Natural radioactivity (nr)

• NR is atomic changes in which unstable nuclei spontaneously shoot out “chunks” (fragments) of mass, energy or both.

• An isotope of unstable atom is called radioactive isotope - radioisotope.

• Examples of radioactive isotopes:

• Natural: Uranium, Radium, and Radon

• Man-made: Iodine-131, Technetium

called

1. Nature of

Radiation emitted by radioisotopes is

ionizing radiation

Ionization is the process of knocking an electron out of orbit

Electron

*

/

it has enough energy to displace one or more electrons from atoms it hits to form positively charged particles

Radiation

/

1. Nature of

ivitv. lonizii

:ion

vpes of ionizing radiation

a

♦

■>

He

2+

neutron

proton

proton

neutron

P

X-rays

n O

e

N

n

type of the ionizing radiation depends o on properties of the radioactive isotope

U

r

1. Nature of

Alpha Radiation

Alpha Radiation is highly ionizing

*Corpuscular type of ionizing radiation *It can easily strip electrons from atoms

Alpha Radiation does not travel far in matter:

□

Approximately 7 cm of air

Stopped by a piece of paper

Can t penetrate the dead outer layer of skin

- •

Beta radiation is less ionizing than alpha radiation

Can penetrate skin and tissue, to about 0.2 cm

	t i -~Vv
1—	’"tt-
,	Ijpj
Stopped by glass, plastic
or aluminium

* It can travel father in matter than alpha:

* Beta particles are about 8000 times less massive than alpha particles

^Gamma Radiation & X-rays

* g- & X-rays are examples of electromagnetic radiation (EMR), *The difference between these types of EMR is their energy

g- & X-rays need to crash directly into an electron to knock it out of orbit, as opposed to a & p particles, which interact at a distance with orbiting electrons, due to the force of their charge.

PP

Penetrating and Ionizing Power

IP

A

mm

max

y

max

mm

1. Half-life (T1/2)

is the time required for half of the radioactive atoms in a sample to have decayed

Safety level: 10 half-lives

io*4.5*io⁹=4.5*io¹⁰

10*28=280 years io*8=8o days

The half-lives of some radioactive isotopes

Radioactive isotope Half-life

Uranium-238,²|fu 4.5 X 10⁹ years

Carbon-14,¹⁴₆C 5.7 X 10³ years

Radium-226, ²ggRa 1.6 x 10³ years

Strontium-90 ⁹gSr 28 years

Iodine-131, 8.1 days

Bismuth-214, ²ggBi 19.7 minutes

Polonium-214,²> 1.5 X IQ"⁴ seconds

2. Radioactivity

(radioactive disintegration rate) is number of radioactive decays which occur per second

SI unit

becquerel, Bq

1 Bq = 1 decay / 1 sec

CGS unit curie, Ci

1 Ci = 3.7 ^x 10¹⁰ Bq

3.1. Exposure dose (air Kinetic Energy Released in MAtter = air KERMA, экспозиционная доза) - is a cumulative charge of ions of the same sign caused by ionizing radiation absorbed by dry air .

SI unit CGS unit

roentgen, R

coulomb, C/kg

1 R = 2.6-ю^-4 C/kg

3.2. Absorbed dose (поглощенная доза) -

is a measure of the energy deposited in a medium by ionizing radiation per unit mass

SI unit CGS unit

gray (Gy)

^{1 G}y= ^{1 J/k}g

2. Ass

adiation Doses

rad = radiation absorbed dose

^{1 G}y = 100 rad

3.3. Equivalent dose (эквивалентная доза) -

is an average measure of the radiation energy- absorbed by a fixed mass of biological tissue

ED takes into account the biological damage from different types of ionizing radiation.

SI unit

sievert (Sv)

1 Sv= 1 J/kg

2. Ass

adiation Doses

CGS unit

rem = roentgen equivalent man

1 Sv = 100 rem