Thomson & Nielsen Electronics Ltd.

Other

Canadian Astronautics Limited

Thompson and Nielson Electronics Ltd.

Ian Thomson

Nicholas Garry Tarr

Andrew Hartshorn

Martin P Brown

Gary F MacKay

In a dosimeter probe comprising a semiconductor diode or a field effect transistor for monitoring levels of radiation during medical procedures, such as the treatment of tumors, the transistor or diode is fabricated epitaxially upon a surface of a substrate and a dummy die, i.e., a slab of material similar to that of the substrate, is positioned adjacent the substrate surface so as to overlie an active region of the transistor or diode and a relatively large area of the substrate surrounding the active region. The arrangement is such that, whatever the direction from which the radiation is incident upon the active region, its path through the device before arriving at the active region will have similar characteristics to the path the radiation takes upon leaving the active region.

Radiation sensor and dosimeter incorporating same

An insulated gate field effect transistor dosimeter has a source and drain defining a channel region, a floating gate having a first portion extending over the channel region, and a second, larger portion extending away from said region, a control gate having at least a portion thereof overlapping a first part of the floating gate, and a charging gate overlapping a second part of the floating gate. The area of the second part of the floating gate is much smaller than the area of the first part, and the charging gate is separated from the channel region by the control gate. The dosimeter is charged, before irradiation, by connecting the source, drain and control gate to a common ground and applying a potential difference between the charging gate and the common ground. The charge is supplied to the floating gate by a path which does not require a significant electric stress to be created in the region of the gate oxide and the channel. The dosimeter may comprise two such transistors fabricated on a common substrate, conveniently with a common source. The pair of transistors may be charged by maintaining the sources, drains and control gates within the normal maximum operating voltage relative to each other, and applying different potential differences between the two charging gates, respectively, and the substrate. Following irradiation, the absorbed radiation does is determined by measuring the difference between the threshold voltages of the two transistors. Preferably, the transistors have charges of opposite polarities. This differential arrangement reduces the effects of temperature variations and enhances sensitivity.

Method of monitoring radiation using a floating gate field effect transistor dosimeter, and dosimeter for use therein

This invention describes a flexible radiation probe which has a pair of insulated gate field effect transistors integrated into the same substrate each having a gate, source and drain. The transistors are mounted at the end of a flexible circuit board. The flexible circuit board has conductive tracks which connect the gate, source and drains of each of the transistors to a connection at an opposite end of the flexible circuit board. This connection end may then be connected to a suitable differential biasing circuit for biasing the transistors, and a circuit for reading the differential threshold voltages of the transistors. This differential threshold voltage being indicative of radiation received by the transistors when exposed in the bias mode. The flexible circuit allows the probe to be used in catheters or similar medical equipment.

Flexible radiation probe

The invention relates to a radiation dosimeter having a pair of insulated gate field effect transistors integrated into the same silicon substrate, in which each of the transistors are operable in a bias mode and a test mode. A circuit element for biasing each of the transistors, during said test mode is provide, so that one of the transistors is more sensitive to ionizing radiation than the other of the transistors. A circuit element is provided for determining, during the test mode, the difference in the threshold voltages of the transistors, whereby the difference voltage is indicative of the radiation dose, and a circuit element is provided for continuously switching the transistors between the bias mode and the test mode, whereby the period of operation of the transistors in the test mode time period is small in comparison to the period of operation of the transistors in the bias mode.

Direct reading dosimeter

A radon gas detector instrument comprising: a filter for trapping alpha radon daughters of said gas, an air pump for drawing ambient air through the filter, a DRAM devoid of an alpha particle barrier layer, located adjacent the filter, for exposure to alpha particles trapped by the filter, apparatus for cyclically relaxing all cells of the DRAM, waiting for a significant period of time for cells of the DRAM to become charged by said alpha particles, then reading the DRAM to determine the number of charged cells in the DRAM, a display connected to the relaxing, waiting and reading means for displaying a count of the number of charged cells in units correlated to the intensity of radon gas in the ambient air.

Radon detector

The invention is a radiation dosimeter and method of operation of its elements comprising a pair of silicon insulated gate field effect transistors integrated into the same substrate, each having a gate, a source and a drain. The dosimeter includes apparatus for measuring a first differential threshold votlage between the transistors, appartus for forward biasing the gate of the first transistor and inhibiting operation of the second, while allowing both to be subjected to ionizing radiation, and apparatus for measuring a second differential threshold voltage between the transistors following the irradiation. The first differential threshold voltage can be subtracted from the second to obtain a measure of the radiation dosage. Threshold drift and offset is thereby substantially eliminated.

Dosimeter

A direct reading dosimeter having a range such that it can be used by personnel workers in the medical, nuclear and industrial fields, and provides and indication of dose rate as well as total received dosage. The dosimeter uses a semiconductor sensor of MOS or bipolar transistor or MOS capacitor form which traps positive charge under the influence of ionizing radiation. A current is applied to the sensor substrate, the voltage across a portion of the substrate is sensed, differentiated and displayed. The dosimeter circuit can be integrated and packaged in a wrist watchcase, in a probe, or other convenient form.

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Nepean, Canada

Ian Thomson