Reed Reactor Experimenter Information

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The reactor specifically aims at providing students with unique educational and research experience, and may not be appropriate for industry use. You may want to use the reactor if:

• You are looking for the presence of an element in a sample.
• You are performing a trace element analysis on a sample.
• You want to study the biological effects of radiation without making the sample itself radioactive.
• You need to use radioactive materials or radiation.

The reactor is available for Reed Student use regardless of your major or type of thesis, and is free of charge. The reactor is available to students at other educational institutions pending a formal proposal.

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Overview

Some materials may require special approval before they are irradiated. Please discuss the exact contents and materials that you plan to use with us long before any experiment is due to begin. We will provide you with the necessary tools, workspace, and step-by-step instructions for preparing your samples for irradiation.

If you want to set up an experiment, contact the director of the reactor, at reactor@reed.edu or in Chem 102.

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Neutron Activation Analysis

Neutron activation analysis (NAA) is a method of analysis that detects one or more nuclides in a sample. NAA can also determine the amount of the nuclide present, even in very small quantities. The sample in question may be solid, liquid, or gaseous. NAA is the experiment type most often performed at the reactor.

Samples are activated in the reactor by neutron absorption. When a nucleus absorbs a neutron, a particle and a gamma ray are generally produced. Each nuclide produces a characteristic gamma ray, so analysis of the energy and frequency of these gamma rays will indicate the presence and amount of a nuclide in a sample.

Not all elements can be activated by neutron absorption, and we can only analyze gamma-emitting nuclides. While this means that not all elements can be found with NAA, it also means that organic materials will be ignored completely in the analysis. However, this does mean that the nuclides that can be found are somewhat limited. Appended is a list of the nuclides that we can find.

There are two usual methods by which we activate samples. One method is for samples that either activate very quickly or have short half-lives. To do this, we rapidly insert and remove the sample from the core via air pressure in the pneumatic transfer system, which is fondly known as the rabbit. Samples are run quickly and counted quickly when using the rabbit, but they must be run individually. If you will need to analyze a large number of samples with short half-lives (e.g. upwards of 25 samples), please be sure to let us know about your experiment at least a month before any implementation.

The other method is for samples that must be irradiated for longer periods of time and have longer half-lives. This method will let unwanted nuclides with short half-lives decay away before analysis is performed. To do this, we insert a number of samples into the rotary specimen rack, known also as the lazy susan. Up to eighty samples may be irradiated at one time with the lazy susan, and the samples may be irradiated for very long periods of time if necessary. Samples irradiated in the lazy susan will generally be counted for longer than those irradiated with the rabbit, so it may be some time before all of your data is available.

If you are planning to look for an element in quantities on the order of micrograms to nanograms, you should talk with us about the minimum detectable quantity of that element in our reactor. If we do not have a suitable known minimum detectable quantity for an appropriate interval of kilowatt-hours on record, we can help you set up an experiment to find the minimum detectable quantity yourself.

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Gamma Irradiation

When something is irradiated with gamma rays instead of neutrons, the sample will not become radioactive itself. This way, the biological effects of radiation can be observed without the hassle of analyzing a radioactive sample. When irradiating a sample with gammas, there will be no spectra produced. You will instead receive your irradiated sample for your own analysis once we are satisfied that it is neither radioactive nor contaminated.

There are several ways in which we can perform gamma irradiation. We can use our gamma irradiation racks, which will put samples next to a gamma source. The source used to provide these gammas is usually Ir-192, which is activated in the reactor and then moved to an in-pool, out-of-core facility to irradiate samples. Dose rates up to 15 rad per hour can be arranged.

The samples may also be put into the lazy susan, set near to the core, or placed into the central thimble while the reactor is shut down. In this configuration the samples will receive a gamma dose of up to 3 rad per hour, and a small neutron dose.

The simplest way to irradiate samples is with out out-of-pool gamma irradiator that can produce a dose up to 2 rad per hour. 

The method used will depend on the size of the sample and the radiation dose needed.

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From Experiment Request to Results: Sample Preparation, Scheduling, and You.

The first thing that you will need to do is to contact us and request an experiment. Do not plan on beginning sample prep until we approve your experiment so we can address any potential concerns. 

If you plan to use the rabbit or lazy susan for NAA, you will prepare your samples for irradiation by putting small amounts of material into clean sample vials. If you plan to use the gamma irradiation racks or out-of-pool irradiator, the sample preparation will vary depending on what you are analyzing. 

Sample preparation often requires a separate trip to the reactor that can last for several hours depending on the type and number of samples. Times when you can prepare samples may be limited, so please contact us to make an appointment. If you are planning on preparing samples outside of the reactor, you must follow our specific guidelines, so discuss this process with us before beginning. When your experiment has been approved we will give you specific instructions for sample preparation. There is a list of elements we can detect, as well as those that require special permissions, below. Once your samples have been prepared, we will schedule a time for your samples to be irradiated.

If you used NAA, your samples will produce characteristic gamma rays when removed from the core, and these gammas will be interpreted by a high purity germanium (HPGe) detector and displayed on a spectrum using the GammaVision program. Once your samples have been counted, you will be able to analyze the spectra produced. We will show you how to interpret the raw data so that you can perform your own analyses. Depending on how you structured your experiment, you will be able to determine what elements are present in your samples and, if desired, the amount of the detected elements.

This entire process may take several weeks. Plan on visiting the reactor several times over the course of 1-4 weeks:

• Sample preparation: This could take 1-8 hours.
• Sample irradiation: You are not required to attend, but are welcome. Depending on the experiment this could take anywhere from a couple of minute to 8 or more hours.
• Decay time: Samples may be allowed to decay before counting, anywhere from 2 minutes to several days or weeks.
• Counting time: Samples are counted for as few as 5 minutes or as long as 8 hours.
• Analysis time: Depending on the experiment this can take up to an hour per sample.

In Conclusion

If you think that the reactor might be a good resource for your experiment talk to us to see how we can best help you. If you have any questions, email reactor@reed.edu or stop by Chem 102.

Good luck!

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Detectable Elements and Detection Limits

The following materials need special approval before irradiation

• samples containing elemental mercury, or substances where mercury is a major component
• material containing more the 1 mg of uranium or thorium per sample container
• samples containing materials which are classified as flammable, water reactive, or corrosive. If approved, such experiments must at minimum be doubly encapsulated.
• organic solvents and other potentially unstable chemicals (even if not flammable). Evaluation of the potential to off-gas, sublime, volatilize or produce aerosols may be required. If approved, such experiments must at minimum be doubly encapsulated.
• samples containing or irradiated in association with more than trace amounts of elements with large neutron-absorption cross sections, including Cd, In, and B. An assessment of the reactivity effect, or the reactivity effect of previously run similar samples, may be required.
• materials which, for any reason, cannot be encapsulated.
• Explosive materials may not be irradiated under any circumstances.
• No experiment shall be performed which may lead to the failure of a fuel element.

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