Karl Johnston

CERN | CERN · Physics Department (PH)

The ISOLDE Scientific Infrastructure at CERN offers a unique range of post-accelerated radioactive beams. The scientific program can be improved with the “Isolde Superconducting Recoil Separator” (ISRS), an innovative spectrometer able to deliver unprecedented (A, Z) resolution. In this paper we present an overview of the physics and ongoing techni...

Emission 57 Fe Mössbauer spectroscopy (eMS), following the implantation of radioactive 57 Mn + ions, has been used to study the temperature dependence of the hyperfine magnetic field at Fe sites in Ba-doped BiFeO 3 (BFO) thin films. 57 Mn β decays (t 1/2 = 90 s) to the 14.4 keV Mössbauer state of 57 Fe, thus allowing online eMS measurements at a se...

There is an apparent mismatch between electron paramagnetic resonance and Mössbauer spectroscopy results on the charge and spin states of dilute Fe impurities in NaCl; Mössbauer spectroscopy data have been interpreted in terms of high-spin Fe 2+ , while electron paramagnetic resonance studies suggest low-spin Fe 1+. In the present study, the charge...

Charge states and lattice sites of Fe ions in virgin and Mn-doped Al x Ga 1- x N samples were investigated using ⁵⁷ Fe emission Mössbauer spectroscopy following radioactive ⁵⁷ Mn ⁺ ion implantation at ISOLDE, CERN. In the undoped Al x Ga 1- x N, Fe ²⁺ on Al/Ga sites associated with nitrogen vacancies and Fe ³⁺ on substitutional Al/Ga sites are iden...

The HIE-ISOLDE facility at CERN can accelerate more than 1000 isotopes of about 70 elements, at collision energies up to 8 MeV/A. Structure and dynamics of nuclear systems far from stability are being investigated by means of Coulomb barrier reactions, nucleon transfer, deep inelastic and fusion-evaporation reactions. The ISRS collaboration has rec...

The magnetic properties of the Fe/V superlattices were studied by conventional Conversion Electron Mössbauer Spectroscopy (CEMS) and online 57Fe+ emission Mössbauer Spectroscopy (eMS) at room temperature (RT) at ISOLDE/CERN. The unique depth-enhanced sensitivity and ultradiluted regime of the probe atoms adopted in this eMS facility enabled the inv...

Van der Waals α-MoO3 samples offer a wide range of attractive catalytic, electronic, and optical properties. We present herein an emission Mössbauer spectroscopy (eMS) study of the electric-field gradient (EFG) anisotropy in crystalline free-standing α-MoO3 samples. Although α-MoO3 is a two dimensional (2D) material, scanning electron microscopy sh...

The nature of quadrupole and octupole collectivity in Rn222 was investigated by determining the electric-quadrupole (E2) and octupole (E3) matrix elements using subbarrier, multistep Coulomb excitation. The radioactive Rn222 beam, accelerated to 4.23 MeV/u, was provided by the HIE-ISOLDE facility at CERN. Data were collected in the Miniball γ-ray s...

The goal of the KArlsruhe TRItrium Neutrino (KATRIN) experiment is the determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c² at 90 % C.L.¹. This goal can only be achieved with a very low background level in the order of 10 mcps² in the detector region of interest. A possible background source are α-decays on the...

The β decay of the neutron-rich In134 and In135 was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z=50 above the N=82 shell. The β-delayed γ-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-io...

The HIE-ISOLDE facility at CERN delivers presently the largest range of low-energy radioactive beam available worldwide. The relevant features of the atomic nucleus are investigated by Coulomb excitation, transfer, deep inelastic and fusion-evaporation reactions. These studies can benefit from the use of a high-resolution spectrometer which selects...

An extension of the online implantation chamber used for emission Mössbauer Spectroscopy (eMS) at ISOLDE/CERN that allows for quick removal of samples for offline low temperature studies is briefly described. We demonstrate how online eMS data obtained during implantation at temperatures between 300 K and 650 K of short-lived parent isotopes combin...

The goal of the KArlsruhe TRItrium Neutrino (KATRIN) experiment is the determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c$^2$ at 90% C.L. This goal can only be achieved with a very low background level in the order of 0.01 counts per second. A possible background source is $\alpha$-decays on the inner surface o...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the standard model of particle physics. Isotopes of both radon and radium have been i...

There is sparse direct experimental evidence that atomic nuclei can exhibit stable “pear” shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole (E3) matrix elements have been determined for transitions in Ra222,228 nuclei using the method of sub-barrier, m...

There is sparse direct experimental evidence that atomic nuclei can exhibit stable pear shapes arising from strong octupole correlations. In order to investigate the nature of octupole collectivity in radium isotopes, electric octupole ($E3$) matrix elements have been determined for transitions in $^{222,228}$Ra nuclei using the method of sub-barri...

Abstract The determination of the effective electron neutrino mass via kinematic analysis of beta and electron capture spectra is considered to be model-independent since it relies on energy and momentum conservation. At the same time the precise description of the expected spectrum goes beyond the simple phase space term. In particular for electro...

One of the most puzzling problems in Nuclear Astrophysics is the “Cosmological Lithium Problem”, i.e the discrepancy between the primordial abundance of Li observed in metal poor halo stars (Asplund et al. in Astrophys J 644:229–259, 2006, [1]), and the one predicted by Big Bang Nucleosynthesis (BBN). One of the reactions that could have an impact...

Background: Biodistribution studies based on organ harvesting represent the gold standard pre-clinical technique for dose extrapolations. However, sequential imaging is becoming increasingly popular as it allows the extraction of longitudinal data from single animals, and a direct correlation with deterministic radiation effects. We assessed the f...

There is a large body of evidence that atomic nuclei can undergo octupole distortion and assume the shape of a pear. This phenomenon is important for measurements of electric-dipole moments of atoms, which would indicate CP violation and hence probe physics beyond the Standard Model of particle physics. Isotopes of both radon and radium have been i...

At the CERN-ISOLDE facility a variety of radioactive ion beams are available to users of the facility. The number of extractable isotopes estimated from yield database data exceeds 1000 and is still increasing. Due to high demand and scarcity of available beam time, precise experiment planning is required. The yield database stores information abou...

Excited states in Sn133 were investigated through the β decay of In133 at the ISOLDE facility. The ISOLDE Resonance Ionization Laser Ion Source (RILIS) provided isomer-selective ionization for In133, allowing us to study separately, and in detail, the β-decay branch of In133Jπ=(9/2+) ground state and its Jπ=(1/2−) isomer. Thanks to the large spin d...

The Be7(n,p) cross section was measured with an ion-implanted Be7 target at a thermal neutron beam of the research reactor LVR-15 in Řež. The cross section to the ground state of Li7 is σ(n,p0)=43800±1400b and the cross section to the first excited state of Li7 is σ(n,p1)=520±260b.

The first 2+ and 3− states of the doubly magic nucleus Sn132 are populated via safe Coulomb excitation employing the recently commissioned HIE-ISOLDE accelerator at CERN in conjunction with the highly efficient MINIBALL array. The Sn132 ions are accelerated to an energy of 5.49 MeV/nucleon and impinged on a Pb206 target. Deexciting γ rays from the...

The properties and performance of TiN thin films are closely related to the concentration and mobility of lattice defects in the thin film structures of TiN. This makes a local atomic scale study of TiN thin films an ever-growing demand. Emission ⁵⁷Fe Mössbauer spectroscopy (eMS) is a powerful tool in this regard, which we apply here to study an ul...

We report on the measurement of the Be7(n,p)Li7 cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight...

We report on the measurement of the $^{7}$Be($n, p$)$^{7}$Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n\_TOF facility at CERN. This reaction plays a key role in the lithium yield of the Big Bang Nucleosynthesis (BBN) for standard cosmology. The only two previous t...

Following the completion of the second neutron beam line and the related experimental area (EAR2) at the n_TOF spallation neutron source at CERN, several experiments were planned and performed. The high instantaneous neutron flux available in EAR2 allows to investigate neutron indiced reactions with charged particles in the exit channel even employ...

Several experiments on the study of the electron neutrino mass are based on high-statistics measurements of the energy spectrum following electron capture of the radionuclide ¹⁶³Ho. They rely on the availability of large, radiochemically pure samples of ¹⁶³Ho. Here, we describe the production, separation, characterization, and sample production wit...

There is significant interest in isotopes of terbium (Tb) for medical applications. The radioisotopes 149,152,155,161Tb have the potential to provide unique theranostic treatment strategies, providing both α- and β- emitting cancer therapies and diagnostic SPECT and PET imaging. To provide a solid foundation for the use of these isotopes in future...

The underlying mechanism driving the structural amorphous-to-crystalline transition in Group VI chalcogenides is still a matter of debate even in the simplest GeTe system. We exploit the extreme sensitivity of ⁵⁷Fe emission Mössbauer spectroscopy, following dilute implantation of ⁵⁷Mn (T1/2 = 1.5 min) at ISOLDE/CERN, to study the electronic charge...

The first experimental investigation of the electron affinity (EA) of a radioactive isotope has been conducted at the CERN-ISOLDE radioactive ion beam facility. The EA of the radioactive iodine isotope ¹²⁸I (t 1/2 = 25 min) was determined to be 3.059 052(38) eV. The experiment was conducted using the newly developed Gothenburg ANion Detector for Af...

The isotope Ho163 is in many ways the best candidate to perform experiments to investigate the value of the electron neutrino mass. It undergoes an electron capture process to Dy163 with an energy available to the decay, QEC, of about 2.8 keV. According to the present knowledge, this is the lowest QEC value for such transitions. Here we discuss a n...

The existence of theragnostic pairs of radionuclides allows the preparation of radiopharmaceuticals for diagnostic and therapeutic purposes. Radiolanthanides, such as (177)Lu, are successfully used for therapeutic purposes; however, a perfect diagnostic match is currently not available for clinical use. A unique, multi-disciplinary study was perfor...

A 3-meter two telescope stellar interferometer has been used to observe fringes for the past year in order to study the feasibility of using long baseline interferometers for astrometry. We have demonstrated that two color fringe measurements are capable of significantly reducing the astrometric error due to atmospheric turbulence. Currently, we ar...

Considerable progress has been made over the last few years in ground based optical interferometery. The Mark III optical interferometer at Mount Wilson which at this time is operating with a 12 meter north south baseline is capable of measuring amplitude and phase. Experience gained from this facility will allow for the development of a large opti...

Solid State research at ISOLDE has been running since the mid-1970s and accounts for about 10-15% of the overall physics programme. ISOLDE is the world flagship for the on-line production of exotic radioactive isotopes, with high yields, high elemental selectivity and isotopic purity. Consequently, it hosts a panoply of state-of-the-art nuclear tec...

140Nd (t1/2 = 3.4 days), owing to its short-lived positron emitting daughter 140Pr (t1/2 = 3.4 min), has promise as an in vivo generator for positron emission tomography (PET). However, the electron capture decay of 140Nd is chemically disruptive to macrocycle-based radiolabeling, meaning that an in vivo redistribution of the daughter 140Pr is expe...

Neutrinos, and in particular their tiny but non-vanishing masses, can be considered one of the doors towards physics beyond the Standard Model. Precision measurements of the kinematics of weak interactions, in particular of the 3H β-decay and the 163Ho electron capture (EC), represent the only model independent approach to determine the absolute sc...

The local environment in titanium dioxide was studied by the time differential perturbed γ-γ angular correlation of 111 In/ 111 Cd and 181 Hf/ 181 Ta at the HISKP, Bonn. An introduction to the implantation methodologies performed at the Bonn Radioisotope Separator is presented. The investigation was carried out on thin films, which were deposited b...

The local environment in titanium dioxide was studied by the time differential perturbed γ-γ angular correlation of 111In/111Cd and 181Hf/181Ta at the Helmholtz-Institut für Strahlen-und Kernphysik, Bonn. An introduction to the implantation methodologies performed at the Bonn Radioisotope Separator is presented. The investigation was carried out on...

The common charge states of Sn are 2+ and 4+. While charge neutrality considerations favour 2+ to be the natural charge state of Sn in ZnO, there are several reports suggesting the 4+ state instead. In order to investigate the charge states, lattice sites, and the effect of the ion implantation process of dilute Sn atoms in ZnO, we have performed <...

149 Tb represents a powerful alternative to currently used α-emitters: the relatively short half-life (T1/2 = 4.1 h), low α-energy (3.97 MeV, Iα = 16.7 %), absence of α-emitting daughters and stable coordination via DOTA are favorable features for potential clinical application. In this letter, we wish to highlight the unique characteristics of149T...

57Fe emission Mössbauer spectroscopy has been applied to study the lattice location and properties of Fe in gadolinium gallium garnet Gd3Ga5O 12 (GGG) single crystals in the temperature interval 300 – 563 K within the extremely dilute (<10−4 at.%) regime following the implantation of57Mn (T 1/2= 1.5 min.) at ISOLDE/CERN. These results are compared...

We present a study of TiO2 single crystals from the point of view of the dopant atom that simultaneously behaves as the probing element. We used gamma-gamma time dependent perturbed angular correlations working with selected tracer elements (¹¹¹In/ ¹¹¹Cd, 111mCd/ ¹¹¹Cd) together to investigate the different behavior of Cd and In dopants, particular...

Time Differential Perturbed Angular Correlation of γ-rays (TDPAC) experiments were performed for the first time in the decay of 68m Cu produced at the ISOLDE facility at CERN. Due to the short half-life of the source isotope, the measurements were carried out online. The intermediate state offers the unique opportunity to study the electromagnetic...

The Electron Capture in \(^{163}\)Ho experiment, ECHo, is designed to investigate the electron neutrino mass in the sub-eV range by means of the analysis of the calorimetrically measured spectrum following the electron capture (EC) in \(^{163}\)Ho. Arrays of low-temperature metallic magnetic calorimeters (MMCs), read-out by microwave SQUID multiple...

Background: Terbium has attracted the attention of researchers and physicians due to the existence of four medically interesting radionuclides, potentially useful for SPECT and PET imaging, as well as for α- and β(-)-radionuclide therapy. The aim of this study was to produce (152)Tb (T 1/2 = 17.5 h, Eβ+av = 1140 keV) and evaluate it in a preclinic...

Emission Mössbauer Spectroscopy (eMS) measurements, following low fluence (<1012 cm−2) implantation of 57Mn (t 1/2 = 1.5 min.) into ZnO single crystals pre-implanted with Ar and C ions, has been utilized to test the sensitivity of the 57Fe eMS technique to the different types of defects generated by the different ion species. The dominant feature o...

Emission Mössbauer spectroscopy has been utilised to characterize dilute 57Fe impurities in In 2O3 following implantation of 57Mn (T 1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In 3+, however the spectra are dominated by spectral lines due to pa...

The VITO (Versatile Ion-polarized Techniques Online) project is a new experimental setup at the ISOLDE facility at CERN. VITO is a dedicated beam line for producing laser-induced spin-polarized beams of both, atoms and ions, and it has been commissioned in response to the continuously growing demand for the use of spin-polarized beams. The new VITO...

Emission Mössbauer Spectroscopy following the implantation of radioactive precursor isotope 57Mn+ (T 1/2= 1.5 min) into ZnO single crystals at ISOLDE/CERN shows that a large fraction of 57Fe atoms produced in the 57Mn beta decay is created as paramagnetic Fe3+ with relatively long spin-lattice relaxation times. Here we report on ZnO pre-implanted w...

Nano-crystalline ZnO has been studied with perturbed angular correlation using 111mCd, implanted at ISOLDE/CERN and X-ray diffraction using Rietveld analysis. The data show a gradual increase in the crystal size and stress for a sample annealed at 600 °C, and reaching nearly properties of standard ZnO with tempering at 1000 °C. The perturbed angula...

The lattice sites, valence states, resulting magnetic behaviour and spin-lattice relaxation of Fe ions in GaN and AlN were investigated by emission Mössbauer spectroscopy following the implantation of radioactive 57Mn+ ions at ISOLDE/CERN. Angle dependent measurements performed at room temperature on the 14.4 keV γ-rays from the 57Fe Mössbauer stat...

Applications of nuclear spectroscopic techniques are well established in chemistry and biochemistry, where, for example, conventional nuclear magnetic resonance (NMR) spectroscopy is an indispensable analytical tool [1]. NMR is used routinely to identify small organic molecules in quality control, and in more complex research applications to elucid...

In search for dilute magnetic semiconductors, the magnetic properties at the atomic-scale of Fe atoms incorporated in ZnO, in a concentration range of more than fi ve orders of magnitude from 1 × 10 −5 to 2.2 at% have been probed using emission 57 Fe Mössbauer spectroscopy on implanted 57 Mn and 57 Co produced at ISOLDE/CERN. In the ultra-dilute re...