NE Introduction to Nuclear Science Spring 2012 Classroom Session 9: Radiation Interaction with Matter  Absorbed Dose (D), Kerma (K) Gray (Gy) = 100 rad  Dose Calculations Analysis of Gamma Information (NAA) Chemical Effects of Nuclear Reactions

Reminder Load TurningPoint Reset slides Load List Homework #3 due February 16 Next Tuesday February 14 – 1 st Demo Session  MCA  Gamma Spectroscopy identification of isotopes  NAA of samples 2

Absorbed Dose, D (Gray, rad) Energy absorbed per kilogram of matter (J/kg) Gray: 1 Gy = 1 J/kg The traditional unit: Rad: 100 rad = 1 Gy rad = Radiation Absorbed Man Dose rate = dose/time

Kerma (Approx. dose for neutrons) Kerma Kinetic Energy of Radiation absorbed per unit MAss For uncharged radiation Kerma is easier to calculate than dose for neutrons Kerma and Dose: same for low energy Kerma over-estimates dose at high energy  No account for “Bremsstrahlung” radiation loses.

Calculating Dose Rate and Kerma Rate  en (E)/  =mass interaction coefficient (table C3) E = particle energy [MeV]  = flux [particles/cm 2 s]  tr (E)/  =mass interaction coefficient (table C3) E = particle energy [MeV]  = flux [particles/cm 2 s] Notice Difference Engineering Equations – PLEASE Watch out for units!

Calculating Dose Rate and Kerma Rate  en (E)/  =mass interaction coefficient (table C3) E = particle energy [MeV]  = flux [particles/cm 2 s]  tr (E)/  =mass interaction coefficient (table C3) E = particle energy [MeV]  = flux [particles/cm 2 s] Notice Difference Engineering Equations – PLEASE Watch out for units!

Dose Calculation Practice Assume a 57 mCi point source of 137 Cs. 137 Cs emits a 0.60 MeV gamma with a frequency of per decay. At a distance of 2 meters from the source, calculate: 1.“Absorbed Dose” rate in tissue

Dose Calculation Practice – find  first S p = 57 mCi E = 0.6 MeV 94.1% of the time r=200 cm , total linear attenuation coefficient (or macroscopic cross section) in air for 0.6 MeV (table C3)

Total linear attenuation coefficient (or macroscopic cross section) in air for 0.6 MeV (table C3) e-2 cm 2 /g e-5 cm e-4 cm e-2 cm 2 /g e-2 cm 2 /g

 =9.69e-5 cm -1

Dose Calculation Practice S p = 57 mCi E = MeV 94.1% of the time r=2 m Linear attenuation coefficient (or macroscopic cross section) in air for 0.6 MeV (table C3)

Now this flux incident in TISSUE (H 2 O)

What is the (  en /  for dose) in tissue for 0.6 MeV (table C3) e-2 cm 2 /g e-2 cm 2 /g e-2 cm 2 /g e-2 cm 2 /g

Flux incident in TISSUE (H 2 O) Table C.3:  en (E)/  =3.284e-2 cm 2 /g in H 2 O 2. Quality factor for gamma is 1, so Dose Equivalent rate is: Time to reach 5 rem (annual limit for radiation workers)?

Not much? But isn’t 57 mCi a lot? Well, let’s see distance… Redo dose at 2 cm? i.e. working with the source? 16

2 cm Dose Calculation Practice S p = 57 mCi E = 0.6 MeV 94.1% of the time r=2 cm Linear attenuation coefficient (or macroscopic cross section) in air for 0.6 MeV (table C3)

2 cm flux incident in TISSUE (H 2 O) Table C.3:  en (E)/  =3.284e-2 cm 2 /g in H 2 O LD50=300 rem, so Lethal Dose in few hours! Distance matters!

Cancer Risk From Radiation Exposure 19 According to the Biological Effects of Ionizing Radiation committee V (BEIR V) The risk of cancer death is 0.08% per rem (0.0008/rem) for doses received rapidly (acute) Might be 2-4 times less than that (0.04% per rem) for doses over a long period (chronic) These risk estimates are an average for all ages, males and females, and all forms of cancer. There is a great deal of uncertainty associated with the estimate. BEIR VII risk estimates for fatal cancer are similar to the values from BEIR V, but they also estimated incidence rates, which were about 50% of the fatal cancer rate. Risk from radiation exposure has been estimated by other scientific groups. The other estimates are not the exact same as the BEIR V estimates, due to differing methods of risk and assumptions used in the calculations, but all are close.

Cancer Risk Estimates Using the linear no-threshold risk model, the 1990 BEIR* V report provided the following estimate: The average lifetime risk of death from cancer following an acute dose equivalent to all body organs of 0.1 Sv (10 rem) is estimated to be 0.8%. This increase in lifetime risk is about 4% of the current baseline risk of death due to cancer in the United States. The current baseline risk of cancer induction in the United States is approximately 25%. Another way of stating this risk: A dose of 10 mrem creates a risk of death from cancer of approximately 1 in 1,000,000. * The National Academy of Sciences Committee on the Biological Effects of Ionizing Radiation (the BEIR Committee) 20

Terrestrial and Internal Radiation Terrestrial Radiation Radioactive isotopes naturally found in: water, soil, vegetation  Uranium  Thorium  Radon Internal Radiation Radioactive isotopes naturally in our bodies from birth.  Potassium- 40  Carbon- 14  Lead- 210

Natural Exposures for Humans