Radiation Measurements

four ways to measure radiation

READ: radioactivity, exposure, absorbed dose, dose equivalent

radioactivity traditional unit

Curie (Ci)

radioactivity SI unit

Becquerel (Bq)

exposure traditional unit

Roentgen (R)

exposure SI unit

Coulomb/kg (C/kg)

absorbed dose traditional unit

Rad

absorbed dose SI unit

Gray (Gy)

dose equivalent traditional unit

Rem

dose equivalent SI unit

Sievert (Sv)

radioactivity definition

radiation measured by the number of atoms disintegrating per unit time

1 Ci = ___ dps

3.7 × 10¹⁰

1 Ci = ___ dpm

2.2 × 10¹²

1 Bq = ___ dps

1

1 Ci = ___ Bq

3.7 × 10¹⁰

1 mCi = ___ MBq

37

exposure definition

amount of charge (coulomb C) liberated in a volume of air from the interaction of γ rays

1 R = ___ C/kg

2.58 × 10⁴

The Roentgen applies to what radiation?

x-rays and gamma-rays

What is the interacting medium for the Roentgen?

air

Roentgens are used in nuclear medicine as a value for __________ readings.

survey meter (GM survey meters or ionization chambers)

absorbed dose definition

amount of energy that radioactive sources deposit in materials through which they pass

1 rad = ___ Gy

.01

1 Gy = ___ rads

100

The Rad applies to what radiation?

all ionizing radiation

What is the interacting medium for the Rad?

any medium, all materials

What measurement do we use for organs of interest?

Rad

dose equivalent definition

measure of the biologic harm imparted to tissue

1 rem = ___ Sv

.01

1 Sv = ___ rem

100

occupational dose dose not include doses from:

• natural background radiation

• medical exposures of the individual

• exposure to persons who have been administered radioactive material and released

• voluntary participation in medical research

• as a member of the public

Who must wear a badge?

anyone likely to receive in 1 year a radiation dose in excess of 10% of the allowable occupational limits

What do thermal luminescent dosimeters contain to absorb energy given off by radiation?

lithium flouride chips

How many times can a thermal luminescent dosimeter be read?

once

What do optically stimulated luminescent dosimeters contain to emit a light signal proportional to the amount of radiation exposure?

aluminum oxide or beryllium oxide

How many times can an optically stimulated luminescent dosimeter be read?

multiple times

dose limit: whole body

5 rem, 50 mSv

dose limit: any organ

50 rem, 500 mSv

dose limit: eye

15 rem, 150 mSv

dose limit: skin/extremities

50 rem, 500 mSv

dose limit: minors

10% of adult worker limits

dose limit: public

0.1 rem, 1 mSv

dose limit: pregnant worker

0.5 rem, 5 mSv for whole pregnancy

total effective dose equivalent (TEDE)

sum of the deep-dose equivalent (external exposures) and the committed dose equivalent (internal exposures)

deep dose equivalent (DDE)

dose equivalent at 1 cm tissue depth, applies to external whole-body exposures

shallow dose equivalent (SDE)

dose equivalent at 0.007 cm tissue depth, applies to external exposure of skin or an extremity

ALARA stands for

as low as reasonably achievable

internal contamination can occur by

ingestion, inhalation, or skin absorption

ways to control external exposure

time, distance, shielding

inverse square law

I₁D₁² = I₂D₂²

shielding methods

syringe shields, lead pigs, lead bricks, L block, portable lead shields, lead-lined waste

half value layer (HVL) definition

amount of lead required to reduce the radiation exposure by half

shielding equation

I = I₀e^-ux

u = 0.693/HVL

What is a GM counter used for?

detecting low levels of radiation

What is an ionization chamber used for?

measuring high radiation areas

What is a well counter used for?

testing small amounts of removable radioactivity