25 - Radioactivity Flashcards by Niwre Abriam

ALPHA RADIATION - nature and charge

particle (helium nucleus), +2e

How well did you know this?

Not at all

Perfectly

ALPHA RADIATION - ionising and penetrating effect

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

How well did you know this?

Not at all

Perfectly

BETA RADIATION - nature and charge

particle (fast electron), -e

How well did you know this?

Not at all

Perfectly

BETA RADIATION - ionising and penetrating effect

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

How well did you know this?

Not at all

Perfectly

GAMMA RADIATION - nature and charge

EM wave, 0

How well did you know this?

Not at all

Perfectly

GAMMA RADIATION - ionising and penetrating effect

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

How well did you know this?

Not at all

Perfectly

range of each type of radiation in air

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

How well did you know this?

Not at all

Perfectly

radioactive decay is the…

emission of a radioactive particle from an unstable nucleus

How well did you know this?

Not at all

Perfectly

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

alpha particle is heavier than beta+ particle so affected less

How well did you know this?

Not at all

Perfectly

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

Fleming’s left hand rule

How well did you know this?

Not at all

Perfectly

dangers of radioactivity and precautions

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

How well did you know this?

Not at all

Perfectly

procedure to investigate the absorption of different radioactive materials

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

How well did you know this?

Not at all

Perfectly

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

positrons and electrons would annihilate each other

How well did you know this?

Not at all

Perfectly

glow in the dark hands on clock explained

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

How well did you know this?

Not at all

Perfectly

what is transmutation?

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

How well did you know this?

Not at all

Perfectly

what is conserved in all nuclear reactions?

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

nuclear transformation equation for alpha decay

A A-4 4
X —> Y + He
Z Z-2 2

nuclear transformation equation for beta minus decay

A A 0 -
X —> Y + e + Ve
Z Z+1 -1

nuclear transformation equation for beta plus decay

A A 0
X —> Y + e + Ve
Z Z-1 +1

why does gamma decay occur?

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

nuclear transformation equation for gamma decay

A A
X —> X + 𝜸
Z Z

why might a decay series/chain occur

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

patterns for stability graph

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

why may count rate be lower than expected?

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

RANDOM nature of decay

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

SPONTANEOUS nature of decay

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

simulation of radioactive decay using dice

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)

define half life of an isotope

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

define activity A of a source

rate at which nuclei decay or disintegrates (number of alpha, beta, gamma photons emitted per unit time)

units of activity

Bq (decays per second)

power equals

A X E activity x energy

decay constant

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

radioactive decay is...

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)

decay constant and half life

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

calculating N when number of half lives is known

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

carbon dating

(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

limitations to carbon dating

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)