Radioactivity Flashcards
mass of electron
9.1* 10^-31 kg
mass of proton
1.67*10^-27 kg (mass of neutron too)
in a nuclear reaction, what happens to A and Z
total sum of A/Z on product side= total sum of A/Z on reactants side
define isotopes
atoms of the same element, having same atomic number but different mass number
which element has most isotopes
tin
types of isotopes
- stable (n=p nearly)
- unstable/radioactive (n > p): undergo radioactive decay
define isobars
atoms of different elements which have the same mass number A, but different atomic number Z
define mirror isobars
if number of protons and neutrons get interchanged inside nucleus (Na and Mg)
define isotones
atoms having different number of protons but same number of neutrons, and different number of electrons
three types of becquerel rays
- positive (alpha)
- negative (beta)
- uncharged (gamma)
define radioactive substances
disintegrate by the spontaneous emissions of radiations (uranium, radium, polonium, thorium, actinium)
effect of physical and chemical changes on nature of radiation emitted by a substance and its rate of decay
no change
define radioactivity
it is a nuclear phenomenon. it is the process of spontaneous emission of alpha or beta and gamma radiations from the nucleus if atoms during their decay
properties of alpha particles
- consists of two protons and two neutrons- same as a doubly ionised helium atom
- mass is roughly four times the mass of proton, and charge is twice of proton
- speed is of the order 10^7 m/s
- strongly ionises the gas through which it passes (strongest ionising power than other two)
- dissipates its energy as it moves through a medium and therefore its penetrating power is quite small (least power)
- positive, so they are deflected by electric and magnetic fields
- affect photographic plate
- cause fluorescence on striking a fluorescent material
- large KE and momentum
- destroy living cells and cause biological damage
mass of alpha particle
6.68 * 10^-27 kg
specific charge of alpha particle
4.79 * 10^7 C/kg
mass of beta particle and charge
mass: 9.110^-31 kg
charge: -1.610^-19 C
specific charge of beta particle
1.76*10^11 C/kg
properties of beta particles
- fast moving electrons emitted from nucleus
- beta particles given out from nucleus of atom, and cathode rays are given out from its orbital electrons
- speed is 10^8 m/s
- ionise the gas through which they pass
- more penetrating power than alpha, less than gamma
- negatively charged so they get deflected by electric and magnetic fields (more deflection than alpha because it is lighter)
- affect photographic plate
- cause fluorescence on striking a fluorescent material
- produce xrays when stopped by metals of high Z and high mp
- cause more biological damage than alpha rays
properties of gamma radiations
- electromagnetic waves like x rays and light but differ in wavelength
- speed is same as speed of light in air
- lowest ionising power
- highest penetrating power (only thick sheet of lead can stop)
- not deflected by electric and magnetic fields as they are uncharged
- affect photographic plate
- cause fluorescence
- diffracted by crystals like x rays
- x rays obtained when there is a transition of electron in inner orbits, and gamma rays are produced when given out from nucleus
- biological damage
- cancer treatment
wavelength of gamma radiationm
10^-4 nm
most energetic radiations
gamma (so they have smaller rate of collisions with atoms of medium through which they pass; least ionising power; max penetrating power
change during emission of alpha and beta rays
change in number of protons and neutrons inside nucleus
change during emission of gamma rays
change in energy of nucleus, not change in number of protons or neutrons
alpha emission
- if an unstable nucleus containing more neutrons than the number of protons, may emit a particle containing two protons and two neutrons tightly bound together known as alpha particle
- if nucleus of radioactive element of A and Z emits an alpha particle, daughter nucleus will have mass number (A-4) and atomic number (Z-2)
beta emission
- neutron changes to proton by emitting an electron for charge conservation
- number of NUCLEONS remains same, neutrons decrease by 1, protons increase by 1
- daughter product is isobar
gamma emission
- occurs when daughter or parent nucleus is in a state of excitation
- takes no charge and no mass from nucleus
- no change in A and Z
daughter product after alpha or beta emission
may be radioactive and may again decay, emitting more alpha or beta rays until nucleus is stable
uses of radio isotopes
- medical
- scientific
- industrial fields
medical use of radio isotopes
- treating leukemia, cancer
- salts of weak radio isotopes used for diagnosis (called tracers)
- radio cardiology
- gamma rays emitted by them used to sterilize bandages, dressings, syringes, other equipments
scientific uses of radio isotopes
- alpha particles emitted used as projectiles for nuclear reactions, helps in estimating size of nucleus
- study the growth of plants by using chemical manure
- age of excavated material of archaeological importance, rocks- calculated by rate of decay of carbon 14 by beta emissions in dead plants (aka carbon dating)
industrial uses of radio isotopes
- fuel for atomic energy reactors
- used by engineers in factories to avoid accumulation of charge on moving parts of machines due to friction
- luminiscent sighs due to ionising effect of radiations
- control thickness of paper, plastic and metal sheets during their manufacture
sources of harmful radiations
- radioactive fallout from nuclear power plants
- nuclear waste
- cosmic radiation and x rays
types of harmful biological effects of nuclear radiations
- short term recoverable effects- diarrhea, sore throat, loss of hair, nausea
- long term irrecoverable effects- leukemia, cancer
- genetic effects
safety measures while establishing nuclear power plants
- ensure workers are not exposed to nuclear radiations and in case of any accident, there is a minimum spread of radiations
- nuclear reactor must be shielded with lead and steel walls
- reactor must be housed in airtight building of strong concrete structure that can withstand earthquakes
- must be back-up cooling system for reactor core, so the core is saved from heating and melting
safety measures while handling radioactive materials
- put on special lead lined aprons and lead gloves
- handle the radioactive materials with long lead tongs
- special film badges used which are tested from timee to time to know the amount of radiations to which a particular person has been exposed
- radioactive substance must be kept in a thick lead container with narrow opening
safety measures in safe disposal of nuclear waste
must be first kept in thick casks, then must be buried in specially constructed deep underground stores,
stores must be made far from populated areas
background radiations
radioactive radiations to which we are all exposed, even in the absence of a visible radioactive source
two types of sources of background radiations
- internal source (K-40, C-14, radium inside body)
- external source (cosmic rays, naturally ocurring radioactive elements like radon-222 and solar)
1 MeV=
1.6 * 10^-13 J
1 amu= ? MeV
931 MeV
1 amu of mass is equivalent to 931 MeV of energy
define nuclear fission
process in which a heavy nucleus splits into two lighter nuclei of nearly the same size, when bombarded with slow neutrons
why is energy released during fission
sum of masses of product nuclei is less than sum of mass of parent nucleus and mass of neutron
what happens when a neutron strikes a uranium nucleus (A= 235)
unstable for of uranium (A= 236) formed, which splits into Barium (144, 56) and Krypton (89, 36). 3 neutrons are released and energy
how much energy is released due to fission of one uranium nucleus
190 MeV
why is U-235 more fissionable than U-238
fission of U-238 nucleus is possible only by the fast neutrons, while fission of U-235 nucleus can occur even by slow neutrons
how is chain reaction controlled
by absorbing some of the neutrons emitted in the fission process by means of cadmium rods and then making them slow by the moderators (graphite, heavy water). the rate of energy generated in fission can be controlled and utilised for constructive purposes
uses of fission
- destructive use
- constructive use
for destructive use
nuclear bomb
for constructive use
nuclear reactor to generate electric power
define nuclear fusion
process in which two light nuclei combine to form a heavy nucleusr
reason for release of energy during fusion
mass of the product nucleus is less than the sum of masses of two combining nuclei
how much energy is totally released when 3 deuterium nuclei fuse to form helium nucleus
21.6 MeV
part of the energy is obtained as KE of neutron and proton
why is fusion not possible at ordinary temperature and pressure
when two nuclei approach each other, due to their positive charge, the electrostatic force of repulsion between them becomes so strong that they do not fuse. high temp and pressure is required. both nuclei due to thermal agitations, acquire enough KE to overcome repulsion and fuse
source of energy of sun
nuclear fusion of light nuclei present at the core at very high temp and pressure
hydrogen bomb working
based on nuclear fusion, at high temp, required for fusion is produced by explosion of nuclear fission bomb
why is energy released by fusion greater than fission for a given mass of heavy nucleus?
for the same mass, the number of light nucleus is much more than the number of heavy nucleus; hence, energy produced per unit mass in fusion is much larger than the energy obtained per unit mass in fission
why can’t energy be produced by fusion in nuclear reactors
at high temperatures like 10^7 K, substance gets ionised, it is in plasma form. it is difficult to store plasma
this can be overcome by storing plasma in nano carbon tubes
