Nuclear astrophysics

Nuclear reactions power our Sun, and they create the chemical elements that are necessary for human life. We study radiative-capture reactions that are important for astrophysics, in precision experiments:

  • In Dresden using ion beams at the surface of the Earth,

  • at LUNA deep underground in the Gran Sasso/Italy,

  • collaborating at the R3B experiment at GSI/FAIR, and

  • in the Felsenkeller shallow underground laboratory. Together with TU Dresden we have installed a high-current 5MV accelerator there.

This page shows our ongoing projects and a brief motivation. For more details on the astrophysics, please see our review papers on LUNA and on the nuclear physics of the Sun. Some possible topics for Master's and Bachelor's theses are listed here. Further detailed information is linked through the web page you are reading now!


News

Feierliche Inbetriebnahme des Felsenkeller 5 MV Untertage-Beschleunigers am 04.07.2019: Physik-Nobelpreisträger Prof. Takaaki Kajita (Bildmitte) gemeinsam mit PD Dr. Daniel Bemmerer (Technischer Leiter Beschleuniger im Felsenkeller), Prof. Gerhard Rödel (Prorektor Forschung, TU Dresden), Prof. Thomas Cowan (Direktor des HZDR-Instituts für Strahlenphysik), Prof. Kai Zuber (Wissenschaftlicher Leiter Beschleuniger im Felsenkeller).

04.07.2019: Ceremonial start of operations in the presence of Physics Nobel Laureate Prof. T. Kajita (Photo: André Wirsig/HZDR).

Richtfest Beschleuniger im Felsenkeller 28.06.2017 Fotoserie 2 Bernd Rimarzig

28.06.2017: Topping out ceremony in the presence of Physics Nobel Laureate Prof. A. McDonald (Photo: Bernd Rimarzig/HZDR).


Felsenkeller underground accelerator

The success of the 0.4 MV LUNA underground accelerator in Italy (with significant involvement by the HZDR group) has led to the call for higher-energy underground accelerators. One of several projects pursued worldwide includes a 5 MV Pelletron accelerator in the Felsenkeller underground facility, Dresden/Germany, co-funded by TU Dresden (Prof. Kai Zuber, supported by the German Excellence Initiative) and by HZDR. 

A background intercomparison has shown that the background in a g-ray detector in Felsenkeller is competitive with a deep-underground site, if an active veto is used. The new accelerator may be used to study solar fusion reactions such as 3He(α,γ)7Be and the reactions of helium burning such as 12C(α,γ)16O, the so-called Holy Grail of nuclear astrophysics.

On 26-28 June 2017, the science case was highlighted during a scientific workshop on "Nuclear Astrophysics at the Dresden Felsenkeller" with 56 participants, further details here.

As of February 2019, both ion sources have been tested successfully in situ underground, and the main accelerator is undergoing re-commissioning.

 

No-beam background in one and the same escape-suppressed HPGe detector overground and in several underground locations.

Felsenkeller, 5 MV Pelletron moved by crane in front of rocks

Photo: HZDR/O. Killig


Big Bang nucleosynthesis studied at LUNA: The 2H(p,γ)3He and 2H(α,γ)6Li reactions

PhD project Klaus Stöckel (2016-2019, DFG BE 4100/4-1), PhD thesis Michael Anders (2009-2013, DFG BE 4100/2-1, thesis)

Motivation: The motivation is driven by recent astronomical observations, on the isotopes 2H and 6Li. The stable nuclide 2H is the first product of Big Bang nucleosynthesis (BBN), in the very first few minutes of the universe. Its yield is strongly dependent on the main 2H destruction reaction, 2H(p,γ)3He. Recent and much more precise 2H observations suggest that BBN may, for the first time in two decades, constrain the cosmic baryon-to-photon number on a similar level of precision as the cosmic microwave background data from the PLANCK mission. Reports of primordial 6Li observations spawned a precise study of the main 6Li producer, 2H(α,γ)6Li.

6Li experiment at LUNA: The cross section for the main 6Li producing reaction, 2H(α,γ)6Li, was studied for the first time in the Big Bang energy window. The data suggest no significant BBN 6Li yield. The initial astronomical 6Li observations that had motivated the 6Li experiment at LUNA study have since been disputed by their own authors, in agreement with our findings.

2H experiment at LUNA: The limiting uncertainty for the BBN 2H prediction is the rate of the main 2H destruction reaction, 2H(p,γ)3He. It is currently under study at LUNA, using a windowless deuterium gas target. Two HPGe and a BGO detector are used in two separate phases to detect the γ ray from the reaction (PhD thesis of Klaus Stöckel).

2H experiment at HZDR: The higher energy range not accessible at LUNA is under study at the HZDR 3 MV Tandetron (Master's thesis of Sebastian Hammer).

Astrophysical S-factor S24 of the 2H(alpha,gamma)6Li reaction from LUNA (Phys. Rev. Lett. 113, 042501 (2014)).

Hydrogen burning in asymptotic giant branch stars and in novae: 22Ne(p,γ)23Na

Master's thesis Franziska Schoger (2018- ), PhD thesis Marcell Takács (2013-2017, NAVI, thesis), Diploma thesis Marie-Luise Menzel (2011-2012, thesis)

22Ne(p,γ)23Na working group coordinators at LUNA: Daniel Bemmerer (HZDR), Antonio Caciolli (Uni Padua).

Motivation: The stable nuclide 22Ne plays an important role in asymptotic giant branch (AGB) stars, in astrophysical novae, and in supernovae where it provides neutrons for neutron-capture driven nucleosynthesis. In a hydrogen-rich scenario, 22Ne is mainly destroyed by the 22Ne(p,γ)23Na reaction. Only upper limits exist on the cross section of this reaction at relevant energies.

Experiment at HZDR: The strengths of several resonances in the 0.4-1.2 MeV energy range have been redetermined using implanted 22Ne targets and high-purity germanium detectors at the HZDR 3 MV Tandetron. One experiment is concluded, a second one under analysis (Master's thesis of Franziska Schoger).

22Ne(p,gamma)23Na reaction, thermonuclear reaction rate

Experiment at LUNA: The reaction has been studied in two phases, both using windowless gas target systems. The first phase used two high-purity germanium detectors and led to the discovery of three new resonances. This finding has significant repercussions on the thermonuclear reaction rate and on nucleosynthesis and led to a number of publications, see below. The second phase, using a 4π bismuth germanate summing crystal, experimentally ruled out two extremely weak putative resonances at low energy, and it precisely studied the direct-capture component. 


Nucleosynthesis in supernovae and 44Ti 

Master's project Konrad Schmidt (2010-2011, thesis), PhD project Konrad Schmidt (2011-2015, DFG, thesis)
Bachelor's project Mirco Dietz (2012)
Master's project Stefan Schulz (2016-2017)

Motivation: The radioactive nucleus 44Ti (halflife 60 years) is created in supernovae. Gamma-rays from the decay of 44Ti have been observed in satellite-based observatories, but there are several surprising findings including the low number of 44Ti-emitting objects found and a possible discrepancy between the decays of 44Ti and is daughter 44Sc. Together with precise nuclear data, the observations may be used to calibrate supernova models.

Experiment at HZDR ion beam center and Felsenkeller: A study of resonance strengths in the 44Ti-producing reaction 40Ca(α,γ)44Ti has been done by the activation and in-beam γ-spectrometry methods. It can be seen from the picture that only in the underground Felsenkeller lab the weak 44Ti activated samples can be studied, overground the 44Ti signal is covered by cosmic-ray induced noise. An offline study of the decay radiation of 44Ti is ongoing.

44Ti activation spectra at the Earth's surface and underground.

Hydrogen burning at lower temperatures: 12C(p,γ)13N, 14N(p,γ)15O, and 15N(p,αγ)12C

PhD theses Louis Wagner (2013-2018, NAVI, thesis), Stefan Reinicke (2013-2018, thesis), project Tobias Reinhardt (2012-2016, NupNET), B. Sc. thesis Martin Serfling (2014), Diplom projects Louis Wagner (2012-2013), Stefan Reinicke (2012-2014), Klaus Stöckel (2014-2015).

PhD thesis M. Marta (2007-2011, thesis), Diplom thesis E. Trompler (2008-2009, thesis)

Motivation: The 14N(p,γ)15O reaction controls the rate of the carbon-nitrogen-oxygen (CNO) cycle. The CNO rate affects low-energy solar neutrinos (under study at the SNO+ detector in Canada and at the Borexino detector in Italy), carbon stars and last not least the age of our universe. It has attracted recent interest because it may help address the solar abundance puzzle. The 12C(p,γ)13N reaction controls the onset of the CNO cycle before equilibrium and the production of 13C, important for the astrophysical s-process. The 15N(p,αγ)12C reaction is a useful tool in hydrogen depth profiling.

Study of resonances at HZDR: Improved data on resonance strengths in the 14N(p,γ)15O and 15N(p,αγ)12C have been measured at the HZDR 3 MV Tandetron.

Off-resonance data at HZDR: Data from an experiment studying the the 14N(p,γ)15O cross section in the 0.4-1.4 MeV energy range has been performed at the HZDR 3 MV Tandetron are now available:

An experiment studying the 12C(p,γ)13N reaction in  inverse kinematics using hydrated targets and an intensive 12C beam at the same accelerator is under analysis.

14N(p,gamma)15O experiment at HZDR 3MV Tandetron, March 2014, experimental setup

Experimental setup at the HZDR 3 MV Tandetron.

Experiment at LUNA: The LUNA study of the 14N(p,γ)15O reaction showed that the CNO rate was only half the previously accepted value:

Experiment at Agata demonstrator Legnaro/Italy: The lifetime of the exited state at 6.79 MeV in 15O is studied by the Doppler shift attenuation method (collaboration with INFN Padova and GANIL Caen/France).


People

Collaborations

  • LUNA collaboration at Gran Sasso / Italy 
  • R3B collaboration at GSI/FAIR
  • COST action 16117 CheTEC "Chemical Elements as Tracers of the Evolution of the Cosmos"

Collaborating institutes

  • TU Dresden: K. Zuber
  • VKTA Dresden: M. Köhler, D. Degering (low-level γ-counting in Felsenkeller shallow-underground laboratory)
  • ATOMKI, Debrecen/Hungary: Zs. Fülöp, Gy. Gyürky, T. Szücs
  • INFN Padua/Italy: C. Broggini, A. Caciolli, R. Menegazzo, R. Depalo
  • INFN Genova/Italy: F. Cavanna
  • Hashemite University, Zarqa/Jordan (DFG incoming fellowship for Prof. Dr. Tariq Al-Abdullah)
  • Paul-Scherrer-Institut, Switzerland: D. Schumann, R. Dressler (long-lived radioisotopes for astrophysics)

Financial support

  • DFG Deutsche Forschungsgemeinschaft: BE 4100/4-1 (2017-2020): LUNA 2H(p,γ)3He, BE 4100/2-1 (2009-2014): LUNA 2H(α,γ)6Li and Tandetron 40Ca(α,γ)44Ti
  • Helmholtz Impulse and Networking Fund (2017-2019): ERC Recognition Award
  • Helmholtz Impulse and Networking Fund (2011-2016): Partner in NAVI (Nuclear Astrophysics Virtual Institute)
  • DAAD German Academic Exchange Service (2015-2016): Two six-month fellowships for Dr. Francesca Cavanna and Dr. Rosanna Depalo
  • INFN Italy (2009-2014): Fondo Affari Internazionali, travel support to visit Gran Sasso
  • TU Dresden Graduate Academy (2014-2017): 4-month scholarships to finalize the PhD theses for Konrad Schmidt, Marcell Takács, and Louis Wagner

Further information


Kontakt

PD Dr. Daniel Bemmerer

Gruppenleiter Nukleare Astrophysik, Technischer Leiter Beschleuniger im Felsenkeller
Kernphysik
d.bemmererAthzdr.de
Tel.: +49 351 260 3581
+49 351 260 3901