Office of Research

VI. Radiation and Contamination Surveys

Each user of radioisotopes is responsible for performing surveys of the use area to assure that radioactive sources are adequately shielded and to check for control of radioactive contamination.  Survey data will be recorded on a blank "radiation / contamination survey data sheet" (attachment) and / or in a radiation safety logbook kept by the users at the authorized place of use.

A.        Survey Frequency

1. Each individual user is personally responsible for checking themselves for contamination before leaving radioactive materials areas where unsealed source material has been handled or when leaving areas contaminated above clean area limits.

2. A contamination survey of the immediate work area should be conducted on any day that unsealed source materials are used. This “use survey” ensures that licensed materials have been properly controlled.

3. A formal survey of the entire work area (laboratory) should be conducted weekly in any use area where unsealed source material has been used in that week.  No survey is required in a week if no radioactive materials work is conducted. 

4. A plan view map of the lab space showing areas of primary use and locations of sample points should be included to document the weekly survey.  Contamination surveys will be reported in units of dpm/100 cm2.

5. During a periods of non-use of radioactive materials there may be  times that no routine contamination surveys are performed.  On the first contamination survey subsequent to a period of non-use, please make a note documenting “no use of radioactive materials since previous survey” or works to this affect.  This will help to identify periods where survey data and/or use records should not be available for review or audit.

 

B.        Radiation Surveys

Radiation surveys to verify exposure rates may be required in certain situations. These surveys are preformed in order to determine the radiation levels in the vicinity of storage areas, work areas, waste containers, and in adjacent unrestricted areas.

  1. Survey requirements

a. These Radiation surveys will be made on a periodic basis in areas where gamma emitting or high-energy beta (>1.0 MeV.) emitting isotopes are used or stored in sufficient quantities to produce whole body exposure rates of >= 2 mrem/hour.

b. Radiation surveys will be conducted with a hand held survey meter that is calibrated in units of mR/hr or mrem/hr.

c. Exposure rates will be documented on the weekly survey form.

2. Exposure rate action levels.

a. General area dose rates unrestricted areas will not exceed .05 mR/hr.  General area dose rates shall be measured with the detector held at waist level and at a distance of no more than 3 feet from the source.

b. Dose rates in a Radioactive Materials Area will not exceed 2 mR/hr when measured at a distance of no more than 12 inches from the source of exposure or at the posted boundary to a Radiation Area.

 

C.        Contamination Surveys

Contamination surveys by direct survey (frisk) will be conducted with hand held radiation detection instruments calibrated in units of counts per minute (cpm) or mR/hr.

1.         Direct Survey (frisk)

Direct monitoring for beta/gamma surface contamination will be by G.M. survey meter equipped with a thin window probe.  The area will be surveyed by slowly moving the instrument probe over the surface in question at a distance of no more than ½ inch and at a rate of no more that 2 inches of travel per second.

 a. The instrument should be set on the slow response setting and in the audible mode if the instrument is equipped with a speaker.

  b. A direct reading of 100 cpm or >.05 mR/hr above background (bkg) indicates a contaminated area or item.  If contamination is indicated by direct survey, a smear survey will be conducted to determine if the contamination is removable.

  c. Survey by direct frisk is not permitted to certify an item or area as "clean" for release to unrestricted areas if the background radiation level is >300 cpm on the meter being used. 

 

2.         Smear Surveys

Smear surveys are conducted by thoroughly wiping a surface with a commercially available cloth, or paper disk, or a "Q-tip", and analyzing the sample with an appropriate detection instrument.

a. Surface contamination is reported in units of dpm / 100 cm.2 (4" X 4"). If the surface is large, 100 cm2 may be approximated by placing the fingertips of the index and middle finger over the disk and, with moderate pressure, drawing an 18" S pattern on the surface.  A "q-tip" may be used for objects smaller than 100 cm2 and the entire surface should be wiped. 

  b. A field evaluation of a smear sample may be obtained using a hand held G.M. instrument with a pancake or end window probe.  Assuming 10% efficiency, a sample with a direct reading of 100 cpm above background has an activity of approximately 1000 dpm.

  c. Hand held detection equipment is not sensitive enough to accurately detect smear sample activities below the 200dpm/100cm2 Unrestricted area limit.  A laboratory counters, such as a liquid scintillation counter is required for accurately analyzing smear samples to the 200 dpm/100cm2 removable contamination limit.

  d. If H-3 is the radioactive nuclide of interest, the smear sample must be analyzed in a liquid scintillation counter.

 

D.        Source Inventory and Leak Check Surveys

1.         Inventory

Each AI shall conduct a physical inventory at intervals not to exceed six (6) months to account for all radioactive material received and possessed under that particular R.S.C. approval.  Records of source inventory and leak checks will be maintained for inspection by the BRH.  These records shall include:

a.         The quantities and kinds of radioactive material

b.         Location of all radioactive material

c.         Date the inventory was conducted, and

d.         Name of the individual conducting the inventory.

 

2. Leak Check Criteria

a. Any beta and/or gamma emitting sealed source with an activity > 10 mCi of radioactive material, other than H-3, with a half-life greater than thirty days and in any form other than gas shall be tested for leakage at intervals not to exceed six months.

b. Alpha or neutron emitting sealed sources with an activity of > 10 mCi will be leak checked at intervals not to exceed six months.

c. All newly obtained sealed sources will be tested for leakage prior to being put into service. If a source has not been removed from the storage location or container since the last leak check, only a physical inventory will be performed.  No leak check will be required until the next time the source is removed from its storage container or location.

 

3. Leak Test Procedure

a. Source leak test will be conducted in accordance with Radiation Protection “Leak Check Procedure" #007.  Survey data will be recorded on "source leak check survey data form" (see attachments).

  b. If the test reveals the presence of 0.005 microcuries or more of removable contamination, the source will immediately be withdrawn from use and shall be decontaminated, repaired, or disposed of in accordance with BRH regulations.

  c. Note: Sealed sources will not be included for disposal in normal D.A.W. waste.  Special approval must be obtained from the disposal site and the BRH for disposal of sealed sources.