Rochester Compact Heavy-Ion Counter: CHICO

University of Rochester

  A schematic view of one half of CHICO showing the 10 PPAC detector panels plus transmission lines to the fast electronics.   Installation of CHICO at Gammasphere by the builders; Mike Simon, Bob Gray, Ching-Yen Wu and Doug Cline  

The position-sensitive heavy ion detector CHICO was developed specifically for use with Gammasphere; it is the fourth generation heavy-ion detector developed at Rochester with NSF support to exploit the advantages of the kinematic coincident technique. CHICO comprises two identical $35.6cm$ diameter hemispherical target chambers, one at forward angles and the other at backward angles. Each hemisphere contains ten $\theta $-$\phi $ position-sensitive parallel-plate avalanche detector panels in a conical array. Each of the panels consists of a $100\mu g/cm^{2}$ segmented aluminized stretched polypropylene anode and a delay line cathode. The cathode is segmented into $1^{\circ }$ wide $\theta $ stripes for MATH and MATH while $\phi $ is measured with $\pm 4.6^{\circ }$ resolution. The detection solid angle is $67\%$ of $4\pi $ with a minimum flight path of $13cm$. The anode time resolution is $\approx 500ps$. The measured mass resolution is $\Delta m/m=5\%$ for binary collisions. During the past decade CHICO has been used in conjunction with Gammasphere for 24 separate experiments involving 58 experimenters from 17 institutions.

A paper describing CHICO has been published. Additional information is available regarding the CHICO fast amplifiers as well as further schematic drawings of CHICO.

Photographs of the use of CHICO with Gammasphere at ATLAS using the FMA beam line during August 2008 are as follows:
Upstream general
Upstream details
Upstream beampipe
Downstream details
These pictures are with the CHICOsignal cables disconnected for clarity.