Extended range radiation dose-rate monitor

• US 4,767,929 A
• Filed: 10/06/1986
• Issued: 08/30/1988
• Est. Priority Date: 10/06/1986
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Department Of Energy
• Original Assignee: The United States of America As Represented By The Secretary of Agriculture
• Inventors: Valentine, Kenneth H.
• Primary Examiner(s): Fields, Carolyn E.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/915,841
• Time in Patent Office: 694 Days
• Field of Search: 250/370 F, 250/370 R, 250/388, 250/371, 250/374, 250/390 B, 307/359, 307/358, 307/519, 340/600
• US Class Current: 250/370.07
• CPC Class Codes: G01T 1/026 Semiconductor dose-rate meters
• CPC Class Codes: G01T 1/17 Circuit arrangements not adapted to a particular type of detector pulse-selection circuits H03K, G01R

Abstract

An extended range dose-rate monitor is provided which utilizes the pulse pileup phenomenon that occurs in conventional counting systems to alter the dynamic response of the system to extend the dose-rate counting range. The current pulses from a solid-state detector generated by radiation events are amplified and shaped prior to applying the pulses to the input of a comparator. The comparator generates one logic pulse for each input pulse which exceeds the comparator reference threshold. These pulses are integrated and applied to a meter calibrated to indicate the measured dose-rate in response to the integrator output. A portion of the output signal from the integrator is fed back to vary the comparator reference threshold in proportion to the output count rate to extend the sensitive dynamic detection range by delaying the asymptotic approach of the integrator output toward full scale as measured by the meter.

Claims

1. An extended range counter system for measuring ionizing radiation dose-rates up to at least 1000 R/h, comprising:

an ionizing radiation detector means for producing current pulses at a rate corresponding to the photon interaction rate of ionizing radiation to be detected and having an amplitude proportional to the charge deposited by each photon of radiation detected;

an amplifier means responsive to each of said current pulses for generating fixed width voltage pulses at an output thereof having an amplitude proportional to the amplitude of said current pulses;

a comparator means having a signal input connected to the output of said amplifier means and a reference voltage input for generating a logic pulses at an output thereof for each input pulse from said amplifier means which exceeds the comparator means threshold determined by a reference voltage level applied to said reference voltage input of said comparator means;

an integrator means connected to the output of said comparator means for integrating said logic pulses to provide an output signal proportional to the rate of logic pulses applied to the input thereof;

a signal feedback means for feeding back a selected portion of the output signal from said integrator means to said reference voltage input of said comparator means to vary the comparator means threshold so that as the radiation dose-rate detected by said detector means increases the comparator means threshold increases to extend the sensitive dynamic range of the system up to at least 1000 R/h; and

a meter connected to the output of said integrator means and calibrated to indicate measured radiation dose-rate in response to the output signal of said integrator means.

2. The system as set forth in claim 1 wherein said detector means is a solid-state radiation detecting element.

3. The system as set forth in claim 3 wherein said signal feedback means includes a potentiometer.

4. The system as set forth in claim 3 wherein said amplifier means includes a charge sensitive preamplifier connected to the output of said detector means and a pulse shaping amplifier connected to the output of said charge sensitive preamplifier and having an output connected to the signal input of said comparator means.

5. The system as set forth in claim 4 further including a frequency meter connected to the output of said comparator means and calibrated to indicate the measured radiation dose rate in response to the rate of pulses generated at the output of said comparator means.