atom, nucleus, radioactivity

Question 1

ernest rutherford

Answer 1

scientist from NZ, 1911 gold foil experiment, proposed nuclear model of atom, approximated size of nucleus (order of 10^-15m)

Question 2

gold foil experiment

Answer 2

bombarded alpha particles (known to be pos.) at thin piece of gold foil
-most undeflected + passed straight through
-some deflected through small angles
- very small number turned back by angles >90 deg.

Question 3

Niels bohr

Answer 3

danish, 1913, proposed model describing how electrons are arranged in orbits around the nucleus using emission spectra

Question 4

emission spectrum

Answer 4

pattern produced when light from a luminous source undergoes dispersion
-continuous
-line spectrum

Question 5

continuous spectrum

Answer 5

produced by an incandescent solid or liquid. all visible wavelengths produced no matter the object

Question 6

line spectrum

Answer 6

produced when a gaseous element gives out light and is then passed through a prism/diff. grating. bright and dark lines formed for each element

Question 7

spectroscopy

Answer 7

where the analysis of a mixture of gases can use line spectrums to identify each element and relative amounts of each

Question 8

energy level

Answer 8

fixed energy value that an electron can have in an atom
-if atom given energy it can move to orbit of higher energy level (excited state)
-electron will eventually fall back to original orbit + emit energy (photon)
- hf = E2 - E1

Question 9

lasers

Answer 9

light amplification by stimulated emission of radiation
-in laser many atoms have electrons in excited state
-all of these atoms stimulated by light of certain freq. –> electrons fall to o.g. orbit
-photons emitted in intense beam

Question 10

uses of lasers

Answer 10

-phone lines (optical fibres)
-burn cancer cells, correct eyesight, remove birthmarks
-cutting + welding in industry

Question 11

atomic number (Z)

Answer 11

no. of protons an element has
(no. protons = no. electrons)

Question 12

mass number (A)

Answer 12

no. of protons + neutrons an element has (atomic weight)
No. neutrons = A - Z

Question 13

isotope

Answer 13

atoms of an element that have the same no. of protons but different no. of neutrons e.g. Hydrogen (1), Deuterium (2)

Question 14

Henri Becquerel

Answer 14

french, 1896 noticed that uranium salt caused nearby plate to go black (exposed)
-concluded salt must be giving out radiation
(discovered radioactivity)

Question 15

radioactivity (nuclear radiation)

Answer 15

the disintegration of the nuclei of certain atoms with the emission of 1 or more types of radiation
-occurs when nuclei of certain isotopes are unstable (excess energy)
1. alpha α
2. beta β
3. gamma γ

Question 16

radioactive

Answer 16

this is when a source’s nucleus emits radiation (excess energy) e.g. uranium, radon etc.

Question 17

alpha radiation

Answer 17

fast moving helium nuclei ejected from the nuclei of radioactive atoms i.e. a-particle = 2 protons + 2 neutrons
-greatest ionising ability
-least penetration ability (stopped by paper)
-charge +2
-deflected same as pos. charge

Question 18

beta radiation

Answer 18

fast moving electrons ejected from the nuclei of radioactive atoms i.e. 1 b-particle = 1 electron
-ionising ability less than a-radiation
-penetration ability more than a-radiation (mm)
-charge -1
-deflected as neg. charge

Question 19

gamma radiation

Answer 19

high freq. electromagnetic radiation in the range of 3x10^-19Hz
emission of gamma rays does not affect structure of nucleus however it loses energy and hence becomes more stable
-least ionising ability
-most penetrating power (cm) lead
-no charge
-undeflected

Question 20

paul villard

Answer 20

french, 1900 discovered gamma radiation.
named by rutherford

Question 21

activity

Answer 21

no. of nuclei in a radioactive substance decaying per sec.
unit: becquerel (Bq) -> 1Bq = 1 radioactive decay per sec

Question 22

law of radioactive decay

Answer 22

-states no. of nuclei decaying per sec (activity) is directly proportional to the no. of nuclei undecayed (N)
i.e. A ∝ N
A = λN

λ = decay constant (unit = s^-1)

decay is a random process

Question 23

half life

Answer 23

time taken for half of the undecayed atoms of a radioactive isotope to undergo decay
in general after n half lives 1/2^n of the original sample remain

-also time taken for activity to decrease by half
-does not depend on size of sample

T1/2 = ln2/λ

Question 24

decay series

Answer 24

series of isotopes formed when an isotope undergoes radioactive decay. process continues until stable isotope formed

Question 25

to show ionising effect of radiation

Answer 25

-charge gold leaf electroscope
-being radioactive source near
-air becomes ionised and starts to conduct electricity
-means charge can leak away, electroscope discharges and gold leaf collapses

Question 26

geiger muller tube

Answer 26

detects radioactivity by the ionisation it produces
-as radiation enters mica window it ionises argon gas
-electrons near anode accelerate + produce further ions (avalanche of electrons produced)
-electrons reach anode and pulse of current flows
-pulses counted with counter e.g. scaler or ratemeter

Question 27

solid state detector

Answer 27

made of a reverse biased p-n junction connected to a counter
-electron hole pairs are formed when radiation strikes depletion layer
-pulse of current flows which is amplified before being detected by counter

Question 28

discovered artificial radioactivity

Answer 28

irene curie + frederic joliot

Question 29

artificial radioactivity

Answer 29

non-radioactive isotope can be made radioactive by bombarding them with neutrons
-usually done in nuclear reactor
-mostly used in medicine + industry

Question 30

uses of radioisotopes

Answer 30

1. medical imaging
2. medical therapy
3. food irradiation
4. radioactive tracers
5. carbon dating
6. industry - detect leaks, cracks, fullness of containers
7. smoke detectors

Question 31

the mole

Answer 31

a mole of any substance is the amount of that substance that contains as many particles as there are atoms in exactly 12 grams of carbon-12
i.e. 1 mole = 6.02x10^23 particles = avogadro’s constant

Question 32

unified atomic mass unit (u)

Answer 32

u = 1.66x10^-27 kg

p47 MT