Experimental Nuclear Physics -- Knutson Group

       Elizabeth George
       Paul Voytas

Students who made meaningful contributions:
       Grads:   Greg Severin,  Sean Cotter
Undergrads:   Li Zhan,  Nawaf Al-Baghli,  Wes Hill,  John Lee

Research Activities:

Our group is working on experiments to measure the shape of the beta spectrum in the decays of oxygen-14, boron-8 and possible carbon-14.  The mass 14 experiments are tests of the CVC theorem, which is a component of the standard model of the weak and electromagnetic interactions.  Boron-8 plays an important role in solar neutrino measurements.  The neutrinos from the decay of this isotope are moderately abundant and are of relatively high energies, and as a result, some solar neutrino detectors see primarily boron-8 neutrinos.  The goal of our experiment is to provide information that is relevant for determining the neutrino spectrum.

The experiments are carried out at the University of Wisconsin Nuclear Physics Laboratory.  The short-lived radioactive nuclei are produced with beams from the Wisconsin EN tandem accelerator and transported to a beta spectrometer for analysis.  The spectrometer is iron-free, with fields provided by a set of superconducting  coils (shown below). Electrons and positrons from beta decay are focussed through a set of copper slits and then onto a Si(Li) detector.  The momentum resolution of the device is about 2%, and the acceptance solid angle is 0.8 sr.


Superconducting Magnet Assembly
Wisconsin EN Tandem Accelerator

calibration data
The graph at the left shows some of the results from a spectrometer calibration run obtained with a bismuth-207 source.  The measurements show the count rate as a function of magnet current.  The peaks are from internal conversion of the 1064 keV transition, with the K line at 5.6 A and the unresolved L, M, and N transitions at 5.96 A.  The crosses are from a Monte-Carlo simulation using known energies and conversion coefficients.