atomic structure Flashcards
how does radiation in smoke detectors work?
-alpha radiation used in smoke detectors
-this ionises the air causing current to flow
-when air has smoke, it absorbs/ stops alpha current is broken = alarm
what is an isotope?
-atoms of same element with different number of neutrons
what is radioactive decay?
-process of emitting high energy particles or waves from unstable nucleus
-process of emitting radiation
what is irradiation?
-process of exposing material to alpha, gamma, or beta radiation
-to sterilise equipment to kill microorganisms
-to sterilise food, makes it last longer
what is contamination?
-unwanted radioactive isotope leaking onto material
-much more harm potential, due to continuous radioactive exposure it will produce
changes to atom structure after:
-alpha decay
-beta decay
-gamma decay
-alpha: mass no. decreases by 4, atomic no. decreases by 2
new element created
-beta: only change, atomic number +1 (neutron changes to proton and an electron, elec is emitted, proton remains.)
half life:
rate at which activity of radioactive material halves.
-time taken for half of nuclei of sample of radioactive isotope to decrease by half
what causes atomic nuclei to become unstable?
-because they are too large
-too many or too few neutrons
-imbalance of forces between particles in nucleus
what is activity?
rate at which instable nuclei decay
what is count rate?
rate at which radioactive emissions detected
what happens when electrons absorb EM radiation?
they move to higher energy levels,
-causes atom to be unstable
-to return to original energy level, it moves back down, and emits EM radiation.
when are electrons knocked out of atom?
-objects rubbed together, elec removed by friction
-elec can absorb EM radiation to gain enough energy to leave atom
-from chemical reactions
prevention of damage from:
-irradiation
-contamination
-IR: lead lined suit, lead absorbs radiation
-CON: air tight suits when working in area that may have radiation leak, prevents atoms getting inside body
what is a dose? how is it measured?
-a dose is amount of radiation received by a person
-measured in sieverts (Sv)
-one Sv is very big
normal dose of person per year: 3mSv (0.003 Sv)
what is a bequerel:
measurement of amount of radiation emitted by source every second
what is counts per second:
number of decays per second????
two ways of nuclear fission
-spontaneously
fission is unforced and happens by itself (very rare)
-absorbing a neutron
can split a nucleus by making it even less stable
name two nuclear fuels
uranium-235, plutonium-239
steps of nuclear fission
-slow moving neutron fired at a large unstable nuclei
-breaks into two smaller nuclei, and two/three neutrons
-energy prod in the form of gamma radiation
-if neutrons slow enough to be absorbed by other large unstable nuclei, chain reaction happens
what is the energy prod from fission used for
to heat water and prod steam, which can drive turbines connected to an electricity generator
pros and cons of nuclear energy
PROS
-U and Pu are cheap
-prod a large and steady amount of energy
-clean; doesn’t prod GH gases
CONS
-power plants, very expensive to build
-nucl waste expensive to get rid of
-risk of major disaster
process of nuclear fusion
-two light nuclei collide at high speeds to prod a heavier nucleus (ex. hydrogen > helium)
-heavier nucleus has less mass than the two separate nuclei, as some mass converted to energy
-creates a lot more energy than fission
-not used to make energy for us as it requires rlly high press & temp
-happens in stars
why does fusion only happen at very high temperatures and pressures?
to overcome the repulsion of the positively charged nuclei
a substance is radioactive when it consists of
unstable isotopes that can decay
describe an alpha particle
-2 protons & 2 neutrons, represented by a helium nucleus
-has charge of 2+
-relatively large, so only travel a few cm and absorbed by paper
-strongly ionising, so can knock electrons off of any atoms they collide w/
describe a beta particle
-an electron
-no mass
-charge of 1-
-one of the neutrons in the nucleus decays as a proton and electron, proton stays in nucleus and electron emitted at high speed
-tiny so moderately ionising and penetrating
describe gamma rays
-waves of electromag radiation
-often emitted after alpha or beta radiation
-no mass or charge, so pass right through materials
-not very ionising
-stopped by thick lead/concrete
describe neutron radiation
if a nucleus has too many neutrons and is unstable, it emits neutrons
for a beta decay equation, the atomic mass (top num.) ……….. and the atomic num ……
-stays the same
-increases by 1
half life can be defined as
- the time taken for the number of radioactive nuclei in a sample to halve
- the time taken for the number of decays or activity to half
what is meant by radioactive activity
overall rate of decay of all isotopes in sample
what is irradiation
the process by which objects are exposed to radiation
what makes ionizing radiation dangerous
- can enter living cells and interact with the molecules inside
- can ionize DNA causing mutations
What factors affect the dosage of radiation
- how far from the source you are
- how long you’re exposed
- how radioactive the substance is
how are medical tracers used in radiation medicine
gamma rays are used
patients are made to swallow radioactive isotope
-movement of isotope is traced in the body to see if organs are working properly and are absorbing the right amount of isotope etc.
- only use isotopes with short half lives
what type of radiation is used for an internal and external treatment
external is gamma
internal is beta
Exposure to low levels of radiation over long periods can lead to cancer.
Why is this?
Radiation can cause mutations in our DNA…
…which may cause our cells to divide uncontrollably
