- Published on 22 October 2019
Useful information about ultrafast light-matter interactions is buried deep in the signals produced by two-colour pump-probe experiments, and requires sophisticated techniques to disentangle it.
When photons of light interact with particles of matter, a diverse variety of physical processes can unfold in ultrafast timescales. To explore them, physicists currently use ‘two-colour pump-probe’ experiments, in which an ultrashort, infrared laser pulse is first fired at a material, causing its constituent electrons to move. After a controllable delay, this pulse is followed by a train of similarly short, extreme-ultraviolet pulses, ionising the material. By measuring the total ionisation following the pulses along with the resulting electron energy spectra, physicists can theoretically learn more about ultrafast, light-matter interactions. In new research published in EPJ D, an international team of physicists, led by Eric Suraud at the University of Toulouse, discovered that these signals are in fact dominated by the less interesting interplay between electrons and the initial infrared laser. They show that more useful information is buried deeper within these signals, and requires sophisticated techniques to disentangle it.
- Published on 09 October 2019
Recent analysis shows precisely how beams of charged particles transfer their energy to water, which has important implications for how these beams are targeted in ion beam cancer therapy.
Hadron beam therapy, which is often used to treat solid tumours, involves irradiating a tumour with a beam of high-energy charged particles, most often protons; these transfer their energy to the tumour cells, destroying them. It is important to understand the precise physics of this energy transfer so the tumour can be targeted precisely. Pablo de Vera of MBN Research Center, Frankfurt, Germany and co-workers in the Universities of Murcia and Alicante, Spain, have produced a consistent theoretical interpretation of the most accurate experimental measurements of ion beams energy deposition in liquid water jets, which is the most relevant substance for simulating interactions with human tissue. Their work is published in EPJ D.
- Published on 03 September 2019
A new study using mass spectrometry is helping piece together what happens when DNA that has been sensitized by the oncology drug 5-fluorouracil is subjected to the ionising radiation used in radiotherapy.
The anti-cancer drug 5-fluorouracil (5FU) acts as a radiosensitizer: it is rapidly taken up into the DNA of cancer cells, making the cells more sensitive to radiotherapy. However, little is known about the precise mechanism through which radiation damages cells. A team of scientists led by Peter van der Burgt at the National University of Ireland in Maynooth, Ireland have now used mass spectrometry to shed some light on this process; their work was recently published in EPJ D. A full understanding of this process could ultimately lead to new ways of protecting normal tissues from the radiation damage caused by essential cancer treatments.
- Published on 15 August 2019
Hall thrusters, which are already used to propel spacecraft and satellites on long missions, could be used for even longer ones if models for minimising surface erosion were taken into account.
The 50th anniversary of the Apollo 11 moon landing has reignited interest in space travel. However, almost any mission beyond the moon, whether manned or unmanned, will require the spacecraft to remain fully operational for at least several years. The Hall thruster is a propulsion system that is often used by craft involved in long missions. A recent study by Andrey Shashkov and co-workers at the Moscow Institute of Physics and Technology, Russia has shown how the operating lives of these systems can be further extended; their work was recently published in EPJ D.
- Published on 05 August 2019
A new quantum-mechanical model has been developed that allows the momentum of quantum particles to be measured using a variant of the classical time-of-flight.
Quantum mechanics is an extraordinarily successful way of understanding the physical world at extremely small scales. Through it, a handful of rules can be used to explain the majority of experimentally observable phenomena. Occasionally, however, we come across a problem in classical mechanics that poses particular difficulties for translation into the quantum world. A new study published in EPJ D has provided some insights into one of them: momentum. The authors, theoretical physicists Fabio Di Pumpo and Matthias Freyberger from Ulm University, Germany, present an elegant mathematical model of quantum momentum that is accessible through another classical concept: time-of-flight.
- Published on 30 July 2019
A new study looked at the way certain molecules found in chemotherapy drugs react to radiation while in water, which is more similar to in the body, compared to previous research that studied them in gas
Cancer treatment often involves a combination of chemotherapy and radiotherapy. Chemotherapy uses medication to stop cancer cells reproducing, but the medication affects the entire body. Radiotherapy uses radiation to kill the cancer cells, and it is targeted to the tumour site. In a recent study, published in the journal EPJ D, researchers from the Leopold-Franzens-University Innsbruck, Austria, studied selected molecules of relevance in this context. They wanted to see how these molecules were individually affected by radiation similar to that used in radiotherapy.
- Published on 23 July 2019
A group of Russian physicists reviews recent developments in the field of laser solitons, which they have made their own and which may have applications in digital information storage.
In almost all situations, even in a vacuum, light cannot travel endlessly without dissipating. Pulses of light known as solitons that propagate along fibres for long distances without changing their shape or losing focus have found applications in data transmission, but even these gradually dissipate unless the medium they travel through has ultra-low absorbance. Nikolay Rosanov of the National Research University of Information Technologies, Mechanics, and Optics (ITMO), St. Petersburg, Russia and his team have been working on a solution to this problem - laser solitons - since the 1980s; a colloquium paper summarising their recent work in this area has now been published in EPJ D.
- Published on 01 July 2019
Computer simulations reveal that magnetic mirrors can be tweaked to confine plasma more effectively, by fine-tuning both the arrangements of their electromagnets, and the initial properties of the plasma itself
When ring-shaped electromagnets are set up in linear arrangements, they can produce magnetic fields resembling a tube with a cone at each end; a structure which repels charged particles entering one cone back along their path of approach. Referred to as ‘magnetic mirrors’, these devices have been known to be a relatively easy way to confine plasma since the 1950s, but they have also proven to be inherently leaky. In a study published in EPJ D, physicists led by Wen-Shan Duan at Northwest Normal University, and Lei Yang at the Chinese Academy of Sciences, both in Lanzhou, China, show that these plasma leaks can be minimised if specific conditions are met. Using computer simulations, the physicists analysed the dynamic properties of a high-energy proton plasma beam within a magnetic mirror and fine-tuned the simulation settings to maximise its confinement.
- Published on 22 May 2019
Plasma probes are well-established diagnostic tools, being relatively simple to construct and easy to handle. The most easily accessible parameter is the floating potential, but the floating potential of a cold probe is not very significant; much more important and relevant is the plasma potential. However, in most types of plasmas, consisting mainly of electrons and only positive ions, the higher mobility of the electrons means that the floating potential is more negative than the plasma potential by a factor proportional to the electron temperature.
In a new Topical Review in EPJD co-authored by teams from Austria, Slovenia, Denmark and Italy, the authors present a review of probes whose floating potential is close or ideally equal to the plasma potential. Such probes are known as Plasma Potential Probes (PPP), and they can either be Electron Emissive Probes (EEPs) or so-called Electron Screening Probes (ESPs). These probes make it possible to measure the plasma potential directly and thus with high temporal resolution.
- Published on 09 April 2019
A new study explores how the characteristics of aromaticity affect the process of Auger decay
When an electron from one of the lower energy levels in an atom is knocked out of the atom, it creates a space which can be filled by one of the higher-energy electrons, also releasing excess energy. This energy is released in an electron called an Auger electron - and produces an effect known as Auger decay. Now, Guoke Zhao from Tsinghua University in Beijing, China and colleagues at Sorbonne University in Paris, France have studied the Auger effect in four hydrocarbon molecules: benzene, cyclohexane, hexatriene and hexadiene. These molecules were chosen because they exhibit different characteristics of aromaticity. The authors found that molecules containing pi bonds have a lower threshold for Auger decay.