Physicists design an experiment to pin down the origin of the elements

Physicists design an experiment to pin down the origin of the elements
A new experiment designed by MIT physicists may help to pin down the rate at which huge, massive stars produce oxygen in the universe. Credit: NASA/ESA/Hubble

Nearly all of the oxygen in our universe is forged in the bellies of massive stars like our sun. As these stars contract and burn, they set off thermonuclear reactions within their cores, where nuclei of carbon and helium can collide and fuse in a rare though essential nuclear reaction that generates much of the oxygen in the universe.

The rate of this oxygen-generating reaction has been incredibly tricky to pin down. But if researchers can get a good enough estimate of what's known as the "radiative capture reaction rate," they can begin to work out the answers to fundamental questions, such as the ratio of carbon to oxygen in the universe. An accurate rate might also help them determine whether an exploding star will settle into the form of a black hole or a neutron star.

Now physicists at MIT's Laboratory for Nuclear Science (LNS) have come up with an experimental design that could help to nail down the rate of this oxygen-generating reaction. The approach requires a type of particle accelerator that is still under construction, in several locations around the world. Once up and running, such "multimegawatt" linear accelerators may provide just the right conditions to run the oxgen-generating reaction in reverse, as if turning back the clock of star formation.

The researchers say such an "inverse reaction" should give them an estimate of the reaction rate that actually occurs in stars, with higher accuracy than has previously been achieved.

"The job description of a physicist is to understand the world, and right now, we don't quite understand where the oxygen in the universe comes from, and, how oxygen and carbon are made," says Richard Milner, professor of physics at MIT. "If we're right, this measurement will help us answer some of these important questions in nuclear physics regarding the origin of the elements."

Milner is a co-author of a paper appearing today in the journal Physical Review C, along with lead author and MIT-LNS postdoc Ivica Friščić and MIT Center for Theoretical Physics Senior Research Scientist T. William Donnelly.

A precipitous drop

The radiative capture reaction rate refers to the reaction between a carbon-12 nucleus and a helium nucleus, also known as an alpha particle, that takes place within a star. When these two nuclei collide, the carbon nucleus effectively "captures" the alpha particle, and in the process, is excited and radiates energy in the form of a photon. What's left behind is an oxygen-16 nucleus, which ultimately decays to a stable form of oxygen that exists in our atmosphere.

But the chances of this reaction occurring naturally in a star are incredibly slim, due to the fact that both an alpha particle and a carbon-12 nucleus are highly positively charged. If they do come in close contact, they are naturally inclined to repel, in what's known as a Coulomb's force. To fuse to form oxygen, the pair would have to collide at sufficiently high energies to overcome Coulomb's force—a rare occurrence. Such an exceedingly low reaction rate would be impossible to detect at the energy levels that exist within stars.

For the past five decades, scientists have attempted to simulate the radiative capture reaction rate, in small yet powerful particle accelerators. They do so by colliding beams of helium and carbon in hopes of fusing nuclei from both beams to produce oxygen. They have been able to measure such reactions and calculate the associated reaction rates. However, the energies at which such accelerators collide particles are far higher than what occurs in a star, so much so that the current estimates of the oxygen-generating reaction rate are difficult to extrapolate to what actually occurs within stars.

"This reaction is rather well-known at higher energies, but it drops off precipitously as you go down in energy, toward the interesting astrophysical region," Friščić says.

Time, in reverse

In the new study, the team decided to resurrect a previous notion, to produce the inverse of the oxygen-generating reaction. The aim, essentially, is to start from oxygen gas and split its nucleus into its starting ingredients: an and a carbon-12 nucleus. The team reasoned that the probability of the reaction happening in reverse should be greater, and therefore more easily measured, than the same reaction run forward. The inverse reaction should also be possible at energies nearer to the energy range within actual stars.

In order to split oxygen, they would need a high-intensity beam, with a super-high concentration of electrons. (The more electrons that bombard a cloud of oxygen atoms, the more chance there is that one electron among billions will have just the right energy and momentum to collide with and split an oxygen nucleus.)

The idea originated with fellow MIT Research Scientist Genya Tsentalovich, who led a proposed experiment at the MIT-Bates South Hall electron storage ring in 2000. Although the experiment was never carried out at the Bates accelerator, which ceased operation in 2005, Donnelly and Milner felt the idea merited to be studed in detail. With the initiation of construction of next-generation linear accelerators in Germany and at Cornell University, having the capability to produce electron beams of high enough intensity, or current, to potentially trigger the inverse reaction, and the arrival of Friščić at MIT in 2016, the study got underway.

"The possibility of these new, high-intensity electron machines, with tens of milliamps of current, reawakened our interest in this [inverse reaction] idea," Milner says.

The team proposed an experiment to produce the inverse reaction by shooting a beam of electrons at a cold, ultradense cloud of oxygen. If an electron successfully collided with and split an oxygen atom, it should scatter away with a certain amount of energy, which physicists have previously predicted. The researchers would isolate the collisions involving electrons within this given energy range, and from these, they would isolate the alpha particles produced in the aftermath.

Alpha particles are produced when O-16 atoms split. The splitting of other oxygen isotopes can also result in alpha particles, but these would scatter away slightly faster—about 10 nanoseconds faster—than alpha particles produced from the splitting of O-16 atoms. So, the team reasoned they would isolate those alpha particles that were slightly slower, with a slightly shorter "time of flight."

The researchers could then calculate the rate of the inverse reaction, given how often slower alpha particles—and by proxy, the splitting of O-16 atoms—occurred. They then developed a model to relate the inverse reaction to the direct, forward reaction of oxygen production that naturally occurs in stars.

"We're essentially doing the time-reverse reaction," Milner says. "If you measure that at the precision we're talking about, you should be able to directly extract the reaction rate, by factors of up to 20 beyond what anybody has done in this region."

Currently, a multimegawatt linear accerator, MESA, is under construction in Germany. Friščić and Milner are collaborating with physicists there to design the experiment, in hopes that, once up and running, they can put their experiment into action to truly pin down the rate at which stars churn oxygen out into the universe.

"If we're right, and we make this measurement, it will allow us to answer how much carbon and is formed in stars, which is the largest uncertainty that we have in our understanding of how evolve," Milner says.


Explore further

Do alpha particle condensates exist in oxygen nuclei?

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Aug 20, 2019
O16 is already stable and is the most common isotope (99.8% abundant).
To me, the 3 x He reaction to make Carbon is the most interesting - since it extends the lifetime of stars by about 40 orders of magnitude. Do we have any data on this?

RNP
Aug 20, 2019
@Anonym514956
To me, the 3 x He reaction to make Carbon is the most interesting - since it extends the lifetime of stars by about 40 orders of magnitude.


Where did you get this idea from?


Aug 20, 2019
@Anonym514956
To me, the 3 x He reaction to make Carbon is the most interesting - since it extends the lifetime of stars by about 40 orders of magnitude.


Where did you get this idea from?

I, too, would like to hear this one….

Aug 20, 2019
There are some things which should NEVER BE experimented with, and reversing the process by which Oxygen is created is one of them. Curiosity is fine, but there should be a limit to such testing, else one day the scientists may start a chain reaction that they will not be able to stop.
Trying to disrupt the Natural Order of the Universe, even out of curiosity, can be dangerous for all Life on Earth and possibly elsewhere.
Scientists have yet to learn and understand that everything in the Universe are related to each other, and that what happens to one could eventually affect all.
The stupidity of humans is mind-boggling.

Aug 20, 2019
Eventually, it is no longer science, but SUICIDE.
In comparison to all of the civilisations that have sprung up and thrived in the far reaches of distant galaxies who have learnt the hard lessons and are wiser for it, you Earthers are barely out of the womb. And yet you imagine yourselves to be all knowing enough that you have no fear or imagination of what is possible to end your existence.

Aug 20, 2019
There are some things which should NEVER BE experimented with, and reversing the process by which Oxygen is created is one of them. Curiosity is fine, but there should be a limit to such testing, else one day the scientists may start a chain reaction that they will not be able to stop.
Trying to disrupt the Natural Order of the Universe, even out of curiosity, can be dangerous for all Life on Earth and possibly elsewhere.
Scientists have yet to learn and understand that everything in the Universe are related to each other, and that what happens to one could eventually affect all.
The stupidity of humans is mind-boggling.


Clown.

Aug 20, 2019
I see that Otto continues in his quest to downvote my comments as he tracks me to whichever article I have made my comments in. My rating now stands at -1423 since several months ago when the rating system was changed. Of course, it could have been RNP who did the deed since he seems to disagree with my opinions. Was it YOU, RNP?'
Or it could just as well have been the Mop man with his "clown" silliness.

Aug 20, 2019
sillyegghead...
considering the depths od stygian stupidity you are willing to sink?

how pathetically fragile is you rego that you would give a ratsass
or care a whitless
for other lunatic's approval?

your life must really suck if you are so desperate for approval on comments on a science site

whats the matter?
the other religious cranks & fakirs find you as tediously boring as we do?

your fellow deluded stoned you off the stupor sites?

isn't it their "christian" duty to piously turn the other ass & accept you to their sanguine cult?
or at least provide comfort & shelter to you & the other mentally infirm?

Aug 21, 2019
There are some things which should NEVER BE experimented with, and reversing the process by which Oxygen is created is one of them.
Surveillance_Egg_Unit

Why?
else one day the scientists may start a chain reaction that they will not be able to stop.
Now you are talking complete and utter science-ignorant BS. Physics tells us 'reversing' the process by which oxygen is created, even if we could and do that, will not magically do something to end the world. The exact reversing of the nuclear reaction in stars that created oxygen will ABSORB more energy that it would release so will certainly NOT lead to a chain reaction to end all life.
The stupidity of humans is mind-boggling.
Only humans like you, not us.

Aug 21, 2019
@Anonym514956
To me, the 3 x He reaction to make Carbon is the most interesting - since it extends the lifetime of stars by about 40 orders of magnitude.


Where did you get this idea from?

I, too, would like to hear this one….


OK, no need to both downvote me and express interest??
I heard it at university - essentially that nuclear reactions are typically on 10^-20s timescales yet stars live or 10^10 years. They should go off like H-bombs, were it not for the fact there are no stable A=5 nucleotides, which breaks the chain. To get above Helium you need a triple-collision, which is thermodynamically very rare. All the glorious detail is here: https://en.wikipe...process. OK there is about 10^-17s of intermediate lifetime in the Be8 nucleus so it's not quite a triple collision, but damn close.

Aug 21, 2019
They should go off like H-bombs

I was taught that stars don't explode like nukes because the gravity is containing the blast inside the star. Stars go supernova when gravity finally looses the fight.

Aug 21, 2019
My above misedit;
"...ABSORB more energy that ..."
should be
"...ABSORB more energy than ..."

Aug 21, 2019
The stupidity of humans is mind-boggling.


Case in point? Everything you post.

Aug 21, 2019
There are some things which should NEVER BE experimented with, and reversing the process by which Oxygen is created is one of them.
Surveillance_Egg_Unit

Why?
else one day the scientists may start a chain reaction that they will not be able to stop.
Now you are talking complete and utter science-ignorant BS. Physics tells us 'reversing' the process by which oxygen is created, even if we could and do that, will not magically do something to end the world. The exact reversing of the nuclear reaction in stars that created oxygen will ABSORB more energy that it would release so will certainly NOT lead to a chain reaction to end all life.
The stupidity of humans is mind-boggling.
Only humans like you, not us.
says humy

Uh Whatever gave you the idea that I am a human?
The Laws of the Universe are still mostly unknown to human scientists and yourself. And due to that ignorance of the Laws, you will all likely blow yourselves up. But not the planet.

Aug 22, 2019
The Laws of the Universe are still mostly unknown
Surveillance_Egg_Unit

What is your premise of your above assertion?
How do you know that 'most' laws are still unknown to us?

due to that ignorance of the Laws, you will all likely blow yourselves up.
Which law could we be ignorant of that would make it "likely" that we would blow ourselves up?
What is your premise for thinking such an unknown law probably exists?

RNP
Aug 22, 2019
@Anonym514956
...the 3 x He reaction to make Carbon is the most interesting - since it extends
the lifetime of stars by about 40 orders of magnitude.

Obviously untrue. (You do realize that 40 orders of magnitude is a factor of 10^40?)

...nuclear reactions are typically on 10^-20s timescales yet stars live or 10^10 years.

You are associating reaction timescales with stellar lifetimes. This makes no sense.

They should go off like H-bombs, were it not for the fact there are no stable A=5 nucleotides, which breaks the chain.

LOL. Funny an untrue. N.B. nucleotides are structural units of RNA and DNA, and have nothing to do with nuclear physics. I think you meant nuclides.

...OK there is about 10^-17s of intermediate lifetime in the Be8 nucleus so it's not quite a triple collision...

This IS the triple-alpha process.

It also remains unclear how you concluded that stellar lifetimes are extended by a factor of 10^40.

Aug 22, 2019
They should go off like H-bombs, were it not for the fact there are no stable A=5 nucleotides, which breaks the chain. To get above Helium you need a triple-collision, which is thermodynamically very rare.


You are funny - the popular description *is* that stars are H-bombs (but gravitationally confined and controlled). It is true that the subsequent steps modulate the lifetime later on, but the main reason small stars burn many times longer is not that nuclear fusion rates somehow changes drastically but that the overall rate is down regulated. Just burning H in a red dwarf takes eons:

"Because low-mass red dwarfs are fully convective, helium does not accumulate at the core, and compared to larger stars such as the Sun, they can burn a larger proportion of their hydrogen before leaving the main sequence. As a result, red dwarfs have estimated lifespans far longer than the present age of the universe, and stars less than 0.8 M☉ have not had time to leave the main sequence."

Aug 22, 2019
- ctd -

[From https://en.wikipe...ed_dwarf .]

The fusion of C is complicated, and in certain circumstances it is it that goes from rare to "bomb like" - a helium flash [ https://en.wikipe..._process ]. In any case, these things (including the CNO fusion cycle) are the general physics what the more specific science described in the article aim for.

Aug 22, 2019
The Laws of the Universe are still mostly unknown


All "laws" or robust patterns will never be completely known since nature is complex. But as it happens the laws are likely completely known for:

- The universe, i.e. the laws of cosmology (standard cosmology). Been there, done that 2018. [ https://pla.esac.esa.int/ ]

- The everyday physics, i.e. the laws of life (standard particles). Been there, done that 2017. [ https://home.cern...rd-model ].

The last part physicists saw coming years earlier:

"The Laws Underlying The Physics of Everyday Life Are Completely Understood ... there's no question that the human goal of figuring out the basic rules by which the easily observable world works was one that was achieved once and for all in the twentieth century."

[ http://blogs.disc...erstood/ ].

So no worries: all is mechanism (no magic).

Aug 22, 2019
The stupidity of humans is mind-boggling.
Only humans like you, not us.
says humy

Uh Whatever gave you the idea that I am a human?

LOL...
Unless you are an AI bot, you are just another insecure human, fearing the end of his/her own time...
So you create an illusionary little story to somehow deny your (unfulfilled) fate... :-)

Aug 22, 2019
Always the Sledge Hammer to Crack a Nut approach

What's left behind is an oxygen-16 nucleus
Which decays to a stable form of oxygen that exists in our atmosphere
The chances of this reaction occurring naturally in a star are slim
due In what's known as a Coulomb's force
To fuse to form oxygen, the pair would have to collide at sufficiently high energies to overcome Coulomb's force—a rare occurrence

Fore this is the purpose of the Neutron
Its unaffected by the Coulomb force and it decays to a Proton

p.s. as a side note, is not oxygen-16 a stable nucleus

Aug 22, 2019
The Laws of the Universe are still mostly unknown
Surveillance_Egg_Unit

What is your premise of your above assertion?
How do you know that 'most' laws are still unknown to us?

due to that ignorance of the Laws, you will all likely blow yourselves up.
Which law could we be ignorant of that would make it "likely" that we would blow ourselves up?
What is your premise for thinking such an unknown law probably exists?
says humy

As I've said and should not have to repeat: the Laws of the Universe are mostly still unknown - to humans. There are many Laws of the Universe that humans in their current state will not know nor have the necessary intelligence and will to find out.
I don't need a 'premise' in order to qualify my initial statement. I have stated what I KNOW, and it is for you and scientists to find out. But it is human ignorance along with bravado and arrogance of belief in your superiourity that will take your specie down.

Aug 22, 2019
The stupidity of humans is mind-boggling.
Only humans like you, not us.
says humy

Uh Whatever gave you the idea that I am a human?

LOL...
Unless you are an AI bot, you are just another insecure human, fearing the end of his/her own time...
So you create an illusionary little story to somehow deny your (unfulfilled) fate... :-)
says Whyde

You have the freedom to believe whatever you want. It is none of my concern.

Aug 22, 2019
LOL I see that Torbjorn has taken up what I have said in many previous comments, namely that the Universe is Mechanistic and all Matter/Energy in the Universe are Mechanisms - similar to Atomic Clocks.
I recall that someone had copied what I had said regarding the nonexistence of 'time' and that it is the Earth's 24 hour rotation cycle of sunrise to sunrise that is the actual mechanism of the Earth's clock, and I had also given the title of "the Clock of the Universe". Since Torbjorn has BLOCKED me, he can't read my posts directly as he somehow thinks I am religious which he hates, so he counts on those who use MY posts as reference to know what it is that I've said. Torbjorn read what someone else had said, and now he says that the Universe is mechanical, as though it was HIS original idea. It is laughable.

Aug 22, 2019
LOL I see that Torbjorn has taken up what I have said in many previous comments, namely that the Universe is Mechanistic and all Matter/Energy in the Universe are Mechanisms - similar to Atomic Clocks.
I recall that someone had copied what I had said regarding the nonexistence of 'time' and that it is the Earth's 24 hour rotation cycle of sunrise to sunrise that is the actual mechanism of the Earth's clock, and I had also given the title of "the Clock of the Universe". Since Torbjorn has BLOCKED me, he can't read my posts directly as he somehow thinks I am religious which he hates, so he counts on those who use MY posts as reference to know what it is that I've said. Torbjorn read what someone else had said, and now he says that the Universe is mechanical, as though it was HIS original idea. It is laughable.
Sorry, but it wasn't YOUR original idea, either....
(See what Einstein said about being a watchmaker)

Aug 23, 2019
I don't need a 'premise' in order to qualify my initial statement. I have stated what I KNOW,
Surveillance_Egg_Unit

In other words, what assertions you say you "know" to be true you don't know to be true because you have no logic or evidence or personal observation to back them up. In other words, you are delusional believing nonsense that your irrational brain got from god knows what idiotic flawed warped nonsense 'reasoning'. Sorry, you must do better than that to convince anyone here of anything.

Aug 23, 2019
I have stated what I know

What you know is how to walk your dog "Precious" and little else.

and it is for you and scientists to find out. But it is human ignorance along with bravado and arrogance of belief in your superiourity that will take your specie down.


lol, you're such a bad troll.

Aug 23, 2019
I don't need a 'premise' in order to qualify my initial statement. I have stated what I KNOW,
Surveillance_Egg_Unit

In other words, what assertions you say you "know" to be true you don't know to be true because you have no logic or evidence or personal observation to back them up. In other words, you are delusional believing nonsense that your irrational brain got from god knows what idiotic flawed warped nonsense 'reasoning'. Sorry, you must do better than that to convince anyone here of anything.
says humy

What makes you THINK that I'm trying to convince anyone of anything? I have stated my case, and if you don't believe what I've said, then that is up to YOU to not believe. Nobody is twisting your arm to even consider what I say, just as I don't have to take what YOU say at face value. Your personal attacks on me are of no problem to me. Humans like you are known for attacking those who bring a message. Jingles has said my dog's name correctly.

Aug 23, 2019
"Once up and running, such "multimegawatt" linear accelerators may provide just the right conditions to run the oxgen-generating reaction in reverse, as if turning back the clock of star formation."

Oh yes. This should prove to be a very interesting experiment.

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