Calcium 40
The 40Ca(α,γ)44Ti reaction using DRAGON
In our every day life we are surrounded by materials composed of the elements of the periodic table. Rarely does one ask where these elements came from. It has been a long process of discovery to understand the precise origin of many of the elements we consider commonplace. It is now believed that the Big-Bang produced only the lightest elements, primarily hydrogen and helium, and that heavier elements were synthesized as the product of nuclear reactions within stars. Occasionally the nuclear reactions that occur within stars produce an isotope of an element which is unstable, radioactive. When a radioactive species decays it emits radiation which is characteristic of the species that decayed. Satellites have been able to detect the characteristic radiation from the decay of several isotopes in the Milky Way. One in particular which has been detected is the isotope of titanium, 44Ti. The decay of 44Ti has been seen in the ashes of exploding stars, vast gas clouds termed supernova remnants. This isotope of titanium eventually decays to a stable isotope of calcium found everywhere on Earth from bones to chalk. It is believed that the bulk of the production in stars of 44Ti occurs as the star explodes, during the supernova. Calculations indicate that among the many possible reactions during a supernova, a particular nuclear reaction, where calcium captures a helium nucleus and fuses into titanium, is the main source of 44Ti. In this work it is detailed how using laboratory equipment on Earth one is able to shed light on the nuclear physics of this particular reaction governing the production of an isotope in our universe.
Journal:
A hybrid surface arc discharge ion source to produce ultra pure Ca+2 beams for 40Ca(α,γ)44Ti reaction studies at ISAC/TRIUMF
ISAC is an accelerator facility primarily dedicated to astrophysical studies. Off-line and online ion sources provide up to 65 keV of stable and radioactive beams to the ISAC accelerators. Initial acceleration is done via a constant velocity radio frequency quadrupole that requires 2 keV/u. Then the beam is further accelerated to 1.5 MeV/u at ISAC-I and 6.5 MeV/u at ISAC-II. To study radiative capture reactions relevant for astrophysics, the recoil mass spectrometer DRAGON was built in the experimental area. 40Ca(α,γ)44Ti is identified as one of the key reactions in supernovae to produce 44Ti and is given highest priority. For this experiment, an ultrapure Ca+2 beam was requested from the off-line ion source. Initial tests showed that, when using conventional ion sources, 40Ar and 40K are the impurities that are most difficult to eliminate. In order to overcome this problem, a new concept was needed and the hybrid surface arc discharge ion source was born. The hybrid surface ion source consists of a small surface ionizer and an arc discharge placed in a solenoid field. A very low ratio of 40Ar/40Ca=8 x10−5 was achieved with this new source and the experiment was completed successfully. The source is described in detail and its performance is discussed in this article.
Journal: Review of Scientific Instruments
The 40Ca(α,ϒ)44Ti reaction at DRAGON
Nuclear reactions play a key role in understanding nucleosynthesis in stars. Recoil mass spectrometers such as DRAGON are well suited to study reactions with respect to astrophysical production because of direct detection of reaction products. Here we present the first stage of an experiment running at the recoil mass spectrometer DRAGON at the ISAC/TRIUMF facility in Vancouver, Canada, to study the reaction 40Ca(α,ϒ)44Ti at astrophysically relevant energies. This reaction is one of the key reactions for production of 44Ti, which has been identified in younf supernova remnants by space based ϒ-ray telescopes onboard COMPTEL and INTEGRAL. In this paper, we focus on technical upgrade of DRAGON for 40Ca(α,ϒ)44Ti and preliminary results at resonances at Ex~9.2 MeV.
Journal: Nuclear Instruments and Methods in Physics Research B
Measurement of the 40Ca(α,γ) 44Ti reaction relevant for supernova nucleosynthesis
The short-lived nuclide 44 Ti is an important nuclide for the understanding of explosive nucle-osynthesis. The main production reaction, 40 Ca(α, γ)44 Ti, has been studied in inverse kinematics with the recoil mass spectrometer DRAGON located at the TRIUMF-ISAC facility in Vancouver, Canada. The temperature range relevant for α-rich freeze-out during a core-collapse supernova has been covered entirely with a 40 Ca beam of 0.60 to 1.15 MeV/nucleon. All relevant quantities for the calculation of the astrophysical reaction rate have been measured directly. Due to many previously undiscovered resonances, the reaction rate derived from the energy dependent 44 Ti yield is higher than the one based on previous prompt γ-ray studies commonly used in supernova models. The presented new rate results in an increased 44 Ti production in supernovae.
Journal: Phys. Rev. C 76 035801 (2007).
40Ca(α,γ) 44Ti and the production of 44Ti in supernovae
The nuclide 44 Ti is predicted to be produced in significant quantities in core-collapse supernovae, and indeed it has been observed in the supernova remnant Cassiopeia-A by space-based γ-ray telescopes. The main production of 44 Ti takes place in the α-rich freeze-out phase deep inside the supernova. The key reactions governing the 44 Ti abundance have been identified in an earlier sensitivity study. Using the recoil mass spectrometer DRAGON at the TRIUMF-ISAC facility in Vancouver, Canada, we measured the main production reaction 40 Ca(α,γ)44 Ti, resulting in an increased reaction rate compared to the rate derived from previous prompt γ-ray studies, which is commonly used in supernova models. The uncertainty of the 44 Ti production is now dominated by the rate of reactions with short-lived nuclides around 44 Ti, namely 45 V(p,γ)46 Cr, 44 Ti(α,p)47 V and 44 Ti(α,γ)48 Cr. The sensitivity of these reactions on the 44 Ti production has been revisited.
Journal: J. Phys. G: Nucl. Part. Phys. 35 014034 (2008)
