Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session FA: The Precision Frontier in Low Energy Nuclear Physics |
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Chair: Peter Mueller, Argonne National Laboratory Room: Plaza I |
Thursday, October 25, 2012 4:00PM - 4:36PM |
FA.00001: Mass and radius measurements of exotic nuclei Invited Speaker: Jens Dilling The understanding of the strong force and the nuclear interaction is on the forefront of today's physics research. More and more detailed theories are successfully used to describe an every increasing set of nuclei on the Segre chart. To further refine the theoretical approaches, such as ab-initio or density functional theories, to name two, one needs accurate and precise measurements to compare predictions to. Two of the key quantities of an atom are mass and size (or radius). The mass of an atom is a basic and fundamental quantity, and provides information of the binding of the many-body quantum mechanical system, and is as such well suited to probe nuclear theory. To overcome the obstacles given by the nature of rare isotopes, we have developed very sensitive and fast methods using ion trap techniques at TITAN (TRIUMF's Ion Trap of Atomic and Nuclear science). Ion traps are typically used in analytical chemistry and atomic physics for stable molecules or isotopes. At TITAN we are able to measure masses, using one single ion in as short as 8ms with 10ppb precision, breaking a new world-record for precision mass spectroscopy. Using this, we are able to probe, in particular, nuclear halos. Moreover, laser spectroscopy, allows one to probe, amongst other quantities, the size of the nucleus. These are very sensitive tests of our understanding and the theoretical approaches, and present state-of-the art in atomic physics techniques applied to nuclear physics. In this talk I will report on such measurements and show how and where they are applied, and what we have learnt so far, as well as where we want to go with these tests and techniques. [Preview Abstract] |
Thursday, October 25, 2012 4:36PM - 5:12PM |
FA.00002: Recent Results from Gamma-Ray Energy Tracking Array GRETINA Invited Speaker: I.-Yang Lee The gamma-ray energy tracking array GRETINA uses 28 Ge crystals, each with 36 segments, to cover $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 4$} $ of the 4$\pi $ solid angle. The gamma ray tracking technique uses detailed pulse shape information from each of the segments. These pulses are analyzed to determine the energy, time, and three-dimensional positions of all gamma-ray interactions. This information is then utilized, together with the characteristics of Compton scattering and pair-production processes, to track the scattering sequences of the gamma rays. Tracking arrays will give higher efficiency, better peak-to-total ratio and much higher position resolution, and thus increases the detection sensitivity by factors of several hundred compared to current arrays used in nuclear physics research. Particularly, for fast beam experiments tracking will provide spectra quality comparable to that from a Compton suppressed array, such as Gammasphere, while having the position resolution needed for the accurate Doppler correction comparable to detectors designed for good position resolution such as SeGA. GRETINA construction at the 88-Inch Cyclotron at LBNL was completed in March 2011. Extensive engineering and commissioning runs were carried out using radioactive sources, and beams from the Cyclotron until March 2012. The data obtained have been used to debug and improve its performance. After the commissioning period, GRETINA was moved to NSCL MSU and installed at the target position of the S800 spectrograph. The experimental program with a total of twenty four experiments will start in July 2012 after successful commissioning runs. I will present preliminary results from these runs and discuss future research plans. [Preview Abstract] |
Thursday, October 25, 2012 5:12PM - 5:48PM |
FA.00003: A Precision Measurement of the $\beta$-$\nu$ Angular Correlation in $^8$Li with the Argonne $\beta$-decay Paul Trap Invited Speaker: Matthew G. Sternberg Precise measurements of the $\beta$-$\nu$ angular correlation coefficient, $a$, provide information on the presence of possible exotic couplings in the weak interaction. In the $\beta$-decay of $^8$Li to $^8$Be$^*$ and subsequent breakup into two alpha particles, the large Q value and the $\beta$-$\alpha$-$\nu$ correlation provide enhanced sensitivity to any potential tensor coupling. In an initial measurement using the $\beta$-decay Paul Trap (BPT) at Argonne National Laboratory $2 \times 10^{4}$ $\beta$-$\alpha$-$\alpha$ coincidences were detected and a value of $a$ was inferred that places an upper limit of $1.5\%$ on any tensor contribution. The BPT has since been upgraded with improved double-sided silicon strip detectors---including finer segmentation, thinner dead layers, and thicker active silicon---along with new plastic scintillators to kinematically over-determine the decay. We will discuss the results from recent experiments where more than $4 \times 10^{5}$ $\beta$-$\alpha$-$\alpha$ coincidences were measured. [Preview Abstract] |
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