In the study, NSCL users from the Institute for Nuclear Physics of the University of Cologne in Germany and Central Michigan University teamed with Krzysztof Starosta, NSCL assistant professor, and other MSU researchers to make a lifetime measurement of an excited state of germanium-64, Ge-64. Measuring the amount of time it takes for an isotope to decay into lower energy state helps nuclear scientists characterize shape and structure exotic nuclei.
All nuclei are made up of protons and neutrons, and the stable form of Ge-73, relatively abundant on Earth and commonly used as a semiconductor in the computing industry, has 32 protons and 41 neutrons. Ge-64, in contrast, has an equivalent number of protons and neutrons — 32 of each — an exceedingly rare combination for this element. The NSCL Coupled Cyclotron Facility is a world-leader in producing exotic, unstable isotopes.
“The fact that at NSCL sufficient beam time could be allocated for a step-by-step development of the new technique was crucial for the success of this experiment”, says Alfred Dewald, a University of Cologne physicist and a coauthor of the paper. “No other facility is so focused on spectroscopy of exotic nuclei using gamma-ray spectroscopy.”
Physicists are interested in isotopes like Ge-64 with mirror-image sets of protons and neutrons that fall within a specific mass region — heavier than nickel and lighter than tin. It is a nuclear neighborhood marked by strange phenomena, including nuclei that rapidly change from being round to cigar- or pancake-shaped. The broad theoretical outlines of shape-shifting behavior are well understood, yet until now, precise experimental observation has been difficult to achieve.
The method applied by the researchers hinges on the Doppler effect — the same principle that makes an approaching ambulance sound higher pitched than one traveling away, or which causes waves to be more closely spaced together in front of a person walking through water than the waves that trail behind.
Gamma rays, a form of light waves, have a set frequency, a measure of how closely the waves are spaced. When a moving nucleus emits a gamma ray, the ray’s wave will appear compressed in forward directions and stretched out in backward directions. By measuring these Doppler shifts, scientists can calculate the speed of the nucleus when it released the gamma ray.
In the study, scientists directed a beam of Ge-64 into a thin metal foil that slowed the beam down without stopping it. The Ge-64 nuclei began in a high-energy state and dropped to a lower state, a de-excitation that could happen before or after passing through the sheet.
Gamma rays emitted before the nucleus reaches the foil will have different Doppler shifts compared to those emitted from nuclei which downshift their state after passing through the foil. This is because the nuclei have slowed down.
By comparing how many gamma rays came from nuclei before or after passing through the foil, scientists can determine the average distance where the excited states in Ge-64 decayed. Knowing this distance, simple calculations relating speed, distance, and time yielded the average amount of time it took for the Ge-64 to change states, information important to understanding shape, structure and other important properties of the nucleus.
NSCL studies isotopes by fragmenting beams of nuclei traveling at more than 62,000 miles per second. This fast-beam method holds certain advantages over alternative means of producing rare isotopes, allowing physicists to study nuclei at the extreme edge of existence. For example, in fast-beam facilities it’s well-understood how nuclei that first strike a target and then impact downstream detectors slow down and stop, a fact that make exacting measurements possible.
But studying such speeding nuclei is rife with challenges, too, such as filtering and purifying the beam and having the right equipment to detect the few sought-after isotopes from the many billions of billions of other particles in the beam. Until now, such challenges had hindered the success of lifetime measurement experiments at fast-beam facilities.
“To make this experiment happen, you need to bring together all the top elements you have available in the lab and from our users,” said Starosta, the paper’s lead author. “You need everything to be optimized, and it happened for this particular experiment.”
Key to the team’s success was a device designed by Dewald that is capable of making highly precise in-flight distance measurements on the sub-micron scale. A micron is one-millionth of a meter.
“At one-third of the velocity of light it takes about 10-14 seconds to travel a micron,” Dewald said. “This precision is an important factor to reach the final precision of about 10-13 seconds with which one measures the lifetimes of nuclear excitations.”
“It is very important to have a new method available to measure lifetimes of exotic nuclei, as from these lifetimes we learn the most about the quantal structure of atomic nuclei” said Jan Jolie, director Institute for Nuclear Physics of the University of Cologne, “Moreover, the new method allows to determine lifetimes for higher excitations than can be reached by the conventional methods.”
The study’s success is significant for another reason — it is only the second time a precise lifetime measurement has been made in the mysterious portion of the nuclear landscape where unusual proton-neutron ratios may cause strange behavior.
“It’s opening up a whole range of possible studies,” said Roderick Clark, a physicist and co-leader of the nuclear structure group at Lawrence Berkeley National Laboratory, who was not involved in the experiment. “That’s as far as you can go, the frontiers of this research. This is one of the areas that NSCL is leading the world in.”
Geoff Koch | EurekAlert!
First chip-scale broadband optical system that can sense molecules in the mid-IR
24.05.2018 | Columbia University School of Engineering and Applied Science
Nuclear physicists leap into quantum computing with first simulations of atomic nucleus
24.05.2018 | DOE/Oak Ridge National Laboratory
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
24.05.2018 | Ecology, The Environment and Conservation
24.05.2018 | Medical Engineering
24.05.2018 | Physics and Astronomy