DIGITAL POCKET RADIATION DOSEMETER

Digital Pocket Radiation Dosemeter (DIGIDOSE) Digital Pocket Radiation Dosemeter (DIGIDOSE)
Model I    Model II

                                                                                                                             

Introduction 

The Digital Pocket Radiation Dosemeter, DIGIDOSE is a semiconductor detector based, low cost, digital radiation dosemeter. It provides continuous digital readout of X & Gamma radiation dose over a wide range (1 microSv to 99999 microSv ). It works on a pair of coin type Lithium battery cells with the battery life exceeding three months if used for 8 hours a day in a 10 microSv/hr radiation field. The dosemeter is available in two models, Model I & II, which differ in the size & type of LCD display used. In another very low cost variation (RADCLICK), the LCD display is dispensed with and a beep tone is produced for every 0.05 microSv of accumulated dose. 

Description 

 The block diagram of the pocket dosemeter is shown in Fig.1. The detector is a low cost commercially available Silicon (Si) rectifier diode operating at a low reverse bias of about 4V. A charge-sensitive amplifier based on a low power CMOS IC amplifies the pulses from the detector due to the incidence of ionising radiation. The part of the circuit consisting of the detector and the amplifier is provided with an energy compensation filter, which also act as electro-magnetic shielding and is potted with an anti-vibration polyurethane compound. The pulses from the amplifier are fed to a discriminator with a

                         

Digital Pocket Radiation Dosemeter (DIGIDOSE)

 threshold voltage adjusted to cut off the noise pulses. The pulses at the output of the discriminator are fed to a programmable divider circuit for calibrating the dosemeter so that one count corresponds to 1microSv (137Cs gamma). After division the counts are accumulated in a 6-digit-counter-LCD-display module. The dosemeter covers a range of 1 microSv to 999999 microSv.

The DIGIDOSE is available in two models. In Model I which uses a small 6-digit LCD-counter module without an integral 'Battery Low' symbol in the display, battery low indication / warning is provided through a blinking LED (Light Emitting Diode). The LED blinks when battery voltage is low. The blinking frequency indicates the Battery State. Blinking starts at a low frequency of one flash per 3-4 seconds, when approximately 8 hours of battery life is still available. In Model II, which makes use of a custom-made LCD with a built-in Low Battery Symbol (LB), LB indication lights up in the LCD display, when battery is low and 8 hours (approximate) of battery life is still available. 

More than 500 dosemeters were fabricated and were on trial for the past one year in BARC and Nuclear power stations of NPCIL. Improvements suggested by various user groups have been incorporated in the current models. The DIGIDOSE has also been subjected to environmental and mechanical tests as per ANSI standards at the Electronics Regional Test Laboratory, Mumbai and they have passed the tests successfully. 

The dosemeters are also available in two versions, one with on-off switch and the other without the on-off switch to meet the requirements in nuclear power stations. The switch-less version is supplied with a specially designed storage rack . The dosemeters are switched off / reset by storing them in the rack. 

In another low cost, radiation beeper version (RADCLICK), the LCD display is dispensed with and locally available components are used. It gives a beep for every 0.05 microSv of accumulated dose and provides continuous vigilance on the presence & relative intensity of X & gamma radiation over a wide range. It works on a 3.6V NiCd rechargeable battery. Battery life exceeds 1month if used continuously in a 10 microSv/hr radiation field. 'Battery low' warning is provided by a continuous background tone. 

Specifications: DIGIDOSE Model I & II

Radiation detected X & Gamma radiation (>40KeV)
Detector used PN junction Si semiconductor
Range of measurement 1 microSv to 99999 microSv.
Energy dependence Within ±30% from 60 KeV to 1.2MeV
Readout accuracy Within ±15% for 137Cs, up to 0.5 Sv/h
Dose rate range Within ±10% (0.5 Sv/h)
Within ±20% (5 Sv /h)
Operating Environment  0 - 45°C; 90% RH (non-condensing)
Battery Coin type Lithium Battery (CR 2320 x 2)
Battery Life Continuous use of 300 hr. (Approximate)
Sensitivity One count per microSv
Display  6 Digit LCD
Dimensions 30(W) X 115 (L) X 14 (D) mm, excluding the Clip ( Model II : 30X125X14 mm)
Weight  Approximately 60 gm
Low Battery Indication

Battery Low LED blinks when battery is low. Blinking frequency is indicative of battery state. Blinking starts at a low frequency of 0.2 pps, when 8 hr. (approximate) of battery life is still available.
(in model II LB indication lights up in the LCD display when battery is low)

 Specifications: RADCLICK radiation beeper

Radiation detected X & Gamma radiation (>40KeV)
Battery Rechargeable NiCd Battery (Type 2/3AAA)
Detector used PN junction Si semiconductor
Battery Life Continuous use of 1month (on full charge)
Sensitivity One beep per 0.05microSv (Approximate)
Others Power on audible tone; continuous low background tone for battery low warning

Application

 Personnel monitoring of radiation workers in Nuclear power stations, Isotope laboratories, Industrial radiography installations, diagnostic & therapeutic radiology centres, etc.

Facilities / manpower requirements for manufacture of DIGIDOSE dosemeters

Qualified electronic Engineers (1) / technicians (1 or 2) with knowledge of analog and digital electronics and familiarity with SMD devices are required.

  1. Automatic / semi-automatic SMD work stations and manual SMD rework facilities are required along with skilled SMD technicians

  2. Radiation source (137Cs and/or 60Co, 2-5 mCi) facilities for calibration of dosemeters are required. Fulfillment of statutory conditions for possessing the radiation source such as AERB certified source storage facilities and certified radiation safety personnel for handling the source is necessary.

For details contact :
   

    Head, Technology Transfer & Collaboration Division,
    BHABHA ATOMIC RESEARCH CENTRE,
    TROMBAY, MUMBAI - 400 085
    Fax : 091-022-25505151
    Email : technology@barc.gov.in

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