Category Archives: nuclear

γ-tomography of a HPGe coaxial detector

We have recently completed the second part of resurrecting an old coaxial HPGe detector disarmed for over 20 years in the lab’s stockroom. The first part was to find out all info about the detector, a difficult task considering we had no tech sheets or accompanying documents. Thankfully, the kind people of Areva/Canberra tracked down a copy of the original (but very limited) specs sheet of our detector based on the serial number and model number. We proceeded to fully characterize our old buddy with point-like radiation sources, estimating its linearity, absolute efficiency and misc. characteristics (inc. DC voltage, FWHM vs energy, LN2 cooling times, etc).

Our GEROS (Germanium for Environmental Radioactivity Studies, an acronym meaning literally “Old man” in greek) detector has moved to phase two of characterization some time ago. Vaso Angelopoulou has taken over the task to try and measure the actual dimensions of the crystal (a coaxial-type by manufacturing) based on the absorption of γ-rays, in fashion similar to tomography. Briefly, a weak γ-emitting source was placed behind a thick lead shield with an open narrow window, availing the bombardment of the detector with known-energy gamma rays. The source was moved across and along a grid of specific (X,Y) coordinates in front of the detector. Depending on the source position and due to the coaxial geometry, different numbers of photons were recorded by the detector. Reconstructing the 3D image, we managed to have a detailed picture of the inside of the detector (See picture below).

GEROS (a reconstruction)

We are now able to simulate the detector using MCNP and Geant4 based on the crystal dimensions consolidated experimentally. Also, a full CT-scan will take place some time soon to get a full 3D image of the inside, obtaining information on additional technical data, such as supporting screws, preamp position etc.

An online database of nuclear moments

The following is a little blog piece I wrote for Science2.0 site.
Here is the direct link to it

If you are into Nuclear Physics there is very good chance you know about nuclear electromagnetic moments. Actually, nuclear electromagnetic moments has been the field of my specialty from the beginning of my scientific career. This is also why my blog in science20.com was named “Moment Zero” and not because there was some zero-time singularity I broke into writing about scientific stuff (not that I have been very active in here either!). The term nuclear electromagnetic moments 90% of the time refer to the magnetic dipole and the electric quadrupole moment. Each of these physics observables have something important to say about the nucleus.

The nuclear magnetic dipole moment, μ, is a unique case of a quantum operator describing the nuclear magnetism in terms of the spin of the state the nucleus resides in. Its uniqueness relies on the fact that it is extremely sensitive on the proton-neutron content -and competition- of the wave function. No other observable can really say anything about individual nucleons participating (and how much each of them contributes to) in the wave function. Thus measuring magnetic dipoles moments we can determine the wave function of a nuclear state in terms of the single-particle degrees of freedom.

On the other hand, the electric quadrupole moment, Q, is a quantity that reveals the shape of the nucleus. Most often the nucleus can be a spheroid or an ellipsoid. Ideal spherical nuclei, such as those considered for nuclei with spin/parity 0+, present a zero electric quadrupole moment. If the shape of the nucleus is elongated along the rotation of the axis, similarly to an upside standing rugby ball, Q has a positive value (prolate shape), while in the opposite case of a lay-down egg shaped nucleus (oblate shape) Q is negative. The relationship between the value of the quadrupole moment and the shape of the nucleus is so strong that very often it is only necessary to determine the sign of the quadrupole moment, and not the value itself, to have a nice physics result.

For either type of nuclear moment, several techniques have been developed over the years, with the best known to the wider physics audience being the Nuclear Magnetic Resonance technique (developed by I.I. Rabi who got the Nobel for it in 1944). Lots of experimental data have been accumulated and with the revolution of radioactive beams taking over the nuclear physics community in the past 15 years a new blooming of phenomena is developing fast. Experimental data had been tabulated already since before WWII and more than ten compilations (with some very important ones) have been put together to offer the community a concise way of finding information. However, there has been no online presence of recent data, despite the big efforts by IAEA and other organizations to develop online tools.

Very recently, an effort started 7 years ago in the University of Athens, resulted in the first online -we claim the fullest and most up-to-date- database with nuclear electromagnetic moments. The database was hosted on a private server (http://magneticmoments.info) for a few year and will continue, however, for the time being this URL is redirecting visitors to the IAEA site where the database is currently hosted. The Nuclear Data Section of IAEA has come into an agreement to host the database with a cutoff date Nov 2015 (this means there is no more major update is in the works and appear online by the end of this year).
So, if you are into experimental data, and especially nuclear physics EM moments, stop by and find little treasures. There is also an accompanying blog (http://magneticmoments.info/wp) where fellow researchers can comment, offer valuable insights or even contribute their data.

You are welcome to visit!

PS A related publication was very recently accepted for publication in NIM A. Please, cite it if you are about to use any of the data in the database in your own work doi: 10.1016/j.nima.2015.10.096

A critical update of the nuclear EM moments database

Some of you know about my efforts to put together a database containing experimental data of nuclear electromagnetic (EM) moments. I am not going to go into details about what a nuclear moments is; all Nuclear Physics textbooks have extended information on them and why they are useful for nuclear structure.

 I have to clarify that I have stood on the shoulders of giants: Several researchers have tabulated experimental data, both on magnetic dipole and electric quadrupole moments, and made them available in print. Already since my PhD years I found myself struggling to find the proper info out of printed copies of those compilations (PDF were very scarce 10-15 years ago). The most recent compilation has been made available by Nick Stone, a colossal work indeed. Still, printed matter is all you can get.

In 2007 I decided I should take over the very hard task to import the existing compilations into a modern database scheme, check the data and update them frequently, as more and more papers were published. With the help of two students, Kostas Stamou and Thanasis Psaltis, both pursuing doctoral studies as we speak, I managed to have a first version in 2009. Lots of things had still to be done from that point. Frequent updates are considered THE top and most important priority in the philosophy behind the database.

Yesterday, I have completed a major update, past due already from July, however, this one was accompanied by a vast cleanup of citation data, references and errors in all kind of things. The database has currently 5352 entries for 1205 isotopes and each single one of them has been checked for integrity. Nevertheless, I can not really brag about this, as experience has shown me in the past that there is always a good experimental error associated to such works. So, please judge me lightly if you spot something missing. And PLEASE LET ME KNOW.

The database can be found here:

http://magneticmoments.info

Version is dated: 10.09.2015 and includes all data up to Feb 2014.

I hope you find it useful.

NuSTRAP Mini-Workshop 06.15

Today was a very very very interesting day for our group. I am particularly happy, we managed to gather in a room, some twenty of us, and go through our first mini-Workshop.
The First NuSTRAP mini-Workshop is a mini one, just because we had only three interesting talks for two hours.

We started at 10 am in a classroom near our lab, had some nice cake and biscuits and coffee, and attended three talks spanning a broad range of subjects, all within the research borders of our group. Ms. Lagaki, a MS student gave a nice overview of ion separation by lasers in ISOLDE, Mr Psaltis followed presenting his talk on p-process nuclei (to be presented in the upcoming p-process Workshop taking place in Cyprus in about 10 days) and Ms Mitsi presented her work on a new analysis code of micro-XRF data collected from ANKA synchrotron facility.

The real profit out of this mini-Workshop is that the whole group gathered together and people working in completely different scientific regimes (from fundamental science to applications) had the opportunity to interact and get informed of the parallel scientific directions the NuSTRAP group has been dealing with the last couple of years. My feeling is that the whole thing was quite successful and deserves to be repeated. September is a very convenient month to do it. I will keep you posted.

1st NuSTRAP Meeting @UoA

The 1st NuSTRAP Meeting @UoA is planned to take place in the Physics Department of the University of Athens on Thursday 04.06.2015, starting 10 am
The draft program is the following:

10’00 – 10’05 Theo J. Mertzimekis / Opening Remarks
10’05 – 11’00 Varvara Lagaki / “Using lasers to separate nuclear isotopes”
11’00 – 11’30 Athanasios Psaltis / “First proton-capture study of the contentious p-nucleus 113-In at astrophysical energies”
11’30 – 12’00 Eleni Mitsi / “RICOCHET: a fast, open-access algorithm to analyze synchrotron μ-XRF data sets”

Room: Nuclear Seminar Room (depending on availability)
Refreshments will be available.

Postcards from HNPS2015

It has been a great time in Ioannina over the last two days during the 24th Symposium of the Hellenic Nuclear Physics Society (HNPS2015, 22-23.05.2015). Ioannina has always been a favorite city, the place where I spent my undergraduate and part of my graduate years and where I still have lots of friends. My visit was quite short; however a great one.

The Symposium itself was a real success. The organizers did their best in providing a majestic experience to all participants. The Conference Center is perhaps the most luxurious I have visited in Greece with hitech facilities and comfortable seat to keep you undistracted during the sessions. The Nuclear Physics community is a rather small one, but very active in a variety of projects ranging from fundamental aspects of the nucleon to applications benefiting the society and the environment. I have attended quite interesting talks about new theoretical works on nuclear astrophysics, medical applications, new reaction codes. Highlight of the Symposium was the presence of the heart and soul of nTOF experiment, Dr Franz Käppeler of KIT, as an invited lecturer who delivered a very interesting overview of recent data as well as future directions. I am sure that the audience, dominated in numbers by undergraduates (65 out of 128 registered people!) were given the chance to open their horizons in their future research directions.

The next Symposium will take place in Athens, organized by INRUSHES and INPP at NCSR Demokritos. If all goes well, our group will be there.

Διαλέξεις INPP

Για τους ενδιαφερόμενους/ες φοιτητές/τριες, έχουν αναρτηθεί και οι πέντε πρώτες διαλέξεις της “Εισαγωγής στην Πυρηνική Φυσική & τα Στοιχειώδη Σωμάτια” στην παραπομπή:

https://dl.dropboxusercontent.com/u/6356899/Class/inpp.html

Ως γνωστό, απαιτείται κλειδάριθμος, ο οποίος μπορεί να αποκτηθεί από το διδάσκοντα με απευθείας επώνυμο email

HNPS2015

The 24th Symposium of the Hellenic Nuclear Physics Society is taking place in the University of Ioannin on 22-23.05.2015.
If you are a fellow researcher or a student working in the field of fundamental and/or applied nuclear physics consider participating to the Symposium.

Abstract submissions and registration is still open (deadline is 08.05.2015 for both). Follow the links of the official website.

The NuSTRAP group are planning a massive participation with 4 posters and 1 oral presentation. Links to posters and DOI will be provided at a later stage.

Department’s website

I have just finished a major update of the Department of Nuclear and Particle Physics Website.

Besides minor things, the Research Section has been redesigned from grounds up. You can find plenty of information of all groups being active in the Department, in both theory and experiment. Information is available in both greek and english.

New members (post-docs, students) have been added. Still missing: the new MSc program of study. It will be available online once official approval is granted.

Here is the URL
http://nuclpart.phys.uoa.gr/