The Radioactive Analysis Laboratory is located in the EHS Office in building N52 and houses the detection equipment for radioactive material, radio-frequency, magnets, lasers, etc. The RPP can use this equipment during inspections, to perform hazard assessments, and to analyze samples.
Bioassays and Whole Body Counting
Radiation workers working at the MITR or quantities of radioactivity that exceed certain limits will need to submit to whole body counting or bioassays as needed. For unsealed radioactivity, workers using 0.1 mCi of 125I, 10 mCi of 3H, 32P, or any other gamma emitter, or any alpha or beta emitter greater than 10 x ALI. The ALI (Annual Limit on Intake) can be found on the Massachusetts Department of Radiation Control website under 105 CMR 120.296.
Radon testing can be performed as needed for the MIT community.
Radiation User Survey
Personnel working in the laboratory are required to do close-down surveys. It is also recommended to perform a start-up survey in the case of a common use area. In the case of a spill, you should follow the procedures found at the Radioactive Spill Page.
For the close-down survey:
- Check the PPE. Proper PPE for radioactive material work includes lab coat, safety glasses, and gloves
- Check street clothes and shoes
- Check the work areas including the floor and adjacent areas
Before starting either of these surveys, the radioactive isotopes being used in the area need to be determined.
For most beta and gamma emitting isotopes (see exceptions below) the standard Geiger-Mueller will be adequate. The probe has a characteristic mylar covering and has a 4-5% counting efficiency for C-14. For example, 2000 counts or count per minute from a meter reading is 40,000 – 50,000 actual decays per minute.
For low energy gamma emitters within the 10 – 60 keV range such as 125I, a NaI probe is the preferred option. The end of the probe is usually white and will not have a mylar window. This probe has a 19% counting efficiency for 125I.
For weak beta emitters such as 3H, a wipe test must be performed and then run on a Liquid Scintillation Counter (LSC). Only removable 3H contamination may be detected. Most LSC readouts will tell the cpm and dpm for a given energy range.
To perform a survey with a GM Meter, there are 3 pre-checks that need to be performed.
- Check the external appearance of the meter. Look for any noticeable damage, make sure all chords are properly connected and ensure the calibration sticker is attached and updated.
- Turn the meter on and test the batteries. The needle will go into the battery test area if they are okay.
- Place the probe against the radioactive check source attached to the side of the meter. You should hear elevated chirps and the needle should move across the meter faceplate. Remember to have the audio on at all times.
Once these three checks have been completed the meter is ready for use. If the meter failed one of the checks, inform Radiation Protection. RPP is able to calibrate meters and perform simple repairs.
When using a portable detector with a probe, be sure to scan at a slow pace. Around 1 inch per second is a good starting point. Remember the inverse square law and scan as close to the surface as possible. 1 cm from surface is a good distance.
Performing a survey with this probe will be exactly the same as with the G-M Meter. This probe is only effective for low energy gamma emitters. It will not detect beta radiation.
Liquid Scintillation Counting
Liquid scintillation counting is the preferred method when performing a survey to detect removable radioactive material. As stated before, the portable tend to by highly inefficient while liquid scintillation has a much greater counter efficiency for almost all isotopes.
Depending on the isotope, quantity, and use of radioactivity, the Radiation Protection Program will either do a weekly or monthly survey. This survey does NOT take the place of close-down surveys that should already be performed by the laboratory.
RPP will perform a meter survey of the rooms where radioactive material is used, stored, or kept as waste. The floor, bench tops, and waste will be monitored to ensure that the laboratory has a dose rate no greater than 2 mR/hr from any radiation source.
RPP will also perform a wipe survey of the same areas to find any removable contamination. If there is removable contamination, the lab will notified and RPP will be back to clean the affected areas.