Applications of Nuclear Physics

MEDICAL DIAGNOSIS AND TREATMENT

Technological advances spurred by the demands of nuclear research have led di"RECT"ly to the creation of research and analytical tools in fields ranging from medicine and environmental science to art and archaeology. These new technologies have also found practical applications ranging from integrated circuit production to weapons verification. Emerging applications of nuclear technology show great potential for addressing the future needs of the nation. Recent examples appear in the remainder of this brochure.

Medical Diagnosis and Treatment

Nuclear diagnostic techniques have revolutionized medicine by providing ways to "see" inside the body without surgery. Today, 3500 hospital-based nuclear medicine departments in the U.S. perform 10 million nuclear medicine procedures each year, generating about $1 billion in business and saving countless lives. In many cases, the practitioners are nuclear physicists who cooperate with physicians to develop and apply the techniques.

Radioactive Isotopes

Many medical procedures require radioactive isotopes. A radiopharmaceutical is a drug containing a radioactive isotope, an unstable nucleus. The isotope concentrates in the relevant part of the body and emits small amounts of radiation, which is sensed by a detector known as a "gamma camera."

Radioimmunoassay is an in vitro procedure which combines radiochemicals and antibodies to detect trace quantities of hormones, vitamins, or drugs in a patient's blood. Physicians rely on radioimmunoassay to monitor the concentration of digitalis, a medication that slows the heart rate, in the blood of coronary patients.

Positron Emission Tomography

Positron emission tomography (PET) is a medical imaging technique which reveals dynamic effects such as blood flow. The patient ingests a radiopharmaceutical which emits a form of anti-matter, a positively charged electron called a positron.

When the positron meets a normal electron, the two annihilate each other, emitting a pair of gamma rays in opposite di"RECT"ions. A circle of detectors pinpoints the location of each annihilation event. In the image below left, a PET scan of a brain, the bright red and yellow colors indicate the presence of malignant head and neck tumors. The high-speed sequence of images can capture the actual motion of the studied organ as in the image of a beating heart in the photograph below right.

PET Scan of a Brain UCLA

Images of a Beating Heart Siemens Medical Systems

Cancer Treatment

Radiation with X-rays is a conventional treatment for cancer. The X-rays are generated by microwave linear accelerators, which are the descendants of nuclear physics research tools. Physicists cooperated with radiologists to optimize versions of these systems for medical treatment.

X-rays deposit most of their energy where they enter the body, then successively less until they leave the body. As a result, normal tissues near the X-ray source receive higher doses of radiation than the tumor itself. The sensitivity of normal tissues to radiation limits the dose which radiologists can safely deliver, especially when a tumor lies near vital organs.

To solve this problem, nuclear physicists and radiologists have developed a new treatment known as proton therapy. Protons penetrate only to a controllable depth, and they deposit most of their energy at the end of their range. They enable radiologists to increase the dose to the tumor while reducing the dose to normal tissues.

The four images below compare the abilities of X-ray beams and proton beams to localize dosage. A tumor of the prostate gland appears in each image. The colors indicate how the energy deposited in the tissue varies with position -- yellow is the maximum energy, followed by red, orange, and purple. The two images in the top row show the energy distribution for X-ray beams; the two in the bottom row for proton beams.

The two images on the left compare the effects of a single X-ray beam and a single proton beam. With the X-ray beam (top left), more energy is deposited in the healthy tissue. With the proton beam (bottom left), more energy is deposited in the tumor.

The two images on the right show the effect of multiple beams. Four X-ray beams (top right) still deliver substantial energy to healthy tissue. But with only three proton beams (bottom right), the energy deposited conforms to the shape of the tumor. Proton therapy is the preferred treatment for cancers near the eye and the spinal cord. Proton Therapy System Loma Linda University

The Effects of X-Ray Beams (top) and Proton Beams (bottom) Loma Linda University

ENVIRONMENTAL SCIENCE

Accelerator mass spectrometry (AMS), a new technique which can find any nucleus in concentrations below 1 part per trillion, is making important contributions to environmental science. AMS has revolutionized carbon-14 dating, which can determine the age of organic material up to 50,000 years old. Traditional techniques measure the decay rate of radioactive carbon-14. AMS is more sensitive because it counts individual carbon-14 nuclei. As a result, AMS can analyze samples a thousand times smaller.

Ocean Circulation Studies and Global Warming

Radioactive dating of the oceans by AMS is helping researchers understand ocean circulation patterns. Carbon-14 atoms, produced in the upper atmosphere when cosmic rays strike nitrogen nuclei, join with oxygen atoms to form carbon dioxide (CO₂). The atmosphere exchanges CO₂ with the ocean, which tends to inhale CO₂ near the poles and to exhale it near the equator. As seawater ages, the carbon-14 content of its CO₂ decreases. Researchers are creating a 3-dimensional map of the age of the oceans based on AMS studies of seawater samples taken at various depths, latitudes, and longitudes. These studies are helping researchers to understand the oceans' large-scale circulation patters and the earth's weather patterns.

Many people are concerned that man-made CO2 contributes to global warming. Since the atmosphere exchanges CO2 with the ocean, the 3-dimensional map of oceanic carbon-14 is also helping researchers learn about the natural fluctuations of the earth's CO2 cycle -- an essential step toward understanding the significance of man-made CO2 in the atmosphere. Water Resources The National Park Service asked hydrologists to evaluate water supply alternatives in the Wawona area of Yosemite National Park. In cooperation with physicists and nuclear geochemists, the hydrologists found that the ground water in Wawona's fractured granitic rocks is vertically segregated.

Sampling Seawater Woods Hole Oceanographic Institute

Wawona Basin Yosemite National Park

AMS measurements of carbon-14 showed that rainfall recently recharged the shallow ground water. But the deeper zone of the aquifer contains a mixture of water from a deep saline source and water from ancient rainfall; it was last recharged about 6,000 years ago. The deep and shallow zones are not hydraulically connected. Since the deep zone recharges slowly, the scientists recommended high altitude springs as a more reliable source of water for Wawona than deep wells.

Air Quality

Since wood contains carbon-14 and fossil fuels do not, AMS studies of particulates in smog can identify the relative contributions of wood burning and fossil fuel burning. These studies have shown that wood burning is the major source of air pollution during winters in Albuquerque and Las Vegas.

Nuclear physicists are studying air pollution in the National Parks by proton-induced X-ray emission (PIXE). Since PIXE can detect constituents of the haze in concentrations below 1 part per trillion, the physicists can often identify the source of the pollution. They identified the Navajo Generating Station, a coal-fired power plant, as the main source of air pollution in the Grand Canyon. Their data convinced plant operators to install scrubbing equipment to reduce emissions by 90%.

Grand Canyon with Poor Air Quality
U.C. Davis

Grand Canyon, Same Spot with Good Air Quality
Aaron Glass Studios

Stratospheric Ozone Depletion

Man-made chlorofluorocarbons in the atmosphere have depleted the ozone layer over Antarctica. In the spring, half the ozone over the South Pole disappears, including nearly 100% of the ozone at altitudes between 10 and 20 kilometers. Since ozone screens the sun's ultraviolet rays, its depletion over populated areas could increase cancer rates. AMS studies of radioisotopes such as beryllium-7 and beryllium-10 are contributing to an understanding of ozone depletion. These beryllium isotopes are created in the stratosphere when cosmic rays strike nitrogen atoms. AMS researchers are studying the concentration of these isotopes in falling snow and in air samples collected by high-altitude aircraft. Since beryllium isotopes attach readily to aerosols, they are helping scientists to understand aerosol movement in the upper atmosphere. Aerosol particles serve as host sites for chemical reactions which create the forms of chlorine that destroy ozone.

Hole in Ozone Layer NASA

ENERGY

On-Line Analysis of Coal

The coal and electric utility industries have installed 600 on-line analyzers which determine the chemical composition of coal by nuclear techniques. On-line analyzers monitor the quality of coal at the mine, sort and blend coal, and streamline the operation of power plants. They are helping the coal and utility industries to reduce air pollution.

Nuclear Fusion

The U.S. and several other countries have established long-range plans to generate electricity with commercial nuclear fusion reactors. These reactors fuse hydrogen nuclei to create helium, thereby liberating energy in a process similar to nuclear reactions in the sun.

MATERIALS

Ion Implantation

Nitrogen ions implanted into surgical alloys help prevent repeated surgery to replace hip prostheses by reducing wear and corrosion from normal body fluids. The photograph below to the right shows a nitrogen-implanted artificial femur.

Ion Implantation System for Semiconductor Manufacturing Varian

Ion Implanted Artificial Femur Oak Ridge National Laboratory

RBS and Channeling

Rutherford back scattering (RBS) and channeling are quality assurance techniques in the semiconductor industry. Both techniques accelerate alpha particles (helium nuclei) toward a chip. RBS experiments study the reflected alpha particles to measure levels of impurities. Channeling experiments check the effectiveness of ion implantation. Implanted boron and phosphorous ions serve their intended purpose as electron donors or receptors only if they sit on a silicon site in the crystal lattice -- not if they occupy random interstitial sites. Since interstitial ions block the transmission of alpha particles through channels in the lattice, channeling experiments can detect them.

ARCHAEOLOGY AND ART

Egyptian Sculpture Nuclear techniques can clarify the histories of archaeological artifacts and works of art by identifying elements present in trace quantities. The Colossi of Memnon, two statues created during the 14th century B.C. on the western plain of Thebes in Egypt, stand nearly sixty feet tall and weigh about 1000 tons. Each was sculpted from a monolith of quartzite. Until recently, archaeologists believed the monoliths came from a quarry in Aswan, 140 miles upstream along the Nile River. When scientists examined the statues and several Egyptian quarries by a technique called neutron activation analysis, they proved that the monoliths actually came from a quarry in Cairo -- 440 miles downstream. Paleolithic Artifacts and the Seuso Treasure Accelerator mass spectrometry makes it possible to apply carbon-14 dating studies to samples too small for conventional techniques. The photographs below show

Colossus of Memnon Lawrence Berkeley Lab

Seuso Treasure Oxford University

Paleolithic Artifacts Oxford University

Ancient Cave Paintings

Paleolithic Cave Painting
Research Laboratory of the French Museums