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Experiment Process

The first step in utilizing the reactor is to file a request for reactor operation. That form must be reviewed and approved by another member of our staff prior to performing the experiment. The request form details what is to be done and explains why it will be safe. Answering the following list of questions will go a long way toward creating the request form.

(1) What do you plan to irradiate, and why (damage, doping, etc.)? Which experimental facility do you plan to use? Do you want fast neutrons, thermal neutrons, or both? To what fluence do you expect to irradiate the samples? What power level(s) do you want? How will the samples be encapsulated? Will anything need to be monitored or powered during the test (e.g. sensors)?  If so, the devices will need to be fused in case there were to be an electrical short that could impact the reactor.

(2) Will all of the samples be irradiated together? If so, some of the samples with higher cross sections may shield the others. Reactivity effects are generally small for small samples, but some may be an issue if the central irradiation facility (CIF) is used.

(3) A primary consideration will be radiation safety. What is the mass of each sample irradiated and its elemental composition? How pure are the samples? Are there significant trace elements present? Which isotopes will be produced, and in what quantities? The online WISE uranium project has a handy activity calculator for thermal activation.  Don't forget about (n,p) and (n,alpha) reactions, if fast neutrons are present. NIST has a calculator that can be used to estimate fast neutron activation.

(4) What dose rates do you expect at the end of irradiation? A common method is to use specific gamma ray constants to estimate dose, but this misses the beta dose. As a general rule, you can expect beta emitters to produce 5 rem/hr per mCi at 10 cm (4"). This can add up quickly. Of course, it may also decrease quickly, depending on the half-lives involved. It is a good idea to calculate the dose rate at some times after the end of the irradiation (1 day, 1 week, etc.).

(5) What do you plan to do with the samples after irradiation? If you plan to make measurements on them here, when will they be safe to handle? If you plan to take them back to your facility, how long will you need to wait before they can be shipped? We can ship excepted packages (UN2910) if your facility has a license to possess radioactive materials.  Otherwise, the samples will have to decay until they are exempt from that requirement. When shipping a UN2910 package, there are activity limits, but the limiting factor is usually dose rate on contact with the package, which cannot exceed 0.5 mrem/hr.

Once we have enough information to write the request form, it will take at least one week to write the request and have someone else review and approve it. Please allow two weeks for the approval process.

Miscellaneous Notes

The depth of the pool is 20' and it is about 16' to the center of the core from the top of the pool.  Any cabling that is run from the experiment to the equipment should be ~25-30' in length.  Equipment may be set up on the workbench to the north of the reactor pool. The workbench is 2'x6', but more space can be allocated if needed and arranged with NRL staff.

Irradiation baskets are available for use in the CIF, the AIF and the PIF.  The ID of the CIF basket is 0.9" and the ID of the AIF/PIF basket is 2.2".  If your sample(s) will not fit within one of these baskets, a rig will have to be machined to hold them.  Use aluminum whenever possible for the experiment rig.  Steel cannot be used in the reactor as it activates easily.  PTFE also cannot be used, as it releases fluorine gas from radiation exposure.  Avoid PVC, as it degrades and activates significantly, and avoid anything with chlorine.

Samples irradiated within the rabbit facility must fit within a polyethylene bottle with a 1.1" ID mouth and a 3.0" body.

Cadmium buttons are also available for use in reducing the thermal neutron component of the flux.  The cadmium buttons are made to hold activation foils measuring one-half of an inch in diameter.  Larger pieces of cadmium are available and may be used when prearranged with NRL staff.

The core is 2 feet tall, but there is some radiation damage above the core. When possible, leave the lowest five feet of fiber bare.

Typically, if there is an active heating element, an independent safety mechanism will be necessary to prevent overheating, such as use of a thermocouple near the outer wall of the test rig that is connected to a controller that is independent of the main experiment controller that can cut heater current. In addition, fuses or breakers in line with heater leads are needed to ensure that there cannot be an electric short that could impact the reactor.

Dosimetry is not typically performed during an experiment.  The neutron flux has been measured in the various irradiation facilities; this can be used to calculate the dose rate to which the experiment will be exposed.

With RG 58 coax cable, a maximum of two cables would fit through the cableway in the shielding plug for the AIF, PIF, or 7" tube.  However, if RG 316 coax cable were used, there would be room for quite a few of those in the cableway (6 - 8?).