All posts by tmertzi

[Paper] Nuclear processes in astrophysics: Recent progress

Nuclear processes in astrophysics: Recent progress

by V. Licciardo et al.
doi: 10.1140/epja/i2018-12648-5

The question about the origin of the elements is a fascinating one, that scientists have been trying to answer for the last seven decades. The formation of light elements in the primordial universe and heavier elements in astrophysical sources occurs through nuclear reactions. We can say that nuclear processes are responsible for the production of energy and synthesis of elements in the various astrophysical sites. Thus, nuclear reactions have a determining role in the existence and evolution of several astrophysical environments, from the Sun to the spectacular explosions of supernovae. Nuclear astrophysics attempts to address the most basic and important questions of our existence and future. There are still many issues that are unresolved, such as how stars and our Galaxy have formed and how they evolve, how and where the heaviest elements are made, what is the abundance of nuclei in the universe and what is the nucleosynthesis output of the various production processes and why the amount of lithium-7 observed is less than predicted. In this paper, we review our current understanding of the different astrophysical nuclear processes leading to the formation of chemical elements and pay particular attention to the formation of heavy elements occurring during high-energy astrophysical events. Thanks to the recent multi-messenger observation of a binary neutron star merger, which also confirmed production of heavy elements, explosive scenarios such as short gamma-ray bursts and the following kilonovae are now strongly supported as nucleosynthesis sites.

[paper] Isoscalar Spin Matrix Elements in s–d Shell Nuclei

Isoscalar Spin Matrix Elements in s–d Shell Nuclei

by Akito Arima and Wolfgang Bentz

doi: 10.7566/JPSCP.23.012011

The quenching of isovector spin matrix elements in s–d shell nuclei is well established experimentally as well as theoretically [1,2,3]. The isoscalar spin gyromagnetic ratios gsIS of nuclei with one nucleon or hole outside of LS closed shells are also quenched by the same mechanism. On the other hand, their isoscalar orbital gyromagnetic ratios gLIS are slightly enhanced by meson exchange currents [1,2]. Then we are interested very much in the following question: Are the isoscalar spin matrix elements generally quenched in s–d shell nuclei? We will try to answer this question in this paper.

Academy of Athens Awards 2018

I feel great honor and joy in announcing that I am this year’s recipient of the prestigious Academy of Athens Award in “Experimental Physics” (Award “G. Foteinos”). The award is related to the published paper in Physical Review C (doi: 10.1103/PhysRevC.96.035806), entitled:
First cross-section measurements of the reactions 107,109Ag(p,γ)108,110Cd at energies relevant to the p process
by A. Khaliel, T.J. Mertzimekis, E.-M. Asimakopoulou, A. Kanellakopoulos, V. Lagaki, A. Psaltis, I. Psyrra, and E. Mavrommatis

This is work carried out by our group at the University of Athens and all co-authors deserve congratulations for their contribution and commitment.

Here is the official announcement by the Academy of Athens (in greek, see #12).

 

Συνάντηση με πρωτοετείς

Ενημερώνονται οι πρωτοετείς που ενδιαφέρθηκαν για συνεργασία ότι θα είμαι διαθέσιμος να σας συναντήσω την Τετάρτη 28.11 μεταξύ 10-12’00 στο γραφείο μου (κτήριο V, 34Β, τομέας Πυρηνικής). Κάποιοι έχετε ήδη λάβει ηλεκτρονική ενημέρωση με τη θεματολογία.

Φάσματα εργαστηρίου κατεύθυνσης

Για κάθε ενδιαφερόμενο/η που έχει ασκηθεί στο Εργαστήριο Κατεύθυνσης και στην άσκηση 4 (Ραδιενέργεια Περιβάλλοντος):

Τα φάσματα που έχουν ληφθεί κατά τη διάρκεια της άσκησης, και τα οποία πρέπει να αναλύσετε, βρίσκονται στη διεύθυνση:

http://users.uoa.gr/~tmertzi/Ergastirio/YYYYMMDD

όπου

YYYY το έτος (πχ 2018)

ΜΜ ο μήνας (πχ 11 για το Νοέμβριο)

DD η ημέρα του μήνα (πχ 06)

τα οποία αναφέρονται στο χρόνο εκτέλεσης της άσκησης. Για παράδειγμα τα φάσματα της 18ης Νοεμβρίου 2018 θα είναι διαθέσιμα στη διεύθυνση

http://users.uoa.gr/~tmertzi/Ergastirio/20181118

Σημειώνεται ότι πρέπει να διαβάζετε το αντίστοιχο αρχείο readme.txt μέσα στο φάκελο, το οποίο δίνει χρήσιμες πληροφορίες για τα φάσματα που θα αναλύσετε.

(Σκληρο)πυρηνική φυσική

Για τους πρωτοετείς φοιτητές που παρακολούθησαν το σεμιναριακό μάθημα της προηγούμενης Πέμπτης καιι εξέφρασαν το ενδιαφέρον τους να μάθουν περισσότερα για την πυρηνική φυσική και τις εφαρμογές της, μπορούν να με συναντήσουν την ερχόμενη Πέμπτη 1.11.2018 μετά τις 13’15 (δηλ. μετά το τέλος και του δεύτερου σεμιναριακού μαθήματος). Ελάτε με καλή διάθεση να μιλήσουμε για ό,τι σας απασχολεί. -ΘΜ

Radioactive molecules in space – a first detection!

After a long search, a cosmic mystery has an answer. Astronomers have made the very first unambiguous detection of a radioactive molecule in space – an isotope of aluminium, found in the heart of a rare nova.

Scientists have long been searching for 26AlF – or Aluminium monofluoride – containing 26Al, but a direct observation has been exceptionally illusive.

Read more here

EIC: a new billion-$$ electron accelerator to look inside protons and neutrons

The next dream machine for U.S. nuclear physicists got an important boost today in a report from the National Academies of Sciences, Engineering, and Medicine. The report committee glowingly approved of the science that could be done with the proposed Electron-Ion Collider (EIC), a billion-dollar accelerator that would probe the innards of protons and neutrons. The endorsement should help the Department of Energy (DOE) justify building the EIC at one of two national laboratories competing to host it, although the project probably won’t get the go-ahead for several years.

“We’re basically saying, ‘You’ve really got to do this,’” says Ani Aprahamian, a nuclear physicist at the University of Notre Dame in South Bend, Indiana, and co-chair of the report committee.

Read full story here

Nuclear-Spin Comagnetometer Based on a Liquid of Identical Molecules

Atomic comagnetometers are used in searches for anomalous spin-dependent interactions. Magnetic field gradients are one of the major sources of systematic errors in such experiments. Here we describe a comagnetometer based on the nuclear spins within an ensemble of identical molecules. The dependence of the measured spin-precession frequency ratio on the first-order magnetic field gradient is suppressed by over an order of magnitude compared to a comagnetometer based on overlapping ensembles of different molecules. Our single-species comagnetometer is capable of measuring the hypothetical spin-dependent gravitational energy of nuclei at the 10−17 eV level, comparable to the most stringent existing constraints. Combined with techniques for enhancing the signal such as parahydrogen-induced polarization, this method of comagnetometry offers the potential to improve constraints on spin-gravity coupling of nucleons by several orders of magnitude.

Figure 2

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