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Radiation and Safety LTT-3306 page 1/2
Examination 22.1.2007
6 guestions

1. Describe the interaction mechanisms between electromagnetic radiation and matter. List at
least three (3) mechanisms.

a. Explain briefly the direct and indirect effect of ionizing radiation in molecular level in a
living cell. 2 points

b. Describe briefly the deterministic and stochastic adverse effects caused by exposure to
ionizing radiation. 4 points

3. Tellabout the basic principles of radiation protection and their implementation in radiology.

4. The activity of 18-F isotope is 400 MBg in the morning at 8.00 o?clock. The isotope is in an
unshielded bottle. Estimate the radiation exposure of a person working behind a thin wall at
3 m distance; exposure time is from 8 to 16 o?clock. 18-F has a half-life of 110 min and it
sends 511 keV gamma radiation with production factor of 1,9*10* mSv/MBg in one metre
distance per hour.

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Radiation and Safety LTT-3306 page 2/2
Examination 22.1.2007
6 guestions

 

In case this is the first exam that you are attending, you may replace one of the following
calculation tasks (lower score) by the points from the exercises. If this is your second
exam, the exercise points are not valid anymore.

5.

6.

 

 

 

 

 

 

 

 

 

 

 

 

 

Radiation type T Weighting Tissue or organ Weighting
factor wr L factor wr

| Bhotonspall energies 1 | | gonads (testes orovaries) 0,20
Electrons and myons, 1 red bone marrow, colon, 0,12

all energies [ängystomaeh

Neutrons with energy adder, breast tissue, 0,05
<l0keV 5 liver, oesophagus, thyroid
10keV<E<100keV 10 | gland

100keV<E<2MeV 20 skin, bone surface 0,01
2MeV<E<20MeV 10 other tissues and organs* 0,05
>20Mev 5 *adrenal, brain, upper large intestine,
Protons, energy 5 small intestine, airways outside thorax,
>2MeV kidney, muscle, pancreas, spleen, thymus
g pha particles, fission 20 and uterus.

gments, heavy nuclei

 

Wr =.
a. Whatis the eguivalent dose for photons if the absorbed dose is 1,25 Gy? — *
C= i

b. Whatis the effective dose for photons in lungs if the absorbed dose is 1,25 Gy?

c. Whatis the effective dose for alpha-radiation in ovaries if the absorbed dose is 1,5
Gy?

d. If both radiation types and both targets are valid simultaneously, what are the
eguivalent doses and what is the effective dose?

e. Which ones (lungs/ovaries) are more sensitive to radiation and why?

In the radiation therapy department an old low energy linear accelerator (4 MV) was
replaced by a higher energy (20 MV) accelerator. The output of the new accelerator at 1 m
distance from the radiation source is 4 Gy/min. When the radiation beam is directed towards
the wall, behind which the control room is located, the distance from the radiation source to
the wall is 4.4 m. The thickness of the concrete wall is 1.6 m. The momentary dose rate
outside the wall may not exceed 15 uSv/h. Is additional steel shielding in the wall needed?
If yes, how thick of a plate of steel? (T VLooncrete =40.0 cm and TVL steet =10.5 cm for 20 MV
X-rays.)
Radiation and Safety, LTT-3306
Examination 27.11.2006

PLEASE ANSWER EACH TASK ON SEPARATE PAPER!

1. What kind of molecular changes does radiation induce in cell? How do the effects of photon
radiation and of electron radiation differ from each other? How can the molecular damage
lead to hazardous health effects?

2. List three (different) methods for detecting radiation and briefly explain the principles of
each of them.

3. Tell about diagnostic reference levels and their use in radiology.

4. An employee has to work long times in a laboratory room. There is a bottle of 131-I with
activity of 100 MBg (Half-life 8 d, most common gamma energy 364 keV, HVL in lead 3.3
mm) on the shelf in the room. The employee protects him/herself from radiation by the
following means:

a) He/She decreases the time in laboratory by doing the work in half of the original time.
b) He/She puts the isotope into a lead container with wall thickness of 1 cm.
c) He/She moves the bottle so that the distance is 2 m instead of 1 m:

Estimate roughly numerically the effectiveness of used shielding methods. Please explain
your calculation. N

You can utilize your points from the exercises in either of the following calculation tasks.

 

 

 

5.
Isotope Decay form Tn [s] M [g/mol] m [g] / [kg/m"]
| 50s pf 122 15 5.0 1,43
| Rnss a 56 220 5.0 9,73

 

 

 

 

 

 

 

 

N4=6,022*10% 1/mol

At time moment /=0 s you have two isotopes, oxygen-15 and radon-220. The mass of both

isotopes is 5.0 g.

a. Describe how they decay as *Xz — 7. You can mark the born nuclide with *Y” if you
don't have the periodic table. Name the particles.

b. Whatare the activities of oxygen and radon at 1=0 s?

What are their activities after 1=5000 s?

d. After what time 1, the activity of radon is the same as for oxygen after 5000 s (the
activity from the previous calculation)?

S

6. In the radiation therapy department an old low energy linear accelerator (4 MV) was
replaced by a higher energy (20 MV) accelerator. The output of the new accelerator at 1 m
distance from the radiation source is 4 Gy/min. When the radiation beam is directed towards
the wall, behind which the control room is located, the distance from the radiation source to
the wall is 4.4 m. The thickness of the concrete wall is 1.6 m. The momentary dose rate
outside the wall may not exceed 15 Sv/h. Is additional steel shielding in the wall needed? If
yes, how thick of a plate of steel? (T VLooncrete =40.0 cm and TVL steet =10.5 cm for 20 MV
X-rays.)