2020-radioactivity-ii-alpha-beta.ppsx

1
© K. Kozlíková, 2020 Radioactivity II - Alpha - Beta Radiation
Radioactivity II
Alpha – Beta Radiation
Assoc. Prof. RNDr. Mgr. Katarína Kozlíková, CSc.
IMPhBPhITM FM CU in Bratislava
katarina.kozlikova@fmed.uniba.sk

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Contents
 Introduction
 Alpha decay
 Interaction of alpha radiation with matter
 Linear energy transfer
 Range, energy spectrum and path of an alpha particle
 Protection against alpha radiation
 Beta decay
 Types of beta decay
 Interaction of beta radiation with matter
 Range, energy spectrum and path of a beta particle
 Protection against beta radiation
 Literature

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 Radioactive isotopes
 Some atoms (isotopes) are unstable
 Their nuclei decay
 Radioactive decay represents spontaneous decay
of nuclei, while
 New nuclei are created
 The energy state of the nucleus changes
 At the radioactive decay a nucleus emits at least
one particle
Introduction

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Radioactive Isotopes
 X: nuclide
 symbol for chemical element
 A: nucleon number
 mass number
 Z: proton number
 atomic number
 N: neutron number
 A = Z + N
𝑍
𝐴
𝑋
Radioactive isotopes related to proton number
and neutron number and coloured according their
half-lives.
Stable isotopes are displayed in black.
[Cit. 1. 3. 2020] Available at:
https://www.quora.com/Which-isotopes-are-radioactive

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Energy release
from radioactive nuclei
 During radioactive decay, energy can be
released from a nucleus in different ways
 Emission of
 A particle
 Electromagnetic radiation
 Their combination
 Creation of more particles at
 Nuclear fission
 Only two nuclei produced,
three neutrons released
 Nuclear spallation
 More nuclei produced,
different particles released
Types of radioactive decay.
https://i.warosu.org/data/sci/img/
0077/28/1450424556115.png
Nuclear fission. [Cit. 1. 3. 2020] Available at:
https://physicsepathshala.blogspot.com/2017/08/nuclear-energy.html

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Alpha decay

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Alpha decay (1)
 Alpha decay is found in heavy nuclei (heavier than lead –
Pb) and in nuclei of some earth metals
 Names
 Parent nucleus
 The original state of nucleus before decay
 Daughter nucleus
 The nucleus obtained when parent nucleus decays and produces another
nucleus following the rules and the conservation laws
 Alpha particle
Alpha decay. [Cit. 8. 3. 2020] Available at:
https://courses.lumenlearning.com/physics/chapter/31-4-nuclear-decay-and-conservation-laws/

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Alpha decay (2)
 General relation
 Nucleon number decreases by 4
 Proton number increases by 2
 A nucleus of helium is emitted
 Examples

4
2
4
2 
 
 Y
X A
Z
A
Z
He
Rn
Ra
He
U
Pu 4
2
222
86
226
88
4
2
235
92
239
94 



Alpha decay of Plutonium-239.
http://www.geocities.ws/muldoon432
/alpha_particle_radiation.htm

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Interaction of alpha radiation with matter (1)
 When passing through a matter medium alpha
particles can cause
 Elastic scattering on electrons and nuclei of the atoms
of the medium without practically no energy loss
 Inelastic scattering with orbital electrons
 Ionisation and excitation of atoms and molecules
 Occasionally dissociation of molecules
 Both connected with energy
loss of alpha particles
Ionisation of an atom by an alpha particle.
http://www.geocities.ws/muldoon432/
alpha_particle_radiation.htm

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Interaction of alpha radiation with matter (2)
 Initial velocity v, with which the particle is
emitted from the nucleus, corresponds to its
energy E
 v  106 ms-1  E  MeV
 Energy loss due to ionisation and excitation of
the atoms of the medium
 Ionising power of the medium is given by the
specific ionisation
 Number of produced ion pairs (n) per unit track length
(l) = n / l

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Specific ionisation of alpha particles (1)
 Specific ionisation in general
 Equals the number of produced ion pairs n per unit
length of charged particle´s path l
(= n / l)
 Increases with electrical charge of the particle
 Decreases with incident particle velocity
 Specific ionisation of an alpha particle in air
 20 000 pairs - 80 000 pairs / 1 cm
An alpha particle detected in
an isopropanol cloud chamber.
https://en.wikipedia.org/wiki/Radiation

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Specific ionisation of alpha particles (2)
 Specific ionisation of alpha particle in air – Bragg
curve
 At path beginning
 Low
 Almost constant
 At path end
 More fold increase
 Abrupt fall
 Bragg peak
Alpha particle specific ionization versus distance traveled in air.
http://nuclearpowertraining.tpub.com/h1013v2/css/Beta-Particle-29.htm

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Linear energy transfer (1)
 Expresses how much energy an ionising particle transfers
to the medium through which it passes
 Is used in dosimetry
 Important factor in assessing potential tissue and organ
damage from exposure to ionising radiation
 Depends on
 The nature of radiation
 The medium (material) through which the radiation passes
 Restricted linear energy transfer L∆
 dE∆ energy loss of the charged particle
due to electronic collisions
 dx travelled distance
 All secondary electrons with kinetic energy Ek > ∆ are excluded
dx
dE
L 
 

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Linear energy transfer (2)
 Energy loss due to ionisation and excitation of the
medium by a particle depends on
 Z atomic number of the stopping medium
(irradiated material)
 z  e electric charge of the particle
 v particle velocity
 m0 resting mass of the particle
𝑑𝐸Δ
𝑑𝑥
≈
𝑍 ⋅ 𝑧2
⋅ 𝑒4
𝑚0 ⋅ 𝑣2

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Linear energy transfer (LET)
and stopping power
 If Δ  ∞
 No electrons with larger energy
 Restricted LET  unrestricted LET  linear
electronic stopping power
 SI unit: N (newton)
 Used units: keV/μm, MeV/cm
 Typical values of LET
 5 MeV alpha particles: 100 keV/μm
 Diagnostic X-rays: 3 keV/μm

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Stopping power of the medium
 Loss of kinetic energy of an ionising particle when
passing through a material of some density
 Energy loss of the particle per unit path length
 Calculated as linear ion density times the average
energy required to produce 1 pair of ions
 Average energy per 1 ion pair in air: ~ 34 eV
 Example
 Total number of ion pairs n, which can be created
by an alpha particle with energy 6.8 MeV
pairs
ion
000
200
eV
34
eV
10
8
.
6 6



n

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Examples of linear energy transfer (LET)
and stopping power (alpha particles)
Compare the shape of curves
LET vs. distance travelled in tissue for α-particles with
2 different initial kinetic energies.
http://jnm.snmjournals.org/content/51/2/311/F2.large.jpg
Stopping power for α-particles in air.
http://physicsopenlab.org/2016/11/06/gold-leaf-thickness-
with-alpha-spectrum/

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Effective range of an alpha particle (1)
 The most probable distance that can be reached by an
emitted -particle from its source when it passes through
a medium (an absorber)
Range of α-particles – measurement (left) and distribution of particles
due to their range (right).
I0: initial intensity of the beam of particles, I: intensity after passing the absorber
https://www.quora.com/How-does-radiation-go-through-metal

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Effective range of an alpha particle (2)
 Effective range R [cm] of a particle depends on
 Energy E [MeV], with which the particle is emitted
 Medium density  [g/cm3]
 Nucleon number A of the medium
 In air
 R ≈ 2 cm to 10 cm
 R [cm] ≈ 0.325 · E3/2 [MeV] for energies 4 MeV – 8 MeV
 In liquids, soft tissues
 R ~ 10 - 100 m
 In aluminium
 About the half distance corresponding to the energy for liquids
Cherry, S. R., Sorenson, J. A., & Phelps,
M. E. (2012). Interaction of Radiation with
Matter. Physics in Nuclear Medicine, 63–
85. doi:10.1016/b978-1-4160-5198-
5.00006-x

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Energy spectrum of an alpha particle
 Energy of emitted particles
 Discrete values
 Energy spectrum
 Line spectrum
Intensity against alpha energy for four isotopes.
https://www.wikiwand.com/en/Alpha-particle_spectroscopy

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Path of an alpha particle
 Particle path
 Linear
 Until it comes very close to the nucleus
Path of alpha particles.
http://www.brooklyn.cuny.edu/bc/ahp/LAD/C3/C3_AtomicCenter.html

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Processes due to interaction
of an alpha particle with medium
 Production of characteristic X-rays
 Luminescence of material
 Chemical processes
 Cause functional and morphological changes of tissues
 Transformation of energy into heat
 Transformation of a nucleus
 Interaction of an  -particle with a nucleus
 Rare

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Protection against alpha radiation
 Alpha radiation is most dangerous
 At internal irradiation (internal contamination)
after inhalation or ingestion
 At irradiation of eyes
 All alpha radiation
is absorbed by
 Surface skin layer
 Sheet of paper
 Air layer thicker
than 10 cm
Penetration of different types of radiation.
https://www.researchgate.net/figure/Figure-22-Penetration-
power-of-ionizing-radiation-40_fig6_307466518

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Beta decay

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Beta decay (1)
 Type of radioactive decay, in which
a proton in the nucleus transforms
to a neutron or vice versa
 The original nuclide is transformed
to an isobar
 The nucleus comes closer to the
optimal ratio of protons and neutrons
 The result of this transformation is
the emission of a beta particle
(positive or negative) from the
nucleus
Types of radioactive decay related to N and Z numbers.
Stable isotopes are coloured in black.
https://en.wikipedia.org/wiki/Stable_nuclide

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Beta decay (2)
 Beta particles are high energy electrons
 They are emitted from an unstable nucleus
 They have elementary electric charge negative or
positive
 Positively charged particle beta is a positron
 Negatively charged particle beta is an electron (negatron)
 The majority of radionuclides used in biomedical
research are beta emitters

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Beta decay (3)
 It is a consequence of the weak force, which is
characterized by relatively lengthy decay times
 It does not change the number (A) of nucleons
in the nucleus, but changes only its charge Z
 Types of beta decay
 Beta minus (negative)
 Beta plus (positive)
 Electron capture
 Example:
 Potassium – a chemical element that occurs in the human
body – isotope 40K undergoes all three types
Decay scheme of 40K. [Cit. 8. 3. 2020] Available at:
https://en.wikipedia.org/wiki/Potassium-40

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Negative beta decay (1)
 Occurs in nuclei with excess of neutrons
 One neutron in the nucleus transforms into a proton
 Proton number increases by one, nucleon number
remains the same
 An electron and
an antineutrino
are emitted
from the nucleus

~
1 

 
 e
Y
X A
Z
A
Z Beta minus decay.
https://courses.lumenlearning.com/physics
/chapter/31-4-nuclear-decay-and-conservation-laws/

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Negative beta decay (2)
 The simplest case
 Change of a free neutron
 Half-life about 13 min
 Occurs in nature
 Example:
 Carbon – a chemical element that occurs in the human body –
isotope 14C undergoes a negative beta decay and transforms into
Nitrogen

~
14
7
14
6 

 
e
N
C

 ~
0
1
1
1
1
0 

 
p
n
Beta minus decay.
https://www.shmoop.com/study-guides
/physics/modern-physics/particle-physics

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Positive beta decay (1)
 Occurs in nuclei with excess of protons
 One proton in the nucleus transforms into a neutron
 Proton number decreases by 1, nucleon number
remains the same
 A positron
and a neutrino
are emitted
from the nucleus



 
 e
Y
X A
Z
A
Z 1 Beta plus decay.
https://courses.lumenlearning.com/physics
/chapter/31-4-nuclear-decay-and-conservation-laws/

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Positive beta decay (2)
 Can occur only in a nucleus
 Rest mass of a proton is smaller
than rest mass of a neutron
 Example:
 Carbon – a chemical element that occurs in the human body – isotope
10C undergoes a negative beta decay and transforms into Boron



 
e
B
C 10
5
10
6
Beta plus decay.
https://www.shmoop.com/study-guides/
physics/modern-physics/particle-physics

 

 
0
1
1
0
1
1 n
p

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Electron capture (1)
 Occurs in nuclei with excess of protons
 Inverse process to positron emission
 Electron from an inner shell (mainly K) of the atom
is captured in the nucleus
 One proton in the nucleus transforms into a neutron
 Proton number decreases by one, nucleon number
remains the same



 
B
e
C 11
5
11
6
Electron capture.
https://education.jlab.org/glossary/electroncapture.html

 

 n
p 1
0
0
1
1
1



 

Y
e
X A
Z
A
Z 1

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Electron capture (2)
 The nucleus absorbs an electron
 A vacancy (hole) is created
 An outer electron replaces the "missing"
electron
 Energy released in form of:
 X-ray: A photon is emitted with energy
equal to the difference between the two
electron shells
 Auger effect: The energy absorbed when
the outer electron replaces the inner
electron is transferred to an outer
electron; the outer electron (Auger
electron) is ejected from the atom,
leaving a positive ion Electron capture and types of energy release.
https://en.wikipedia.org/wiki/Electron_capture

34
Energy spectrum of beta particles
 Continuous
spectrum
 Kinetic energy of beta
particles
 A part of the energy is
carried by the
neutrino
 Maximal kinetic
energy (endpoint of
spectrum) is typical
for a given decay
Energy spectrum of beta particles emitted from the nuclei during beta decay.
[Cit. 8. 3. 2020] Available at: https://sk.pinterest.com/

35
Interaction of beta particles with matter (1)
 When passing through a matter medium,
beta particles loose their energy due to
 Ionisation and excitation of atoms and molecules
 Bremsstrahlung (braking radiation)
 Cherenkov radiation
Ionisation and excitation of an atom by a charged particle.
https://slideplayer.com/slide/11479998/

36
 Initial velocity v, with which the particle is emitted
from the nucleus
 v  108 ms-1 (v  c)
 Relativistic mass of the particle
2
2
0
1
c
v
m
m


Ionisation of medium produced by an electron.
http://www.sprawls.org/ppmi2/INTERACT/

37
 Interaction with matter
 Collisions, scattering
 Zig-zag path
 Back-scattering
 Angle of scattering Ɵ > 90°
 Influences
 The measurement
 Protection against radiation
Back-scattering. [Cit. 1. 3. 2020] Available at:
http://www.ujf.cas.cz/en/departments/department-of-
neutron-physics/historie/methods/methods_rbs.html
Beta particle path and range. [Cit. 1. 3. 2020] Available at:
http://www.biologydiscussion.com/biochemistry/radioisotope-
techniques/interaction-of-radioactivity-with-matter/12933

38
Effective range of beta particles
 Effective range R [mg/cm2] depends on
 Energy E [MeV], with which the particle is emitted
 In air
 R ~ 0.1 m – 1 m
 In liquids, soft tissues
 R  1 cm
 Path of the particle
is about 4-times
longer than its range
𝑅 = 𝑎 · 𝐸 − 𝑏
Range-energy curves for beta rays. [Cit. 1. 3. 2020] Available at:
https://courses.ecampus.oregonstate.edu/ne581/three/index3.htm

39
Braking radiation „Bremsstrahlung“ (1)
 Means braking or slowing of electrons
 Is the interaction between incident electrons and the force
field of the target atom nucleus
 X-ray photons are formed when the incident electrons are
slowed down and release the energy being lost
 The photon energy of a Bremsstrahlung X-ray is
determined by
 The distance from the target nucleus
 The closer the incident electron is to the nucleus,
the stronger the interaction and
the higher energy photons are created
 The initial speed (kinetic energy)
of the incident electron
 The beam spectrum is heterogeneous
Principle of Bremsstrahlung.
https://quizlet.com/344379140/rad-
226-exam-3-flash-cards/

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Braking radiation „Bremsstrahlung“ (2)
 Generation depends on the proton number of the absorbing
material
 The higher the proton number, the more energy of the beta particle is
lost in form of Bremsstrahlung
 Important when choosing a suitable material for beta
radiation protection with shielding
 Materials with lower proton number are taken
 Organic glass (plexi glass)
 Aluminium
 Never lead!
Shielding in beta radiation protection.
https://www.slideserve.com/dieter-tucker/university-
of-notre-dame-powerpoint-ppt-presentation

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 Specific ionisation energy
 Stopping power of medium about 10-times lower than for
alpha particles
 Mass of beta particle about 8 000-times lower than the mass of the
alpha particle
 Electric charge 2-times smaller
Alpha and beta particles detected in a cloud chamber.
https://www.nuclear-power.net/nuclear-power/reactor-
physics/atomic-nuclear-physics/radiation/shielding-of-
ionizing-radiation/shielding-beta-radiation/
A beta particle detected in an isopropanol cloud chamber.
https://en.wikipedia.org/wiki/Radiation

42
 Specific ionisation s of beta radiation in air
 Average number of ion pairs produced by a beta particle
  = 46 pairs/cm
 v velocity of beta particle
 c velocity of light in vacuum
2









v
c
s
Relationship of beta particle energy to specific ionization of air
https://courses.ecampus.oregonstate.edu/ne581/three/index3.htm

43
Cherenkov radiation
 If the velocity of the flying β
particle is larger than the velocity
of light in the given medium
 Analogous to a sonic boom
 Photons of electromagnetic
radiation with wavelengths
between ultraviolet and visible
light are produced
 Appears in nuclear reactors
 Can be used to detect beta
particles Cherenkov radiation caused by beta particles.
[Cit. 8. 3. 2020] Available at: https://reactor.mst.edu/cerenkov/

44
Processes due to interaction
of a beta particle with medium
 Effects
 Chemical
 Photochemical
 Biological
 Emission of characteristic X-rays
 Bremsstrahlung
 Deflection from the original direction of the particle path
in the electric field of the nucleus
Electron (left) and positron (right) interaction with matter.
http://www.geocities.ws/muldoon432/beta_particle_radiation.htm

45
Physical factors of protection against external radiation
Physical factors of protection against radiation.
https://www.env.go.jp/en/chemi/rhm/basic-info/1st/04-03-01.html

46
Shielding as protection against radiation
 Depends on radiation penetration in different materials
 Alpha radiation is absorbed by
 Surface skin layer
 Sheet of paper
 Air layer thicker than 10 cm
 Beta radiation is absorbed by
 A layer of soft tissue (several cm)
 Aluminium sheet (several mm)
 Plastic sheet (several mm)
 Gamma radiation is absorbed by
 A lead block (several cm)
Penetration of different types of radiation.
http://iamtechnical.com/radiation-penetration

47
Decay scheme
Example of negative beta decay
accompanied by gamma decay
Decay scheme of Boron-12 – it is almost always transformed to Carbon-12.
https://pdfs.semanticscholar.org/4712/c645a8b3b3df225fe090f24a92b96732b0a8.pdf

48
How to distinguish types of radioactive
radiation using magnetic field
Radiation in magnetic field.
https://slideplayer.com/slide/5095891/
 A radioactive beam is directed
into a region with a magnetic
field
 Gamma particles are not deflected –
they carry no electric charge
 Alpha particles are deflected upwards
– they carry positive electric charge
 Beta particles (electrons) are
deflected downwards – they carry
negative electric charge
 Beta particles (positrons) would be
deflected upwards – they carry positive
electric charge

49
Literature
 ALLISY-ROBERTS, P., WILLIAMS, J. Farr’s Physics for Medical Imaging.
Edinburgh : Saunders - Elsevier, 2008. 207 p. ISBN 978-0-7020-2844-1
 HRAZDIRA, I., MORNSTEIN, V., BOUREK, A., ŠKORPÍKOVÁ, J.
Fundamentals of Biophysics and Medical Technology. 2nd revised edition.
Brno : Masaryk University, Faculty of Medicine, 2012. 325 p. ISBN 978-
80-210-5758-6.
 JIRÁK, D., VÍTEK, F. Basics of Medical Physics. Praha : Charles University,
Karolinum Press, 2017. 223 p. ISBN 978-80-246-3810-2.
 KOZLÍKOVÁ, K., MARTINKA, J. Theory And Tasks For Practicals On Medical
Biophysics. Brno : Librix, 2010. 248 p. ISBN 978-80-7399-881-3
 RONTÓ, G., TARJÁN, I. (eds.) An Introduction To Biophysics With Medical
Orientation. Budapest : Akadémiai Kiadó, 1997. 447 p. ISBN 963-05-
7607-4.
 STN EN ISO 80000-10: Veličiny a jednotky. Časť 10: Atómová a jadrová
fyzika (ISO 80000-10: 2009). Bratislava : Úrad pre normalizáciu,
metrológiu a skúšobníctvo SR, 2017. 80 s.
 Electronic sources listed directly in the text.

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