Photoneutron production cross-sections of beryllium and deuterium at a number of gamma energies below 3 MeV

828

Letters to the editors

Photoneutron production cross-sections of beryllium and deuterium at a number of gamma energies below 3 MeV (Received 23 July 1973) MEASUREMENTS of the (y, n)-cross-sections a,,, of $Be (JAKOBSON,1961; JOHN 1960; WALTER, 1960; GIBBONS, 1959) and of *H (BISHOP, 1950; SNELL, 1950) are scarce, and experimental values are stated with uncertainties up to 10 per cent (WALTER, 1960). Discrepancies between the values given by different authors are even greater, which is especially true for the sharp uY, peak at a gamma energy of 1.692 MeV (JAKOBSON,1961). It might therefore be interesting to note that our measurements of the yield values of photoneutron sources allow uYn to be determined for a number of gamma energies. In a previous publication (BENSCH, 1969) we defined this yield value (Wattenberg constant) pto-in accordance with Wattenberg’s concept (WATTENBERG, 1947, 1949; RUSSELL 1948)--as the neutron emission (in s-3 of 1 g of a target material located in a distance of 1 cm from a 1 Ci point gamma source. Then (BENSCH, 1969, equation 3),

,ur = 3.70 x lO*Oe(N/p)a&47r) where E = fraction of those gamma quanta (per disintegration)

(1) responsible

for neutron production

N = number of target nuclei per unit volume, cm-* p = density of the target material,

g cm-*

u,,,, = photoneutron production cross-section of a target nucleus at the energy E. of the neutron producing gamma quanta, cm*. A. Deuterium a,, (10-8a m2) Gamma emitter

E. (MeV)

This work

SNELL (1950), exp.

HULTHEN(1953), theor.

‘*Ga Z4Na

2.504 2.753

9.26 rt 3 % 13.35 f 3 %

10.6 & 10 % 14.3 f 7.5 %

9.92 14.8

B. Beryllium a,, ( 1O-88m*) E.

Gamma emitter

(MeV)

larSb llsIn 24Na

1.692 2.112 2.753

This work 12.62 f 3 % 2.81 f 4.5 % 5.51 f 3 %

* As read from his Fig. I.-Jakobson

JAKOB~ON(1961)+ 11.6 + 9 % 2.8 f 10 % 6.0 f 10 % does not give any tabulated results.

The quantity plo, which is a handy tool in practical work with photoneutron sources, can be determined directly by way of experiment without reference to equation (1) and, therefore, without Alternatively, if ,u~ and E are known, equation (1) can knowledge of the nuclear data e and 0,. be utilized to give urn at the respective gamma energy. In fact, equivalent schemes have always been used for the determination of eYn. Using our experimental values of & (BENSCH, 1969) and the results of MUECK (1973) on photoneutron spectra, together with e values given in the Nuclear Data Sheets, we derive from (1) the following (7, n)-cross-sections: F. VESELY Atominstitut der Oesterreichischen Hochschulen and F. BENSCH Schuettelstrasse 115 A-1020, Vienna, Austria

Letters to the editors

829

REFERENCES BEN~CHF. and VESELYF. (1969) J. nucl. Energy 23, 537. Bts~op G, R., COLLIEC. H., HALBAN H., HEDGRAN A., SIEGBAHNK., Du TOIT S. and WILSON R. (1950) Phys. Rev. 80,211. GIBBONSJ. H., MACKLIN R. L., MARION J. B. and SCHM~-I-IH. W. (1959) Phys. Reo. 114,1319. HULTHBNL. and NAGEL B. C. H. (1953) Phys. Rev. 90,62. JAKOB~ONM. J. (1961) Phys. Rev. 123,229. JOHN W., LOMBARDF. J., MOORE E. T. and PRO~.%RJ. M. (1960) Bull. Am. Phys. Sot. 5,44. MUECK K. and BENSCHF. (J. nucl. Energy), in press. RUSSELLB., SACHS D., WA~ENBERG A. and FIELDS R. (1948) Phys. Rev. 73, 545. SNELL A. H., BARKER E. C. and STERNBERGR. L. (1950) Phys. Reo. 80,637. WALTER R. L., SHEA M. F. and MILLER W. C. (1960) Bull. Am. Phys. Sot. 5,229. WATTENBERGA. (1947) Phys. Rev. 71,497. WATTENBERGA. (1949) NRC-Preliminary Report No. 6.