Safe Handling of Radiation
Basics of Radiation

ISBN978-4-905025-01-6
大学等放射線施設協議会

113-0032 東京都文京区弥生2-11-16
東京大学アイソトープ総合センター内
電話: 03-5841-3058 Fax: 03-5841-3050
E-mail: kyogikai@ric.u-tokyo.ac.jp

Radiation-Related Units
ItemUnit

Description

Definition

Exposure

Coulombs/kg(C/kg)

A measure of the ionization produced in airby X or gamma radiation.

1R (Roentgen) =2.58×10-4 C/kg

Absorbed dose, DGray(Gy)The fundamental dose quantity given by themean energy imparted to matter of mass byionizing radiation.

1Gy=1J/kg(=100rad)

Equivalent dose, HT

Sievert(Sv)

The dose in a tissue or organ given byradiation-weighted (wR) sum of the mean
absorbed dose (DT,R) from radiation (R).

HT   wRDT , R

Effective dose, ESievert(Sv)

The dose in a whole body given by tissueweighted (wT) sum of the equivalent doses(HT) in all specified tissues and organs (T).

E   wTHTRadioactivity

Becquerel(Bq)

The number of nuclear transformations(decays) occurring in a given quantity ofmaterial per unit time.

1Bq=1 decay/sec(1Ci=3.7×1010Bq)

Radiation Energy

Electron Volt(eV)

The energy gained by an electron in passing
through a potential difference of 1 V.
大学等放射線施設協議会

RT

1eV=1.6×10-19J

Microscopic world

All Materials

Atom(electron, nucleus)

10-10mNucleus

Nucleon（proton, neutron)（Quark)10-15m

大学等放射線施設協議会

10-16mAtomic Structure
Component

Approximate
Diameter (m)Atom

1 x 10-10

Nucleus1 x 10-15

ElectronProtonChargepositive
negative1 x 10-16

positive
K

Neutron1 x 10-16

neutral

大学等放射線施設協議会

LMNotation of Isotope

Mass Number

32

Element

Atomic Number1517 Neutron Number

大学等放射線施設協議会

Isotopes of Hydrogen

TermHydrogen

DeuteriumTritium

Number ofProtons

111

Number ofNeutrons

012

NaturalAbundance [%]99.98850.0115noneRadioactivity

nonoyes

大学等放射線施設協議会

Radioactive decay
Radioactive decay is the disintegration of the nucleus of an unstable
nuclide by spontaneous emission of charged particles and/or photons.
Every decay process has a specific half-life.

Relative Activity

1
T: Physical Half-Life
1/2
1/4
1/8
2TTTime

大学等放射線施設協議会

3T

Activity (A)The number of nuclear decay occurring in a given amount of material perunit timedN N  Adt
N  N 0e  tln 2 0.693
TT
1/ 2

N: number of nuclei

t: a short period of time: decay constantN0: number of nuclei at t=0A0: activity at t=0T1/2: half life

1/ 2A t    N(t)  N 0e  t   N 0e 0.693 t / T 1 / 2  A 0e 0.693 t / T 1 / 2
alternativelytt1 T 1 2
1 T 1 2A t    N(t)  N 0e   N 0    A0  
2 
2 
大学等放射線施設協議会
 tExample: Decay of Phosphorus-32

T1/2: 14.3 days

A0: 1 MBqt: 7 days

A  A 0e 0.693 t / T 1 / 2  1  e 0.693 7 /14.3  1  e 0.339  0.712
t

714.3

1 T 1 2
1 A  A0    1   
2 
2 

 0.712

大学等放射線施設協議会

Major types of radiation
a-ray (helium nucleus)b--ray (electron)

emitted from radionuclides

b+-ray (positron)
Charged particle

protons
deuterons
electron rays

generated by accelerators

heavy ions
Uncharged
particleElectromagnetic
wave

neutrons

generated by reactors,
accelerators andradionuclides

X-ray- Characteristic X-ray- Bremsstrahlung

generated outside atomicnucleus

g-ray

emitted from atomic nucleus
大学等放射線施設協議会

Major types of radioactive decay
Decay processes undergone by unstable nuclides to become more stablea-decay

emission of helium nucleus (a-ray)b--decayemission of electron (b--ray)b+-decayemission of positron (b+-ray)

Electroncapturecapture of an orbital electron by nucleus
emission of electromagnetic wave (g-ray)

Other types

emission of conversion electron(internal conversion )emission of electron and positron(internal pair production )大学等放射線施設協議会

a-decay (a-ray)a-particle= helium nucleus= a-rayRadium-226

Radon-222

proton88
neutron 138

proton86
neutron 136

大学等放射線施設協議会

bdecay (bray)electron= b- particle= b-rayTritium
protonneutronHelium-3
12

protonneutron21

electron
Phosphorous-32

Sulfur-32

protonneutronprotonneutron15
17

大学等放射線施設協議会

1616

Decay scheme for 32P

Continuous energy distribution

大学等放射線施設協議会

b+-decay

positron= b+ particle= b+-ray

Carbon-11

Boron-11

protonneutronprotonneutron65

大学等放射線施設協議会

56

Electron capture

orbitalnucleusvacantorbitalThallium-201

Mercury-201

protonneutronprotonneutron81
120

大学等放射線施設協議会

80
121

Emission following electron capture
Auger electron

K-electron capture

Characteristic
X-rays

大学等放射線施設協議会

Other types of energy dissipationfrom unstable nuclei
Gamma emission (g-ray)
Emission of highly-energetic, short-wave electromagnetic radiation from thenucleus of an atom. In general, a and b- decays and always the fission
process are accompanied by gamma emission.

Internal conversion
Direct transfer of excess energy to one of its own orbital electrons, thereby
ejecting the electron from the atom (conversion electron). It always
accompanies the predominant process of gamma emission.

Internal pair production
Direct conversion of energy within the electromagnetic field of a nucleus into
an electron and a positron that are emitted together. This requires that theexcess energy of the unstable nucleus be at least equivalent to the combined
masses of an electron and a positron (in excess of 1,020,000 electron volts).
大学等放射線施設協議会

Decay scheme for 125I

大学等放射線施設協議会

Electromagnetic radiations
Gamma-rays (g-rays)
These are defined as mono-energetic electromagnetic radiations that areemitted from nuclei of excited atoms following radioactive transformations. In
most cases, following a- or b- decay processes, gamma emission is themechanism by which a nucleus loses energy going from a high energy excitedstate down to a low energy stable state.

X-ray
These are defined as electromagnetic radiations generated outside the atomic
nucleus. There are two distinct types of X-ray.
- Characteristic X-ray- Bremsstrahlung

大学等放射線施設協議会

Characteristic X-rays

A collision of fast-moving electrons with an atom first causes a tightly boundinner-shell electron to be ejected from the atom; a loosely bound outer-shellelectron then falls into the inner shell to fill the vacancy. In the process, a single
photon (characteristic X-ray) is emitted by the atom with an energy equal to thedifference between the inner-shell and outer-shell vacancy states. This energy
difference (Ex) usually corresponds to the photon wavelengths in the X-ray
region of the spectrum.
Alternatively, one of the orbital electrons is given excitation energy and kickedout of the atom. This electron is called an Auger electron. The energy of Auger
electron is given by ‘Ex - Eb’ where Eb is binding energy (energy necessary torelease electron from the atom).大学等放射線施設協議会

Bremsstrahlung(German: Breaking radiation)

Bremsstrahlung is emitted when electrons (Ee) are quickly decelerated by aninteraction with the electric fields surrounding atomic nuclei. The energy of theresultant photon (Ex) is related to the energy of the incident electron as well as
the electric field strength. These forces are greater in nuclei with a high atomicnumber.
大学等放射線施設協議会

Generation of X-rays
X-rays are generated by slowing-down electrons or heavy charged particles(Characteristic X-rays, Bremsstrahlung). In an X-ray tube, electrons areaccelerated by means of high direct voltage to bombard a metal electrode.

Simplified sectional drawing of an X-ray tube (UH: heater voltage, K: cathode,
A: anode, e: electrons exiting in the cathode and accelerated to the anode, R:
x-ray shielding, F: beam hole)
http://www.euronuclear.org/info/encyclopedia/x/x-radiation.htm

大学等放射線施設協議会

Electromagnetic wave spectrum"Electromagnetic wave spectrum." Online . Britannica Student Encyclopedia. 6 Apr. 2009

大学等放射線施設協議会

Relationships among radioactivity,radiation and radioisotopes
Radioactivity
The spontaneous decay of disintegration of a radionuclide, an unstable atomic
nucleus, accompanied by the emission of radiation.

Radioisotope
A radioactive isotope. A common term for a radionuclide.

radiation

aroma from coffee

radioactivity

coffeeSuppose aroma from coffee is radiation, coffee itself has radioactivity and is a radioisotope.
大学等放射線施設協議会

Ionization and excitation
Free electron
Ionization

Ion pairInteraction

Charged particle

Cationenergydissipation
Excitation

ground state

大学等放射線施設協議会

excited stateRadiation interaction with mattera-particles•

Electrostatic attraction on the outer orbital electrons of atoms nearwhich a-particles pass– resulting that some electrons will be attracted away from their parent
atoms and that ions will be produced (ionization).

•A double positively charged and low velocity due to their large mass– cause a-particles to lose their energy over a distance as short as 4cm inair in straight lines.

大学等放射線施設協議会

Radiation interaction with matterb-particles (electron)•Negative charge of b-particles interacts with the negative charge oforbital electrons– ejecting orbital electrons from their orbits (producing ion pairs) or
causing excitation until the electron has lost enough energy to be
captured by a nucleus.

•Small mass, high velocity and single negative charge– enable b-particle to travel through the matter further than an a-particle
before producing an ionizing effect, resulting in longer range in air fromup to 790cm.
– cause large deflection with each interaction, resulting in many pathchanges and scattering.
大学等放射線施設協議会

Radiation interaction with matterb+-particles (positron)•

Positive charge of positron interacts with the negative charge oforbital electrons– losing its kinetic energy through ionizations and excitations, similar to b-particle.

•In addition, a positron will also combine with an electron. Then two
particles are annihilated– producing two 0.511 MeV gamma rays called annihilation radiation in
exactly opposite directions.

positronelectronannihilation radiation大学等放射線施設協議会

Radiation interaction in matterelectromagnetic radiation• Photoelectric effect– A photon imparts all its energy to an orbital electron and then vanishes.
– If the energy of the photon is greater than the binding energy of theelectron, an electron will be ejected from the atom.

• Compton effect (scattering)– A photon transfers only a portion of its energy to an orbital electron andthen continues in an alternate direction.

• Pair production– A photon passing through an atom in the region of the nucleus
undergoes a conversion into a positron and an electron.
大学等放射線施設協議会

Photoelectric effectsecondary ionization

characteristic X-ray

photoelectron (Ee-)

Ee- = hu - Eb
ionization
photon (ｈｖ)
ＫＬ

大学等放射線施設協議会

Compton effect (scattering)further Compton effectdeflected photon (ｈｖ’)
ionization

Ee- =ｈｖ-ｈｖ’

photon (ｈｖ)electron (Ee-)
ＫＬ

secondary ionization
大学等放射線施設協議会

Pair production
positron(0.511 MeV)

electronannihilation radiation

photon(>1.022MeV)

electron(0.511 MeV)

secondary ionization

大学等放射線施設協議会

Radiation detectors• Gas-filled detectors– Ionization chamber– Proportional counter– Geiger-Mueller (GM) counter• Scintillation detectors– Crystal scintillation counter– Liquid scintillation counter• Semiconductor detectors– Silicon (Si(Li)) detector– Germanium (Ge(Li)) detector• Other luminescence-based detectors– Thermoluminescence (TLD) dosimeter– Radiophotoluminescence (RPL) dosimeter– Optically stimulated luminescence (OSL) dosimeter– Photostimulated luminescence detector (Imaging plate)
大学等放射線施設協議会

Gas-filled detectors
gas-filled chamber
voltage source
ionizing radiation-anode (+)+cathode (-)

大学等放射線施設協議会

electricalcurrent
measuringdevice

Operating voltages for gas-filled detectors

Ionizationchamber

Applied voltage (V)
大学等放射線施設協議会

Scintillation detectors

crystal scintillator
photomultiplier tube
ionizing radiation

(-)

light

measuring
deviceanode

optical window

photocathode

大学等放射線施設協議会

Semiconductor detector
ionizing radiation
metallization

pre-amplifiers
shapers

SiO2
implant, p+-typebulk, n-type
electrons

holes

backplane,
n+-type silicon+ bias voltage

大学等放射線施設協議会

Semiconductor detector

holeelectronHPGe（High Purity Germanium) detector+－p+-type contact

n+-type layer

p+-type germanium

大学等放射線施設協議会

Luminescence-based detectors
for personnel monitoring for external radiation

Thermoluminescence- TLD badge

Radiophotoluminescence (RPL)- GLASS badge
Optically stimulated luminescence (OSL)- LUXEL badge

大学等放射線施設協議会