Radiation Quantities

Question 1

1 amp = _____

Answer 1

1 amp = 1 Coulomb sec^-1

Question 2

1 watt = _____

Answer 2

1 watt = 1 Joule sec^-1

Question 3

1 eV = _____ ergs

Answer 3

1 eV = 1.6 x 10^-12 ergs

Question 4

1 eV = _____ Joules

Answer 4

1 eV = 1.6 x 10^-19 Joules

Question 5

1 Å (angstrom) = _____ m

Answer 5

1 Å (angstrom) = 10^-10 m

Question 6

1 inch = _____ cm

Answer 6

1 inch = 2.54 cm

Question 7

1 ft = _____ cm

Answer 7

1 ft = 30.48 cm

Question 8

1 u = _____ kg

Answer 8

1 u = 1.66 x 10^-27 kg

Question 9

1 u = _____ MeV

Answer 9

1 u = 931.5 MeV

Question 10

1 Ci = _____ dps

Answer 10

1 Ci = 3.7 x 10¹⁰ dps

Question 11

1 Ci = _____ dpm

Answer 11

1 Ci = 2.22 x 10¹² dpm

Question 12

1 R = ______ C kg^-1

Answer 12

1 R = 2.58 x 10^-4 C kg^-1

Question 13

1 rad = _____ J kg^-1

1 Gy = _____ J kg^-1

Answer 13

1 rad = 0.01 J kg^-1

1 Gy = 1 J kg^-1

Question 14

1 rad = _____ MeV g^-1

Answer 14

1 rad = 6.242 x 10⁷ MeV g^-1

Question 15

1 rad = _____ erg g^-1

Answer 15

1 rad = 100 erg g^-1

Question 16

1 R = _____ ergs g^-1 of air

Answer 16

1 R = 86.9 ergs g^-1 air

* based on 33.7 eV/ion pair

Question 17

1 R = _____ ergs g^-1 of soft tissue

Answer 17

1 R = 98 ergs g^-1 soft tissue

* based on 33.7 eV/ion pair

Question 18

1 dpm = _____ pCi

Answer 18

1 dpm = 0.45 pCi

Question 19

1 day = _____ sec

Answer 19

1 day = 86,400 sec

Question 20

1 day = _____ min

Answer 20

1 day = 1,440 sec

Question 21

1 year = _____ sec

Answer 21

1 year = 3.15 x 10⁷ second

Question 22

What does exposure measure?

Answer 22

The ability of photons to produce ionizations in air.

Question 23

Three major limitations for the use of the roentgen

Answer 23

1. The roentgen applies only to photons.
2. The roentgen applies only in air.
3. The roengten is defined only for E<3MeV

Question 24

Define

Absorbed Dose

Answer 24

• Unit: rad (“Roentgen Absorbed Dose”)
• Measures the energy which is actually deposited in some given mass.
• One rad is equivalent to 100 ergs of energy deposited per gram of material.

Question 25

Define

Quality Factor

Radiation Weighting Factor

Answer 25

It is a modifying factor by which the absorbed dose at a point can be multiplied to determine the risk of biological injury corresponding to the irradiation conditions. Values are a function of LET.

NRC / DOE / NCRP

• Symbol: Q
• Unit: rem rad^-1

2007 ICRP

• Symbol: w_R
• Unit: Sv Gy^-1

Question 26

Define

Dose Equivalent

Equivalent Dose

Answer 26

Biologically weighted absorbed dose. Takes absorbed dose (in rad/Gy) and converts to a risk factor.

NRC / DOE / NCRP

• “Dose Equivalent”
• Symbol: H_T
• Unit: rem, Sievert
• Equation: H_T = D Q

2007 ICRP

• “Equivalent Dose”
• Symbol: H_T
• Unit: Sievert
• Equation: H_T = Σw_RD

Question 27

Define

Tissue Weighting Factor (w_T)

Answer 27

Takes into account the reduced risk of cancer mortality and genetic effects when only some body organs receive a dose.

Question 28

Define

Effective Dose Equivalent

Effective dose

Answer 28

Whole body dose equivalent of partial exposure.

NRC / DOE / NCRP

• Symbol: H_E
• Unit: rem, Sievert
• Equation: H_E = Σw_TH_T

2007 ICRP

• Symbol: E
• Unit: Sievert
• Equation: E = Σw_TH_T

Question 29

Define

Committed Dose Equivalent (CDE)

Committed Equivalent Dose

Answer 29

Pre-2007 ICRP

• Symbol: H_T,50 or CDE
• Unit: rem, Sievert
• 50 year organ dose from internal emitters

2007 ICRP

• Symbol: H_T(50)
• Unit: Sievert
• 50 year organ dose from internal emitters

Question 30

Define

Committed Effective Dose Equivalent (CEDE)

Committed Effective Dose

Answer 30

Pre-2007 ICRP

• Symbol: H_E,50 (CEDE)
• Unit: rem, Sievert
• Equation: H_E,50 = Σw_TH_T,50
• 50 year body dose from internal emitters

2007 ICRP

• Symbol: E(50)
• Unit: Sievert
• Equation: E(50) = Σw_TH_T(50)
• 50 year body dose from internal emitters

Question 31

Thumb Rule

When can you treat a line source as a point source for calculation purposes?

Answer 31

As long as the distance away from the source is at least three times the longest dimension of the source, then inverse square law calculations will give the correct answer to within one percent.

Question 32

Equation

Calculate Dose Rate using the Bragg-Gray equation

Answer 32

Through the use of this equation, an exposure or exposure rate measurement in air can be converted into an accurate dose or dose rate in tissue.

• S = stopping power
• W = erg/ion pair
• e = Coul/ion pair

Question 33

Define

Relaxation length

Answer 33

• The thickness of a shield for which photon intensity in a narrow beam is reduced to 1/e (0.368) of its original value.
• One relaxation length is the mean free path (1/µ)
• µx = # of mean free paths

Question 34

How do absorbed fractions compare between α/β and X/γ-rays?

Answer 34

Charged particles (α/β)

• AF(T←S) = 1 if T = S
• AF(T←S) = 0 if T ≠ S

X-ray and γ-rays

• 0 < AF(T←S) < 1

Question 35

What is the ICRP 26 risk factor for stochastic effects?

Answer 35

1×10^-4 rem^-1

Question 36

Explain why the equation I = I₀e^-µx does not apply in relation to photon shielding for broad beam conditions or for very thick materials.

Answer 36

• Primary interaction of photons is Compton scattering which leads to scattered secondary photons referred to collectively as buildup.
• The given equation does not include the variable B and therefore only accounts for initial/uncollided photons