Fusion Gamma Research Articles

Fusion gamma-ray measurements for D–3He experiments at JT-60U

Fusion gamma rays were measured in D–3He experiments using negative ion-based neutral beam injection (N-NBI) in reverse shear plasmas of the JT-60 tokamak. He3 gas was puffed at plasma initiation and just before N-NB injection. The D–3He reaction produces 3.6 MeV alphas and 14.7 MeV protons, but there is also a small branch which provides Li5 and 16.7 MeV gamma rays. The total D–3He reaction rate can be evaluated from measurement of gamma rays of the He3 (d,γ) 5Li reactions using a 3 in. diam by 3 in. long Bi4Ge3O12 scintillator. The gamma-ray detector was located 17 m below the plasma center and measured the gamma-rays in a vertical line of sight. The detector was mounted inside a heavy collimator with polyethylene and lead shielding. The floor penetration, a 4×8 cm2 hole, was used as a precollimator. Energy calibration of the detector was done with photopeaks for neutron capture gamma rays from the structural materials in D–D discharges. The detection efficiency was calculated with Monte Carlo code MCNP-4B for 16.7 MeV gammas. The pulse height analysis of the gamma rays resulted in the D–3He fusion power of 110±30 kW in this experiment.

Absence of anomalous entrance channel effects in sub-barrier heavy ion fusion.

Fusion cross sections and gamma ray multiplicities have been measured for the $^{28}\mathrm{Si}$${+}^{142}$Ce, $^{32}\mathrm{S}$${+}^{138}$Ba, and $^{48}\mathrm{Ti}$${+}^{122}$Sn entrance channels leading to the $^{170}\mathrm{Hf}$ compound nucleus. The mean spins deduced from the gamma multiplicities do not show any anomalous behavior as observed in some other measurements.

Gamma ray to charged particle branching ratios for the radiative capture of deuterons by 2H, 6Li, and 10B

The gamma to charged particle branching ratios for the radiative capture reactions of deuterons by 2H, 6Li, and 10B have been measured between center of mass energies of 20 and 40 keV, 80 and 110 keV, and 150 and 170 keV, respectively. The branching ratios for these very high-energy gamma rays, having values of 23.8, 22.3, and 25.2 MeV for the targets 2H, 6Li, and 10B, respectively, constitutes the data base for the gamma ray diagnostics of the corresponding fusion plasmas. For the fusion gamma ray detector on TFTR, counting rates for these gamma rays as a function of the total fusion reaction rate will be presented.

Absolute calibration of fusion gamma ray detector on TFTR

An in situ measurement of the absolute detection efficiency of the fusion gamma ray detector on TFTR has been completed. The efficiency was determined by measuring the yield of the 4.44 MeV gamma ray from a plutonium-berrylium source situated within the vacuum vessel. The absolute detection efficiency at 4.44 MeV is extended to higher energies using the known energy dependence of the gamma ray attenuation coefficients in the vessel port cover, the detector neutron moderator, and the scintillator. The absolute detection efficiency (full energy peak detected gamma rays per source gamma ray) varies from 8.6E−9 at 4.44 MeV to 1.1E−8 at 17 MeV and is insensitive at the few percent level to relatively large variations in the radial profile of the gamma ray source distribution in the plasma. The absolute detection efficiency is used to determine the total d-3He reaction rate during recent deuterium neutral beam heated 3He plasmas on TFTR.

More searches for cold fusion

Following the announcement of cold nuclear fusion being observed in electrochemical cells by Fleischmann and Pons1 and by Jones,2 we have searched for the characteristic radiations of thed+d andp+d fusion reactions in cells similar to those described in Refs. 1 and 2. No fusion product neutrons or gamma rays have been observed from either palladium or titanium cathodes. From measured D/Pd ratios in the systems with the palladium cathodes, we set upper limits on the fusion rates for our systems.

Performance of the fusion gamma diagnostic on TFTR

A gamma-ray spectrometer has been implemented on TFTR which features a count rate capability in excess of 10 MHz. The detector consists of a fast NE226 scintillator (∼2 ns decay time) and a Thorn-EMI 9791-KA photomultiplier tube (∼1.5 ns rise time) which is nested in shielding structures appropriate for suppression of magnetic pickup, rf noise, and the neutron/gamma radiation background. Gamma spectra are obtained on Δt≤1 ms time scales by linear fanout of the photomultiplier signal to 15 single-channel analyzers consisting of Phillips Scientific NIM Model 730 threshold/ΔE-window discriminators. Planned applications of the fusion gamma diagnostic include measurement of the ∼17 MeV prompt gamma emission from both the d(3He,γ)5Li and the p(7Li,γ)8Be reactions during ICRF minority heating of the 3He and proton species, respectively.

Gamma ray measurements during deuterium and 3He discharges on TFTR

Gamma ray count rates and energy spectra have been measured in TFTR deuterium plasmas during ohmic heating and during injection of deuterium neutral beams for total neutron source strengths up to 6 × 10 15 neutrons per second. The gamma ray measurements for the deuterium plasmas are in general agreement with predictions obtained using simplified transport models. The 16.6 MeV fusion gamma ray from the direct capture reaction D( 3He, γ) 5Li was observed during deuterium neutral beam injection into 3He plasmas for beam powers up to 7 MW. The measured yield of the 16.6 MeV gamma ray is consistent with the predicted yield. The observation of this capture gamma ray establishes the spectroscopy of the fusion gamma rays from the D- 3He reactions as a viable diagnostic of total fusion reaction rates and benchmarks the modeling for extension of the technique to D-T plasmas.

Nuclear reaction diagnostics of fast confined and escaping alpha particles

The resonant nuclear reactions D(α,γ) 6Li, 6Li(α,γ) 10B, and 7Li(α,γ) 11B are examined as diagnostics of the energy distribution of confined fast alpha particles in tokamak plasmas. Reaction rates for Q=1 D-T plasmas are estimated. The design of and preliminary results from the prototype fusion gamma ray detector on the tokamak fusion test reactor (TFTR) will be presented. The activation reactions 10B(α,n) 13N, 14N(α,γ) 18F, 25Mg(α,p) 28Al, and 27Al(α,p) 30P are similarly examined as diagnostics of fast escaping alpha particles. Count rate estimates for Q=1 D-T plasmas will be presented.

Fusion gamma diagnostics

Nuclear reactions of interest in fusion research often possess a branch yielding prompt emission of gamma radiation in excess of 15 MeV which can be exploited to provide a new fusion reaction diagnostic having applications similar to conventional neutron emission measurements. Conceptual aspects of fusion gamma diagnostics are discussed with emphasis on application to the Tokamak Fusion Test Reactor (TFTR) during deuterium neutral beam heating of D–T and D–3He plasmas. Recent measurements of the D (T, γ)5He, D(3He, γ)5Li, and D(D, γ)4He branching ratios at low center-of-mass energy (30–100 keV) and of the response of a large volume Ne226 detector for gamma detection in high neutron backgrounds are presented. Using a well-shielded Ne226 detector during 20 MW–120 kV deuterium beam heating of a tritium plasma in TFTR, the D(T, γ)5He gamma signal level is estimated to be 3.5×105 cps.

Muonic Molecules in Liquid Hydrogen

We have studied the yield and time distribution of 5.5-MeV gamma rays from the fusion reaction $p+d\ensuremath{\rightarrow}{\mathrm{He}}^{3}+\ensuremath{\gamma}$. The reaction was catalyzed by muons from the Nevis synchrocyclotron which were stopped in a target containing high-purity liquid hydrogen. A digitron of 30-nsec resolving time was used to study the yield of gamma rays as a function of the time that elapsed between the stopping of a muon and the emission of a gamma ray and as a function of the deuterium concentration, which was varied from 1 ppm to 25%. Analysis of the experimental distributions gives rates (in ${\mathrm{sec}}^{\ensuremath{-}1}$) for the following muonic molecular processes: $p\ensuremath{\mu}+p\ensuremath{\rightarrow}p\ensuremath{\mu}p, {\ensuremath{\lambda}}_{\mathrm{pp}}=(1.89\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}{10}^{6},$ $p\ensuremath{\mu}+d\ensuremath{\rightarrow}d\ensuremath{\mu}+p, {\ensuremath{\lambda}}_{e}=(1.43\ifmmode\pm\else\textpm\fi{}0.13)\ifmmode\times\else\texttimes\fi{}{10}^{10},$ $d\ensuremath{\mu}+p\ensuremath{\rightarrow}p\ensuremath{\mu}d, {\ensuremath{\lambda}}_{\mathrm{pd}}=(5.80\ifmmode\pm\else\textpm\fi{}0.30)\ifmmode\times\else\texttimes\fi{}{10}^{6},$ $p\ensuremath{\mu}d\ensuremath{\rightarrow}{\mathrm{He}}^{3}+\ensuremath{\gamma}, {\ensuremath{\lambda}}_{f}=(0.305\ifmmode\pm\else\textpm\fi{}0.010)\ifmmode\times\else\texttimes\fi{}{10}^{6}.$ The yield of fusion gamma rays was observed to increase with increasing deuterium concentration until it reached a saturation value of (14.0\ifmmode\pm\else\textpm\fi{}2.4)% at 1% concentration. At 25% deuterium concentration the yield was observed to increase by a factor of 1.17\ifmmode\pm\else\textpm\fi{}0.01 above the saturation yield. This effect is in agreement with a prediction of Wolfenstein and Gershtein. When neon was in solution in the hydrogen at a concentration of 1%, all of the muons transferred to the neon and the disappearance rate of muons bound to neon was measured to be (0.658\ifmmode\pm\else\textpm\fi{}0.010)\ifmmode\times\else\texttimes\fi{}${10}^{6}$ ${\mathrm{sec}}^{\ensuremath{-}1}$.

μ-Mesonic Molecules in Liquid Hydrogen

Muon catalysis of the reaction p + d yields He/sup 3/ + Q (5.4 Mev) is studied in order to obtain information on the reaction mu /sup -/ + p yields n + nu in liquid hydrogen. Obseration of the molecular systems p mu p and p mu d and measurement of the fusion rate initiated in an s state are thus facilitated. The yield of fusion gamma from pure hydrogen is measured as a function of time relative to mu stopping at six D concentrations. (L.N.N.)