- 01 Overview
- 02 TITAN Science Highlights
- 03 How it Works
TITAN, TRIUMF’s Ion Trap for Atomic and Nuclear science, is one of the world’s fastest and most precise tools for measuring the mass of a single atom, and the only facility able to do so with highly charged, rare isotopes.
The most scientifically interesting isotopes for nuclear science research are those at the extreme, ones that have an extreme, rather than stable, ratio of neutrons and protons. The challenge is that extreme isotopes are also very unstable: they radioactively decay to more stable isotopes in hundredths-of-a-second. So, TRIUMF researchers need to produce, prepare and measure these isotopes in far less time than the blink of an eye.
The current TITAN world-record is for lithium-11 (11Li), measured with TITAN in under four hundredths-of-a-second. TITAN also holds the record for the mass measurements of the next 10 shortest-lived isotopes. TITAN’s measurements are scientifically valuable because they are enormously precise and accurate. Its mass measurement sensitivity is analogous to being able to determine whether or not, on a 747-airplane loaded with passengers, one person is missing a single page from her passport. TITAN’s world-leading precise mass measurements of extremely neutron-rich, or poor, isotopes are providing unique insights into nuclear structure, tests of the Standard Model via fundamental symmetry studies, and key astrophysical reaction paths. These measurements are also providing the foundation for extending nuclear physics as an applied field. The rare isotope mass measurements, for example, could point the way to new isotopes for nuclear medicine to treat cancers, and new ways to treat and handle nuclear wastes.
02 TITAN Science Highlights
The Case of the Missing NeutrinosThe Case of the Missing Neutrinos: After 15 years of solar-neutrino measurements, 13% of the theoretically expected flux, or number, of neutrinos is unobserved. This is leading physicists to explore a variety of possible reasons, from the underlying nuclear physics to detector design. One proposed reason is the energetic cost of the detector material to capture a neutrino. To explore this, TITAN deployed its high-accuracy, high-precision Penning trap, the only one in the world coupled to a charge breeder. The charge breeder's removal of electrons boosted the precision of the measurements with gallium and germanium isotopes and allowed for a novel radioactive-beam purification. As reported in Physical Letters B (2013), TITAN measurements validate the final piece of the nuclear physics underpinning the predicted neutrino flux, and thus the cause of the missing neutrinos remains an open case.
Mass cartography of the island of inversion points to strong correlation energyMass cartography of the island of inversion points to strong correlation energy: Analogous to electron shells in chemistry, neutrons and protons occupy similar, exceptionally stable configurations, which are seen as sharp ridges in mass cartography. As the ratio of protons to neutrons changes, this stability can disappear, for example around sodium-31 (31Na). The neighbourhood is difficult to examine due to low production rates and half-lives, too short for a typical Penning-trap mass spectrometer. TITAN, however, routinely measures isotopes with half-lives below 50 ms, or thousands of a second. TITAN's ongoing survey reveals a singularity: The energy, or mass cost, of two neutrons is higher for magnesium-33 (33Mg) than for aluminum-34 (34Al). As reported in Physical Review C (2015) investigating with premier shell-model calculations points to gains in correlation energy as the cause.
TITAN reveals shell model breakdown at the extremeTITAN reveals shell model breakdown at the extreme: Certain combinations of protons and neutrons form exceptionally stable nuclei. While these closed-shell configurations are well understood in stable nuclei, they change in exotic nuclei. Previous mass determinations with TITAN found a closed shell for calcium (Ca) with 32 neutrons. Now, as reported in Physical Review Letters (2018), TITAN’s measurements of neighbouring titanium isotopes shows that the shell weakens more quickly than predicted by state-of-the-art nuclear theory. The results are also noteworthy as TITAN’s first measurements with its Multi-Reflection Time-Of-Flight mass separator (MR-TOF). The MR-TOF has a remarkable sensitivity, able to make precise measurements with just a single radioactive nucleus.
03 How it Works
TITAN determines an ion’s mass by measuring its energy frequency. This is because mass and energy are interchangeable, as revealed by Einstein’s famous equation E=mc2 where Energy = mass x (speed of light) squared.
To make a mass measurement, TITAN uses a multistep process to produce, prepare, contain and measure ions, and a variety of ion traps, devices that use electric and sometimes magnetic fields to confine charged isotopes, or ions, within a small space.
First, charged isotopes produced by ISAC arrive at TITAN via a beamline and are stopped, and bunched by electric and radiofrequency fields and cooled through collisions with neutral helium gas.
Second, the ion can be further charged. This is important because the higher the charge state of an isotope the more precise the mass measurement. To do this, TITAN’s second stage includes an Electron-Beam Ion Trap in which charged isotopes can be bombarded with high-energy electrons. This physically strips electrons via impact ionization to produce very positively charged ions, which are then sorted and selected based on their charge.
Third, the ions, re-energized by the electron bombardment, are cooled using TITAN’s unique Cooler Penning Trap. Ironically, it operates by sending the ions through a plasma of electrons. It’s analogous to a kind of electron wind tunnel in which the ions are all cooled to a common energy but pass through the electrons so quickly the electrons don’t bond with the ions.
Finally, it’s time for the cyclotron frequency measurement and mass calculation. This is done using a Penning ion trap, which provides the most accurate and precise mass measurement of any technique.
In the Penning trap, the ions are confined using a strong magnetic field to hold them side-to-side in the trap, and a static electric field to confine them front-to-back.
What’s critical is that since the magnetic field strength and the ion’s charge are known, TITAN scientists can calculate the ion’s mass by measuring its cyclotron frequency in the Penning trap.
To do this, TITAN scientists pulse the ions with fine-tuned radiofrequencies, measuring whether this changes how long it takes an ion to travel from the trap to a detector. When the radio frequency is identical to the ion’s cyclotron frequency there’s a resonance, and the ion experiences an energy kick, travelling faster to the detector. Now the scientists know the ion’s exact frequency, or energy level, and can precisely calculate its mass.
What’s all the more remarkable is that this measurement requires that TITAN scientists control the trap to hold a single ion at a time. The measurement of two ions together might include the mass of the energetic interaction between the ions.
You can learn more on the TRIUMF TITAN website.