COMPARISON WITH OTHER DOSIMETERS & DETECTORS

A wide variety of radiation detectors and dosimeters have been developed. Radiation detectors are highly sensitive and can detect very low levels (e.g., a millirad/hour) of radiation, characterize the types of isotopes involved in producing the radiation and determine the radiation dose. These equipment can detect both high- and low-LET radiation. They are compared in Table 1 below.

Table 1: Comparison of different radiation detectors and dosimeters.
 

	Electronic	Quartz	Film	TLD	OSL/Luxel	SIRAD
	(Geiger)	Fiber	(AgBr)			E.g., RADTriage
Approx. price	$100	$50	$100(1)	$100(1)	$100(1)	~$20
Dose range (rad)	NA	0-1,000	0-100	0-1,000	0-1,000	0-1,000
LLD (rad)	Very high	0.1	<0.001	<0.001	0.0001	~ 1(2)
Sensitivity	Most	High	High	High	Very high	Low
Results	Instant	Instant	Days	Days	Days	Instant
Reusable	Yes	Yes	No	Yes	Yes	No
Disposable	--	--	Yes	--	--	Yes
Size	Bulky	Bulky	Small	Small	Small	Smallest
Effect of ambient	NA	NA	Light	Light	NA	UV(3)
Conditions			Heat	Heat		Heat(4)
			Humidity	Humidity	NA	None
Shock	Sturdy	Fragile	Sturdy	Sturdy	Sturdy	Sturdiest
Radiation	X-ray	X-ray	Most	Most	Most	X-ray(4)
Archiving	No	No	Yes	No	Yes	Yes
Shelf life	NA	NA	Month	Months	Months	One year+

TLD = Thermoluminescence Dosimeter.
LLD = Lowest Limit of Detection.
OSL = Optically Stimulated Luminescence.
Luxel = Registered trademark of Landauer Inc.
(1) The price includes logistic costs including analysis service by supplier.
(2) One rad can be visually noticed and lower dose can be monitored with a spectrophotometer.
(3) Negligible effect with black protective cover.
(4) SIRAD can monitor very high energy (~1 MeV) electrons

SIRAD badge can’t be used for detecting/monitoring low dose (below one rad) of radiation. Low dose/level of x-ray is monitored with Geiger-Muller type and other counters and dose is monitored by badges, such as silver halide X-ray film, OSL (optically simulated luminescence) and TLD (Thermo Luminescence) dosimeters. Radiation detectors are expensive and bulky. Film, OSL and TLD dosimeters have capability of monitoring one millirad (0.001 rad) dose while SIRAD’s lowest detection limit is about a few rads. The film, OSL and TLD dosimeters are not instant and they need to be sent to an analytical laboratory for their analysis. SIRAD is light weight and instant. SIRAD is a casualty dosimeter for monitoring 1-1,000 rads. In an event of dirty bomb detonation and nuclear accident, one needs to monitor this dose range as soon as possible. As can be seen from the table above, SIRAD is ideal for a high range of doses at a very low cost. Some widely used radiation detectors and dosimeters are outlined below:

RADIATION DOSIMETERS

A. ACTIVE MONITORING
A.1 Electronic Dosimeters:

• Examples: Geiger-Muller or semiconductor detector
• Detection: Detect x-rays and gamma radiation
• Properties: Relatively expensive, usually quite rugged, reusable

A.2 Quartz Fiber Electroscope (QFE):

• Consist of a small ionization chamber and quartz fiber
• Radiation change the deflects the quartz fiber
• Deflection is displayed in the eyepiece lens
• Major disadvantage: Easily damaged if dropped or roughly handled.

B. PASSIVE MONITORING
B.1 Film Dosimeters/Badges

• Used as a personal dosimeter
• Use highly sensitivity silver halide film
• Fitted with a range of filters
• Distinguish beta, x-ray, gamma and thermal neutrons
• Dose is determined by degree of blackening (optical density) and comparing it with calibrated films
• Provides permanent record of an individual’s dose
• Adverse effects of light and heat
• Relatively short shelf life (months)
• Require dark room facilities (development chemicals)
• Significant manual handling during assessment

B.2 Thermoluminescent Dosimeters (TLDs)

• Used as personal and environmental dosimeter
• Use Thermo-Luminescent (TL) materials
• Electrons are raised/trapped at higher energy levels
• The energy is released as light when heated
• Light emitted is converted into an electrical signal
• Light emitted is proportional to incident radiation
• Lithium (LiF:Mn) based TLDs for personal dosimetry: Because they are tissue-equivalent
• Calcium (CaF₂:Dy, CaSO₄:Dy) based TLDs for environmental monitoring: due to their high sensitivity
• Lithium borate (Li₂B₄O₇:Mn) TLDs for high dose range dosimetry
• TL materials are available in many different forms: e.g. powder, hot pressed chips, pellets, impregnated Teflon disks 
• Read-out instrument (reader):are required
• Method to heat the TLD material: Electrical, hot gas or a radiofrequency heater, Heated in an inert gas during read-out
• Device to convert the light output to an electrical pulse
• Light signal is amplified using a photomultiplier (PM)
• Small size (only milligram quantities of TL material is needed)
• TLDs can be reused

Disadvantages of TLDs

• Only one time reading during heating, cannot be repeated
• Subject to fading (due to temperature or light effects)

B.3 Nuclear emulsion or track etch dosimeters

• Neutron dosimetry and alpha particles (e.g., from radon)

For additional information visit the following websites
http://www.cs.nsw.gov.au/rpa/pet/radtraining/radtrainman.shtml 
http://www.cs.nsw.gov.au/rpa/pet/radtraining/PersonalDosimetry.htm