Transcript Chapter 9: Nuclear Radiation

Chapter 9: Nuclear Radiation
 Most isotopes with less than 20 protons are stable.
 proton to proton repulsions are minimalized by the
neutrons.
 Isotopes of elements with 20 to 83 protons may be
unstable.
 most even, even nuclei are stable and most odd, odd are
unstable.
Nuclear Radiation
 All isotopes with more than 83 protons are unstable.
 the nucleus is just too large.
 When an unstable nuclei decays, it releases
_____________ in the form of small particles and / or
energy.
Isotopic Symbols
 In chapter three, we wrote isotopic symbols.
Mass # = p + n
Atomic # = p
131
53
I
Learning Check
 How many protons, neutrons, and electrons does each
have?
131
55
C s and
212
85
At
 Identify an isotope with 31 protons and 41 neutrons.
Types of Particles
 There are several common particles that are produced
when a nuclei decays.
 Alpha (a) – consists of two protons and two neutrons
like a helium nuclei.
 Beta (b-) – is a high energy electron that comes from the
nucleus.
 Gamma (g) – is a high energy photon that comes from
the nucleus.
 Positron (b+) – is a positively charged electron from the
nucleus.
Types of Particles
Radiation Protection
 To protect yourself from radiation in the workplace
requires diligence.
 Proper shielding depends on the type of radiation.
 Alpha particles are the heaviest and are stopped by our
skin. These require minimal shielding.
 Beta and positrons can penetrate as far as 0.5cm of
tissue. These require thick clothing for shielding.
Radiation Protection
 Gamma particles can
pass through your
entire body. These
require several feet of
concrete and lead for
shielding.
Radiation Protection
 Radiation decreases dramatically with distance.
 Like sound waves, if you double your distance, then
the intensity decreases by ¼.
E =
1
d
2
Nuclear Equations
 A nuclear equation shows a nuclear decay or other
process.
 Mass and atomic numbers are always written.
 Sum of all mass numbers must be equal.
 Sum of all atomic numbers must be equal.
Nuclear Equations
238
92
U

Parent Nuclei
234
90
Th +
Daughter Nuclei
4
2
He
Radioactive particle
 Notice that the atomic numbers add to 92 and the
mass numbers add to 238.
Nuclear Equations
Writing a Decay
 Smoke detectors contain Am-241 which is an alpha
emitter. Write the balanced nuclear equation.
 Iodine-131, a beta emitter, is used to check thyroid
function. Write the balanced nuclear equation.
Writing a Decay
 Carbon-11, a positron emitter, is used to detect brain
damage. Write the balanced nuclear equation.
 Cobalt-60, a gamma emitter, is used to destroy
harmful pathogens in food. Write the balanced
nuclear equation.
Producing Radioactive Isotopes
 Many useful isotopes are produced from nuclear
bombardment.
 collision of one nuclei by another
 Also known as _______________
 All isotopes with atomic number greater than 92 are
man-made.
249
98
Cf +
15
7
N 
260
105
Db + 4 n
1
0
Medically Important Isotopes
 Many of these man-made isotopes are produced for
medical purposes in hospitals.
 One example is Tc-99, which is widely used to detect
tumors.
98
42
1
0
Mo +
99
42
Mo 
n 
99m
43
99
42
Mo
Tc +
0
-1
β
Learning Check
 Identify the missing particle in the transmutation
reaction below.
58
28
Ni +
1
1
H 
4
2
He + ?
Measurement and Detection
 A Geiger tube is often used to detect radiation.
 Consists of a metal tube filled with a gas like Argon.
 When radiation enters the tube, it ionizes the gas.
 The ions are attracted to a negative charged wire and
the electrons are then counted.
Measurement and Detection
Activity
 The Curie (named for Marie Curie) was the amount of
radiation for one gram of Radium.
 1 Ci = 3.7 x 1010 disintegrations / second.
 A “disintegration” could be an alpha, beta, gamma, etc.
produced.
3.7  10
10
disintigrations
1 C i  sec
Learning Check
 An I-131 source has an activity of 25mCi. How many
beta particles are produced in 1.0 minutes?
RAD, RBE, and REM
 RAD = radiation absorbed dosage
 1 RAD = 1.0 x 10-2 J / kg of body tissue
 RBE = a multiplier for each type of radiation.
 alpha = 20; protons, neutrons = 10; betas, positrons, and
gammas = 1.
 REM = radiation equivalent in humans
 REM = RAD x RBE
Background Radiation
 We are all exposed to radiation EVERY single day.
 Ground contains radioactive isotopes like U-238.
 Air contains Rn-222 and C-14.
 Food contains K-40 and C-14.
 Water contains Rn-222.
Background Radiation
 People who fly frequently or who live at high altitudes
receive higher levels of cosmic rays.
 Fact: people living in Denver receive twice as much
background radiation as we do.
 Fact: Cigarette smokers receive alpha radiation from
Po-210 – which comes from phosphate fertilizers.
Background Radiation
 FACT: CRT style TV’s emit radiation.
 Exposure to x-rays (essentially a beta particle) may
have a cumulative effect.
 The average person receives about 170mrem per year.
Radiation Levels
 LD50 = lethal dose for 50% of people receiving that
dosage.
 A whole body exposure of _____ rem
 A dosage of ___ rem reduces the white blood cell count
to zero.
 A dosage of 100 rem reduces these same cells
significantly.
 Patients often die from secondary infections.
Radiation Levels
 Exposure to 25 rem or less usually cannot be detected.
 Alexander Litvinenko, a former Russian spy, was
given Po-210 in a drink on November 1st, 2006 and
died a few weeks later.
 ...this may be the time to say one or two things to the person
responsible for my present condition. You may succeed in silencing me
but that silence comes at a price. You have shown yourself to be as
barbaric and ruthless as your most hostile critics have claimed. You
have shown yourself to have no respect for life, liberty or any civilized
value. You have shown yourself to be unworthy of your office, to be
unworthy of the trust of civilized men and women. You may succeed in
silencing one man but the howl of protest from around the world will
reverberate, Mr. Putin, in your ears for the rest of your life. May God
forgive you for what you have done, not only to me but to beloved
Russia and its people.
OSHA
 Any person working with or
around radiation wears a
device to detect radiation
exposure.
 The maximum dosage
permitted is ___ rem per year.
 Most workers receive much
less than 1 rem per year.
Biological Effects
 Alpha particles cannot penetrate our skin, yet
internally they can cause massive damage on soft
tissues like the lungs and intestinal linings.
 Beta particles can cause a burn on the outer portion of
the skin.
 Gamma particles penetrate completely and if exposed
to large quantities is deadly.
Biological Effects
 Radiation affects those cells in our body that undergo
rapid cell division like bone marrow, intestinal lining,
and the skin.
 Radiation tends not to affect cells that remain
unchanged like our brain, liver, muscles, etc.
How It Works…
 When radiation hits a molecule like water, it ionizes.
H 2 O + radiation

H 2O
+1
+ 1e
-
 This water molecule reacts with another water
molecule.
H 2O
+1
+ H 2 O  H 3O
+1
+  OH
How It Works…
 The “dot” on the OH is an odd electron.
 Molecules with an odd electron are called
_______________.
 ___________ are electron scavengers and interfere with
electron transfer reactions – many of which are vital in
the function of the body.
Medical Applications
 Medical uses of radioisotopes fall into two categories.
 Diagnostic
 Therapeutic
Diagnostic
 A standard x-ray cannot produce an image of an organ
like the heart, liver, pancreas, blood vessels, etc.
 To illuminate the targeted region, a radioisotope is
injected into the body.
 Radioisotopes used are low dosages with a short halflife.
 localized 0.1 to 50 rem doses are common
CAT & PET scans
 A computerized tomography scan is an enhanced x-ray
machine using multiple beams capable of producing a
3D image.
 A positron emission tomography scan uses a positron
emitter to generate a 3D image.
CAT & PET scans
MRI
 In magnetic resonance imaging, a powerful magnetic
field is used along with low energy radio frequency to
generate an image.
 Based on the premise that hydrogen atoms have “spin.”
 In a powerful magnetic field, these hydrogen atoms
can be made to flip between the two spin states.
MRI
Therapeutic
 In radiation therapy, radiation is used to target cancer
cells.
 Radiation levels are in very high dosages.
 localized 4000 – 6000rem doses are common
 Cyberknife treatment uses computer technology to
aim 100’s of x-ray beams precisely at a tumor.
Learning Check
 The dosage of Tc-99 for a lung scan is 20.mCi/kg of
body tissue. What dosage should a 121 pound patient
receive?
Half-Life
 A half-life is the amount of time that it takes for one-
half of a radioisotope sample to decay.
 Half-life's can be very short to very long.
 Tc-99 has a half-life of 6 hours
 K-40 has a half-life of 1.25 x 109 years
Half-Life
Learning Check
 The isotope Cr-51 has a half-life of 28 days. How much
of a 160.mg sample would remain after 112 days?
 A patient is injected with N-13, which has a half-life of
10 minutes. If the original activity of the sample is 40
mCi, what activity would be remain after 40 minutes?
 The amount of F-18 decreases from 40.mg to 10.mg in
220 minutes. What is the half-life of this radioisotope?
Fission
 Nuclear fission is the process by which a larger nuclei




is _____ into two smaller ones.
During this process, a small percentage of the mass is
converted to energy as predicted by Einstein.
E = mc2 ; where c = speed of light.
1 x 10-3 g “lost” can generate 9.0 x 1010 kJ of energy.
Only two fissionable isotopes are known.
 U-235 and Pu-239
Fission
 Begins when a neutron strikes a U-235 atom.
 The products are numerous – below is just one
example.
235
92
U +
1
0
n 
139
56
Ba +
94
36
Kr + 3 n + energy
1
0
 On average, three new neutrons are produced.
 Each new neutron can split another U-235.
Fission
 In a nuclear weapon, a
____________ of U235 is imploded
producing an
uncontrolled chain
reaction.
Fission
Fission
 In a nuclear power plant, the quantity of U-235 cannot
sustain a chain reaction.
 Control rods absorb excess neutrons.
 Waste products, with long half-life’s, from spent fuel
rods are stored in large pools at the power plant.
Fission
Fusion
 Fusion involves taking two or more smaller nuclei and
fusing them together.
 Once again, mass is converted to energy.
 This is the process by which all stars work.
1
1
H+ H+ H+ H
1
1
1
1
1
1
4
2
He + 2 β
0
+1
Fusion
 On our planet, fusion has been achieved.
2
1
H +
3
1
H 
4
2
He +
1
0
n
 The temperatures required are extremely high.
 Currently, more energy is required to achieve fusion
than we get back from the reaction.
 Research continues as this represents the “holy grail”
of energy.
Learning Check
 In one possible fission reaction for U-235, the U-235 is
bombarded with a neutron producing Kr-91, three
neutrons, and another nuclei. What is the
unidentified nuclei?