history and introduction

History and Introduction

(Lfrances@hunter.cuny.edu)

Why Radiochemistry

IGERT program at Hunter College

Why Radiochemistry and Why Should I Care About Radiation?

• Medical applications Molecular Imaging of disease

Single Photon Emission Computed Tomography (SPECT)Positron Emission Tomography (PET)

Radiotherapy to treat disease• Energy applications• Environmental applications• National Security

Radioactivity

Radioactivity is emitted by atoms which are unstable and undergo radioactive decay

Many elements in the periodic table are naturally radioactiveother radioactive elements can be produced

Doing chemistry with radioactive elements is called “radiochemistry”

In 1895, Röntgen discovered X-rays when he worked with electrons in a cathode ray tube—they penetrated black paper.

Röntgen won the Nobel Prize in physics in 1901 for this discovery.

Brief history of radiochemistry

In 1896, Becquerel discovered radioactivity working with uranium compounds. Images were seen on photographic plates on exposure to the uranium compounds, even in the absence of any light.

Brief history of radiochemistry

Radiation emitted by the uranium was different from X-rays. It could be deflected by a magnetic field and therefore must consist of charged particles.

Becquerel was awarded the1903 Nobel Prize in physics for his discovery of radioactivity.

Brief history of radiochemistry

The term radioactivity was coined by Marie Curie. Working with uranium ore, she and Pierre Curie discovered the radioactive elements polonium (Po) and radium (Ra).

The Curies were awarded the 1903 Nobel Prize in physics for their work on radioactivity.

1898 – Marie and Pierre Curie

1912 — George de Hevesy

Father of the “radiotracer” experiment.

1923: 212Pb to study the absorption and translocation of Pb(NO3)2 in bean plants.

Received the Nobel Prize in chemistry in 1943 for his concept of “radiotracers”

atomic radius ~ 100 pm = 1 x 10-10 m

nuclear radius ~ 5 x 10-3 pm = 5 x 10-15 m

Rutherford’s Model of the Atom

Radioactivity: reactions of the nucleus of the atom

Reactions of the nucleus of the atom: Subatomic Particles

mass p = mass n = 1840 x mass e-

mass alpha particle = mass 2 p + mass 2 n

mass alpha particle = 7360 x mass e- (beta particle)

Radioactivity: reactions of the nucleus of the atom

Nuclear decay often results in a transmutation reaction which is the process of an atom changing atomic number and becoming a different element Example: 00

-01

147

146 βNC

Parent nuclideDaughter nuclide

Radiation

Radioactivity: reactions of the nucleus of the atom

Half-lives (t½): — time required for ½ of the material to decay

0 20 40 60 80 1000

200

400

600

800

1000

N1i

N2i

N3i

M1j

M2j

M3j

,,,,,i i i j j jtime (minutes)

num

ber o

f nuc

lei r

emai

ning

t½ = 15 m t½ = 30 m

t½ = 50 m

½

0.693 tt

t 0N N e

Radioactive Decay

Ionizing Radiation

* Radioactive decay emits ionizing radiation

* Ionizing radiation consists of particles or waves with enough energy to remove electrons from surrounding atoms or molecules

IonizingRadiation

Non-IonizingRadiation

Electromagnetic Spectrum

We try to “harness” ionizing radiation for useful purposes, specifically diagnosis of disease (imaging) and therapy of disease

- alpha particle—He2+ nucleus

---beta particle—e- ejected by nucleus

+--positron—e+ ejected by nucleus– Undergoes annihilation to emit two

0.511 MeV photons at 180o

--gamma ray—photon emitted by nucleus

Types of Ionizing Radiation

Ionizing Radiation Fact Book, 2007. U.S. Environmental Protection Agency. http://www.epa.gov/radiation/docs/402-f-06-061.pdf (accessed Jun 7, 2011).

Types of Ionizing Radiation

Betaβ+ or

positronβ- or

electron

Gammax-ray or

photon

Alpha or 242α

242He

Applications of Radiation

Ionization Technology. U.S. Environmental Protection Agency. http://www.epa.gov/rpdweb00/sources/smoke_ion.html (accessed Jun 8, 2011).

Smoke

Alarm

CurrentDisrupte

d

• Nuclear Power• Nuclear Medicine• Nuclear Forensics• Drug design• Smoke Detectors