Unit 1.2 Flashcards
Radioactivity
Alpha?
4 He
2
2 protons + 2 neutrons
charge of 2+
most harmful in the body - can’t get through the skin
least penetrating
most ionising
stops with either a sheet of thin paper or a few cm of air
ionising def?
collides with other molecules, knocking off eelectrons
deflected towards a negative plate in a magnetic field
deflected by a magnetic field according to Flemmings left hand rule
Example of Alpha?
234 U —- 234 + 4 He
90 90 2
Beta?
stream of high energy electrons which = negatively charged
moderately penetrating
moderately ionising
in a magnetic field, its directly opposite deflected than alpha
in an electric field, its deflected towards a positive plate
1 mm of air
5 mm of Al
Equation for beta?
14 C —- 14 N+ 0 B
6 7 -1
Gamma?
electromagnetic wave of high energy
high energy electromagnetic radiation with no charge
not deflected with an electric or magnetic field
weakly ionising but strongly penetrating
can pass through several cm of lead
Inverse Beta decay?
electron capture
an orbital electron is captured by a proton in the nucleus and forms a neutron which releases an electron neutrino
Equation for this>
40 K + 0 e ——– 40 Ar
19 -1 18
one place to the left
Inverse beta decay?
B-
Beta positive decay?
proton emission
Proton = converted to a neutron, releasing a positive positron
( positive electron)
Example?
23 Mg —- 23 Na + 0 B+
12 11 -1
what is half life?
the time taken for half of the atoms in a radioisotope to decay or to fall to half of their intial value
there are 2 types of half equations
the time taken to fall to a fraction of its intial value
finding the mass after a given time
Example?
28 Mg ‘s Half life = 21 hours
how long until it falls to an 1/8th of its value?
1— 1/2 —- 1/ 4—– 1/8
takes 63 hours
example 2
if you start with 2g of Mg, how much remains after 84 hours?
84/21 = 4 hours
2 — 1/2 — 1/4 —– 1/8
1/8 of a gram = 0.125 g
Radiation on living cells?
cells = ionised
damages the Dna of the cell which leads to mutations + the forming of cancerous cells
Alpha = more dangerous inside the body as it is strongly ionising
Gamma = more dangerous outside the body due to its penetrating power
Protection for radiation workers?
wearing lead lined suits
also photographic film badges = worn which become fogged when exposed to radiation
Benefits of radioactivity?
Medical?
Cobalt - 60
used in radioactivity for cancer treatment + is high energy gamma radiation
prevents malignant tumours
Technetium - 99
medical tracer
taken up by tissues
Geological?
Radio dating
aging plant , animal ot tock material
e.g carbon 14 half life of 5570 years
Carbon 14 is inhaled during respiration + remains in body until death
possible to measure the ratio of carbon 12 + Carbon 14 in a dead organism to calculate the age of death
Analytical?
dilution anylasis
used to find an isotope in a complex mixture + can be isolated (extracted) in a pure state but the process is not quantitative ( measuring the thickness of paper + would use Beta)
the paper is passed through a radioactive source and a detector
if thickness exceeds the Penetrating power of Beta, an atom is signalled
what is K 40 used for?
half life of 1300 million years
used to estimate the geological age of rocks + K40 decays to Ar40
what is an atomic orbital?
region in an atom that can hold up to 2 electrons with opposite spins
S - spherical
P - dumb bell
d - 3 p’s overlapped
Aufbau principle?
orbitals fill in order of increasing energy
Hund?
Orbitals fill with 1 electron first
Paulli?
Exclusion principle- mass of 2 electrons in every orbital with opposite spins
