5. Nuclear physics (22, 23) Flashcards
Describe the structure of an atom
positively charged nucleus and negatively charged electrons in orbit around the nucleus
Describe how the scattering of alpha (α) particles by a sheet of thin metal supports the nuclear model of the atom, by providing evidence for
(a) a very small nucleus surrounded by mostly empty space
(b) a nucleus containing most of the mass of the atom
(c) a nucleus that is positively charged
Define the terms proton number (atomic number) Z and nucleon number (mass number) A
State the relative charges of protons, neutrons
and electrons a
nuclide notation
PN- atomic no. relative charge of nucleus
NN- mass no.- proton+neutron. relative mass of nucleus
protons, neutrons and electrons as +1, 0 and –1
A X
Z
what is meant by an isotope
atoms of an element with same no. of proton and different no. of neutron. elements may have more than one isotope
Describe the processes of nuclear fission and nuclear fusion
process by which energy is released by splitting of a large heavy unstable nucleus into two or more smaller nuclei. neutrons are released from nucleus, large release of energy.
process by which energy is released when two light nuclei join together to form a heavy nucleus. (produces more energy and needs higher temperature- stars)
Equation of nuclear fission and nuclear fusion
21H +21H →32He +10n
what is meant by background radiation
sources that make a significant contribution to background radiation
radiation from environment to which we are exposed all the time
(a) radon gas (in the air)
(b) rocks and buildings
(c) food and drink
(d) cosmic rays
how can ionising nuclear radiation be measured
ionising nuclear radiation can be measured using a detector connected to a counter
count rate measured in counts/s or counts/minute
Describe the emission of radiation from a nucleus
spontaneous and random in direction
Identify alpha (α), beta (β) and gamma (γ) emissions from the nucleus
(a) their nature
(b) their relative ionising effects
(c) their relative penetrating abilities
2 proton+ 2 neutron- 1 electron- em wave
charge- 2+ 1- 0
mass- high medium low
ionisation- high medium low
absorption- high medium low
penetration- low medium high
speed- low medium high
a- largest charge and slowest- collide with air molecule- knock an electron and become charged. strongly ionising
b- less charge and moves faster so more likely to travel straight past an air mol without interacting. so it can travel further through air without being absorbed
g- uncharged and moves fastest so readily absorbed in air- least ionising. lead absorbs- dense. more penetrating- greater range
Describe the deflection of α-particles, β-particles and γ-radiation in electric fields and magnetic fields
A particle is deflected in an electric field if it has charge. magnetic field if it has charge and is moving perpendicular to it.
(γ) particles have no charge, they are not deflected by either electric or magnetic fields
Electric Fields-
Alpha particles are deflected towards the negative plate. Beta particles- positive plate
Alpha particles are heavier than beta particles. Therefore, beta particles are deflected more in the electric field.
Magnetic Fields
They are deflected in opposite directions due to their opposite charges.
beta-electron-current in opposite direction. fleming lhr.
Explain their relative ionising effects
(a) kinetic energy
(b) electric charge
The greater the charge (mass) of the radiation, the more ionising it is. alpha radiation is the most ionising as it has a charge of +2. beta particle has a charge of –1 so is moderately ionising. gamma radiation is the least ionising as it has a charge of 0.
The higher the kinetic energy of the radiation, the more ionising it is. alpha particle is still the most ionising because it has the greatest mass. However, a beta particle is very light (it is an electron) but travels at high speeds, therefore, it has a lot of kinetic energy and is still moderately ionising. Gamma radiation has virtually no mass so is weakly ionising
Describe radioactive decay and state why isotopes of an element may be radioactive
a change in an unstable nucleus that can result in the emission of α-particles or β-particles and/or γ-radiation
and these changes are spontaneous and random
isotopes of an element may be radioactive due to an excess of neutrons in the nucleus and/or the nucleus being too heavy
Describe the effect of α-decay, β-decay and γ-emissions on the nucleus
during α-decay or β-decay, the nucleus changes to that of a different element
an increase in stability and a reduction in the number of excess neutrons;
the following change in the nucleus occurs during β-emission- neutron → proton + electron/beta particle
Use decay equations, using nuclide notation, to show the emission of α-particles, β-particles and γ-radiation
a- 2 protons and two neutrons emitted. proton no. decreased by 2 and nucleon no. decreased by 4.
b- a neutron splits into a proton and an electron. proton no. increases by 1 and nucleon no. is same.
g- emission of energy from nucleus so doesn’t change particles in nucleus.
