Description: The Shepherd Mark I Irradiator contains 4000 Curies of Cesium 137. The Irradiator is located in Room 113 Ullmann and is accessible only to authorized researchers. It is used for the irradiation of cell cultures and small animals. There are three positions inside the irradiator that the researcher can use to irradiate their samples. These three positions give dose rates of 1388, 407 and 286 Rads / minute.
Safety Features: The Shepherd Irradiator has an interlock system that will not permit access to the irradiator chamber while the Cs-137 source is in the on position. It also will not permit researchers to raise the source into the on position while the door is open. This is critical as the dose from this unit is extremely high.
In addition there are two radiation monitors included with the Irradiator that are constantly monitoring the dose rates in the room while the unit is operating. These monitors would sound an alarm and activate a warning light should the dose rate exceed a certain limit.
Qualified User: Only those individuals who are deemed qualified by the Radiation Safety Officer shall be permitted to use the Irradiator. To begin the process the individual's Principal Investigator must request that he/she be permitted to use the Irradiator. These individuals must be at least 18 years of age and an employee, graduate or medical student or a Post Doc at AECOM. The only exception to this requirement are unpaid Research Associates, who may be qualified to use the Irradiator. The individual must have been trained by the Radiation Safety Officer in the use of this unit and taken a test confirming he/she knows how to use the unit. The researcher must obtain and wear a dosimeter when using the irradiator.
Requesting Use: An individual needing to use the Irradiator should contact the Safety Office at least 24 hours prior to the time he/she wishes to use it. This will insure that the individual has the time needed to do the irradiation. The individual should ask for only enough time to do the irradiation. Do not request the key unless you plan to use the irradiator at the time you take it. The secretary taking the call will confirm that the individual is authorized to use the Irradiator, based on a list of Authorized Users. If the individual is not on that list he/she will not be scheduled to use the Irradiator.
There is a key at the Security Guard station at the main entrance to Forchheimer. This key is available to Authorized Users after hours (5:00 pm to 9:00 am) on weekdays and weekends. It is obtained on a “first come first serve” basis and must be returned upon completing the irradiation.
Picking Up Keys: When picking up the keys from the Safety Office, you should arrive on time and have your security issued ID. Write into the log at the front table, the date, the PIs name, the time and the researcher’s signature and telephone number. A secretary will give you the key.
Use of the Irradiator: When arriving at Room 113 Ullmann the individual should have his/her dosimeter, the keys and samples to be irradiated. Follow the Irradiator Operating Procedures when using the Irradiator. Note that the various steps have been numbered to make it easier for the researcher to follow the instructions. It is important to pay particular attention to the “Warnings” for the use of the irradiator. You should pay particular attention to confirm that the source has returned to the storage chamber when the irradiation is complete. There are three methods for determining this; the “source raise” light will go off, the “Source Return” light comes on and the mechanical indicator on the black tower goes down.
Figure 1. Control Panel and Mechanical Indicator
There are three positions for irradiation of samples:
- Position 1 which is closest to the back wall of the Irradiator and provides 1388 rads / minute.
- Position 2 which is further out and provides 407 rads / minute.
- Position 3 which is closest to the door and provides 286 rads / minute.
Position 1 is best used for irradiating cells in conical tubes. This position provides the maximum dose rate available in the chamber. Positions 2 and 3 are best for culture dishes and animal containers. It is important that when you use these positions you place the samples in the region of the chamber that provides 100% of the dose rate. The areas near the floor and ceiling of the chamber provide dose rates as low as 75% of the desired dose rates. Also the right and left walls provide too high dose rates, up to 155% of the desired dose rate. The regions are posted on the bulletin board in 113 Ullmann and can be found in Shepherd & Associates, "Operating Manual For Mark I Series Research Irradiation Facility", also available in 113 Ullmann.
Figure 2: Possible Geometries for Irradiating Samples
When using positions 2 and 3, use the base plate to hold your samples.
Use of the conical tube holders insures that the samples are in the 100% dose rate region for position 1. For position 2 and 3 the researcher may need to improvise to insure that the samples fall within the 100% region.
When irradiating animals you may use a small cage raised up to insure that the animal are in the 100% dose rate region. Whatever you use to contain the animal, it is important that they cannot escape from the cage while in the irradiator.
If you leave the room while the irradiation occurs, insure that you take the key to the door so you will be able to re-enter the room.
Completing Irradiation: After completing the irradiation, clean up after yourself and remove all items that you brought with you to do the irradiation. Return the keys to the Safety Office and document that you are done in the log book.
Emergency Procedures: If the source fails to return to the storage chamber as indicated by the “source raise” light, the “Source Return” light or the mechanical indicator, the individual should push the "Source Return" button. If this does not return the source to the chamber immediately contact the Safety Office (x2243).
If for what ever reason the radiation monitors alarm the individuals should push the "Source Return" button and leave the room. He/she should call the Safety Office and report the problem (x2243)
Enforcement Policy: If an individual is frequently late returning the key or keeps the key out over night he/she will be restricted from using the irradiator for one month. If an individual leaves the room in a mess after using it, he/she will be restricted from using the irradiator for one month.
Use of the Irradiator is a very serious matter. If an individual is found to be using the Irradiator in an unsafe manner, he/she will be permanently barred from using the Irradiator.
Quiz: There is a 10 question quiz for individuals to become qualified to use the Irradiator. After reading this document and the Operation Procedures for the Shepherd Irradiator contact the Radiation Safety Officer for a copy of the quiz. Email him at firstname.lastname@example.org.