Sebastian Bachmann

1
Radiation and radiation safety at the
Physikalische Institut
What is radiation?
Harm to the human body
Safeguards
2
What is ionising radiation?
?
n
?
?
Matter
Ionising radiation can harm in particular human
bodies!
3
Impact of ionising radiation on human bodies
4
Nuclear reactions and decay modes
Alpha-decay Nucleus emits an alpha-particle (2
protons und 2 neutrons).
Beta-decay Nucleus emits an eletron or a
positron.
Gamma-decay Nucleus emits a high-energetic
Photon.
Nuclear fission Nucleus decays into two nuclei
of abut the same size and emits some free neutrons
5
X-rays

• High energetic electromagnetic radiation
  (photons), emitted by an X-ray source.

• Penetrating radiation

6
Half-life period
Half-life period of a nucleus is given by the time

• when half of the nuclei have been decayed.
• When the activity decayed to half of its initial
  value.

Each nucleus has ist characteristic half-life
period.
Values for the half-life period go from fractions
of a milisecond to billions of years.
7
Activity
Activity gives the number of nuclei of a
radioactive probe Decaying per second.
1 Becquerel 1 decay per second 1 Bq 1/s
8
Dose
Ionising radiation causes
modifications of matter.
The dose gives quantitative values of these
modifications
9
Absorbed dose --- Effective dose
Unit Gray (Gy) 1 Gy 1J/kg
Unit Sievert (Sv)
Relation between absorbed dose and effective dose
is given by the radiation weighting factor.
10
Radiation weighting factors
Effective dose radiation weighting factor
absorbed dose
radiation weighting
factor X-rays and gamma
1 beta-radiation
1 neutrons 520

(depends on
energy) Alphas 20
11
Dose rate
dose time
dose rate
Unit for the dose rate mSv/h or µSv/h
12
Exposition to radiation in germany
medical 2,0 mSv
Industrie 0,01 mSv Tschernobyl 0,01
mSv Kernwaffentests 0,005 mSv Flugreisen 0,005
mSv Beruf 0,002 mSv fossile Energieträger 0,002
mSv Kernkraftwerke 0,001 mSv Industrieprodukte 0,0
01 mSv
Cosmic radiation 0,3 mSv
Terrestic radiation 0,4 mSv
Natural internal radiation 1,4 mSv
Mean total dose per year 4,1 mSv
13
Deterministic harm
Deterministische Schäden bei Teilkörperexposition
der Haut

• Occurance of harm above threshold
• exampleschanges of the skin, changes of the
  blood count, loss of hair, sickness
• Severity of the harm depends on dose and dose.

Determistic harm over a threshold of 250 mSv!
14
Stochastic harm
Risk for mortal cancer in germany 2025

• - Probability for the occurance of harm depends
  on dose.
• examplescancer, leukemia, hereditary harms

15
Professional exposition to radiation
category AEffective dose above 6 mSv per year
(maximum allowed dose 20mSv per year)
categoy BEffective dose above 1 mSv per year
No professional exposition to radiationif
effective dose is below 1 mSv per year
16
Radiation safety area
Überwachungsbereich (surveyed area)

• exclusion area (Sperrbereich) dose rate
  gt3 mSv/h
• controlled areaannual dose gt6 mSv
• surveyed area (Überwachungsbereich)ann
  ual dose gt1 mSv

Kontrollbereich (controlled area)
Sperr- Bereich (exclusion area)
These specifications are with respect to a
possible dose. The dose may not be reached.
17
Marking radiation safety areas
Controlled areas and exclusion areas have to be
demarcated and have to be marked in a clearly
visible and enduring way.
Examples
5.5.2
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General safeguards
Avoid any needless exposition to radiation!
All inevitable expositions must be kept at the
minimum possible level!
19
Safeguards Keep distance!
Distance is one of the simplest and most
effective means of reducing radiation exposure.
The relationship between distance and dose rate
from a radiation point source follows the inverse
square law. This means, that as a rough
approximation, doubling the distance from a
radioactive source can reduce the exposure rate
by up to a factor of 4. Therefore, increasing the
distance from a radiation source can
significantly reduce radiation exposure. The use
of tongs or other handling devices that increase
distance from a radioactive material can
significantly reduce extremity and body
exposures.
20
Safeguards Limit your time to stay!
Radiation dose is directly proportional to the
length of time an individual is exposed to a
source of ionising radiation. Therefore, the less
time spent near a radiation source, the smaller
the total dose received.
21
Safeguards Use shielding!
Properly shielding devices can dramatically
reduce radiation exposure. Possible shielding
materials are given below
?-radiation, e.g. 60Co (1.3 MeV), 40K (1.5 MeV )
 shielding material with high atomic number
(lead, copper,..) ß-radiation, e.g. 90Sr (0.55
MeV), 32P (1.7 MeV), 14C (0.16 MeV)  range in
water 1cm shielding material acrylic glass,
aluminium (low atomic numbers) shielding
material with high atomic number causes
Bremsstrahlung a-radiation, e.g. 222Rn (5.5
MeV), 252Cf (6.1 MeV) range in air few
centimeters range in matter few hundredth of a
millimeter neutron radiation produced in nuclear
reactions shielding with high content of
hydrogen (acrylic glass, concrete)
22
Shielding of different types of radiation
The figure clarifies the different shielding
possibilities for alpha, beta, gamma and neutron
radiation
23
Pathes of irradiation
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closed radioactive substances
These means No risk of incorporation.
(assuming reasonable treatment of the source)

25
Open radioactive substances

• Non-closed radioactive substances are called open
  substances
• examples
• liquids
• powder
• gases
• Aerosole
• Solid bodies with dimensions below 2mm.

Working with open sources implies risk of
incoporation!
5.7.1
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Safeguards Protect against incorporation

• To protect against incorporation while handling
  radioactive substances
• do not eat
• do not drink
• do not smoke
• do not put your makeup on
• Wash your hands when you finish your work

6.5.2
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_____________________ Name ____________________
_ Vorname _____________________ Geburtsdatum _
____________________ Telefon
Please send to Sebastian Bachmann Physikalisches
Institut Philosophenweg 12 69120
Heidelberg Deutschland
Hereby I declare, that I have been informed about
possible risks stemming from the exposition to
ionising irradiation or the handling of
radioactive substances. I have been also informed
abobut the necessary safeguards for radiation
matters.
___________________
_____________ Ort und Datum Unterschrift