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ORIGINAL ARTICLE
Year : 2021  |  Volume : 44  |  Issue : 1  |  Page : 19-21  

Development of a desktop radiation monitoring system


1 Radiation Safety Systems Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
2 Health Physics Division, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
3 Department of Physics, Nowrosjee Wadia College, Pune, Maharashtra, India

Date of Submission08-Mar-2021
Date of Decision15-Mar-2021
Date of Acceptance16-Mar-2021
Date of Web Publication07-Jun-2021

Correspondence Address:
Vaishali M Thakur
Radiation Safety Systems Division, Bhabha Atomic Research Centre, Trombay, Mumbai - 000 085, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/rpe.rpe_6_21

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  Abstract 


This article presents the design and development of a digital desktop gamma radiation monitoring system using Geiger–Muller tube detector and microcontroller. The radiation detector, battery, signal processing circuits, and the microcontroller board are housed inside a tabletop wooden model with an analog watch and a digital display of radiation dose rate. The alarm level has been set at 1 μSv/h and indicated through buzzer and LED. The system has been calibrated using 137Cs standard source and has a sensitivity of 0.7364 cps/μSv/h. This model can be displayed on any table/desk or kept near a doorway to continuously monitor background radiation level, without drawing public attention, to detect any movement or presence of radiation source.

Keywords: D values, gamma radiation, Geiger–Muller tube, radiation monitor


How to cite this article:
Thakur VM, Jain A, Sawant P, Ashokkumar P, Chaudhari L M, Chaudhury P. Development of a desktop radiation monitoring system. Radiat Prot Environ 2021;44:19-21

How to cite this URL:
Thakur VM, Jain A, Sawant P, Ashokkumar P, Chaudhari L M, Chaudhury P. Development of a desktop radiation monitoring system. Radiat Prot Environ [serial online] 2021 [cited 2021 Jun 24];44:19-21. Available from: https://www.rpe.org.in/text.asp?2021/44/1/19/317951




  Introduction Top


The use of radioactive sources in various fields is increasing and so the number of people handling these sources is also increased. Radioactive materials in the form of sealed sources are used for applications in industry, medicine, research, and in a number of consumer products on sale to the general public. They are used in varying magnitude and activity levels for radiography, sterilization units, radiotherapy, nuclear medicine, well logging, nucleonic gauges, and consumer products such as smoke detectors. There is a potential of these radioactive sources reaching to the hands of radical elements with failure of security control leading to the unacceptable malevolent activities and thereby unrest in the society. Preventing nonstate actors from using nuclear or radiological material to carry out malicious act in the country is a top national priority. Many sophisticated handheld radiation detection systems are commercially available for detection of suspected radioactive materials[1],[2],[3] and also installed radiation portal monitors are an important means of detecting illicit transportation of radioactive materials. This article describes the development of desktop radiation monitors. It is an innovative development to carry out radiological surveillance at vulnerable locations without drawing the attention. Desktop radiation monitor is a gamma radiation monitor which is low cost, reliable, compact, and with minimum electronics.


  Materials and Methods Top


The system consists of Geiger–Muller (GM) tube, high-voltage (HV) generator, pulse processing circuit, microcontroller module, liquid crystal display (LCD), a buzzer, and a LED indicator. An in-house developed HV (500V) board is used to bias the GM tube. Stable HV is generated without transformers or voltage multipliers using an inductor, a switch transistor, a rectifier, and a reservoir capacitor in the circuit. The output voltage is directly proportional to the peak inductor current and is independent of the battery voltage. It converts the peak inductor current to output voltage in a ratio that depends only on the inductor and the associated capacitance.

Signals from detector are converted to Transistor Transistor Logic (TTL) pulses by the following processing electronics circuit using OPAMP. These TTL pulses are counted using Philips P89 LPC917 microcontroller module. The system's electronics is wired on one-layer printed circuit board of 5 cm × 5 cm. The complete electronics along with the detector has been enclosed inside a wooden model having a front panel with commercially available analog watch and LCD display, as shown in [Figure 1].
Figure 1: Desktop radiation monitoring system housing Geiger–Muller detector and associated electronics

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The microcontroller's program memory of 2 kilobyte was used to burn embedded software. The software was developed in the Keil environment using assembly language. The block diagram for the system is given in [Figure 2].
Figure 2: Block diagram of the Geiger–Muller-based desktop radiation monitoring system

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GM detector LND 713 has a sensitivity factor of 0.75 cps/μSv/h;[4] therefore, the counting time has been set as 25 s for radiation dose rate <1 μSv/h. Above this radiation level, the acquisition will be automatically set at multiple of second to obtain a faster response for sources of threat potential. The average value of the last acquired five count data is used to arrive at the dose rate value at dose rate <1 μSv/h. If the radiation dose rate at the vicinity of the detector crosses the set alarm level, the microcontroller activates LED and buzzer. The audio/visual alarm is inactive for a dose rate of ≤1 μSv/h. For the dose rate ≤1 μSv/h, system's response time is 25 s averaged over 125 s. With the change in radiological status below the set alarm level, system's response time is 125 s. The response time of the system is between 1 and 20 s for a dose rate 1 μSv/h and above. Once the alarm is set, actual dose rate is displayed on LCD and each reading is the current status of last data acquired. System's specifications are given in [Table 1].
Table 1: Specifications of desktop radiation monitor

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  Results and Discussion Top


The system was calibrated using 137Cs standard gamma source by exposing to different dose rates using the standard radiation calibration facility available at Bhabha Atomic Research Center. The system was tested from 0.5 μSv/h to 10,000 μSv/h and the response is linear. It may be noted that the observed behavior of the system matches with the gamma sensitivity specified by the manufacture.[4] A sensitivity factor of 0.7364 CPS/μSv/h was observed [Figure 3].
Figure 3: The observed sensitivity of the system

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This factor has been utilized to convert the counts to dose rate. The system is powered using a 4000 mAh rechargeable battery housed in the system. For <1.0 μSv/h dose rate, the system can work uninterrupted over a week and to be recharged once in a week. The analog watch runs on a separate cell.

Radioactive sources of varying strength are extensively used for the benefits of humankind. Their categorization is based on the concept of “dangerous sources” which are quantified in terms of “D values.”[5] A D-value is the quantity of radioactive material which is considered a dangerous source. A dangerous source is one that, if uncontrolled, could result in death or a permanent injury which decreases that person's quality of life. The detection levels of the system for certain radionuclides, namely 60Co, 137Cs, 192Ir, 226Ra, and 131I (unshielded at 1 m distance) which are used in industrial and medical applications such as radiography and Brachy-therapy are given in [Table 2] along with typical activity for the specific application and its D-value. It may be noted that the present system can detect much lower activity levels compared to the D-values. For example, the system will give an alarm if 4.48 MBq of 192Ir is brought within 1 m vicinity and its D-value is 0.08 TBq.
Table 2: The detection level of the system (unshielded at 1 m) for certain common radionuclides

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  Conclusions Top


A dual-purpose GM-based gamma monitor has been developed. We have fabricated 25 such systems in different models and distributed them among various offices. This system would simultaneously serve as a display of radiation dose rate at places surrounding it such as reception counter, VIP lounge, security, or customs desk. Such systems deployed in large numbers at public places can be utilized for the detection of radioactive sources and also serve as an efficient technical means to counter radiological terrorist threats and prevention of other activities such as illegal possession, transfer, and trafficking of radioactive substances and materials.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
User's manual “IdentiFINDER-Ultra”, ICx Radiation (formerly target system electronic gmbh), publication number 1.1, 2005.  Back to cited text no. 1
    
2.
Rosenstock R, Berky W, Cheml S, Friedrich H, Koble T, Risse M, et al. Handheld devices for detection of clandestine nuclear materials on-site. In: Symposium on International Safeguards: Preparing for Future Verification Challenges. Vienna, Austria: IAEA; 2010.  Back to cited text no. 2
    
3.
Thermo Fisher Scientific Inc. Thermo ELECTRON CORPORATION: RadEye Selection Guide; 2008. Available from: http://www.thermo.com. [Last accessed on 2021 Dec to Jan].  Back to cited text no. 3
    
4.
713 - LND | Nuclear Radiation Detectors (lndinc.com), LND, Inc., 3230 Lawson Blvd., Oceanside, New York, USA 11572. Available from: https://www.lndinc.com/products/geiger-mueller-tubes/713/.  Back to cited text no. 4
    
5.
International Atomic Energy Agency. Categorization of Radioactive Sources. Vienna: IAEA Safety Standards Series No. RS-G-1.9; 2005.  Back to cited text no. 5
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2]



 

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