KJM5900 - Autumn 2004

KJM 5900 Exercise 5: Neutron activation of silver.

Introduction

In this exercise you are going to irradiate silver with neutrons. Then you will use a gamma detector to measure the decay curve of the activated silver. By using different irradiation times the exercise will high-light basic principles behind nuclear reactions.

Learning goals:

You shall understand how neutrons can induce radioactivity in stable materials.
You shall be able to separate components in a decay curve which have different half lives.
You shall understand how the induced radioactivity is a function of both half life and irradiation time. I.e. you shall understand in-growth curves.

The theory behind this exercise you can find here: In English and Norwegian.

Preparations

Before you can start, we want to make sure you understand what will be going on. Therefore you are required to submit a pre-lab report where you answer some questions and do some calculations related to what you will be doing in the remote controlled laboratory. We have prepared a list of question and exercises you need to do. Answer these in writing and submit them as an attachment to e-mail to your supervisor. When they are corrected and approved you can start the actual laboratory exercise.

The Remote Controlled Laboratory Exercise

Link to the virtual instrument interface for the remote controlled lab: http://sievert.uio.no/lab4.html.

Before you start look through this slide show. It explains how to use the remote controlled laboratory. If you are unable to run the slide show or want a printout, you can download the slides as a PDF file.

Picture of the VI interface (how it looks like on your screen): JPEG file.

Procedure:

Measure the background for 300 seconds.
Measure the decay curves for the following neutron irradiation times: 12, 24, 48, 72 and 144 seconds. Record your results on the counting form and logarithmic plots found below. Calculate and plot uncertainties for all points.
Analyse the decay curves and determine R0, the count rate at the end of irradiation, for both isotopes of silver. If you want to use a computer program for this you must weight your results with respect to uncertainty (beware that the uncertainty do not transfer linearly when you switch from linear to logarithmic scale). Estimate the uncertainties for the R0 values by judging the fittet decay curves.
Enter your measured R0 values in the table found below. Assume R0 for the 144 s irradiation of the longest lived silver isotope is "true". Use this value and calculate the values for the other irradiation times for both isotopes and the 144 s value for the short lived isotope. Enter the values in the second half of the table.
Plot both experimental and calculated R0 values in a linear plot. Do the experimental and theoretical values agree?

Prepared counting forms and logarithmic plots for this exercise:

A4 formatted logarithmic plot (it's better to use the A3 format if you have a suitable printer) (in PDF format).
A3 formatted logarithmic plot (in PDF format).
Origin document suitable for plotting data (do not use for analysis), can be used instead of the A4 or A3 plots above.
Counting form (in PDF format).
Table for experimental and calculated R0 results (in PDF format).
A4 formatted plot for plotting in-growth curve (in PDF format) (in Origin format) .

Journal

Yes, you should write one! Use the pre-lab report as a staring point and report on your experiment and results. The report should be submitted not later than 3 days after you perform the experiment.

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Last updated 7. October 2004 by Jon Petter Omtvedt