Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Solving a long-standing atomic mass difference puzzle paves way to the neutrino mass


How heavy are neutrinos? To find out, radioactive decays are studied in which they are emitted. An essential ingredient is the decay energy which corresponds to the mass difference between the mother and daughter nuclei. It must be known with highest precision.

A team of scientists now succeeded to resolve a severe discrepancy of the decay energy for the artificial holmium (Ho) isotope with mass number 163. It decays by electron capture to the stable dysprosium-163 (¹⁶³Dy) and appears well suited to measure the neutrino mass. The team prepared pure samples of ¹⁶³Ho and ¹⁶³Dy and directly measured their mass difference with high accuracy using the Penning-trap mass spectrometer SHIPTRAP.

Photo of the SHIPTRAP setup at GSI Darmstadt, Germany.

photo: GSI

The new result (red) confirms the recent results for the decay energy of ¹⁶³Ho. The various symbols stand for different measurement techniques.

graphics: MPIK

Neutrinos are everywhere. Hundred trillion neutrinos are traversing every human per second, but one of their fundamental properties, the mass, is still unknown. While the standard model of particle physics predicts neutrinos to be massless, observations proof that neutrinos must have a tiny mass. By studying neutrino masses, scientists thus explore physics beyond this otherwise so successful model.

So far, only upper limits of the neutrino mass could be determined, confirming it to be tiny. This makes a direct mass measurement a challenging task, but spectroscopy of radioactive beta decay or electron capture in suitable nuclei is among the most promising approaches. All radiation emitted in the radioactive decay can be precisely measured, with the exception of the fleeting neutrino, which escapes detection. The neutrino mass is thus deduced from comparing the sum of all detectable radiation to that available for the decay.

An artificial isotope of holmium, with mass number 163, is in the focus of several large collaborations aiming at extracting the neutrino mass from measurements of the energy emitted in the electron capture decay of ¹⁶³Ho to the stable ¹⁶³Dy. Currently in the lead is the ECHo collaboration, centred at the University of Heidelberg, Germany. The sensitivity that can be reached in this experiment relies on a precise value of the ¹⁶³Ho decay energy.

Thus, prior clarification concerning the various values reported for the ¹⁶³Ho decay energy is mandatory. Values that span the quite large range from about 2400 to 2900 eV were published over the past decades from indirect measurements performed using different methods. The value recommended in data tables is on the lower end of this band, but the more recent results are some 100 eV higher than this recommended value casting doubt on its validity.

To solve this puzzle, a German-Russian-Swiss-French team of physicists, chemists, and engineers combined their expertise and unique instrumentation. While natural dysprosium contains sufficient amounts of ¹⁶³Dy, samples of ¹⁶³Ho, which does not occur in nature, first had to be prepared from natural erbium enriched in ¹⁶²Er by intense neutron irradiation in the high-flux research reactor at the Institut LaueLangevin at Grenoble, France.

Sample purification and processing was done at Paul Scherrer Institute Villigen, Switzerland and Johannes Gutenberg University Mainz. The atomic mass difference of ¹⁶³Ho and ¹⁶³Dy was directly measured using the SHIPTRAP Penning-trap mass spectrometer at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Based on the equivalence of mass and energy according to Einstein’s famous equation E = mc², the mass difference translates into the energy available for the decay.

“To determine the masses of holmium and dysprosium, we measured the frequencies of their ion's circular motion in the strong magnetic field of the ion trap, using the novel phase-imaging ion-cyclotron-resonance technique, which allows measurements with highest precision”, explains lead scientist Sergey Eliseev from the Max-Planck-Institut für Kernphysik (MPIK) in Heidelberg, “This circular motion is projected onto a position-sensitive detector in a way, that even small mass differences can be determined much faster and more precisely compared to previous methods.” ¹⁶³Ho and ¹⁶³Dy were measured alternately in intervals of 5 minutes for several days.

An averaging procedure resulted in a final value of the decay energy of 2833 eV with an uncertainty of only a few tens of eV. This confirms the recent results, settles the long-standing discrepancy and thus provides confidence to the approach proposed by the ECHo collaboration.

“For the statistics expected in the first phase of the ECHo experiment called ECHo-1k, recently funded by the DFG with a Research Unit, we will reach a sensitivity below 10 eV for the neutrino mass, which is more than a factor of ten below the current upper limit”, says the ECHo spokesperson Loredana Gastaldo from the University of Heidelberg. “Future mass measurements using the new PENTATRAP device will improve the accuracy of the decay energy value by an order of magnitude. This will pave the way to reach sub-eV sensitivity for the neutrino mass”, adds Klaus Blaum, director at the MPIK.

Original Publication:
Direct measurement of the mass difference of ¹⁶³Ho and ¹⁶³Dy solves Q-value puzzle for the neutrino mass determination
S. Eliseev et al.
Physical Review Letters 115, 062501 (2015)

Dr. Sergey Eliseev
MPI für Kernphysik Heidelberg
Phone: +49 6221 516-670

Prof. Dr. Klaus Blaum
MPI für Kernphysik Heidelberg
Phone: +49 6221 516-851

Dr. Bernold Feuerstein | Max-Planck-Institut für Kernphysik
Further information:

Further reports about: Kernphysik MPI artificial isotope mass mass spectrometer

More articles from Physics and Astronomy:

nachricht Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst

nachricht Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>



Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

More VideoLinks >>>