Problems:

Tell whether the new element has a higher or lower atomic number than the starting element for the following cases.

a) alpha decay

b) electron capture

c) electron emission 

d) positron emission 

e) nuclear fission  

USES OF RADIOISOTOPES

A) Tracers - study where the compound or element goes. The original amount is in too small a concentration to measure. By using a radioactive element in the compound, the compound can be 'seen' by the radioactivity coming off, by using a counter or a radiograph.

B) Irradiation of foods It kills microorganisms responsible for spoilage.

C) Radiation therapy Used in the treatment of cancer. Radiation can kill cells. The rapidly dividing cells, like cancer cells, are more susceptible to being killed. Getting the dosage correct is important, since normal cells will also be killed in the process.

D) Diagnostic uses

1. Iodine-131 in KI. Used for hyperthyroid and thyroid cancer. The thyroid produces a hormone, thyroxin, which has iodine as part of the molecule. The radioactive iodine will concentrate in the thyroid. The radiation given off will kill the rapidly dividing cells. The half-life of Iodine-131 is 8.1 days. Beta and gamma rays are given off.

2. Gadolinium-153 Used to measure bone demineralization. It gives off gamma and x-rays. Scanning the bone and measurement of the bone densities are determined.

3. Technetium-99^m The 'm' means metastable. It will give off radiation and go to being a more stable element.

99m                                   99
       Tc    ------------->         Tc   +   g
43                                      43

It has a half life of 6 hours. Technetium-99 is formed from Molybdenum-99.

4. Positron Emission Tomography - PET scans
Use positron emitting isotopes. The positron reacts with an electron and two gamma rays are formed. The gamma rays are given off in opposite directions. The gamma rays are measured. The instrument looks like a big donut. The patient's head or body is passed into this hole and the radiation recorded. The computer part of the instrument can 'see' where the positron and electron collided.

11                    11                   0
C ----------->     B         +       e (aka b )
6                      5                    +1

  0             0
     e    +      e -------> 2 g
+1            -1

E) Carbon dating
Carbon-14 is formed by the bombardment of Nitrogen-14 with neutrons

14            1                       14           1
    N    +    n     --------->     C    +    H
7             0                          6           1

Carbon-14 has a half life of 5730 years. If an old dead plant had one half the C-14 which is found in the earth's CO₂, that means the plant was alive one half-life ago or 5730 years.

The shroud of Turin was found to be from the time period of 1260 to 1390 A.D. So it is not the shroud used to wrap Christ.

RADIATION AND MEDICINE

Detection of Radiation

Film Badges - Photographic film darkens as exposed to radiation. Use different layers for different penetrating ability to determine if alpha, beta, or gamma.

Geiger Counter - Uses electrons. Ions are created and measured. Hear >clicks=.

Scintillation Counter - Uses flashes of light. Gives disintigrations per minute (dpm).

Units of Radioactivity

Curie (Ci) Named after Madame Curie is disintigrations per second (dps)

         1 Ci = 3.7 x 10¹⁰ dps
Usually use millicurie or microcurie

Becquerel (Bq) Named after Henry Becquerel

1 Bq = 1 dps

Rad is the measure of energy absorbed in matter as a result to any form of radiation

(Rad)     x    (Relative Biological Effect)  =  Roentgen Equivalent Man
                                RBE                                       Rem

Normal environmental exposure is 350 millirem/year
Gives the average exposure to radiation from common sources.

Lethal dose 500 rem kills 50% of people in 30 days

Radiation Intensity

The Intensity of Radiation decreases with the square of the distance.

Example: A radioactive compound has an intensity of 28 mCi at a 1.0 m distance. What would the intensity be at 2.0 m distance?

   I₁             (d₂)²
-----    =    ------
   I₂             (d₁)²

  28      =     (2)²
   x              (1)²

x = 7.0 mCi

1. Iodine-131 in KI. Used for hyperthyroid and thyroid cancer. The thyroid produces a hormone, thyroxin, which has iodine as part of the molecule. The radioactive iodine will concentrate in the thyroid. The radiation given off will kill the rapidly dividing cells. The half-life of Iodine-131 is 8.1 days. Beta and gamma rays are given off.

2. Gadolinium-153 Used to measure bone demineralization. It gives off gamma and x-rays. Scanning the bone and measurment of the bone densities are determined.

3. Technetium-99^m The 'm' means meta stable. It will give off radiation and go to being a more stable element.

99m                           99
     Tc ------------->     Tc + g
  43                           43

It has a half life of 6 hours. Technetium-99 is formed from Molybdenum-99.

4. Positron Emission Tomography - PET scans Use positron emitting isotopes. The positron reacts with an electron and two gamma rays are formed. The gamma rays are given off in opposite directions.

The gamma rays are measured. The instrument looks like a big donut. The patient's head or body is passed into this hole and the radiation recorded. The computer part of the instrument can 'see' where the positron and electron collided.

11                 11 0
    C   ------>    B + e (e = b )
6                  5 +!

  0           0
    e     +    e -------> 2 g
+1         -1

5. Computer Aided Tomography CAT scans
Short bursts of x-rays A circular array of detectors around body give readings which are translated in a computer readout.

6. Magnetic Resonance Imaging MRI
The body is placed in a field of strong electromagnetic field and simultaneously exposed to A radio frequency field. Protons behave as tiny magnets and align themselves in the field. A computer reads the differences in the different parts of the body.

7. Autoradiography
A small amount of radioactivity in a given compound can be used to visualize (photographic plate) or measure a compound in concentrations which would be undetected by chemical methods.

8. Tagged Antibodies
A radioactive form of an element is incorporated into a compound. This labeled compound is then added to an antibody. The antibody seeks out the antigen (protein of a cancer cell) and attaches itself to the antigen. The radioactivity is now given off in a small area and kills the cancer cells.

E) Carbon dating

Carbon-14 is formed by the bombardment of Nitrogen-14 with neutrons.

14                 1                        14           1
   N        +       n        ----->        C    +     H
7                   0                          6           1

Carbon-14 has a half life of 5730 years. If an old dead plant had one half the C-14 which is found in the earth's CO₂, that means the plant was alive one half-life ago or 5730 years.