Physics of Radiation Therapy (Chapter 2)
Much of the present knowledge of the structure of nuclei comes from experiments in which a particular nuclide A is bombarded with a projectile a. The projectile undergoes one of three possible interactions:
1. Elastic scattering 2. Inelastic scattering 3. Nuclear reaction
All the series terminate at the stable isotopes of lead with mass numbers __, __, and __ respectively.
206, 207, 208
All naturally occurring radioactive elements have been grouped into what three series?
Uranium, Actinium, Thorium
The average energy of β particles is about __ of the maximum energy.
1/3
There are a total of __ elements known today. Of these, the first __ occur naturally. The others have been produced artificially.
117, 92
As a result of α decay, the atomic number of the nucleus is reduced by __ and the mass number is reduced by __
2, 4
It appears that as the number of protons in the nucleus increases beyond __ the Coulomb forces of repulsion between the protons become large enough to overcome the nuclear forces that bind the nucleons together.
82
All elements with Z greater than __ are radioactive.
82 (lead)
The __ series starts from 235U with a half-life of 7.13 × 10^8 years and the thorium series begins with 232Th with a half-life of 1.39 × 10^10 years.
Actinium series
The rate of disintegration, ∆N/∆t , is also called
Activity
What are 2 identical particles with opposite spins, that carry no charge and practically no mass.
Antineutrino and neutrino
Who first discovered radioactivity and in what year?
Antonio Henri Becquerel in 1896
As discussed in the case of the electron capture, the ejection of an orbital electron by internal conversion will create a vacancy in the involved shell, resulting in the production of characteristic photons or __
Auger electrons
The SI (System International) unit of activity is the
Becquerel (Bq)
This is defined as 1 disintegration/sec of 1 dps.
Becquerel (Bq)
Radioactive sources used in radiation therapy are produced by __ in nuclear reactors or particle accelerators.
Bombarding nuclides
The unit of activity is the
Curie (Ci)
This is defined as 1 Ci = 3.7×10^10 disintegrations/sec (dps)1
Curie (Ci)
The parent nuclide gives rise to a radioactive product nuclide, called the
Daughter
Neither of the β- or β+ particles exists as such inside the nucleus but is created at the instant of the __ process.
Decay
Positron-emitting nuclides have a __ of neutrons, and their n/p ratios are __ than those of the stable nuclei of the same atomic number or neutron number.
Deficit, lower
λ is a constant called the __
Disintegration constant
In this type of scattering, no energy transfer occurs; however, the projectile changes trajectory
Elastic scattering
A phenomenon in which one of the orbital electrons is captured by the nucleus, thus transforming a proton into a neutron:
Electron capture
A process in which a nucleus captures an orbital electron, thus transforming one of its protons into a neutron:
Electron capture
The __ is an alternative process to the positron decay.
Electron capture
If the half-life of the parent is longer than that of the daughter, then after a certain time, a condition of __ will be achieved
Equilibrium
If the ratio of daughter activity to parent activity becomes constant, a condition of __ has been achieved
Equilibrium
Radioactive nuclides (Radionuclides) decay because of __
Excess energy
The radionuclides with an __ number of neutrons or a __ neutron-to- proton (n/p) ratio lie above the region of stability. These nuclei tend to reduce the n/p ratio to achieve stability.
Excessive, high
In nuclear __ high Z nucleus is split into two lower Z nuclei
Fission
This type of reaction is produced by bombarding certain high-atomic-number nuclei by neutrons. The nucleus, after absorbing the neutron, splits into nuclei of lower atomic number as well as additional neutrons.
Fission
In nuclear __ , lighter nuclei are fused together into heavier ones.
Fusion
Nuclear __ may be considered the reverse of nuclear fission; that is, low-mass nuclei are combined to produce one nucleus.
Fusion
The time required for either the activity or the number of radioactive atoms to decay to half the initial value.
Half life
The apparent decay rate of the daughter nuclide is then governed by the __ or __ of the parent.
Half-life or disintegration rate
Fusion of __ into __ is the source of our sun's energy.
Hydrogen nuclei into helium nuclei
For position-emitting nuclides to achieve stability, the decay mode must result in an __ of the n/p ratio.
Increase
The unstable nuclei with neutron deficiency may __ their n/p ratio to gain stability by electron capture.
Increase
As the number of particles inside the nucleus __, the forces that keep the particles together become __ effective and, therefore, the chances of particle emission are __.
Increases, less, increased
In this type of scattering, the projectile enters the nucleus and is reemitted with less energy and in a different direction
Inelastic scattering
A nucleus still left in the excited state after a nuclear transformation may get rid of its excess energy by the emission of γ-ray or by a process called __.
Internal conversion
In this process, the excess nuclear energy is passed on to one of the orbital electrons, which is then ejected from the atom.
Internal conversion
What is it referred to when a nucleus captures one of its own K shell orbital electrons, a proton transforms into a neutron and a neutrino is ejected.
K- capture
In both nuclear fission and fusion, a __ amount of energy is released in the process.
Large
In general, the elements with __ Z tend to be stable, whereas the ones with __ Z are radioactive.
Lower, higher
The average lifetime for the decay of radioactive atoms is called the
Mean or average life
A negative electron is termed __ and a positive electron is termed __
Negatron, positron
In this interaction, the projectile a enters the nucleus A, which is transformed into nucleus B and a different particle b is emitted
Nuclear reaction
__ can be produced by bombarding heavier nuclides with lighter nuclides or particles.
Nuclear reactions
The original nuclide is called the
Parent
What process is responsible for contamination of the high-energy x-ray beams generated by linear accelerators?
Photodisintegration process
The number of atoms disintegrating per unit time (∆N/∆t) is __ to the number of radioactive atoms (N) present at any given time.
Proportional
A statistical phenomenon in which a certain proportion of atoms (actually nuclei) in a radioactive material predictably disintegrate in a given interval of time.
Radioactive decay
A process in which a nucleus with excess energy (excited nucleus) emits radiation to get rid of its excess energy. This can occur in one or more than one step.
Radioactivity
At __ equilibrium and thereafter, the activity A1 of the Parent is equal to the activity A2 of the daughter. A2=A1
Secular equilibrium
If the half-life of the parent is much longer than that of the daughter, then it can give rise to what is known as the __
Secular equilibrium.
The Becquerel is a __ but more __ unit than the curie
Smaller, basic
What are the two kinds of radioactive equilibria, depending on the half-lives of the parent and the daughter nuclides?
Transient and Secular equilibrium
After __ equilibrium, the ratio of Activity A2 of the Daughter to the activity A1 of the parent is constant.
Transient equilibrium
If the half-life of the parent is not much longer than that of the daughter, then the type of equilibrium established is called the __
Transient equilibrium
Radium occurs in the __ series and gives rise to many daughter products before settling down to stable lead.
Uranium series
The __ series originates with 238U having a half-life of 4.51 × 10^9 years and goes through a series of transformations involving the emission of α and β particles. γ rays are also produced as a result of some of these transformations.
Uranium series
Radioactive nuclides with very high atomic numbers (>82) decay most frequently with the emission of an __
α particle.
The unstable nucleus emits a particle composed of two protons and two neutrons. This particle, which is in fact a helium nucleus, is called the __
α particle.
The process of radioactive decay, which is accompanied by the ejection of a positive or a negative electron from the nucleus, is called the __
β decay
The negative electron, or negatron, is denoted by __, and the positive electron, or positron, is represented by __
β-, β+
There are many different possible modes of nuclear decay but some of the common ones involve the following:
• α-particledecay • β-particledecay • ElectronCapture • InternalConversion • γ-Emission • Isomeric transition
