Nature of spontaneous signal and detection of radiation emitted from hydrogen Rydberg matter

Research groups from Gothenburg University have reported that when hydrogen flows through an iron oxide Rydberg state catalyst containing potassium, clusters of hydrogen Rydberg matter (HRM) are formed, which will eventually emit radiation.¹ This article comprehensively addresses the longstanding need for independent examination and experimental exploration of these published results.

The signature of radiation from HRM can be obtained in two ways: laser pulse-induced radiation and spontaneous radiation that initially needs activation. The laser-induced radiation that is observed when periodic laser pulses are made incident on a metal target results in an extremely fast bunch of particles with energy much higher than that observed in a laser ablation process. It can be interpreted as fast 10–50 keV electrons or 10–50 MeV protons depending on the assumed mass in the time-of-flight estimation. The researchers have also reported on the production of gamma rays, neutrons, and electron–positron pairs.^2–5 Spontaneous radiation initially needs to be activated using a laser and has a different type of radiation⁶ of unknown origin. The research group utilized a special simple detector setup to study the characteristics of this radiation in 2014.⁷ The functionality of the detector is discussed in Refs. 1, 8, and 9. In these papers, Professor Leif Holmlid (LH) et al. presented and concluded that muons and mesons are being emitted as the spontaneous radiation signal.

No research group has published a replication paper of this radiation as LH has reported.^6,10–12 The following work has been done experimentally in two labs over the past four years: one at the University of Iceland and one at the company Norrønt AS in Norway. This was done in cooperation with LH at University of Gothenburg. The experimental work, data collection, analyzing software, and methods have evolved significantly over these years, with instrumentation built in Norway and Iceland at the same time. The observation of laser-activated spontaneous radiation has been verified in both labs with different scientific equipment and equal and different detectors. This paper outlines the instrumentation and detection mechanisms, presents the experimental results, and delves into a discussion of the potential nature of this spontaneous radiation.

A picture of the experimental setup for hydrogen Rydberg matter research is shown Fig. 1.

A bent aluminum rack is used for testing isotropic radiation properties during experiments. A schematic drawing of the same experimental setup for hydrogen Rydberg matter research along with the placement of detectors is shown in Fig. 2. It is similar to that described by LH in Ref. 13.

A schematic of the experimental setup is shown in Fig. 2.

The experiment uses a 6-in. spherical octagon UHV chamber made of stainless steel 304L obtained from Kimball Physics to house a catalyst and a laser target. A 10 Hz pulsed Nd:YAG laser (532 nm) with a maximum pulse energy of 500 mJ and a pulse duration of 8 ns is used during the experiments. The laser beam is focused above a metal target in the chamber’s center with an f = 270 mm short-pass dichroic spherical lens. A set of mirrors is mounted on three-axis stages, allowing the laser beam focal spot to be moved during experiments. The metal laser target is also attached to an XYZ motion manipulator to control the target position during measurements. The laser target is constructed with a 0.5-mm-thick 99.999% tantalum foil.

The hydrogen Rydberg matter source is constructed from a solid block of stainless steel 321 with perforated holes where Rydberg state catalysts are placed. A laser target is shaped into a foil cone and placed in the center. An ATEX-certified high-temperature band heater surrounds the source and provides heat to the catalysts and the laser target foil. Hydrogen and deuterium gases will flow through the gas lines into the cone and through the catalysts. Pt-100 temperature sensors are attached to the laser target and the catalyst holder for temperature control during experiments. The Rydberg state catalysts are made from iron oxide and doped with potassium. The source is usually heated with a 3 A AC source, resulting in an operating temperature of 110–180 °C.

The hydrogen gas source is of 99.999% purity and is admitted through a needle valve, which gives a steady gas pressure in the range of 10⁻³ to 10⁻⁷ mbar. An Edwards E2M28 Rotary Vacuum Pump and a TMU 261 turbomolecular pump can evacuate the chamber to a base pressure of 10⁻⁷ mbar.

The activation process involved in producing hydrogen Rydberg matter is the same as described by LH in the article.^14,15 The typical activation process involves filling the chamber to 10 bar and flowing heated hydrogen gas through the catalyst. The catalysts, target, and hydrogen gas need to interact in the chamber for days before activation can be seen. Therefore, the initial activation of a new experiment may take several weeks.

Surface contaminants, such as silicon and oxide, can make activation harder. Therefore, all components of the chamber went through methodical cleaning methods for the removal of impurities. The cleaning methods used are described by Taraborelli.¹⁶ 

Following activation, the system enables the measurement of both laser-induced and spontaneous radiation. A detector, placed at a distance of 0–16 m from the reactor, is used to capture the radiation. The arrangement used to detect radiation from hydrogen Rydberg matter is depicted in Fig. 3. This setup mirrors the detector and the method used by LH et al.¹¹ 

The photomultiplier tube (PMT) detector used in most of these experiments is a 9813B from ET Enterprises¹⁷ with a spectra range between 290 and 630 nm and a rise time of 4 ns. The PMT is equipped with a 638D voltage divider with a negative high voltage (HV) DC-coupled anode load, designed for photon counting and high-energy physics.¹⁸ The nonlinear resistor configuration provides higher amplification at later dynode stages and can cope with short bursts of pulses with variable intensity. The PMT is set at −1600 V and connected to an Ortec V120 preamplifier with a bandwidth of 10–350 MHz and a fast amplification gain of 200. This makes the electronics sensitive to external noise pickup, and careful screening is therefore needed to minimize its influences. Usually, a charge-integrating preamplifier is connected to a PMT that absorbs any noise. In addition, a pulse shaping amplifier (Ortec 440A) with a shaping time of 0.5 μs was used to increase the possible count rate during measurements. The signals from the PMT are analyzed using a 2048 multichannel analyzer (MCA) (Ortec EASY-MCA-2k) with the Maestro software with a standard acquisition time per spectrum of 500 s. The PMT detector is constructed of a light-tight and vacuum-tight enclosure made of a KF-50 stainless steel tube and flanges. The 5 mm cap covering the front of the PMT housing can be changed from Al to SS. The experiment uses a 5 mm Al cap, a 5 mm SS cap, a combination of both, or black fabric. The aluminum attached to the surface of the PMT is a 15 μm aluminum foil folded 2–8 times and mounted on the front of the PMT glass with no grounding. The standard number of foil layers was 4, which are attached directly to the glass. During changes in detector operation, the casing was opened in darkness without applying HV to the PMT.

The heart of all radiation detectors is the scintillator, which interacts with the incoming radiation. Here, Al foils are used in the same manner as done by LH.¹¹ This is not expected to be a full-energy scintillator by any means, as no scintillation crystal is used. Figure 4 shows the detector’s response.

To ensure optimal functionality of the detector, it is crucial to operate the photomultiplier tube (PMT) at a high amplification level. This requirement stems from the diminished scintillation signal observed when aluminum foils are affixed to the PMT’s surface. The operating voltage set for the PMT is 1600 V, which is below the maximum allowable voltage of 2100 V.

Figure 4 presents the spectral analysis for a chamber exhibiting slight activity as the quantity of aluminum (Al) layers is adjusted. Notably, the detector demonstrates a significantly enhanced signal across all channels when equipped with four layers of aluminum foil, showcasing an intensity more than tenfold higher than that with a single layer. The interval between consecutive measurements was ∼2 min. Throughout this process, the PMT’s position remained constant, with no adjustments made to its location or the experimental settings. These measurements were meticulously conducted by the author, ensuring consistency and reliability in the data obtained.

When the PMT does not have an aluminum foil, the detector only shows the dark current spectrum. Most of the intensity increases are found in the first 10–50 channels of the spectrum. The higher pulse spectrum changes but has a qualitatively similar behavior. The aluminum layers are immersed in air containing moisture; therefore, a scintillation mechanism is possible here, and radiation of any kind can cause local photoelectron excitation through an aluminum oxide layer. This can cause local charging and local potential formation, which, combined with the acceleration of ionized air molecules, causes scintillation photons in the energy range up to 100 eV to pass at least some of the aluminum foils and reach the PMT quartz surface. This scintillation arrangement has one obvious consequence: it absorbs only a small part of the energy contained in high-energy particles. These events are shifted down in energy and intermixed with particles that have a lower energy, which can be seen in Fig. 4.

Photoelectron multiplier tubes (PMTs), when placed in total darkness, always show the presence of a dark current or dark pulses. Dark pulses originate mainly from thermal electron emission at the photocathode and the dynodes. Thermionic emission of electrons is the main source of the dark current in PMTs at room temperature. When PMTs are cooled, the thermionic dark current decreases with temperature according to Richardson’s law.¹⁹  Figure 5 shows the PMT setup submerged in dry ice.

Due to this radiation behavior, we cooled the PMT to observe the change in the dark counting rate.

The effect of cryogenic cooling on the PMT with the four-layer aluminum foil in front is shown in Fig. 6. The PMT housing with the PMT, voltage divider, and preamplifier was placed in a Styrofoam box before the detector was surrounded with dry ice pellets. Dry ice cooled the PMT to −87 °C (measured with a non-calibrated low-temperature sensor). We record the spectrum and temperature during cooling and the reduction in counts using an Ortec EASY-MCA-2k. The count rate at room temperature was 170 cps; this gradually drops to 72.5 cps at −87 °C.

In a study by Krall,²⁰ gamma rays and charged particles were observed to cause scintillation within PMT glass. To characterize the spectrum of gamma in a PMT with aluminum foil, we placed two sources, Cs¹³⁷ and Na²², 30 cm in front of the detector. Cs¹³⁷ is a radioactive isotope that emits both beta particles and gamma rays. During its decay process, Cs¹³⁷ transforms into Ba-137m, a metastable isomer responsible for gamma emission. The Cs¹³⁷ source used in the calibration had a steel cap that blocked beta radiation.

The spectra shown in Fig. 7 are from the detector with four layers of aluminum foil and PMT when exposed to different point sources, showing the PMT sensitivity to gamma rays from both Cs¹³⁷ and Na²² sources. PMT count rates are measured when exposed to Cs¹³⁷ and Na²² point sources, where Cs¹³⁷ emits 662 keV gamma rays, while Na²² emits 511 and 1275 keV gamma rays. The count rate increases as expected when the detector is exposed to a radioactive source. No pulses above channel 440 can be seen in the spectra with little correlation to the energy of the gamma source. Therefore, no energy information can be gained from the spectra. Therefore, the detector acts almost like a blind Geiger counter.

In Fig. 8, we measure the Na²² source 30 cm in front of the detector at three different times during the day to look for time variations, fluctuating counts, or voltage supply changes that power the PMT.

In Fig. 8, a Na²² source is positioned in front of the detector and measurements are performed during the day to check the stability of the detector. Fluctuations in the electronics and HV power supplies could cause the count rate to vary during the day while the radiating source is fixed. As we can see in the spectra, the detector response shows a mean of 346.33 cps with a standard deviation of 1.7.

The catalyst is activated by flowing heated hydrogen through the catalyst and then keeping the catalyst immersed in 100–250 mbar pressure of H₂ gas for a longer period of 2 h. After some time, the catalyst starts to emit isotropic radiation that can be detected up to several meters away with the PMT detector. Isotropic radiation has been confirmed by moving the detector around the experiment. This change in intensity observed by the PMT detector before and after activation can be seen in Fig. 9. To observe this radiation, the PMT has to be enclosed in a light-tight enclosure and have aluminum attached to the front glass of the PMT.

The figure shows that PMT counts from an activated catalyst producing hydrogen Rydberg matter increase by a factor of 8. The intensity not only increases in the region between channels 0 and 800 but also produces a second peak between channels 1000 and 1700. The suspected radiation appears to pass through 3–10 mm of steel walls in the chamber, 2 m of air, a 5 mm solid aluminum flange, and four layers of aluminum foil before being detected in the PMT. Radiation cannot be detected if the aluminum foil on the front glass of the PMT is removed. The spectra do not vary with the position of the detector around the chamber but are slightly changing in intensity with distance from the source.

Activation of the catalyst and chamber can give different emitted intensities of radiation. A historic record of the increase in intensity recorded using the PMT + Al assembly for 2 years can be seen in Fig. 10.

The historic record of the intensity of radiation detected using the PMT + Al detector from HRM was seen to depend greatly on the operating parameters of the catalyst, impurities, gas composition, and the laser interaction parameter with HRM on the target.

When the intensity was recorded, the detector was placed 2 m away from the hydrogen Rydberg matter source. When irradiating hydrogen Rydberg matter with a low-energy laser, we can increase the emitted radiation from the chambers by a factor of above 200. During periods when data are missing, either the reactor was under construction or decommissioning, or other experiments were running. The background level of the PMT found at that time was in the 175–200 cps range.

The intensity of the radiation from the catalyst activated by D₂ gas can be seen in Fig. 9. The PMT is positioned 188 cm away from the chamber and has 120 μm thick aluminum foil (eight layers) in front. Note here that we use a PMT detector with a 5 mm SS steel cap-lid closing the detector instead of an Al cap-lid.

This reduces the typical background level from 150 cps down to 5 cps. In addition, eight layers of aluminum are used as a scintillator instead of four layers in front of the PMT. Less penetration of radiation through the SS steel cap-lid also seems to lower the intensity.

Figure 11 shows the radiation emitted from the deuterium Rydberg matter when it transitions from an inactive chamber to an active chamber through a series of gas loading procedures and laser interaction with the catalyst and the target. Green bars show the counting rate when both the vacuum pump and laser are turned off, blue bars show the counting rate when pressure is 10⁻⁵ mbar and the laser is turned off, and red bars show the counting rate when the vacuum pump is on and the laser is irradiating the deuterium Rydberg matter. From a baseline of 4 cps, the emitted radiation can reach above 40 cps with the vacuum pump turned on and the laser turned off. No external trigger mechanism causes the emitted radiation other than when low-pressure pumping is performed. The radiation emitted increases to 64 cps when the vacuum pump and laser are turned on.

Radiation arriving at the photomultiplier tube (PMT) detector can be effectively identified through activation by both normal hydrogen and deuterium gases. Figure 12 illustrates the timeline of these changes. By analyzing the intensity of the counting rate depicted in the graph, it is possible to infer the use of a four-layer aluminum (Al) foil in front of the PMT, as well as an aluminum cap detection configuration.

For a longer period, the catalyst was operated with hydrogen as seen between February 5 and 12 [Figs. 12(a)–12(i)], where the catalyst was operated in a pure hydrogen atmosphere. Around the noon of February 12 [Fig. 12(j)], the gas was changed to deuterium, which increased the counting rate to 1542 cps. We can see an immediate spike in radiation from 502 to 1542 cps, and a high-energy peak at channel 800 appears. In the green spectra, the chamber was pumped, the high-energy peak seen in Fig. 9 was reduced, the radiation decreased between channels 150 and 1150, and the sum of radiation was slightly reduced to 1485 cps. We kept pumping the chamber, and in the evening, the radiation in channels 150–1150 had increased slightly, but the sum of counts had been reduced to 1166 cps. When evacuating the chamber on February 13 [Fig. 12(m)], we can see an increase in the counting rate to 1603 cps, which gradually drops during the day to 698 cps.

Photomultiplier tubes can detect a variety of radiation indirectly, and to check the PMT sensitivity for x rays, we placed the PMT Al-foil setup near an x-ray XRF tube source. Figure 13 shows the results.

The PMT was capped with four layers of aluminum foil. The x rays were produced using a digital x-ray source: anode, Rh; voltage, 0–45 kV; and current, tube current 0–200 μA. The detector was placed 30 cm away from the x-ray source and turned on for 500 s for each measurement. The voltage of the x rays could be manually set and increased from 25 to 45 kV, and the current was adjusted automatically by the XRF.

For comparison, the small inset figure shows the x-ray spectrum of a tube with a Rh anode (Z = 45).²¹ 

When the chamber is activated, the observed pulses from the PMT after the fast high-bandwidth amplifier VT-120 have a structure of many combined small pulses arriving in a short period with a quiet period thereafter. Under the same conditions as the PMT and the electronics, these pulses are shown in Fig. 14 for four different raw pulses recorded with the oscilloscope before and after chamber activation.

When the chamber has low activity at 175 cps, this multi-excitation pulse structure is not present, and the normal background pulses are clean. Data were collected using a 4Ch 1 GHz Keysight Agilent HP DSO8104A oscilloscope with a 2 m 50 ohm BNC cable. Figure 14(a) shows a single pulse when the catalyst is not activated, Fig. 14(b) shows two excitations arriving very close in time, Fig. 14(c) shows four fast excitations where the fastest excitation has the lowest amplitude, and Fig. 14(d) shows seven excitations arising during the same raw pulse.

To verify the presence of x rays with another method, we placed a dental x-ray film directly on the surface of the chamber and recorded the activity. In Figs. 15(a)–15(d), we can see the placement in the HRM chamber, the lead attached to the x-ray film, blank test, and x-ray emission, respectively.

A self-developing Eco30 x-ray film was attached to the surface of the vacuum chamber containing hydrogen Rydberg matter [Fig. 15(a)] with a 1 mm lead foil [Fig. 15(b)] taped to the x-ray film. The x-ray film was attached to the chamber from November 18, 2020, to January 18, 2021, without any laser excitation entering the chamber. The radiation activity from hydrogen Rydberg matter can easily be seen as a shadow in Fig. 15(d) from the lead foil on the x-ray film compared to a blind test x-ray film shown in Fig. 15(c).

The data presented in this paper are from experiments performed over four years on detecting radiation and spontaneous radiation from a chamber containing hydrogen Rydberg matter. The observed radiation verifies some of the experimental work performed by Professor Leif Holmlid and his research group at University of Gothenburg but does not necessarily confirm his scientific conclusions. After activation of the catalyst, the chamber starts to emit isotropic radiation that can be detected several meters away through a cm-thick steel and can be observed with both hydrogen and deuterium gases in the chamber. The source can be activated in different ways, and the radiation emitted can be monitored for days and weeks after activation.

It should be noted that all detector assemblies consisting of PMT, HV supply, and amplifier were tested and retested several times for stability, noise, grounding, drifting, and other artificial error sources. To verify the behavior and stability of the detector during temperature changes, the PMT detector was cooled using dry ice from 20 to −87 °C, and the dark current was observed for the low active chamber. During cooling, the PMT dark current count rate decreased from 170 cps to 72.5 cps. The variations in room temperature give about one cps per degree increase in the temperature of the detector. Therefore, the temperature variations in the room cannot be the cause of the observed radiation increase since it is too small.

The radiation emitted from the hydrogen Rydberg matter can be seen after days to weeks after the catalyst has been loaded with hydrogen and activated. Changes in chamber activity using different activation methods are shown in Fig. 11, where a series of vacuum pumping, gas loading, and laser irradiation actions affect chamber activity.

Another activation method and the time trend on the activation strength are shown in Fig. 10. Going from a low-active hydrogen chamber to a high-active deuterium chamber is shown in Fig. 12, where the radiation emitted increases instantly by a factor of three. The spectrum shows a peak at higher channels short after deuterium activation and evolves to a broader spectrum before gradually decaying.

The PMT used in the detector is sensitive to light in the range of 290–630 nm; it is enclosed in a light-tight and vacuum-tight stainless steel enclosure, so nothing can interact with the PMT except radiation that can penetrate the outer casing. Therefore, light in this range or heat variations in the lab can be ruled out as the source of the signal in the PMT detector. In addition, chemiluminescence or photoluminescence in the Al foil can be excluded because the PMT is encased in a light-tight SS cylinder.

The spectra from Cs¹³⁷ with 662 keV, Na²² with 511 keV, and Na²² with 1275 keV shown in Fig. 7 are similar; the main conclusion from that observation is that no γ energy information or calibration can be obtained for the detector. Electrons of energy lower than 20 keV arriving at the detector can also be ruled out because they cannot penetrate or induce x rays in the Al/SS cap, enclosure, or PMT glass.

A NaI gamma scintillator attached to the same PMT showed an unchanged spectrum between spontaneously active and nonactive chambers. Therefore, gamma γ radiation in the range of 100 keV–2 MeV can be ruled out. The PMT was tested for neutron sensitivity with an Am–Be neutron source at the University of Iceland. It did not respond to neutrons; therefore, neutrons can be ruled out.

A large area Li6 neutron detector 1 m from the RM source did not detect an increase in count when the chamber was active. However, during laser excitation, the Li6 neutron detector recorded an increase in neutron activity, but that is not within the scope of this paper.

We have ruled out low-energy electrons, gamma rays, and neutrons as radiation emitted from the active chamber. The next likely candidate is x rays. Therefore, the detector calibration with an XRF source was performed, as shown in Fig. 11. The figure also shows the spectrum of the Rh (45) XRF 50 keV electron excited source as an inset. This highest bremsstrahlung of 50 keV corresponds to channel 800, whereas the shoulder at channel 200 corresponds to 21 keV x rays. We can conclude from Fig. 10 that the aluminum foil-mounted PMT detector acts as a simplified primitive low-energy resolution x-ray detector. The spectra generated using the x-ray source have, as we can see in Fig. 13, in comparison with the active catalyst spectrum, a different shape. None of the x-ray spectra shows any features around channel 1450. Therefore, x rays are the most likely cause of spontaneous radiation from the active chamber in addition to a different type of radiation that is not yet fully understood.

However, this conclusion is, in fact, impossible, since the active chamber has no ongoing excitation with a laser or high voltage. Hydrogen has only entered a particular catalyst, and x-ray emission from such a chemical process is generally regarded as an impossibility.

Next, we have to add the pulse-shape observations. Radiation emitted from the active chamber can come in bursts of multiple events within an event, as shown in Fig. 14. One raw pulse can contain up to 6–9 individual faster peaks, indicating that the radiation emitted is also a combination or succession of pulse trains, packets, or clusters. We do not see random smaller-amplitude pulses between the main pulse clusters. From this, we can only conclude that we are most likely observing x-ray bunches coming as random events from the chamber.

The x-ray emission is further investigated when a self-developing dental x-ray film is added to the outside of the chamber wall with a 1 mm lead foil between the chamber and the x-ray film. The x-ray film was left on the surface of the chamber wall when no experiments were performed from November 18, 2020, to January 18, 2021, without any laser excitation of the hydrogen Rydberg matter source. A shadow of the x rays is seen on the x-ray film where the lead foil was placed. This further verifies the emission of x rays from an active, spontaneous system containing hydrogen Rydberg matter. The PMT detector showed 7200 cps from the 45 kV, 2 µA x-ray XRF source at a distance of 30 cm. If all the radiation from hydrogen Rydberg matter at 1542 cps measured at the Al-PMT detector is x rays and the distance to the chamber is 1 m, then this corresponds to the HRM chamber source being equivalent to a constantly running unscreened XRF source of twice the strength!

The early understanding of researchers at the University of Gothenburg is that the radiation emitted from hydrogen Rydberg matter is a mixture of exotic particles, such as pions, that decay into muons.²² After careful analysis of the data provided by the Al-PMT detector, we disagree that sole use of the PMT dector can verify the existence of muons. Instead, we can exclude gamma rays, low-energy electrons, light, and neutrons as the radiation emitted from spontaneous hydrogen Rydberg matter and confirm the radiation as x rays. The limited function of the Al-PMT detector makes it difficult to fully interpret some of the data presented; further research with more advanced detectors is needed to fully understand the signature of the radiation and the energy of the emitted radiation.

The data from these experiments suggest that when hydrogen is introduced to an iron oxide Rydberg state catalyst containing potassium, there might be an emission of radiation resembling x rays. This radiation appears to be detectable using several detector methods. Interestingly, the radiation seems to be emitted from a chamber without any external trigger mechanisms. However, these observations warrant further experimental validation, which is currently ongoing. To fully grasp the mechanism and characteristics of the possible emitted radiation from the hydrogen Rydberg matter system, more experiments and theoretical insights are essential. If validated, the emission of x-ray-like radiation from hydrogen Rydberg matter might hold implications for nuclear physics and the future, although this remains to be seen. This paper has gone through rigorous reviews in multiple journals, all of which have requested additional experimental evidence, such as more reliable x-ray detectors, before publication. This work is currently in progress and will take some time. Therefore, this paper is being submitted to allow other research teams to examine this physics.

The published results are part of a larger research and development project and were funded by Norway Grants (EEA and Norway Grants) (Grant No. 248497), Horizon 2020 Framework Program (H2020) Project (No. 951974), NORNEC (Nordic Nuclear Energy Corporation), the Icelandic Research Fund (Award No. 217577-051), and Norrønt AS.

The authors have no conflicts to disclose.

S. A Zeiner-Gundersen: Formal analysis (equal); Investigation (equal); Project administration (equal); Writing – original draft (equal). S. Olafsson: Investigation (equal); Supervision (equal); Validation (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.