constructed a new apparatus designed to study the exotic negative ions in superfluid helium-4 previously observed. Our apparatus is similar to that used by Ihas and Sanders, and by Eden and McClintock. The ions are generated from an electrical discharge in the vapor above the surface of the liquid and the mobility is measured by the time-of-flight method. We have detected eleven exotic ions with distinct mobility, and have measured their mobility as a function of temperature. In addition to the peaks in the time-of-flight signal due to the different exotic ions, there is a smoothly varying and continuous background signal. The variation of the background with field and temperature appears to be inconsistent with any explanation invoking the decay of one exotic ion into another, and supports the idea it arises from negative ions with a continuous distribution of mobility. This is a striking result because it would indicate that these ions have a continuous size distribution.

Entangled states of trapped ions allow measuring the magnetic field gradient produced by a single atomic spin

We propose detecting the magnetic field gradient produced by the magnetic dipole moment of a single atom by using ions in an entangled state trapped a few μm from the dipole. This requires measuring magnetic field gradients of order 10−13 tesla/μm. We discuss applications in determining magnetic moments of a wide variety of ion species, for investigating the magnetic substructure of ions with level structures that are not suitable for laser cooling and detection, and for studying exotic or rare ions, and molecular ions. The scheme may also be used for measuring spin imbalances of neutral atoms or atomic ensembles trapped by optical dipole forces. As the proposed method relies on techniques that are well established in ion trap quantum information processing, it is within reach of current technology.

Three-body negative ions under Coulomb interaction

The ground state energy eigenvalues of the symmetric three-body exotic negative ions p+π−π− and p+K−K− have been determined variationally for the first time using an explicitly correlated Hylleraas basis set. Ground state energies of Ps− and p+μ−μ− were also determined to check the accuracy of the present methodology by comparing those results to a few accurate earlier results for these systems.

Perspectives for the gamma-ray spectroscopy at LNL: the GALILEO project

GALILEO is a new 4π high-resolution γ-ray array in which GASP tapered detectors and Gammapool Cluster detectors will be used together. The array will be located at the Laboratori Nazionali di Legnaro and it will make use of the stable beams provided by the Tandem-ALPI-PIAVE accelerator complex and, in the future, of the exotic radioactive ion beams provided by SPES. The project requires the transformation of the original EUROBALL 7-capsules cluster detectors into triple cluster detectors and several R&D activities are ongoing for the development of a triple cluster cryostat and for building the corresponding anti-Compton shields. The development of the front-end, digital sampling, preprocessing and readout electronics is taking advantage of the most recent advances obtained within the AGATA project. A strong physics case was made for the building of the GALILEO array based on Letters of Intent submitted by several research groups from all over the world. In the present paper a brief summary of the status and the perspectives of the GALILEO project is given.

Hyperspherical Three-Body Calculation for Exotic Atoms

Ground state energies of atomic three-body systems like negatively charged hydrogen, normal helium, positively charged-lithium, beryllium, carbon, oxygen, neon and negatively charged exotic- muonium and positronium atoms have been calculated adopting hyperspherical harmonics expansion method. Calculation of matrix elements of two body interactions needed in the hyperspherical harmonics expansion method for a three body system is greatly simplified by expanding the bra- and ket-vector states in the hyperspherical harmonics (HH) basis states appropriate for the partition corresponding to the interacting pair. This involves the Raynal–Revai coefficients (RRC), which are the transformation coefficients between the HH bases corresponding to the two partitions. Use of RRC become particularly essential for the numerical solution of three-body Schrődinger equation where the two-body potentials are other than Coulomb or harmonic. However in the present work the technique is used for two electron atoms 1H−(p + e − e −), D−(d + e − e −), Mu−(μ + e − e −),4He(4 He 2+ e − e −),6Li(6 Li 3+ e − e −),10Be(10 Be 4+ e − e −),12C(12 C 6+ e − e −),16O(16 O 8+ e − e −) etc. and the exotic positronium negative ion Ps −(e + e − e −) where the interactions are purely Coulomb. The relative convergence in ground state binding energy with increasing K max for 20Ne has been demonstrated as a representative case. The calculated energies at K max = 28 using RRC’s have been compared with those obtained by a straight forward manner in some representative cases to demonstrate the appropriateness of the use of RRC. The extrapolated energies have also been compared with those found in the literature. The calculated binding energies agree within the computational error.

The exotic ions arrangement in the pyrochlore-type framework of protonic conductor K0.88Nb2O7.58H4.28for intermediate temperature PSOFCs

The exotic ions arrangement in the pyrochlore-type framework of protonic conductor K_0.88Nb₂O_7.58H_4.28for intermediate temperature PSOFCs

WATER-USE EFFICIENCY WITHIN A SELECTION OF INDIGENOUS AND EXOTIC TREE SPECIES IN SOUTH AFRICA AS DETERMINED USING SAP FLOW AND BIOMASS MEASUREMENTS

South Africa has limited indigenous timber-producin g forests. Recognition early in the 20 th century that demand for timber had exceeded the su pply available from indigenous forests forced South Africa to accelerat e the expansion of its own exotic plantation forest industry. This then resulted in c oncerns about impacts on water resources, and led to regulation of the industry. N umerous local and international studies have subsequently proven that exotic forest plantat ions do consume more water than the grasslands or scrublands they typically replace, an d hence reduce water yield (streamflow) from afforested catchments. Conversely, there is a widespread perception that indigenous tree species, in contrast to exotic plantation species, are water-wise and deserve to be planted more widely to expand forestr y while still conserving our scarce water resources. However, data on the water-use of indigenous trees and forests are scarce and indirect. To broaden understanding of both the growth and water-use rates of indigenous tree species, research was undertaken on their water-use efficiency (WUE), defined as mass of utilisable wood produced per uni t of water transpired. Hourly sap flow rates (water use) over a 12-month period were recor ded in a diverse selection of six indigenous tree species, while stem and branch dime nsions were recorded at fixed positions on the trees at the start and end of the monitoring period, to permit whole-tree volume growth increments to be recorded. Rates of growth and water-use were used to calculate WUE and were compared to existing data for exotic plantation species. WUE in the indigenous species studied was lower than for e xotic plantation species, however overall water-use was also low in the indigenous sp ecies. It was concluded that the relatively lower WUE of the indigenous species stud ied was more a consequence of slow growth rates as opposed to high water-use rates.

An essentially exact many body calculation for muonic molecular ions and exotic coulombic systems

The L = 0 bound states and the structural properties of muonic molecular ions and exotic nuclear molecular ions are calculated by a hyperspherical harmonics expansion method, which is an essentially exact method for three-body systems. We examine the convergence rate of this method and also examine its crucial dependence on the mass ratio ℛ (ratio of the masses of similar to dissimilar particles). An a priori criterion for the rate of convergence and the required size of the expansion basis for a predetermined precision have been suggested. Our calculation reveals the cluster type of structure of these systems.

Precision Penning trap mass measurements on exotic ions: status and perspectives

Penning traps are powerful instruments for the precise and accurate mass determination of rare isotopes. At present, many Penning trap facilities installed at radioactive beam facilities provide key data for nuclear astrophysics, for the study of nuclear structure evolution far from stability, and the test of fundamental interactions. This article summarizes the present status and current limits in the field of high-precision Penning trap mass measurements on short-lived exotic ions.

Electrons in Superfluid Helium-4

We review the current status of theory and experiment concerning electrons in superfluid helium-4 with an emphasis on some of the unsolved problems. Although calculations of the bubble structure have been confirmed in detail by measurements of the optical absorption spectrum, the energy of interaction of a bubble with a vortex is not understood. We discuss the theory behind a proposed experiment that may shed light on the physical nature of the exotic ions.

High-accuracy Penning trap mass measurements with stored and cooled exotic ions

The technique of Penning trap mass spectrometry is briefly reviewed particularly in view of precision experiments on unstable nuclei, performed at different facilities worldwide. Selected examples of recent results emphasize the importance of high-precision mass measurements in various fields of physics.

Constraints on the spectra of 17,19C

Diverse means are used to investigate the spectra of the radioactive, exotic ions, 17,19C. First, estimates have been made using a shell model for the systems. Information from those shell model studies were then used in evaluating cross sections of the scattering of 70 A MeV 17,19C ions from hydrogen. Complementing those studies, a multichannel algebraic scattering (MCAS) theory for n+ 16,18C coupled-channel problems has been used to identify structures of the compound systems. The results show that the shell model structure assumed for these ions is reasonable with little need of effective charges. The conditions that two excited states exist within a few hundred keV of the ground state places some restriction upon the structure models. Other positive parity states are expected in the low-lying spectra of the two nuclei.

Online test of the FRS Ion Catcher at GSI

At the FRS Ion Catcher at GSI, relativistic exotic ions produced by projectile fragmentation/fission are range-focused, slowed down and thermalised in a gas-filled stopping cell, extracted and made available to high-precision experiments with ions almost at rest. It is a prototype for a gas cell system at the Low-Energy Branch of the Super-FRS at FAIR. In an online experiment, the FRS Ion Catcher was commissioned successfully with relativistic nickel fragments. The overall efficiency of the system was measured as (1.8±0.3)% and can be divided into a stopping efficiency of (5.0±1.1)% and an extraction and transport efficiency of (35.8±9.4)%. The overall efficiency is hence limited mostly by the stopping efficiency, which could be increased in the future by operating at higher gas cell pressures. From extraction time measurements of polyatomic ions formed in the gas cell extraction times of atomic ions of 20–50ms can be derived. The potential of the system was illustrated by the half-life measurement of 54Co with a short half-life of 193ms only.

A rapid, non‐destructive method of detecting diagenetic alteration in fossil bone using Raman spectroscopy

AbstractBiogenic isotopes of analytical interest may be stripped from bone during burial, reducing the utility of fossil specimens for paleobiological and paleoenvironmental reconstruction. Denudation of the bone lattice coupled with the addition of exotic ions can influence the Raman spectra of fossil bone. Modern bone samples (n = 43) were used to establish an unaltered bone standard, and a suite of synthetic apatite samples were produced to simulate the addition of various ions into the bone mineral lattice. Diagenetic alteration produces distinct spectral characters, providing qualifications for major ionic substitution, ionic heterogeneity, the abundance of structural carbonate, the presence of calcium carbonate and the presence of luminescent ions. Spectral indicators (proxies) provide the means of rapidly and nondestructively evaluating the degree of alteration and thus the analytical utility of fossil bones, potentially avoiding exhaustive and destructive analysis on finite material. Copyright © 2007 John Wiley & Sons, Ltd.

EXOTIC MOLECULAR IONS (HeH)2+ AND ${\rm He}_2^{3+}$ IN A STRONG MAGNETIC FIELD: LOW-LYING STATES

The Coulombic systems (αpe) and (ααe), (αppe), (ααpe) and ( Li 3+ Li 3+e) placed in a magnetic field B ≳ 1011 G are studied. It is demonstrated a theoretical existence of the exotic ion ( He H )2+ for B ≳ 5 × 1012 G in parallel configuration (the magnetic field is directed along internuclear axis) as optimal as well as its excited states 1π, 1δ. As for the exotic ion [Formula: see text] it is shown that in spite of strong electrostatic repulsion of α-particles this ion can also exist for B ≳ 100 a.u. (= 2.35 × 1011 G ) in parallel configuration as optimal in the states 1σg (ground state), 1πu, 1δg. Upon appearance both ions are unstable towards dissociation with He + in the final state but with very large lifetime. However, at B ≳ 10000 a.u. , the ion ( He H )2+ becomes stable, while at B ≳ 1000 a.u. , the ion [Formula: see text] becomes stable. For both ions the vibrational and rotational energies are calculated. With a magnetic field growth, both exotic ions become more and more tightly bound and compact, their lowest rotational and vibrational energies grow drastically. At the edge of applicability of nonrelativistic approximation, B ~ 4.414 × 1013 G , there are indications that three more exotic linear ions ( H – He – H )3+, ( He – H – He )4+ and even [Formula: see text] in parallel configuration may also occur.