NASA’s new detectors could improve views of gamma-ray events

NASA's new detectors could improve views of gamma-ray events

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In a practical application such as the design of this sounding rocket test instrument, a gamma-ray observatory would use multiple layers of Astropix sensors, which could then trace a trajectory of three-dimensional particles through an array of pixelated two-dimensional detectors. Credit: Regina Caputo

Using technology similar to that found in smartphone cameras, NASA scientists are developing updated sensors to reveal more details about exploding black holes and exploding stars, all while being less power hungry and easier to detect. mass-produce than the detectors used today.

“When you think of black holes actively destroying stars, or neutron stars exploding and creating bursts of high-energy light, you are looking at the most extreme events in the universe,” said research astrophysicist Dr. Regina Caputo. “To observe these events, you need to look at the highest energy form of light: gamma rays.”

Caputo leads an instrument development effort called AstroPix at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The silicon pixel sensors in the AstroPix, still in development and testing, are reminiscent of the semiconductor sensors that allow smartphone cameras to be so small.

“Gamma rays are notoriously difficult to measure because of the way the incoming particle interacts with your detector,” said Dr. Amanda Steinhebel, a NASA postdoctoral fellow working with Caputo.

Gamma rays are wavelengths of light that are more energetic than ultraviolet and X-rays, and their photons act more like particles than waves. “Instead of just being absorbed by a sensor like visible light,” Steinhebel said, “gamma rays just bounce around.”

NASA’s Fermi Gamma-ray Space Telescope, which has been studying the gamma-ray sky since 2008, solved the “bounce” problem in its main instrument by using strip-shaped sensor towers. This table-sized cube, Fermi’s Large Area Telescope, was itself groundbreaking technology when the mission launched.

Each stripe maps a gamma ray in a single dimension, while layers of strips oriented perpendicular to each other record the second dimension. Gamma rays cascade energy blasts through multiple layers, providing a map pointing to the source.

About the size of a golf bag, a space telescope instrument using AstroPix sensors would require half as many layers as Fermi strip detector technology, Caputo said.


Gamma-ray bursts are the brightest explosions in the cosmos. Astronomers think most occur when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a black hole, as illustrated in this animation. The black hole then pushes jets of particles that pierce all over the collapsing star at nearly the speed of light. These jets streak across the star, emitting X-rays and gamma (magenta) rays as they pour out into space. They then penetrate the material surrounding the doomed star and produce a multi-wavelength afterglow that gradually fades away. The closer we approach one of these jets head-on, the brighter it appears. Credit: NASA Goddard Space Flight Center

“It’s easier to tell exactly where the particles are interacting,” Steinhebel said, “because you simply identify the point in the grid that it has interacted with. Then you use multiple layers to literally plot the paths the particles have taken through it.”

The AstroPix could record lower-energy gamma rays than current technology, Steinhebel explained, because these photons tend to get lost as they filter through the multiple layers of a strip detector. Capturing them would provide more insight into what happens during short-lived energy events. “These low-energy gamma rays are most common during the peak brightness of the burst,” she explained.

The pixel detectors also use less electricity to operate, Caputo said, a big boon for future missions planning their power consumption.

Pixelated silicon detectors have been tried in particle accelerator experiments, he said, and their common use and mass production for cell phones and digital cameras make them easier and cheaper to obtain.

Developing several prototypes over several years and seeing AstroPix create accurate graphs of gamma-ray light has been exhilarating and extremely satisfying, Steinhebel said.

As the team continues to work on developing and improving its technology, Caputo said the next step would be to launch the technology on a short sounding rocket flight for further testing above Earth’s atmosphere.

They hope to benefit from a future gamma-ray mission intended to further the study of high-energy universe events.

“We can do such an interesting science with this,” Caputo said. “I just want to see it happen.”

#NASAs #detectors #improve #views #gammaray #events

Precision Nuclear Physics in the Indium-115 Beta Decay Spectrum Using Cryogenic Detectors

Precision Nuclear Physics in the Indium-115 Beta Decay Spectrum Using Cryogenic Detectors

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(a) Example of a simulation showing the interactions within the LiInSe2 crystal detector. (b) The simulations (red) are combined with the predicted but incorrectly reconstructed event distribution (dashed blue) to extract a single In-115 spectrum (solid) from the data (black). Credit: Daniel Mayer/Alexander Leder

Some isotopes such as Indium-115 (In-115) are extremely long-lived, taking over 100 trillion years for half of the indium atoms to decompose. These isotopes allow scientists to probe the precise internal processes that govern other extremely long-lived isotopes. New research is helping scientists improve the structures they use to calculate half-lives and other nuclear properties, such as the structure of protons/neutrons within the nucleus.

Using background subtraction/simulation techniques pioneered in other ton-scale nuclear decay experiments, the scientists extracted the energy spectrum of the outgoing electrons from In-115 decays that occurred within a LiInSe2 crystal. At the same time, the scientists also performed the world’s most precise measurement of the decay rate of In-115. This work expands scientific understanding of nuclear structure and paves the way for future experiments to probe nuclear structure for a variety of isotope sizes.

The physical processes that drive the decay rate of medium-sized nuclei are difficult for scientists to probe. This is due to the large number of intermediate nuclear energy states. This study shows the feasibility of extracting clean electron (beta) energy spectra from various long-lived nuclei using low-temperature crystal detectors.

The research allows scientists to reduce the uncertainties related to the intermediate energy states that play a role in long-lived nuclei. This would then allow for better modeling of complex nuclear systems, such as the double beta decay of tellurium-130. Reducing these uncertainties plays a key role in improving the performance of other Department of Energy-sponsored ton-scale nuclear decay experiments.

A collaboration between the University of California-Berkeley, Massachusetts Institute of Technology, Jyvasklya University in Finland, Paris-Saclay University and RMD Inc. has commissioned a new LiInSe2 detector to explore the possibility of high-quality, low-background bolometric detectors for use in nuclear decay model verification.

The researchers collected data at temperatures close to absolute zero to detect and record the smallest temperature peaks due to particle interactions, such as those of In-115 beta decays, using highly sensitive thermometers. The study rejected background events such as external gamma rays using a combination of particle simulations and close examination of the individual decays recorded.

The result was a clean In-115 decay spectrum of the emitted electrons. Scientists at the University of California at Berkeley compared this spectrum to a library of predicted spectra generated at the University of Jyvaskyla and found the predicted spectrum most closely matched the collected data. This extracted the most precise measurement to date of the decay rate of In-115. This measurement opens the door to a better understanding of the physics governing the decays of extremely long-lived isotopes, such as tellurium-130.

The work is published in the journal Physical Review Letters.

More information:
AF Leder et al, Determination of gA/gV with high resolution spectral measurements using a LiInSe2 bolometer, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.129.232502

About the magazine:
Physical Review Letters

#Precision #Nuclear #Physics #Indium115 #Beta #Decay #Spectrum #Cryogenic #Detectors