22 - 23 Theory Flashcards
State law of electrostatics
Identical charges exert a repelling force on each other
What is nuclear force?
The force exits between nucleons that holds nuclear constituents together (pre- vent the repelling of identical charges, charge-independent)
What is mass defect?
The mass of a nucleus is less than the mass of its constituent nucleons.
(The reason the actual mass is different from the masses of the components is because some of the mass is released as energy when protons and neutrons bind in the atomic nucleu)
What are nucleons?
Protons and neutrons
What is binding energy of nucleons
The energy corresponding to the mass defect
What is Binding energy per nucleon?
The strength of a nuclear bond
What are isotopes
Atoms of the same element with
- the same number of protons
- different numbers of neutrons
- different mass number
Light nucleus are most stable when ____
N=Z
Heavy nuclei are most stable when
N>Z
Describe nuclear stability
As the number of protons increases, the Coulomb force increases and so more neutrons are needed to keep the nucleus stable
3 stability rules
(1) There are more stable nuclei with even, than with odd number atomic num- bers
(2) There are more stable nuclei with even, than with odd number neutron numbers
(3) There are more stable nuclei with even, than with odd number mass num- bers
What is radioactivity?
the spontaneous release of energy in the form of particles or electromagnetic waves
the result of decay of unstable nuclei
What is radioactive decay?
Spontaneous decay of unstable parent nucleus into a more stable daughter nucleus & constituents/particles & energy
What is activity of radioactive decay?
number of nuclei decayed in a unit time (characterizes the quantity and quality of radioactive substances)
State the law of radioactive decay
The rate of decay is proportional to the number of radioactive nuclei present.
What is specific activity?
activity in a unit mass of isotope (Bq/kg)
Describe average lifetime of radioactive nuclei
The time within which the number of atomic nuclei is decreased exponentially with the decay constant and half-life
What is half-life (T) of radioactive decay?
A period during which number of undecayed nuclei is decreased to half of the original number
2 things that activity depends on
the type of isotope and
the size of the population of unstable (radioactive) nuclei
Which types of radiation participate in direct ionization?
Which types of radiation participate in indirect ionization?
Describe alpha-decay
- For heavy atoms
- A parent nucleus → A daughter nucleus + alpha particle
- Alpha particle = 2 protons + 2 electrons
Why do protons and electrons usually fall off from the parent nucleus on the edge?
Because that is where there is less strong nuclear force and greater electrostatic force
Do all alpha particles have same velocity and kinetic energy? Why?
Yes
→ Because the decay is always the same
Characteristics of spectrum of alpha particle
Line spectrum → shows that the kinetic energy of particles has an exactly determined value
2 types of beta decay
- Beta minus decay
- Beta positive decay
Describe the spectrum of beta decay.
It is continuous
→ Because electrons have different energies
→ The spectrum shows that low number of beta particles possess the maximum number
Do beta particles take all the energy?
Yes, they do not share the energy with other particles
Describe beta minus decay
- When parent nucleus is unstable because there are too many neutrons & too little protons
- Neutron → proton + electron + anti-neutrino
Characteristics of anti-neutrino
- An anti particle of neutrino - has the mass of an electron but no charge
- Why it appears? → Because turning a neutral particle to a positive one should should involve the production of a negative particle as well
Does the mass number of atom stays the same after beta minus decay? Why?
It stays the same
→ No neutron or protons fall out while atomic number changes by +1 with the addition of proton (give a different chemical identity)
Describe Beta positive decay
- When parent nucleus is unstable → because there are too many protons and too little neutrons
- Protons → Neutron + positron + neutrino
- The daughter nucleus has the atomic number -1
what is positron?
- Anti-matter of electron
- Having the same mass but opposite charge as
Medical application of Beta plus decay
Used in POSITRON EMISSION TOMOGRAPHY (PET) SCAN
Describe gamma decay
- When a nucleus loses & releases energy in the form of high frequency gamma photons
- Unstable nucleus dissipates excess energy by a spontaneous electromagnetic process in the from of gamma radiation
- Result → No change in atomic mass or atomic numbers
Can alpha and beta particles escape the body easily?
No, only gamma
Describe the spectrum of gamma radiation
- It is discrete → photons have a particular wavelength
Describe penetration depth of alpha radiation
- Alpha particles are large and charged
→ Directly ionize atoms over a short distance
→ Low penetration depth and short effective range
→ High linear ion density (concentrated over area)
Describe penetration depth of beta minus radiation
Beta particles is small and charged
→ Directly ionize atoms of matter but less energy loss
→ change the direction when they collide
→ The path is not linear and charge are distributed
→ Larger penetration depth and longer effective range
Describe interaction of beta plus radiation
Undergo annihilation (not pair production)
→ masses of an electron and positron are converted to gamma photon energy upon collision
→
Describe interaction of gamma radiation with matter
Because gamma radiation is not charged
→ Indirectly ionizes (producing charged particles which then interaction with matter)
→ No effective range
→ Follow exponential attenuation law
→ Photoeffect + Compton scattering
