Atomic Physics

Mass no.: Number of Protons and neutrons in nucleus

Atomic no:Number of protons                            Number of neutrons: Mass no - Atomic no

DEF: Atoms of the same element have same proton no. but different mass no. due to different no. of neutrons inside nucleus.

Have same chemical properties--> same number of electrons 

Have different physical properties

DEF: It is the random and spontaneous emission of alpha, beta, and gamma Radiation from unstable nuclei.

Random decay: The decay doesn't follow a certain pattern and each nuclei have equal probability of decaying at any instant.

consequences:

• it is impossible to know which nucleus decays first
• The radiation level readings are always fluctuating and never constant

Spontaneous  decay: The decay is not affected by external factors such as change in temp or pressure

Helium nucleus

Mass--> 4 --> (2x1)+(2x1)

charge--> +2

Ionization--> Greatest ionization as it has the greatest momentum and greatest charge, greater force on air molecule so greatest density of ionizations.

smallest penetration-->completely absorbed by Paper or skin. In air: 5-10 cm

A single high energy electron which is emmited from Unstable nucleus causing one of the neutrons to turn into a proton. emmited with a range of energies from the same source.

Mass--> ~1/2000

Charge--> -1

Ionization:weak 

Penetration:completely absorbed by a thin Aluminum sheet.  In Air:(5-10 m)

Electromagnetic waves are emitted from the nucleus of an unstable nucleus.

Mass-->0

charge-->0

Ionization--> V.weak

penetration--> greatest. A sheet of several cm of lead or concrete wall will absorb most of the gamma rays but in Air-->5-10 km

Beta particles greatest deflection as it has less mass (mass is the property of body that resists change in motion)

gamma rays no defection as it is neutral 

alpha particles deflect to -ve plate as it's positively charged (+2)

beta particles deflect to +ve plate as it's negatively charged (-1)

Larger deflection of Beta particle as it has lower mass (mass is the property of the body that resists change in motion)

Accoridng to fleming's left hand rule, a positively charged particle will experience an upwards force if the magnetic field is directed inward(in paper), and negatively charged partice will experience the opposite force which is downwards.

DEF: the time required for half of  undecayed nuclei to decay.

half life of a radioactive isotope is 1 week: (--> means 1 week)

16-->8-->4-->2 (After 3 weeks the number of undecayed nuclei is 2)

Exponential decay. Theoretically, it will never reach 0

• Photographic film:

Becomes blackened when exposed to radioactivity.the darker the film the more radioactivity, though it doesn't provide a numerical value.

• GM tube:

Main detector used, connected to a count rate meter giving reading in counts per unit time

def: radiation detected by a detector without a close radioactive source which is caused by both natural and artificial sources.

detected by the GM tube when the radiation enters the detection range of the GM tube

(An average is calculated because the readings are not constant, they fluctuate due to the radioactive nature of source)

25-35 counts/min

Nautral:

• Cosmic rays from sun
• radon gases in atmosphere
• Rocks and fossils(potassium uranium rubidium) Underground 
• +man made

• Medical:
  • Treatment of cancer
  • sterilization of medical equipment
  • medical tracers
• Industrial
  • Thickness control

• carbon dating:C14 is one of the isotopes of carbon, the living organism absorbs C14 till they die, and it has half-life of 6000 years,the amount of C14 in a body is measured and time of death is determined accordingly.
• smoke detector
• pipe leakage control

• Wear overalls
• use long handling tools to deal with radioactive source
• store in labeled lead box
• don't place food near radioactive source 
• wash hands after handing source even if gloves were worn

human exposure to iozinzing radiation could cause:

Hair loss, radiation/skin burns, fetus brain damage and cancer(long term exposure) 

an experiment conducted by rutherford and his students geiger and marsden to discover the main structure of the atom.

Alpha particles are fired toward a metal foil and their scattering is observed.

• Most Of them were undeviated : The atom is mainly empty
• A few were deviated (<90): the nucleus is positively charged
• A very few were deviated >90: The mass of atom is concentrated in a tiny nucleus

The whole apparatus is in vacuum so that the alpha particles don't lose energy by ionizing air molecules before reaching the metal foil.