The EconomistNovember 23rd 2019 Science & technology 73O
ne fearraised by those who oppose
Britain’s leaving the European Union
without a deal is that the import of radioac-
tive isotopes for medicine would be at risk.
These short-lived substances might, peo-
ple worry, encounter bureaucratic obsta-
cles that slowed down their delivery and
thus increased the fraction lost to radioac-
tive decay.
Particular concern surrounds moly-
bdenum-99 (^99 Mo), the workhorse of diag-
nostic nuclear-imaging.^99 Mo, which has a
half-life of just 66 hours, decays into a sub-
stance called technetium-99m (99mTc) that
has a half-life of six hours. 99mTc emits gam-
ma rays, so its location in the body is easy
to see using appropriate cameras. And it
can be incorporated into a variety of chem-
icals, called radiopharmaceuticals, that ac-
cumulate preferentially in different bodily
organs. This lets doctors observe what is
going on in those organs. About 80% of di-
agnostic nuclear-imaging of this kind in-
volves 99mTc, so without a continuous sup-
ply of^99 Mo to make it from, this whole
branch of medicine would grind to a halt.
For American doctors, who carry out
40,000 scans a day involving 99mTc, the
threat is not hypothetical. In 2009 Ameri-
ca’s clinics and hospitals were cut off for
several weeks from their main supplier,
Canadian Nuclear Laboratories, by a leakthat caused the shutdown of the reactor
used to make the isotope. Last year the cut-
off became permanent when the reactor
was closed. There are other manufacturers,
but they are in Europe, South Africa and
Australia. So the American government is
encouraging new ones to step in—and is
sponsoring new ways to make the stuff.
The current process bombards uranium
enriched in a fissile isotope,^235 U, with
high-velocity neutrons from a reactor. Ab-
sorbing a neutron causes an atom of^235 U to
split in two (the same process lies at the
heart of nuclear power stations and ura-
nium atom bombs).^99 Mo is a common pro-
duct of this fission, and can be separated
chemically from the bombarded uranium
with reasonable ease.
Some people, however, think they have
better ways to make^99 Mo—ways that do
not involve a reactor. Niowave, a firm in
Lansing, Michigan, is one such. Instead of
neutrons, its researchers are firing high-
velocity electrons at enriched uranium.
They speed the electrons up to something
approaching that of light using a machine
called a linear accelerator, then launch
them into a uranium target, splitting its(^235) U atoms, after which (^99) Mo can be extract-
ed from the target in the normal way.
Niowave’s accelerator employs super-
conductivity to generate the powerful elec-
triccurrentsneededto achieve all this.
That requires a suitable material, niobium,
to carry the current, and a suitable tem-
perature, that of liquid helium, to make the
niobium superconducting.
Mike Zamiara, Niowave’s boss, says the
firm has already made test batches of^99 Mo.
The company plans to pump up the volume
over the next few years. The aim is to reach
commercial levels in 2025. By 2026, Mr Za-
miara says, Niowave should be able to sup-
ply 40% of American demand.
Phoenix, a firm in Monona, Wisconsin,
plans to make^99 Mo more convention-
ally—by neutron bombardment. The un-
conventional part of its approach is the
neutrons’ source. Instead of a fission reac-
tor, Phoenix employs a small-scale version
of a process that some hope will one day
lead to fusion reactors (and which already
lies at the heart of hydrogen bombs). Like
Niowave’s, this method starts with a parti-
cle accelerator. The particles accelerated,
though, are not electrons but deuterons.
A deuteron is the atomic nucleus of a
type of heavy hydrogen called deuterium,
and consists of a proton and a neutron.
Phoenix’s neutron generators fire deuter-
ons into chambers full of tritium, an even
heavier form of hydrogen that has a proton
and two neutrons as its nucleus. A high-
speed collision between a deuteron and a
tritium nucleus causes the two to fuse, cre-
ating helium (two protons and two neu-
trons) and spitting out a neutron. Properly
tweaked, such a neutron generator can pro-
duce 46 trillion of the particles a second.
Evan Sengbusch, Phoenix’s president,
says the company is supplying eight accel-
erators for a new isotope factory to be run
by its collaborator, shineMedical of Janes-
ville, also in Wisconsin. shine’s boss, Greg
Piefer, says the facility will be finished in
2021, with the first production shortly
thereafter. By 2023, he hopes, shinewill be
the biggest supplier of^99 Mo in the world. 7
New ways to make a crucial medical isotope
Diagnostic nuclear-imaging
Moly-coddling
Painted by technetium
Flying into the atmosphere
Source:“TheProductionGap”bySEI,IISD,ODI,
ClimateAnalytics,CICEROandUNEP, 2019
Forecast global CO2 emissions from fossil fuels
Gigatonnes
FORECAST
0
10
20
30
40
2010 15 20 25 30 35 40
Impliedbycountries’fossil-fuelproductionplans
Impliedbyemissions-reductionpledges
Neededtolimitglobalwarmingto2°C
Needed to limit global warming to 1.5°C
Range
Median
At a summit in Paris in 2015, 188 countries
pledged to curb their greenhouse-gas
emissions. Collectively, these pledges,
known as “nationally determined
contributions” or NDCs, fall well short of
what is needed to achieve another part of
the Paris agreement, which is to avoid
more than 2°C of warming above
pre-industrial temperature levels. A
report by the United Nations Environment
Programme finds, however, that even
these unambitious targets will probably
be missed. Researchers studied policy
documents from big fossil-fuel-producing
countries to calculate how much coal, oil
and natural gas is likely to be extracted
over the next 20 years. According to these
documents, global CO 2 emissions from
fossil fuels will reach 41 gigatonnes by
- That is higher than the 36
gigatonnes implied by the NDCs—and well
above the 19 gigatonnes needed to keep
warming below 2°C.
Shortfall