NIST logo
*
Bookmark and Share

Ionizing Radiation Measurements

Dosimetry of X Rays, Gamma Rays, and Electrons

Rate our Services

Technical Contacts:
C. Michelle O'Brien
46010C-46050S
Tel: 301-975-2014
E-mail: michelle.obrien@nist.gov

Ronaldo Minniti
46010C-46110C
Tel: 301-975-5586
E-mail: ronaldo.minniti@nist.gov

Michael G. Mitch
47010C-47040S
Tel: 301-975-5491
E-mail: michael.mitch@nist.gov

Please contact the technical staff before shipping instruments or standards to the address listed below.

Mailing Address:
National Institute of Standards and Technology
100 Bureau Drive, Stop 8460
Gaithersburg, MD 20899-8460
Fax: 301-869-7682

Service ID
Number
Description of Services Fee ($)
X-Ray and Gamma-Ray Measuring Instruments
Air Kerma (Exposure)
46010C Radiation Detectors-Calibration in 60 Co and 137 Cs Gamma-Ray, per Detector, per Set-up, per Beam Code 2088
46011C Radiation Detectors-Calibration in X-Ray Beams (see Tables 6, 7 and 8), per Detector, per Set-up, per Beam Code 1997
46020C Passive Dosimeters-Irradiation of Up to Six, One Beam Quality at One Set-Up 2331
46021C Up to Six Additional Dosimeters at Same Setup and Beam Quality 1450
46030S Special Tests of High-Gain Electrometers-Charge Sensitivity, One Set of Switch Positions, with 46010C/46011C, by Prearrangement 1506
46040S Special Tests of kV Measuring Devices At Cost
46050S Special Tests of X-Ray and Gamma-Ray Measuring Instruments At Cost
Absorbed Dose to Water from 60Co Beam
46110C Radiation Detectors-Calibration in a 60 Co Gamma-Ray Beam 2567
Sealed Gamma-Ray Sources or Beta-Particle Sources, and Measuring Instruments
47010C Gamma-Ray Sources Similar to NIST Standards - 60Co or 137Cs, Having Air-Kerma Strengths 10 µGy m2/h to 1500 µGy m2/h; and 192Ir Sources of the Same Type Used to Calibrate Reentrant Chamber Having Air-Kerma Strengths 0.1 µGy m2/h to 30 µGy m2/h 3892
47011C Each Additional Gamma-Ray Source of Same Radionuclide 3741
47020C 125I or 103Pd Sources: Seeds Having Air-Kerma Strengths 0.5 µGy m2/h to 100 µGy m2/h 2939
47021C Each Additional 125I or 103Pd Source of Same Radionuclide/Design Submitted with Above 2847
47030C Beta-Particle Sources Calibrated for Surface Dose Rate 1211
47035C Beta-Particle Sources Calibrated for Radiation Protection 985
47036C Ionization Chambers Calibrated with Beta-Particle Sources for Radiation Protection 985
47040S Special Tests of Gamma-Ray and Beta-Particle Sources At Cost
Fees are subject to change without notice.

back to top of page | back to index of ionizing radiation measurements

Special Instructions for Using Electron and Photon Dosimetry Services (46010C-47040S )

The NIST dosimetry calibration and test services for x-rays, gamma-rays, beta particles, and electrons are performed in NIST's laboratories at Gaithersburg, Maryland. Inquiries should be addressed to the appropriate technical contacts listed at the beginning of this section. The inquirer must provide the name and telephone number of an individual who can answer technical questions that may arise in any inquiry, order, or shipment.

Upon receipt of a purchase order, a report number is assigned. Calibrations are generally performed in the sequence established by those numbers, except when greater efficiency can be achieved by combining similar calibrations, or when work for a calibration laboratory is given a higher priority. Arrangements for calibration must be made in advance by letter, fax, e-mail or telephone, so that the instrument or source to be calibrated will not be shipped to NIST until the time of its scheduled calibration approaches. Inquiry should be made as to scheduling and turn-around time.

Except in the event of negligence by its personnel, NIST assumes no responsibility for loss of or damage to the instruments or sources while in its possession. The risk should be covered by insurance.

The report of calibration or test will carry a DG number (e.g., DG 9603/95). Subsequent reference to that calibration or test should cite the DG number.

back to top of page | back to index of ionizing radiation measurements


X-Ray and Gamma-Ray Measuring Instruments (46010C-46110C)

NIST calibrated x-ray measuring instruments are calibrated in terms of air kerma or exposure by a substitution method in an x-ray beam at a point where the rate has been determined by means of a free-air ionization chamber standard. In order to provide instrument calibrations over a wide range of x-ray beam qualities, many combinations of generating potential and filtration are available. Tungsten (W) anode, x-ray beams with U.S. established beam qualities are listed in Table 6 as lightly (L), moderately (M), and heavily (H) filtered beams. Two beam qualities that do not fit into these categories are considered as special (S) qualities. Cobalt-60 and cesium-137 gamma-ray beams are also listed in Table 6. New W-anode, ISO x-ray beam qualities, listed in Table 7 have been installed. Molybdenum (Mo) and rhodium (Rh) anode x-ray beam qualities, with application to mammography, are listed in Table 8. Tungsten-anode beam qualities used in international comparisons are listed in Table 9. Beam qualities are identified by beam codes given in the first column. The calibration beam qualities requested should be appropriate to the instrument submitted.

Gamma-ray measuring instruments are calibrated in terms of air kerma or absorbed dose at points in the collimated cobalt-60 and cesium-137 gamma-ray beams that have been standardized by means of graphite cavity chambers or a water (or graphite) calorimeter. Rates at the time of calibration are computed from the original beam standardization data and appropriate decay corrections. Ionization chambers submitted for an air kerma calibration should have sufficient wall thickness to provide electron equilibrium for the highest energy selected. Ionization chambers submitted for an absorbed-dose calibration must be suitable for calibration in a phantom.

An ionization chamber and electrometer combination, with the electrometer scale in units of air kerma, exposure, or absorbed dose, is calibrated by providing a dimensionless calibration factor for the electrometer scale. An ionization chamber and electrometer combination marked in electrical units is calibrated as follows: (1) the chamber is calibrated in terms of air kerma or absorbed dose per unit charge using an NIST electrometer; (2) the customer's electrometer is checked for linearity and charge measurement accuracy; and (3) the combination of chamber and electrometer is checked for consistency. An ionization chamber submitted without an electrometer is calibrated in terms of air kerma or absorbed dose per unit charge. Calibration can be based on measurements for positive or negative polarizing potential, or on the mean of measurements for both potentials, as requested. The ratio of ionization currents for full and half polarizing potentials and the corresponding ionization current will be stated in the calibration certificate, based on pre-calibration measurements.

Ionization chambers are tested, prior to calibration, for connection to the atmosphere. Chambers found unsuitable for calibration will be returned with a statement of the reason for rejection. A charge may be made for time incurred on the tests.

Each instrument submitted to NIST for dosimetry calibration or test must be uniquely identified, usually by the manufacturer's name, model number, and instrument serial number. When the serial number is lacking, an alternative identifying mark should be provided. If none is found, NIST will mark the piece with an identification number. If the apparatus submitted has been calibrated previously by NIST, the serial number or identifying mark should be given on the new order so that a continuing record of stability can be maintained.

All shipments to NIST of instruments for dosimetry calibration must be in reusable containers. Even if properly packed, there can be no assurance that a calibrated instrument has maintained its calibration during shipment unless a method of verifying instrument stability has been established. Measurement should be made of the instrument response both before and after shipment, using a long-lived radioactive source and a highly reproducible measurement procedure. A long-term record of instrument stability using a suitable constancy check procedure is the most effective method for assuring the validity of the instrument calibration.

Irradiation of passive dosimeters, for readout by the customer, is available for most of the beam qualities listed in Table 6. These irradiations are generally in terms of air kerma; for passive dosimeters suitable for insertion in a phantom, irradiation in terms of absorbed dose can be provided by in-phantom irradiation using cobalt-60 gamma rays.

Calibrations of x-ray and gamma-ray measuring instruments and of passive dosimeters, described above, have a relative expanded uncertainty of 1%.

back to top of page | back to index of ionizing radiation measurements

Table 6. Tungsten-Anode X-Ray and Gamma-Ray Beam-Quality Parameters

Beam
codea
Additional filtrationb
Half-value layerc (HVL) Homogeneity Coefficientd (HC) Effective
Energy
(keV)

Al
(mm)
Cu
(mm)
Sn
(mm)
Pb
(mm)
Al
(mm)
Cu
(mm)
Al Cu
X-Ray Beam Qualities
L10 0


0.037
86

L15 0


0.059
70

L20 0


0.070
72

L30 0.3


0.23
60

L40 0.53


0.52
61

L50 0.71


0.79
63

L80 1.45


1.81
56

L100 1.98


2.80
58

M20 0.27


0.15
72

M30 0.5


0.36
65

M40 0.89


0.74
67

M50 1.07


1.04
68

M60 1.81


1.64 0.052 63 60
M80 2.86


2.98 0.10 68 61
M100 5.25


5.00 0.20 74 55
M120 7.12


6.72 0.31 77 53
M150 5.25 0.25

10.1 0.66 88 63
M200 4.35 1.12

14.7 1.64 94 68
M250 5.25 3.2

18.3 3.2 98 85
M300 4.25
6.5
21.7 5.3 100 97
H10 0.105


0.051
77

H15 0.5


0.16
87

H20 1.01


0.36
89

H30 4.50


1.20
86

H40 4.53 0.26

2.93
94

H50 4.0

0.1 4.2 0.14 93 93 38
H60 4.0 0.61

6.0 0.25 94 94 46
H100 4.0 5.2

13.4 1.15 97 92 80
H150 4.0 4 1.51
16.9 2.43 100 96 120
H200 4.0 0.6 4.16 0.77 19.7 4.10 99 99 166
H250 4.0 0.6 1.04 2.72 22 5.19 99 98 211
H300 4.1
3.0
5.0 23 6.19 99 98 252
S60 4.35


2.79 0.09 76 66
S75 1.50


1.81
58

Gamma-Ray Beams
137Cs




10.8

662
60Co




14.9

1250

aFor the x-ray beam codes, the letter indicates light (L), moderate (M), heavy (H) and special (S) filtration, and the number is the constant potential in kilovolts.
bThe additional filtration value does not include the inherent filtration. The inherent filtration is approximately 1.0 mm Be for beam codes L10-L100, M20-M50, H10-H40 and S75; and 3.0 mm Be for beam codes M60-M300, H50-H300 and S60.
cThe HVL values were determined for the tubes installed in 2006 and 2008. For 137Cs and 60Co, the half-value layers are calculated,
d The homogeneity coefficient is taken as 100 (1st HVL / 2nd HVL).

back to top of page | back to index of ionizing radiation measurements

Table 7. Tungsten-Anode ISO X-Ray Beam-Quality Parameters

Beam code Additional filtration (mm)a First HVLb Second HVLb

Al Cu Sn Pb Al
(mm)
Cu
(mm)
Al
(mm)
Cu
(mm)
HK10



0.042
0.045

HK20 0.15


0.128
0.170

HK30 0.52


0.408
0.569

HK60 3.19



0.079
0.113
HK100 3.90 0.15


0.298
0.463
HK200
1.15


1.669
2.447
HK250
1.60


2.463
3.37
HK280
3.06


3.493
4.089
HK300
2.51


3.474
4.205
WS60
0.3


0.179
0.206
WS80
0.529


0.337
0.44
WS110
2.0295


0.97
1.13
WS150

1.03

1.88
2.13
WS200

2.01

3.09
3.35
WS250

4.01

4.30
4.50
WS300

6.54

5.23
5.38
NS10 0.095


0.049
0.061
NS15 0.49


0.153
0.167
NS20 0.90


0.324
0.351
NS25 2.04


0.691
0.762
NS30 4.02


1.154
1.374
NS40
0.21


0.082
0.094
NS60
0.6


0.241
0.271
NS80
2.0


0.59
0.62
NS100
5.0


1.14
1.19
NS120
4.99 1.04

1.76
1.84
NS150

2.50

2.41
2.57
NS200
2.04 2.98

4.09
4.20
NS250

2.01 2.97
5.34
5.40
NS300

2.99 4.99
6.17
6.30
LK10 0.30


0.061


LK20 2.04


0.441


LK30 3.98 0.18

1.492


LK35
0.25

2.21


LK55
1.19


0.260

LK70
2.64


0.509

LK100
0.52 2.0

1.27

LK125
1.0 4.0

2.107
2.094
LK170
1.0 3.0 1.5
3.565
3.952
LK210
0.5 2.0 3.5
4.726
4.733
LK240
0.5 2.0 5.5
5.515
5.542

aThe additional filtration does not include the inherent filtration. The inherent filtration is a combination of the filtration due to the monitor chamber plus 1 mm Be for beam codes LK10-LK30, NS10-NS30, HK10-HK30; for all other techniques the inherent filtration is adjusted to 4 mm Al. 
bThe HVL values were determined for the tubes installed in 2006 and 2008.

back to top of page | back to index of ionizing radiation measurements

Table 8. Mammography X-Ray Beam-Quality Parameters

Beam code Tube
voltage
(kV)
Additional
filtrationa
(mm)
Half-value layer
(mm Al)
Mo Anodeb
Mo/Mo23 23 0.032 Mo 0.288
Mo/Mo25 25 0.032 Mo 0.313
Mo/Mo28 28 0.032 Mo 0.346
Mo/Mo30 30 0.032 Mo 0.370
Mo/Mo35 35 0.032 Mo 0.404
Mo/Rh28 28 0.029 Rh 0.420
Mo/Rh32 32 0.029 Rh 0.453
Mo/Mo25x 25 0.030 Mo + 2.0 Al 0.551
Mo/Mo28x 28 0.030 Mo + 2.0 Al 0.589
Mo/Mo30x 30 0.030 Mo + 2.0 Al 0.633
Mo/Mo35x 35 0.030 Mo + 2.0 Al 0.715
Rh Anode
Rh/Rh25 25 0.029 Rh 0.351
Rh/Rh30 30 0.029 Rh 0.438
Rh/Rh35 35 0.029 Rh 0.512
Rh/Rh40 40 0.029 Rh 0.559
Rh/Rh30x 30 0.029 Rh + 2.0 Al 0.814
Rh/Rh35x 35 0.029 Rh + 2.0 Al 0.898

aThe additional filtration value does not include the inherent filtration, which is comprised of 1.0 mm Be from the x-ray tube window and 0.075 mm polyamide from the transmission monitor.
bThe HVL values were measured directly using the Mo anode installed in December 2008.

back to top of page | back to index of ionizing radiation measurements


Table 9. CCRIa Medium-Energy X-Ray Beam Quality Parameters Offered at NIST

Beam code Tube
voltage
(kV)
Additional
filtrationb
Half-value
layerc
(mm Cu)
voltage
(kV)
    (mm Al) (mm Cu)  
BIPM100 100 3.248   0.149
BIPM135 135 1.060 0.265 0.496
BIPM180 180 3.842 0.482
1.003
BIPM250 250 3.842 1.618 2.502

a BIPM, Qualites de rayonnements, Consultative Committee for Ionizing Radiation (CCEMRI) (Section I), 1972, 2, R15. Details of these reference radiation qualities can be found in the following: Burns, D. T. and O'Brien, M. , "Comparison of the NIST and BIPM Standards for Air Kerma in Medium-Energy X-rays," J.Res. Natl. Inst. Stand. Technol. 111, 385-391 (2006).
b The additional filtration does not include the inherent filtration of the MXR321 x-ray tube.
c The HVL values were determined for the tube installed in 2006.

back to top of page | back to index of ionizing radiation measurements

Gamma-Ray Sources, Beta-Particle Sources, and Measuring Instruments (47010C-47040S)

Sources submitted to NIST for dosimetry calibration are subject to the following conditions:

A. Preparation: Sources submitted for calibration must be sealed so that there can be no escape of any radioactive material, including any gaseous decay products. The sources, shielding, and packaging must be free of contamination. Contaminated or leaking sources cannot be measured and may cause considerable loss of time and damage to laboratory facilities. Sources must have been sealed for a sufficient time to be substantially in radioactive equilibrium with their decay products when these contribute to the emitted radiation.

B. Packaging for shipment: Packages must be in compliance with the regulations of the Department of Transportation as specified in DOT 49CFR173.401-173.476. Radionuclides must be packaged as Limited Quantities (DOT 49CFR173.421-173.422) or in Type A packages (DOT 49CFR173.412 and 173.433). Type A packages must bear the appropriate radioactive-hazard labels (DOT 49CFR172.403). If the source is considered by the shipper to be in DOT Special Form, a Special Form certificate must be furnished to NIST in strict compliance with DOT 49CFR173.476. Copies of the codes are available from the Government Printing Office, Washington, DC 20402.

All shipments to NIST of gamma-ray and beta-particle sources should be in reusable containers. A drawing showing the source container and a description of the method of source removal should be provided before the shipment is received at NIST.

If the nature of the shipment requires a Type B container subject to an NRC quality assurance program, documentation should be supplied to NIST certifying that the use of the container by NIST is part of the program of the shipper.

C. Possession of licensed materials: In submitting a source for calibration, it is necessary for the submitter to certify that he is duly authorized to possess the source under license by the applicable authority. In the case of individuals residing in a State that has entered into agreement with the Nuclear Regulatory Commission, State regulations are applicable to all sources. In the case of other individuals, NRC regulations are applicable. This certification may be by letter, by a suitable statement on the purchase order covering the calibration fee, or by a clear copy of the submitter's Possession License for the source.

Calibration in terms of air-kerma strength (air-kerma rate in free space times the square of the distance of the calibration point from the source center along the perpendicular bisector) is provided for gamma-ray sources of cobalt-60, cesium-137, iridium-192, iodine-125, and palladium-103. Calibration in terms of absorbed-dose rate is provided for suitable encapsulated beta-particle sources; the dose rate to a low-atomic-number material (graphite or plastic) is determined by measurement with an extrapolation chamber. The beta-particle sources may be either small-area sources such as ophthalmic applicators, or large-area plaques, and will be calibrated for absorbed dose rate to water either at the source surface or at a specified distance.

Ionization chambers to be calibrated with beta-particle sources must be parallel-plate chambers with thin walls. They can be calibrated with the radionuclides 90Sr + 90Y, or 204Tl, or 85Kr, or 147Pm.

Measurement services in this series have uncertainties listed in Tables 9 and 10.

back to top of page | back to index of ionizing radiation measurements


Table 10. Uncertainties for Gamma-Ray Source Calibrations

Source Relative Expanded Uncertainty
(%)
60Co 2
137Cs 2
192Ir 2
125I 2 a
103Pd 3 a

a Typical value. Actual value depends on characteristics of submitted source.

back to top of page | back to index of ionizing radiation measurements


Table 11. Uncertainties for Beta-Particle Source and Instrument Calibrations

Service ID Item Relative Expanded Uncertainty
(%)
47030C Sources calibrated for surface dose rate 12
47035C Sources calibrated for radiation protection, 90Sr + 90Y 4.5

Sources calibrated for radiation protection, 204Tl, 85Kr 4.5

Sources calibrated for radiation protection, 147Pm 9
47036C Transfer ionization chambers for radiation protection same as 47035C

Extrapolation chambers for radiation protection, absolute same as 47035C

Extrapolation chambers for radiation protection, relative to NIST standard chamber in reference field 1 a

aTypical value. Actual value depends on response characteristics of submitted chamber.

back to top of page | back to index of ionizing radiation measurements


References-Dosimetry of X-Rays,Gamma-Rays, and Electrons

X-Ray and Gamma-Ray Measuring Instruments

Calibration of a 137Cs γ-ray beam irradiator using large size chambers, R. Minniti, S. M. Seltzer, Applied Radiation and Isotopes 65, (2007) 401-406.

Absorbed Dose to Water Calibration of Ionization Chambers in a 60Co Gamma-Ray Beam, R. Minniti, J. Shobe, S. M. Seltzer, H. Chen-Mayer, S. R. Domen, NIST Special Publ. 250-74, (Mar. 2007).

NIST Measurement Services: Calibration of X-Ray and Gamma-Ray Measuring Instruments, P. J. Lamperti, and M. O'Brien, Natl. Inst. Stand. Technol. Spec. Publ. 250-58 (Apr. 2001).

The photon-fluence scaling theorem for Compton-scattered radiation, J. S. Pruitt and R. Loevinger, Med. Phys. 9, 176 (1982).

The Graphite Calorimeter as a Standard of Absorbed Dose for Cobalt-60 Gamma Radiation, J. S. Pruitt, S. R. Domen, and R. Loevinger, J. Res. Natl. Bur. Stand. (U.S.) 86 (5), 495-502 (1981).

Medical Dosimetry Standards Program of the National Bureau of Standards, R. Loevinger, Proc. Symp. on Natl. and Intl. Standardization in Rad. Dosimetry, Atlanta, GA, Dec. 5-9, 1977, Intl. Atomic Energy Agency, Vienna (1978). (This article provides references for earlier publications on NBS exposure and absorbed-dose standards.)

Uncertainty in the Delivery of Absorbed Dose, R. Loevinger and T. P. Loftus, Ionizing Radiation Metrology, International Course at Varenna, Italy, 1974 (E. Casnati, Ed.) G-6, 459, Editrice Compositori, Bologna (1977).

Exposure Spectra from the NBS Vertical-Beam 60Co Gamma-Ray Source , M. Ehrlich and C. G. Soares, Natl. Bur. Stand. (U.S.) NBSIR 76-1117 (1976).

Spectrometry of a 60Co Gamma-Ray Beam Used for Instrument Calibration, M. Ehrlich, S. M. Seltzer, M. J. Bielefeld, and J. I. Trombka, Metrologia 12, 169 (1976).

back to top of page | back to index of ionizing radiation measurements


Gamma-Ray Sources, Beta-Particle Sources, and Measuring Instruments

A Method for the Calibration of Concave 90SR + 90Y Ophthalmic Applicators, C. G. Soares, Phys. Med. Biol. 37, 1005 (1992).

Calibration of ophthalmic applicators at NIST - A revised approach, C. G. Soares, Med. Phys. 18, 787 (1991).

NBS Measurement Services: Calibration of Gamma-Ray-Emitting Brachytherapy Sources, J. T. Weaver, T. P. Loftus, and R. Loevinger, Natl. Bur. Stand. (U.S.) Spec. Publ. 250-19 (1988).

NBS Measurement Services: Calibration of Beta-Particle Radiation Instrumentation and Sources, J. S. Pruitt, C. G. Soares, and M. Ehrlich, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-21 (Apr. 1988).

NBS Measurement Services: Calibration of Beta-Particle-Emitting Ophthalmic Applicators, J. S. Pruitt, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-9 (July 1987).

Calibration of Beta-Particle Ophthalmic Applicators at the National Bureau of Standards, J. S. Pruitt, J. Res. Natl. Bur. Stand. (U.S.) 91, 165 (1986).

The Effect of Altitude on Beta-Ray Source Calibrations, J. S. Pruitt, Radial. Protec. Dosim. 11, 151 (1984).

Exposure Standardization of Iodine-125 Seeds Used for Brachytherapy, T. P. Loftus, J. Res. Natl. Bur. Stand. (U.S.) 89, 295 (1984).

Standardization of Iridium-192 Gamma-Ray Sources in Terms of Exposure, T. P. Loftus, J. Res. Natl. Bur. Stand. (U.S.) 85, 19 (1980).

Medical Dosimetry Standards Program of the National Bureau of Standards, R. Loevinger, Proc. Symp. on Natl. and Intl. Standardization in Rad. Dosimetry, Atlanta, GA, Dec. 5-9, 1977, Intl. Atomic Energy Agency, Vienna (1978). (This article provides references for earlier publications on NBS exposure and absorbed-dose standards.)

Standardization of Cesium-137 Gamma-Ray Sources in Terms of Exposure Units (Roentgens), T. P. Loftus, J. Res. Natl. Bur. Stand. (U.S.), 74A, 1 (1970).

back to top of page | back to index of ionizing radiation measurements

Program questions: Calibrations 
Phone: 301-975-5454, Fax: 301-975-2950
NIST, 100 Bureau Drive, Stop 8363, Gaithersburg, MD 20899-8363