3/2003 Rev 1 I.3.8&10 – slide 1 of 23

Part I Review of Fundamentals

Module 3 Interaction of Radiation with Matter

Session 8&10 Neutron Activation

Session I.3.8&10

IAEA Post Graduate Educational CourseRadiation Protection and Safety of Radiation Sources

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Introduction

Neutron activation will be discussed

Students will learn about principles of neutron activation, the activation equation, concept of maximum or saturation activity, and solve a problem

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Content

Importance of neutron activation to health physics

Production rate of an isotope under neutron bombardment

Activation equation

Concept of maximum or saturation activity

Solve a problem

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Overview

Principles of neutron activation of stable isotopes will be discussed

Health physics significance of neutron activation will be discussed

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Neutron Capture in 23Na

23Na (n,) 24Na

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Examples of Importance of Neutron Activation

Production of isotopes (for example 60Co, 192Ir, etc.)

Accident dosimetry (for example 24Na in blood)

Crime detection in forensic medicine

(for example Napoleon’s hair)

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Activation analysis for measurement of trace elements

Activation products in a reactor are major sources of radiation exposure to workers (for example 60Co)

Activation products can give a radiation dose to members of the public (e.g. direct gamma radiation from 16N in steam from a BWR)

Examples of Importance of Neutron Activation

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Determination of fast neutron radiation component at Hiroshima

Fast neutron activation of Cu in building materials created 63Ni by reaction

63Cu (n, p) 63Ni

Accelerator mass spectrometry of 63Ni (half-life = 100 years)

Examples of Importance of Neutron Activation

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Concept of Reaction RateNeutron Bombardment

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= No - NdNdt

Differential Equation forNeutron Activation

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N(t) = No(1 - e-t)

Equation for RadionuclideProduction by Neutron Activation

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N(t) = No (1 - e-t)A(t) =

Activation Equation Expressedin Terms of Activity

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for t << 1

e(-t ) = 1 - t

Useful Rule of Thumb forSimplifying Exponential Terms

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N() = No

Equation for Maximumor Saturation Activity

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Buildup of a RadionuclideUnder Neutron Bombardment

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Buildup and Decay Following Neutron Activation

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Time to Reach SaturationFunction of Product Half-Life

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Problem 1

One gram of cobalt is introduced into a neutron flux of 1 x 1014 neutrons cm-2 sec-1. Calculate:

the resultant activity of 60Co in TBq after one year and

the maximum (saturation) activity of 60Co

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Problem 1 – Given Conditions

Given:

% abundance of 59Co = 100%

# of atoms in 1 mole of 59Co = 6.02 x 1023

cross section = 19 barns

1 barn = 10-24 cm2

half-life of 60Co = 5.2 years

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Solution to Problem 1

Activity of 60Co is given by A = No (1 - e-t)

= 1014 neutrons cm-2 second-1

= 19 x 10-24 cm2

No = 1 g x 6.02 x 1023 atoms mole-1 x = 1.02 x 1022 atoms

t = x 1 y = 0.13

(1 - e-t) = (1 - e-0.13) = (1 - 0.878) = 0.12

1 mole59 g

0.6935.2 y

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Solution to Problem 1

Solving for A we have:

(a) A = (1014) x (19 x 10-24) x (1.02 x 1022) x (0.12) = 2.33x 1012 dps of 60Co = 2.33 TBq

60Co

(b) The maximum or saturation activity of 60Co is given by: A() = N = No

since (1 - exp-) = 1

No = (1014) x (19 x 10-24) x (1.02 x 1022) = 1.94 x 1013 dps = 19.4 TBq 60Co

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Summary

Neutron activation was discussed

We learned about the health physics significance and principles of neutron activation, the activation equation, concept of maximum or saturation activity, and solved a problem dealing with radionuclide production by neutron activation

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Where to Get More Information

Cember, H., Johnson, T. E., Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2008)

Martin, A., Harbison, S. A., Beach, K., Cole, P., An Introduction to Radiation Protection, 6th Edition, Hodder Arnold, London (2012)

Attix, F. H., Introduction to Radiological Physics and Radiation Dosimetry, Wiley and Sons, Chichester (1986)

Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8th Edition, 1999 update), Wiley, New York (1999)