Tutorial 3

RADIATION SCIENCE Tutorial 3 1.

Write the frequency and wavelength of the radiation are used in medical system below Frequency ( Hz )

Wavelength ( m )

i) ii) iii)

MRI 106 - 108 Hz x-ray 10 - 1024 Hz Optical Imaging 10 - 1024 Hz

1 - 102 m 10 -12 10 - 10 m 4-7 - 7-7 m

2. Write 4 types of ionizing radiation and the ionization distance air and tissue Type of radiation

Approximately energy ( MeV )

Alpha particle Beta particle Gamma ray X-ray

4–7 MeV Up to 6 MeV Up to 5 MeV Up to 10 MeV

Ionization element In air In tissue 1 – 10 cm Up to 10 cm Up to 100 m Up to 100 m

Up to mm Up to cm Up to cm Up to cm

0.1

Radiation origin

3

Heavy radionuclide Radionuclide

30

Radionuclide

30

Electron cloud

3. Explain, what the police radiation below i ) Alpha → The alpha particle is a helium nucleus containing 2 proton, 2 electrons, 2neutron and 4 unit mass. The alpha particle emitted from heavy nuclide element with heavy velocity through matter. The average alpha particle passes 4 – 7 meV of kinetic energy and ionize 40.000 atom for energy centimeter of tranverse through air. The energy of ionizing is quickly lost. So, the ionization of alpha particle in air is short range ( 5em ) and ress than 100 km in tissue. ii ) Beta → The beta particle is an electron was carries negative charges. Beta particle originate in the nuclide of radioactive atom and there electron in the outer shell of the nuclide of atom. The ionization of beta particle is 10 – 100 cm in air and about 1 – 3 cm in soft tissue.

iii ) Gamma → and often called

The gamma ray formed of electromagnetic radiation “photon”. The gamma ray is emitted from the nucleus

of radioisotopes and usually assoociated with alpha and beta particle. iv ) X-ray → The x-ray formed of electromagnetic radiation and often called “photon”. The x-ray is produced from outside the nucleus of the electron shells.

4. Find the units of exposure and calculate the exposure when the tissue exposure to the x-ray rate 25 mR / sec at 5 minutes 25 mR / s x ( 5 min ) ( 60 s ) = 7500 mR 5.

Find the absorbed dose when the intensity of x-ray is 23 μR on the 5 g tissue Absorption dose = Absorption energy = 23 x 10-6 Material 5 = 4.6 x 10-6 R / g

6.

Calculate the dose rate of absorbed at 2.3 m sec Dose rate = dose absorption = 2.3 x 10-4 Gy time 23 m sec = 1 x 10-5 Gy / m sec

7. The intensity of the x-ray operate at 70 kVp, 40 mAs is 400 mR at distance 185 cm. I 1I0

=

I 1 d 12

=

d2 d1

2

I 1 d 22

400 mR ( 100 )2 =

I2

( 185 )

2

400 000 mR =

I2

( 34225 )

I 2(

34225 ) = ( 400 000 mR )

I2

= 116.87 mR

I

= 10.81 mR