Study of radiative-capture reactions at LUNA and in Dresden

Nuclear reactions power our sun, and they create the chemical elements that are necessary for human life. In order to correctly understand the nuclear processes in stars, both astronomical observations and nuclear data are necessary. Recent investments in satellite-based astronomy and in neutrino observatories have enabled a breakthrough in the precision of the observations. This calls for new nuclear data of similar precision.

Radiative-capture reactions of importance for astrophysics are studied in precision experiments: in Dresden using ion beams at the surface of the Earth, in the Felsenkeller shallow underground counting facility, and at LUNA deep underground in the Gran Sasso laboratory in Italy. We are currently discussing whether to upgrade the Felsenkeller laboratory by installing an accelerator of 2-3 MV accelerating potential.

News

21 June 2010: Experiment on ⁴⁰Ca(α,γ)⁴⁴Ti started: Physics, experiment, ELOG.

28-30 April 2010: Workshop in Dresden on underground accelerators. More details here. See also article in Physik-Journal, June 2010.

7 December 2009: Michael Anders joined the group as new PhD student on LUNA.

August 2009: Our research is included in FZD-Journal (only German).

6 April 2009: The Gran Sasso laboratory was not harmed by the earthquake in L'Aquila on 6 April 2009. We call for solidarity towards the earthquake victims, e.g. here.

The ²H(α,γ)⁶Li reaction: Nucleosynthesis in the Big Bang

PhD project M. Anders (2009-2012)

Motivation: This reaction controls the production of ⁶Li in big-bang nucleosynthesis. In very old stars, lithium-6 is found in quantities greatly exceeding the value predicted by standard big-bang nucleosynthesis calculations.

Experiment: The first experiment studying this reaction directly at big-bang energies is in preparation at LUNA. Further details can be found here.

The ¹⁴N(p,γ)¹⁵O reaction: The Bethe-Weizsäcker cycle of hydrogen burning

PhD project M. Marta (2007-2010), Masters project E. Trompler (2008-2009, thesis)

Motivation: This reaction controls the rate of the carbon-nitrogen-oxygen (CNO) cycle, first proposed in 1938 by Bethe and Weizsäcker. 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 of its contribution to directly measure the content of carbon and nitrogen in the solar core.

Experiment at the FZD ion beam facility: An experiment at E = 0.6 - 2 MeV, complementary to the previous lower-energy study at LUNA, has been performed in Dresden (2008 and 2009). Improved data on resonance strengths in the ¹⁴N(p,γ)¹⁵O and ¹⁵N(p,αγ)¹²C are now available. The off-resonance data are still under analysis.

Phys. Rev. C 2010 Marta et al.

Experiment at LUNA: The LUNA study of this reaction showed that the CNO rate was only half the previously accepted value:

Phys. Lett. B 2004 Formicola et al.
Astron. Astrophys. 2004 Imbriani et al.
Phys. Lett. B 2006 Lemut et al.
Nucl. Phys. A 2006 Bemmerer et al.
Phys. Rev. C 2008 Marta et al.

Experiment at Agata demonstrator Legnaro/Italy: The lifetime of the exited state at 6.79 MeV in ¹⁵O is to be studied by the Doppler shift attenuation method.

The ⁴⁰Ca(α,γ)⁴⁴Ti reaction: Nucleosynthesis in supernovae

Masters project K. Schmidt (2010-2011)

Motivation: The radioactive nucleus ⁴⁴Ti (halflife 59 years) is created in supernovae. Gamma-rays from the decay of ⁴⁴Ti have been observed in satellite-based observatories. Together with precise nuclear data, the observations can be used to calibrate supernova models.

Experiment at FZD ion-beam facility and Felsenkeller: A study of resonance strengths in the ⁴⁴Ti-producing reaction ⁴⁰Ca(α,γ)⁴⁴Ti is running on for 21.-30. June 2010. More info on the science here; more info on technical details here (local access).

The ¹⁵N(p,γ)¹⁶O reaction - CNO cycles II and III

Motivation: This reaction lies at the branching point between CNO cycles I and II, controlling the amount of nucleosynthetic material passed to the higher CNO and subsequent NeNa and MgAl cycles.

Experiment at LUNA: The cross section has been measured with nitrogen targets of natural isotopic composition (0.37% ¹⁵N), see below paper. Further experiments with enriched ¹⁵N targets, using first a HPGe and then a 4π BGO summing detector, are presently under analysis.

J. Phys. G 2009 D. Bemmerer et al.

The ³He(α,γ)⁷Be reaction - thermometer of the center of the Sun

Motivation: The flux of solar ⁸B neutrinos has been measured with 3.5% precision (2006) by the SuperKamiokande neutrino detector in Japan. The uncertainty in the predicted ⁸B neutrino flux is dominated by the ³He(α,γ)⁷Be reaction.

Experiment at LUNA: The ³He(α,γ)⁷Be reaction has been studied experimentally with a systematic uncertainty as low as 3.0%, decisively improving the precision of the prediction:

Phys. Rev. Lett. 2006 Bemmerer et al.
Phys. Rev. C 2007 Gyürky et al.
Phys. Rev. C 2007 Confortola et al.
Nucl. Phys. A 2008 Costantini et al.

γ-ray background measurements at LUNA

LUNA = Laboratory Underground for Nuclear Astrophysics

The international LUNA collaboration aims to provide nuclear data directly at energies of astrophysical interest and thus remove the need for theoretical extrapolations. LUNA is located deep underground in the Gran Sasso laboratory in Italy. The Gran Sasso mountain strongly reduces the γ-ray laboratory background, enabling sensitive experiments:

Study of the γ-ray background at LUNA for E_γ > 3 MeV
Study of the γ-ray background at LUNA for E_γ < 3 MeV
Study of the γ-ray background at LUNA with an escape-suppressed detector

A similar background study is ongoing at Felsenkeller.

Technical experiment pages (local access only)

⁴⁰Ca(α,γ)⁴⁴Ti measurement, 21.-30. June 2010, FZD Tandetron
¹⁴N(p,γ)¹⁵O high-energy, July-August 2008, 10.-20. August 2009, FZD Tandetron
¹⁵N(p,γ)¹⁶O target study for LUNA, 06.-11.03.2009 and 20.-21.04.2009, FZD Tandetron

People

Dr. Daniel Bemmerer
Dr. Zoltan Elekes
M. Sc. Michele Marta
Dipl.-Phys. Michael Anders
cand. phys. Konrad Schmidt
András Szepesi (Herbert Quandt fellow 2010)

Alumni

Dipl.-Phys. Erik Trompler (Master's student at TU Dresden, 2008-2009, thesis download here)
M. Sc. Tamás Szücs (Herbert Quandt fellow from Debrecen/Hungary April-Sept 2009)

Formal collaborations

LUNA collaboration

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
INFN Padua/Italy: C. Broggini, A. Caciolli, M. Erhard, R. Menegazzo

Informal collaborations

Paul-Scherrer-Institut, Switzerland: D. Schumann (long-lived radioisotopes for astrophysics)

Financial support

Deutsche Forschungsgemeinschaft DFG BE 4100/2-1 (2009-2012)
European Union, FP7 SPIRIT, transnational access (2009-)
European Union, FP6 ILIAS, transnational access (2006-2009)
European Union, FP6 AIM, transnational access (2008-2009)
INFN Italy, Fondo Affari Internazionali (2009)
Herbert-Quandt-Foundation (Fellowships for Tamás Szücs April-September 2009, András Szepesi April-July 2010)

Further information

Recent papers and talks (links to FZD library).
Information on the city of Dresden in Italian language.
Vorlesung Nukleon-Nukleon-Reaktionen an der TU Dresden, Sommersemester 2008


Dr. Bemmerer, Daniel - 23.06.2010