SGSPD Seminar Fri. 27 12:00

SGSPD Committee sgspd at triumf.ca
Fri Feb 20 14:16:41 PST 2015


Dear Grad Students and Postdocs,

We will have a seminar from two of our own PhD students Friday (27 Feb) 
12:00-13:00 in the Auditorium.  Andrea Teigelhoefer will tell us about 
commissioning the ion-guide laser ion source and Aaron Gallant the first 
experiment with its beam.  Show some support, learn something about your 
colleagues, and eat some pizza.  Ensure a slice for all by signing up on 
the Doodle poll <http://doodle.com/vskmv7mhubbh9i5y>; order goes in 
Thursday 11:00.

We hope to see you there!
Your SGSPD Committee

*Speaker*: Andrea Teigelhoefer
*Title*: Pure radioactive ion beam production
*Abstract*: Radioactive isotopes at TRIUMF are produced by bombarding 
the nuclei of a target material with the 500MeV proton beam from the 
TRIUMF cyclotron. This causes fragmentation, spallation and fission of 
the target nuclei and produces a multitude of isotopes. In order to 
provide these isotopes to the experiments located in ISAC, they must be 
ionized, so that they can be manipulated by means of electric and 
magnetic fields. At TRIUMF three different ion sources are available: 
(1) surface-, (2) electron impact, and (3) laser resonance- ion source. 
  Only the resonance ionization laser ion source (T RILIS) ionizes 
element specific. Since TRILIS is commonly used with a hot transfer tube 
(aka. surface ion source), a considerable amount of isobaric background 
from elements with low ionization potential (e.g. alkali metals) can be 
present in certain mass regions, which at times precludes experiments 
due to insufficient signal to noise ratios. In order to overcome the 
limitations due to surface ionized background, the hot cavity of the 
classical RILIS was replaced by a cold RF ion guide. In April 2014 this 
ion-guide laser ion source (IG-LIS) has been successfully tested. With 
this new ion source it is possible to suppress the isobaric background 
up to the order of 10^6  and thus provide beams virtually free of 
isobaric background contamination.

*Speaker*: Aaron Gallant
*Title*: TITAN + IG-LIS: Testing the Isobaric Multiplet Mass Equation A 
= 20, 21
*Abstract*: Much of our knowledge on increasingly exotic nuclei has been 
obtained through the use of rare isotope beam (RIB) facilities. 
High-precision mass spectrometers have made use of RIB to refine 
nucleosynthesis abundance calculations, to increase our understanding of 
fundamental aspects of the strong force, and to provide signatures of 
exotic phenomena, such as halo formation. Quite often, however, a beam 
of interest can not be measured due to large amounts of isobaric 
contamination. Here we present the first direct mass measurements of the 
nuclides 20,21Mg, which were completed with the TITAN Penning trap mass 
spectrometer. These measurements were only possible by using the newly 
developed ion-guide laser ion source (IG-LIS), located at TRIUMF's ISAC 
facility, suppressing the unwanted sodium background by a factor of 
10^6, resulting in an improvement in the signal-to-noise ratio of more 
than 10^4. These Mg isotopes are interesting, as they belong to the A = 
20 and 21 isobaric multiplets, and as such, their binding energies 
should follow the quadratic behaviour predicted by the isobaric 
multiplet mass equation (IMME). With the rise of high precision mass 
measurements, large deviations from the expected quadratic behaviour of 
the IMME has been seen in several multiplets, e.g. A = 8, 9 and 32. With 
our new mass values, the A = 20 and 21 multiplets now show large 
deviations from the expected behaviour. Calculations using the USDA/B 
isospin non-conserving Hamiltonian and interactions based on chiral 
effective field theory using two- and three-nucleon forces have been 
conducted, and are compared to the present measurements.
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