Explosive nucleosynthesis in classical novae
 

Local collaboration:
Tom Brown (Research Associate, now at Mary Bird Cancer Center), Brent Delbridge (Undergraduate Student), Blake Freeman (Undergraduate Student), Alejandro Garcia (Professor), Andreas Knecht (Research Associate), Anne Sallaska (Graduate Student, now at University of North Carolina), Derek Storm (Research Professor Emeritus), Chris Wrede (Research Associate)


A classical nova is a violent thermonuclear explosion that takes place on the surface of an extremely dense (white dwarf) star when its strong gravitational field attracts nuclear fuel (hydrogen) from another star.

Huge quantities of long-lived radioactive isotopes are produced in these explosions and ejected into space. Satellites in orbit around the Earth with gamma-ray telescopes onboard are used to search the Galaxy for the decays of the radioactive isotopes sodium-22 and aluminum-26 produced in novae. At the Center for Experimental Nuclear Physics and Astrophysics at the University of Washington, we are measuring and studying the nuclear reactions that affect the creation and destruction and sodium-22 and aluminum-26 in novae. Our results are used to make accurate comparisons between gamma-ray observations of novae and theoretical models of novae. In 2010, Dr. Anne Sallaska successfully defended her Ph.D. thesis on a measurement of proton capture on sodium-22 using the Van de Graaff accelerator at CENPA and a sodium-22 target from TRIUMF-ISAC. Her work has shown that sodium-22 is destroyed much more efficiently in novae than was previously thought possible.

Publications:

A. Sallaska et al., Phys. Rev. C (in press), arxiv

A. Sallaska et al., Phys. Rev. Lett. 105, 152501 (2010), arxiv

T.A.D. Brown et al., Nucl. Instrum. Methods B 267, 3302 (2009)

C. Wrede, Phys. Rev. C 79, 035803 (2009)

The material ejected from novae can condense to form micron-sized grains with isotopic ratios that are characteristic of the underlying nucleosynthesis process. Grains that have found their way to the Earth embedded in primitive meteorites are known as “presolar grains” and their unique isotopic ratios can be measured in the laboratory. At CENPA, we are studying the nuclear reactions that influence the expected silicon and sulfur isotopic ratios of presolar grains to help identify grains of nova origin. For example, undergraduate student Blake Freeman and collaborators recently measured the gamma-ray branches of proton capture on sulfur-33. An isotopically pure, ion-implanted sulfur-33 target was prepared at CENPA using a sulfur ion beam, and the target was bombarded with a proton beam from the tandem Van de Graaff accelerator at energies that correspond to nova temperatures.

Publications:

B.M. Freeman et al., Phys. Rev. C (submitted), arxiv

Our work on novae is often carried out in collaboration with other institutions including Argonne National Lab, Maier Leibnitz Laboratorium, McMaster University, the National Superconducting Cyclotron Lab, TRIUMF-ISAC, UPC Barcelona, and Yale University. Some of this work is carried out offsite.  In recent years CENPA’s contributions to the offsite experiments have been led by postdoctoral Research Associate Dr. Chris Wrede.

Publications:

C. Wrede et al., Phys. Rev. C 82, 035805 (2010)

C. Wrede et al., Phys. Rev. C 81, 055503 (2010)

C. Wrede et al., Nucl. Instrum. Methods B 268, 3482 (2010)

K. Setoodehnia et al., Phys. Rev. C 82, 022801(R) (2010), Physics Synopsis

L. Erikson et al., Phys. Rev. C 81, 045808 (2010)

C. Wrede et al., Phys. Rev. C 79, 045808 (2009)

C. Wrede et al., Phys. Rev. C 79, 045803 (2009), Physics Synopsis

Solar fusion cross sections

In the past decade, direct cross-section measurements have been made at CENPA of solar fusion reactions such as alpha particle capture on helium-3 and proton capture on beryllium-7. Each of these reactions is part of a minor branch in the nuclear-reaction cycles that fuse hydrogen into helium in the center of the Sun, producing the most of the energy that sustains life on Earth. Together they produce high-energy neutrinos that can be used to study the center of the Sun and the fundamental properties of neutrinos from Earth.

Publications:

T.A.D. Brown et al., Phys Rev. C 76, 055801 (2007)

A.R. Junghans et al., Phys. Rev. C 68, 065803 (2003)