This is a semiconductor detector based, low cost, digital radiation dosemeter. It provides continuous digital readout of X-and Gamma radiation dose over a wide range of 1 µSv to 99999 µSv. It works on a pair of coin type Lithium battery cells.
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 (1microSv 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.
| Sr. No. | Specification | Value |
|---|---|---|
| 1 | Radiation detected | X & Gamma radiation (>40KeV) |
| 2 | Detector used | PN junction Si semiconductor |
| 3 | Range of measurement | 1 microSv to 99999 microSv |
| 4 | Energy dependence | Within ±25% from 60KeV to 1.2MeV |
Personnel monitoring of radiation workers in Nuclear power stations, Isotope laboratories, Industrial radiography installations, diagnostic & therapeutic radiology centres, etc.
INTRODUCTION
Over 100,000 persons in India are working in radiation environment - in nuclear power stations, radiography installations, cancer therapy hospitals, diagnostic X-ray centres, nuclear research institutions, universities, colleges, etc. - engaged in harnessing the peaceful uses of ionising radiation for the benefit of mankind. To ensure the health and safety of these persons it is necessary to periodically monitor the radiation dose received by them and maintain a record. Presently about 41,000 radiation workers from more than 3000 institutions are being monitored. A PC based auto TLD badge reader can process up to 50 badges loaded in a magazine at a time. The BARC TLD badge contains an Aluminium card holding 3 TL dosimeters sandwiched between energy discrimination filters to distinguish the beta, X & gamma radiations. The readout time is typically 100 sec. per badge and 50 badges are read in about 90 minutes.
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 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.
| Sr. No. | Specification | Value |
|---|---|---|
| 1 | Radiation detected | X & Gamma radiation (>40KeV) |
| 2 | Detector used | PN junction Si semiconductor |
| 3 | Range of measurement | 1 microSv to 99999 microSv. |
| 4 | Energy dependence | Within ±30% from 60 KeV to 1.2MeV |
| 5 | Readout accuracy | Within ±15% for 137Cs, up to 0.5 Sv/h |
| 6 | Dose rate range | Within ±10% (0.5 Sv/h) Within ±20% (5 Sv /h) |
| 7 | Operating Environment | 0 - 45°C; 90% RH (non-condensing) |
| 8 | Battery | Coin type Lithium Battery (CR 2320 x 2) |
| 9 | Battery Life | Continuous use of 300 hr. (Approximate) |
| 10 | Sensitivity | One count per microSv |
| 11 | Display | 6 Digit LCD |
| 12 | Dimensions | 30(W) X 115 (L) X 14 (D) mm, excluding the Clip ( Model II : 30X125X14 mm) |
| 13 | Weight | Approximately 60 gm |
| 14 | 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) |
| 15 | Safeguards | Heater / Gas flow Failure: The heater and gas flow are checked for failure in every dosimeter readout cycle. In the event of failure of heater or gas flow the readout is terminated and a message indicating heater / gas flow failure is flashed on the PC monitor. |
| Sr. No. | Specification | Value |
|---|---|---|
| 1 | Radiation detected | X & Gamma radiation (>40KeV) |
| 2 | Battery | Rechargeable NiCd Battery (Type 2/3AAA) |
| 3 | Detector used | PN junction Si semiconductor |
| 4 | Battery Life | Continuous use of 1month (on full charge) |
| 5 | Sensitivity | One beep per 0.05microSv (Approximate) |
| 5 | Others | Power on audible tone; continuous low background tone for battery low warning |
Personnel monitoring of radiation workers in Nuclear power stations, Isotope laboratories, Industrial radiography installations, diagnostic & therapeutic radiology centres, etc.
Qualified electronic Engineers (1) / technicians (1 or 2) with knowledge of analog and digital electronics and familiarity with SMD devices are required.
