Physicist finds colder isn't always slower as electron emissions increase at temps to -452 F

April 28, 2010, Indiana University

Using two different photomultipliers (denoted by triangles and squares), Meyer found that dark rate electron emission decreased as the temperature (noted above in Kelvin) decreased until about -63.4 F (220 K), when the emission rate then began increasing while temperatures continued dropping to -452 F (4 K).
( -- Science is detective work so it was not unexpected that new questions would follow old ones as Indiana University Bloomington nuclear physicist Hans-Otto Meyer's work progressed on testing a fundamental symmetry of nature that could lead to understanding the matter-antimatter asymmetry in the universe.

At the heart of this search to uncover a violation of time-reversal symmetry by observing a permanent electric dipole moment of the neutron (nEDM) is the $25 million nEDM experiment that Meyer and 60 other researchers from 15 institutes are working on.

But while searching for a non-zero separation of positive and negative charge inside a neutron (the symmetry-violating nEDM), Meyer ran into another mystery scientists have yet to explain.

Working with highly sensitive photomultipliers intended to detect the scintillation light given off during the nEDM experiment as charged particles emerge from reactions between neutrons and a rare isotope of helium, Meyer identified new attributes to a phenomenon called cryogenic .

In a recent paper in Europhysics Letters (Vol. 89, Issue 5), Meyer presents a thorough experimental investigation of the electron emission rate in the absence of light -- called the dark rate -- in which the rate of electron emission unexpectedly increases as a is cooled to temperature.

Once the temperature hit around -64 F (220 K) and as it continued down to the lowest temperature measured during the experiment, -452 degrees F (4 K), electron emission from the cathode surface of the photomultiplier steadily increased. This is in contrast to the usual behavior of nature where processes tend to slow down as things get colder.

Meyer saw the electrons being emitted in bursts, noted that the burst duration distribution followed a power law and, as the temperature decreased, that both the rate of bursts and their size increased. Furthermore, he found that while the bursts occurred at random times, that within a given burst the emission of electrons obeyed a peculiar pattern in time.

Scientists have known about cryogenic emission for about 50 years. While other types of spontaneous electron emission without light are understood (thermal or heat, electrical field, and penetrating radiation electron emission), Meyer points out, "at this time, regrettably, a quantitative explanation of the observed characteristics of cryogenic emission is still eluding us."

"Most likely, this observation can eventually be explained within the known laws of physics, but there is always a small chance that we are seeing something new, and that this is a real discovery," he said.

Meyer suggests a trapping mechanism may be at work. How the trap is created and how it fills with or empties itself of electrons might be related to the behavior of traps in semiconductors. One clue pointing to a trap mechanism is the longer intervals between emitted electrons, from about three microseconds apart to three milliseconds apart as a given burst evolved.

A trap would hold electrons until full, then empty some electrons that become dark events measured by the photomultiplier, while others would recombine with an electron hole and thus go undetected. As fewer electrons remained, the release rate would slow.

Retired from teaching duties at the IU College of Arts and Sciences' Department of Physics and having graduated his last student two years ago, Meyer is still active in research at the IU Cyclotron Facility's new Center for Matter and Beams. He estimated continuing the experiment would cost about $500,000.

"I would be very pleased if someone younger would take up this investigation," he said.

And if someone else were to take up this mystery, a semi-retired Meyer has some thoughts on how to proceed.

"Ideally you would want to build an apparatus capable of presenting different surfaces of your choice, like copper, carbon or silicon for example, to an electron multiplier," he said. "The apparatus requires ultra-high vacuum, and the surfaces must be cooled to cryogenic temperatures. Such an experiment will tell us whether these trapping events are present only in semiconductors such as the of a photomultiplier, or are of a more general nature."

Explore further: Cryogenic electron emission phenomenon has no known physics explanation

Related Stories

Shining a Brighter Light

June 14, 2005

New lighting technology developed at UC Davis offers quality, cost and environmental benefits compared with existing types of lighting, according to Charles E. Hunt, professor of electrical and computer engineering. Field ...

Switchyard for single electrons

February 25, 2008

German scientists achieved to transfer very small charge "packets", comprising a well-defined number of few electrons, between metallic electrons precisely by using a single-electron pump. A single-electron transistor, being ...

New plasma transistor could create sharper displays

February 4, 2009

( -- By integrating a solid-state electron emitter and a microcavity plasma device, researchers at the University of Illinois have created a plasma transistor that could be used to make lighter, less expensive ...

How Cagey Electrons Keep Hydrated

December 20, 2007

Water, despite its essential role in nature, remains a deeply mysterious substance. A long list of water's unusual properties tantalizes researchers even today, and scientists at the Stanford Synchrotron Radiation Laboratory ...

Recommended for you

CMS gets first result using largest-ever LHC data sample

February 15, 2019

Just under three months after the final proton–proton collisions from the Large Hadron Collider (LHC)'s second run (Run 2), the CMS collaboration has submitted its first paper based on the full LHC dataset collected in ...

Gravitational waves will settle cosmic conundrum

February 14, 2019

Measurements of gravitational waves from approximately 50 binary neutron stars over the next decade will definitively resolve an intense debate about how quickly our universe is expanding, according to findings from an international ...


Adjust slider to filter visible comments by rank

Display comments: newest first

Apr 28, 2010
This comment has been removed by a moderator.
5 / 5 (4) Apr 28, 2010
Wasn't an article about exactly this research by this scientist posted on physorg a month ago?

Yes, I do believe it was

Why post it again?
2.3 / 5 (3) Apr 28, 2010
what does F stand for? As in -452 F???
5 / 5 (1) Apr 28, 2010
Serious science should use Kelvin instead of Fahrenheit. One can just wonder how much money and confusion we would have saved if we used the same units? I recall a crash on Mars, caused by wrong metric/miles.
5 / 5 (3) Apr 28, 2010
what does F stand for? As in -452 F???

A 'Failure' to use proper temperature measurements.
Apr 29, 2010
This comment has been removed by a moderator.
3 / 5 (2) Apr 29, 2010
I would like to know if they found a separation of charge inside the neutron??
Yes, they did. Down quarks are heavier, so they're concentrating at center of neutron.

not rated yet Apr 29, 2010
It is clearly sudden release of some built up of energy, the trigger should be really sensitive. This mean it may work as detector of something, with sensitivity increasing when temperature lowers. What this something may be is pure speculation of course, but together with all kind of exotic particles I would not forget gravitational waves. To search for correlation in two identical settings close to each other would be interesting for beginning (should trigger if this something is whatever waves), and then to look for possible relation to earth movement of course (should trigger if this something are whatever particles).
not rated yet Apr 29, 2010
Serious science should use Kelvin instead of Fahrenheit.

The diagram does use Kelvin, so does the scien(ce)tist. It's those damned Yanks and their insistence on using the imperial measurement system that's forced the inclusion of Fahrenheit conversions.
3 / 5 (2) Apr 29, 2010
A glitch in the PR department of Indiana University?
PhysOrg collects news from both primary, both secondary sources, which explains the number of duplicated articles.
not rated yet May 03, 2010
Serious science should use Kelvin instead of Fahrenheit. One can just wonder how much money and confusion we would have saved if we used the same units? I recall a crash on Mars, caused by wrong metric/miles.

That was just a cover story.
not rated yet May 03, 2010
as for a lack of an explanation... and morphing into what will turn out to be asymmetry, Maxwell covered that in his original un-edited equations of 20 equations in 20 unknowns.

Maxwell, via the math, stated flat our that symmetry in the system did not exist. Heaviside shortened it and took most of the asymmetry and the mathematical explanation out - to simplify for pen and pencil based electric motor design. Lorentz removed the last bits of asymmetry, and thus cursed us to having to go over this ground for the umpteenth time...160 years later.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.