The Microball consists of 95 CsI(Tl) scintillators closely packed to cover the angular range 4.0o - 172o. The detectors are arranged in 9 rings with increasing forward segmentation. The device is optimally designed to be used in conjunction with Gammasphere. The scintillator light is collected by silicon photodiodes that provide high quantum efficiency and minimal mass. The signals are processed through a charge sensitive preamplifier followed by a slow shaper. Particle identification for 1,2,3H, 3,4He, Li, Be and B ions is accomplished by pulse shape discrimination.
The features of the Microball are summarized below:
Here are some overview pictures and sketches of the Microball.
There are 9 rings of detectors spanning the angular range between 4.0o and 171o relative to the beam as seen in Fig. 1.1.
An overview of the Gammasphere with the Microball in place is shown in Fig. 1.2.
A close-up photograph of the Microball in the Gammasphere is shown in Fig. 1.3.
The parameters of the Microball are summarized in Table 1.1. The number of the detectors and their distance from the target in each ring are given in the second and third rows, respectively. The fourth and fifth rows give the polar angles, q, at the center of each ring and the corresponding half angle. A spherical polar coordinate system is used with the beam along the z axis. The azimuthal angle f = 0 is at the top and increases clockwise when going with the beam. Columns six and seven give the solid angle for one detector at each ring in milli-steradians and the normalized solid angle relative to a detector in the first ring. The next column gives the light guide thickness in mm. The last 6 rows give the average CsI(Tl) thicknesses in each ring for the two devices, as well as the maximum energies of protons and alpha particles that stop in the detectors.
(Also available in a text-only format.)
Quantity\Ring | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
---|---|---|---|---|---|---|---|---|---|
# of Detectors | 6 | 10 | 12 | 12 | 14 | 14 | 12 | 10 | 6 |
Distance (mm) | 110 | 80 | 60 | 50 | 50 | 50 | 45 | 47 | 50 |
Theta, q | 9.0 | 21.0 | 36.0 | 52.0 | 70.0 | 90.0 | 111.5 | 135.0 | 159.0 |
Half-Theta, Dq/2 | 5.0 | 7.0 | 8.0 | 8.0 | 10.0 | 10.0 | 11.5 | 12.0 | 12.0 |
DW(q) (msr) | 28.2 | 54.4 | 85.3 | 113.2 | 144.7 | 154.1 | 192.1 | 182.9 | 154.5 |
DW(q) / DW(9o) | 1.0 | 1.93 | 3.02 | 4.01 | 5.13 | 5.46 | 6.81 | 6.49 | 5.48 |
Light guide (mm) | 8.0 | 7.5 | 6.0 | 6.0 | 6.0 | 7.0 | 7.0 | 7.5 | 8.0 |
mBall-1, CsI (mm) | 2.7 | 2.4 | 2.2 | 1.9 | 1.6 | 1.5 | 1.5 | 1.3 | 1.1 |
p range (MeV) | 24.5 | 22.8 | 21.7 | 19.9 | 17.9 | 17.3 | 17.3 | 15.8 | 14.3 |
a range (MeV) | 97.0 | 90.4 | 85.6 | 78.7 | 71.0 | 68.3 | 68.3 | 62.7 | 56.6 |
mBall-2, CsI (mm) | 9.2 | 7.2 | 6.4 | 6.0 | 5.6 | 5.2 | 4.1 | 3.6 | 3.5 |
p range (MeV) | 50.1 | 43.5 | 40.6 | 39.1 | 37.6 | 36.0 | 31.3 | 29.0 | 28.6 |
a range (MeV) | 198.6 | 172.3 | 161.0 | 155.1 | 149.1 | 142.7 | 124.1 | 115.0 | 113.2 |
The details of the design and the performance characteristics of the Microball are available in a publication in Nuclear Instruments and Methods, A381, 418 (1996). For reprints in color contact D.G. Sarantites at dgs@wuchem.wustl.edu.
To read a PDF file (3.0 MB) of the Microball NIM paper in black and white click here Microball-NIM. To see the Microball Pictures in color just go to Microball Images in the Front Page or look at some of them just above in this page.
There is also a NIM paper describing simulations of the Gammasphere performance through the Microball. There you will also find what the (H,k) response of the Gammasphere is with or without the Hevimet Shields in place. For the simulations paper (780 kB) click here Gammasphere Simulations NIM paper.
Last update: Wednesday, 19 November 1997; 10:06 PM.