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Hydrogen-6 Experiment Reveals Unexpected Properties of Neutron-Neutron Interactions

Among the most fundamental questions in nuclear physics is one that seems simple yet profound: How many neutrons can an atomic nucleus accommodate?

Recently, a research team from Johannes Gutenberg University Mainz (JGU) achieved a significant breakthrough—they successfully produced the hydrogen-6 isotope using electron scattering experiments for the first time. This extremely neutron-rich atom contains 1 proton and 5 neutrons. The experimental results revealed a series of surprising phenomena that may challenge our traditional understanding of nuclear structure.

Unexpected Discoveries in the Experiment​

The research team used the electron beam from the Mainz Microtron (MAMI) to bombard a lithium-7 target, successfully producing hydrogen-6 through an ingenious two-step process. Surprisingly, the experimental data showed:

  1. The ground state energy of hydrogen-6 is far lower than theoretical expectations
  2. The strength of neutron-neutron interactions is significantly higher than predicted by the standard model
  3. The conversion efficiency from lithium-7 to hydrogen-6 is abnormally high

Particularly noteworthy is that researchers found the production efficiency of hydrogen-6 reached its maximum value near a specific electron beam energy (about 855 MeV), suggesting the possible existence of some kind of energy resonance phenomenon.

The Mystery of Neutron-Neutron Interactions​

Traditional nuclear physics theory suggests that when the number of neutrons far exceeds protons, the nucleus should be extremely unstable. Indeed, hydrogen-6 is very short-lived, with a half-life of only about 10^-21 seconds (zeptosecond scale), but some of its properties are unexpected.

Most thought-provoking is the strength of neutron-neutron interactions. The standard nuclear force model predicts that interactions between neutrons should be relatively weak, but experimental data for hydrogen-6 indicates that in such an extremely neutron-rich environment, neutron-neutron interactions may be much stronger than expected.

Why is this the case? When the number of neutrons reaches a certain critical value, does the interaction between them undergo a qualitative change? These questions currently remain without definitive answers.

The Curious Relationship Between Lithium-7 and Hydrogen-6​

Another striking phenomenon is the relationship between lithium-7 and hydrogen-6. In traditional understanding, the transformation of lithium-7 (3 protons, 4 neutrons) to hydrogen-6 (1 proton, 5 neutrons) requires removing 2 protons and adding 1 neutron, which energetically does not seem very "natural."

However, the JGU experiment shows that under carefully controlled conditions, this conversion can be achieved relatively efficiently. This phenomenon suggests there may be some special correlation between lithium-7 and hydrogen-6 that is currently unknown.

Technical Breakthroughs in the Experiment​

It is worth mentioning that the success of this research was inseparable from technological innovation. The research team used an unconventional experimental setup:

  • A 45mm long, 0.75mm thick lithium plate
  • Electron beam traveling along the 45mm length
  • Three high-resolution magnetic spectrometers operating simultaneously

This special setup was made possible thanks to the excellent beam quality of the MAMI particle accelerator, particularly its highly focused and stable electron beam.

Implications for Future Research​

Research on hydrogen-6 is not only an exploration of extreme nuclei but may also prompt us to rethink the fundamental nature of nuclear forces. If neutron-neutron interactions exhibit abnormal strength under specific conditions, we may need to modify or extend existing theoretical frameworks.

A question worth pondering is: When the number of neutrons reaches a certain critical value, does some kind of qualitative change occur—where interactions are no longer simply linear superpositions but present entirely new patterns?

Equally thought-provoking is, if hydrogen-6 exhibits unexpected properties, what about hydrogen-7 (1 proton, 6 neutrons) or even heavier hydrogen isotopes? These extreme cases may open new windows for understanding the fundamental properties of atomic nuclei.

Outlook: The Value of Boundary Exploration​

Research on superheavy hydrogen isotopes, especially extreme cases like hydrogen-6, represents the frontier of boundary exploration in nuclear physics. Under these extreme conditions, nature often reveals its most profound mysteries.

If we can understand what allows 5 neutrons to combine (even if extremely briefly) with a single proton, we might come closer to understanding the essential nature of nuclear structure.

In scientific exploration, boundary cases are often catalysts for theoretical breakthroughs. Research on hydrogen-6 may be just such an opportunity, prompting us to reexamine the fundamental assumptions of nuclear physics and open new theoretical perspectives.

Want to get specific predictions and key observation points for hydrogen-6 research? I've compiled a set of predictive equations based on standard model extensions that might help design new experiments. See details