Beta-delayed Proton Decay Research Articles

Assessment of the beta-delayed proton decay rate of 11Be

The 11Be neutron halo nucleus appears to decay into 10Be with a rate that exceeds expectations. Neutron disappearance into dark matter, beta decay of a halo neutron, or beta-delayed proton decay have been offered as explanations. In this work we study the latter option; we carry out shell model calculations and sequential decay analysis examining the beta-delayed proton decay going through a resonance in 11B. The narrow energy window, lack of states with sufficient spectroscopic strength, overwhelming alpha decay branch, all make reconciling the observed rate with beta-delayed proton decay difficult.

Experimental Study of Beta-Delayed Proton Emission of 36,37Ca

The investigation of beta-delayed proton decay mode has become a powerful probe to study the proton-rich nuclei and their nuclear structure. To study exotic nuclei with extremely low purity produced by the Radioactive Ion Beam Line in Lanzhou, we perform an experiment of beta-delayed proton emission of 36,37Ca under a high-intensity continuous-beam mode. Ions are implanted into a double-sided silicon strip detector, where the subsequent decays are correlated to the preceding implantations in time sequence. The energy spectra of delayed protons from 36,37Caβ decay, half-lives and decay branching ratios are measured. The experimental results confirm the previous literature data and some improved results are obtained as well, demonstrating the feasibility of our detection approach and the reliability of our data analysis procedure. This allows for the development of more powerful detection arrays and further research on nuclei closer to proton-drip line on the basis of present work.

Beta decay to continuum states: the case of11Be

Beta decay in exotic nuclei can lead to multi-particle final states. This contri- bution discusses briefly what decay mechanisms may enter in such decays and presents, on behalf of the IS541 collaboration at ISOLDE/CERN, preliminary data from a search for the beta-delayed proton decay of the halo nucleus 11 Be.

The Beta-Delayed Proton and Gamma Decay of 27P for Nuclear Astrophysics

The creation site of 26Al is still under debate. It is thought to be produced in hydrogen burning and in explosive helium burning in novae and supernovae, and possibly also in the H-burning in outer shells of red giant stars. Also, the reactions for its creation or destruction are not completely known. When 26Al is created in novae, the reaction chain is: 24Mg(p,γ)25AI(β+v)25 Mg(p,γ)26Al, but this chain can be by-passed by another chain, 25Al(p, γ)26Si(p, γ)27P and it can also be destroyed directly. The reaction 26m Al (p, γ)27 Si* is another avenue to bypass the production of 26Al and it is dominated by resonant capture. We find and study these resonances by an indirect method, through the beta-decay of 27P. A clean and abundant source of 27P was produced for the first time and separated with MARS. A new implantation-decay station which allows increased efficiency for low energy protons and for high-energy gamma-rays was used. We measured gamma-rays and beta-delayed protons emitted from states above the proton threshold in the daughter nucleus 27Si to identify and characterize the resonances. The lifetime of 27P was also measured with accuracy under 2%.

Decay spectroscopy for nuclear astrophysics: β- and β-delayed proton decay

In several radiative proton capture reactions important in novae and XRBs, the resonant parts play the capital role. We use decay spectroscopy techniques to find these resonances and study their properties. We have developed techniques to measure beta- and beta-delayed proton decay of sd-shell, proton-rich nuclei produced and separated with the MARS recoil spectrometer of Texas A&M University. The short-lived radioactive species are produced in-flight, separated, then slowed down (from about 40 MeV/u) and implanted in the middle of very thin Si detectors. This allows us to measure protons with energies as low as 200 keV from nuclei with lifetimes of 100 ms or less. At the same time we measure gamma-rays up to 8 MeV with high resolution HPGe detectors. We have studied the decay of 23Al, 27P, 31Cl, all important for understanding explosive H-burning in novae. The technique has shown a remarkable selectivity to beta-delayed charged-particle emission and works even at radioactive beam rates of a few pps. The states populated are resonances for the radiative proton capture reactions 22Na(p,γ)23Mg (crucial for the depletion of 22Na in novae), 26mAl(p,γ)27Si and 30P(p,γ)31S (bottleneck in novae and XRB burning), respectively. Lastly, results with a new detector that allowed us to measure down to about 80 keV proton energy are announced.

Beta decay of 57Zn*

Beta-delayed proton decay of 57Zn has been investigated at the GSI on-line isotope separator. The studied 57Zn nuclei were produced in fusion evaporation reactions by using a 150 MeV 32S beam on a 28Si target. Beta-delayed protons were measured by a charged-particle telescope detector. The observed decay pattern was used to construct the level scheme of 57Cu and to extract the beta feeding distribution. The experimental results are compared with shell-model calculations.

Fine structure in the beta-delayed proton decay of 33Ar

Low-energy beta-delayed protons from 33Ar have been measured for the first time. The data reveal states, which, despite unfavourable barrier penetrability values, strongly decay to the first excited 2 + state in 32S. The observation is discussed in terms of the standard shell model. A natural explanation is provided by the large spectroscopic amplitudes, involving s 1 2 and d 3 2 orbitals, as well as the l = 0 barrier penetrability, favouring the decay to the 2 + state.

Beta-delayed proton decay of 28

Beta-delayed proton radioactivity has been observed for the 28S isotope ( T z = −2), produced by projectile fragmentation of 85 MeV/u 36Ar. The measured half-life of 28S is 125 ± 10 ms. Energy spectra of beta-delayed protons have been measured. The lowest T = 2 state in the daughter nucleus 28P has been located at an excitation energy of 5900 ± 21 keV. A comparison of the experimental data to the quadratic form of the isobaric multiplet mass equation shows that the energies of the five T = 2 states of the A = 28 quintet are well represented by that relation. Shell-model predictions for the half-life of 28S and the location and decay properties of the lowest T= 2 state of 28P are in good agreement with experimental data.

Delayed proton emission of N=81 odd-odd precursors: 148Ho, 150Tm, and 152Lu.

Beta-delayed proton decay was observed in $^{148}\mathrm{Ho}$, $^{150}\mathrm{Tm}$, and $^{152}\mathrm{Lu}$ for the first time. Contrary to neighboring even-Z N=81 isotones, the proton spectra appear structureless and statistical in nature. Proton branching ratios for the high-spin isomers in these isotopes, based on the intensity of \ensuremath{\gamma}-ray transitions in the intermediate nuclei, are (${8}_{\mathrm{\ensuremath{-}}2}^{+1}$)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$, (${1.2}_{\mathrm{\ensuremath{-}}0.4}^{+0.2}$)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}2}$, and (1.5\ifmmode\pm\else\textpm\fi{}0.7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}1}$, respectively. The onset of proton emission in all three cases occurs at a proton to \ensuremath{\gamma} width ratio of about ${10}^{\mathrm{\ensuremath{-}}4}$. Protons were found to be in coincidence with x rays, \ensuremath{\gamma} rays, and positrons. Coincident K x rays served to identify the Z of the precursor, while the \ensuremath{\gamma} rays gave quantitative information about proton decay to excited states in the daughter nuclei. By comparing the final state branching ratios with statistical model calculations, it was concluded that $^{148}\mathrm{Ho}$ and $^{150}\mathrm{Tm}$ both have isomers with probable spin values of ${1}^{+}$ and ${6}^{\mathrm{\ensuremath{-}}}$. Statistical model calculations with ``standard'' prescriptions for level densities and \ensuremath{\gamma} widths, and with a reduced level density parameter are compared to experiment. To reproduce the shape of the proton spectrum it was necessary to assume Gaussian-shaped Gamow-Teller \ensuremath{\beta} strength functions centered near 8 MeV excitation energy. In the course of these experiments \ensuremath{\beta}-delayed proton emission in $^{148}\mathrm{Er}$ was also identified.

Beta-delayed proton decay of 61Ge.

The ${T}_{z}$=-(3/2), A=4n+1 nuclide $^{61}\mathrm{Ge}$ has been produced via the $^{40}\mathrm{Ca}$${(}^{24}$Mg,3n) reaction and identified by its beta-delayed proton emission. A single proton group at 3.11\ifmmode\pm\else\textpm\fi{}0.03 MeV with ${t}_{1/2}$=40\ifmmode\pm\else\textpm\fi{}15 ms has been observed, corresponding to decay of the T=(3/2) isobaric analog state in $^{61}\mathrm{Ga}$ to the ground state of $^{60}\mathrm{Zn}$. Searches for the beta-delayed proton decay of the next member of this series, $^{65}\mathrm{Se}$, to be produced by the $^{40}\mathrm{Ca}$${(}^{28}$Si,3n) reaction, have proven unsuccessful.

Beta-delayed proton decay of the Tz = −2 isotope 26P

The 28Si( 3He, p4n) 26P reaction at 110–130 MeV has been used to discover the odd-odd T z = −2 nuclide 26 P( 1 2 ≈ 20 ms) , which was predicted to lie on or beyond the proton drip line. Beta-delayed protons from its decay establish the mass excess of the lowest T = 2 state in 26Si as 5.936 ± 0.015 MeV. Possible beta-delayed two-proton emission from this isotope is discussed.

Direct and beta-delayed proton decay of very neutron-deficient rare-earth isotopes produced in the reaction58Ni+92Mo

Using on-line mass separation of evaporation residues from the reaction58Ni +92Mo→150Yb*, a proton line of 1,055±6 keV energy and 0.42±0.10 s half-life was observed at mass number 147. The origin of this activity is very likely the direct proton decay of147Tm. Beta-delayed protons registered at the same mass position show a pronounced peak structure in their energy distribution. A lower limit of their half-life was set to 1 s.

Beta-delayed proton decay of 13O: A violation of mirror symmetry

Beta-delayed protons, E lab > 1.2 MeV, were observed following the decay of 13O, τ 1 2 = 8.95±0.20 ms . Comparison of 13O decay-rates with those of the mirror nuclide 13B indicates a 15% deviation from mirror symmetry.