Peter Thirolf

• Professor
• Group Leader at Ludwig-Maximilians-Universität in Munich

A noncollinear resonator with two beams circulating and intersecting in the focus allows resonator-assisted high-harmonic generation of high-power femtosecond pulses with efficient geometrical output coupling. However, the synchronization of the two pulses and alignment of the two beams is a challenge. We describe a resonator design employing wedge...

A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the Th 229 m nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of Th 229 m embedded are determined for single crystalline CaF 2 , MgF 2 , LiSrAlF 6 , AlN, and a...

Radioactive ion beams (RIB) are a key focus of current research in nuclear physics. Already long ago it was proposed that they could have applications in cancer therapy. In fact, while charged particle therapy is potentially the most effective radiotherapy technique available, it is highly susceptible to uncertainties in the beam range. RIB are wel...

A comparative vacuum ultraviolet spectroscopy study conducted at ISOLDE-CERN of the radiative decay of the $^{229m}$Th nuclear clock isomer embedded in different host materials is reported. The ratio of the number of radiative decay photons and the number of $^{229m}$Th embedded are determined for single crystalline CaF$_2$, MgF$_2$, LiSrAlF$_6$, A...

Optical atomic clocks$^{1,2}$ use electronic energy levels to precisely keep track of time. A clock based on nuclear energy levels promises a next-generation platform for precision metrology and fundamental physics studies. Thorium-229 nuclei exhibit a uniquely low energy nuclear transition within reach of state-of-the-art vacuum ultraviolet (VUV)...

Zusammenfassung Das Thoriumisomer 229m Th besitzt den mit zirka 8,3 eV niederenergetischsten angeregten Zustand aller bekannten Atomkerne, der zudem langlebig ist. Damit bietet ²²⁹ Th die Möglichkeit, den Kernübergang zwischen Grundzustand und angeregtem Isomer zum Bau einer sogenannten Kernuhr einzusetzen. Sie wäre eine Ergänzung zu den bislang ge...

Compton cameras (CCs) allow for spatially resolved $\gamma $ detection. The $\gamma $ -ray origins are reconstructed by measuring the interaction positions and energy deposits in the scatter and absorber components, allowing to determine the scattering angle. Consequently, the energy resolution of the CC components plays a major role in compone...

Today’s most precise timekeeping is based on optical atomic clocks. However, those could potentially be outperformed by a nuclear clock, based on a nuclear transition instead of an atomic shell transition. Such a nuclear clock promises intriguing applications in applied as well as fundamental physics, ranging from geodesy and seismology to the inve...

The next years will see the completion of several new facilities at Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud (LNS) opening up new possibilities in the fields of nuclear structure, nuclear dynamics, nuclear astrophysics and applications. These include a new line for high-intensity cyclotron beams, a new facility for in-fl...

Objective: We designed a geometrical solution for a small animal in-beam positron emission tomography (PET) scanner to be used in the project SIRMIO (Small animal proton irradiator for research in molecular image-guided radiation-oncology). The system is based on 56 scintillator blocks of pixelated LYSO crystals. The crystals are arranged providin...

The electric E 1 and magnetic M 1 dipole responses of the $$N=Z$$ N = Z nucleus $$^{24}$$ 24 Mg were investigated in an inelastic photon scattering experiment. The 13.0 MeV electrons, which were used to produce the unpolarised bremsstrahlung in the entrance channel of the $$^{24}$$ 24 Mg( $$\gamma ,\gamma ^{\prime }$$ γ , γ ′ ) reaction, were deliv...

At the FRS Ion Catcher (FRS-IC), projectile and fission fragments are produced at relativistic energies, separated in-flight, energy-bunched, slowed down, and thermalized in the ultra-pure helium gas-filled cryogenic stopping cell (CSC). Thermalized nuclei are extracted from the CSC using a combination of DC and RF electric fields and gas flow. Thi...

For the realization of an optical nuclear clock, the first isomeric excited state of thorium-229 (229mTh) is currently the only candidate due to its exceptionally low-lying excitation energy (8.338±0.024 eV). Such a nuclear clock holds promise not only to be a very precise metrological device but also to extend the knowledge of fundamental physics...

The results presented in this manuscript are divided in two main parts. The aim of the presented work is to conduct feasibility tests on a Compton camera setup to be later scaled up and used for PET and triple coincidence γ-PET purposes. The first part is focused on laboratory characterization of a monolithic LaBr3(Ce) scintillator coupled to a 64-...

Th229 with a low-lying nuclear isomeric state is an essential candidate for a nuclear clock as well as many other applications. Laser excitation of the isomeric state has been a long-standing goal. With relativistic Th229 ions in storage rings, high-power lasers with wavelengths in the visible range or longer can be used to achieve high excitation...

The radionuclide thorium-229 features an isomer with an exceptionally low excitation energy that enables direct laser manipulation of nuclear states. It constitutes one of the leading candidates for use in next-generation optical clocks1–3. This nuclear clock will be a unique tool for precise tests of fundamental physics4–9. Whereas indirect experi...

The Centre for Advanced Laser Applications in Garching, Germany, is home to the ATLAS-3000 multi-petawatt laser, dedicated to research on laser particle acceleration and its applications. A control system based on Tango Controls is implemented for both the laser and four experimental areas. The device server approach features high modularity, which...

Direct mass measurements in the region of the heaviest elements were performed with the Penning-trap mass spectrometer SHIPTRAP at GSI Darmstadt. Utilizing the phase-imaging ion-cyclotron-resonance mass-spectrometry technique, the atomic masses of No251 (Z=102), Lr254 (Z=103), and Rf257 (Z=104) available at rates down to one detected ion per day we...

We present here simulation results of the laser-driven acceleration of gold ions using the EPOCH code. Recently, an experiment reported the acceleration of gold ions up to 7 MeV/nucleon with a strong dependency of the charge-state distribution on target thickness and the detection of the highest charge states Z∼72\documentclass[12pt]{minimal} \usep...

The nucleus of the radioisotope thorium-229 (${}^{229}$Th) features an isomer with an exceptionally low excitation energy that enables direct laser manipulation of nuclear states. For this reason, it is a leading candidate for use in next-generation optical clocks. This nuclear clock will be a unique tool, amongst others, for tests of fundamental p...

Hybrid imaging systems, comprising PET and Compton camera modules, have recently gained in interest, due to their capability to simultaneously detect positron annihilation photons and γ-rays from single-photon emitting sources as also used in SPECT. A unique feature of such systems, however, is the capability to also be operated in a so called γ-PE...

{229}$Th with a low-lying nuclear isomeric state is an essential candidate for a nuclear clock as well as many other applications. Laser excitation of the isomeric state has been a long-standing goal. With relativistic $^{229}$Th ions in storage rings, high-power lasers with wavelengths in the visible range or longer can be used to achieve high pro...

The last decade has seen unprecedented effort in dark matter model building at all mass scales coupled with the design of numerous new detection strategies. Transformative advances in quantum technologies have led to a plethora of new high-precision quantum sensors and dark matter detection strategies for ultralight ($<10\,$eV) bosonic dark matter...

In the past years, the interest in the laser-driven acceleration of heavy ions in the mass range of A≈200 has been increasing due to promising application ideas like the fission-fusion nuclear reaction mechanism, aiming at the production of neutron-rich isotopes relevant for the astrophysical r-process nucleosynthesis. In this paper, we report on t...

Physics Opportunities with the Gamma Factory The front cover shows the principle of the Gamma Factory, the subject of this special issue, as covered by the fourteen Research Articles and the Review Article (2100284). Secondary photons are produced by scattering laser light on partially stripped ultrarelativistic ions.

The first nuclear excited state in 229Th possesses the lowest excitation energy of all currently known nuclear levels. The energy difference between the ground- and first-excited (isomeric) state (denoted with 229mTh) amounts only to ≈8.2 eV (≈151.2 nm), which results in several interesting consequences: Since the excitation energy is in the same e...

The fission probability of 238Np was measured as a function of the excitation energy in the energy range of E∗=5.4-6.2 MeV in order to search for transmission fission resonances. A radioactive 237Np target was bombarded with deuterons of Ed = 12 MeV, whereas the energy of the protons was analyzed with a superior resolution of ΔE = 8 keV. The experi...

The Gamma Factory (GF) is an ambitious proposal, currently explored within the CERN Physics Beyond Colliders program, for a source of photons with energies up to ≈400 MeV and photon fluxes (up to ≈1017 photons s−1) exceeding those of the currently available gamma sources by orders of magnitude. The high‐energy (secondary) photons are produced via r...

High power lasers have proven being capable to produce high energy gamma rays, charged particles and neutrons to induce all kinds of nuclear reactions. At ELI, the studies with high power lasers will enter for the first time into new domains of power and intensities.

Given the drastic progress achieved during recent years in our knowledge on the decay and nuclear properties of the thorium isomer 229mTh, the focus of research on this potential nuclear clock transition will turn in the near future from the nuclear physics driven `search and characterization phase' towards a laser physics driven `consolidation and...

Several techniques are under development for image-guidance in particle therapy. Positron (β⁺) emission tomography (PET) is in use since many years, because accelerated ions generate positron-emitting isotopes by nuclear fragmentation in the human body. In heavy ion therapy, a major part of the PET signals is produced by β⁺-emitters generated via p...

In this work, we present the development and application of a Convolutional Neural Networks (CNN)-based algorithm to precisely determine the interaction position of γ-quanta in large monolithic scintillators. Those are used as an absorber component of a Compton Camera (CC) system under development for ion beam range verification via prompt gamma im...

In this study, we propose a staggered 3-layer depth-of-interaction (DOI) detector with a 1 mm crystal pitch and 19.8 mm total crystal thickness for a high-resolution and high-sensitivity small animal in-beam PET scanner. A three-layered stacked LYSO scintillation array (0.9 × 0.9 × 6.6 mm3crystals, 23 × 22 mm2surface area) read out by a SiPM array...

The Gamma Factory (GF) is an ambitious proposal, currently explored within the CERN Physics Beyond Colliders program, for a source of photons with energies up to $\approx 400\,$MeV and photon fluxes (up to $\approx 10^{17}$ photons per second) exceeding those of the currently available gamma sources by orders of magnitude. The high-energy (secondar...

The dispersive behavior of materials with atomic charge numbers varing from Z = 4 (beryllium, Be) to Z = 82 (lead, Pb) was investigated experimentally and theoretically at γ-ray energies up to 2 MeV. The experiment was performed at the double-crystal gamma spectrometer GAMS6 of the ILL in Grenoble. The experimental results were compared with theore...

In the past years, the interest in the laser-driven acceleration of heavy ions in the mass range of A ~ 200 has been increasing due to promising application ideas like the fission-fusion nuclear reaction mechanism, aiming at the production of neutron-rich isotopes relevant for the astrophysical r-process nucleosynthesis. In this paper, we report on...

The low-energy, long-lived isomer in 229Th, first studied in the 1970s as an exotic feature in nuclear physics, continues to inspire a multidisciplinary community of physicists. It has stimulated innovative ideas and studies that expand the understanding of atomic and nuclear structure of heavy elements and of the interaction of nuclei with bound e...

The low-energy, long-lived isomer in $^{229}$Th, first studied in the 1970s as an exotic feature in nuclear physics, continues to inspire a multidisciplinary community of physicists. Using the nuclear resonance frequency, determined by the strong and electromagnetic interactions inside the nucleus, it is possible to build a highly precise nuclear c...

MLLTRAP is a double Penning trap mass spectrometer that was initially designed to be located at the Maier-Leibnitz-Laboratory (MLL) in Garching (Germany) for high precision mass measurements of exotic nuclei. A second double-trap assembly, dedicated this time to in-trap α decay spectroscopy, has been developed and is the object of this paper. This...

The ‘Centre for Advanced Laser Applications’ (CALA) is a new research institute for laser-based acceleration of electron beams for brilliant x-ray generation, laser-driven sub-nanosecond bunches of protons and heavy ions for biomedical applications like imaging and tumour therapy as well as for nuclear and high-field physics. The radiation sources...

A comprehensive theoretical study of direct laser excitation of a nuclear state based on the density matrix formalism is presented. The nuclear clock isomer \(^{229\text {m}}\)Th is discussed in detail, as it could allow for direct laser excitation using existing technology and provides the motivation for this work. The optical Bloch equations are...

The excitation of the 8 eV Th229m isomer through the electronic bridge mechanism in highly charged ions is investigated theoretically. By exploiting the rich level scheme of open 4f orbitals and the robustness of highly charged ions against photoionization, a pulsed high-intensity optical laser can be used to efficiently drive the nuclear transitio...

A comprehensive theoretical study of direct laser excitation of a nuclear state based on the density matrix formalism is presented. The nuclear clock isomer $^{229\text{m}}$Th is discussed in detail, as it could allow for direct laser excitation using existing technology and provides the motivation for this work. The optical Bloch equations are der...

The excitation of the 8 eV $^{229m}$Th isomer through the electronic bridge mechanism in highly charged ions is investigated theoretically. By exploiting the rich level scheme of open $4f$ orbitals and the robustness of highly charged ions against photoionization, a pulsed high-intensity optical laser can be used to efficiently drive the nuclear tr...

The elusive ‘thorium isomer’, i.e. the isomeric first excited state of ²²⁹ Th, has puzzled the nuclear and fundamental physics communities for more than 40 years. With an exceptionally low excitation energy and a long lifetime it represents the only known candidate so far for an ultra-precise nuclear frequency standard (‘nuclear clock’), potentiall...

Owing to its low excitation energy and long radiative lifetime, the first excited isomeric state of thorium-229, 229mTh, can be optically controlled by a laser1,2 and is an ideal candidate for the creation of a nuclear optical clock³, which is expected to complement and outperform current electronic-shell-based atomic clocks⁴. A nuclear clock will...

Background: Precision small animal radiotherapy research is a young emerging field aiming to provide new experimental insights into tumor and normal tissue models in different microenvironments, to unravel complex mechanisms of radiation damage in target and non-target tissues and assess efficacy of novel therapeutic strategies. For photon therapy,...

The first nuclear excited state of $^{229}$Th offers the unique opportunity for laser-based optical control of a nucleus. Its exceptional properties allow for the development of a nuclear optical clock which offers a complementary technology and is expected to outperform current electronic-shell based atomic clocks. The development of a nuclear clo...

In article number 1800381, Peter G. Thirolf and co‐workers discuss the introduction of the low‐energy, isomeric first excited state of 229Th as a candidate for an ultra‐precise nuclear frequency standard. Various applications for such a ‘nuclear clock’ are given, from improved accuracy of satellite‐based navigation to chronometric geodesy, dark mat...

The Technological Laboratory of LMU Munich supplies various types of solid-state target for laser plasma experiments at the Centre for Advanced Laser Applications in Garching. Our main focus here is on the production of free-standing, thin foil targets, such as diamond-like-carbon foils, carbon nanotube foams (CNFs), plastic, and gold foils. The pr...

The ISOL facility ALTO, located at Orsay in France, provides stable ion beams from a 15 MV Tandem accelerator and neutron-rich radioactive ion beams (RIB) from the interaction of a γ-flux induced by a 50 MeV 10 μA electron beam in a uranium carbide target. A magnetic dipole mass separator and a resonance ionization laser ion source allow to select...

MLLTRAP is a double Penning-trap designed for high precision mass measurements of exotic nuclei. It was built and commissioned off-line at the Maier-Leibnitz Laboratory (MLL)in Garching and is currently installed at the ALTO facility at IPNO, awaiting online commissioning. A complementary double-trap assembly dedicated to in-trap decay spectroscopy...

The fission–fusion reaction mechanism was proposed in order to generate extremely neutron-rich nuclei close to the waiting point N = 126 of the rapid neutron capture nucleosynthesis process (r-process). The production of such isotopes and the measurement of their nuclear properties would fundamentally help to increase the understanding of the nucle...

Th is the only nucleus currently under investigation for the development of a nuclear optical clock (NOC) of ultra-high accuracy. The insufficient knowledge of the first nuclear excitation energy of ²²⁹Th has so far hindered direct nuclear laser spectroscopy of thorium ions and thus the development of a NOC. Here, a nuclear laser excitation scheme...

Th is the only known nucleus with an excited state that offers the possibility for a direct laser excitation using existing laser technology. Its excitation energy has been measured indirectly to be 7.8(5) eV (≈160 nm). The energy and lifetime of the isomeric state make it the presently only suitable candidate for a nuclear optical clock, the uncer...

{229}$Th is the only known nucleus with an excited state that offers the possibility for a direct laser excitation using existing laser technology. Its excitation energy has been measured indirectly to be 7.8(5) eV ($\approx$160 nm). The energy and lifetime of the isomeric state make it the presently only suitable candidate for a nuclear optical cl...

The fission-fusion reaction mechanism was proposed in order to generate extremely neutron-rich nuclei close to the waiting point N = 126 of the rapid neutron capture nucleosynthesis process (r-process). The production of such isotopes and the measurement of their nuclear properties would fundamentally help to increase the understanding of the nucle...

Laser-based ion acceleration is driven by electrical fields emerging when target electrons absorb laser energy and consecutively leave the target material. A direct correlation between these electrons and the accelerated ions is thus to be expected and predicted by theoretical models. We report on a modified wide-angle spectrometer allowing the sim...

The dispersive behavior of materials with atomic charge numbers varying from Z=4 (beryllium, Be) to Z=82 (lead, Pb) was investigated experimentally and theoretically at γ-ray energies up to 2 MeV. The experiment was performed at the double-crystal γ spectrometer GAMS6 of the Institut Laue-Langevin in Grenoble. The experimental results were compared...

The dispersive behavior of materials with atomic charge numbers varing from $Z = 4$ (beryllium, Be) to $Z = 82$ (lead, Pb) was investigated experimentally and theoretically at $\gamma$-ray energies up to 2 MeV. The experiment was performed at the double-crystal gamma spectrometer GAMS6 of the ILL in Grenoble. The experimental results were compared...

The availability of high-power, short-pulse laser systems has created over the last two decades a novel branch of accelerator physics. Laser-driven electron and ion acceleration based on the enormous acceleration fields that can be realized over very short acceleration lengths during ultra-short pulse periods has gained enormous interest and huge e...

The isotope 229Th is the only nucleus known to possess an excited state 229mTh in the energy range of a few electron volts, a transition energy typical for electrons in the valence shell of atoms, but about four orders of magnitude lower than common nuclear excitation energies. A number of applications of this unique nuclear system, which is access...

An overview of the current status of the development of a nuclear clock based on the state of lowest known nuclear excitation energy in ²²⁹Th is presented. The text is especially written for the interested reader without any particular knowledge in this field of research. It is thus ideal as an introductory reading to get a broad overview of the va...

Often, the interpretation of experiments concerning the manipulation of the energy distribution of laser-accelerated ion bunches is complicated by the multitude of competing dynamic processes simultaneously contributing to recorded ion signals. Here we demonstrate experimentally the acceleration of a clean proton bunch. This was achieved with a mic...

Laser-based ion acceleration is driven by electrical fields emerging when target electrons absorb laser energy and consecutively leave the target material. A direct correlation between these electrons and the accelerated ions is thus to be expected and predicted by theoretical models. We report on a modified wide-angle spectrometer, allowing the si...

Prompt-γ based medical imaging, in particular exploiting the Compton scattering kinematics in a Compton camera detector arrangement, is one of the presently explored techniques targeting an in-vivo particle beam range monitoring in hadron therapy. To evaluate the performance of different Compton camera setup options, we characterized a detector sys...

Direct laser excitation of the lowest known nuclear excited state in Th229 has been a long-standing objective. It is generally assumed that reaching this goal would require a considerably reduced uncertainty of the isomer’s excitation energy compared to the presently adopted value of (7.8±0.5) eV. Here we present a direct laser excitation scheme fo...

A Compton camera prototype for ion beam range monitoring via prompt (< 1 ns) gamma detection in hadron therapy is being developed and characterized at the Medical Physics Department of LMU Munich. The system consists of a large (50x50x30 mm3) monolithic LaBr3(Ce) scintillation crystal as absorber component to detect the multi-MeV Compton scattered...

Proton ranges in water between 145 MeV to 227 MeV initial energy have been measured at a clinical superconducting synchrocyclotron using the acoustic signal induced by the ion dose deposition (ionoacoustic effect). Detection of ultrasound waves was performed by a very sensitive hydrophone and signals were stored in a digital oscilloscope triggered...

The refractive index of silicon at γ-ray energies from 181 to 1959 keV was investigated using the GAMS6 double crystal spectrometer and found to follow the predictions of the classical scattering model. This is in contrast to earlier measurements on the GAMS5 spectrometer, which suggested a sign change in the refractive index for photon energies ab...

Laser-driven acceleration of ions has inspired novel applications, that can benefit from ion bunch properties different from conventionally (non-laser based) accelerated particle beams. Those differences range from extremely short bunch durations, broad energy spectra, large divergence angles and small source sizes to ultra-high ion bunch densities...