Semi – Automatic TLD Badge Reader

Semi – Automatic TLD Badge Reader [TYPE : TL1010S]

Technical Data
manual

Semi Auto TLD Badge Reader TL1010S is a personal monitoring system, designed to read the TLD card (TL dosimeters) worn by radiation workers.

This Semi Auto TLD Badge Reader system is designed using state of art electronics, improvised electro-mechanical system, embedded code and software to load and read the TLD cards for TL glow curve / dose. System facilitates entry of ID number for the person and his dose record and glow curve can be stored in the system. TL dosimeter is heated by hot gas (N2) jet to 280°C using a SS heater assembly & TL output is recorded using PMT where integral of the current output is proportional to the dose.

It is a Thermoluminescent dosimeter based personnel monitoring system. Thermoluminescent dosimeters make use of the property of certain materials which absorb energy when exposed to X, Gamma or Beta radiation. On heating, the absorbed energy is released in the form of visible light. A plot of light intensity emitted against temperature is known as a glow curve. For a given heating rate, the temperature at which the maximum light emission occurs, is called the glow-peak temperature and it is characteristic, of the individual TL material (also called phosphor).

The quantity of the visible light emitted (TL output) is found to be proportional to the energy absorbed by the TL material.

The TLD personnel monitoring system essentially consists of two major parts: TLD badge and the TLD badge reader.

The TLD Badge Reader comprises of a plastic cassette containing three Teflon TLD discs (13.3mm and 0.8mm thick) that are mechanically clipped on to circular holes (12.0mm) punched in an aluminium card (52 x 30 x 1mm).

The TLD Badge Reader is designed to measure X, Gamma and Beta radiation dose. The metal filter combination (1mm Al + 0.9mm Cu) is provided to reduce the photon energy dependence of the TL discs. The TL badge reader is calibrated such that the TL output of the disc under the metallic filter reads directly the gamma radiation dose.

Features
A. HARDWARE SPECIFICATIONS
Dosimeter : Three-element BARC CaSO4 (Dy) PTFE disc dosimeter badge.
Light Measurement System : Photo-multiplier tube (R6094 or its equivalent) bialkali Light measuring system (LMS). The I-F converter linearity is better than 100μA.
Dark current : Dark current is 1 µSv (CaSO4) equivalent with software-based sampling & subtraction.
Heater Element : Nichrome wire heater assembly.
Heating Method : Hot gas (N2) heating.
Nitrogen flow rate measurement : Digital flow rate meter.
Heating Cycle : The temperature is raised to 280°C in 8 sec and clamped at 280°C
Dose Range : Reader is capable of reading badges from 50 μSv to 2.0Sv automatically and the dose response is linear over the entire range.
50μSv – 10Sv (Gamma) and 100μSv – 10Sv (Beta).
Dose Threshold : <50 µSv.
Readout time : 100 sec. per badge.
Residual Signal : 8 to 12% of initial TL in the linear dose range specified.
Light source : Temperature stabilized LED light source or Ni63 based light source card is provided for PMT check & gain adjust.
Flow Rate Measurement : A digital flow measurement system is provided for flow rate measurement & failure check.
Facilities Available : Entry of personnel for badges editing of calibration factor etc. Storage of dose and glow curve data of badges in database. Stepper motor based drive assembly is provided for magazine & TLD card transport in a magazine. Digital linear actuators are used for TLD card raise & shutter control.
Software : Win 7 compatible software developed on .net platform for storage of readings in a database and display of glow curves, computations of dose & generation of dose reports.
Temperature Monitoring : Two Chromel Alumel thermocouples in hot gas stream, one called ‘Heater Thermocouple’ inside heater & the second called ‘Air Thermocouple’, in hot gas stream.
Range Selection : Auto-changeover.
Calibration : Coarse adjustment by varying the EHT through a potentiometer in the EHT circuit; fine through software.
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.
Mechanical Failure : Any mechanical failure during readout cycle is sensed by the programme and the cycle is terminated with an option for the user to restart the cycle. EHT & input circuit (I-F converter) are also sensed and reading cycle is terminated in case of failure.
Nominal Power Supply : Power supply : 230V, 50Hz : +/-10%
Power requirements: 500 VA (max including PC).
PC Requirements: Suitable latest PC configuration with win 7 Operating system or as requested.
Applications: Personnel Monitoring of radiation workers in Nuclear power stations, Isotope laboratories, Industrial radiography installations, diagnostic & therapeutic radiology centres, etc.
Suggested spares:
Additional Accessories / Items Required for personnel monitoring TLD Lab

(i) Three element (BARC Developed) CaSO4 (Dy) PTFE disc dosimeter badges.

(ii) Cassette holder.

(iii) Annealing oven.

(iv) Nitrogen cylinder / Generator with regulator.

(v) Radioactive source exposure device for TLD cards calibration.

(vi) Light Source Card.

Note: Manufactured by NUCLEONIX SYSTEMS based on Technology from Bhabha Atomic Research Center, Mumbai.

B. SOFTWARE FOR TLD BADGE READER

The software for TL Badge reader serves as comprehensive ‘TL Dose records management software’. It is user-friendly, reliable and feature rich. It has powerful fault diagnostics reporting capabilities.

Key features of Software:
C. ACCESSORIES
(i) HOT AIR ANNEALING OVEN

In Hot Air Annealing oven there is one path of circulating Hot Air in between the inner chamber and insulation. Forced Air Moved by the motorised blower is called Perfect System. It result minimum temperature variation at any point in working space. Temperature controlled by PID type Digital controller cum indicator with safety alarm from room temperature to 350/4000 C with a sensitivity of +/- 10 C cr better in Bare Oven. Working chamber is made of stainless steel and outside made of mild steel painted with good stoving enemel with adjustable trays. To work on 220 /230 volts A.C single phase supply.

Specifications
Working Chamber size : 14” x 14” x 14” (Appox) ; Litres :43.
No. of trays : Two
Heaters: 80/200 Nichrome elements.
Working Temperature : From ambient to 3500 C/4000 C.
Temperture Accuracy : + / -1 0 C , in bare oven.
Temperture Indication & Control : Tempreture controlled by PID type digital controller cum indicator with safety alarm.
Digital timer : Digital timer of (0-99) Hrs can be set.
Air circulation System : For maximum uniformity of temperature inside the working chamber ,air circulating system is provided by means of a meter driven fan
Heaters : Heaters are made out of best quality Nichrome Wire insulated with refractory runners and enclosed in stainless sheet and fitted to the sides of the Oven.
Cinstruction of Oven Body:
Interior : Polised stainless steel 304/ Anodizwd Aluminum / SS.316 (GMP Model).
Exterior : Heavy gauge Mild steel / SS304 (GMP model).
Chamber : Double Walled.
Ventillation : Air Ventilators are provided near the top of the sides for removing hot gases and fumes.
Insulation: 75mm thick Mineralwool.
Shelves : sturedy Elegant –fabricated precisely to give minimum resistancs to air circulation.
Finish : Finished with attractive and durable powder coated in pleasant shade.
Door: an insulated hinged side swinging type double walled door with asbestos gasket , ball catch lock and handle provided for easy and effortless closing & opening of door.
Insulation: High grade ceramic fibre blanket insulation is provided on all the six sides of the Oven Power Rating:2.5 K.W.
Input Supply : Single phase AC, 230 Volts.
( ii) TLD CARD

In Hot Air Annealing oven there is one path of circulating Hot Air in between the inner chamber and insulation. Forced Air Moved by the motorised blower is called Perfect System. It result minimum temperature variation at any point in working space. Temperature controlled by PID type Digital controller cum indicator with safety alarm from room temperature to 350/4000 C with a sensitivity of +/- 10 C cr better in Bare Oven. Working chamber is made of stainless steel and outside made of mild steel painted with good stoving enemel with adjustable trays. To work on 220 /230 volts A.C single phase supply.

Characteristics of CaSO4 : Dy Teflon TLD disc
Ratio of CaSO4 : Dy and Teflon : 1: 3
Effective Atomic Number (Z) : 15.1
Density of the TLD Disc : 2.52 g/cm3
Softening Point of Teflon : 330o C
Main Glow Peak Temperature : 230o C
Sensitivity of TLD Disc : About 30-40 times more than LiF TLD-100
Fading : 2-3% in six months
Climactic Effect : Negligible
Effect of Sunlight : Negligible when covered by paper wrapper & polythene pouch and loaded in the badge
Useful Linear Dose Range : 0.10 mSV to 20 SV (linearity within + 10%)
Reusability : 20 cycles
Beta Response : 60% of 60Co gammas for Nat.U (effective energy 0.8Mev)
Thermal Neutron Response : 60Co gamma ray equivalent to 2.4 mGy per 1010 n/cm2
Fast Neutron Response : Negligible

( iii ) TLD Cassette

Three well-defined regions in the plastic cassette / holder corresponding to three TLD discs of the TLD card.

i. Disc D1- sandwiched between a pair of filter combination of 1.0mm thick Cu (Copper filter nearer to the disc).
ii. Disc D2- sandwitched between a pair of 1.6mm thick (180mg/cm2) plastic filters and
iii. Disc D3- under a circular open window.

The asymmetric “V” cut of the card permits its loading in the plastic cassette in only one orientation and ensures proper positioning of three disc.

There are two types of TLD badges/ cassettes in use namely
1. Chest Badge for whole body monitoring and
2. Wrist Badge for extremity dosimetry

Though the dosimeter and design of both TLD badges are same, they have different attachment (clip/strap) for wearing purpose depending on their use.

TLD CASSETTE DIMENSIONS

In this design of the TLD cassette, dimension of some of the filters was altered and crocodile clip was replaced by a smaller size clip. The cassette was made of ABS plastic (white) and filters were embedded into the plastic body.