3/2003 Rev 1 I.3.7 – slide 1 of 23 Part I Review of Fundamentals Module 3Interaction of Radiation with Matter Session 7Neutron Interactions Module I.3.7 IAEA Post Graduate Educational Course Radiation Protection and Safety of Radiation Sources

3/2003 Rev 1 I.3.7 – slide 2 of 23 Introduction  Neutron interactions with matter will be discussed  Students will learn about neutron interaction mechanisms, neutron energy categories, the concept of neutron cross section, and neutron removal from a beam

3/2003 Rev 1 I.3.7 – slide 3 of 23 Content  Neutron interaction mechanisms  Neutron energy categories  Radiative capture  Charged particle emission  Fission  Elastic and inelastic scattering  Neutron cross sections and removal

3/2003 Rev 1 I.3.7 – slide 4 of 23 Overview  Mechanisms of neutron interactions with matter will be discussed  Health physics significance of neutron interactions will be discussed

3/2003 Rev 1 I.3.7 – slide 5 of 23 Charged Particle Interactions Ionizing radiation is divided into two categories: Directly Ionizing alpha and beta Indirectly Ionizing photons and neutrons

3/2003 Rev 1 I.3.7 – slide 6 of 23 Neutron Interactions  Neutrons have no charge and thus are indirectly ionizing  There is always a “mixed” field of neutrons and gamma rays  The biological effects of neutrons are strongly energy dependent  Neutrons are arbitrarily divided into “slow” (thermal) or “fast” (energies of 1 MeV and above)

3/2003 Rev 1 I.3.7 – slide 7 of 23 Neutron Energy Categories Name/TitleEnergy Cold 0 < eV Thermal eV Epithermal < 0.4 eV Cadmium 0.4  0.6 eV Epicadmium 0.6 < 1 eV Slow 1  10 eV Resonance 10 < 300 eV Intermediate 300 eV  1 MeV Fast 1 < 20 MeV Relativistic > 20 MeV

3/2003 Rev 1 I.3.7 – slide 8 of 23 Radiative Capture 1 n + 1 H  2 H +  1 H(n,  ) 2 H Slow Neutron Interactions

3/2003 Rev 1 I.3.7 – slide 9 of 23 Radiative Capture 1 n Cd  114 Cd +  113 Cd(n,  ) 114 Cd Slow Neutron Interactions

3/2003 Rev 1 I.3.7 – slide 10 of 23 Charged Particle Emission 1 n + 10 B  7 Li + 4 He 10 B(n,  ) 7 Li Slow Neutron Interactions

3/2003 Rev 1 I.3.7 – slide 11 of 23 Charged Particle Emission 1 n + 14 N  14 C + p 14 N(n, p) 14 C Slow Neutron Interactions

3/2003 Rev 1 I.3.7 – slide 12 of 23 Fission 1 n U  fission products available for more fission Slow Neutron Interactions

3/2003 Rev 1 I.3.7 – slide 13 of 23 Fission

3/2003 Rev 1 I.3.7 – slide 14 of 23 Fast Neutron Interactions  Elastic scattering - neutrons interact with particles of approximately the same mass such as protons (billiard ball analogy)  Occurs in materials rich in hydrogen such as water, paraffin wax, concrete  Accounts for about 80% of fast neutron dose to tissue

3/2003 Rev 1 I.3.7 – slide 15 of 23 Fast Neutron Interactions Inelastic scattering – neutrons interact with particles of much greater mass (e.g. iron nuclei) (analogy of ping pong ball striking bowling ball)

3/2003 Rev 1 I.3.7 – slide 16 of 23 Elastic Scattering

3/2003 Rev 1 I.3.7 – slide 17 of 23 Inelastic Scattering

3/2003 Rev 1 I.3.7 – slide 18 of 23 Neutron Cross Sections  Probability that neutron will interact with a given material  Unit is “barn” where 1 barn = cm 2  Leads to concepts of “microscopic” and “macroscopic” cross sections

3/2003 Rev 1 I.3.7 – slide 19 of 23 Microscopic Cross Section Sum of separate cross sections for all processes which may occur with a given atom. Unit is cm 2  total =  scatter +  capture +  fission

3/2003 Rev 1 I.3.7 – slide 20 of 23 Macroscopic Cross Section Product of microscopic cross section and the total number of atoms per cm 3 in the material. Unit is cm -1  total = N  total where N = number of atoms/cm 3

3/2003 Rev 1 I.3.7 – slide 21 of 23 Neutron Removal by an Absorber I = I 0 e where I = neutrons passing through the absorber I 0 = neutrons incident on the absorber N  total = total macroscopic cross section x = absorber thickness - N  total x

3/2003 Rev 1 I.3.7 – slide 22 of 23 Summary  Neutron interactions with matter were discussed  Neutron interaction mechanisms, neutron energy categories, the concept of neutron cross section, and neutron removal from a beam were described

3/2003 Rev 1 I.3.7 – slide 23 of 23 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, 6 th 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 (8 th Edition, 1999 update), Wiley, New York (1999)