radioactivity manos papadopoulos nuclear medicine department castle hill hospital hull & east...
TRANSCRIPT
![Page 1: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/1.jpg)
Radioactivity
Manos PapadopoulosNuclear Medicine DepartmentCastle Hill HospitalHull & East Yorkshire Hospitals NHS Trust
![Page 2: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/2.jpg)
RADIOACTIVE DECAY
Only certain combinations of nucleons form a stable nucleus
Unstable nuclei
spontaneous nuclear transformation
formation of new elements
emission of radiation
These unstable isotopes are called
radioactive isotopes
The spontaneous nuclear transformation is called
radioactivity or radioactive decay / disintegration
![Page 3: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/3.jpg)
RADIOACTIVE DECAY
An unstable “parent” (P) nuclide is transformed into a more
stable daughter (D) nuclide through various processes
where d1 + d2 + … signify the emitted particles
The process is usually accompanied by the emission of
gamma radiation
...21 ddDP
![Page 4: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/4.jpg)
RADIOACTIVITY
![Page 5: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/5.jpg)
ACTIVITY
Activity (A) is defined as:
the number of radioactive atoms (N) undergoing nuclear
transformations per unit time (t)
dt
dNA
![Page 6: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/6.jpg)
UNITS OF ACTIVITY
Traditionally, expressed in units of curies (Ci)
1 Ci = 3.7 × 1010 disintegrations/second
Typical activities for imaging: 0.1 to 30 mCi
for therapy: up to 300 mCi
The Système International (SI) unit is the becquerel
(Bq)
1 Bq = 1 disintegration/second
![Page 7: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/7.jpg)
DECAY CONSTANT
Radioactive decay is a random process
The number of atoms decaying per unit time (dN/dt)
is proportional to the number of unstable atoms (N)
where λ is the transformation constant (or decay constant)
being characteristic of each radionuclide
ANdt
dN N
dt
dN
![Page 8: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/8.jpg)
HALF-LIFE
The half-life (τ1/2) is defined as:
the time required for the number of radioactive atoms in a
sample to decrease by one half
λ and τ1/2 are related as follows:
where ln2 denotes the natural logarithm of 2
Both λ and τ1/2 are
unique for each radionuclide
2/12/1
693.02ln
![Page 9: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/9.jpg)
![Page 10: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/10.jpg)
RADIOACTIVE DECAY LAW
The rate at which a radioactive isotope disintegrates is defined by the following DECAY LAW:
Where N(t): number of radioactive atoms at time t
N0: initial number of radioactive atoms (at time zero)
τ1/2: half-life
e: base of natural logarithm ( ≈ 2.718) λ: decay constant
t
t eNeNtN
2/1
2ln
00
![Page 11: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/11.jpg)
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
1000000
0 10000 20000 30000 40000 50000
Years
Nu
mb
er o
f 14
C a
tom
s
τ1/2 = 5730y
5730
1/ 2 1/ 2 1/ 20 0 0 0/ 2 / 4 / 8t t tN N N N
N0
RADIOACTIVE DECAY LAW
![Page 12: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/12.jpg)
PROBLEM
A nuclear medicine technologist injects a patient with
800 MBq of [99Tcm]-SestaMIBI (τ1/2=6.02 hours). One
hour later the patient is imaged. Assuming that none of
the activity is excreted, how much activity remains at
the time of imaging?
![Page 13: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/13.jpg)
SOLUTION
A0 = 800 MBq
λ = 0.693/6.02 hours = 0.115 hours-1
t = 1 hour
MBqA
MBqA
eMBqA
eMBqA
eAAhourhours
t
713
891.0800
800
800115.0
1)115.0(
0
1
![Page 14: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/14.jpg)
RADIOACTIVE DECAY TYPES
Radioactive decays are classified by the types of particles that are
emitted during the decay:
Alpha decay (α)
Beta decay (β)
Gamma decay (γ)
Isomeric transition (ΙΤ)
Electron capture (ε or ec)
Internal conversion (IC)
Spontaneous fission (SF)
Neutron emission (n)
![Page 15: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/15.jpg)
ALPHA DECAY
Spontaneous emission of an alpha (α) particle
from the nucleus
An α particle is a Helium nucleus
containing two protons and two neutrons
42particle He
![Page 16: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/16.jpg)
ALPHA DECAY
Typically occurs Heavy nuclides (A>150)
Emission of gamma and characteristic X-Rays
DP A
ZAZ
42
![Page 17: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/17.jpg)
ALPHA DECAY
Alpha particle emitted from the atomic nucleus Alpha particle and daughter nucleus have equal and
opposite momentums
241 237 495 93 2Am Np He
![Page 18: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/18.jpg)
ΑLPHA PARTICLES
Not used in medical imaging
range in solids and liquids
few micrometres
range in air
few centimetres
Alpha particles cannot penetrate the dead layer of the
skin
Health hazard only when enter the body
![Page 19: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/19.jpg)
ΒETA DECAY
Beta positive (β+) decay:Proton (p+) → neutron + positron (β+) + neutrino
Beta negative (β-) decay:Neutron → proton (p+) + electron (β-) + antineutrino
_1
1 vDP AZ
AZ
vDP AZ
AZ
1
![Page 20: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/20.jpg)
converts one neutron into a proton and an electron no change of A, but different element occurs with nuclides with an excess number of neutrons
3 31 2 eH He e
β- DECAY
![Page 21: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/21.jpg)
β+ DECAY
11 116 5 eC B e
converts one proton into a neutron and a positron no change of A, but different element occurs with nuclides with an excess number of protons
![Page 22: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/22.jpg)
ΒΕΤΑ PARTICLES Electron (β-) Positron (β+) As beta particles traverse lose energy Positron interacts with an electron Annihilation radiation
two opposite directed 511 keV photons threshold for positron decay 2×511 keV = 1.02 MeV
Used in Medical Imaging Positron emitting radiopharmaceuticals Positron Emission Tomography (PET)
Anti-particles
![Page 23: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/23.jpg)
ΒΕΤΑ PARTICLES
Positron Emission and Annihilation
![Page 24: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/24.jpg)
GAMMA DECAY
Nucleus in excited state (surplus of energy)
Release of excess energy emission of γ-rays
nucleus returns to its ground state
XX AZ
AZ
*
![Page 25: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/25.jpg)
GAMMA DECAY
3 * 32 2He He
no change of A or Z – same element release of photon usually occurs in conjunction with other decay
![Page 26: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/26.jpg)
GAMMA DECAY
Decay scheme of Cs13755
![Page 27: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/27.jpg)
ISOMERIC TRANSITION
Half-lives from 10-12 sec – 600 years
These excited states are called
metastable or isomeric states
No change in
atomic number
mass number
neutron number
![Page 28: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/28.jpg)
ISOMERIC TRANSITION
Isomeric transition is a radioactive decay process
excited nucleus decays to lower energy state
gamma radiation emitted
no emission of corpuscular radiation (i.e. particles)
no capture of particle by the nucleus
XX AZ
mAZ
![Page 29: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/29.jpg)
Mo-99 DECAY SCHEME
![Page 30: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/30.jpg)
Mo-99 DECAY SCHEME
99Mo decays by β- decay
into 99Tcm (i.e. 99Tcm metastable state of 99Tc)
half-life = 66 hours
99Tcm decays by isomeric transition
into 99Tc ground state with 6 hr half-life
half-life = 6.01 hours
![Page 31: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/31.jpg)
ELECTRON CAPTURE
Nucleus captures orbital electron (usually a K- or L-shell)
conversion of a proton into a neutron
simultaneous ejection of a neutrino
Emission of
characteristic X-rays
Auger electrons
energyvYeX AZ
AZ
1
![Page 32: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/32.jpg)
7 74 3
ECeBe e B
ELECTRON CAPTURE
converts one proton into a neutron no change of A – but different element occurs with nuclides with an excess number of protons
![Page 33: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/33.jpg)
Tl-201 DECAY SCHEME
201Tl decays by electron capture
into 201Hg
half-life = 73.1 hours
201Hg-characteristic X-Rays
68.9-80.3 keV
Emission of characteristic X-Rays used in myocardial perfusion
![Page 34: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/34.jpg)
INTERNAL CONVERSION
Nucleus in excited state (surplus of energy)
De-excitation through
ejection of a tightly bound electron (K- or L-shell)
alternative mechanism to electron capture
No change of Z – same element
![Page 35: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/35.jpg)
SPONTANEOUS FISSION
Heavy nuclei decay by splitting into two daughter
nuclei
release of neutrons
release of energy
![Page 36: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/36.jpg)
SUMMARY I
Half-Life (τ1/2)
the time required for radioactivity to decay to half its initial value
Decay Constant (λ) the probability that an atom will decay/transform per
unit time
Activity rate of decay/transformation
At = A0 e-λt
![Page 37: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/37.jpg)
SUMMARY II
Radioactive Decay Modes depending on the emitted radiation
Alpha particles Helium nuclei – used in radionuclide therapies
Beta particles used in imaging (e.g. positrons - PET)
used in therapy (e.g. 131I, 32P)
Gamma ray photons used in imaging (e.g. 99Tcm, 201Tl)
![Page 38: Radioactivity Manos Papadopoulos Nuclear Medicine Department Castle Hill Hospital Hull & East Yorkshire Hospitals NHS Trust](https://reader036.vdocuments.net/reader036/viewer/2022062321/56649f285503460f94c40d3d/html5/thumbnails/38.jpg)
THE END
Any questions
?