L 1: Atomic and nuclear structure Flashcards
How are mass and energy related
E=MC2, interchangeable.
Stability of the nucleus depends on
Neutron proton ratio
nucleon pairing
binding energy per nucleon
Most stable nuclei has even number of n & p
Least stable nuclei has odd number of n & p
Transition of electrons in between shells
going to a higher shell: absorption of energy in form of photon
going to a lower shell: release of energy in form of x-rays (Auger electron)
Electron orbits
K,L,M,N
inner most is K
Number of electrons in an orbit
- 2n square
- n = orbit number
Number of electrones in subshells:
2(2L+1)
See the picture for solving problems
A
Atomic mass number = # of protons + neutrons
Z
Atomic number = # of protons
# of protons is equal as # of electrons in the atom (stable atom)
N
Neutrons = A - Z
IsotoPes
2 atoms have same # of protons so same Z
P=protons
IsotoNes
2 atoms have same # of neutrons so same A - Z
N=neutrons
IsobArs
2 atoms have same mass number so same A
A=atomic mass
IsomErs
2 atoms have same neutons and protns but different Energy levels
E=energy
1 Atomic mass unit is
1.66 x 10 to the power -27 kg
1 Electron volt
1.6 x 10 to the power -19 J
Mass of E, P , N
Neutron > Proton > Electron
To remove an electron we need how much energy?
0.511 MeV
To remove an proton/neutron we need how much energy?
931 MeV
Forces in nature
- Gravitational forces
- Weak Nuclear forces
- Electromagnetic forces
- Strong nuclear forces
Order of strength: 4 > 3 > 2 > 1
Weak nuclear forces
Seen in radioactive decay
Relation between wavelength, frequency and energy
As the wavelength becomes shorter, frequency becomes large and so does energy.
frequency and energy are proportional. Wavelength in inversly proportion
atomic mass between
Stable nucleus is seen
A between 24 -128
Transient Equilibrium
T1/2 life of parent and daughter nuclei is similar
T1/2 (P) > T1/2 (d)
Secular Equilibrium
T1/2 life of parent is way larger than daughter nuclei
T1/2 (P) >»_space;>T1/2 (d)
years vs days
hint: Parents are very secured!
Types of radioactive decay
- Alpha decay
- Beta +ve decay
- Beta -ve decay
- Electromagnetic decay
As the atomic number increases
the ratio of protons and neutrons increase
Most stable elements are
Z < 20
smaller elements
Alpha Decay
Decay of a heavy particle with emission of alpha particle
must have kinetic energy between 5-10 MeV to emit alpha particle
Beta -ve decay
- Negatron emission
- 1.7 MeV energy is emitted
- High n/p ratio gives B-ve decay
- So neutron rich elements
Beta +ve decay
- Positron emission
- Energy is emitted
- Low n/p ratio gives B+ve decay & Electron capture
- So proton rich elements
Electron Capture
- Electron is added to the nucleus of the radioactive material
- so 1 proton is transformed into neutron to maintain stability of the nucleus
- It produces a new substance with z-1 = atomic number + Neutrino + energy
- Characteristics x-rays and or Auger electrons are produced when the empty space in the orbit is filled by the outter electron
- Low n/p ratio gives B+ve decay & Electron capture
- So proton rich elements
Unit of activity
Curie/Bq
1 Ci = ? Bq
curie
3.7 x 10 to the power 10 Bq
1 bq = 1 dps
t 1/2 =
It is an intrinsic, unchanging property of a radioisotope.
0.693 / lamda
T1/2 is independent of temp, pressure, composition
Mean life =
1/lamda = 1.44 t1/2
Activity of radioactive element / Decay Constant =
A= Ao x e to the power 0.693/t1/2
Gamma emission
Nuclear de-excitation: The nucleus emits a gamma ray and there is no change in either A or Z
Velocity of electromagnetic waves =
Velocity (c) = lamda x frequency (v)
Energy of photon =
E = h x frequency (v)
E = 1.24 x 10 to the power -6
Radiation emission from the nucleus
- gamma rays
- particles
- or both
Nuclear Fission
Splitting higher Z in to 2 lower Z nuclei
Nuclear Fussion
- Lighter nuclei fuse to form a heavier nuclei
- Large energy is produced in this process
- Fusion of H nuclei forms helium = sun’s energy source
Naturally occuring Isotopes
- C-14
- K-40
- U-238
- Th-232
- Ra-226
At what atomic mass does binding energy pr nucleon peak??
56-62
Nuclei with atomic masses 24 - 128 have high binding energy as repellent electromagnetic forces are balanced out by strong nuclear forces.
Protons is made of?
- 2 up quarks
- 1 down quark
- gluons
all these mediate to bind them together
Internal Conversion
- X-rays:
* electron cascade down to lower energy unoccupied shell.
* Emits x-rays with discrete energy. - Auger electron emmision:
* A vaccancy in an inner shell is filled by an electron in the outer shell adn another outer shell electron is ejected.
Isomeric Transition
Nucleus retains its stored energy and becomes meta-stable
Decay diagrams
- Higher the level of element, higher its mass energy state
- B-decay= arrow points down and right
- B+decay/electron capture= arrow down and left
- Gamma rays emmision = down arrow
- meta-stable elements = have excess energy = drawn on y axis
UV Rays
- UV B rays cause cancer
- UV A rays cause prematuring of the skin
- UV C rays are filtered out by earth’s atmosphere
Mass Defect
Tha actual mass of the nucleus is as such less than the individual mass of the neutron and proton.
