X-ray detecting system having negative feedback for gain stabilization

Apparatus for detecting radiant energy comprising,

• a first light source for providing an input light signal,
• first photoelectric transducing means having an input surface responsive to incident light energy for converting incident light energy on said input surface into a corresponding output electrical signal,
• a second light source separate from said first light source, said second light source comprising second photoelectric transducing means responsive to an electrical signal for providing an output light signal representative of the electrical signal,
• means for illuminating said first photoelectric transducing means input surface with said input and output light signals so that the latter provides an electrical output signal representative of the combination of said input and output light signals,
• means for coupling the output electrical signal from said first photoelectric transducing means to the input of said second light source whereby a reduction and increase in the intensity of said input light signal from said first light source is accompanied by an increase and reduction respectively in the intensity of said output light signal from said second light source,
• third photoelectric transducing means for converting incident light energy into a representative electrical signal,
• and means for coupling said output light signal to said third photoelectric transducing means to provide an electrical output signal from the latter representative of the intensity of said input light signal.

Apparatus for detecting X-ray radiation comprising,

• a scintillating crystal responsive to incident X-ray radiation for emitting light to provide an input light signal,
• a photomultiplier tube having a photocathode responsive to incident light energy for converting incident light energy on said photocathode into a corresponding output electrical signal,
• a light-emitting diode responsive to an electrical signal for providing an output light signal representative of the electrical signal,
• means for exposing said photocathode of said photomultiplier tube to the light emitted by said scintillating crystal and to the light emitted by said light emitting diode so that said photomultiplier tube provides an electrical output signal representative of a combination of said input and output light signals,
• and means for coupling said output electrical signal from said photomultiplier tube to said light emitting diode whereby a reduction and increase in the intensity of said input light signal from said scintillating crystal is accompanied by an increase and reduction respectively in the intensity of said output light signal from said light emitting diode.

Apparatus for detecting X-rays comprising,

• an X-ray source,
• a first light source comprising scintillation means responsive to X-rays emitted by said X-ray source for emitting light energy at a level representative of the intensity of the X-ray radiation incident upon said scintillation means,
• first photoelectric transducing means having an input surface responsive to incident light energy for converting incident light energy on said input surface into an electrical signal,
• a second light source separate from said scintillation means, said second light source comprising second photoelectric transducing means responsive to said electrical signal from said first photoelectric transducing means for emitting light energy at a level related to the magnitude of said electrical signal,
• said scintillation means and said first and second transducing means being so positioned relative to one another that said input surface of said first photoelectric transducing means is illuminated by light energy emitted from both said scintillation means and from said second photoelectric transducing means whereby the electrical signal from said first transducing means is representative of the incident combined light energies emitted by said scintillating means and by said second light source, a reduction in the intensity of the X-ray radiation incident on said scintillation means being operative to increase the light energy emitted by said second light source onto said input surface of said first photoelectric transducing means,
• and further light-sensitive means responsive to the light energy which is emitted by said second light source for producing an output electrical signal representative of the X-rays incident on said scintillation means.