In 2017, the COHERENT collaboration at the Oak Ridge Spallation Neutron Source produced the first detection of coherent elastic neutrino-nucleus scattering (CEvNS) — a prediction made by Daniel Freedman in 1974 and waited 43 years to confirm. The COHERENT measurement used pion-decay neutrinos at moderately high energies (a few tens of MeV) in a pulsed beam.
Since then, attention has shifted to a complementary regime: CEvNS at reactor antineutrino energies (a few MeV). Reactor measurements present harder technical challenges — much lower nuclear recoil energies (typically below 1 keV), continuous flux without the pulsed timing structure that COHERENT exploited, and very strict background requirements. But the physics potential is substantial. Reactors provide intense, well-characterized antineutrino sources, and reactor CEvNS measurements probe a different kinematic regime than COHERENT’s accelerator-based detection.
Three experiments are leading the development of reactor CEvNS detection: NUCLEUS at the Chooz reactor in France, CONUS at the Brokdorf reactor in Germany, and RICOCHET at the Institut Laue-Langevin (ILL) research reactor in Grenoble. Each uses a different detector technology; each is pushing toward precision CEvNS measurements that will sharpen tests of the Standard Model and constrain new-physics scenarios.
This article surveys the three programs.
Why reactor CEvNS
Reactor antineutrinos arrive at typical energies of 1-10 MeV with a known spectrum. They are produced in enormous quantities — a typical commercial reactor emits about 6 × 10²⁰ antineutrinos per second.
For CEvNS detection, reactors have several advantages compared to accelerator-based sources.
High flux. The antineutrino flux at distances of a few tens of meters from a reactor is much higher than from any practical accelerator-based source. This compensates for the smaller cross-section at the lower energies.
Continuous operation. Reactors run continuously rather than in pulses, allowing long integration times to accumulate statistics.
Well-understood spectrum. Decades of reactor antineutrino physics — particularly from Daya Bay, RENO, and the broader reactor-experiment program — have characterized the reactor antineutrino spectrum to a few percent precision.
Different kinematics. The lower reactor-antineutrino energies produce different recoil energy spectra in the target nuclei than higher-energy accelerator neutrinos. The complementary kinematic regime provides cross-checks and tests of the CEvNS theoretical predictions across a wide energy range.
The challenges, on the other hand, are real. Nuclear recoils from CEvNS at reactor energies are typically below 1 keV — often below 100 eV. Detector technologies capable of identifying such low-energy recoils with high efficiency, while maintaining sufficiently low backgrounds, are at the cutting edge of nuclear-physics instrumentation.
NUCLEUS at Chooz
The NUCLEUS experiment is located at the Chooz B nuclear power plant in northeastern France — the same facility that hosts the Double Chooz long-baseline reactor experiment. NUCLEUS deploys a compact cryogenic detector at about 100 meters from the reactor core.
The detector uses calcium tungstate (CaWO₄) crystals operated as transition-edge sensors at sub-Kelvin temperatures (typically around 15 millikelvin). When a neutrino-induced nuclear recoil deposits a tiny amount of energy in the crystal, the resulting temperature pulse is registered by the transition-edge sensor. The crystals also emit scintillation light, providing a second signal that helps distinguish nuclear recoils from electromagnetic-background events.
The choice of calcium tungstate gives NUCLEUS sensitivity through both calcium (relatively light) and tungsten (relatively heavy) nuclei. The cross-section scales approximately as the square of the neutron number, so tungsten contributes substantially more per nucleon than calcium. The mixed-target nature allows NUCLEUS to test the predicted N² scaling of the CEvNS cross-section.
NUCLEUS’s target mass is currently about 10 grams — small by 0νββ-experiment standards but compensated by the high reactor antineutrino flux at the short standoff distance. The total expected event rate is on the order of tens of CEvNS events per kilogram-day at the relevant kinematic regime.
The first NUCLEUS science runs are accumulating data, with first-detection results expected in the next few years.
CONUS at Brokdorf
CONUS (Coherent Neutrino-Nucleus Scattering) operated at the Brokdorf nuclear power plant in northern Germany from 2018 onward. The experiment used high-purity germanium detectors — the same technology used in LEGEND-style 0νββ experiments but optimized for very-low-threshold operation rather than for 0νββ.
The germanium detectors had an energy threshold around 300 eV — high enough to miss the lowest-energy CEvNS recoils but adequate for the higher-recoil-energy tail of the CEvNS spectrum.
CONUS’s results, published across several papers, set competitive limits on CEvNS at reactor energies and constrained various beyond-Standard-Model physics scenarios. The experiment was decommissioned after Brokdorf was shut down in late 2021 (as part of Germany’s nuclear-phaseout policy).
A successor experiment, CONUS+, has been deployed at a different German reactor and continues the program with improved detectors and a longer planned run.
RICOCHET at ILL Grenoble
RICOCHET is deployed at the Institut Laue-Langevin research reactor in Grenoble, France — the same facility that hosts the STEREO experiment for short-baseline sterile-neutrino searches. RICOCHET uses cryogenic bolometers of various materials (germanium, zinc, and other targets) to achieve very low energy thresholds.
The ILL reactor is a research reactor (58 MW thermal) rather than a power reactor, with somewhat different characteristics — particularly highly-enriched uranium-235 fuel and a known operating pattern. This makes the reactor antineutrino flux at ILL particularly well-characterized, which is valuable for precision CEvNS measurements.
RICOCHET’s target masses are at the kilogram scale, and its energy threshold approaches 100 eV — well into the regime where CEvNS recoils dominate. The detector is positioned about 10 meters from the reactor core, providing high antineutrino flux.
What the experiments will test
Reactor CEvNS measurements at the precision these experiments target will probe a range of physics.
Standard Model verification. The CEvNS cross-section is predicted by the Standard Model with about 2-3% theoretical uncertainty. Precision measurements at this level test the theory directly. Significant deviations would indicate new physics.
Non-standard neutrino interactions (NSI). Various proposed extensions of the Standard Model predict modifications to neutrino-nucleus cross-sections that would show up in CEvNS measurements. The reactor experiments will constrain these scenarios at precision levels not previously achievable.
Sterile neutrinos. Sterile neutrinos at the parameters suggested by various anomalies could affect the reactor antineutrino spectrum at short distances. CEvNS detection is sensitive to these effects independently of the inverse-beta-decay channels that constrain the reactor anomaly.
Neutrino magnetic moments. A non-zero neutrino magnetic moment would produce an additional electromagnetic contribution to neutrino-electron scattering and (at low energies) to neutrino-nucleus scattering. Precise CEvNS measurements probe magnetic-moment values below current limits.
Coupling structure. The detailed kinematic dependence of CEvNS depends on the relative contributions of vector and axial-vector couplings. Precision measurements help characterize the weak-interaction couplings at low energies.
Future directions
Beyond the current generation of experiments, several additional efforts are in development.
Larger target masses. Future reactor CEvNS experiments are planning kilogram-to-ton-scale targets, with correspondingly higher statistics. The technology to scale up the cryogenic-detector arrays is mature; the bigger challenges are typically infrastructure and operational rather than fundamental.
Higher precision. Current measurements have statistical and systematic uncertainties at the 10-20% level. Future experiments aim for sub-percent precision, sufficient to discriminate between competing theoretical models.
Different targets. The CEvNS cross-section scales as N², so different target nuclei produce different recoil-energy distributions. Future experiments will deploy a wider range of target materials to characterize the cross-section across the periodic table.
Combination with COHERENT-style sources. A complete CEvNS picture requires measurements at both reactor and accelerator energies. The reactor experiments and ongoing COHERENT measurements complement each other.
The non-proliferation application
Beyond pure physics, the development of compact, low-threshold CEvNS detectors has direct applications for reactor monitoring. A successfully demonstrated CEvNS detector at the kilogram scale, capable of characterizing a reactor’s antineutrino spectrum, can in principle be deployed for non-proliferation monitoring purposes.
NUCLEUS, CONUS, and RICOCHET are not directly non-proliferation experiments. But their work develops the underlying technology that could eventually support deployment for safeguards monitoring. The dual-use nature of the technology — fundamental physics demonstrations that also support safeguards capability — has helped justify the funding and effort going into these programs.
A precision program building toward maturity
The three experiments are at slightly different stages of development. CONUS produced first measurements and was succeeded by CONUS+. NUCLEUS is accumulating data toward first-detection publication. RICOCHET is in commissioning and early science phases.
By the late 2020s, the combined results from these experiments — plus the ongoing COHERENT measurements at accelerator-based sources — should produce CEvNS measurements at precisions sufficient to test the Standard Model at the few-percent level and constrain various new-physics scenarios.
The CEvNS field is, in many ways, in the early stages that the broader neutrino field was in the 1960s — a fundamental interaction has been confirmed, and the precision-measurement program is just beginning. The decade ahead will produce substantial advances in both the underlying physics understanding and the practical applications that follow from the technology.
For the discovery of CEvNS, see CEvNS: the neutrino interaction that took 43 years to detect. For the non-proliferation application, see Reactor neutrino monitoring. For the related reactor-antineutrino oscillation experiments, see Daya Bay and RENO and PROSPECT/STEREO.
Frequently asked
What are NUCLEUS, CONUS, and RICOCHET?
These are three of the leading experiments developing compact cryogenic detectors to measure coherent elastic neutrino-nucleus scattering (CEvNS) at nuclear reactors. NUCLEUS uses cryogenic calcium tungstate crystals at the Chooz reactor in France. CONUS uses germanium detectors at the Brokdorf reactor in Germany. RICOCHET uses cryogenic bolometers at the Institut Laue-Langevin reactor in Grenoble. All three target CEvNS measurements at reactor antineutrino energies.
Why measure CEvNS at reactors?
Because reactors provide an extraordinarily intense, well-understood source of low-energy antineutrinos — the right energy range for CEvNS. Measuring the CEvNS cross-section precisely tests the Standard Model prediction and constrains a wide range of beyond-Standard-Model physics, including non-standard neutrino interactions, sterile neutrinos, neutrino magnetic moments, and certain dark-matter scenarios.
How is reactor CEvNS detection different from the COHERENT measurement?
COHERENT made the first detection of CEvNS using pion-decay neutrinos at a spallation neutron source — relatively high energies and a pulsed beam structure. Reactor CEvNS uses much lower-energy antineutrinos in a continuous flux. The advantages of reactor measurements include the higher antineutrino flux, the better-understood antineutrino spectrum, and the smaller detector mass required per event due to favorable cross-sections at the relevant energies.
What do these detectors require?
Extremely low energy thresholds — nuclear recoils from CEvNS at reactor energies are typically below 1 keV, often below 100 eV. This requires either cryogenic detectors operating at sub-Kelvin temperatures (NUCLEUS, RICOCHET) or specially-developed semiconductor detectors with very low electrical noise (CONUS). The detector backgrounds also need to be very low, requiring careful materials selection and shielding.
What does this enable for non-proliferation monitoring?
Demonstrated CEvNS detection at reactors validates the underlying physics that compact reactor-monitoring detectors would use. If CEvNS-based detectors at the few-kilogram scale can characterize a reactor's antineutrino spectrum, the same technology can in principle be deployed for verification of nuclear-fuel composition and reactor operation as part of non-proliferation monitoring frameworks.
Cite this article 5 formats
APA
Neutrino Times Editorial Team. (2026, January 28). NUCLEUS, CONUS, and RICOCHET: the reactor CEvNS experiments pushing for percent-level precision. Neutrino Times. https://neutrino-times.com/articles/nucleus-conus-ricochet-reactor-cevns-experiments/
Chicago
Neutrino Times Editorial Team. "NUCLEUS, CONUS, and RICOCHET: the reactor CEvNS experiments pushing for percent-level precision." Neutrino Times, January 28, 2026. https://neutrino-times.com/articles/nucleus-conus-ricochet-reactor-cevns-experiments/.
MLA
Neutrino Times Editorial Team. "NUCLEUS, CONUS, and RICOCHET: the reactor CEvNS experiments pushing for percent-level precision." Neutrino Times, 28 Jan. 2026, https://neutrino-times.com/articles/nucleus-conus-ricochet-reactor-cevns-experiments/.
BibTeX
@misc{neutrino-times-nucleus-conus-ricochet-reactor-cevns-experiments,
author = {Neutrino Times Editorial Team},
title = {NUCLEUS, CONUS, and RICOCHET: the reactor CEvNS experiments pushing for percent-level precision},
howpublished = {Neutrino Times},
year = {2026},
month = {jan},
url = {https://neutrino-times.com/articles/nucleus-conus-ricochet-reactor-cevns-experiments/},
note = {Accessed: 2026-01-28}
} RIS
TY - GEN TI - NUCLEUS, CONUS, and RICOCHET: the reactor CEvNS experiments pushing for percent-level precision AU - Neutrino Times Editorial Team PY - 2026 DA - 2026-01-28 PB - Neutrino Times UR - https://neutrino-times.com/articles/nucleus-conus-ricochet-reactor-cevns-experiments/ ER -