Monochromatic Gamma Rays Research Articles

Design of a Liquid Xenon Calorimeter for the Observation of Cosmic Gamma Ray Lines in the 1∼100 GeV Region

A liquid xenon calorimeter has recently been designed. The main purpose is to show the capability of observing monochromatic cosmic gamma ray lines in the 1∼100 GeV region. The calorimeter has a geometric factor of ∼1 m2·sr, an energy resolution of ∼0.4% and an angular resolution of about 1 degree for GeV-region gamma rays. These characteristics will meet the conditions required for the observation of gamma ray lines produced by the pair annihilation of hypothetical SUSY heavy Majorana fermions which might exist in the galactic halo as dark matter. The calorimeter is also applicable to the search for point sources emitting gamma rays as well as the investigation of diffuse gamma rays at high energies.

Gamma ray line astronomy as a probe of cold dark matter

Abstract Some annihilation processes of cold dark matter particles in the galactic halo may result in monochromatic gamma rays with an astrophysically significant rate. This paper summarizes the calculation of these rates and discusses the expected gamma ray line flux in comparison with the diffuse cosmic background.

Annihilation of heavy-neutral-fermion pairs into monochromatic gamma rays and its astrophysical implications.

We present estimates for the rates of the processes xixi/r arrow/..gamma gamma..and xixi/r arrow//ital V/..gamma.., where xi is a heavy-neutral-fermion candidatefor galactic cold dark matter and /ital V/ is a vector quarkonium state/ital J///psi/(3097) or UPSILON(9460). A discrepancy with a previous estimateof the rate of the photino pair annihilation process/gamma/tilde ///gamma/tilde ///r arrow/..gamma gamma.. is uncovered and its origin discussed. We explorethe possibility that some of the processes considered may be astrophysicallysignificant sources of monochromatic ..gamma..-ray lines, in the energy rangeof a few to a few tens of GeV, for which theoretical estimates of thebackground ..gamma..-ray flux are unfortunately subject to large uncertainties.

Search for narrow states by detection of monochromatic gamma rays in p-barp annihilation at rest.

We measured inclusive \ensuremath{\gamma}-ray spectra from p\ifmmode\bar\else\textasciimacron\fi{}p annihilation at rest to search for narrow \ensuremath{\gamma} lines associated with the production of baryonia. The measurement was done with statistics several times as high as those of earlier experiments by using modularized NaI(Tl) detectors. We have not observed any narrow states, i.e., baryonium candidates, with statistical significance higher than 4\ensuremath{\sigma}. The 4\ensuremath{\sigma} upper limits for the yield of p\ifmmode\bar\else\textasciimacron\fi{}p\ensuremath{\rightarrow}\ensuremath{\gamma}B times the decay branching ratio of B into ${N}_{\mathrm{ch}}$-prong states is (1.2--0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ at \ensuremath{\gamma}-ray energy of 80--938 MeV for the sum over ${N}_{\mathrm{ch}}$, (0.3--0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ for each of ${N}_{\mathrm{ch}}$=0 and \ensuremath{\ge}6, and (0.8--0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ for each of ${N}_{\mathrm{ch}}$=2 and 4. At 2 to 3\ensuremath{\sigma} levels, however, we have seen nine narrow \ensuremath{\gamma}-ray peaks with individual yields between ${10}^{\mathrm{\ensuremath{-}}4}$ and ${10}^{\mathrm{\ensuremath{-}}3}$ for various charge multiplicities.

Self-scattering in gamma ray sources used in compton scattering experiments

The energy degradation of various monochromatic gamma ray sources due to self-scattering has been studied by Monte Carlo simulation techniques. A direct measurement of the energy spectrum of the 198Au source used for Compton scattering experiments at the Hahn-Meitner Institute (HMI) confirms the predictions of the emission of a low energy tail. The effect of the tail on Compton profiles is examined and a method of correction is proposed and applied to measurements made at the HMI.

Search for narrow states by detection of monochromatic gamma rays in p̄p annihilation at rest

An inclusive γ ray spectrum in p̄p annihilation at rest has been measured with modularized NaI(Tℓ) detectors with statistics several times higher than before. The aim of the experiment was to search for baryonium B in p̄p → γB by detection of narrow lines in the γ ray spectrum. We have not observed any narrow state B with yield greater than 1.5 × 10 −3 per annihilation and with statistical significance higher than 2σ.

High Resolution Photofission Measuremfnts Using Proton Capture Gamma Rays

High intensity proton beams from the Dynamitron at Brooklyn College are used to generate monochromatic gamma rays from known (p, r) resonances in various nuclei. The gamma rays, whose energy varies continuously as a function of the angle with the proton beam, are used in turn to measure photofission cross sections in 238U and 232Th. The number of suitable (p, r) resonances is sufficient to cover the 5 - 13 MeV range of excitation energy with an average step of ~ 100 keV. For a resonance of average strength the yield is 103 photons per μA of protons on target. The energy spread is typically 20 - 40 keV and a gamma ray energy resolution of 200 eV can easily be reached. This resolution is adequate for investigating structure in the photofission cross sections resulting from class II states in the second well of the fission barrier.

Analyses of monochromatic gamma-ray and annihilation radiation spectra obtained with Ge(Li) detectors

First, analysis of the monochromatic gamma-ray peak is described. The peak center was precisely determined by fitting of a Gaussian function. A response function of the gamma-ray peak is expressed by a Gaussian and a tailing function. Secondly, two kinds of the unfolding methods of the Doppler broadened annihilation spectrum are described. These methods are useful for both the precision energy measurement and the study of the position annihilation in various materials. Annihilation spectra for 23 samples were successfully unfolded by an iterative unfolding method and intrinsic distributions of the annihilation radiations were obtained.

Production of Monochromatic γ Rays from Thin Crystal of Silicon

An experiment has been made on production of monochromatic gamma rays by strongly collimating the coherent bremsstrahlung from a single crystal of silicon around the beam axis. The internal electron beam with the energy of 1 GeV in the synchrotron was collimated on the crystal target by a set of beam scrapers distributed at the straight sections. The energy spectrum shows a sharp spike at the photon energy k =185 MeV with the signal-to-background ratio as large as 12 and the width at the half maximum intensity of Δ k =±8 MeV. The maximum intensity of 2×10 4 photons/MeV · sec has been obtained at the spike. The obtained spectrum is in good agreement with theory based on Uberall's treatment, if the primary angular divergence of the incident electrons and the multiple Coulomb scattering in the radiator are taken into account.

The observation of sidebands produced when monochromatic radiation passes through a vibrated resonant medium

Monochromatic (Mossbauer) gamma rays are passed through a medium containing resonant nuclei. When the medium is vibrated at ultrasonic frequencies, the emerging radiation analysed by a Mossbauer spectrometer contains sidebands separated from the original frequency by multiples of the ultrasonic frequency. The conditions for the production of these sidebands and their intensities are discussed.

Standard spectrum method for the analysis of gamma-ray spectra from semiconductor detectors

A new attempt is described to analyse the gamma-ray spectra by the least squares technique which uses a standard spectrum for the shape function so as to express the line shape accurately with a small number of parameters and to analyse complex overlapping peaks simultaneously. The standard spectrum is directly made from the observed spectrum, which corresponds to the incident monochromatic gamma-ray, through the subtraction of background gamma-rays and smoothing of the data. The peak component of each photopeak is given correctly for each channel by integrating the standard spectrum over the width of the channel in order to lessen the dependence of fitting results to the channel width of a pulse height analyser. It is confirmed that the complicated gamma-ray spectrum with multiple photopeaks can be fitted accurately to the standard spectrum and the linear background continuum by the present method. The effectiveness of integral representation for the peak component is also confirmed.

Cible à deutérium liquide

Abstract An original liquid deuterium target has been built at the Orsay Linear Accelerator Laboratory to study the interaction of monochromatic gamma rays of 400 MeV with deuterons. We give here the description and the performances of the target and of the automatic system which provides it with liquid deuterium during several weeks, without any human intervention.

A Ge(Li) two crystal compton spectrometer

The performance of Compton spectrometers using two Ge(Li) gamma-ray detectors is demonstrated. Two different configurations of detectors have been used, together with on-line computer methods to show that a nearly-single-peak spectrum of good resolution can be obtained for a monochromatic gamma ray. Further, the peak is due to purely single Compton scattering of well determined scattering angle despite the large solid angles of the scattering and detecting crystals. These considerations make the device well suited to use as a gamma-ray polarimeter.

Une méthode numérique d'analyse des spectres gamma

A gamma spectrometer can be represented by means of a matrix. The construction of such a matrix (100 × 50) by using a few radioactives sources of monochromatic gamma rays is described. The application of this method, namely to the activation analysis and the diffusion of gamma rays through shielding, is considered. The accuracy reached with this method is greater than by graphical methods.

Inelastic Scattering of Monochromatic Photons from the 7.64-MeV Level ofNi62

The nuclear resonant scattering of the monochromatic iron capture gamma rays from natural nickel was studied with a single NaI crystal and a three-crystal pair spectrometer. The spectrum of the scattered photons exhibits three photon groups of 7.64, 6.47, and 5.38 MeV with relative intensities 0.69, 0.08, and 0.23, respectively. The spectrum of the low-energy cascade photons in coincidence with the scattered photons identifies these groups with the transitions from the 7.64-MeV resonant level to the ${0}^{+}$ ground state and the first (${2}^{+}$, 1.17 MeV) and second (${0}^{+}$, 2.05 MeV) vibrational levels in ${\mathrm{Ni}}^{62}$. Angular distribution measurements of the elastically scattered photons show that the 7.64-MeV level in ${\mathrm{Ni}}^{62}$ has angular momentum 1. The elastic-scattering cross section averaged over the incident gamma rays was determined to be $〈{\ensuremath{\sigma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}〉=190\ifmmode\pm\else\textpm\fi{}40$ mb.

Inelastic Scattering of Iron-Capture Gamma Rays from the 7.64-MeV Level ofCd112

In the resonant-scattering experiment of the monochromatic iron-capture gamma rays from natural cadmium, five inelastically scattered photon groups were observed in addition to the 7.64-MeV elastic group. The spectrum of the low-energy cascade photons in coincidence with the scattered photons identifies the inelastic groups to be the transitions to the low-lying levels of ${\mathrm{Cd}}^{112}$, including the three ${2}^{+}$ vibrational levels at 0.61, 1.29, and 1.46 MeV. Angular-distribution measurements show that the 7.64-MeV resonance level in ${\mathrm{Cd}}^{112}$ has angular momentum 1. The average elastic-scattering cross section and the branching ratio for the ground-state transitions are $〈{\ensuremath{\sigma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}〉=0.17\ifmmode\pm\else\textpm\fi{}0.02$ b and $\frac{{\ensuremath{\Gamma}}_{0}}{\ensuremath{\Gamma}}=0.48\ifmmode\pm\else\textpm\fi{}0.06$, respectively. Using these values, the self-absorption measurements determined the ground-state transition width to be ${\ensuremath{\Gamma}}_{0}={{0.6}_{\ensuremath{-}0.1}}^{+0.2}$ eV.

C12(γ, n)C11Giant Resonance with Gamma Rays

The photonuclear reaction $^{12}\mathrm{C}(\ensuremath{\gamma}, n)^{11}\mathrm{C}$ was produced in natural carbon by means of the monochromatic gamma rays from $\mathrm{T}(p, \ensuremath{\gamma})\mathrm{He}$ in the range of $21<{E}_{\ensuremath{\gamma}}<26.7$ MeV. The reaction was detected by means of the positron radioactivity of $^{11}\mathrm{C}$ using coincidences of the annihilation gamma radiation from the positrons. The cross section was determined absolutely to an accuracy of 10%. The gamma-ray energy width or resolution varied from about 0.1 MeV at ${E}_{\ensuremath{\gamma}}=22 \mathrm{MeV} \mathrm{to} 0.2 \mathrm{MeV}$ at ${E}_{\ensuremath{\gamma}}=26$ MeV. The peak cross section is 7.8 mb at both 22.15 and 23.0 MeV, and additional structure is observed at 25.6 MeV. The integrated cross section from 20 to 27 MeV is 36 MeV mb. Comparison is made with other reported measurements and with theoretical calculations. Some agreement is found with the deformed-nucleus calculation of Nilsson, Sawicki, and Glendenning. Also, some indication is observed of transition to excited states of $^{11}\mathrm{C}$ suggesting two-hole-two-particle excitation in $^{12}\mathrm{C}$.

Photoreactions in 28Si Nucleus by Monochromatic Gamma-Rays

The structure of the giant resonance in 28 Si has been studied using monochromatic gamma-rays ( Δ E γ / E γ ≈1%) from proton capture reactions. A silicon solid-state detector served both as target and detector. Total cross sections for the 28 Si (γ, p 0 ), (γ, p 1 ), (γ, p 2 ), (γ, α 0 ) and (γ, α 1 ) reactions were obtained from 17.4 to 22.3 MeV and the integrated cross sections were 34.4, 18.9, 17.6, 1.6 and 2.7 mb·MeV, respectively. The excitation functions of proton emission showed many discernible fine structures. Most of the peaks of the cross sections for different exit channels occurred at the same gamma-ray energy and the number of resonance states involved in a peak seems to be a few. The (γ, α 0 )-reaction excitation functions revealed several humps which are possibly caused by an E 1 absorption. Isotopic-spin selection rule seems no longer to be valid for the present (γ, α 0 ) reaction. Comparisons were made with the calculated absorption probability from the Nilsson model.

O16(γ, n)O15Reaction Near 17.6 MeV

The photonuclear activation cross section of ${\mathrm{O}}^{16}$ near 17.6 MeV has been investigated using monochromatic gamma rays from the ${\mathrm{Li}}^{7}(p, \ensuremath{\gamma})$ reaction. The proton energy was set for the 441-keV resonance and the gamma-ray energy angular dependence was used to determine the relative ($\ensuremath{\gamma}, n$) cross section at the energies 17.571, 17.618, and 17.666 MeV. The absolute cross section was determined at 17.618-MeV photon energy to be 0.55\ifmmode\pm\else\textpm\fi{}0.08 mb.

Photoneutron Cross Sections ofPb206,Pb207,Pb208, andBi209

Cross sections for ($\ensuremath{\gamma}, n$) and ($\ensuremath{\gamma}, 2n$) reactions on ${\mathrm{Pb}}^{206}$, ${\mathrm{Pb}}^{207}$, ${\mathrm{Pb}}^{208}$, and ${\mathrm{Bi}}^{209}$ have been measured using monochromatic gamma rays having an energy resolution of 3%. The peak cross sections for $\ensuremath{\sigma}[(\ensuremath{\gamma}, n)+(\ensuremath{\gamma}, np)]$ are 515, 475, 495, and 515 mb, respectively, and for $\ensuremath{\sigma}(\ensuremath{\gamma}, 2n)$ are 76, 80, 117, and 105 mb, respectively. Integrated cross sections for $\ensuremath{\sigma}(\ensuremath{\gamma}, n)$ up to 28 MeV are 2.22, 2.05, 1.96, and 2.17 MeV-b, while for $\ensuremath{\sigma}(\ensuremath{\gamma}, 2n)$ are 0.56, 0.60, 0.95, and 0.76 MeV-b, respectively. Level-density parameters for the residual nuclei ${\mathrm{Pb}}^{205}$, ${\mathrm{Pb}}^{206}$, ${\mathrm{Pb}}^{207}$, and ${\mathrm{Bi}}^{208}$ were found to be 6.6, 13.5, 9.6, and 10.2 Me${\mathrm{V}}^{\ensuremath{-}1}$, respectively, each determined to \ifmmode\pm\else\textpm\fi{} 11%. Values obtained for ${\ensuremath{\sigma}}_{\ensuremath{-}2}$ are 15.6, 14.5, 14.1, and 16.6 mb/MeV, respectively.