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Performance testing of selected types of electronic personal dosimeters used in Sudan
Radiation Measurements 45 (2010) 1582e1584
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Performance testing of selected types of electronic personal dosimeters used in Sudan I.I. Suliman*,1, E.H. Yousif, A.A. Beineen, B.E. Yousif, M. Hassan Radiation Safety Institute, Sudan Atomic Energy Commission, P.O. Box 3001, Khartoum, Sudan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 November 2009 Received in revised form 5 May 2010 Accepted 21 May 2010
Measurements were carried out for calibration and performance testing of a set of 10 electronic personal dosimeters (EPDs) at the Secondary Standard Dosimetry Laboratory of Sudan. Calibrations were carried out at three X-ray beam qualities described in ISO standard 4037 in addition to 137Cs and 60Co gamma ray beams. The experimental was performed with EPDs mounted on ICRU Slab phantom. X-ray and g-ray beams were characterized in terms of air kerma free-in-air which were converted to the known delivered personal dose equivalent, Hp(10) using appropriate the air kerma to personal dose equivalent conversion coefficients. Dosimeters tested showed excellent energy and angular response and relative error of indication within the recommended limit for photon energies from 65 keV to 1.25 MeV. The study showed encouraging results for using electronic dosimeters in personal dosimetry. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Radiation dosimetry Electronic personal dosimeters Personal dose equivalent
1. Introduction Radiation monitoring of workers to assess exposure due to external sources of radiation and intakes of radionuclides is an essential component of any occupational radiation protection program. In order to limit the risk of adverse health effects, international commission on radiological protection (ICRP) has recommended limits to the annual dose due to occupational exposure to ionizing radiation (ICRP, 1991, 2007). Programs must be in place to monitor the exposure by dosimetry. In order to be an effective tool in limiting the exposure, this dosimetry must comply with adequate quality standards which in general means that dosimeters must be used which are issued by services that are approved by the relevant authorities. On the other hand and for radiation monitoring instrument, it’s important to have performance test being carried out to assess whether the dosimeter performs adequately and thus suitable for its intended use. Periodic calibration furthermore ensures the traceability of chain of measurements to the international measurement system. This study was initiated with objectives of calibration and performance testing of selected types electronic personal dosimeters currently used in Sudan. It is anticipated that performance testing will provide means for quality assurance of EPDs and therefore improve the accuracy required for effective personal
* Corresponding author. Tel.: þ249(0)9 15091631. E-mail address: [email protected] (I.I. Suliman). 1 Regular Associate, ICTP. 1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2010.05.032
dosimetry. Electronic personal dosimeters (EPD) based on miniature GM counters or silicon Detectors are available with the measurement range down to 30 keV photon energy and are very useful at the emergency situation for immediate read out of the doses received by workers. 2. Materials and methods Measurements were carried out for performance testing of ten electronic personal dosimeters representing two kinds of EPDs commonly used in Sudan. The experimental was carried out at the Secondary Standard Dosimetry Laboratory of Sudan. Parameters tested included: EPD relative error of indication, energy and angular response. Six EPDs were of type Rad 60s (Rados, Turku, Finland) whereas four EPDs were of type Graetz 150 (GRAETZ GmbH, Altena , Germany). Main specifications of these EPDs are presented in Table 1. 2.1. The laboratory and the irradiation facilities Dosimeter irradiations and measurements were performed at the Secondary Standard Dosimetry Laboratory (SSDL) of the Sudan Atomic Energy Commission. Beam conditions and characteristics follow the international standard ISO 4037 for photon reference radiation (ISO,1996). Radiation qualities used were the narrow X-ray series N80, N120, N150 in addition to gamma rays from 137Cs and 60 Co with energies of 65, 100, 118, 662 and 1250 keV, respectively. The air kerma rate were between 1 mGy/h and few mGy/h at the reference point of calibration. The X-ray beam were generated by a Pantak HF 60 power supply unit and a Phillips X-ray tube with an
I.I. Suliman et al. / Radiation Measurements 45 (2010) 1582e1584 Table 1 Characteristics of electronic personal dosimeters. Parameter
RADOS-60
Graetz ED 150
N Detector Measurement Range Energy Response Dose Rate Dose Rate Linearity Weight (g) Size (mm) Country of origin
6 Si-Diode Hp (10):1 mSve10 Sv Better than 25% 5 mSv/he3 Sv/h Better than 15% up to 3 Sv/h 80 78 67 22 Finland
4 GM tube Hp (10):0,1 mSve10 Sv 55 keVe3 MeV 1 mSv/he1,5 Sv/h NA 160 36 40 17 Germany
equivalent window of 7 mm Be. The 137Cs g-ray beam was produced by Bucher OB 85 gamma irradiator. This is a collimated beam with field diameter of 50 cm at a reference calibration distance of 2 m. A set of lead attenuators are placed at the exit window of the irradiator to vary the air kerma rate that is required cover the instrument scale. Radiation doses were measured using 0.6 cc Farmer type ionization chamber model PTW 3001 connected to UNIDOS universal dosimeter (PTW, Freigburg, Germany). This chamber was calibrated by the manufacture with its calibration traceable to the German Standard Laboratory (PTB). The quality of the dosimetry system was maintained by performing stability test using radioactive check source measurements on regular basis. ICRU slab phantom was used for the experiment. This is 30 30 15 cm3 made of Polymethyl methacrylate (PMMA) and represents the human torso. 2.2. Measurements of personal dose equivalent, Hp(10) The X-ray and g-ray beams used here were characterized in terms of air kerma free-in-air. Both the International Electrotechnical Commission (IEC) and the International Atomic Energy Agency (IAEA) recommend that personal dosimeters be calibrated in terms of the personal dose equivalent, Hp(d) (IEC, 1998; IAEA, 2000). Hp(d) is defined as a dose equivalent in soft tissue bellow specified point in the body at a depth, d mm, where d ¼ 10 mm for strongly penetrating radiation and d ¼ 0.07 mm for weakly penetrating radiation . An assessment of Hp(10) is meant to give a reasonable estimate of the limiting radiation protection quantity effective dose from penetrating external radiation (IEC, 1998). Air kerma values in this study were converted to the known delivered personal dose equivalent using the air kerma free-in-air to personal dose equivalent conversion coefficients given in ICRU Report 57 (ICRU, 1998). To investigate energy and angular response, EPDs were fixed at the center of ICRU slab phantom and exposed to a nominal personal dose equivalent Hp(10).
(20 þ x) % where x is the uncertainty of the conventional true value of the dose equivalent (x must not exceed 10%). Thus, I must not exceed 25% assuming maximum allowable uncertainty for the conventional true value of the dose equivalent (IEC, 1998). 2.4. Variation of dosimeter response with radiation energy and angle of incident Electronic dosimeters were placed on ICRU slab phantom and irradiated with photon energies 65, 100, 118 keV X-rays in addition to 662 and 1250 keV gamma rays from 137Cs and 60Co sources, respectively. These energies were selected from the list of photon reference radiation specified in the international standard ISO 4037 for narrow beam air kerma rate series. The response of the dosimeter is the ratio of the dosimeter’s indicated value, Hi to the conventional true value, Ht
R ¼
(2)
3. Result and discussion 3.1. Relative error of indication Relative error of indications was determined for EPDs included in the study according to formula (1). All dosimeters showed relative error of indications that were far less than 30% acceptable deviation given by IEC (1998). However, the error of indications was 1.2
1.1
(1)
For dosimeters irradiated with 137Cs reference source, IEC recommend that the relative error of indication, I, should not exceed
Normalised response
The electronic dosimeters were attached in this study to the PMMA slab phantom at phantom’s center in the direction of the beam and irradiated to a nominal personal dose equivalent rate at calibration distance of 2 m. The distance was such that the radiation beam covers the entire phantom. Dosimeters were irradiated with 137Cs reference source as recommended in international standards (ISO, 1999; IEC, 1998). The relative error of indication, I is the quotient of error of indication of a measured quantity, Hi by the conventional true value, Ht of that measured quantity. It can be expressed as a percentage:
ðHi Ht Þ 100 Ht
Hi Ht
IEC recommend that the response for Hp (10) in the calibration direction to incident radiation shall not differ by more than 30% from the response to 137Cs (662 keV) reference gamma radiation (IEC, 1998). The relative energy response is determined by normalized to that of standard 137Cs beam quality given as: Rr ¼ RQ =RCs where RQ is the response of EPD at a particular beam quality Q and RCs is the response of EPD at a standard 137Cs beam quality. For testing angular response, dosimeters were placed on ICRU slab phantom in its normal position of use, with the source of radiation in the reference direction for calibration purposes specified by the manufacturer. The reading in this position was noted. For horizontal plane, the dosimeter and the phantom were rated to angles of þ20 , 20 , þ40 , 40 , þ60 , 60 . The dosimeter readings were taken at all these orientations. According to IEC the ratio of the dosimeter Hp (10) readings at a relative to the reading at a ¼ 0 for angles þ60 , 60 shall be within 20% of ratios given in IEC (1998).
2.3. Determination of relative error of indication
I% ¼
1583
1.0
0.9
Rad 60s Graetz 150
0.8
0.7
0.6
0.5 0
100
200
300
400
500
600
700
Energy (keV) Fig. 1. Normalized mean energy response for Rad 60s and Graetz EPDs.
1584
I.I. Suliman et al. / Radiation Measurements 45 (2010) 1582e1584
Table 2 Variation of energy response with angle of radiation incident. EPDs
Rad 60s (n ¼ 6)
Graetz (n ¼ 4)
Radiation quality (keV) Angle
1250
0 20 40 60 0 20 40 60
0.97 0.92 0.93 0.95 1.12 1.12 1.11 1.13
0.12 0.09 0.14 0.25 0.11 0.08 0.23 0.04
662 0.99 0.94 0.96 1.00 1.04 0.96 0.97 1.02
not determined for the whole instrument scale due to the low output at distance greater than 2 m. At these distances, an EPD would require more than half an hour to deliver air kerma of few mGy. 3.2. Energy and angular response Fig. 1 gives the response of the tested EPDs to photon energies of 65, 100,118 keV X-rays, 662 keV. It can be seen from the figures that all EPDs showed similar response for the same radiation quality. However, relative response was slightly different from that of the 137Cs beam, in particular the response for the lower photon energies but still within the recommended acceptable limit (IEC, 1998). The high response for 65e100 keV could be due to the fact that photo electric absorption is the predominant interaction mechanism. Study in Tanzania showed similar increase of the response at lower energies for LiF:Mn,Cu,P but for X-ray qualities used for diagnostic radiology (Muhogora et al., 2000). Study in Greece showed that the response of EPDs type Rad 60s decreases significantly for photon energies below 65 keV (Boziari and Hourdakis, 2006). Texier et al. (2001) in France reported the response of each EPD as a function of the energy, normalized at 662 keV. The standard deviation in that study was of the order of 2% for all experimental points. It was observed that below 50 keV the response of the majority of the dosemeters falls sharply and does not meet the standard required limits of 30%. Table 2 shows the variation of energy response with angle of radiation incidence for the tested EPDs. As it can be seen from the Table, dosimeters tested showed excellent angular response for fore the entire photon energies (65 keVe1.25 MeV) which was within 20% limit recommended by IEC (1998). The variation of energy response with angle of incident was not that large indicating an outstanding energy and angular response for the investigated dosimeters. The excellent energy and angular response for the studied EPDs suggest that electronic active dosimeters will compete favorably with their counterpart active dosimeters. 4. Conclusions Electronic personal dosimeters are important in radiation protection monitoring. The advantages of EPDs over passive dosimeters (TLDs), are mainly related to alarm feature and direct
118 0.19 0.14 0.16 0.21 0.07 0.08 0.06 0.18
1.01 0.75 0.95 1.14 0.94 0.97 1.11 0.95
0.18 0.05 0.18 0.11 0.18 0.16 0.17 0.22
100
65
0.98 0.02 0.73 0.11 0.89 0.08 1.06 0.01 0.83 0.21 0.98 0.05 0.97 0.09 1.1 0.07
1.35 0.74 0.96 1.26 0.77 1.16 0.85 0.92
0.08 0.18 0.16 0.20 0.11 0.24 0.12 0.21
reading. There is also good agreement on calibration procedures. Even though, greater efforts are needed to gather and analyze experience of different types of EPDs. The dosimeters tested in this study demonstrated encouraging results with regard to energy and angular response. This information can be of great importance for improvement in personal dosimetry standards. Acknowledgements The authors are grateful to the organizing committee of the 11th Neutron and Ion Beam Dosimetry Symposium (Neudos11) for sponsoring the first author (I.I. Suliman) to attend the conference and present this work. The authors are grateful to the Abdu Salam International Centre for Theoretical physics (ICTP) for sponsoring the first author (I.I. Suliman) in residence as an associate during the writing process of this article. References Boziari, A., Hourdakis, C.J., 2006. Calibration, performance and type testing of personal dosemeters used in ionising-radiation applications in Greece. Radiation Protection Dosimetry 125 (1e4), 79e83. IAEA, 2000. Calibration of radiation protection monitoring instrument. In: IAEA Safety Report Series. No. 16. IAEA, Vienna. ICRP, 1991. 1990 Recommendations of the international commission on radiological protection. ICRP Publication 60. Annals of the ICRP 21 (1e3). ICRP, 2007. Publication 103: recommendations of the international commission on radiological protection. Annals of the ICRP 37/2e4. ICRU (International Commission on Radiation Units and Measurements), 1998. Conversion Coefficients for use in Radiological Protection against External. ICRU Report 57. ICRU, Bethesda. IEC (International Electrotechnical Commission), 1998. IEC 61526:1998. Radiation protection instrumentation. Measurement of personal dose equivalents Hp(10) and Hp(0,07) for X, gamma and beta radiations. Direct reading personal dose equivalent and/or dose equivalent rate dosimeters. ISO (International Organisation for Standardisation), 1996. ISO 4037-1:1996. X and gamma reference radiation for calibrating dosimeters and doserate meters and for determining their response as a function of photon energy d Part 1: Radiation characteristics and production methods. ISO (International Standardization Organization), 1999. ISO 4037-3:1999. X and gamma reference radiation for calibrating dosimeters and dose rate meters and for determining their response as a function of photon energy d Part 3: Calibration of area and personal dosimeters and the measurement of their response as a function of energy and angle of incidence. Muhogora, W.E., Ngoye, W.N., Lema, U.S., Mwalongo, D., 2000. Energy response of LiF: Mg, Ti dosimeters to ISO 4037 and typical diagnostic x-ray beams in Tanzania. Journal of Radiological Protection 22, 175e184. Texier, C., Itié, C., Servièré, H., Gressier, V., Bolognese-Milsztajn, T., 2001. Study of the photon radiation performance of electronic personal dosemeters. Radiation Protection Dosimetry 96 (1e3), 245e249.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Performance testing of selected types of electronic personal dosimeters used in Sudan I.I. Suliman*,1, E.H. Yousif, A.A. Beineen, B.E. Yousif, M. Hassan Radiation Safety Institute, Sudan Atomic Energy Commission, P.O. Box 3001, Khartoum, Sudan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 November 2009 Received in revised form 5 May 2010 Accepted 21 May 2010
Measurements were carried out for calibration and performance testing of a set of 10 electronic personal dosimeters (EPDs) at the Secondary Standard Dosimetry Laboratory of Sudan. Calibrations were carried out at three X-ray beam qualities described in ISO standard 4037 in addition to 137Cs and 60Co gamma ray beams. The experimental was performed with EPDs mounted on ICRU Slab phantom. X-ray and g-ray beams were characterized in terms of air kerma free-in-air which were converted to the known delivered personal dose equivalent, Hp(10) using appropriate the air kerma to personal dose equivalent conversion coefficients. Dosimeters tested showed excellent energy and angular response and relative error of indication within the recommended limit for photon energies from 65 keV to 1.25 MeV. The study showed encouraging results for using electronic dosimeters in personal dosimetry. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: Radiation dosimetry Electronic personal dosimeters Personal dose equivalent
1. Introduction Radiation monitoring of workers to assess exposure due to external sources of radiation and intakes of radionuclides is an essential component of any occupational radiation protection program. In order to limit the risk of adverse health effects, international commission on radiological protection (ICRP) has recommended limits to the annual dose due to occupational exposure to ionizing radiation (ICRP, 1991, 2007). Programs must be in place to monitor the exposure by dosimetry. In order to be an effective tool in limiting the exposure, this dosimetry must comply with adequate quality standards which in general means that dosimeters must be used which are issued by services that are approved by the relevant authorities. On the other hand and for radiation monitoring instrument, it’s important to have performance test being carried out to assess whether the dosimeter performs adequately and thus suitable for its intended use. Periodic calibration furthermore ensures the traceability of chain of measurements to the international measurement system. This study was initiated with objectives of calibration and performance testing of selected types electronic personal dosimeters currently used in Sudan. It is anticipated that performance testing will provide means for quality assurance of EPDs and therefore improve the accuracy required for effective personal
* Corresponding author. Tel.: þ249(0)9 15091631. E-mail address: [email protected] (I.I. Suliman). 1 Regular Associate, ICTP. 1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2010.05.032
dosimetry. Electronic personal dosimeters (EPD) based on miniature GM counters or silicon Detectors are available with the measurement range down to 30 keV photon energy and are very useful at the emergency situation for immediate read out of the doses received by workers. 2. Materials and methods Measurements were carried out for performance testing of ten electronic personal dosimeters representing two kinds of EPDs commonly used in Sudan. The experimental was carried out at the Secondary Standard Dosimetry Laboratory of Sudan. Parameters tested included: EPD relative error of indication, energy and angular response. Six EPDs were of type Rad 60s (Rados, Turku, Finland) whereas four EPDs were of type Graetz 150 (GRAETZ GmbH, Altena , Germany). Main specifications of these EPDs are presented in Table 1. 2.1. The laboratory and the irradiation facilities Dosimeter irradiations and measurements were performed at the Secondary Standard Dosimetry Laboratory (SSDL) of the Sudan Atomic Energy Commission. Beam conditions and characteristics follow the international standard ISO 4037 for photon reference radiation (ISO,1996). Radiation qualities used were the narrow X-ray series N80, N120, N150 in addition to gamma rays from 137Cs and 60 Co with energies of 65, 100, 118, 662 and 1250 keV, respectively. The air kerma rate were between 1 mGy/h and few mGy/h at the reference point of calibration. The X-ray beam were generated by a Pantak HF 60 power supply unit and a Phillips X-ray tube with an
I.I. Suliman et al. / Radiation Measurements 45 (2010) 1582e1584 Table 1 Characteristics of electronic personal dosimeters. Parameter
RADOS-60
Graetz ED 150
N Detector Measurement Range Energy Response Dose Rate Dose Rate Linearity Weight (g) Size (mm) Country of origin
6 Si-Diode Hp (10):1 mSve10 Sv Better than 25% 5 mSv/he3 Sv/h Better than 15% up to 3 Sv/h 80 78 67 22 Finland
4 GM tube Hp (10):0,1 mSve10 Sv 55 keVe3 MeV 1 mSv/he1,5 Sv/h NA 160 36 40 17 Germany
equivalent window of 7 mm Be. The 137Cs g-ray beam was produced by Bucher OB 85 gamma irradiator. This is a collimated beam with field diameter of 50 cm at a reference calibration distance of 2 m. A set of lead attenuators are placed at the exit window of the irradiator to vary the air kerma rate that is required cover the instrument scale. Radiation doses were measured using 0.6 cc Farmer type ionization chamber model PTW 3001 connected to UNIDOS universal dosimeter (PTW, Freigburg, Germany). This chamber was calibrated by the manufacture with its calibration traceable to the German Standard Laboratory (PTB). The quality of the dosimetry system was maintained by performing stability test using radioactive check source measurements on regular basis. ICRU slab phantom was used for the experiment. This is 30 30 15 cm3 made of Polymethyl methacrylate (PMMA) and represents the human torso. 2.2. Measurements of personal dose equivalent, Hp(10) The X-ray and g-ray beams used here were characterized in terms of air kerma free-in-air. Both the International Electrotechnical Commission (IEC) and the International Atomic Energy Agency (IAEA) recommend that personal dosimeters be calibrated in terms of the personal dose equivalent, Hp(d) (IEC, 1998; IAEA, 2000). Hp(d) is defined as a dose equivalent in soft tissue bellow specified point in the body at a depth, d mm, where d ¼ 10 mm for strongly penetrating radiation and d ¼ 0.07 mm for weakly penetrating radiation . An assessment of Hp(10) is meant to give a reasonable estimate of the limiting radiation protection quantity effective dose from penetrating external radiation (IEC, 1998). Air kerma values in this study were converted to the known delivered personal dose equivalent using the air kerma free-in-air to personal dose equivalent conversion coefficients given in ICRU Report 57 (ICRU, 1998). To investigate energy and angular response, EPDs were fixed at the center of ICRU slab phantom and exposed to a nominal personal dose equivalent Hp(10).
(20 þ x) % where x is the uncertainty of the conventional true value of the dose equivalent (x must not exceed 10%). Thus, I must not exceed 25% assuming maximum allowable uncertainty for the conventional true value of the dose equivalent (IEC, 1998). 2.4. Variation of dosimeter response with radiation energy and angle of incident Electronic dosimeters were placed on ICRU slab phantom and irradiated with photon energies 65, 100, 118 keV X-rays in addition to 662 and 1250 keV gamma rays from 137Cs and 60Co sources, respectively. These energies were selected from the list of photon reference radiation specified in the international standard ISO 4037 for narrow beam air kerma rate series. The response of the dosimeter is the ratio of the dosimeter’s indicated value, Hi to the conventional true value, Ht
R ¼
(2)
3. Result and discussion 3.1. Relative error of indication Relative error of indications was determined for EPDs included in the study according to formula (1). All dosimeters showed relative error of indications that were far less than 30% acceptable deviation given by IEC (1998). However, the error of indications was 1.2
1.1
(1)
For dosimeters irradiated with 137Cs reference source, IEC recommend that the relative error of indication, I, should not exceed
Normalised response
The electronic dosimeters were attached in this study to the PMMA slab phantom at phantom’s center in the direction of the beam and irradiated to a nominal personal dose equivalent rate at calibration distance of 2 m. The distance was such that the radiation beam covers the entire phantom. Dosimeters were irradiated with 137Cs reference source as recommended in international standards (ISO, 1999; IEC, 1998). The relative error of indication, I is the quotient of error of indication of a measured quantity, Hi by the conventional true value, Ht of that measured quantity. It can be expressed as a percentage:
ðHi Ht Þ 100 Ht
Hi Ht
IEC recommend that the response for Hp (10) in the calibration direction to incident radiation shall not differ by more than 30% from the response to 137Cs (662 keV) reference gamma radiation (IEC, 1998). The relative energy response is determined by normalized to that of standard 137Cs beam quality given as: Rr ¼ RQ =RCs where RQ is the response of EPD at a particular beam quality Q and RCs is the response of EPD at a standard 137Cs beam quality. For testing angular response, dosimeters were placed on ICRU slab phantom in its normal position of use, with the source of radiation in the reference direction for calibration purposes specified by the manufacturer. The reading in this position was noted. For horizontal plane, the dosimeter and the phantom were rated to angles of þ20 , 20 , þ40 , 40 , þ60 , 60 . The dosimeter readings were taken at all these orientations. According to IEC the ratio of the dosimeter Hp (10) readings at a relative to the reading at a ¼ 0 for angles þ60 , 60 shall be within 20% of ratios given in IEC (1998).
2.3. Determination of relative error of indication
I% ¼
1583
1.0
0.9
Rad 60s Graetz 150
0.8
0.7
0.6
0.5 0
100
200
300
400
500
600
700
Energy (keV) Fig. 1. Normalized mean energy response for Rad 60s and Graetz EPDs.
1584
I.I. Suliman et al. / Radiation Measurements 45 (2010) 1582e1584
Table 2 Variation of energy response with angle of radiation incident. EPDs
Rad 60s (n ¼ 6)
Graetz (n ¼ 4)
Radiation quality (keV) Angle
1250
0 20 40 60 0 20 40 60
0.97 0.92 0.93 0.95 1.12 1.12 1.11 1.13
0.12 0.09 0.14 0.25 0.11 0.08 0.23 0.04
662 0.99 0.94 0.96 1.00 1.04 0.96 0.97 1.02
not determined for the whole instrument scale due to the low output at distance greater than 2 m. At these distances, an EPD would require more than half an hour to deliver air kerma of few mGy. 3.2. Energy and angular response Fig. 1 gives the response of the tested EPDs to photon energies of 65, 100,118 keV X-rays, 662 keV. It can be seen from the figures that all EPDs showed similar response for the same radiation quality. However, relative response was slightly different from that of the 137Cs beam, in particular the response for the lower photon energies but still within the recommended acceptable limit (IEC, 1998). The high response for 65e100 keV could be due to the fact that photo electric absorption is the predominant interaction mechanism. Study in Tanzania showed similar increase of the response at lower energies for LiF:Mn,Cu,P but for X-ray qualities used for diagnostic radiology (Muhogora et al., 2000). Study in Greece showed that the response of EPDs type Rad 60s decreases significantly for photon energies below 65 keV (Boziari and Hourdakis, 2006). Texier et al. (2001) in France reported the response of each EPD as a function of the energy, normalized at 662 keV. The standard deviation in that study was of the order of 2% for all experimental points. It was observed that below 50 keV the response of the majority of the dosemeters falls sharply and does not meet the standard required limits of 30%. Table 2 shows the variation of energy response with angle of radiation incidence for the tested EPDs. As it can be seen from the Table, dosimeters tested showed excellent angular response for fore the entire photon energies (65 keVe1.25 MeV) which was within 20% limit recommended by IEC (1998). The variation of energy response with angle of incident was not that large indicating an outstanding energy and angular response for the investigated dosimeters. The excellent energy and angular response for the studied EPDs suggest that electronic active dosimeters will compete favorably with their counterpart active dosimeters. 4. Conclusions Electronic personal dosimeters are important in radiation protection monitoring. The advantages of EPDs over passive dosimeters (TLDs), are mainly related to alarm feature and direct
118 0.19 0.14 0.16 0.21 0.07 0.08 0.06 0.18
1.01 0.75 0.95 1.14 0.94 0.97 1.11 0.95
0.18 0.05 0.18 0.11 0.18 0.16 0.17 0.22
100
65
0.98 0.02 0.73 0.11 0.89 0.08 1.06 0.01 0.83 0.21 0.98 0.05 0.97 0.09 1.1 0.07
1.35 0.74 0.96 1.26 0.77 1.16 0.85 0.92
0.08 0.18 0.16 0.20 0.11 0.24 0.12 0.21
reading. There is also good agreement on calibration procedures. Even though, greater efforts are needed to gather and analyze experience of different types of EPDs. The dosimeters tested in this study demonstrated encouraging results with regard to energy and angular response. This information can be of great importance for improvement in personal dosimetry standards. Acknowledgements The authors are grateful to the organizing committee of the 11th Neutron and Ion Beam Dosimetry Symposium (Neudos11) for sponsoring the first author (I.I. Suliman) to attend the conference and present this work. The authors are grateful to the Abdu Salam International Centre for Theoretical physics (ICTP) for sponsoring the first author (I.I. Suliman) in residence as an associate during the writing process of this article. References Boziari, A., Hourdakis, C.J., 2006. Calibration, performance and type testing of personal dosemeters used in ionising-radiation applications in Greece. Radiation Protection Dosimetry 125 (1e4), 79e83. IAEA, 2000. Calibration of radiation protection monitoring instrument. In: IAEA Safety Report Series. No. 16. IAEA, Vienna. ICRP, 1991. 1990 Recommendations of the international commission on radiological protection. ICRP Publication 60. Annals of the ICRP 21 (1e3). ICRP, 2007. Publication 103: recommendations of the international commission on radiological protection. Annals of the ICRP 37/2e4. ICRU (International Commission on Radiation Units and Measurements), 1998. Conversion Coefficients for use in Radiological Protection against External. ICRU Report 57. ICRU, Bethesda. IEC (International Electrotechnical Commission), 1998. IEC 61526:1998. Radiation protection instrumentation. Measurement of personal dose equivalents Hp(10) and Hp(0,07) for X, gamma and beta radiations. Direct reading personal dose equivalent and/or dose equivalent rate dosimeters. ISO (International Organisation for Standardisation), 1996. ISO 4037-1:1996. X and gamma reference radiation for calibrating dosimeters and doserate meters and for determining their response as a function of photon energy d Part 1: Radiation characteristics and production methods. ISO (International Standardization Organization), 1999. ISO 4037-3:1999. X and gamma reference radiation for calibrating dosimeters and dose rate meters and for determining their response as a function of photon energy d Part 3: Calibration of area and personal dosimeters and the measurement of their response as a function of energy and angle of incidence. Muhogora, W.E., Ngoye, W.N., Lema, U.S., Mwalongo, D., 2000. Energy response of LiF: Mg, Ti dosimeters to ISO 4037 and typical diagnostic x-ray beams in Tanzania. Journal of Radiological Protection 22, 175e184. Texier, C., Itié, C., Servièré, H., Gressier, V., Bolognese-Milsztajn, T., 2001. Study of the photon radiation performance of electronic personal dosemeters. Radiation Protection Dosimetry 96 (1e3), 245e249.