1-22-08

Chemistry 115

Lecture 5 Outline

Chapter 24Nuclear TransmutationRadiation, DosagesNuclear Medicine

HW3: Due Friday, Jan 25 (Quiz 2)

Recitation: Ch 24: Radioactive Decay. Nuclear Stability

Radiation Dosage, Nuclear Medicine Binding Energy, Nuclear Power

Nuclear Transmutation

Nuclear transmutation – transform 1 element into another - like Alchemy Example: 14

7N + 42He 1

1H + 178O Rutherford, 1919

This led to the discovery of the neutron – like a gamma ray (neutral charge), but heavy like a proton.

This approach is used to make the transuranium elements And studied in accelerators

Linear Accelerator

Fig. 24.7Ion Cyclotron

Inside a large accelerator

Nuclear Transmutations

Radiation

Radiation when it interacts with matter can cause two effects:

Non-ionizing radation – causes atoms to vibrate matter gains heat

Ionizing radiation – causes loss of electron(s):

Atom ion+ + e- This type of radiation can be dangerous because it

causes reactive radical species.

Radiation Penetrating Power

Units of Radioactivity

Activity or disintegrations (transformations) per unit of time is expressed in units of curies (Ci) or in the SI unit of becquerels (Bq)

One becquerel = 1 disintegration per second (s-1).

One curie = 3.7 x 1010 disintegrations per second = 3.7 x 1010 becquerels

Units of Dose

Not all types of radiation are absorbed to the same extent. Different types of radiation deposit different amounts of energy when absorbed by the body.

A Gray is the SI unit of absorbed dose.gy = 1 joule / kg of body tissue = 100 rads

Radiation Equivalents

Particle Relative energy deposited Relative Biological Effectiveness

1

e- 1

11p 5

10n 1 - 100

42He 20

rem = RBE x rads

Radiation Damage

1 gy = 1 J/kg

4 gy/ 1 g H2O raises the temperature by 4oC

Radiation damage is not due to heating, it results from breaking chemical bonds in a body producing free radicals.

Free radical, unpaired e-

Radiation Damage

The body can handle and repair a certain amount of free radical damage whether it is caused by radiation, drinking alcohol, heavy labor, heavy exercise, eating slightly rancid food, or from wounds. Radiation sickness is a free radical disease just as a hang-over is.

Radiation Damage

The body can handle a certain amount of free radicals before the free radicals overwhelm the body's free radical scavenging system. When overwhelmed, part of the free radical damage consists of damage to the body's free radical scavenging system creating a vicious cycle.

Radiation kills by breaking cells DNA. As a consequence, cells can no longer reproduce. LD50 is approximately 2.5 - 4 Gy (250 – 400 rem) depending on length of exposure and treatment.

Nuclear Medicine

Nuclear medicine: •uses radioactive substances (radiopharmaceuticals)•radioactive substances are administered and the radiation emitted is measured•usually involves the formation of an image•radionuclides are also administered to treat disease or provide pain relief.

•iodine-131 is often used for the treatment of thyrotoxicosis and thyroid cancer.

99Mo 99mTc + e- 99Mo: t1/2 = 66 h99mTc 99Tc + 99mTc: t1/2 = 6 h

γ-rays behave like x-rays, they pass through tissue.

Cardiolite distributes in the heart proportionally to the blood flow in the heart’s muscle

Thyroid Images

131I 99Tc

Nuclear ReactionsPositron Emission, +-decay

Positron Emission: decay by loss of an a positron, a particle with the same mass as an electron but with a positive charge (a positive electron).

116C 11

5B + 01e

The positron interacts with an electron, and the two annihilate each other.  All of their mass is converted into energy––two 0.511 MeV gamma rays are produced.

0–1e    +   0

+1e    2 (0.511 MeV each)

PET

Positron Emission Tomography + + - 2 (0.511 MeV each, in opposite directions)

Nuclear Chemistry: PET Imaging

PET

18O + 1p 18F + 1n 18F 18O + e+

Brain with blunt force trauma

DNA mapping

3215P: Image DNA fragments

Photographic image formed from decay of 32P