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A LEVEL PHYSICS > 25 - Radioactivity > Flashcards

25 - Radioactivity Flashcards

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1
Q

ALPHA RADIATION - nature and charge

A

particle (helium nucleus), +2e

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1
Q

ALPHA RADIATION - ionising and penetrating effect

A

most ionising, least penetrating (stopped by a few mm of paper)

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2
Q

BETA RADIATION - nature and charge

A

particle (fast electron), -e

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3
Q

BETA RADIATION - ionising and penetrating effect

A

(medium) ionising effect, stopped by a few mm of aluminium

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4
Q

GAMMA RADIATION - nature and charge

A

EM wave, 0

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5
Q

GAMMA RADIATION - ionising and penetrating effect

A

least ionising, most penetrating (stopped by many cm of lead)

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6
Q

range of each type of radiation in air

A

alpha - a few cm
beta - a few m
gamma - a few km

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7
Q

radioactive decay is the…

A

emission of a radioactive particle from an unstable nucleus

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8
Q

why is alpha particle deflected less towards the negative plate when passing perpendicular to a uniform electric field?

A

alpha particle is heavier than beta+ particle so affected less

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9
Q

how to find the direction of deflection of particles due to a magnetic field?

A

Fleming’s left hand rule

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10
Q

dangers of radioactivity and precautions

A

ionising effect of radiation can destroy cells and mutate them (could lead to cancer)
so lead-lined storage, pair of tongs with long handles, not handling sources with hands

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11
Q

procedure to investigate the absorption of different radioactive materials

A

using GM tube and Geiger Counter, measure background count rate without source. Do three times and calculate average

number of particles = count rate / time interval

place source and calculate count rate for this source when a material is placed at fixed distance in front of it. vary thickness and make sure to minus background count rate to get count rate for source.

+ mention safety precautions

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12
Q

why is it not possible to carry out absorption experiments with positrons in the school lab?

A

positrons and electrons would annihilate each other

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13
Q

glow in the dark hands on clock explained

A

painted with zinc sulfide and radium. zinc sulfide glows in the dark due to being near the decay of radium emitting alpha particles

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14
Q

what is transmutation?

A

process of radioisotopes stabilising to create stable isotopes, releasing energy and matter from nucleus to a new element (parent to daughter nuclei)

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15
Q

what is conserved in all nuclear reactions?

A

nucleon number, proton number
conservation of energy and mass (energy released produced from mass)

16
Q

nuclear transformation equation for alpha decay

A

A A-4 4
X —> Y + He
Z Z-2 2

17
Q

nuclear transformation equation for beta minus decay

A

A A 0 -
X —> Y + e + Ve
Z Z+1 -1

18
Q

nuclear transformation equation for beta plus decay

A

A A 0
X —> Y + e + Ve
Z Z-1 +1

19
Q

why does gamma decay occur?

A

gamma only emitted if a nucleus has surplus energy following alpha or beta emission (composition of nucleus remains same)

20
Q

nuclear transformation equation for gamma decay

A

A A
X —> X + 𝜸
Z Z

21
Q

why might a decay series/chain occur

A

some daughter nuclei are still unstable so will continue to decay until stable

22
Q

patterns for stability graph

A

all stable nuclei on narrow stability band surrounded by possible unstable nuclei, prediction of decay based on relative position to band

Z>82, decays by alpha emission
right of band, proton rich, beta + decay
left of band, neutron rich, beta - decay

23
Q

why may count rate be lower than expected?

A

not all radiation travels in direction of detector (random + spontaneous)

24
Q

RANDOM nature of decay

A

cannot predict when a nucleus will decay or which one will decay next (each nucleus has same chance of decaying per unit time)

25
Q

SPONTANEOUS nature of decay

A

decay of nuclei unaffected by presence of other nuclei in sample and external factors such as pressure

26
Q

simulation of radioactive decay using dice

A

each die has one side coloured black
roll all dice and count ‘decayed’ nuclei (black dice)
repeat until all dice have decayed
plot undecayed nuclei against roll number

(decay rate high at start and as number of undecayed nuclei decreases, so does decay rate)

27
Q

define half life of an isotope

A

average time it takes for half the number of active nuclei in a sample to decay

28
Q

define activity A of a source

A

rate at which nuclei decay or disintegrates

(number of alpha, beta, gamma photons emitted per unit time)

29
Q

units of activity

A

Bq
(decays per second)

30
Q

power equals

A

A X E
activity x energy

31
Q

decay constant

A

defined as the probability of decay of an individual nucleus per unit time

ΔN∝NΔt
ΔN/Δt∝-N (-ve sign to show nuclei in sample is decrasing)
A=λN

32
Q

radioactive decay is…

A

an exponential decrease

N=Noe^-λt
A=Aoe^-λt

N - number of undecayed nuclei
A - activity

also…
C=Coe^-λt (count rate)
P=Poe^-λt (power)

33
Q

decay constant and half life

A

at t=t1/2, N=No/2
λt1/2 = ln2
therefore decay constant and half life are inversely proportional to each other

34
Q

calculating N when number of half lives is known

A

N=(0.5)^n x No
N is number of nuclei left
n is number of half lives elapsed
No is nuclei at t=0
n is equal to t/t1/2

35
Q

carbon dating

A

(method for determining age of of organic material)

1) the ratio of carbon-12 to carbon-14 is constant in all living things
2) once a living organism dies, it stops absorbing carbon and the carbon-14 continues to decay
3) the ratio of carbon-12 to carbon-14 is measured in a dead and a living sample
4) the activity equation is used to estimate the age of the sample

36
Q

limitations to carbon dating

A

assumes the ratio of carbon-12 to carbon-14 is constant over time - may not be true due to increased emission of CO2 due to burning fossil fuels, volcanic eruptions)
carbon-14 cant date very old objects as its half life is not long enough (e.g. rocks)

A LEVEL PHYSICS (21 decks)

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