P4 – Radiation for life

beepedblacksmithUrban and Civil

Nov 29, 2013 (3 years and 9 months ago)

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P4


Radiation for life

NB This is not yet in its final form.
Some material may be in duplicate.


Insulating materials can
become charged when
rubbed with
another insulating
material.



What are the two
kinds of
charge?



When
some
materials are
rubbed they attract
other
objects:


small
pieces of paper or cork to a
rubbed comb
or
strip of
plastic;


certain
types of dusting brushes
become charged
and
attract dust as they pass
over it
.



How is it possible to get an electrostatic shock from
charged objects, such as synthetic clothing?



People can get electrostatic shock if they become charged
and then become earthed,


such as when they walk over thick carpet and touch a metal
door handle


touching water pipes after walking a floor covered with an
insulating material e.g. vinyl.



Static electricity can be described in terms of the electrons:


positive charge is due to?


negative charge is due to?.



Like charges _________________and unlike charges
________________.




Electrostatic phenomena are
caused by the transfer of
electrons.



Static electricity can be dangerous when:



in
atmospheres where explosions
could occur
e.g. inflammable
gases or
vapours

or with
high concentrations of
oxygen;


in
situations where large quantities
of charge
could flow
through the body to earth.



Static electricity
can be a
nuisance:



dirt
and dust attracted to insulators (
plastic containers
, TV
monitors etc
);


causing
clothing to “cling”.




The chance of receiving an electric shock can be
reduced by:



correct earthing;


use of insulating mats;


using shoes with insulating soles.



Why is it necessary to earth lorries containing
inflammable gases and liquids and powders
before unloading?



How can anti
-
static sprays, liquids and cloths help
reduce the problems of static electricity?



Static
electricity
can be useful:



restarting
a heart when it has
stopped (defibrillator);


photocopiers/laser printers;


removing
dust from smoke in
chimneys;


paint
spraying.

Electrostatic
dust
precipitator


Defibrillator


paddles charged;


good
electrical contact with patient’s
chest;


charge
passed through patient to
make heart contract;


care
taken not to shock operator.



Electrostatic
dust precipitators to remove
smoke particles
etc from
chimneys:


metal
plates/grids put into
chimneys;


connected
to a high
PD


dust
particles attracted to
plate/grid;


dust
attracts together to form
larger particles;


dust
falls back down chimney
when particles
are heavy enough.



Paint spraying:


spray
gun
charged;


paint
particles
charged;


repel
giving fine
spray;


object
charged oppositely to
paint;


attracts paint;


even
coat, less waste, shadows painted
.

Uses of Electrostatics

Paint Spraying


Spray Gun is
charged


all of the paint gets the same charge


Like charges
repel



paint particles spread out giving a fine spray


Object being painted is
given the opposite charge


paint is attracted to object and sticks to it.




Advantages

:
less wasted paint;
even coat of paint;
awkward places are painted
.

Electrostatic Dust Precipitators


Removes harmful smoke particles from a chimney.


1.
Metal grid/wires placed in chimney

2.
Grid connected to high voltage supply

3.
Dust particles attracted to metal grid

4.
Dust particles stick together

5.
Large particles fall down chimney

6.
Soot used to make building blocks


What is required
for
a circuit
to
work?



An
earthed conductor cannot
become live


why?



What is a resistors, and what can it
be
used for?



Plug wiring



live


____________;


neutral


_____________;


earth


____________________.



A circuit breaker is a fuse that can be reset


why is this more useful
than a normal fuse?



Objects and appliances that are
“double
insulated” do
not need
earthing


why?


What is a variable resistor?



What is the equation that links current
,
potential
difference
(pd) and
resistance?



For
a given resistor, current increases as
pd increases
and vice
versa; for
a fixed pd, current decreases as
resistance increases
and vice versa.



Functions
of the live,
neutral and
earth
wires


live


carries the high
voltage;


neutral


the second wire to complete
the circuit;


earth


a safety wire to stop the
appliance becoming
live
.



The unit of resistance is the Ohm, Ω. Resistance, current and
voltage (potential difference) are related by this equation:



resistance (Ω ) = voltage (V) / current (A)



Example:



Question What is the resistance of a bulb that has 0.4A of current
flowing through it when a potential difference of 2V is put across it?




voltage = current x resistance


current = voltage / resistance



Example


Question What potential difference causes a current of 3A to flow
through an 80Ω resistor?



How does a wire fuse work?



A w
ire fuse reduces the risk of fire if the
appliance develops a fault:



too large a current causes the fuse melt;


preventing flow of current;


prevents flex overheating and causing fire


prevents further damage to appliance.


Current Electricity


Electric Circuits


must be COMPLETE to allow electricity to flow
from + to


terminals on a cell/battery.



A Cell provides POTENTIAL DIFFERENCE
(Voltage) in VOLTS.
This provides the FORCE to move the charge
carriers
(in wires


electrons; in electrolysis


ions)



The resulting flow of charge is called CURRENT
measured in AMPS.


Current always flows from + to


(even though the electrons flow
from


to +!)

A Circuit to measure resistance

A

V

A variable resistor
varies the current
in the circuit

The component
which is having its
resistance
measured

A voltmeter
measures Potential
Difference in Volts

An ammeter
measures Current
in Amps

Resistance =


Potential difference
÷

Current

R = V
÷

I

Ohm’s Law


“For a metallic conductor at constant
temperature, the ration of Potential
difference (V) to Current (I) is constant”.


The constant is called Resistance, R
measured in ohms, symbol
Ω
.



So
R = V
÷

I
, also V = I x R and I = V
÷

R

R

I

V

x

÷

÷

Cover up
what you
want to find

Mains Electricity


Live
(brown)
brings supply to
house


Neutral
(blue)
is

return path
to power station


Earth
(green and
yellow)


carries current to 0V
if the
casing becomes live.
This
blows the FUSE which cuts
off the supply.


Fuse is in series with the
Live

wire.

Fuses come in various
values; 2A,3A,5A,13A.

A 13Amp fuse blows when
current through it exceeds
13Amps

A circuit
-
breaker is a re
-
settable fuse which can be
re
-
set at the flick of a switch

These have replaced fuse wire in the main fuse box.


Ultrasound
is a
longitudinal wave, what is the other
type of wave called?



Define the following words:


amplitude;


wavelength;


frequency;


compression;


rarefaction
.



Ultrasound
can
be used
in
medicine:


to
look inside people by scanning the
body;


to
break down kidney and other
stones;


to
measure the speed of blood flow in
the body
.


The
frequency
of ultrasound
is higher than the
upper threshold of


human hearing
.



What is the motion
of particles in longitudinal
and transverse waves?



In body scans ultrasound works by comparing the
reflections
from
different layers



Ultrasound is used instead of x
-
rays


able
to produce images of soft
tissue;


does
not damage living cells.

Ultrasound
-

sound waves beyond the human hearing range


Range of human hearing is
20


20,000Hz

so
beyond that is Ultrasound

Sound waves are LONGITUDINAL


the vibrations of
the particles are in the same direction as the wave

Compression


particles in wave squashed
together


Rarefaction


particles in wave spread out.


Wavelength


distance occupied by one
complete wave (unit


metres)


Frequency


number of complete waves per
second (unit


hertz)


Amplitude


maximum distance a particle
moves from its normal position.

Uses of Ultrasound


Check the condition of a foetus


Investigate heart and liver problems


Look for tumours
in the body


Break down kidney stones
and stones elsewhere in
the body


Measure the speed of blood flow
in vessels when a
blockage of a vein or artery is suspected


Cataract surgery

Non


medical uses :
dentists

shake plaque and dirt off teeth;


jewellers

clean delicate pieces of jewellery and watches


Nuclear
radiation is used in medicine
. See
http://
www.youtube.com/watch?gl=GB&v=7_24jzgLCpw



X
-
rays
and gamma rays
are electromagnetic
waves
.



Nuclear
radiation can damage cells.



Gamma
rays are used to
treat cancer
.



Nuclear
radiation is used to
sterilize hospital
equipment
.



The person in
hospitals who takes
x
-
rays and
uses radiation
is
a?


O
nly
beta and gamma radiation
can pass
through
skin.


gamma
rays are given out from the nucleus
of certain
radioactive
materials;


X
-
rays
are made by firing high
speed electrons
at metal
targets;


X
-
rays
are easier to control than gamma rays.



Beta
or gamma emitters are used
as tracers
in the body.



Radioactive
sources are used
in medicine to treat cancer:


gamma
rays focused on
tumour
;


wide
beam
used;


rotated
round the patient with
tumour

at centre;


limiting
damage to non
-
cancerous tissue.



Radioactive sources are used as tracers:


beta or gamma emitter;


drunk/eaten/ingested/injected into the body;


allowed to spread through the body;


followed on the outside by a radiation detector.



X
-
rays and gamma rays have similar wavelengths,
but are produced in different ways



Radioactivity of an object is measured by the
number of nuclear decays emitted per second.



Radioactivity decreases with time.




Radiation
comes from
the?



Radioactive substances decay naturally and giving out
nuclear radiation in the form of alpha, beta and
gamma.



Radioactivity as comes from the nucleus of an atom
that is unstable.



An alpha particle is a helium nucleus, whilst a beta
particle is a fast moving electron.



What is half
-
life?





When an alpha particle is emitted the following happens to a nucleus


mass
number decreases by
4;


nucleus
has two less
neutrons;


nucleus
has two less
protons;


atomic
number decreases by
2;


new
element formed.



When a beta particle is emitted the following happens to the nucleus


nucleus
has one less
neutron;


nucleus
has one more
proton;


atomic
number increases by one.



Simple
equations
can be constructed in
terms
of mass
numbers and
atomic numbers to represent


alpha
and beta decay.


There
is
background radiation
in the environment which is
always present.



Where does this background radiation come from?



Alpha
sources are used in
some smoke
detectors
.


Uses
of tracers:


to
track dispersal of
waste;


to
find leaks/blockages in
underground pipes;


to
find the route of underground pipes.




To find leaks in underground pipes


radioactive
material put into
pipe;


gamma
source used so that it can
penetrate to
the
surface;


progress
tracked with detector
above ground;


leak/blockage
shown by
reduces/no radioactivity
after
this point
.




How does a smoke detector with an alpha source work?



Radioactivity can be used to date rocks (using uranium)



And old material (that contains carbon)



The measurements of the activity of radioactive carbon can lead to
an approximate age for different materials:



the amount of Carbon 14 in the air has not changed for thousands of
years;


when an object dies (e.g. wood) gaseous exchange with the air stops;


as the Carbon 14 in the wood decays the activity of the sample
decreases;


the ratio of current activity from living matter to the activity of the
sample leads to a reasonably accurate date.



What is the fuel in a nuclear
power
station?



What are the main
stages in the production
of
electricity:


source
of
__________;


used
to produce
___________;


used
to produce electricity.



The
decay of uranium can be a
chain reaction.



A

nuclear bomb is a chain
reaction that
has gone out of
control
.



How can materials
be made
radioactive?


Domestic
electricity
generated
at
a nuclear
power
station:


nuclear reaction;


producing heat;


producing steam;


turning
a
turbine;


turning
a generator.



To allow uranium
to
release energy:


uranium
nucleus hit by
neutron;


causes
nucleus to
split;


energy
released.



What is nuclear fission?



Nuclear fission produces radioactive waste, materials
become radioactive when they absorb extra neutrons.



Chain reaction:


when each uranium nucleus splits more than one neutron
is given out;


these neutrons can cause further uranium nuclei to split.



Scientists stop nuclear reactions going out of control:


rods placed in the reactor;


to absorb some of the neutrons;


allowing enough neutrons to remain to keep the process
operating.


Radiotherapy and Diagnosis


Gamma rays
γ


High frequency/energy
electromagnetic waves

emitted from the nucleus of a
radioactive isotope


Very penetrating


can pass
into the body to treat internal
organs


Can damage living cells


over
exposure should be avoided




X rays


High frequency/energy
electromagnetic waves
emitted when high speed
electrons are decelerated


Very penetrating


Can damage living cells


An X
-
ray machine can
produce and control X
-
rays of
different energies


so some
X
-
rays can have higher energy
than
γ

rays

Alpha, Beta and Gamma emissions

Radiation

Alpha

Beta

Gamma

Ionising Power

Very strong

Medium

Weak

Range in air

About 5cm

About 1m

Very large, its
intensity
decreases with
distance

What stops it?

paper

A few

mm of
Aluminium

Reduced by lead
and concrete

Ionisation



the ability to remove an electron from an atom, causing
the atom to become charged.

Alpha has 2 + charges
so has a great ionising effect,
beta has 1


charge
so a lesser ionising effect.

Alpha and Beta particles are not good inside the body


they cannot escape from inside


so
don’t swallow any


remember Mr Litvinienko?


killed with Polonium 210, an alpha emitter!

Using Gamma radiation


Treating cancer


large doses can kill and
destroy cancer cells. A ‘gamma knife’ is rotated around a
cancer to give the cancer a high dose but the healthy
tissue a low dose. Side effects of this kind of therapy can
be unpleasant but slows down the growth of the cancer.


Sterilising hospital equipment


Gamma kills bacteria and prevents the spread of disease.

Tracers


some radioactive isotopes

(in very low doses!) can be injected into the
body to highlight places where a cancer may be
growing.


Common isotopes are

Technetium


99
and
Iodine
-

123

Radiographers


carry
out procedures using
X
-
rays and nuclear
radiation.

Lead prevents tissue
absorbing radiation.

Radioactivity
-

discovered by Becquerel and researched by
Pierre & Marie Curie (among others)


Some atoms naturally break up because the nuclear forces
holding them together are not strong enough.


Radioactive substances decay naturally and give out
Alpha
(
α
), Beta (
β
)
and
Gamma (
γ
)

radiation.


Radioactivity is a random process that cannot be controlled by
external conditions such as temperature, pressure etc. Neither
can the decay be predicted.


Radioactivity is detected usually with a Geiger
-
Müller (GM)
tube and a ratemeter.


Activity is measured by counting the average number of nuclei
that decay every second, unit


Becquerels (Bq).

Half Life


The time taken for the
activity of a sample to
fall to one half of its
original activity,

OR


The time for half of the
atoms in a radioactive
isotope to have
decayed.


It is different for every
radioisotope


A Typical Decay curve

Alpha Decay




An alpha particle (or helium nucleus) contains 4 nucleons (2p + 2n)



When
α

is emitted,
A decreases by 4, Z decreases by 2


The new element formed is
two places lower
in the Periodic table
than the original radioisotope.



92
U
2
α

+
90
Th

Remember :
A is the mass number = protons + neutrons


Z is the proton number = number of protons OR electrons

238

4

234

Beta Decay

-
1
β



A beta particle is a high energy electron


emitted from the nucleus (!)


[This is because a neutron decays to a proton, an electron and a bit of antimatter]


When
β
-

is emitted
, A
does not change








Z
increases

by 1







(
because it has an extra proton).



6
C
-
1
β

+
7
N


A new element is formed that is one place higher in the periodic table than the
original radioisotope.



14

0

14

0

Background Radiation


This is ionising radiation that is
always present in
the environment.



The level of background radiation is
low and does
not cause harm.


E.g. Granite contains small amounts of Uranium which decays to Radon, a
radioactive gas.


Sources (7):
radioactivity in the air
;
radiation
from Space (cosmic rays);
rocks
;
food
;
medical
uses
;
nuclear power
;
nuclear weapons testing
(these last two make up just 1%).

Uses of Radioactivity


Alpha is used in Smoke detectors
Americium
-
241


Beta is used to monitor the thickness of paper


Strontium
-
90


Gamma is used to treat cancer; to search for leaks from pipes; to
check welds in castings.

Dating:


Uranium/Lead levels
are used to date rocks


VERY OLD!


Potassium/Argon levels
date rocks up to about 100,000 years old


Carbon 14/Carbon12 levels

are used to check organic material up to 60,000 years old


Nuclear Fission


U
235

can become unstable
when bombarded with
neutrons.


It accepts a neutron, becomes
U
236
, which decays readily to
Kr
92
, Ba
141

and extra neutrons.
(These may go on to strike the nuclei of other
atoms causing further fission reactions



a CHAIN REACTION).


It also releases
massive amounts of
energy!!!

A Nuclear Power Station

The output of a Nuclear Reactor is controlled by:

A graphite moderator
between the fuel rods
slows down fast
-
moving neutrons

Boron control rods absorb neutrons and so control the rate of fission.

Control Rods in a
reactor core