Physics of the atom. radiaoctive decay.

1. Detection of Radioactivity
Characteristics of the Three Types of Emission Nuclear
Reactions
Half-Life
Uses of Radioactive Isotopes Including Safety
Precautions

2. Describe the detection of alpha-particles, beta-particles and gamma-rays
by appropriate methods.

3.  Radioactivity is the process whereby
unstable atomic nuclei release energetic
subatomic particles.
 Radioactivity was first discovered in 1896 by
the French scientist Henri Becquerel, after
which the SI unit for radiation, the
Becquerel, is named.
Radioactivity 3

5.  Radiation can not be detected with our five
senses, special detectors are therefore
needed.
 Several devices have been developed to
detect radioactivity, with the earliest being an
unexposed photographic plate placed in the
vicinity of a source being detected.
 Other devices include:
 the cloud chamber,
 electroscopes,
 the Geiger-Müller tube
Radioactivity 5

6.  It was named for Hans Geiger who invented the device in 1908 and Walther
Müller who collaborated with Geiger in developing further in 1928
Radioactivity 6

7. Radioactivity 7

8. Cloud chamber

12. • When radiation passes through a gas,
some of the gas molecules may lose
electrons and this causes ions to be
formed. The gas is considered ionized.
• In descending order of ionizing power:
α, β and γ
Ionizing Power

13.  The products of radioactivity could be
analyzed into three distinct species by
either a magnetic field or an electric field.
15

15. Radioactive decay

18. Half-life
The half-life of a radioactive substance is
the time taken for half of the nuclei in a
sample to undego radioactive decay.

23. Half-life calculations

26. A radioactive element has a half-life of 40
minutes. The initial count rate was 1000 per
minute. How long will it take for the count rate
to drop to 250 per minute?
Half-life = 40 min
1000----500----250 (3 half-lives)
3 x 40 min = 120 min

27. Nuclear Fission

30. Nuclear Fusion

32.  We cannot do much to reduce our exposure
to natural background radiation, but great
care is needed when handling radioactive
materials. Precautions include:
Radioactivity 72

33.  wearing protective clothing
Radioactivity 73

34.  keeping as far away as is practicable -
for example, by using tongs or robotic
arms.
Radioactivity 74

35.  keeping radioactive materials in lead-
lined containers, labelled with the
appropriate hazard symbol.
Radioactivity 75

36.  keeping your exposure time as short
as possible
Radioactivity 76

37. Discuss the way in which the type of radiation emitted and the half-life
determine the use for the material.

38.  A radioactive isotope is introduced into a living
system, where it flows along the bloodstream,
following the path of chemical processes
therein.
 It is easily detected using a scanner or Geiger
counter. The scanner take pictures and are run
together in rapid succession, giving physicians
a movie-like view of the isotope's path.
 When the procedure is finished the isotope is
flushed out of the body along with other
waste products.
Radioactivity 78

40.  A common procedure is the injection of
iodine- 131 for the observation of the thyroid
gland.
 A healthy thyroid will accumulate any iodine
entering the body.
 When a physician scans the patient, if iodine-
131 is present in the thyroid, the gland is
working properly.
 However, if the trace element has not collected
in the thyroid, the physician knows the gland is
failing.
Radioactivity 80

41. Radioactivity 81

42.  A method for determining the position of a
leak in a conduit or pipeline.
 Short-lived radioisotope is inserted into the
conduit or pipeline and is caused to move
along it by pressuring up the conduit or
pipeline from one or both ends thereof with
fluid, for example water.
 The carrier body travels to the leak but no
further and its location is detected from
outside the conduit or pipeline using a
radiation detector.
Radioactivity 82

43. Radioactivity 83

44.  A source of beta radiation is used to pass beta
particles through the paper.
 A detector on the other side of the paper detects
the beta particles that pass through.
 The detector is connected to a hydraulic control via
a
processor unit.
 If the radiation level detected drops it means the
paper is too thick so the hydraulic control pushes
rollers closer together in order to reduce the paper
thickness.
 If the radiation level detected increases it means
the paper is too thin so the hydraulic control pulls
the rollers apart so the paper thickness can be
increased. Radioactivity 84

45. Radioactivity 85

46.  Radiocarbon dating uses the amount of Carbon 14
(C14) available in living creatures as a measuring
stick.
 All living things maintain a content of carbon 14 in
equilibrium with that available in the atmosphere,
right up to the moment of death. When an organism
dies, the amount of C14 available within it begins to
decay at a half life rate of 5700 years
 Comparing the amount of C14 in a dead organism to
available levels in the atmosphere, produces an
estimate of when that organism died.
88
https://www.youtube.com/watch?v=L8Eyyh2Vpfs&t=609s

47. Carbon-14 has a half-life of 5700 years.
1. Cro-Magnon man is one of our ancestors. Five adult
skeletons were found near Les Eyzies in France. A 1 g
sample of charcoal from this site produced a
radioactive count of 0.5 counts per minute. A modern
sample of charcoal of same mass produces a count rate
of 32 counts per minute. Both counts were corrected
for background radiation. How long ago did Cro-
Magnon man live?
2. A 10-g sample of wood cut recently from a living tree
has an activity of 160 counts/minute. A piece of
charcoal taken from a prehistoric campsites also weighs
10 g but has an activity of 40 counts/minute. Estimate
the age of the charcoal.
Radioactivity 89

48. 3. A wooden post from an archaeological dig
produces 150 counts per minute. Wood from an
identical species of tree currently alive gives 600
counts per minute. How long ago did the wood
from the archaeological dig die?
4. In a carbon-dating experiment a sample of wood
from an object was burnt and the carbon dioxide
produced was collected. The activity of the carbon
dioxide was equivalent to 2.25 count per minute
per gram of carbon. When the same experiment
was repeated using wood from a modern source,
the corrected counts was 18 count per minute per
gram of carbon. What is the likely age of the find?