Precise measurement of radioactivity in tiny samples
iStock.com/Dan Comaniciu
Researchers at the US National Institute of Standards and Technology (NIST) claim to have developed a new and faster method for detecting and measuring the radioactivity of minuscule amounts of radioactive material.
T
heir innovative technique, known as
cryogenic decay energy spectrometry (DES), could have far-reaching impacts, from improving cancer treatments to ensuring the safety of
the capability to record individual radioactive
nuclear waste clean-up. It has been described
decay events, in which an unstable atom releases
in the journal Metrologia.
one or more particles. By building up data from many individual decays, researchers can
Rapid detection and measurement
then identify which unstable atoms, known as
Traditional methods have proved effective at
radionuclides, produce the events.
either measuring the amount of radioactivity or
“The TES is much more advanced than a
identifying which radioactive atoms are present
familiar Geiger counter or other detectors used
— not both. Fully characterising a sample thus
today,” Fitzgerald said. “Instead of just clicking to
required the use of multiple techniques and
indicate radiation, or giving a blurry indication of
intricate procedures using additional materials
the decay energy, it gives us a detailed fingerprint
called tracers or calibrants.
of what’s there.”
Inkjet precision
The new method offers a streamlined
The TES device operates at extremely low
In their method, the researchers use a specialised
approach, identifying radioactive elements and
temperatures, near absolute zero. When a
inkjet device to carefully dispense tiny amounts,
quantifying their level of radioactivity in even
radioactive decay occurs in a sample, the energy
less than 1 millionth of a gram, of a radioactive
tiny samples — without needing extra materials.
released is absorbed by the TES. This absorbed
solution onto thin gold foils. These gold foils have
This allows scientists to better monitor, use and
energy causes a tiny change in the electrical
a surface dotted with tiny pores just billionths of a
safeguard radioactive materials that affect public
resistance of the TES.
metre in size. These nanopores help to absorb the
health and safety.
The researchers precisely measured this
tiny droplets of the radioactive solution.
“Instead of waiting months for results, we
change in resistance, which provides a high-
By precisely measuring the mass of the
can now get a full radioactivity profile in just a
resolution ‘energy signature’ of the decay event.
solution that was dispensed using the inkjet and
few days from a tiny sample,” said NIST physicist
By analysing the detailed energy spectrum from
then measuring the radioactivity of the dried
Ryan Fitzgerald.
multiple events, the researchers can identify the
sample on the gold foils, the researchers can
The key to the technique is a transition-edge
specific radioactive atom undergoing decay. This
calculate the radioactivity per unit mass, or the
sensor (TES), a high-tech device widely used to
is possible because different radioactive atoms
‘massic activity’, of the sample. This inkjet method
measure radiation signatures. The TES provides
release unique energy signatures when they decay.
allows them to work with extremely small amounts
30 | LAB+LIFE SCIENTIST - August/September 2025
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