EP2641106A1

EP2641106A1 - System for monitoring environmental dosimetry, dosimeter and environmental dosimetry method

Info

Publication number: EP2641106A1
Application number: EP11799327.9A
Authority: EP
Inventors: Patrick Pailler; Christian Chatellier; Yoann Hilairet; Grégory JEAN
Original assignee: WYTEK
Current assignee: WYTEK
Priority date: 2010-11-17
Filing date: 2011-11-17
Publication date: 2013-09-25
Also published as: FR2967504A1; WO2012066497A1; US20130270430A1; FR2967504B1

Abstract

The invention relates to a real-time dosimetry monitoring system which is simple to deploy, efficient and economical and which limits the production of waste. For this purpose, the subject of the invention is a system for monitoring environmental dosimetry, comprising: a plurality of dosimeters (100, 110) not equipped with a display screen or radioactive dose calculator, but each comprising a photodiode (101) sensitive to the radiation to be detected and a discriminator (102) that transforms a pulse representative of radiation detection into a pulse that can be counted by a supervision unit (103), said supervision unit being connected to a wireless transceiver (104) for transmitting raw data representative of the radiation detected by each dosimeter; and at least one relay terminal (200) comprising a wireless transceiver (201) that can communicate with at least some of the transceivers of the dosimeters and with at least one central unit (300) for tracking environmental dosimetry, said central unit being able to calculate the radiation dose sensed by each dosimeter on the basis of the raw data transmitted by each dosimeter.

Description

DOSIMETER DOSIMETRY MONITORING SYSTEM, DOSIMETER AND SURFACE DOSIMETRY METHOD.

The invention relates to a room dosimetry monitoring system, a dosimeter for measuring ambient radioactivity and a room dosimetry method.

A dosimeter is a device that measures radiation. Dosimeters are used to monitor a radioactive environment in a room or monitor the amount of radiation a dosimeter user is exposed to.

The present invention relates to the measurement of ambient radioactivity.

More particularly, a dosimeter measures the equivalent of ambient dose (or flow), and / or of the directional dose equivalent (or flow) due to external exposure to beta, X and gamma radiation, for energies less than 10 MeV, for the purpose of radiation protection.

The method for determining the ambient and directional dose (or flow) equivalent at the test point is given in ISO 4037-3.

An ambient dose equivalent, denoted H * (10), is a dose equivalent at a point in a radiation field that would be produced by the corresponding unidirectional and expanded field, in the sphere ICUR ("ICRU sphere" in English), at a depth of 10 mm, on the radius that faces the direction of the unidirectional field.

The unit of the international dose equivalent system is J.kg- ¹ . His special name is sievert (Sv): 1 Sv = 1 J.kg ^-1

Most ambient dosimeters are said to be passive. They consist of a strip of radiation-sensitive material. As soon as a photon crosses this band, it is impressed like a photo film. In this case we talk about passive badges.

These badges are distributed in the premises, or on the devices, whose radioactivity must be monitored. At the end of a period of defined time, depending on the legislation in force, the passive badges are recorded and their precise location referenced to ensure the traceability of the information. Once the badges are collected (and replaced by new passive badges), they are sent to the laboratory for analysis. This can take several days so that the knowledge of a radioactivity incident is necessarily offset in time with respect to the occurrence of the incident itself. This is how the wrong setting of radiotherapy instruments was detected several days later. If this time had been shortened, it would have prevented the contamination of many patients.

In addition to this important detection time, the passive badges currently in use require significant stewardship for their positioning, their collection, the referencing of their position, their sending to the analysis laboratories, the collection of the results and the writing of the reports. The time spent managing the ambient dosimetry measurement may represent the equivalent of several full working hours for the larger hospitals.

Finally, the unique use of ambient dosimeters generates excessively high costs, but also significant waste, further increasing the costs of waste reprocessing.

Another type of dosimeter exists. It is a so-called active dosimeter, constituted by an electronic device comprising a power supply connected to a measurement system sensitive to radiation to be detected. As soon as the detector receives radiation, it calculates the received dose and sends the result to a display screen. This structure of the dosimeter is mandatory according to certain standards, such as for example the standard NF EN 61526 concerning direct reading dosimeters used in operational dosimetry, ie dedicated to the protection of people and it must be worn by the user.

Users must necessarily connect their active dosimeter to a data collection kiosk when they leave the supervised area. The only advantage that these electronic dosimeters provide is the immediate calculation of the detected radiation dose, this dose being known as soon as the dosimeters are connected to the monitoring terminal of dosimetry, without having to wait several days or weeks.

This type of dosimeter is therefore not substitutable for passive badges currently used in ambient dosimetry because they represent a very high cost, and the data recovery infrastructure designed for operational dosimetry is not adapted to dosimetry. atmosphere. The collection of data is just as costly and exacting as for ambient dosimeters since it would be necessary to regularly record in situ the doses calculated and displayed by each dosimeter.

The present invention therefore aims to provide a room dosimetry monitoring system to know in a centralized and almost immediate dose detected by all the dosimeters deployed at the scale of a room or a building. This system that uses wireless communications is easy to deploy in pre-existing premises without having to do extensive installation work, performing well because part of the maintenance can be done remotely, and economic because requiring no installation stewardship / uninstallation and requiring only limited mandatory annual maintenance and avoiding the generation of waste.

To remedy this problem, the invention proposes a room dosimetry monitoring system comprising dosimeters that are very energy efficient and can communicate remotely with a central unit which itself performs dose calculations received by the dosimeters from raw data transmitted by the dosimeters.

The person skilled in the art would not have an incentive to modify the operational dosimeters of the state of the art to allow a collection of calculated doses easier because by equipping such dosimeters with a wireless transceiver, the power consumption would be very high. important and the batteries should be replaced or the batteries recharged at least weekly. The cost of electricity consumption would therefore be prohibitive, handling just as important as what is currently required in ambient dosimetry to replace passive badges, and the quantity and cost of waste generated would still be significant if the power supply is provided by non-rechargeable batteries.

More specifically, the subject of the invention is a room dosimetry monitoring system, comprising:

a plurality of dosimeters devoid of a display screen, each comprising a radiation-sensitive photodiode to be detected, a discriminator transforming a pulse representative of the detection of radiation into a pulse that can be counted by a control unit, at least one charge amplifier arranged between the radiation sensitive photodiode to be detected and the discriminator, the control unit itself being connected to a wireless transceiver for transmission of data representative of the radiation detected by each dosimeter;

at least one relay terminal comprising a wireless transceiver capable of communicating with at least some of the dosimeter transceivers and with at least one central unit for monitoring the ambient dosimetry.

According to other embodiments:

The plurality of dosimeters may also be devoid of a radioactive dose calculator, in which the control unit is able to transmit, via the wireless transceiver, raw data representative of the radiation detected by each dosimeter, and CPU is able to calculate the radiation dose captured by each dosimeter from the raw data;

· The transceiver of each dosimeter can operate asymmetrically so that each dosimeter has less raw data transmission time than information reception time from said at least one central unit via said at least one relay terminal;

The system may furthermore comprise a memory for storing the doses calculated by the central unit; and or

The system may further comprise an alarm that can be activated by the central unit in the event that a calculated dose exceeds a predefined threshold.

The invention also relates to a dosimeter for the implementation of the ambient dosimetry monitoring system according to the invention, comprising at least one radiation sensitive photodiode to be detected, characterized in that the or each photodiode is connected to a control unit via a discriminator transforming a pulse representative of the detection of radiation into a pulse that can be counted by the control unit, at least one charge amplifier arranged between the radiation sensitive photodiode detecting and the discriminator, the control unit itself being connected to a transceiver for transmitting the data detected by the diode, the dosimeter being devoid of a display screen.

According to other embodiments:

The dosimeter may preferably be devoid of a calculator of the detected radioactive dose, the control unit being able to transmit, via the transceiver, raw data generated by the discriminator;

The control unit may comprise a clock for controlling the transceiver asymmetrically so that it has a transmission time shorter than a reception time;

The control unit can be connected to a calibration filter able to transform binary pulses, emitted by the control unit and whose duration is configurable, into pulses identical to what the photodiode produces when it is subjected to radiation to adjust the discriminator; The control unit can be connected to a potentiometer controllable by the control unit to electrically adjust a detection threshold of the discriminator of a radiation; and or

• The control unit can be connected to a diode whose ignition is controlled by the control unit and which is arranged to illuminate the radiation sensitive photodiode to be detected to verify the proper operation of the dosimeter.

The invention also relates to an ambient dosimetry method using a room dosimetry monitoring system according to the invention and comprising the following steps:

a) Activate the dosimeters;

b) convert electrical signals generated by the photodiode of each dosimeter into a data signal representative of the detected radiation;

c) Send at least a portion of the data signal from the wireless transceiver to the central unit, possibly via at least one relay terminal.

According to other embodiments:

Step b) may consist of converting electrical signals generated by the photodiode of each dosimeter into a raw data signal, the method further comprising a step d) of computing with the central unit of the radiation dose sensed by each photodiode from the transmitted raw data signal;

The method may furthermore comprise a step of calculating the dose of radiation sensed by each photodiode per unit of time, the dose rate, to determine the trend of temporal evolution of the sensed dose;

The method may further comprise a step of activating an alarm when the dose rate exceeds a predetermined threshold; the transceiver of each dosimeter can be controlled asymmetrically so that it has a transmission time shorter than a reception time;

the raw data signal of step b) may be a binary signal, and in which step c) may consist of sending all the binary signal, the raw data signal of step b) may be a binary signal , and wherein step c) may consist of sending only a part of the binary signal, this part corresponding to an effective detection of a radiation, the non-transmitted part corresponding to the absence of detection.

the method may further comprise a step of testing the operation of one or more dosimeters, this step comprising the following sub-steps:

sending a test command from the central unit to one or more dosimeters, this test command being received by the wireless receiver of the or each dosimeter;

- transmit the test command received to the control unit;

control, via the control unit, a lighting of predefined duration of a diode arranged to illuminate the photodiode sensitive to radiation to be detected;

converting electrical signals generated by the photodiode of each dosimeter into a data signal;

sending at least a part of the data signal by the wireless transceiver to the central unit, possibly via a relay terminal;

- with the central unit, check that the signal received corresponds to the test command sent;

- activate an alarm if the received signal does not correspond to the test command.

the method may further comprise a step of generating an alarm signal when the calculated dose exceeds a tolerance threshold predetermined, or when a communication failure between a dosimeter and the central unit is detected, or when a malfunction of a dosimeter is detected;

the method may further comprise a calibration step comprising the following sub-steps:

sending a calibration command from the central unit to one or more dosimeters, this calibration command being received by the wireless receiver of the or each dosimeter;

- transmit the received calibration command to the control unit;

in the absence of any irradiation of the photodiode, to seek with the control unit a position of a controllable potentiometer such that the discriminator does not send a pulse despite an electronic noise of the charge amplifier;

generating, with the control unit, at least three sets of a fixed number of binary pulses of fixed amplitude, the pulses of the first series having a duration of 10 μs, the pulses of the second series having a duration of 20 μs; ps, the pulses of the first series having a duration of 30 ps, the other series having a pulse duration incremented by 10 ps between each series, these binary pulses being transmitted to a calibration filter;

transforming with the calibration filter the binary pulses into pulses identical to what the photodiode produces when it is subjected to a photon;

counting the number of pulses generated by the discriminator and transmitted to the control unit for each pulse series; - relate the number of pulses of each series and the number of pulses generated in response by the discriminator;

- adjust the controllable potentiometer until about 10% of the pulses of the first series generate a response from the discriminator, that about 30% of the pulses of the second series generate a response of the discriminator and that about 50% of the pulses of the third series generate a discriminator response; and or

The method may further comprise a step of adjusting the detection sensitivity of one or more dosimeters, comprising the following sub-steps:

- measure the sensitivity of one or more dosimeters at different energies between 10 and 3000 keV (kilo electron volts) relative to cesium 137;

- if the sensitivity of one or more dosimeters is greater than 1, 4 or less than 0.6:

sending a sensitivity adjustment command from the central unit to the dosimeter (s), this sensitivity adjustment command being received by the wireless receiver of the or each dosimeter;

o transmit the sensitivity adjustment command to the control unit;

o control, via the control unit, a controllable potentiometer to set the detection threshold of the discriminator until the sensitivity of the dosimeter (s) is between 0.6 and 1, 4.

Other features of the invention will be set forth in the detailed description below, made with reference to the appended figures which represent, respectively: FIG. 1, a schematic representation of a room dosimetry monitoring system according to the invention;

FIG. 2, a schematic representation of a room dosimetry monitoring system according to the invention provided with a dosimeter according to the invention;

FIG. 3, a schematic representation of a second embodiment of a dosimeter according to the invention; and

FIG. 4, a curve representing the sensitivity of a dosimeter according to the invention at different energies relative to cesium 137.

A room dosimetry monitoring system according to the invention is illustrated schematically in FIGS. 1 and 2. The solid lines between the various elements of the system represent wired communications and the dashed lines represent wireless links.

This system comprises a plurality of dosimeters 100 each comprising at least one radiation-sensitive photodiode 101 to be detected, at least one discriminator 102 transforming a pulse representative of the detection of radiation by the or each photodiode 101 into a pulse that can be counted by a control unit 103, at least one charge amplifier 1 1 1 arranged between the radiation sensitive photodiode to be detected and the discriminator, the control unit being itself connected to a wireless transceiver 104 for the transmission of raw data representative of the radiation detected by each dosimeter.

The charge amplifier 1 1 1 amplifies the signal provided by the photodiode 101 when it is traversed by a photon. This amplifier must be chosen to minimize the power consumption.

According to the invention, the dosimeters are devoid of a display screen, which saves energy. Advantageously, the dosimeters according to the invention are also devoid of dose calculator radioactive and transmit at least a portion of the raw data, preferably binary data. Also advantageously, the dosimeters according to the invention are devoid of audible or visual alarm.

The control unit 103 may be any type of programmable logic circuit such as a microcontroller, a FPGA ("field-programmable trick array"), a SOC ("System on chip" in English) which is of interest. to integrate both a microcontroller 103 and a radio transceiver 104, etc.

The system according to the invention also comprises at least one relay terminal 200 comprising a wireless transceiver 201 able to communicate with at least some of the transceivers 101 of the dosimeters 100 and with at least one central unit 300 followed by the dosimetry atmosphere.

The central unit 300 is able to receive the dose of radiation calculated by each dosimeter, but alternatively and preferentially, the central unit 300 is able to calculate the dose of radiation captured by each dosimeter from the raw data transmitted by each dosimeter 100. In this preferred embodiment, the dosimeters do not calculate the received dose themselves, which saves electrical energy.

The monitoring of the ambient dosimetry according to the invention comprises the following steps:

a) Activate the dosimeters;

b) Convert electrical signals generated by the photodiode of each dosimeter into a raw data signal; c) Send at least a portion of the raw data signal from the wireless transceiver to the central unit, possibly via a relay terminal;

d) With the central unit, calculate the dose of radiation captured by each photodiode from the raw data signal transmitted. In this way, the dosimeters (which are electrically powered by batteries or rechargeable batteries) consume little energy because the dose is calculated relocated by the central unit 300 which is connected to the electrical network.

The central unit 300 is advantageously connected to a memory 400 which can store the calculated doses received by each dosimeter, but also the raw data, the time of transmission of the data, the evolution of the calculated dose received per unit time for determine the trend of temporal evolution of the dose collected, etc.

This memory may comprise at least one hard disk, flash memory, a USB key, a CD-ROM or a Blue Ray, a magnetic cassette, or any other data storage device.

Each dosimeter can also store its own raw data in a clean memory, such as a flash memory for example.

Of course, other devices can communicate with the relay terminals 200, such as 500 laptops, digital personal digital assistants (PDAs), mobile phones, etc.

Advantageously, the ambient dosimetry monitoring system according to the invention comprises an alarm that can be activated by the central unit in the case where a calculated dose exceeds a predefined threshold.

The monitoring of the ambient dosimetry according to the invention may further comprise a step of calculating the dose of radiation picked up by each photodiode per unit of time in order to determine the trend of temporal evolution of the dose received (flow rate of dose).

The monitoring of the ambient dosimetry according to the invention may furthermore comprise a step of activating an alarm if the trend of temporal evolution of the sensed dose exceeds a predetermined threshold.

Thanks to the wireless transmission between the dosimeters according to the invention and the relay terminal or terminals, the ambient dosimetry monitoring system according to the invention can be very easily deployed in different rooms and / or in different buildings, as can be found in some hospitals.

With current technologies, it is very easy to install relay terminals 200 with sufficient range to communicate with several communicating dosimeters according to the invention. Those skilled in the art will perfectly optimize the placement of the relay terminals depending on the configuration of the building or buildings to be equipped to monitor the ambient dosimetry.

Regarding dosimeters 100, it is sufficient to place them in the rooms to be monitored or on the devices to be monitored, as for the passive badges of ambient dosimetry known from the state of the art. Unlike the latter, the dosimeters according to the invention do not require periodic installation / uninstallation (daily, weekly or monthly). In addition, their power consumption is very low so that one can achieve autonomy of several months, or even at least a year.

Indeed, thanks to the absence of display screen, the ambient dosimetry monitoring system according to the invention allows an optimization of the power consumption of the dosimeters according to the invention.

Preferably, according to the invention, the transceiver of each dosimeter also operates asymmetrically so that each dosimeter has less time for transmitting the raw data than time for receiving information from said at least one central unit via said at least one relay terminal. We distinguish the transmission time of the show itself, as we distinguish the reception time of the reception itself. In other words, it is not because the transceiver is in transmission mode that it transmits data: the transmission of data may be shorter than the transmission time. Similarly, it is not because the transceiver is in receive mode that it receives data. Thanks to this asymmetrical operation, the dosimeters do not waste energy to be emitted continuously to the central unit via the relay terminals. The broadcast is made at regular intervals, between much longer periods of "listening". For this purpose, the control unit 103 of each dosimeter 100 includes a clock for controlling the transceiver asymmetrically so that it has a shorter transmit time than a receive time. This technical feature also saves the energy resource of each dosimeter.

For example, the teledosimeter can be set to transmit

(have the floor) for a very short time of 2 ms and to receive (listening time) for a time 30 ms (when it receives for example an acknowledgment of receipt). The power consumption in listening is lower than in emission. In this context, we can send a frame every 30 seconds for 1 year or about 1 million frames per year. In this example, the onboard energy must have a capacity of the order of 2200 mAh.

The dosimeters 100 transmit only binary data by transforming, by their discriminator 102, the pulses emitted by their photodiode 101 into pulses that can be counted by their control unit 103.

Thus, the dosimeters do not expend electrical energy to calculate the received radiation dose and transmit this multi-bit coded value. They transmit only 1 (corresponding to a pulse emitted by the photodiode) and 0 (corresponding to the absence of pulse emitted by the photodiode), which constitutes both a saving of energy of the calculation and the transmission in terms of quantity and speed, the 1s and 0s being values very easy to transmit without multi-bit coding, contrary to what should be done if the dosimeter were to send the value of the dose and its unity. It is only the central unit that calculates the dose received from the data emitted by each dosimeter. In addition, the dosimeters according to the invention are devoid of a display screen.

During the step of sending the raw data (step c), all the binary signal can be sent.

Advantageously, to save even more energy, only a part of the binary signal is sent to the central unit, this part corresponding to an effective detection of a radiation (sending of the 1 of the binary signal), the non-transmitted part (the 0 of the binary signal) corresponding to the absence of detection.

It is interesting that each dosimeter transmits no data if it detects no radiation, as long as there are indications that the dosimeter is working properly and that it is well on the network. For this, the central unit can interrogate at regular intervals and test it as will be described later. Alternatively, each dosimeter may transmit to the central unit 300, at regular intervals relatively spaced, a signal called "active waiting" or "polling" in English, according to which the dosimeter is still active and present on the network. Without receiving this signal (network or dosimeter power supply problem), the CPU 300 may be configured to activate an alarm in the event of a dosimeter failure, radio failure or power failure.

The dosimeters according to the invention can thus have an autonomy of several months, or even at least a year.

This ambient dosimetry monitoring system according to the invention is therefore both easy to deploy, energy efficient and allows a "real time" monitoring of the ambient dosimetry by the central unit 300. In addition, for example, if the threshold is exceeded, the evolution is worrying, the network or batteries fail, an alarm can be issued by the central unit, but also be transmitted to other devices capable of communicating with the relay terminals, such as PDAs from doctors, nurses or technicians competent in radio protection. The type of wireless communication is advantageously chosen to reach sufficiently large to limit the number of relay terminals 200 and to communicate through the structure of buildings. Advantageously, a radio communication (such as WiFi 802.1 1n or preferably Zig Bee 802.15.4) will be chosen between the dosimeters 100 and the relay terminals 200.

The latter can, for their part, be equipped with several types of communication means, so as to be able to communicate with, of course, the central unit 300 and the dosimeters 100, but also other types of apparatus such as mobile phones, PDAs, personal computers, etc. For example, the relay terminals can be equipped for wired communication, such as Ethernet or CPL, and / or for wireless communication, such as GSM, WiFi, Zig Bee, GPRS, Bluetooth, Infra red, etc. .

A second embodiment of a dosimeter according to the invention is illustrated in FIG.

This embodiment makes it possible to use the possibility given to the dosimeter according to the invention of electronically receiving information from the central unit 300 via the relay terminals 200.

Besides the fact that it includes the same components 101, 102,

103 and 104 that the embodiment 100 of Figure 2, this second embodiment comprises a controllable potentiometer 1 13 (E ² POT) arranged between the discriminator and the control unit 103, and a calibration filter 1 12 arranged between the control unit 103 and the charge amplifier 1 1 1.

An exemplary embodiment of a dosimeter according to the invention may comprise the following electronic components:

A silicon PIN photodiode Bpw34 from the company Siemens;

• an H4083 amplifier from Hamamatsu;

• a single open drain discriminator MCP6546 / LP21 1 DR from Microchip / Texas Instruments; • a controllable potentiometer E ² P0T AD5259 from Analog Devices;

• an MSP430 control unit from Texas Instruments; and

• a transceiver CC2500 from Texas Instruments.

Once a year, the dosimeter must be calibrated, ie it is checked that it measures well the right dose values in the energy range that is specific to it. During this calibration, an auto-calibration is first performed in order to reposition the detection threshold of the discriminator. Then the dosimeter is irradiated to see if the answer is always what it should be. If the answer is not correct, you can adjust its sensitivity with the controllable potentiometer (E ² POT) 1 13.

To this end, the calibration filter 1 12, connected to the control unit 103, is capable of transforming a binary pulse, emitted by the control unit and the width of which can be parameterized, into a pulse identical to that produced by the photodiode when irradiated to calibrate the discriminator.

Indeed, without radiation detected, the output of the charge amplifier 1 1 1 has a noise amplitude Δ _Β . The detection threshold of the discriminator 102 must therefore be set so that there is a count only when a radiation is detected and not because of the noise of the charge amplifier 1 1 1.

The auto-calibration comprises a first step of sending a calibration command from the central unit 300 to one or more dosimeters 1 10, this calibration command being received by the wireless receiver 104 of the or each dosimeter.

Then, the received calibration command is transmitted to the control unit 103.

Then, in the absence of any irradiation of the photodiode 101, it seeks with the control unit 103 a position of the controllable potentiometer 1 13 such that the discriminator 102 does not send a pulse despite the electronic noise of the amplifier load 1 1 1. So In practice, from an initial position of the controllable potentiometer, the position is modified to stop the generation of a pulse by the discriminator if, at the initial position, the discriminator generates pulses despite the absence of irradiation ( these pulses are then due to the electronic noise of the amplifier), or to cause the generation of a pulse by the discriminator if, at the initial position, the discriminator generates no pulse. In the latter case, we then return to a position of the controllable potentiometer in which the discriminator no longer generates a pulse.

Then, at least three sets of a defined number of binary pulses of fixed amplitude (for example 3.3 volts) are generated with the control unit 103, the pulses of the first series having a duration of 10 μs, the pulses of the second series having a duration of 20 μs, the pulses of the first series having a duration of 30 μs. The number of pulses in each series is, for example, one million.

Other series can be generated and the duration of each pulse is then incremented by 10 ps between each series. These binary pulses are then transmitted to the calibration filter 1 12. Thus, with the calibration filter, the binary pulses are transformed into pulses identical to what the photodiode produces when it is subjected to a photon. The variable duration of the pulses makes it possible to vary the energy of the pulses received by the amplifier.

Next, the number of pulses generated by the discriminator and transmitted to the control unit 103 for each pulse series is counted, then a ratio is entered between the number of pulses of each series and the number of pulses generated. in response by the discriminator.

Finally, the controllable potentiometer is adjusted until approximately 10% of the pulses of the first series generate a response of the discriminator, that approximately 30% of the pulses of the second series generate a discriminator response and that about 50% of the third series pulses generate a discriminator response.

We thus obtain an optimal detection threshold specific to each dosimeter.

However, the standard requires the standards require that the sensitivity of the dosimeters is between 1, 4 and 0.6 compared to cesium 137.

The optimal detection threshold determined by the auto-calibration may be lower than this sensitivity. It is therefore necessary to "degrade" the sensitivity of the dosimeter so that it enters the norm.

The controllable potentiometer 1 13 (E ² POT) makes it possible to electrically adjust the sensitivity of the dosimeter.

To know the sensitivity of each dosimeter, it is necessary to measure the energy response curve of the dosimeter which is given in FIG.

This consists of knowing the number of pulses counted per unit of radioactivity. The sievert and its variations milisievert (mSv) and microsievert (MSV) are generally used in this field.

This curve represents the sensitivity of the dosimeter at different energies relative to cesium 137, which has a sensitivity of 1.

Setting the detection sensitivity of one or more dosimeters includes the following steps:

measuring the sensitivity of one or more dosimeters at different energies between 10 and 3000 keV (kilo electron volts) relative to cesium 137 which has a sensitivity arbitrarily set at 1;

sending a sensitivity adjustment command from the central unit to the dosimeter (s), this sensitivity adjustment command being received by the wireless receiver of the or each dosimeter; o transmit the sensitivity adjustment command to the control unit;

o modifying, via the control unit, the position of the controllable potentiometer E ² POT to set the detection threshold of the discriminator until the sensitivity of the dosimeter (s) is between 0.6 and 1, 4.

The sensitivity of the ambient dosimeters of the state of the art is usually adjusted by adding material to the sensitive band that will capture a certain portion of the radiation and thus decrease the sensitivity of the sensor.

According to the invention, the sensitivity is set via the potentiometer E ² POT 1 13, the setting of which affects the sensitivity of the sensor. This is a simple technical means to compensate for the sensitivity of the sensor in case of deviation of the response. This compensation is done electronically and remotely, which avoids a technician to move.

Alternatively or in combination, the control unit of a dosimeter according to the invention is connected to a diode 1 14 whose ignition is controlled by the control unit 103 and which is able to illuminate, for a definite time adjustable , the photodiode 101 sensitive to radiation to be detected in order to verify the proper functioning of the dosimeter.

This functional test of one or more dosemeters comprises the following steps:

- transmit the test command received to the control unit;

- Control, via the control unit, an ignition of predefined duration of a diode 1 14 arranged to illuminate the photodiode 101 sensitive to radiation to be detected; converting electrical signals generated by the photodiode of each dosimeter into a data signal, preferably binary raw data;

The invention therefore proposes a room dosimetry monitoring system that makes it possible to know, almost immediately, the detected dose, easy to deploy in extensive pre-existing premises and without having to carry out any substantial installation work, which is efficient because the calibration of dosimeters can be done automatically and remotely, and economical because it does not require any install / uninstall stewardship, it only requires limited annual maintenance, and it limits the generation of waste to the batteries changed annually.

According to other embodiments, the dosimeter may comprise several photodiodes (for example two) each connected to a discriminator. This simplifies detection in case of high dose.

In addition to the different commands that each dosimeter can receive during the "listening" phase of the transceiver 104, the invention provides that each dosimeter can receive an acknowledgment of the data from the central unit. Thus, in the event of absence of this acknowledgment, provision can be made for a retransmission of the data and / or the sending of an alarm signal, via the relay terminals, to devices such as portable computers 500, digital personal assistants (PDAs), mobile phones, etc. However, the dosimeter according to the invention is devoid of audible or visual alarm. He may simply transmit a signal that activates a remote alarm, this alarm being carried by the devices receiving the alarm signal.

Moreover, the structure of the dosimeter according to the invention and the dosimetry system according to the invention allows to reprogram a punctual dosimeter so that it serves as a relay terminal. This reprogramming must be punctual because the relay terminal function consumes energy.

An example of application of such a reprogramming is the punctual dosimetric follow-up (a few days) of a room which is out of reach of the relay terminals 200 but not a dosimeter 600 according to the invention (see FIG. 1). For example, it may be necessary to follow the room dosimetry of a room where a patient is assigned from time to time. In this case, the dosimeter 100 or 1 10 (which is within communication range of the dosimeter 700 temporarily installed in the chamber) is reprogrammed via the central unit so that it becomes a relay dosimeter 600 which relays the data sent by the dosimeter 700 at the relay terminals 200 and at the central unit 300.

Thus, the ambient dosimetry monitoring system according to the invention is not only easy to deploy, but also very easily adaptable to the conditions and the operating opportunities of premises whose ambient dosimetry must be followed.

Claims

1. Ambient dosimetry monitoring system, characterized in that it comprises:

a plurality of dosimeters (100, 1 10) devoid of a display screen, each comprising a radiation-sensitive photodiode (101) to be detected, a discriminator (102) transforming a pulse representative of the detection of a radiation into a radiation detector; pulse which can be counted by a control unit (103), at least one charge amplifier (11) arranged between the radiation sensitive photodiode (101) to be detected and the discriminator (102), the control unit (103) itself being connected to a wireless transceiver (104) for transmitting data representative of the radiation detected by each dosimeter;

at least one relay terminal (200) comprising a wireless transceiver (201) able to communicate with at least some of the transceivers (104) of the dosimeters and with at least one central unit (300) for monitoring the dosimetry atmosphere.

2. Ambient dosimetry monitoring system according to claim 1, wherein the plurality of dosimeters is also devoid of radioactive dose calculator, wherein the control unit is able to transmit via the wireless transceiver. , raw data representative of the radiation detected by each dosimeter, and in which the central unit is able to calculate the dose of radiation captured by each dosimeter from the raw data.

The ambient dosimetry monitoring system according to any one of claims 1 or 2, wherein the transceiver of each dosimeter operates asymmetrically so that each dosimeter has less data transmission time. raw time of receiving information from said at least one central unit via said at least one relay terminal.

4. The ambient dosimetry monitoring system according to any one of claims 1 to 3, further comprising a storage memory doses calculated by the central unit.

5. The ambient dosimetry monitoring system according to any one of claims 1 to 4, further comprising an alarm activatable by the central unit in case a calculated dose exceeds a predefined threshold.

6. Dosimeter for the implementation of the ambient dosimetry monitoring system according to any one of claims 1 to 5, comprising at least one photodiode (101) sensitive to radiation to be detected, characterized in that the or each photodiode is connected to a control unit (103) via a discriminator (102) transforming a pulse representative of the detection of radiation into a pulse that can be counted by the control unit, at least one amplifier of charge (1 1 1) arranged between the radiation sensitive photodiode (101) to be detected and the discriminator (102), the control unit being itself connected to a transceiver for transmitting the data detected by the diode, the dosimeter being devoid of a display screen.

7. Dosimeter according to the preceding claim, which being devoid of calculator of the detected radioactive dose, the control unit (103) being able to transmit, via the transceiver (104), raw data generated by the discriminator (102). ).

The dosimeter of any one of claims 6 or 7, wherein the control unit comprises a clock for controlling the transceiver asymmetrically so that it has a transmission time shorter than a time. reception.

9. Dosimeter according to any one of claims 6 to 8, wherein the control unit (103) is connected to a calibration filter (12) adapted to transform binary pulses emitted by the control unit and whose the duration is configurable, in pulses identical to what the photodiode produces when it is exposed to radiation in order to adjust the discriminator

10. Dosimeter according to any one of claims 6 to 9, wherein the control unit is connected to a potentiometer (E ² P0T) controllable by the control unit to electrically adjust a detection threshold of the discriminator of a radiation.

1 1. dosimeter according to any one of claims 6 to 10, wherein the control unit is connected to a diode whose ignition is controlled by the control unit and which is arranged to illuminate the radiation sensitive photodiode to detect in order to check the proper functioning of the dosimeter.

12. A method of ambient dosimetry characterized in that it consists in using a room dosimetry monitoring system according to any one of claims 1 to 5 and in that it comprises the following steps:

a) Activate the dosimeters;

13. The ambient dosimetry method according to the preceding claim, wherein step b) consists in converting electrical signals generated by the photodiode of each dosimeter into a raw data signal, the method further comprising a step of ) computes with the central unit the dose of radiation captured by each photodiode from the raw data signal transmitted.

14. A method of ambient dosimetry according to the preceding claim, further comprising a step of calculating the dose of radiation captured by each photodiode per unit of time, the dose rate, to determine the trend of temporal evolution of the dose.

15. The ambient dosimetry method according to the preceding claim, further comprising a step of activating an alarm when the dose rate exceeds a predetermined threshold.

The ambient dosimetry method according to any one of claims 12 to 15, wherein the transceiver of each dosimeter is asymmetrically controlled so that it has a shorter transmit time than reception time.

The ambient dosimetry method according to any one of claims 13 to 16, wherein the raw data signal of step b) is a binary signal, and wherein step c) is to send the entire data signal. binary signal.

The ambient dosimetry method according to any one of claims 13 to 16, wherein the raw data signal of step b) is a binary signal, and wherein step c) is to send that a part of the binary signal, this part corresponding to an effective detection of a radiation, the non-transmitted part corresponding to the absence of detection.

The ambient dosimetry method according to any one of claims 13 to 18, further comprising a step of testing the operation of one or more dosimeters, this step comprising the following sub-steps:

- transmit the test command received to the control unit;

control, via the control unit, a lighting of predefined duration of a diode arranged to illuminate the photodiode sensitive to radiation to be detected; converting electrical signals generated by the photodiode of each dosimeter into a data signal;

The ambient dosimetry method according to any one of claims 12 to 19, further comprising a step of generating an alarm signal when the calculated dose exceeds a predetermined tolerance threshold, or when a communication failure between a dosimeter and the central unit is detected, or when a malfunction of a dosimeter is detected.

21. The ambient dosimetry method according to any one of claims 12 to 20, further comprising a calibration step comprising the following sub-steps:

- transmit the received calibration command to the control unit;

- In the absence of any irradiation of the photodiode (101), search with the control unit a position of a controllable potentiometer such that the discriminator does not send a pulse despite an electronic noise of the charge amplifier (1 1 1);

- generating with the control unit (103) at least three sets of a fixed number of binary pulses of fixed amplitude, the pulses of the first series having a duration of 10 ps, the pulses of the second series having a duration of 20 ps, the pulses of the first series having a duration of 30 ps, the other series having an incremented pulse duration of 10 μS between each series, these binary pulses being transmitted to a calibration filter (12);

counting the number of pulses generated by the discriminator and transmitted to the control unit (103) for each pulse series;

- relate the number of pulses of each series and the number of pulses generated in response by the discriminator;

- adjust the controllable potentiometer until about 10% of the pulses of the first series generate a response from the discriminator, that about 30% of the pulses of the second series generate a response of the discriminator and that about 50% of the pulses of the third series generate a discriminator response.

22. The ambient dosimetry method according to any one of claims 12 to 21, further comprising a step of adjusting the detection sensitivity of one or more dosimeters, comprising the following sub-steps:

o transmit the sensitivity adjustment command to the control unit; o control, via the control unit, a controllable potentiometer (E ² POT) to adjust the detection threshold of the discriminator until the sensitivity of the dosimeter (s) is between 0.6 and 1, 4.