The 40Ca(α,γ)44Ti reaction

Masters project K. Schmidt (2010-2011), PhD project K. Schmidt (2011-2014)


  • List of activated samples you find here (local access only).
  • Here is information on a possible Master's thesis on the 44Ti(α,p)47V reaction reaction (in German).
  • On our homepage you find more nuclear reactions for astrophysics, studied at LUNA and in Dresden.



The radioactive nuclide 44Ti (half-life 58.9 ± 0.3 years [Ah06]) is thought to be produced in supernova explosions. So by observing the γ rays from the decay of this nuclide, one can find a signature of supernova explosion that has taken place in the last few centuries, a very short time span for astronomical purposes.

This is what has been done in recent years, with space-based γ-ray observatories such as the INTEGRAL satellite (image: ESA). Much to the surprise of astrophysicists, so far the 44Ti decay radiation has been observed only for one supernova remnant called Cassiopeia A [Re06]. Several other remnants of recent supernovae studied did not show the expected emission, which leads to the question whether the currently accepted supernova models are correct [Th06].

Nuclear reaction rates determined in the laboratory are one important aspect of the models. Dedicated sensitivity studies have shown that the 40Ca(α,γ)44Ti reaction plays an important role in this context [Th98].

Recent experiments [Na06], [Vo07], [Ho10], and [Ro12] show some discrepancies for several sharp resonances near 4.5 MeV α energy. This problem prevents a precise prediction of the 44Ti yield even in an astronomically well-studied system such as Cassiopeia A (image: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration). In the framework of the present project, these resonances should be studied again, hoping to resolve the discrepancies. To that end, very thin CaO targets will be fabricated at the GSI target lab and at ATOMKI, in order to resolve the resonances which are separated in energy by less than 20 keV.

The resonance strength shall then be determined using several techniques: in-beam γ-spectrometry, offline counting at the Felsenkeller low-activity counting lab, and possibly even by accelerator mass spectrometry.

A final aim is to study with precision the strength of the resonance at 2.7 MeV α energy, so far only known on the 30 % precision level. This should be pursued in a coming beam time. It is an important resonance because its share of the thermonuclear rate dominates at temperatures up to 2·109 K.

Previous Experiments at Eα = 4,5 MeV

In 1971 Simpson, Dixon and Storey published their study [Si71] of the nucleus 44Ti. They used a beam of 4He Ions from a 4-MV Van de Graaff accelerator at the National Research Council of Canada. Targets consisted of various thicknesses of CaO, in the range of 8 to 176 nm (3 to 60 µg/cm²). Thereby they measured a resonance strength at 4.52 MeV α energy of ωγ = 6.

One of their next works [Di77] contains the uncertainties of the resonance strength like ωγ = (6 ± 1) eV.

Three resonances were found at about 4.5 MeV in their paper [Di80]. They specify strengths of (0.5 ± 0.1) eV at 4.497 MeV, (5.8 ± 1.2) eV at 4.510 MeV, and (2.0 ± 0.4) eV at 4.523 MeV α energy.

The work [Vo07] of Vockenhuber et al. was published in 2007. They used the recoil mass spectrometer DRAGON located at the TRIUMF-ISAC facility in Vancouver, Canada. In inverse kinematics they bombarded a He gas target with a 40Ca beam of 0.60 to 1.15 MeV/nucleon. Listed energy levels do not correspond to the levels of previous work because of the energy loss in the gas target. But nevertheless two of the three resonances can be identified by the strength of (7.6 ± 1.1) eV and (2.4 ± 0.6) eV with corresponding α energies at 4.510 and 4.523 MeV.

Hoffman et al. [Ho10] measured a resonance strength of (16 ± 3) eV at 4.54 MeV α energy. The target consisted of natural CaO with a thickness of at least 1.1 mm. A 10 MV FN Tandetron Van de Graaff accelerator at the Lawrence Livermore National Laboratory, Center for Accelerator Mass Spectroscopy was used.

"Via direct γ counting and the 4π-summing technique, utilizing a previously characterized 12 inch × 12 inch single NaI crystal", Robertson et al. [Ro12] determined a resonance strength of (9.0 ± 1.2) eV.

Previous Experiments at Eα = 2,758 MeV

In 1977 Cooperman, Shapiro and Winkler published “Helium burning of 40Ca” [Co77]. The CSULA 4 MV Van de Graaff accelerator at the California State University, Los Angeles, provided the α-particle beams in the energy region Eα = 2.75-4.00 MeV. Natural calcium metal on tantalum backing was used as target. A resonance strength of (0.013 ± 0.003) eV has been measured.

Vockenhuber et al. [Vo07] also found a resonance strength of (0.016 ± 0.007) as a corresponding α energy at 2.758 MeV.

Characterization and Calibration of Weak 44Ti Sources

In 2009 five 44Ti calibration sources supplied by Paul-Scherrer-Institute have been studied. They are necessary for measurements of the 40Ca(α,γ)44TiTi-44 P-690 reaction. First, maps of activity distribution have been created by an Image-Plate-System. Furthermore the activities have been determined by gamma spectroscopy. Hence there are standards which are calibrated to ± 1.2 %. The image shows the areal distribution of one of the five sources. There, PSL is a quantification unit name which is abbreviation of Photo-Stimulated-Luminescence.



I. Ahmad et al.,_Improved measurement of the 44Ti half-life from a 14-year long study. Phys. Rev. C 74, 065803 (2006).


E. L. Cooperman et al.,_Helium burning of 40Ca. Nucl. Phys. A 284, 163 (1977).


W. R. Dixon et al.,_Levels of 44Ti from the 40Ca(α,γ)44Ti reaction. Phys. Rev. C 15, 1896 (1977).


W. R. Dixon et al.,_An isospin-mixed triplet in 44Ti. Can. J. Phys. 58, 1360 (1980).


R. Hoffman et al.,_Reaction rate sensitivity of 44Ti production in massive stars and implications of a thick target yield measurement of 40Ca(α,γ)44Ti. Astrophys. J. 715, 1383 (2010).


H. Nassar et al.,_40Ca(α,γ)44Ti Reaction in the Energy Regime of Supernova Nucleosynthesis. Phys. Rev. Lett. 96, 041102 (2006).


M. Renaud et al.,_The signature of 44Ti in Cassiopeia A revealed by IBIS/ISGRI of INTEGRAL. Astrophys. J. 647, L41 (2006).


D. Robertson et al.,_New measurement of the astrophysically important 40Ca(α,γ)44Ti reaction. Phys. Rev. C 85, 045810 (2012).


J. J. Simpson et al.,_Study of 44Ti by the 40Ca(α,γ)44Ti Reaction. Phys. Rev. C 4, 443 (1971).


L.-S. The et al.,_Nuclear Reactions Governing the Nucleosynthesis of 44Ti. Astrophys. J. 504, 500 (1998).


L.-S. The et al.,_Are 44Ti-producing supernovae exceptional? Astron. Astrophys. 450, 1037 (2006).


C. Vockenhuber et al.,_Measurement of the 40Ca(α,γ)44Ti reaction relevant for supernova nucleosynthesis. Phys. Rev. C 76, 035801 (2007).