radioactive decay Flashcards
1
Q
half life and rate of decay
A
- Radioactivity is a random event; we do not know which atom will decay at what time
- We can use probability and statistics to tell us how many of the atoms will decay ina certain period of time
- The equation used to determine how much will decay in that time period is:
look at ppt
2
Q
Decay constant
A
- The decay constant is different for different isotopes the greater the decay constant the radioactive the isotope
3
Q
Radioactive decay law
A
- The previous equation can be arranged to find the number of atoms left after specified amount of time to decay
- look at ppt
- The number of decays per second is called the activity of the sample
- To signify how fast an isotope decays, the term ‘half-life’ is used. The half-life of an isotope is the time it takes half of the original sample to decay.
4
Q
Half life
A
- Varies from 10^22 seconds to 10^28 seconds (about 10^28 years)
- Most tables and charts show half life as T1/2
- The half lie and decay constant have an inverse relationship to one another; the longer the half life the lower the decay constant (the more slowly it decays)
- The precise relationship is:
look at ppt
5
Q
Sample problem
A
- The decay constant of a given nucleus is 5.4 x10-3 sec
- What is its half life
- How much remains of an intial 100- g sample after 6 hours
look at ppt
6
Q
Technetium Tc 99m
A
- create images of the brain following a stroke, bone scans and also helps to locate stomach and bowel infections e.g sepsis.
- Stroke - assess how much blood is being absorbed into the blood vessels in the brain to determine if parts of the brain are working less efficiently than is normally expected.
- Tc-99m is attached to the chelating agent HMPAO to create technetium (99mTc) exametazime
look at ppt
7
Q
Nuclear fission
A
- Process in which the nucleus of a large, radioactive atom splits into 2 or more small nuclei- caused by collision with a energetic neutron
- A heavy nucleus (mass number >200) divides to form smaller nuclei of intermediate mass and one or more neutrons
- Release a large amount of energy
- Urnanium-235
8
Q
What is fission-
A
- A large nucleus splitting into smaller ones
- The class one is:
look at ppt
9
Q
Fission chain reaction
A
look at ppt
10
Q
What is fusion
A
- Combination to light nuclei into a heavy one a good example is:
- look at ppt
- It is not quite that simple because the nucleus is very small and protons repel a tremendous amount of energy is needed to get this reaction to go (about 40,000,000 K)
11
Q
Nuclear fusion
A
- Process in which 2 nuclei of the small elements are united to form one heavier nucleus
- Requires temperatures on the order of tens of millions of degrees for initation
- The mass difference between the small atoms and the heavier product atom is liberated in the form of energy
- Responsible for tremendous energy output of stars like our sun
12
Q
Artificial transmutation
A
- Rutherford 1919
- Transmutation of lead into gold was achieved by glenn seaborg, who suceedeed in transmuting a small quantity of lead in 1980. He also first isolated plutonium for the atomic bomb and discovered ‘created’ many elements
- There is an earlier report (1972) in which soviet physicists at a nuclear research facility in Siberia accidentally discovered a reaction for turning lead into gold when they found the lead shielding of an experimental reactor had changed to gold
13
Q
What is ionizing radiation?
A
- Ionizing radiation is radiation that has enough energy to remove electrons from atoms or molecules
- The loss of an electron with its negative charge causes the atom (or molecule) to become positively charged (cation).
- Ionisation can also result in gain of an electron by an atom or molecule to form an anion
- Note: Microwave, infrared (IR) and ultra-violet (UV) radiation are examples of non-ionizing radiation. Non-ionizing radiation does not have enough energy to remove electrons.
14
Q
What properties are considered when ionizing radiation is measured?
A
- Ionizing radiation is measured in terms of:
- the strength or radioactivity of the radiation source,
- the energy of the radiation,
- the level of radiation in the environment, and
- the radiation dose or the amount of radiation energy absorbed by the human body.
Occupational exposure limits like the Threshold Limit Values (TLV) are given in terms of the permitted maximum dose. The risk of radiation-induced diseases depends on the total radiation dose that a person receives over time.
15
Q
What units are used for measuring radioactivity
A
- Radioactivity or the strength of radioactive source is Measured in units of becquerel (Bq).
- 1 Bq = 1 disintegration per second.
- One becquerel is an extremely small amount of radioactivity.
- Commonly used multiples of the Bq unit are kBq (kilobecquerel), MBq (megabecquerel), and GBq (gigabecquerel) (109).
- An old and still popular unit of measuring radioactivity is the curie (Ci).
- 1 Ci = 37 GBq = 37000 MBq.
- One curie is a large amount of radioactivity.
- Commonly used subunits are mCi (millicurie), µCi (microcurie), nCi (nanocurie), and pCi (picocurie).
- Another useful conversion formula is: 1 Bq = 27 pCi.
- Becquerel (Bq) or Curie (Ci) is a measure of the rate (not energy) of radiation emission from a source.
