Understanding the Inner Workings of Novae

A measurement of an important nuclear reaction that occurs in novae has been made by the DRAGON group at TRIUMF. Novae are cataclysmic events that occur as a result of material from one star falling onto another. This generates vast amounts of energy causing a violent explosion and the ejection of matter into space. In the aftermath of these outbursts one isotope of interest is 18F. There is hope that its radioactive decay can be observed by satellites which could give us a unique insight to the inner workings of novae. 

In order to exploit any future observations, however, the expected amount of 18F formed in nova explosions needs to be properly characterized, requiring experimental knowledge of key nuclear reactions such as 18F + p → 19Ne. The problem with observing these reactions in the laboratory is that as 18F is radioactive, making a target out of it isn't practicable, as it would decay away in a matter of hours. The solution to this is to produce radioactive beams of nuclei, which can be sent to the experiment in a matter of milliseconds after they are produced.

Whilst observing the reaction of interest, 18F + p → 19Ne, DRAGON was able to successfully resolve just two 19Ne particles out of one thousand billion 18F beam particles. This is the first such successful observation of the reaction in a laboratory.

By utilizing a high-energy cyclotron, TRIUMF is one of the few places on earth that can produce the necessary intensity of radioactive ion beams for experiments such as this. The laboratory is also home to the DRAGON Facility, which stands for the “Detection of Recoils And Gammas Of Nuclear reactions”. It consists of a gas target, containing either hydrogen or helium, and a high-resolution mass separator, which can filter out nuclei of interest from other contaminating particles. Beam is delivered to the target where the nuclear reaction of interest takes place, then exits into the separator. Such a facility is required when using radioactive and stable beams as any products produced are hidden amongst the vastly more abundant beam particles (for more information see http://astro.triumf.ca/dragon/system).

The experiment was performed by the local DRAGON Group, Canadian and international collaborators, including those from McMaster University, the University of York, University of Edinburgh, Colorado School of Mines, Michigan State University, Pacific Northwest Laboratories and Oak Ridge National Laboratory. The data were analyzed by University of York/TRIUMF graduate student Charlie Akers (pictured). The experimental results are the first stage in a measurement campaign aiming to make all the necessary experimental measurements of reactions that produce and destroy 18F in the novae environment. The important result was recently published in Physical Review Letters (http://prl.aps.org/abstract/PRL/v110/i26/e262502). The high suppression of contaminants, together with the radioactive beam intensities available, make DRAGON at TRIUMF one of only a handful of facilities on earth that can conduct this kind of research.