Lab Exercise - Neutron Activation Analysis

Learning Goals

• Understand how neutron activation analysis works
• Be able to find elemental concentrations from gamma ray counts
• Gain experience in handling the various instruments involved

Explanation and Exercise Guide

Theory

Introduction to Neutron Activation Analysis (read)

Experimental Procedure

The exercise will consist of two main parts:

1. Thermal INAA of total chlorine in organic solutions using HPGe gamma spectroscopy.

• Lectures/demonstrations in the 4 application areas radio-pharmacy, radio-ecology, radioactive waste management and reactor operations.
• The students are divided first into two groups. Each group follows the procedure below.
• The NAA laboratory is inside a barrier. Accordingly, students have to observe and adapt the following procedure:
• All participants have to bring personal dose-meters and a lab-coat.

2. Put on lab-coat and dose-meter on the outside of the barrier.
3. Put on shoe cover (plastic) according to the demonstrations of the laboratory assistant and enter into the “hot” side of the barrier. Bring a minimum of papers into the laboratory.
4. The NAA laboratory facility, which originally consists of 3 wet-chemistry labs and 2 instrument labs, has temporarily only available 1 wet-chemistry lab and 1 instrument lab. All sample preparation, including sample transfer to and from the reactor, is performed in the chemistry lab. As soon as the sample is irradiated, prepared and ready for detection, it is transferred to the instrument, or counting lab.
5. Detection will be carried out with an HPGe detector coupled to common nuclear electronics and a PC-operated MCA based on the Maestro-program from Ortec.
6. It is important that the students strictly follow the instructions from the lab.-assistant(s) and not operate on “their own”.
7. When the practical tasks in the laboratory is finished, it is time to leave the NAA-laboratory. Collect your belongings and follow the procedure:
- Go to the wardrobe with the barrier
- Check your hands and lab-coat for contamination with a contamination monitor.
- Take off the lab-coat and place it in a designed plastic bag.
- Wash your hands
- Remove the shoe plastic cover according to demonstration by the lab-assistant.
- Enter the non-radioactive side of the barrier.
- Carry out all calculations in the assigned conference room.

Determination of Total Cl in Organic Liquids

Natural Cl has the two stable isotopes ³⁵Cl (35%) and ³⁷Cl (65%). Thermal neutrons induce the two reactions ³⁵Cl (n,γ) ³⁶Cl (T_1/2 = 3*10⁵ ) and ³⁷Cl (n,γ) ³⁸Cl (T_1/2 = 37.3 min). Only the second reaction is useful here. The actual gamma energies for ³⁸Cl are 1642.7 keV and 2167.6 keV.
The detailed procedure is:

1. Team 1 and Team 2 go to the detector room where a teacher will demonstrate the counting equipment. These teams will then be well prepared for the counting procedure after the following practical procedure.
2. Team 3 and Team 4 go to the preparation laboratory and carry out the following procedure:
3. Prepare a Cl-standard: Dry KCl in a heating cabinet at 110 ^oC for 24 h. Cool in a desiccator. Weigh exactly in ca. 0.21 g KCl and dissolve to 100.00 mL in a measuring flask with distilled water. This standard is approximately 1000 ppm.
4. For the present analysis we will operate with a working standard of about 100 ppm. Take an aliquot of 10 mL from the standard and dilute to 100 mL with distilled water.
5. Prepare 4 plastic irradiation ampoules by heat-sealing adequate lengths of a plastic (polyethylene) tubing in one end.
6. To one ampoule transfer a fraction of 1.00 mL from the working standard. Heat-seal and label.
7. To the three others transfer 3 parallels of 1.00 mL of the organic unknown sample. Heat-seal and label.
8. Pack the ampoules into a rabbit container.
9. Arrange irradiation with the reactor control room.
10. Irradiate the sample 5 min and transfer back to the lab.
11. After irradiation wash the ampoules on the outside with the washing solution sequence acetone-water-acid mixture-water-acetone. Every ampoule is washed for 5-10 s in each solution.
12. Samples are transferred to the counting laboratory and a demonstration is given of the counting equipment for teams 3 and 4.
13. Position the first sample in front of the detector inside the lead shield and start counting. Start the stop-clock. Counting time 5-10 min.
14. Count the two other samples and the standard in the end.
15. Integrate the appropriate peaks and note the results.

Questions for the Students

Here there should be relevant questions regarding the theory of the exercise which should be possible to answer after the exercises have been performed. The questions should be molded into the report that the students write after the exercises in such a way that it feels natural.

Other

How to do calculations or other important aspects for the theory that is not directly related to exercise.

Safety Aspects

Here the safety aspects of the exercises should be written. Because of the different rules in different countries this will probably never be correct for every user. It should at least contain HMDS for the chemical compounds used or relevant links to used equipment.

Equipment

Description of the equipment needed and used during the exercises.

Preparation for the lab Supervisor

The preparation that the lab Supervisor needs to do to ready the lab.

Feedback from Users and Supervisors

Here there should be a link to a open page where people who have used the exercise can leave feedback. How the exercises worked and troubles in performing it.