Overview:

A CCD sensor can be implemented to form a sensitive radiation detector that provides spatial data on a particle passing through the detection array. As high energy photons or ionizing radiation is incident on the CCD surface, electrons in the silicon substrate are excited by the photoelectric effect (silicon has a work function of 1.14 eV). The excited electrons are collected by an electrode on the ccd array and the total charge on each pixel is registered and digitalized.

Vertex detectors are arrays of CCD sensors used to compute particle trajectory and origin by interpolating a particle path from known points where it passed through a CCD sensor.

This vertex detector prototype was originally designed for use with the 100keV particle accelerator, however accurate reproducible results could not be obtained due to electron beam attenuation and electrical interference from the high voltage supplies. The vertex detector operates perfectly when used with a gamma ray source such as Americium 241. CCD sensor was cooled to 0 C to reduce detector noise.

CCD Pixel With Incident Photon:

Incident photon excites electrons in P-Type Semi conductor by the photoelectric effect and are collected on the electrodes. Pixels with no charge are black, pixels with charge are different shades of gray proportional to the magnitude of charge on the electrode.

Modified CCD Detector:

A black and white CCD camera was modified to function as a vertex detector. The lens of the CCD camera was removed and the CCD array was covered with a thin reflective plastic to prevent light from entering the detector. Americium 241 (2.7 uCi) was used as a gamma ray source (Alpha particles are blocked by the glass covering the silicon in the CCD sensor). A secondary light shield covered the detector preventing any light from entering.

Gamma Ray Detection Process:

Gamma rays pass through the light shield and glass and excite electrons in the CCD elements. Excited electrons are picked up by the electrodes and the charge is digitized into a video signal. Gamma ray detections show up as white dots on the screen.

CCD Setup:

Americium 241 gamma ray source on shielded CCD array.

CCD Setup:

CCD camera mounted and connected to video capture card.

Detection Frame Grabs:

These are the superimposed frames captured at 640x480 at 30fps over a 10 sec interval using a cooled CCD sensor. Image resized to fit panel.

• Video
• Full size image

Useful links:

• http://zebu.uoregon.edu/ccd.html ---------------------------- CCD Design
• http://www2.slac.stanford.edu/vvc/detectors.html ------- Vertex Detectors

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