The beam used for experimentation at the NSRL facility will result in activation of material exposed to it. All materials irradiated in the NSRL target room are to be controlled as radioactive until surveyed and released by a BNL Radiological Controls Technician (RCT). Samples that have had radioactive tracers such as 3H or 14C added to them shall be controlled as radioactive through out the entire process and will not be released as non-radioactive. When liquid samples are activated, there exists a potential for dispersion of radioactive material through spilling of the sample during handling or manipulation creating a contamination area. Activated samples containing liquids that are manipulated required additional Radiological Training (Benchtop/Dispersable Training), a designated (Posted) radiological area to perform work in, and a Radiation Work Permit (RWP). When samples have had enough time to decay they again become non-dispersible and no special radiological handling is required. Correct and appropriate biological handling techniques always apply regardless of the sample’s radiological status.
Below are tables indicating the type of beam delivered to the sample (proton or ion), absorbed dose delivered, and the required decay time for a sample to be considered non-dispersible. These tables must be considered when planning work to determine if your samples will be considered to be radioactive dispersible, which would require additional training and special handling. Work on the samples can proceed by workers with the appropriate training. If work on the samples is planned, notification should be given to either the Medical Department or the Biology Department, as appropriate.
If activated samples need to come back to Medical, users are asked to let the NSRL Medical Liaison Scientist (631-344-2913) know well in advance so the Facility Support Division can have hoods/incubators posted and Radiological Work Permits written as appropriate. Teams are urged to have at least 2 team members with Dispersibles Training in case of an unexpected emergency. An HP Tech at NSRL will still need to survey materials and place a RAM tag on the samples. Transportation arrangements can be made for users to get from NSRL to Medical with activated samples. Users are authorized to transport properly contained activated samples in a government vehicle if they have a valid guest appointment and a valid driver’s license. The Long Term Support Facility (LTSF) staff in Medical is also available for transportation needs. Please advise the NSRL Medical Liaison of your plans ahead of time (i.e. before the run starts) so proper arrangements can be made.
Human cells must have “close proximity” double containment during irradiations at NSRL unless they are listed as Biosafety Level One by a vendor or cell repository. The most convenient method for this containment has been to place the entire holder in a zip-lock baggy. The team from the Biology Department will provide a variety of different sized bags at NSRL.
The activation decay times are presented as graphs, in tabular form, with a fuller description following.
If exposure times are long, i.e. are no longer negligible compared to the decay times of the relevant isotopes (20 minutes for 11C), then the tables below are an overestimate of the activation decay times, and users may want to make use of a dynamic decay time calculator that assumes a linear activation profile convoluted with the exponential decays of the activation products. This calculator can be accessed here. Contact the NSRL Liaison Physicist (631-344-3072 or 631-344-5830) or the RCT if you require assistance in using this application.
Figure 1: Activation Decay Times for Exposures of 0-10 Gray total. Horizontal axis is logarithmic.
Figure 2: Activation Decay Times for Exposures of 0-10 Gray total. Horizontal axis is linear.
Figure 3: Activation Decay Times for Exposures of 0-1 Gray total.
Here is the same information presented in tabular format.
Radioactive Decay of Activated Dispersible Materials at the NSRL
We have to comply with Suffolk County, DOE and BNL limits for concentrations of radioactivity that could be released into the environment or spilled. DOE specified activity (DPM) per area, calculated to be from a spill that is 0.5 cm deep.
Figure 1 shows the activity of these types of radionuclides as a function of time. R1 (11C) has a short half life, and over the period of 240 minutes has decayed substantially. R2 (7Be) and R3 have long half-lives, and their activities remain essentially constant during this time.
2. Multiple Radionuclide Decay
But we actually measure the sum of these disintegrations (DPM per unit volume), and their sum is the property that must be less than Suffolk County/DOE/BNL limits. The sum of these disintegrations per volume is shown in Figure 2
Figure 2. Sum of decay of three radionuclides, R1 (short half-life),and two longer-lived species, R2 and R3., shown as the black circles. The red line is the line for single isotope decay of R1. The net effect of the presence of the longer-lived species is to increase the time required for the mixed isotope sample to decay to the release limit, as shown.
3. Concentration effect.
· The release limits (Suffolk County/DOE/BNL) are based on concentration.
· If sample #1 of 1 milliliter is irradiated with 10 Gy of an ion from the NSRL beam, it is activated to 10Y DPM/1 ml, and we must wait N minutes (from the Table as calculated for that ion) for it to decay to meet the release limit.
· If we irradiated a similar 1 ml sample with 1 Gy, it would be activated to 1 Y DPM per 1 ml; if we had irradiated another 1 ml sample with 0.1 Gy, it would be activated to 0.1 Y per 1 ml.
4. Post Irradiation Sample Processing Effects
· Some experimental protocols require the use of the samples and solutions in the same conditions in which they were irradiated. In this case, the considerations in Paragraph 3 and times in the Table pertain directly.
· Other experimental protocols require the dilution of the irradiated samples/solutions with fresh, unirradiated, non-radioactive solution. Here are two examples:
o If sample #1 (1 ml, irradiated with 10 Gy, activated to 10Y DPM/ml), is diluted to a final volume of 10 ml with fresh, unirradiated, non-radioactive solution, it will contain Y DPM/ml. We see that this corresponds to the activity level induced by 1 Gy, and we can use the times corresponding to 1 Gy in the Table.
o Likewise, if sample #1 is diluted to a final volume (solution as in c) of 100 ml, it will contain 0.1 Y DPM/ml, corresponding to the activity level induced by 0.1 Gy, and we can use the times corresponding to 0.1 Gy in the Table.