Trace Element Analysis of Geological, Biological & Environmental Materials by Neutron Activation Analysis: An Exposure

Exams

Starting with the second session, there will be a brief quiz during each session. Each review quiz counts for 5% of the course grade.

Question 1

In a house in Cambridge, the water from the faucet suddenly started showing some particulate matter, which is suspected to be copper from a pipe. It was brought to the MIT Reactor for analysis. You are asked to calculate the activity that would be produced by thermal neutron activation, if 1 gram of copper is irradiated in the reactor flux of 4 x 10¹² n.cm^-2.sec^-1 for 2 hours.

1. On removal what is the activity of each copper isotope?
2. What will be the activity of each isotope 1 hour after the removal from the reactor?

The answer should contain: the activity equation, the parameters and values used, and the activity calculated.

Suggested Use

1. The Chart of Nuclide Handout,
2. Table of Nuclides Appendix D, pp. 606-650, and Gamma-ray sources Appendix E, pp. 651-660. In Nuclear and Radiochemistry, by G. Friedlander, J. Kennedy, E. S. Macias, and J. M. Miller.

Question 2

An entrepreneur wants to know whether a particular area of interest has Molybdenum and Antimony. So what are the radioisotopes that can be used for the thermal neutron activation analysis. Provide all the relevant information of the X (n,γ)Y reaction, identify the parent and daughter nuclei, the activation cross section, the half-life of the daughter product, and the predominant gamma-ray energy for identification.

Suggested Use

1. Table of Nuclides Appendix D, pp. 606-650, and Gamma-ray sources Appendix E, pp. 651-660. In Nuclear and Radiochemistry, by G. Friedlander, J. Kennedy, E. S. Macias, and J. M. Miller.

Question 3

An unknown sample powder was found in an envelope. It was brought to the reactor for analysis. The gamma spectrum revealed significant gamma-ray peaks of energy 320 KeV, 1368 keV and 2754 keV. Identify the content of the powder.

Suggested Use

1. Appendix 5, Table 2. Neutron Activation Analysis, by D. De Soete, R. Gijbels, and J. Hoste.

Question 4

The weights of empty vial, empty vial + sample powder were taken 6 times. Write the formula for the propagation of errors, calculate the error in the weight of the sample powder. Interpret the results.

Weights (in grams) of the empty vial, weighed separately for 6 times:
1.14470, 1.14475, 1.14472, 1.14476, 1.14478, 1.14475

Weights (in grams) of the vial + sample powder, weighed separately for 6 times:
1.35041, 1.35040, 1.35029, 1.35018, 1.35026, 1.35035

Question 5

Arsenic is determined in river sediment samples. The abundance of As in the standard is 145 ppm. The gamma-ray energy of 76As is 559 keV. The gamma peak areas of the sample and standard are respectively, 32699, and 1533496 for the same counting times. The delays from the end of irradiation for the sample and the standard counting are 5.953 d, and 4.252 d. The weights of the sample and standard are 0.38476 g and 0.41669 g. Calculate the abundance in the sample. Estimate the propagation of errors. You may use the weighing error from problem 4 above.

Question 6

In the MIT-EAPS INAA Laboratory, an internal standard has been analyzed 10 times. Nd is one of the Rare Earth Elements. Its measured abundance values (in ppm) are

24.0 ± 0.7, 23.7 ± 0.7, 24.0 ± 0.5, 24.3 ± 0.9, 23.7 ± 1.0, 24.3 ± 1.0, 24.0 ± 0.7, 23.8 ± 0.6, 24.0 ± 0.7, 24.7 ± 0.9.

The reference value of this standard is 24.7 ± 0.3. Write the formulae and calculate the precision and accuracy of this measurement. Express the precision and accuracy in percentage.

Question 7

Our department chairperson came to know that an equipment grant would be available soon. So a memo was sent to our gamma-spectroscopy group asking the importance of gamma spectrometer. Write the usefulness of a gamma spectrometer. Describe the components of a gamma spectrometer. Look at the latest products. To look at the Web site Canberra and look under product category and do a write up - one or two lines of each product you want to select.

Question 8

The Department of Agriculture came to know that some fruit trees in Florida got contaminated. So they want to send some dry leaves for analysis of arsenic. Suggest a suitable standard.

Suggested Use

1. National Institute of Standards and Technology, Look under NIST Products and Services. Using the online Catalog (click on), Advanced Search (click on), Enter Keyword (suggested keywords: agriculture, leaves), View Certificate of Report and note down the information, Suggest your choice of the standard.

Question 9

The MIT Libraries has asked you for some suggestions for new books on neutron activation analysis. What book titles can you suggest, which they do not already own?

Suggestions

1. Vera: Virtual Electronic Resource Access, Type Books in Print in the search box. The next window opens, Type keyword in the Quick search box (suggested keywords: Neutron activation analysis, Nuclear analytical, Environmental geochemistry…, any keyword of your interest or field), You may search the Title in the Barton Search box to see whether that book already exists in the MIT library. Barton, the Libraries online catalog.

Question 10

Now that you are familiar with trace element analysis of materials by neutron activation analysis, briefly describe its application by giving one example.