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USNDP

3H (1987TI07)


(Not illustrated)

GENERAL:

Ground State:

Jπ = 1/2+,

μ = 2.978960 ± 0.000001 nm,

M - A = 14.94991 ± 0.00003 MeV.

The wave function for the triton bound state is calculated to be mostly S-state (≈ 90%) with S'-state (≈ 1%) and D-state (≈ 9%) admixtures depending on the potentials used (1979SA15, 1986IS06). See also (1980HA10, 1980LO091983FR19, 1984CI05, 1984CI09, 1984MU23). The measured magnetic moment for 3H is μ = 2.978960 ± 0.000001 nm (1978LEZA). Calculations which include both impulse and pion exchange contributions are in fairly good agreement with the measured trinucleon magnetic moments (1985TO21). Recent calculation with a six-quark bag model (1986BH05) are also compatible with the data for 3H and 3He. See also (1982WO03, 1983BU07).

The rms charge and magnetic radii for 3H determined from electron scattering (see reaction 8 (a)) are γcrms = 1.63 ± 0.03 fm and γmrms = 1.72 ± 0.06 fm. In general two-body force calculations give values of γcrms which are ≈ 10% too large (1986GIZS). This discrepancy has not yet been fully resolved by the addition of three-body forces although there are calculations (1986IS06) which, when extrapolated to give the correct triton binding energies, are in resonable agreement with γcrms (exp). (However, the form factor problem remains (1986GIZS)). See also (1985FR12, 1986SAZG) which examine the way in which the triton bound state observables scale with binding energy.

The binding energy of 3H is 8.481855 ± 0.000013 MeV (1985WA02). Many calculations have been done to predict the binding energy of 3H and 3He (see the reviews of (1984FR16), 1986FRZU, 1986GIZS) and references given below. It is observed in (1986GIZS) that two-body force calculations with realistic forces underbind 3H by ≈ 1 MeV whereas calculations with three-body forces give binding energies too large by ≈ 0.5 MeV, although it is pointed out in (1986SA2A) that three-body force calculations can give correct biding energies if the cut-off mass is taken to be 700 MeV.

Charge and magnetic form factors for 3H have been determined from electron scattering experiments (see reaction 8 (a)). Measurements for q2 from 23 to 31 fm-2 are reported in (1985JU01). The available data indicate that the magnetic form factor is similar to that for 3H which has a diffraction minimum at a higher value of q than predicted by impulse approximation calculations. The isobar model of (1983ST11) with meson-exchange currents satisfactorily accounts for the differences. (See also (1986SA07, 1986SA08).) Calculations of the charge form factor with two-body potentials are in serious disagreement with experiment for 3He in that the theoretical momentum transfer at the first minimum is too high, and the height of the second maximum is too low. (See also reaction 8 (a).) However it is pointed out in (1987PL2A, 1987ST09) that the 3H charge form factor is well described by theory if the correct pseudoscalar vector coupling for the pion-nucleon vertex is used in the calculation of the exchange current contributions. For other recent calculations see (1985BO44, 1985MA24, 1986CI05, 1986FR15, 1986HA12, 1986KI17, 1986LI09, 1986SA07, 1986SA08). The addition of a three-body force increases the calculated value of the charge form factor in the region of the second maximum by 50%, but a factor of three is needed (1986GIZS). The very recent work of (1987BE30) reporting on measurements of 3H and 3He isoscalar and isovector form factors also reviews the extent of agreement between current theories and experiment.

The review of (1986FRZU) notes that calculational techniques for the trinucleon system have progressed to the point where critical examinations of three-nucleon forces, relativistic effects of nucleon motion, and explicit non-nuclear degrees of freedom such as pions, isobars, quarks etc. can be made with some confidence.

A great deal of work has been done to explore three-body force effects. See for example the conference proceedings (1984FA2A, 1986BE2A) and summaries (1986CA2A, 1986CH2C, 1986FRZU, 1986GIZS, 1986TO2A) and the review (1984FR16). See also recent calculations of (1976HA40, 1977HE22, 1979OS08, 1979YA03, 1981CA14, 1981CO2B, 1981LO08, 1982CO04, 1982DA06, 1982DA19, 1982DA20, 1982DA25, 1982GL05, 1982MU13, 1982ZA01, 1983CA10, 1983CO17, 1983ME14, 1983MU06, 1983WI05, 1984CO18, 1984IS04, 1984UE01, 1984WI12, 1985CH17, 1985CH22, 1985RO02, 1986CH13, 1986SA08, 1987NA02, 1987ST09).

Relativistic effects in the trinucleon bound state are considered in (1977BA25, 1979HA36, 1980MA22, 1981GA15, 1981KO02, 1986GL01). The effects of including tensor forces in three-body calculations are discussed in (1986OS04, 1986OS07).

The quark structure of the trinucleon and the effect of quark clusters on its ground state properties have been studied by (1983BE08, 1983NE08, 1983NE12, 1984GR18, 1984SU03, 1985FA01, 1985KO02, 1985MA24, 1985MA30, 1985MA67, 1985VE15, 1986AB02, 1986BH05, 1986CH22, 1986GU12, 1986KI17, 1986OE02, 1986SA02).

Trinucleon asymptotic normalization constants have been calculated by (1976LE01, 1979GI2B, 1979KI03, 1980HA03, 1980SA23, 1982BO22, 1982FR07, 1984FR16, 1986IS01).

Binding energy calculations in addition to those mentioned above have been carried out by ( 1975HE11, 1976DZ01, 1976SH16, 1977EL05, 1977GL07, 1977HE16, 1977NU2A, 1978BI02, 1978CH21, 1978EF01, 1978GI10, 1978KI14, 1979HA27, 1979OS02, 1979SA15, 1980BA21, 1980GO10, 1980MI19, 1980PA12, 1981HA41, 1982BA58, 1982DA24, 1983HA19, 1983OR06, 1984GI01, 1984JI05, 1984OR02, 1985AB12, 1985EF01, 1985OR03, 1985OR05, 1985OR06, 1985OR08, 1985RU04, 1986BE25, 1986HA10, 1986HA36, 1986KE07, 1986NA10, 1986PE08, 1987TO04).

Theoretical papers not mentioned elsewhere are (1975AF01, 1975GO04, 1975MC17, 1977AF02, 1977BA20, 1977BE61, 1977BL11, 1977EM01, 1977SO05, 1978HY01, 1978ST28, 1979BE09, 1979DE13, 1979PE06, 1980ZN01, 1981KO37, 1981LE22, 1981PA05, 1981SA27, 1982AT01, 1983GR24, 1983ME06, 1985BO17).

1. 3H(β-)3He Qm = 18.594 keV

Early measurements of the half-life are reviewed in (1975FI08). A recent evaluation of available experimental data was carried out by (1984HO2A). The recommended value is τ1/2 is 12.3 ± 0.1 years. The standard deviation on the recommended value is based on the disagreement between the evaluated measurements. A very recent measurement reported in (1987SI01) gave τ1/2 = 12.32 ± 0.03 years. The Q-value adopted by (1985WA02) is 18.594 ± 0.008 keV. A recent measurement by (1985SI07) with a tritium implanted Si(Li) detector gave 18.577 ± 0.007 KeV for the 3H end point energy. See also the related mass-difference measurements of (1981SM02, 1984LI24, 1984NI16, 1985LI02).

Using the evaluated data for the half life and end-point beta-decay energy, (1978RA2A) obtained a value for the Gamow-Teller matrix element, < σ · τ > = √ 3(square root of 3)(0.975 ± 0.007). This was based on a value of the ratio of axial-vector to polar-vector coupling constants |GA/GV'| = 1.237 ± 0.008. On the basis of more recent data, (1982BA20) has suggested using |GA/GV'| = 1.259 ± 0.009. This results in a value for the Gamow-Teller matrix element of < σ · τ > = √ 3(square root of 3)(0.958 ± 0.008) which (1982BA20) compares with calculated values in various approximations. The value calculated using π- and ρ- exchange with point couplings agrees with this modified value. calculation of < σ · τ > including axial meson exchange current effects (1984CI01) gave agreement with experiment. An experiment to measure < σ · τ > in a model-independent way is discussed in (1985BUZZ). The effect of the atomic and molecular environment on the value of < σ · τ > deduced from experiment was studied by (1983BU13) and found to be significant, and could imply a higher probability of finding delta isobars in the triton. An analysis by (1984BO03) of experimental results which included 3H beta decay placed limits on unusual coupling constants.

Measurements of the 3H beta spectrum to determine the antineutrino mass were carried out by (1981SI18, 1983DE47) who determined mν < 65 eV and mν < 50 eV, respectively. The experiment of (1980KO2A, 1980LU2A, 1981LU07) on the 3H beta spectrum in the valine molecule indicated a finite antineutrino mass, 14 < mν < 46 eV. The effects of molecular structure on the 3H beta spectrum shape were studied by (1982KA1X, 1983KA33) who determined that the lower limit of 14 eV should be replaced by a higher value. See also (1985KA21). However, the experiments of (1980KO2A, 1980LU2A, 1981LU07) were re-evaluated by (1984SI2B) and (1985BE01) who found that there is no conclusive evidence for mν > 0. More recent studies by (1985BO34, 1985BO53) with improved apparatus and techniques found mν > 20 eV. Very recently an analysis (1987BO07) of 3H decay in valine gave a neutrino mass of 30.3+2-8 eV while measurements of free molecular tritium decay reported in (1987WI07) gave an upper limit of 27 eV for mν. In other work bearing on the antineutrino mass measurements it was found that the effects of Coulomb corrections (1983WU01) and radiative-spectrum corrections (1983RE13) could prove important in the determination of the neutrino mass from the 3H beta spectrum. The effects of atomic final state interactions on the neutrino mass-determination problem were studied by (1983WI02) and found to be negligible. Two-step processes were examined by (1984ST09) and found to be unimportant. See also the recent work of (1986EM01, 1986LI08, 1987DR03). An experiment utilizing free atomic and molecular tritium is described in (1985KNZX). The beta spectrum of the tritium molecule is computed by (1985FA05), and it is shown that molecular effects are crucial in determinations of the neutrino mass. See also the recent work of (1986AR07, 1986AR18, 1986AR19, 1987SZ01). Electron energy losses were studied in (1986GE03) for the effect on neutrino mass determinations. A method for determining the neutrino mass by means of the photon spectrum from radiative beta capture in 3H is discussed by (1985PA25) which also contains a review of neutrino mass determinations. A study of the effects of a possible neutrino mass on 3H longitudinal polarization etc. was reported in (1986KE08). The possibility of an influence by intense electromagnetic waves on the beta decay of polarized (1983TE04, 1983TE06, 1984TE02, 1984TE03) or unpolarized (1983TE03) 3H has been studied. An experimental test of laser enhancement of 3H beta decay (1985BE26) found no effect. The possibility of observing recoilless resonant neutrino absorption in 3H beta decay was pointed out (1983KE07). Other calculations are found in (1975BE49).

2. 2H(n, γ)3H Qm = 6.257 Eb = 6.257

Measurements of the cross section cited in the previous review (1975FI08) included a measurement at 0.01 eV, six measurements at thermal energies, one at 2.4 MeV and one at 14.4 MeV. No information on gamma angular distributions had been obtained. More recent measurements made at thermal energies (1973IS08, 1979ALZL, 1982JU01) are listed in Table 3.1 (in PDF or PS).

As noted in (1975FI08) the calculation of (1973HA30) which included meson exchange currents gave a thermal neutron capture cross section of 0.52 ± 0.05 mb in good agreement with experiment. See also (1981SH25) for a review of experimental and theoretical results for this reaction. A recent calculation (1983TO12) investigated the role of meson currents along with the use of wave functions obtained from the Faddeev equations using realistic NN forces as well as the effects of three-nucleon forces. The capture of thermal neutrons by deuterons proceeds predominantly via a magnetic dipole transition into the S' state of mixed spatial symmetry in 3H (1975FI08). The effects of S' and D state admixtures in 3H are discussed by (1973HA30, 1981SH25, 1983TO12).

Measurements of doubly radiative thermal neutron capture have been made by (1977MC05) who found an upper limit σ(2γ) = 8 ± 15 μb for 700 keV < Eγ < 5550 keV. See also (1979WU05). Calculations with a single-particle direct capture model (1976LE27) gave σ(2γ) = 21 nb, while a detailed three-particle calculation (1977MC05) gave σ(2γ) = 26 nb.

An analysis (1974MC06) of parity non-conserving amplitudes in 2H(n, γ)3H indicates that gamma circular polarization and asymmetry depends on isoscalar and isovector parity non-conserving interactions respectively. See also (1986DE24, 1986DU14). The asymmetry of the photons from polarized thermal neutron capture was measured by (1984AV2A) to be (7.8 ± 3.4) × 10-6. A very recent measurement is reported in (1986AV04). Values of the weak coupling constants from the implied parity violations are discussed by (1985DO02, 1985MI10).

At higher neutron energies, measurements of differential cross sections σ(θ) and analyzing powers A(θ) have been made by (1986MI17) and are listed in Table 3.2 (in PDF or PS).

Absolute values for the angle-integrated cross section after detailed balancing are in good agreement with the inverse reaction (see section on 3H(γ, n)). The fore-aft asymmetry, defined by

as = [σ(f) - σ(a)]/[σ(f) + σ(a)],

where the fore and aft angles are the zeros of P2(θ) (approximately 55° and 125°), indicates an anomalously large E2 strength in the 2H(n, γ) reaction. By using the (p, γ) asymmetries from (1984KI06), the ratio as(n, γ)/as(p, γ) is determined to be ≈ -0.5 in disagreement with the factor of -0.2 expected from effective charge arguments. This result is consistent with the result obtained from the inverse reaction measurements of (1981SK02).

3. 2H(n, n)2H Eb = 6.257

Measurements of total cross sections up to 270 GeV, differential scattering cross sections up to 152 MeV, and polarizations and analyzing powers upt to 35 MeV have been reviewed in (1975FI08). More recently total cross-section measurements were made at 4.2 MeV by (1975CA30) and from 0.07 to 20 MeV by (1980PH01). References for differential scattering, polarization and analyzing power measurements reported since (1975FI08) are listed in Tables 3.3 (in PDF or PS) and 3.4 (in PDF or PS).

The values cited in the neutron cross-section compilation of (1981MUZQ) for the two scattering lengths (2S+1a) for low energy nd scattering (S is the channel spin) are 4a = 6.34 ± 0.02 fm and 2a = 0.65 ± 0.03 fm. (Note however the measurement of (1975CA30) which is in disagreement.) These values are consistent with theoretical calculations cited in (1975FI08) and are well reproduced by the calculation of (1982PA21) based on a formulation using zero-energy Faddeev-type equations and the s-wave interaction model of Malfliet and Tjon (1969MA2A). Other calculations of 4a and 2a were made by (1975BA2B, 1975WH02, 1978AL22, 1980HA40, 1981BE18, 1983PE18, and 1983ZA06, 1986PE08). The possible effect of the three-nucleon force on 2a has been studied by (1984DE20). For discussions of the correlation between the nd scattering lengths and the triton binding energy, see the 3H General section of this compilation.

Phase-shift analyses for cross sections and polarization data have been carried out at 2.45 MeV (1974BO04 and 1978BO28), and at 15 - 50 MeV (1986KL04). Theoretical predictions of nd phase shifts for energies below 45 MeV were made by (1974LA16, 1975AL07, 1975WH02, 1978FU01, 1978ST06, 1980HA40, 1982DU20, 1983KU08, 1987TO04). A phase shift calculation near the deuteron-breakup threshold was done by (1983PO04).

Calculations of elastic scattering cross sections for En below 50 MeV have been made by (1975AL07, 1975MO17, 1975ST11, 1976BE19, 1977OR01, 1978AL22, 1978ST06, 1980HA40, 1981ZA06, 1982DU20, 1983KU08, 1986HA36).

Theoretical predictions of polarizations and analyzing powers in nd scattering below 50 MeV have been made by (1974DO2A, 1975ST11, 1976BE19, 1978ST06, and 1981ZA06, 1986HA36). See also (1981ZH02, 1983MO24). A calculation of differential cross section and deuteron tensor analyzing power for incident energies 0.3 to 1 GeV taking into account the contributions of tribaryon resonances has been done by (1981KO09). Variational methods with separable potentials were used by (1974BR01, 1979ST17) for calculating off-shell amplitudes for 2H(n, n).

Most of the aforementioned calculations of three-nucleon observables involved solution of some version of the Faddeev equtions or application of various approximation methods in the framework of the Faddeev equations. (See the General discussion on 3H for more details.)

4. 2H(n, p)2n Qm = -2.225 Eb = 6.257

Measurements and summaries (S) of deuteron breakup by neutrons published from 1974 to the present are listed in Table 3.5 (in PDF or PS). Earlier work is reviewed in (1975FI08). In a three-particle reaction, five kinematic variables must be measured to make the experiment kinematically complete (e.g. Eni, θn1, En2, θn2, Ep). Table 3.5 (in PDF or PS) indicates the particles detected and the coincidence requirements. Detector angles are not given explicitly, but the type of geometry, the main emphasis of each experiment and the region of phase space explored is indicated.

Some of the experimental difficulties associated with measurements of the breakup process are discussed in (1974TH2A). A system designed for detecting two neutrons is presented, and various ways to reduce the background are discussed. Measuremants of neutron analyzing power in the n + d breakup reaction have been made at incident neutron energies of 14.3 and 29.6 MeV by (1978FI2A) (see Table 3.5 (in PDF or PS)). No others have been reported. References to several early reviews of experimental and theoretical wrok on the three-body breakup reactions are given in (1975FI08) along with a brief discussion of the general features of the cross section and particle spectra. For more recent reviews see (1976SL2A, 1978KU13, 1978SL2A).

The total cross section for n + d breakup measured by (1975PA21) and others (see reviews (1976SL2A, 1978KU13)) increases almost linearly from zero at threshold (3.34 MeV) to a maximum of ≈ 180 mb at 12.2 MeV and then decreases slowly to ≈ 100 mb at 47 MeV. The peaks or enhancements in the proton energy distribution observed in nd breakup are associated (1975FI08) with the np and nn final state interactions (FSI) and the nn and np quasifree scattering (QFS). See (1975KU25, 1976SL2A, 1978KU13) for extensive discussions of these features including the kinematics of the processes. Calculations based on Faddeev formalism and simple NN interactions correctly predict both shapes and magnitudes of the breakup spectra (1976SL2A, 1978KU13). Experimental and theoretical investigations of the QFS portion of the proton spectra are reviewed and discussed in (1976SL2A and 1978KU13). See also (1975BO15, 1977FU05, 1978CA2A, 1979SO02, 1980GU11, 1980VO06).

Many measurements of the 2H(n, p)2n reaction have been carried out for the purpose of extracting the nn scattering length ann and the effective range γnn. Early work is reviewed in (1975FI08). For more recent work see references of Table 3.5 (in PDF or PS) and the reviews mentioned above. An exhaustive review of experimental and theoretical methods of determining ann including discussions of possible charge-symmetry breaking and violations of charge independence implied by the results is given in (1975KU25). The review of (1976SL2A) discusses all aspects of the n + d breakup reaction with emphasis on experimental data and the relative accuracy of various methods for extracting ann. It is apparent in these reviews that the values quoted vary slightly depending on the classes and subclasses of experiments that are included in the averages and the type of analysis. An average value of ann = -16.3 ± 0.6 fm is obtained (1976SL2A) from kinematically complete 2H(n, p)2n experiments using Faddeev theory (see also 1978SL2A). For the nn effective range γnn, the value obtained by (1985SL2A) is γnn = 2.76 ± 0.11 fm. It is concluded (1975KU25) that the difference between ann and the neutron proton scattering length anp provides clearcut evidence for charge independence violation, but a discrepancy between ann and the proton-proton scattering length app (after Coulomb correction) may not necessarily imply breaking of charge symmetry because of the dependence of the extracted value of app on off-energy-shell deuteron breakup by protons as well as neutrons.

The effect of three-nucleon forces (i.e. forces which depend in an irreducible way on the simultaneous coordinates of three nucleons when only nucleon degrees of freedom are taken into account) on the nd breakup process is investigated by (1984ME03), and it is determined that such a force could produce noticeable effects. In (1982SL2A) it is suggested that the difference between the accepted value of ann (-16.3 ± 0.6 fm) and the value obtained from the 2H(π-, p)2n reaction (-18.6 ± 0.48 fm) can be explained by a three-body force and that the effects of this force are different for neutron pickup and proton knock-on processes in the 2H(n, p)2n reaction. This suggestion is examined in the review of trinucleon properties by (1984FR16), and it is concluded here that evidence for significant three-nucleon force effects is largely circumstantial, but nontrivial. See also the reviews of (1986GIZS, 1986TO2A). It is shown in work reported in (1984SL02) that corrections arising from the magnetic dipole interactions are relevant to the discrepancy in scattering parameters deduced from defferent reactions.

It is suggested (1982SV01, 1984FR16) that the triple differential cross sections for 2H(n, p)2n could be used to test for the presence of tensor force effects. See also the calculations of (1977ST16, 1979ST05) which show significant differences in the predictions of breakup reaction observables by different potential models.

5. 2H(p, π+)3H Qm = -134.6 Eb = 5.494

Many new experimental and theoretical studies of the 2H(p, π+)3H reaction have been made in the past few years. Measurements and summaries of differential cross sections and analyzing powers obtained with polarized proton beams published since the previous compilation (1975FI08) are listed in Table 3.6 (in PDF or PS).

A survey of experimental and theoretical work on (p, π+) reactions, including reaction 5, can be found in (1981FE2A). See also the reviews of (1979HO2A, 1979ME2A).

The differential cross section for the reaction is forward peaked. For example at 5°(lab) (1977AS06) has reported σ(θ) = 47, 28, 8 μb/sr at Ep = 410, 605 and 809 MeV respectively, while at back angles 110° < θcm < 160° the cross section is nearly flat and within the range 0.9 to 1.25 μb/sr at Ep = 425, 450, 475, 500 MeV (1984AB2A). Analyzing power angular distributions are characterized (1984LO08, 1982LO17) by a gradual change in shape from a negtive maximum near 100° at 277 MeV to a large positive maximum near 90° at 500 MeV (1981CA08). Recent data at 650 and 800 MeV (1984KI2D) show unexpected energy and back-angle structure in both differential cross section and analyzing power at 800 MeV, and the authors speculate that the anomaly is related to the delta-delta component in the deuterion ground state. Also, large structure were seen in the 0.6 - 1.5 GeV back angle data of (1985BE46), who suggest possible baryonic delta excitations in the intermediate state.

Experimental and theoretical interest in the (p, π+) reaction on light nuclei was originally stimulated by the prospect that the reaction would provide a probe of nuclear structure at high momentum transfer, but problems with understanding the reaction mechanism have proved to be a barrier to this objective. Various theoretical approaches to the problem (DWBA single-nucleon mechanisms, other single-nucleon mechanisms, and two-nucleon models) are reviewed in (1979HO2A, 1979ME2A, 1981FE2A). The theoretical situation for 2H(p, π+)3H is unsatisfactory. No detailed calculations have been sucessful in describing both differential cross sections and analyzing powers (1984LO08). Work in development since the previous review includes the microscopic two-nucleon model calculations of (1982IQ2A) and (1982DI2A) and the isobar-doorway model work of (1984KE02). Various wave function effects within the coupled channels delta-isobar model were investigated by (1982SA25). A recent calculation of all helicity amplitudes for 2H(p, π+) in the GeV region with the relativistic model is reported in (1986LO02). For other recent theoretical work see (1977GI06, 1978IS06, 1979GR03, 1979GR12, 1979GR19, 1979LA02, 1981BL12, 1981KO04).

6. 3H(γ, π-)3He Qm = -139.039

Only one measurement for this reaction has been reported since the pervious compilation (1975FI08). Measurements of neutral and charged pion photoproduction in 3H and 3He by bremsstrahlung photons with Emax = 500 MeV were reported in (1984BE08). See also reactions 6 and 7 in 3He for related information.

7. (a) 3H(γ, n)2H Qm = -6.257
(b) 3H(γ, p)2n Qm = -8.482

Only a few measurements of the photodisintegration of 3H had been done prior to 1974, and they are listed in the previous compilation (1975FI08). More recently, both the two-body reaction (a) and the three-body reaction (b) photodisintegration cross sections were measured simultaneously from threshold to ≈ 25 - 32 MeV (1980FA03, 1981FA03). Monoenergetic photons were used and neutrons were detected. (See also 1981FA03) for a thorough review of experimental work.) For reaction (a) the cross section rises sharply from threshold to maximum of ≈ 0.9 mb at 12 MeV, then decreases only slightly to 0.8 mb at 19 MeV. For reaction (b) the cross section rises sharply from threshold to a maximum of ≈ 0.9 mb at 14 MeV and then falls smoothly to ≈ 0.4 mb at 26 MeV. The experiments of (1981FA03) included measurements of the 3He(γ, n)2p reaction by the same techniques used for reactions (a) and (b). Detailed comparisons of the three reactions measured and of previous 3He(γ, p)2H data (1973TI05, 1975FI08) were made. The results were (a) the two-body breakup cross sections for 3H and 3He have nearly the same shape but the3He cross section is lower in magnitude, (b) the three-body breakup cross section for 3He is higher in magnitude, broader in the peak region, and rises less sharply from threshold than for 3H, and (c) the differences between the cross sections for the breakup modes largely compensate in their sum so that the total photon absorption cross section is nearly the same for 3H and 3He. The integrated cross sections and their first and second moments (1981FA03) are listed in Table 3.7 (in PDF or PS).

Measurements of differential cross sections for reaction (a) at angles from 45° - 135° at photon energies of 6.7, 7.6, and 9.0 MeV, and at 90° over the energy range from 18 - 31 MeV were listed in (1975FI08). More recently (1981SK02) measured the cross section at 55°, 90°, and 125° over the energy range from 15 - 36 MeV by detecting the deuterons. From these data and published data for 3He(γ, p) (see section on 3He(γ, p)) the 3H fore-aft asymmetry (see section on 2H(n, γ)) is found not to be -1/5 that for 3He as predicted by simple effective charge arguments, but (although negative) it is only about half the magnitude of that of 3He(γ, p), and has approximately the same energy dependence. This is consistent with the results obtained from the inverse reaction (1986MI17) (see section on 2H(n, γ)).

For reaction (b) measurements of the differential cross section for angles 45° - 135° made at a photon energy of 10.8 MeV, and at 90° for photon energies 18 - 31 MeV are listed in (1975FI08), No new measurements of the 3H(γ, p)2n differential cross section have been reported.

Many theoretical treatments of the trinucleon photoeffect do not distinguish between 3H and 3He. Thus the section on 3He should be consulted in addition to the work listed here. The previous compilation (1975FI08) includes references to a number of calculations of the excitation function for 3H(γ, n) as well as calculations of the integrated and bremsstrahlung-weighted cross sections and discussions of sum rules for A = 3 photodisintegrations. See also the review of (1977CI2A) and see (1981FA03) which contains an extensive summary of theoretical work for trinucleon photodisintergration. A calculation by (1975GI01) using a separable-potential Faddeev mode explored the charge dependence and asymmetry effects in 3H(γ, n) and 3He(γ, p). Agreement with the two-body photodisintegration (reaction a) data of (1981FA03) is fair, but some details are incorrectly predicted, e.g. the 3H(γ, n) cross section is underestimated at energies below the peak. Electric dipole transitions are calculated by (1977MY01, 1979MA03) and comparisons with sum rules are discussed. A recent calculation by (1977VO11, 1981VO07) for 3H(γ, n) and 3H(γ, p) total cross sections used realistic NN potentials and the method of hyperspherical functions with an interpolation approach. The energy range considered was 10 - 8 MeV and the agreement with experiment was satisfactory over this range, but see (1981FA03) for a detailed comparison.

A discussion of the integrated cross sections and moments of Table 3.7 (in PDF or PS) and comparison with calculated sum rules is given in (1981FA03). As noted there the value for the 3He integrated total photodisintegration cross section σ(int) is 28.2 ± 2.8 MeV mb at 30 MeV (obtained by combining data in Table 3.7 (in PDF or PS) with published data for 3He(γ, p) (1975FI08)). This comparable to the corredponding 3H value of 29.0 ± 3.0 MeV mb.These values are about 40% of the strength predicted by (1978DR02) for the entire three-body photodisintegration cross section integrated up to the pion threshold. Agreement of the moments σ-1 and σ-2 with sum rules is poor (1981FA03) and raises questions about the adequacy of the calculations and the principle of charge symmetry.

8. (a) 3H(e, e)3H
(b) 3H(e, e'n)2H Qm = -6.257
(c) 3H(e, e'p)2n Qm = -8.482

Measurements of elastic and inelastic electron scattering cross sections up to q2 (four-momentum squared) of 8 fm-2 are summarized by (1975FI08). More recent measurements are listed in Table 3.8 (in PDF or PS) and 3.9 (in PDF or PS). The 3H charge form factor was measured in the range 0.29 < q2 < 1 fm-2 by (1982BE10). Both the charge and magnetic form factors were measured in the range 0.0477 < q2 < 2.96 fm-2 by (1984BE46). Measurements of the charge form factor for 0.3 > q2 > 22.9 fm-2 and the magnetic form factor for 3.1 > q2 > 31.3 fm-2 were reported in (1985JU01). A very recent measurement of the isoscalar and isovector form factors for 3H and 3He for momentum transfer 0.09 > q2 > 8.4 is reported in (1987BE30). Charge and magnetic radii are quoted by (1984BE46) as rcrms = 1.63 ± 0.03 fm and rmrms = 1.72 ± 0.06 fm; by (1985JU01) as rcrms = 1.76 ± 0.04 fm and rmrms = 1.72 ± 0.02 fm; and by (1986MA2A) as rcrms = 1.81 ± 0.05 fm and rmrms = 1.80 ± 0.09 fm.

Theoretical calculations for thr charge form factor of 3H and 3He were reviewed in (1977CI2A), who came to the conclusion that it is inadequate to use nonrelativistic wave functions resulting from conventional models of the two-body potentials, and to include only nucleon degrees of freedom in the electron-nucleus interaction Hamiltonian. A variational calculation with correlated basis functions was carried out for 3H and compared with the results of other methods by (1985CI04).

The effect of many-body exchange currents on tri-nucleon charge form factors is to increase the height of the second maximum hence reducing the discrepancy between calculated and empirical values (1977RI15). The effects of the experimental uncertainty of the neutron charge form factor on the charge form factors of 3H and 3He have been investigated and are seen to be sizable (1975BR22). Analysis of parity-violating asymmetries in elastic electron-nucleus scattering was made by (1981FI05). The effect of meson exchange currents on the charge and magnetic form factors of 3H was investigated by (1975BA08, 1976HA33, 1976KL02, 1977HA03, 1977RI15, 1979GI08, 1981FR15, 1982HA09, 1983BE08, 1983DR12, 1983HA04, 1984MA26). Inclusion of meson exchange currents considerably improves the impulse approximation fits to the experimental data. See also the work of (1985TO21) on the calculation of trinucleon magnetic moments. The effect on the charge and magnetic form factors of clustering in the 3H nucleus was investigated by (1976TA06). Recent calculations reported in (1987ST09) include single-Δ isobar admixtures in the three-nucleon wave function. A discussion of electromagnetic form factors of 3H is included in the review of trinucleon properties by (1984FR16) and in the very recent experimental paper of (1987BE30). The upper limit of the probability of the interior six-quark compound states in 3H and 3He was calculated from the electron scattering data by (1985KO02), and the effect of such states on magnetic moments was investigated by (1984KA25). However (1985KI12) find the method used to be unreliable and conclude that the meson-exchange current efects dominate those of the six-quark compound states.

No new experimental data have been published on reactions (b) since the compilation of (1975FI08), though a preliminary experiment has been reported by (1984FR2B), however, recent data on reaction (c) at 500, 560 MeV is reported in (1986BA17). A calculation of threshold two-body electrodisintegration of 3H and 3He within the context of exact three-body theory is reported in (1977HE22). A theory for calculating spectral functions and angular distrobutions for electrodisintegration processes on 3H and 3He has been proposed by (1978CI2A, 1979CI2A). In (1979CI2A) a calculation was made of the quasi-elastic peak of 3H and 3He obtained by incoherently summing the cross sections for the two-body and three-body electrodisintegration processes, after integrating over the energy and the direction of the ejected nucleon. A variational three-body wave function is used in the calculations. The importance of final state interactions is pointed out.

9. (a) 3H(π±, π±)3H
(b) 3H(π+, π0)3He Qm = 4.623
(c) 3H(π+, γ)3He Qm = 139.587

Only a few experiments involving pions on tritium targets have been performed. See the review of (1978NE2B) which notes elastic scattering measurements at incident energies 132 - 187 MeV at angles 75° - 135°, 25° - 60°. Measurements of the charge exchange reaction (b) at Eπ = 132 - 148 MeV and angles 100° - 150° and of the capture reaction (c) at 132 - 148 MeV and angles 105° - 130° are also listed. More recent measurements of pion charge exchange on tritium were carried out by (1980GL01) at incident pion momenta of 232 and 252 MeV/c and compared to theoretical predictions. Charge-independence bounds were determined from elastic scattering cross sections.

10. (a) 3ΛH(π-)3He Qm = 43.12
(b) 3ΛH(π-)2H, 1H Qm = 37.62
(c) 3ΛH(π-)1H1H, n Qm = 35.40

Recent reviews of light hypernuclei are found in (1984BO2B, 1984SH07, 1986BO1E, 1986GI2B, 1987SH1H, ). For earlier work see the review of (1975GA2A), and see (1973JU2A, 1977RO04) and references listed in (1975FI08).

Little new experimental information on 3ΛH has been published since the previous compilation (1975FI08). As noted there the ground state spin is J = 1/2, and some evidence exists for a J = 3/2 excited state. The binding energy of 3ΛH was measured (1973JU2A) to be 0.13 ± 0.05 MeV. Results of several measurements of the lifetime of 3ΛH are given in (1975FI08). A more recent measurement described in (1973KE2A) gives τ(3ΛH) = (2.47 + 0.62, -0.41) × 10-10 s for the mean lifetime.

Theoretical calculations of the 3ΛH binding energy are discussed in (1973DA2A, 1974BH2A, 1974GI2A, 1977KO2A, 1977RO04, 1980GE1X, 1980GI2A, 1980OG2A, 1980VE2B, 1981KO2D, 1981TO2B, 1982VE2A, 1983HA2B, 1984BO2B, 1984SH07, 1984SU2B, 1986BO1E, 1986GI2B, 1987SH1H). Calculations of the lifetime and two-body decay mode branching ratios are presented in (1979MA2B). Polarization effects are discussed in (1985LY2A), and a method of calculating the 3ΛH magnetic moment is presented in (1985NA2A). Considerations of charge-symmetry breaking are discussed in (1977GI2B, 1977RO2B).