Delayed Proton Decay Research Articles

Nuclear Structure and Decay Data for A=44 Isobars

Experimental nuclear spectroscopic data are evaluated for 12 known nuclides of mass number A=44 (Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V, Cr, Mn). Detailed evaluated information are presented for each reaction and decay. Recommended values combining all available data are provided for all spectroscopic properties of each level, γ-ray, and decay radiation. No excited states have yet been identified in 44Si, 44P, 44Cr, and 44Mn. Information for excited states in 44Cl and 44V are limited. Nuclides of 44S, 44Ar and 44K have been studied via only a few reactions and decays, while 44Ca, 44Sc and 44Ti are the most investigated nuclides through various reactions and decays. Evaluators note that the half-life of the g.s. of 44S has been measured independently, with fairly good statistics, in three references, most precise being 100 ms 1 by 2004Gr20, but this value is in disagreement with the values of 125.5 ms 25 and 119 ms 6 by 2022Tr03, and 123 ms 10 by 1995So03. We adopted the unweighted average of this discrepant dataset. Another outstanding issue is that of the β+-delayed proton decay of 44Cr g.s. to 44V, where the T=2, 0+ IAS state in 44V is expected to be strongly populated by a superallowed β transition, but has not been definitely identified as discussed in detail by 2020Fu05. A detailed study of 44Cr decay is required to unravel the status of the T=2, 0+ IAS state in 44V. This work supersedes earlier ENSDF evaluations of A=44 by 2011Ch39 and 1999Ca45.

Low-energy Al23β -delayed proton decay and Na22 destruction in novae

The radionuclide $^{22}$Na is a target of $\gamma$-ray astronomy searches, predicted to be produced during thermonuclear runaways driving classical novae. The $^{22}$Na(p,$\gamma$)$^{23}$Mg reaction is the main destruction channel of $^{22}$Na during a nova, hence, its rate is needed to accurately predict the $^{22}$Na yield. However, experimental determinations of the resonance strengths have led to inconsistent results. In this work, we report a measurement of the branching ratios of the $^{23}$Al $\beta$-delayed protons, as a probe of the key 204--keV (center-of-mass) $^{22}$Na(p,$\gamma$)$^{23}$Mg resonance strength. We report a factor of 5 lower branching ratio compared to the most recent literature value. The variation in $^{22}$Na yield due to nuclear data inconsistencies was assessed using a series of hydrodynamic nova outburst simulations and has increased to a factor of 3.8, corresponding to a factor of $\sim$2 uncertainty in the maximum detectability distance. This is the first reported scientific measurement using the Gaseous Detector with Germanium Tagging (GADGET) system.

High-precision mass measurement ofS31with the double Penning trap JYFLTRAP improves the mass value forCl32

The mass of $^{31}\mathrm{S}$ has been measured with the JYFLTRAP double Penning trap mass spectrometer. The new mass excess value of $\ensuremath{-}19 042.55(24) \mathrm{keV}$ deviates from the adopted value of $\ensuremath{-}19 044.6(15) \mathrm{keV}$ by $1.4\ensuremath{\sigma}$. The mass value of $^{32}\mathrm{Cl}$ has been revised with the new $^{31}\mathrm{S}$ result and the latest data from $\ensuremath{\beta}$-delayed proton decay of $^{32}\mathrm{Cl}$. The new mass excess value for $^{32}\mathrm{Cl}$ is $\ensuremath{-}13 334.88(65) \mathrm{keV}$, which is the most precise value for $^{32}\mathrm{Cl}$ so far and in agreement with the recent ($^{3}\mathrm{He},t$) data. The isobaric multiplet mass equation has been tested in the $T=2$ quintet at $A=32$, and the cubic form of the equation has been found to agree with the experimental data. The ${Q}_{\mathit{EC}}$ value for the $\ensuremath{\beta}$ decay of $T=1/2$ mirror nucleus $^{31}\mathrm{S}$ has been determined as ${Q}_{\mathit{EC}}=5397.99(24) \mathrm{keV}$, which slightly deviates from the previously adopted value.

β-delayed proton decays of theTz=1/2series nuclei,81Zrand85Mo

The decays of ${T}_{z}=1/2$ series nuclei ${}^{81}\mathrm{Zr}$ and ${}^{85}\mathrm{Mo}$ have been restudied via their $\ensuremath{\beta}$-delayed proton decay by using p-$\ensuremath{\gamma}$ coincidence measurements. The $\ensuremath{\beta}$-delayed proton spectra populating the first excited states of the final nuclei have been obtained. By using statistical model calculations with level densities calculated with a backshifted Fermi gas model, the spin and parity for the ground state of ${}^{81}\mathrm{Zr}$ have been tentatively assigned to be ${3/2}^{\ensuremath{-}}$ and those for ${}^{85}\mathrm{Mo}$ to be ${1/2}^{\ensuremath{-}}.$ Their ${Q}_{\mathrm{e}.\mathrm{c}.}\ensuremath{-}{B}_{p}$ values are $4.7\ifmmode\pm\else\textpm\fi{}0.2$ and $5.1\ifmmode\pm\else\textpm\fi{}0.2 \mathrm{MeV},$ which correspond to mass excesses of $\ensuremath{-}58.3\ifmmode\pm\else\textpm\fi{}0.2 \mathrm{MeV}$ for ${}^{81}\mathrm{Zr}$ and of $\ensuremath{-}59.1\ifmmode\pm\else\textpm\fi{}0.4 \mathrm{MeV}$ for ${}^{85}\mathrm{Mo},$ respectively. Combining the measured half-lives with the calculated partial ones yields branches of $\ensuremath{\beta}$-delayed proton decay for ${}^{81}\mathrm{Zr}$ and ${}^{85}\mathrm{Mo}$ of $(1.2\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and $(1.4\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3},$ respectively.

Beta-delayed proton spectroscopy of

Recently an experiment has been carried out at RIKEN, Japan, using the projectile fragment separator RIPS to test a new approach of studying -delayed proton emitters. The approach consists of reduction of contamination from neighbouring isotones and isotopes by using a set of Al absorbers at the RIPS focal plane and stopping the fragments of interest on a thin foil placed in front of a gas -Si E detector telescope for delayed proton measurement. These two together have led to a remarkable reduction of -background in the delayed proton spectrum of and a number of new levels in decaying by proton emission to have been observed. The details of the technique and the results obtained from the -delayed proton decay of will be discussed.

Proton branching ratios in theβ-delayed proton decay of87Mo

The nuclide {sup 87}Mo with A=4n+3 and T{sub z}=3/2 was reinvestigated via its {beta}-delayed proton decay with p-{gamma} coincidence. The proton branching ratios in the decay of {sup 87}Mo populating the first 2{sup +}, 4{sup +}, and 6{sup +} excited states in {sup 86}Zr have been measured to be (11{plus_minus}6){percent}, (2{plus_minus}1){percent}, and (2{plus_minus}1){percent}, respectively, which revise the previous results. {copyright} {ital 1997} {ital The American Physical Society}

Gamma decays of proton unbound levels in 37K.

Large discrepancies have been reported between the Gamow-Teller strengths determined from $^{37}\mathrm{Ca}$ \ensuremath{\beta}-delayed proton decay, and the isospin-analog strengths deduced from $^{37}\mathrm{Cl}$(p,n) studies. Some of these discrepancies could be removed if the $^{37}\mathrm{Ca}$ daughter level at 3.24 MeV in $^{37}\mathrm{K}$ had ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$ forty times bigger than its ${\mathrm{\ensuremath{\Gamma}}}_{\mathit{p}}$, and not negligibly small as assumed in the initial analysis of the $^{37}\mathrm{Ca}$ \ensuremath{\beta} decay. We studied proton and \ensuremath{\gamma}-ray branching ratios of low-lying $^{37}\mathrm{K}$ levels populated via the $^{40}\mathrm{Ca}$(p,\ensuremath{\alpha}) reaction. We find that the 3.24 MeV level has ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$/${\mathrm{\ensuremath{\Gamma}}}_{\mathit{p}}$>8, and that the 2.75 and 3.08 MeV levels have ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$/${\mathrm{\ensuremath{\Gamma}}}_{\mathit{p}}$=0.52\ifmmode\pm\else\textpm\fi{}0.23 and ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$/${\mathrm{\ensuremath{\Gamma}}}_{\mathit{p}}$=0.41\ifmmode\pm\else\textpm\fi{}0.014, respectively. In addition we identified new $^{37}\mathrm{K}$ levels at ${\mathit{E}}_{\mathit{x}}$=3.272\ifmmode\pm\else\textpm\fi{}0.002 and 2.967\ifmmode\pm\else\textpm\fi{}0.002 MeV.

Measurement of the resonance at ER=1422 keV in 36Ar(p, gamma )37K.

A new resonance at [ital E][sub [ital R]]=1422 keV has been found in the reaction [sup 36]Ar([ital p],[gamma])[sup 37]K. From its measured resonance strength of [omega][gamma]=(6.0[plus minus]1.5)[times]10[sup [minus]4] eV the proton partial width [Gamma][sub [ital p]] can be calculated. Our data suggest a value of [Gamma][sub [gamma]]/[Gamma][sub [ital p]][approx]40 for the ratio of [gamma] to proton partial width for the corresponding state at [ital E][sub [ital x]]=3241 keV in [sup 37]K. We find that the corrected distribution of Gamow-Teller strength below the isobaric analog state as obtained from the [beta]-delayed proton decay of [sup 37]Ca is in agreement with the results inferred from the [sup 37]Cl([ital p],[ital n])[sup 37]Ar reaction.

Beta -delayed proton decay of 20Mg and its astrophysical implications.

We have studied the {beta}-delayed proton decay of {sup 20}Mg to search for the 2645 keV state in {sup 20}Na. This state is of astrophysical interest, because any proton capture through this state would dominate the stellar reaction rate of the reaction {sup 19}Ne({ital p},{gamma}){sup 20}Na. This reaction determines the break out from the hot CNO cycle. Several proton groups have been observed and their log{ital ft} values have been determined. No protons from the 2645 keV state were seen and a lower limit of log{ital ft}{ge}5.85 has been established. The impact of this result on the {sup 19}Ne({ital p},{gamma}) rate is discussed.

37Ca beta + decay and the efficiency of the 37Cl detector for high energy neutrinos.

There is a qualitative disagreement between the Gamow-Teller strength function extracted from the \ensuremath{\beta}-delayed proton decay of $^{37}\mathrm{Ca}$ and that estimated using the $^{37}\mathrm{Cl}$(p,n) reaction. Adelberger and Haxton have shown that this could be explained by the strong tendency of high energy states in $^{37}\mathrm{K}$ to proton decay to $^{36}\mathrm{Ar}$ in its first excited state. We present the results of an experiment confirming this idea. By detecting proton-\ensuremath{\gamma} coincidences we determined that the fraction of $^{37}\mathrm{Ca}$ decays that feed the first excited state of $^{36}\mathrm{Ar}$ is 2.9\ifmmode\pm\else\textpm\fi{}0.8 %. This should be compared to a shell model prediction of 1.80\ifmmode\pm\else\textpm\fi{}0.20 %. We also present some information on the \ensuremath{\beta} decay of $^{25}\mathrm{Si}$ obtained as a by- product of our experiment.

Doorway-state formation and structure in beta -delayed proton decay.

The structure in the /beta/-delayed proton spectra of the precursors /sup 1//sub 66//sup 47/Dy/sup /ital g//, /sup 1//sub 68//sup 49/Er/sup /ital g//, and /sup 1//sub 70//sup 51/Yb/sup /ital g// is analyzed within the framework of a doorway-state model. Indications from /gamma/-ray decay studies, /beta/ strength-function measurements, and calculations of state densities and Gamow-Teller strength distributions, lead us to suggest that some of the observed proton transitions arise from the preequilibrium decay of doorway states populated in /beta//sup +/ decay or electron capture.

Decay of 149Erg+m by positron and delayed proton emission and by electron capture.

In this study the decay of $^{149}\mathrm{Er}^{\mathrm{g}+\mathrm{m}}$ by positron emission, electron capture, and \ensuremath{\beta}-delayed proton emission was investigated. Gamma rays associated with $^{149}\mathrm{Er}^{\mathrm{m}}$ decay were placed in a decay scheme on the basis of \ensuremath{\gamma}\ensuremath{\gamma} and x\ensuremath{\gamma} coincidences and half-life. We assigned 120 \ensuremath{\gamma} rays deexciting 91 levels in $^{149}\mathrm{Ho}$ to 8.9\ifmmode\pm\else\textpm\fi{}0.2 s $^{149}\mathrm{Er}^{\mathrm{m}}$ decay. The \ensuremath{\pi}${s}_{1/2}$ single-particle state in $^{149}\mathrm{Ho}$ was observed to occur at 49.0 keV above the \ensuremath{\pi}${h}_{11/2}$ ground state. A (3.5\ifmmode\pm\else\textpm\fi{}0.7) % isomeric transition decay branch and a (0.18\ifmmode\pm\else\textpm\fi{}0.07) % \ensuremath{\beta}-delayed proton decay branch were determined for $^{149}\mathrm{Er}^{\mathrm{m}}$ decay. Three additional \ensuremath{\gamma} rays were assigned to 4\ifmmode\pm\else\textpm\fi{}2 s $^{149}\mathrm{Er}^{\mathrm{g}}$ decay and a (7\ifmmode\pm\else\textpm\fi{}2) % \ensuremath{\beta}-delayed proton decay branch was determined. Measured EC/${\ensuremath{\beta}}^{+}$ ratios to proton emitting states in $^{149}\mathrm{Ho}$ resulted in a (${\mathit{Q}}_{\mathit{EC}}$-${\mathit{S}}_{\mathit{p}}$)=7.${0}_{\mathrm{\ensuremath{-}}0.4}^{+5.0}$ MeV for $^{149}\mathrm{ER}^{8}$ decay and a ${\mathit{S}}_{\mathit{p}}$=1.${4}_{\mathrm{\ensuremath{-}}0.6}^{+10}$ MeV for Ho. The \ensuremath{\beta}-delayed proton spectrum from $^{149}\mathrm{Er}^{\mathrm{g}}$ consisted of a highly structured component corresponding to the deexcitation of levels between 4 and 5 MeV in $^{149}\mathrm{Ho}$ and a structureless component corresponding to decay from higher levels. The \ensuremath{\beta}-strength function for $^{149}\mathrm{Er}^{\mathrm{g}+\mathrm{m}}$ decay is discussed in terms of single-particle shell-model structure, weak coupling to the $^{148}\mathrm{Dy}$ core, and decay of \ensuremath{\pi}${h}_{11/2}$ protons across the shell closure to the \ensuremath{\nu}${h}_{9/2}$ neutron orbital.

The decays of the [formula omitted] β-delayed proton precursors 83Zr, 87Mo and 91mRu

The decays of the nuclides 83Zr, 87Mo and 91mRu have been studied with singles proton counting as well as with pX and pγ coincidences. The half-lives for the three nuclides were measured to be 37.8 ± 1.1 s, 13.3 ± 0.4 s and 7.6 ± 0.8 s, respectively. The proton branch in the decay of 83Zr that populates the first excited state in 82Sr was measured to be (6 ± 4) % of the total delayed proton decay. The corresponding branch in the decay of 87Mo, populating the first excited state in 86Zr was measured to be (15 ± 8) %. Restrictions to the possible spin and parity assignments of 83Zr and 87Mo were deduced from comparisons between the experimental excited-state branches, and those predicted from a statistical model of delayed particle decay. Fits to the endpoints of the delayed proton spectra from 83Zr and 87Mo yielded values of the energy available for delayed proton decay ( Q e.c.− B p) of 2.75 ± 0.10 MeV and 3.7 ± 0.3 MeV, respectively. Comparison between calculated and experimental proton spectra was used as an argument that the source of 91Ru activity is actually a 1 2 − isomer.