- Email: [email protected]
The 14·6 MeV fission cross-section of 241Am
J. Nuc~.
Energy.Part A:
Reactor Science,1960,Vol. 11, Pp. 191to 195. PergamonPress Ltd. Printedin Northern
_-----l&l”1
EKS
-‘1 V
-__1 HE
Ireland
--_-A-F.
l9Jll
VKY
pulses from the counter. The E-particle pulses from the photomultiplier tube were cut off by a fast discriminator incorporating a type DC-S3 crystal diode. The pulses passed by the diode were then stretched, amplified, and fed to a single channel analyser. Fig. 1 shows the differential energy spectrum of the fission fragments from za1Am which was obtained. The small pulses are due not only to cc-particle pile-up but also to pulses caused by nuclear reactions induced by the neutrons in the material of the photo-multiplier. It can be seen that the fission fragment pulses are sufficiently well separated from the background pulses, For the discriminator bias chosen, the number of background pulses was less than 1 per cent of the total number of fission pulses. Counting of the fission pulses continued until a statistical accuracy of 2 per cent was attained and during these measurements the neutron flux at the target was monitored continuously. On the basis of the author’s earlier results,‘&’it was possible to assume that the fraction of 241Am fissions caused by scattered neutrons was negligibly small. The final result obtained for the zalAm fission cross-section for 14.6 MeV neutrons was
The 14.6 MeV fission cross-section of 241Am* (Received 22 September 1958) VALUESof the a41Am fission cross-section for neutrons having energies up to 7 MeV have already been reported.(1*2J In this note, we report the result of a measurement of this cross-section for 14.6 MeV neutrons provided by the reaction T(d,n)lHe. The americium was electroplated upon a platinum disk to form a target 15 mm in diameter which was then placed at a distance of 30 mm from the neutron source. The amount of americium present in the target was deduced from the cc-activity and the known half-life 7 = 458.1 i 0.5 year:13J it was 12pg. The purity of the americium was checked using an cc-spectrometer analysing magnet and it was found that no significant amounts of fissionable impurities were present. The amount of zssPu present was less than 0.6 per cent. A description of the method used to determine the neutron flux at the target and of the procedure used in calculating the fission cross-section have been given previously.(*) Because of the high cc-activity of the americium target a xenonfilled gas scintillation counter was used to count the fission
CT= 2.35 & 0.15 barn. Acknowledgements-The authors thank G. I. KHLEBMKOVfor preparing the target and V. G. NEDOVESOVfor making the magnetic spectrometer analysis of the sample purity. A. N. PROTOPOPOV Iu. A. SELITSKII S. M. SOLOV’EV REFERENCES 1. NOBLES R. A., HENKEL R. L. and SMITHR. K., Bull. Amer. Phys. Sot. 30, 16 (1955). 2. HULETE. K., HOFF R. W., BOWMANH. R. and MICHELM. C. Phys. Rev. 107, 1294 (1957). 3. HALL G .R. and MARKIN T. L., J. Znorg. Nucl. Chem. 4,137 (1957). 4. PROTOPOPOVA. N., SELITSKIIIv. A. and SOLOV’EVS. M., Atomnaya Energiya 4, 2, 190 (1958).
11
_A, 0
10
20
I
,
r
I
30
40
50
60
Pulse height,
70
r
V
FIG. 1.-z41Am fission fragment spectrum measured by single channel analyser with 50 channel width. The arrow indicates discriminator bias defining the lower limit of the integrated fission fragment count.
fragments. A tetra-phenyl coating, applied to the internal walls of the counter, was used to convert the ultra-violet radiation from the xenon into visible light. Following a check of the stability of the counter it was found that over a period of 24 hr the tetra-phenyl vapour given off from the walls reduced the light output by 10 per cent. However, since the duration of the crosssection measurements was less than two hours the counter could be considered as being sufficiently stable. A photo-multiplier type FEU-33 which had a high resolution and delivered a large output current was used to detect the light * Translated from Atomnaya
Capture of electrons into the acceleration regime in betratrons and synchrotrons* (Received 10 February 1958) IN order to make a theoretical analysis of the problem of electron capture into the acceleration regime in betratrons and synchrotrons it is necessary to find a self-consistent solution to the many electron problems taking the initial and boundary conditions into account. Ignoring the effects of space charge, the initial equations of motion of the electrons in the median
Energiya 6, 67 (1959).
* Translated from Atomnaya Energiya 6, 8 (1959). 191
Energy.Part A:
Reactor Science,1960,Vol. 11, Pp. 191to 195. PergamonPress Ltd. Printedin Northern
_-----l&l”1
EKS
-‘1 V
-__1 HE
Ireland
--_-A-F.
l9Jll
VKY
pulses from the counter. The E-particle pulses from the photomultiplier tube were cut off by a fast discriminator incorporating a type DC-S3 crystal diode. The pulses passed by the diode were then stretched, amplified, and fed to a single channel analyser. Fig. 1 shows the differential energy spectrum of the fission fragments from za1Am which was obtained. The small pulses are due not only to cc-particle pile-up but also to pulses caused by nuclear reactions induced by the neutrons in the material of the photo-multiplier. It can be seen that the fission fragment pulses are sufficiently well separated from the background pulses, For the discriminator bias chosen, the number of background pulses was less than 1 per cent of the total number of fission pulses. Counting of the fission pulses continued until a statistical accuracy of 2 per cent was attained and during these measurements the neutron flux at the target was monitored continuously. On the basis of the author’s earlier results,‘&’it was possible to assume that the fraction of 241Am fissions caused by scattered neutrons was negligibly small. The final result obtained for the zalAm fission cross-section for 14.6 MeV neutrons was
The 14.6 MeV fission cross-section of 241Am* (Received 22 September 1958) VALUESof the a41Am fission cross-section for neutrons having energies up to 7 MeV have already been reported.(1*2J In this note, we report the result of a measurement of this cross-section for 14.6 MeV neutrons provided by the reaction T(d,n)lHe. The americium was electroplated upon a platinum disk to form a target 15 mm in diameter which was then placed at a distance of 30 mm from the neutron source. The amount of americium present in the target was deduced from the cc-activity and the known half-life 7 = 458.1 i 0.5 year:13J it was 12pg. The purity of the americium was checked using an cc-spectrometer analysing magnet and it was found that no significant amounts of fissionable impurities were present. The amount of zssPu present was less than 0.6 per cent. A description of the method used to determine the neutron flux at the target and of the procedure used in calculating the fission cross-section have been given previously.(*) Because of the high cc-activity of the americium target a xenonfilled gas scintillation counter was used to count the fission
CT= 2.35 & 0.15 barn. Acknowledgements-The authors thank G. I. KHLEBMKOVfor preparing the target and V. G. NEDOVESOVfor making the magnetic spectrometer analysis of the sample purity. A. N. PROTOPOPOV Iu. A. SELITSKII S. M. SOLOV’EV REFERENCES 1. NOBLES R. A., HENKEL R. L. and SMITHR. K., Bull. Amer. Phys. Sot. 30, 16 (1955). 2. HULETE. K., HOFF R. W., BOWMANH. R. and MICHELM. C. Phys. Rev. 107, 1294 (1957). 3. HALL G .R. and MARKIN T. L., J. Znorg. Nucl. Chem. 4,137 (1957). 4. PROTOPOPOVA. N., SELITSKIIIv. A. and SOLOV’EVS. M., Atomnaya Energiya 4, 2, 190 (1958).
11
_A, 0
10
20
I
,
r
I
30
40
50
60
Pulse height,
70
r
V
FIG. 1.-z41Am fission fragment spectrum measured by single channel analyser with 50 channel width. The arrow indicates discriminator bias defining the lower limit of the integrated fission fragment count.
fragments. A tetra-phenyl coating, applied to the internal walls of the counter, was used to convert the ultra-violet radiation from the xenon into visible light. Following a check of the stability of the counter it was found that over a period of 24 hr the tetra-phenyl vapour given off from the walls reduced the light output by 10 per cent. However, since the duration of the crosssection measurements was less than two hours the counter could be considered as being sufficiently stable. A photo-multiplier type FEU-33 which had a high resolution and delivered a large output current was used to detect the light * Translated from Atomnaya
Capture of electrons into the acceleration regime in betratrons and synchrotrons* (Received 10 February 1958) IN order to make a theoretical analysis of the problem of electron capture into the acceleration regime in betratrons and synchrotrons it is necessary to find a self-consistent solution to the many electron problems taking the initial and boundary conditions into account. Ignoring the effects of space charge, the initial equations of motion of the electrons in the median
Energiya 6, 67 (1959).
* Translated from Atomnaya Energiya 6, 8 (1959). 191