Category Archives: nuclear

Structure of the Lightest Tin Isotopes

We link the structure of nuclei around 100Sn, the heaviest doubly magic nucleus with equal neutron and proton numbers (N=Z=50), to nucleon-nucleon (NN) and three-nucleon (NNN) forces constrained by data of few-nucleon systems. Our results indicate that 100Sn is doubly magic, and we predict its quadrupole collectivity. We present precise computations of 101Sn based on three-particle–two-hole excitations of 100Sn, and we find that one interaction accurately reproduces the small splitting between the lowest Jπ=7/2+ and 5/2+ states.

PhysRevLett.120.152503.png

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Formation of Superheavy Elements in Nature

It is shown that superheavy elements may also be formed in the main r process responsible for the formation of the heaviest elements observed in nature. Under conditions of a high neutron density, the nucleosynthesis region lies close to the neutron drip line, so that the r process may circumvent the region where nuclei undergo spontaneous fissions and therefore have short lifetimes. However, a high induced-fission rate, which increases with the charge number, may prevent the nucleosynthesis wave from overcoming the region of isotopes heavier than curium, and the beta-decay chain leading to an increase in the charge number of product elements inevitably results in the spontaneous fission of the majority of product nuclei. Calculations of nucleosynthesis that were performed with available nuclear data within the scenario of a neutron-star merger reveal that only Z < 106 superheavy elements are formed. Their abundance at the end of the r process is commensurate with the abundance of uranium, but their lifetime does not exceed several years, so that they fast undergo decay.

 

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Micro-scale fusion in dense relativistic nanowire array plasmas

Nuclear fusion is regularly created in spherical plasma compressions driven by multi-kilojoule pulses from the world’s largest lasers. Here we demonstrate a dense fusion environment created by irradiating arrays of deuterated nanostructures with joule-level pulses from a compact ultrafast laser. The irradiation of ordered deuterated polyethylene nanowires arrays with femtosecond pulses of relativistic intensity creates ultra-high energy density plasmas in which deuterons (D) are accelerated up to MeV energies, efficiently driving D–D fusion reactions and ultrafast neutron bursts. We measure up to 2 × 106 fusion neutrons per joule, an increase of about 500 times with respect to flat solid targets, a record yield for joule-level lasers. Moreover, in accordance with simulation predictions, we observe a rapid increase in neutron yield with laser pulse energy. The results will impact nuclear science and high energy density research and can lead to bright ultrafast quasi-monoenergetic neutron point sources for imaging and materials studies.

Fig. 2

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Έναρξη μαθημάτων Εισαγωγή στην Πυρηνική Φυσική & τα Στοιχειώδη Σωμάτια

Ανακοινώνεται ότι το Τμήμα Α του μαθήματος Εισαγωγή στην Πυρηνική Φυσική & Στοιχειώδη Σωμάτια (Βασιλείου-Μερτζιμέκης) θα ξεκινήσει παραδόσεις την Τετάρτη 14.02.2018 στο Αμφιθέατρο “Θαλής”.

Αναλυτικότερα το πρόγραμμα για το συγκεκριμένο τμήμα:

Τρίτη 09’00-12’00 (Αμφ. “Ίππαρχος”)

Τετάρτη 11’00-13’00 (Αμφ. “Θαλής”)

Καλή αρχή σε όλους και όλες

Προσωρινοί πίνακες κατάταξης ΕΛΙΔΕΚ – Μεταδιδάκτορες

Μόλις πριν λίγο αναρτήθηκαν οι προσωρινοί πίνακες κατάταξης για τη δράση ΕΛΙΔΕΚ “ενίσχυση μεταδιδακτόρων”. Για τις φυσικές επιστήμες, υπάρχει το όριο των 24 προτάσεων προς χρηματοδότηση, το οποίο αντιστοιχεί σε βαθμολογία 84.

Έγκριση Προσωρινών Πινάκων Κατάταξης για επτά (7) Επιστημονικές Περιοχές, στο πλαίσιο της 1ης Προκήρυξης ερευνητικών έργων ΕΛΙΔΕΚ για την ενίσχυση Μεταδιδακτόρων Ερευνητών/τριών

Στην Πυρηνική Φυσική (βασική ή εφαρμογές) δεν υπάρχει καμία που να ξεπερνά το όριο αυτό, νομίζω 75 είναι η πιο υψηλή που βρίσκεται. Εξαιρετικά ανησυχητικό για το μέλλον του πεδίου, καθώς οι μεταδιδάκτορες πρέπει να ενισχυθούν για να είναι έτοιμοι να αποτελέσουν την επόμενη γενιά μελών ΔΕΠ στο αντικείμενο. Χωρίς εμπειρία δεν υπάρχει περίπτωση να συνεχίσουν προς αυτήν την κατεύθυνση.

Πρόγραμμα εξεταστικής Φεβ 2018

Έχει αναρτηθεί το πρόγραμμα της εξεταστικής (κανονική και πτυχιακή). Μπορείτε να το βρείτε εδώ

 

Ειδικότερα για τα μαθήματα που με αφορούν:

Χειμ. εξάμηνο

  • Πυρηνική Φυσική Ι, 31.01.2018,14’00-17’00, Αμφ. “Δημόκριτος”

Εαρινό εξάμηνο

  • Εισαγωγή στην Πυρηνική Φυσική και τα Στοιχειώδη Σωμάτια, 23.02.2018, 18’00-21’00, όλα τα αμφιθέατρα
  • Ατομική και Μοριακή Φυσική, 26.02.2018, 18’00-21’00, Αμφ. Ίππαρχος

 

 

Can hell break out of a .2% difference in Planck’s constant?

This is an untold story, part of my personal history in academia, when all things were still coming up roses on me. Somehow, the news regarding the update of four of the fundamental constants we use in Physics and science triggered a memory.

It is 2001, last few months of data analysis towards my PhD thesis. A shared data set between my folder and a senior German collaborator’s one is analyzed in parallel with two different methods. Final results show up eventually from both sides and we immediately see that there is a constant 0.2% difference in the extracted values, despite that they should be exaclty the same in principle. Intense discussion breaks out among all collaborators why this is happening. As a student I was the easy target: “you, Theo, have made a mistake”. New round of independent analysis breaks out by a post-doc. He comes back with the same results I produced and still a persistent 0.2% difference with the German guy’s values.

A month later, we are still stuck. The 0.2% does not go away whatever the effort. Then, I decide to dig better. I revisit the fundamental constants, Planck’s h and speed of light, c I found in the CODATA evaluated tables. Cross-checking with the German collaborator shows he had used values found in an appendix of a nuclear structure book published in the ’60s. The values merely differed by exactly 0.2%. A couple of hours after our discovery, I get chinese for lunch and a fortune cookie offers me a metaphysical touch with the quote: “The truth is in the numbers”.

I remembered this story earlier in the morning, when I read about the update of the fundamental constants. The new values can be found in this paper. Just use them cautiously; they might give you hell. Especially if you are a PhD student.