ne 301 - introduction to nuclear science spring 2012

NE 301 - Introduction to Nuclear ScienceSpring 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

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ReminderLoad TurningPoint Reset slides Load List Homework #3 due February 16 Next Tuesday February 14 – 1st Demo

Session MCA Gamma Spectroscopy identification of

isotopes NAA of samples

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/timeDose = dose rate 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/cm2 s]

10 2 2 1( )[ / ] 1.602 10 [ ] [ / ] [ ]en ED Gy s E MeV cm g cm s

tr(E)/ =mass interaction coefficient (table C3)E = particle energy [MeV] = flux [particles/cm2 s]

10 2 2 1( )[ / ] 1.602 10 [ ] [ / ] [ ]tr EK Gy s E MeV cm g cm s

Notice Difference

Engineering Equations – PLEASE Watch out for units!

Dose Calculation PracticeAssume a 57 mCi point source of 137Cs. 137Cs emits a 0.60 MeV gamma with a frequency of 0.941 per decay. At a distance of 2 meters from the source, calculate:

1. “Absorbed Dose” rate in tissue

Dose Calculation Practice – find firstSp = 57 mCi E = 0.6 MeV gamma @ 94.1% of the timer=200 cm

, total linear attenuation coefficient (or macroscopic cross section) in air for 0.6 MeV (table C3)

2( ) ( )4

rAFlux I r r er

Total linear attenuation coefficient (or macroscopic cross section) in air for 0.6 MeV (table C3)

3.289e-2 cm2/g

9.69e-5 cm-1

3.289e-4 cm-1

3.284e-2 cm2/g

8.040e-2 cm2/g

0% 0% 0%0%0%

1. 8.940e-2 cm2/g2. 9.69e-5 cm-1

3. 3.289e-4 cm-1

4. 3.284e-2 cm2/g5. 8.040e-2 cm2/g

28.040 2[ / ]e cm g

=9.69e-5 cm-1

Dose Calculation PracticeSp = 57 mCi E = 0.662 MeV gamma @ 94.1% of the timer=2 mLinear attenuation coefficient (or macroscopic cross section) in air for 0.6 MeV (table C3)

22 3

3

2

22

2 2

10

8.040 10 1.205 10 2003

2 2

( ) =8.040 104 4

3.7 101 57 mCi 0.94110 1 ( )

4 200

( ) 3872.4

rp pr

disss cm g cm

g cm

cm s

S S cmr e er r g

CimCi Cir ecm

r

228.040 10 cmg

Now this flux incident in TISSUE (H2O)


8.939e-2 cm2/g

8.940e-2 cm2/g

3.289e-2 cm2/g

3.284e-2 cm2/g

0% 0%0%0%

What is the (en/ for dose) in tissue for 0.6 MeV (table C3)1. 8.939e-2 cm2/g2. 8.940e-2 cm2/g3. 3.289e-2 cm2/g4. 3.284e-2 cm2/g

Flux incident in TISSUE (H2O)Table C.3: en(E)/ =3.284e-2 cm2/g in H2O


10 2 2 2 1[Gy/s] 1.602 10 0.6 MeV 3.284 10 / 3872.4

[Gy/s] 1.22 8 Gy/s = 1.22 6 rad/s 1.22 rad/s=4.4 mrad/hr

D cm g cm s

D e e

[Sv/s] 1.18 8 Gy/s 1= 1.18 8 Sv/s = 1.18 6 rem/s =1.18 rem/s=4.2 mrem/hrH e e e

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?

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2 cm Dose Calculation PracticeSp = 57 mCi E = 0.6 MeV gamma @ 94.1% of the timer=2 cmLinear attenuation coefficient (or macroscopic cross section) in air for 0.6 MeV (table C3)

22 3

3

2

22

2 2

10

8.040 10 1.205 10 23

2 2

7

( ) =8.040 104 4

3.7 101 57 mCi 0.94110 1 ( )

4 2

( ) 3.95 10

rp pr

disss cm g cm

g cm

cm s

S S cmr e er r g

CimCi Cir ecm

r

228.040 10 cmg

2 cm flux incident in TISSUE (H2O)

Table C.3: en(E)/ =3.284e-2 cm2/g in H2O


10 2 2 2 1[Gy/s] 1.602 10 0.662 3.284 10 / 3.95 7

[Gy/s] 1.4 4 Gy/s = 0.014 rad/s 3600 s = 50 rad/hr

D cm g e cm s

D e

LD50=300 rem, so Lethal Dose in few hours!

Distance matters!

Cancer Risk From Radiation Exposure

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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)

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Terrestrial and Internal Radiation

Terrestrial Radiation

Radioactive isotopes naturally found in:water, soil, vegetation

Uranium Thorium Radon

Internal RadiationRadioactive isotopes naturally in our bodies from birth.

Potassium- 40 Carbon- 14 Lead- 210

Natural Exposures for Humans

ne 301 - introduction to nuclear science spring 2012

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