Nuclear Processes at Solar Energy

LUNA, Laboratory for Underground Nuclear Astrophysics at Gran Sasso, is measuring fusion cross sections down to the energy of the nucleosynthesis inside stars. Outstanding results obtained up to now are the cross-section measurements within the Gamow peak of the Sun of $^{3}He(^{3}He,2p)^{4}He$ and the $D(p,\gamma)^{3}He$. The former plays a big role in the proton-proton chain, largely affecting the calculated solar neutrino luminosity, whereas the latter is the reaction that rules the proto-star life during the pre-main sequence phase. The implications of such measurements will be discussed. Preliminary results obtained last year on the study of $^{14}N(p,\gamma)^{15}O$, the slowest reaction of the CNO cycle, will also be shown.Comment: Invited talk at the XXIII Physics in Collisions Conference (PIC03), Zeuthen, Germany, June 2003, 10 pages, LaTeX, 3 EPS figures. PSN THAT0

Search for correlations between solar flares and decay rate of radioactive nuclei

The deacay rate of three different radioactive sources 40K, 137Cs and natTh has been measured with NaI and Ge detectors. Data have been analyzed to search for possible variations in coincidence with the two strongest solar flares of the years 2011 and 2012. No significant deviations from standard expectation have been observed, with a few 10-4 sensitivity. As a consequence, we could not find any effect like that recently reported by Jenkins and Fischbach: a few per mil decrease in the decay rate of 54Mn during solar flares in December 2006.Comment: 5 pages, 3 figure

Precise measurement of the 222Rn half-life: a probe to monitor the stability of radioactivity

We give the results of a study on the 222Rn decay we performed in the Gran Sasso Laboratory (LNGS) by detecting the gamma rays from the radon progeny. The motivation was to monitor the stability of radioactivity measuring several times per year the half-life of a short lifetime (days) source instead of measuring over a long period the activity of a long lifetime (tens or hundreds of years) source. In particular, we give a possible reason of the large periodical fluctuations in the count rate of the gamma rays due to radon inside a closed canister which has been described in literature and which has been attributed to a possible influence of a component in the solar irradiation affecting the nuclear decay rates. We then provide the result of four half-life measurements we performed underground at LNGS in the period from May 2014 to January 2015 with radon diffused into olive oil. Briefly, we did not measure any change of the 222Rn half-life with a 8*10^-5 precision. Finally, we provide the most precise value for the 222Rn half-life: 3.82146(16){stat}(4){syst} days.Comment: Accepted for publication in Physics Letters B, 6 pages, 6 figure

The Luna experiment

LUNA is a pilot project initially focused on the 3 He ( 3 He , 2 p ) 4 He cross section measurement within the thermal energy region of the Sun (15–27 KeV ). A compact high current 50 KV ion accelerator facility including a windowless gas target system, a beam calorimeter and four detector telescopes has been built, tested and installed underground at the Laboratori Nazionali del Gran Sasso. The sensitivity has been improved by more than four orders of magnitude, as compared to the previous experiment. In particular, thanks to the cosmic ray suppression, we could attain a background level of less than 1 event per week, a rate similar to the one expected from 3 He ( 3 He ,2 p ) 4 He at the lower edge of the Sun thermal energy region

LUNA: Nuclear Astrophysics Deep Underground

Nuclear astrophysics strives for a comprehensive picture of the nuclear reactions responsible for synthesizing the chemical elements and for powering the stellar evolution engine. Deep underground in the Gran Sasso laboratory the cross sections of the key reactions of the proton-proton chain and of the Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the energies of astrophysical interest. The salient features of underground nuclear astrophysics are summarized here. The main results obtained by LUNA in the last twenty years are reviewed, and their influence on the comprehension of the properties of the neutrino, of the Sun and of the Universe itself are discussed. Future directions of underground nuclear astrophysics towards the study of helium and carbon burning and of stellar neutron sources in stars are pointed out.Comment: Invited review, submitted to Annu. Rev. Nucl. Part. Scienc

Search for time modulations in the decay rate of 40K and 232Th

Time modulations at per mil level have been reported to take place in the decay constant of about 15 nuclei with period of one year (most cases) but also of about one month or one day. In this paper we give the results of the activity measurement of a 40K source and a 232Th one. The two experiments have been done at the Gran Sasso Laboratory during a period of about 500 days, above ground (40K) and underground (232Th) with a target sensitivity of a few parts over 10^5. We also give the results of the activity measurement at the time of the X-class solar flares which took place in May 2013. Briefly, our measurements do not show any evidence of unexpected time dependence in the decay rate of 40K and 232Th.Comment: version accepted for publication (Astroparticle Physics

Search for time modulations in the decay constant of 40K and 226Ra at the underground Gran Sasso Laboratory

Time modulations at per mil level have been reported to take place in the decay constant of several nuclei with period of one year (most cases) but also of about one month or one day. On the other hand, experiments with similar or better sensitivity have been unable to detect any modulation. In this letter we give the results of the activity study of two different sources: 40K and 226Ra. The two gamma spectrometry experiments have been performed underground at the Gran Sasso Laboratory, this way suppressing the time dependent cosmic ray background. Briefly, our measurements reached the sensitivity of 3.4 and 3.5 parts over 10^6 for 40K and 226Ra, respectively (1 sigma) and they do not show any statistically significant evidence of time dependence in the decay constant. We also give the results of the activity measurement at the time of the two strong X-class solar flares which took place in September 2017. Our data do not show any unexpected time dependence in the decay rate of 40K in correspondence with the two flares. To the best of our knowledge, these are the most precise and accurate results on the stability of the decay constant as function of time.Comment: Accepted for publication in Physics Letters B, 6 pages, 8 figures. arXiv admin note: text overlap with arXiv:1311.704

study of the time dependence of radioactivity

The activity of a 137Cs source was measured using a germanium detector installed deep underground in the Gran Sasso Laboratory. In total about 5100 energy spectra, one hour measuring time each, were collected and used to search for time variations of the decay constant with periods from a few hours to 1 year. No signal with amplitude larger than 9.6 × 10−5 at 95% C.L. was detected. These limits are more than one order of magnitude lower than the values on the oscillation amplitude reported in the literature. The same data give a value of 29.96±0.08 years for the 137Cs half life, which is in good agreement with the world mean value of 30.05 ± 0.08 years

The Luna experiment

One of the main ingredients of nuclear astrophysics is the cross section of the thermonuclear reactions which power the stars and synthesize the chemical elements in the Universe. Deep underground in the Gran Sasso Laboratory the cross section of the key reactions of the proton-proton chain and of the Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the energies of astrophysical interest. The main results obtained during the solar phase of LUNA are reviewed before describing the current LUNA program devoted to the study of the nucleosynthesis of the light elements in AGB stars and Classical Novae. Finally, the future of LUNA with the new 3.5 MV accelerator devoted to the study of helium and carbon burning is discussed

Search for the time dependence of the 137Cs decay constant

Starting from June 2011, the activity of a 137Cs source has been measured by means of a HPGe detector installed deep underground in the Gran Sasso Laboratory. In total about 5100 energy spectra, one hour measuring time each, have been collected. These data allowed the search for time variations of the decay constant with periods from a few hours to 1 year. No signal with amplitude larger than 9.6{\cdot}10-5 at 95% C.L. has been detected. These limits are more than one order of magnitude lower than the values on the oscillation amplitude reported in literature. In particular, for 1 year period an oscillation amplitude larger than 8.5{\cdot}10-5 has been excluded at 95% C.L., independently of the phase. The same data give a value of 29.96{\pm}0.08 years for the 137Cs half life, in good agreement with the world mean value of 30.05{\pm}0.08 years.Comment: 5 pages, 4 figure