Dosimetry
DC 20234.

Radiological Equipment-Gamma-ray Sources

231.120 General.

Direct inquiries to, and mark shipments for the attention of:
Section, RAD PC205, National Bureau of Standards, Washington,
Telephone: 301-921-2361.

Fees for the regular services described in these schedules are listed in Part 8 of this publication. Fees for z items and other services have not been fixed and charges will be made for actual costs incurred. Upon request, estimates will be furnished for specific tasks which should provide a close approximation of actual cost.

231.121 X- and gamma-ray measuring instruments in exposure units

X-ray exposure-indicating instruments are calibrated to within [2 percent by a substitution method in an x-ray beam at a point where the exposure rate (R/min) has been determined by means of a standard free-air ionization chamber. In order to provide instrument calibration over a wide spectrum of x-ray energies, many combinations of kilovoltage and filtration are available. These are given in the tables below. The calibration technique chosen should be appropriate to the particular instrument submitted.

231.121a Calibration of one x-ray exposure or exposure-rate indicating instrument of one range for each technique or setup listed under "LIGHTLY FILTERED X RAYS" or "MODERATELY FILTERED X RAYS".

231.121b

231.121c

231.121d

Calibration of each additional x-ray exposure or exposure-rate indicating instrument of the same range by the same technique as selected under 231.121a and not requiring a change in setup. Calibration of one x-ray exposure or exposure-rate indicating instrument for each technique listed under "HEAVILY FILTERED X RAYS".

Calibration of each additional x-ray exposure or exposure-rate indicating instrument of the same range by the same technique as selected under 231.121c, not requiring a change in setup.

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231.121e

231.121f

Instrument calibrations for cobalt 60 and cesium 137 gamma
radiation
performed by exposure of the instrument to the
gamma rays at points in the collimated beams which have been
calibrated to within about ±2 percent by means of carbon wall
cavity ionization chambers. The exposure rates at the time of
the measurements are computed from the original calibration
data and appropriate decay corrections. Ionization chambers
submitted for calibration should have sufficient wall thickness
for electronic equilibrium for the gamma-ray energy selected.
Calibration of one instrument for gamma rays when no stem effect
is considered:

(1)

(2)

Exposure-rate indicating instrument for each exposure-rate between 0.01 and 15 R/min; or

Exposure-indicating instruments with full scale readings from 0.1 to 100 R.

When the chamber must be calibrated with the stem exposed and protected, the fee will be the sum of fees for 231.121e and f. Calibration of each additional instrument having the same exposure or exposure-rate range as under 231.121e, when the instruments are submitted at the same time, and when no stem effect is considered.

When the chamber must be calibrated with the stem exposed and
protected the fee will be the sum of fees for 231.121e and f.

Guard-ring type cavity
cavity ionization chambers independent of
electrometers may be calibrated for x and gamma rays in terms
of amperes per roentgen per minute. Calibrations are performed
for both positive and negative collection
collection potentials. The
ratio of ionization
for full- and half-voltage

collection

currents

potentials and the exposure rate used in the

calibration will be stated.

231.121g Calibration of one guard-ring-type cavity ionization chamber for each x-ray technique or gamma-ray energy listed.

231.121z

Calibration of one x- or gamma-ray exposure or exposure-rate indicating instrument:

(1) Calibrations of higher accuracy or greater range than that routinely furnished; or

(2) Calibrations on x rays of energies other than those listed under 204.501a, c, or e; or

(3) Calibrations

procedure.

requiring

a special setup or special

Only a limited number of special calibrations can be undertaker and requests for such should be submitted with full details for consideration.

Radioactive preparations submitted to the Bureau for test ect to the following conditions:

(a) Financial responsibility: The Bureau assumes onsibility for loss or damage to radioactive preparations while in ession. The risk should be covered by insurance.

are

no

its

(b) Period of measurement: Approximately 10 days are required measurement of these radioactive preparations.

(c) Preparation of specimens: Radioactive preparations itted for test must be sealed carefully so that there can be no escape ny radioactive material, including any gaseous decay products. The arations, shielding, and packaging must be free of contamination. aminated or leaking preparations cannot be measured and and may cause iderable loss of time and damage to laboratory facilities. arations must have been sealed for a sufficient time to tantially in radioactive equilibrium with their decay products when e contribute to the gamma emission (at least 30 days for radium).

be

(d) Packaging for shipment: Regulations of the Interstate erce Commission regarding the shipment of radioactive substances by must be complied with. These regulations are enforceable by law and pective shippers of these substances need to be familiar with them. es of the regulations can be obtained from the Interstate Commerce ission, Washington, DC 20423. Postal regulations prohibit mailing oactive materials which require a caution label under ICC regulations. effectively prohibits placing radioactive preparations in the mail.

(e) Possession of licensed material: In submitting specimens of 1t 60 or other licensed source material (except radium, which is not nsed) for calibration, it will be necessary for the submitter to ify that he is duly authorized to possess the material under license by USAEC, except in the case of individuals residing in a State which has red into agreement with the USAEC, in which case State regulations icable. This certification may be by letter, by a suitable statement he purchase order covering the calibration fee, or by a clear copy of submitter's Possession License for the source material.

em

122a

Description

are

Radium is calibrated in terms of milligrams of equivalent radium
content measured relative to the National Radium Standard
through comparison of the gamma radiation from the specimen and
the standard. Where the details of encapsulation of the
specimen are known, corrections can be made to obtain
milligrams of radium content. Cobalt 60 is calibrated in terms
of exposure rate, milliroentgens per hour at one meter, based
on comparison with derived standards of cobalt 60.
Gamma-ray measurement of one radioactive preparation: 0.5 to 15
mg radium or encapsulated cobalt 60 having exposure rates from
0.5 to 15 mRhm (milliroentgens per hour at one meter).
Measurement to ±0.7 percent for radium and to ±3 percent for
cobalt 60.

231.122b

231.122c

231.122d

231.122e

231.122z

Gamma-ray measurement of one radioactive preparation: 15+ to 100 mg radium or encapsulated cobalt 60 having exposure rates from 15+ to 100 mRhm (milliroentgens per hour at one meter). Measurement to ±0.7 percent for radium and to +3 percent for cobalt 60.

Gamma-ray measurement of one radioactive preparation: 100+ to 250 mg radium or encapsulated cobalt 60 having exposure rates from 100+ to 200 mRhm (milliroentgens per hour at one meter). Measurement to ±0.7 percent for radium and to ±3 percent for cobalt 60.

For measurements in groups not exceeding 10 preparations, double the fee for preparations of same content as the total content of the group.

For

handling and examination of a shipment containing contaminated or leaking preparations, the fee will be the same as for measurements of a preparation having a content equal to the total nominal radioactive content of the shipment.

As only a limited number of special tests can be carried out prior arrangements must be made, including submission of full details concerning the required measurement.

231.123 Dosimetry in high-energy electron beams.

(a) The Bureau will prepare and mail dosimeters to users requesting assistance with absorbed-dose measurements in high-energy electron beams. The dosimeters employed will consist of ferrous sulfate (Fricke) solution in radiation-resistant silica-glass spectrophotometer cells. The users will expose all but two of the furnished dosimeters to between 5,000 and 8,000 rads at electron energies between 5 and 50 MeV, employing the exposure geometry (field size, phantom, position of dosimeter in phantom) given in the "Protocol for Dosimetry of High-Energy Electrons," Physics in Medicine and Biology 11, 505 (1966).

(b) After irradiation, the dosimeters will be returned to the Bureau for spectrophotometric evaluation of the ferric-ion concentration in terms of absorbed dose in the phantom, using the G-value given in the Protocol.

(c) The Bureau provides this service four times a year.

(d) Through a subsidy provided by the National Center for Radiological Health, Public Health Service, Department of Health, Education, and Welfare, a reduction in fee may become available to all medical users interested in a check of the absorbed dose calibrations employed in high energy electron beam therapy. For details contact the Dosimetry Section, National Bureau of Standards.

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