### Speaker

Mr
Andrew MacLean
(University of Guelph)

### Description

When a excited nuclear state emits successive $\gamma$-rays in a $\gamma-\gamma$ cascade, $X^{**} \rightarrow X^{*} + \gamma_{1} \rightarrow X + \gamma_{2}$ an anisotropy is found in the spatial distribution of $\gamma_{2}$ with respect to $\gamma_{1}$. By defining the direction of $\gamma_{1}$ to be the z-axis, the intermediate level, $X^{*} $, in general will have an uneven distribution of m-states. This causes an anisotropy in the angular correlation of the second $\gamma$-ray with respect to the first. The correlations depend on the sequence of spin-parity values for the nuclear states involved as well as the multipolarities and mixing ratios of the emitted $\gamma$-rays. These angular correlations are expressed by the $W(\theta)$ function:
\begin{center}
$W(\theta) = 1 + \sum\limits_{k = even}^{2L} a_{k}P_{k}(cos\theta)$
\end{center}
where $L$ is the lowest multipole order of the emitted $\gamma$-rays and the $a_{k}$ are coefficients\part{title} for all of the $P_{k}(cos\theta)$ Legendre polynomials.
Angular correlations can be used for the assignment of spins and parities to nuclear states and thus provide a powerful means to elucidate the structure of nuclei away from stability through $\beta-\gamma-\gamma$ coincidence measurements. In order to explore the sensitivity of the new 16 clover-detector GRIFFIN $\gamma$-ray spectrometer at TRIUMF-ISAC to such $\gamma-\gamma$ angular correlations, and to optimize its performance for these measurements, we have studied a well known $4^{+}\rightarrow 2^{+}\rightarrow 0^{+}$ $\gamma-\gamma$ cascade from $^{60}$Co decay through both experimental measurements and Geant4 simulations. Results of these investigations will be presented in this talk.

### Primary author

Mr
Andrew MacLean
(University of Guelph)

### Co-authors

Mr
Adam Garnsworthy
(TRIUMF)
Mr
Alex Laffoley
(University of Guelph)
Mr
Bill Mills
(TRIUMF)
Mr
Carl Svensson
(University of Guelph)
Mr
David Miller
(TRIUMF)
Mr
Evan Rand
(University of Guelph)
Mrs
Jenna Smith
(TRIUMF)
Mr
Paul Garrett
(University of Guelph)
Mr
Peter Bender
(TRIUMF)
Mr
Ryan Dunlop
(University of Guelph)
Mr
Vinzenz Bildstein
(University of Guelph)